Glycerine Purification

Glycerine purification via bio-catalysis and column adsorption

for high-quality applications

Report nr. 0656632-R06 Date: 26-10-2007 Page: 2 of 90 www.ingenia.nl

Responsibility Title Glycerine purification via bio-catalysis and column adsorption for high-

quality applications

Commissioner SenterNovem

Project number 0656.632

Document 0656632-R06

Author(s) Ir. A. Hoogendoorn, Ir. T. Adriaans (Ingenia)

Dr.ir. J.M.N. van Kasteren, K.M. Jayaraj B.Sc. (TU/e)

Number of pages 90

Authorisation A. Hoogendoorn

Date 12 November 2007

Dit project is uitgevoerd met subsidie van het Ministerie voor Economische Zaken; Besluit Energie Onderzoek Subsidie: Lange

Termijn (NEO)

This project was executed with a grant from the Dutch Ministry of Economic Affairs; Besluit Energie Onderzoek Subsidie:

Lange Termijn (NEO)

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Index

1 Introduction.....................................................................................................7

1.1 Objective....................................................................................................................7

1.2 Background................................................................................................................7

2 Current situation in biodiesel-based glycerin ..................................................9

2.1 Biodiesel production technology overview ................................................................9

2.2 Biodiesel market development ................................................................................11

2.3 Number of plants, feedstock, development in time .................................................13

2.4 Glycerin from biodiesel production ..........................................................................13

2.5 Current glycerin market and typical glycerin applications .......................................15

2.6 Quality requirements for high-purity applications ....................................................21

3 Producing cleaner glycerin at the biodiesel plant..........................................23

3.1 Biodiesel production with heterogeneous bio-catalysts ..........................................23

3.1.1 Process explanation & literature reviews ................................................................23

3.1.2 Types of enzymes and lipases ................................................................................26

3.1.3 Factors affecting lipase activity & enzymatic transesterification .............................27

3.1.4 Comparison with chemical trans-esterification ........................................................31

3.1.5 Relationship between bio-catalyst and purity ..........................................................31

3.1.6 Critical points of biodiesel production with bio-catalysts .........................................32

3.2 Biodiesel production with heterogeneous metallic catalysts ...................................34

3.3 Conclusions .............................................................................................................35

4 Existing and new glycerin purification technologies ......................................36


4.1 Soap splitting as a glycerin pre-treatment step .......................................................38

4.2 Conventional processes for glycerin purification.....................................................39

4.3 Recent development in glycerol purification processes ..........................................41

4.4 Chromatography and regenerative column adsorption ...........................................44

4.5 Energy Comparison.................................................................................................48

4.5.1 Energy balance calculation......................................................................................48

4.5.2 Investigation of energy consuming step ..................................................................49

5 Economical comparison of enzymatic biodiesel production and glycerin

purification .................................................................................................................51

6 Transformation of glycerin into high-quality products....................................53

6.1 Investigation of alternative high-quality products from glycerin...............................53

6.2 Conversion of glycerol to methanol .........................................................................56

6.3 Conversion of Glycerol to Hydrogen .......................................................................56

6.3.1 Virent’s APR (Aqueous-Phase Reforming) process................................................56

6.4 Conversion of glycerol to useful chemicals via bacteria..........................................60

6.4.1 Hydrogen and Ethanol Production from Bacteria Enterobacter aerogenes HU-10160

6.4.2 Glycerol catabolism by Bacteria Pediococcus pentosaceus ...................................62

6.4.3 Microbial Conversion of Glycerol to 1,3-Propanediol ..............................................62

6.5 Glycerol hydrogenolysis to glycols ..........................................................................63

6.6 Pyrolysis of glycerol.................................................................................................64

6.7 Conversion of glycerol by Fischer–Tropsch process ..............................................67

6.8 Selective etherification of glycerol to polyglycerols .................................................71

6.9 Glycerolysis–hydrolysis of canola oil in supercritical carbon dioxide ......................71


6.10 Converting glycerin to propylene glycol...................................................................72

6.11 Glycerol conversion in the presence of noble metals as catalysts..........................73

6.11.1 Glycerol tri-butyl ether (GTBE) ................................................................................75

6.11.2 Mono-, di-, and tri-tert-butyl ethers of glycerol.........................................................78

6.12 Conclusions .............................................................................................................79

7 Conclusions ..................................................................................................81

8 Future Outlook..............................................................................................83

Appendices APPENDIX A Literature cited ................................................................................................................ 85 APPENDIX B Some glycerine market data by ADM Connemann (2003)............................................ 90

Figures Figure 2-1 Schematic of commonly used glycerin splitting at biodiesel factories ................................... 9 Figure 2-2 Process chart of a continuous biodiesel plant by Energea.................................................. 10 Figure 2-3 Biodiesel production capacity in Germany 1998 – 2006 [UFOP.de] ................................... 12 Figure 2-4 Development of biodiesel production capacity and estimated glycerin production ............. 12 Figure 2-5 Reaction schematic of transesterification of triglycerides to biodiesel [4] ........................... 13 Figure 2-6 Conventional and biodiesel glycerin pathways and applications........................................ 15 Figure 2-7 End uses of glycerin with regional variations according to [7] ............................................. 16 Figure 2-8 Traditional glycerin applications [9]...................................................................................... 16 Figure 2-9 Bioking 200 kWth glycerin/bio-oil burner and boiler (left), gas turbine duct burner running on

crude glycerin (Heat Power & Ingenia; right) ................................................................................. 19 Figure 2-10 Impact of biodiesel glycerin on the glycerin market prices (99,5%, $/pound) ................... 21 Figure 3-1 Advantages & process characteristics of enzymatic biodiesel production according to

Lanxess [58]................................................................................................................................... 24


Figure 3-2 Reactions with three-step methanol addition. 1,2,3, storage tanks for step-wise addition of

methanol; 4,5, fixed-bed reactor with immobilized lipase; 6, pump; 7, receiver of reaction mixture

[19] ................................................................................................................................................. 28 Figure 3-3 Methanolysis of vegetable oil with varying amounts of methanol using immobilized

Candida antarctica lipase. Conversion is expressed as the amount of methanol consumed. ...... 29 Figure 4-1 Process flow charts of integrated biodiesel production and glycerin purification by Buss-

SMS-Canzler (top) and MEGTEC (bottom) ................................................................................... 37 Figure 4-2 Laboratory test with vacuum glycerin distilling & 80% glycerin (left) and 95% glycerin (right)

....................................................................................................................................................... 38 Figure 4-3 Gel permeation principle..................................................................................................... 46 Figure 4-4 Pressure drop calculations for an ion exchange column by Lanxess [58].......................... 47 Figure 4-5 Column adsorption of enzymatically produced glycerine on laboratory scale (using ordinary

clay minerals) ................................................................................................................................. 48 Figure 6-1 Overview [26] of the production of hydrogen from biodiesel waste ....................................... 58 Figure 6-2 Preliminary [24] cost model for APR production of H2 from glycerol..................................... 60 Figure 6-3 Experimental [42] setup of the tubular reactor.................................................................... 64 Figure 6-4 Formation [42] of acetaldehyde, acrolein and formaldehyde............................................... 66 Figure 6-5 Performance [45] of supported Pt catalysts with Variation with time-on-stream. ................ 69 Figure 6-6 Selective analysis [36] GTBE/diesel ratio for isobutene and glycerol as reactants............. 77 Figure 8-1 The glycerin pillow according to Connemann/ADM [5]........................................................ 90 Figure 8-2 Some market numbers on 2003 by Connemann/ADM [5]................................................... 90

Tables Table 2-1 Typical composition of crude glycerin from biodiesel production [8] .................................... 14 Table 5-1 Economic comparison of conventional versus enzymatic biodiesel production ................... 52


1 Introduction Ingenia and Eindhoven University of Technology were commissioned by SenterNovem, the Dutch

agency for energy and environment, to execute a survey on high-quality applications of glycerin that

arises from biodiesel production.

1.1 Objective The goal of this survey is the execution of a feasibility study for the more cost effective upgrade of

glycerin and consequent transformation to high-quality products. Herein both the filter materials and

the side products like oil, biodiesel and soapstocks that arise during purification should be regenerated

(find a useful application). The original ambitions of the project partners were to come to:

• A crude glycerin that is inherently far less contaminated because of the addition of bio-

catalysts during the biodiesel production process;

• The feasible application of regenerative column adsorption techniques for further purification;

• A glycerin refinement that is twice as cost effective, more energy efficient and more simple;

• Regeneration of both adsorbentia and side products (oil, biodiesel and soap stocks);

• Identification of the most promising transformation routes to high-quality products (in chemistry

and pharmacy);

• The determination of the feasibility of a completely new industrial process with a high-quality

chemical or pharmaceutical end product.

1.2 Background The regular production of biodiesel from oils and fats implies the production of about 12-15 wt% crude

glycerin as a side product. The EU production of biodiesel currently amounts to about 7 million tonnes

per year (production capacity of 11,5 Mtonnes; [FO Licht 2007]). It is expected that this amount will

double during the next five years, in line with the EU’s goals on energy security and sustainable

mobility (EG 2003/30 etc.).

The current annual amount of glycerin arising from this biodiesel production amounts to some 1,9

Mtonnes and will continue to rise proportionally. The existing world market for pure glycerol for high-

quality industrial applications (chemical and pharmaceutical) only covers some 0,9 -1,0 Mtonnes per


year (2007). This means that either new applications for glycerin need to be developed and/or the

existing (pharmaceutical/chemical) pathways need to be expanded. This should be possible as there

are more than a thousand potential applications for glycerin can be identified.

Crude glycerin (purity 50% - 90%), as it is produced during biodiesel production, unfortunately

contains too many contaminants to find a useful application in chemistry or pharmacy without

treatment. For example, the ash content can amount to several percents whereas only ppm levels of

contaminants may be allowed. As a result of the high purification cost of glycerin the application of

glcyerine in high-quality pharmaceutical and chemical applications is still only limited. The glycerin is

increasingly used in crude form, for instance as a fuel in cement kilns or exported to China to be used

there as a fuel in coal fired power plants, waste combustion installations and cement kilns.

It can be concluded that the current problems around glycerin are bivalent (and with increasing

severity):

1. Refinement of glycerin currently is very expensive and complex, which disqualifies the product

for high-quality use. The market is overwhelmed with crude glycerin with a price window of 0

to +150 Euro/tonne, with a low-quality application in combustion, digestion and a sharply

increasing export to USA and China.

2. The amount of glycerin production from biodiesel is at 1,9 Mtonnes/yr so high, compared to

the current market of 0,9 Mtonnes/yr, that additional high-quality chemical and pharmaceutical

applications need to be identified.

The European Union also recognises this issue and has reserved a separate amount of money for

research into useful applications of glycerin within the Seventh Framework Programme (FP7).


2 Current situation in biodiesel-based glycerin

2.1 Biodiesel production technology overview Biodiesel is produced by the reaction of vegetable oil or animal fat with methanol to create methyl

esters of fatty acids. A major by-product of biodiesel production is glycerol or 1,2,3-propanetriol, a

trivalent alcohol. Common industrial biodiesel plant suppliers are AT, BDI, Energea, Man Ferrostaal,

Axens and Mecan. The smaller sized plants (< 30 ktonnes/yr) are most often equipped with batch type

reactors while the newer large size biodiesel plants have commonly continuous reactors.

A typical biodiesel plant uses around 1-2 wt-% of KOH (wt-% on oil basis) as a homogeneous catalyst

while this catalyst remains as an unwanted pollutant in the crude glycerin. Most biodiesel plants are

very sensitive towards Free Fatty Acids, Phosphorous, polymers and water in the feed stock flows.

Figure 2.1 shows the glycerin upgrading from 50-60% purity towards 75-85% purity by means of soap

splitting. These kind of sophisticated process options are only used at bigger sized biodiesel plants

(typically > 50 ktonnes/yr). Figure 2.2 shows a rather sophisticated process flow chart of a biodiesel

plant built by the Austrian company Energea in which acid esterification and a splitting of the crude

glycerin into 80% glycerin, K2SO4 and Free Fatty Acids takes place. The Free Fatty Acids are used to

produce biodiesel in an acid catalysed esterification step (not so common).

Figure 2-1 Schematic of commonly used glycerin splitting at biodiesel factories

Crude glycerine(50-60%)

+Acid wash water

Crude glycerine(80% pure)

FFA’s for biodiesel

K2SO4 Fertiliser


Figure 2-2 Process chart of a continuous biodiesel plant by Energea


2.2 Biodiesel market development In Europe biodiesel was first produced in Austria and Germany. Renewed interest in the product after

the oil crises arose in the 1980’s. The first lab synthesis by Mittelbach at Graz University took place in

1983. At the same time researchers in South Africa, Germany and New Zealand started working on

biodiesel production. In 1985 a small pilot plant in Silberberg, Austria, started its production of

rapeseed oil methyl esters, based on an innovative low-pressure, low-temperature technology, which

had been developed by Mittelbach et al. (1986). The first industrial production plant for RME followed

in 1991 (Aschach/Donau, Austria), and in 1996 two large-scale industrial plants in Rouen, France, and

Leer, Germany, documented the rapid growth of the young biodiesel industry [1]. Since that time, the

French and the German biodiesel production capacity continued to grow fastest in Europe. At this

moment the installed German capacity for producing biodiesel from rapeseed oil and other vegetable

and animal oils and fats, including waste frying oil, has reached some 4,8 Mtonnes/year (December

2007). The figure below documents the growth of the German biodiesel production capacity over

recent years. The main motives for development of the sector were:

• An alternative product from agriculture

• Securing domestic energy supply

• Reducing man-made CO2 emissions

• Reducing traffic emissions like CO, SO2 and NOx

World biodiesel production capacity will grow to around 23 Mtonnes (December 2007) while actual

production will probably be around 2/3 of that figure. These production numbers equate to around 1,9

Mtonnes of crude glycerin production at year end 2007 (figure 2.2).


Figure 2-3 Biodiesel production capacity in Germany 1998 – 2006 [UFOP.de]

0

5

10

15

20

25

30

35

Dec. 2006 Dec. 2007 Dec. 2008

Bio

dies

el p

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paci

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0,50

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2,50

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Biodiesel EU25 Biodiesel world Est. world crude glycerine prod

Figure 2-4 Development of biodiesel production capacity and estimated glycerin production


2.3 Number of plants, feedstock, development in time The German market is discussed as this represents almost 50% of the European market on its own.

Furthermore excessive data about this market can be found. By the end of 2006 Germany counted

some 50 biodiesel factories, ranging in scale from 10.000 tonnes/year to >250.000 tonnes/year. The

vast majority of these plants can work with relatively clean vegetable oils with an iodine number

between 90 and 120 (like rapeseed, soy and sunflower oil). Blending of cheaper feedstock like used

frying oil, palm oil and animal fat is usually only limited to guarantee process stability and product

quality.

Some plants can work with a considerably higher fraction of these feedstocks (Petrotec, Saria),

sometimes up to 100%. Usually, the process inside these factories is completely different, leading to a

different crude glycerin composition as well. By the end of the 1990’s it was believed that 30

ktonnes/year would be the maximum economic scale of a biodiesel factory. This soon turned out a

wrong assumption and by 2005 the pressure on the installation suppliers was so large that they would

not even issue offers for installations smaller than 60 ktonnes/year [3].

2.4 Glycerin from biodiesel production Glycerin is an inherent side product of the transesterification of triglycerides with a monovalent alcohol

(methanol, ethanol, etc.) to fatty acid alkyl esters, as is shown in the figure below.

Figure 2-5 Reaction schematic of transesterification of triglycerides to biodiesel [4]


Using stoichiometry it can be calculated that 10 wt% of glycerin is formed. However, that value holds

for pure glycerin. The so-called crude glycerin that falls free from biodiesel synthesis usually has a

purity between 55% and 90% where the larger biodiesel plants tend to have the highest purities of

often around 75% - 80%. The remainder of the crude glycerin consists primarily of unconverted

triglycerides, unconverted methanol, biodiesel, soaps and contamination. This dilution means that the

actual amount of glycerin formed is much larger, between 100/90 (1,1) and 100/55 (1,8) times as

much.

In the table below some typical composition data for biodiesel-derived glycerin are given. Most of the

contaminants can be traced back to the biodiesel synthesis process, for example the unreacted

methanol that was not completely evaporated. Furthermore the concentrations of Na and K can tell

whether caustic soda (sodium hydroxide, NaOH) or potash lye (potassium hydroxide, KOH) was used

as a catalyst for the transesterification. Alkali metals like Na, K, Ca and Mg are naturally present in

vegetable oils. Sulphate and phosphate may remain from neutralisation of the mixture with sulphuric

or phosphoric acid.

Table 2-1 Typical composition of crude glycerin from biodiesel production [8]

Property Value Unit

Genetically modified origin Possible

Glycerol content 77 – 90% wt% A.R.

Ash content 3,5 – 7% wt% A.R.

Moisture content 0,1 – 13,5% wt% A.R.

Lower calorific value 14,9 – 17,5 MJ/kg A.R.

Kinematic viscosity 120 mm2/s

3-monopropylenediol 200 – 13.500 ppm

Methanol 0,01 – 3,0% wt%

MONG* 1,6 – 7,5% wt%

pH 4,5 – 7,4

Sulphate 0,01 – 1,04 wt%

Phosphate 0,02 – 1,45 wt%

Acetate 0,01 – 6,0 wt%


Na 0,4 – 20 g/kg

K 0,03 – 40 g/kg

Ca 0,1 – 65 mg/kg

Mg 0,02 – 55 mg/kg

Fe 0,1 – 30 mg/kg

Mn <0,5 mg/kg

* MONG = matter organic non glycerol

2.5 Current glycerin market and typical glycerin applications

The current annual global glycerin market is mainly dominated by high-purity and hence high-value

applications and amounts to 0,9 – 1,0 Mtonnes/yr. This glycerin is produced from both palm oil and

tallow by companies like P&G, Cognis, Uniqema, Vitusa, Dow Chemical and Dial. The glycerin

production from biodiesel exceeds the current conventional glycerin production by around 1

Mtonnes/yr (see figure 2.2) and, although of a lesser quality, is competing with conventional glycerin

production (see figure below).

Current applications of crude glycerine from biodiesel and conventional glycerine

Crude glycerine (50-80%) Convent. glycerine productionbiodiesel production from palm oil & tallow 1,9 Mtonnes/yr P&G, Cognis, Uniqema, Vitusa…

0,9 Mtonnes/yr @ 99,5%0-150 €/t

Glycerine purification into 99,5%0-150 €/t 425-450 €/t

Fossil fuel Biogas Feed Food Farmaceutical &Chemical industrysubstitute 600 m3/ton f.i. 2-5% inclusionbag filter needed in poultry, pig dietFuel value 100-140 €/t GMP certification

Figure 2-6 Conventional and biodiesel glycerin pathways and applications

According to [7] important applications are regionally determined. For Europe the largest discerned

single application is personal and oral care (22%). In the figure below the regional difference between

the size of this share in Europe, USA and Japan is well visible. In Japan the largest discerned single


application of glycerin (25%) is for pharmaceuticals. Some 10% of the European glycerin market is

intended for application in food and beverages, with a 8% contribution for pharmaceuticals. Polyether

polyols have their largest share in the European market with about 12% compared to 8% in the USA

and 6% in Japan.

Figure 2-7 End uses of glycerin with regional variations according to [7]

According to a presentation by Mr. Van Loo from the Dutch company Procede the traditional

applications of glycerin can be discerned as follows:

Figure 2-8 Traditional glycerin applications [9]


Most of the existing glycerin applications from the pie-chart are explained below:

Drugs • Used in medical and pharmaceutical preparations, mainly as a means of improving smoothness,

providing lubrication and as a humectants. Also may be used to lower intracranial and intraocular

pressures.

• Laxative suppositories and cough syrups.

Personal care: • Used in toothpaste, mouthwashes, skin care products, hair care products and soaps.

• Serves as an emollient, humectants, solvent and lubricant in personal care products.

• Competes with sorbitol although glycerin has better taste and higher solubility.

• A component of glycerin soap.

Foods and beverages • Serves as humectants, solvent and sweetener, may help preserve foods.

• Solvent for flavors (such as vanilla) and food coloring.

• Humectants and softening agent in candy, cakes and casings for meats and cheeses.

• Manufacture of mono- and di-glycerides for use as emulsifiers

• Used in manufacture of polyglycerol esters going into shortenings and margarine.

• Used as filler in low-fat food products (i.e., cookies).

• Glycerin has approximately 27 food calories per teaspoon and is 60% as sweet as table sugar.

Polyether polyols • One of the major raw materials for the manufacture of polyols for flexible foams

and to a lesser extent rigid polyurethane foams.

• Glycerin is the initiator to which propylene oxide/ethylene oxide is added.

Alkyd resins (plastics) and cellophane • Used in surface coatings and paints.

• Used as a softener and plasticizer to impart flexibility, pliability and toughness.


• Uses include meat casings, collagen casings (medical applications) and non meat packaging.

• Plasticizer in cellophane.

High-explosives Nitroglycerin [11] is extremely powerful. A mere 10 ml will expand 10,000 times into 100 litres of gas at

an explosive velocity of 7,700 metres per second (17,224 miles per hour) -- more powerful than TNT.

Heart disease drug In one of the more curious coincidences of science, the first modern high explosive -- nitroglycerin --

also became one of the very first man-made drugs. To this day, it remains the most commonplace

treatment for chronic angina, the chest pain of heart disease.

Love potion Nitroglycerin's action as an effective vasodilator led in 1998 to the release of RESTORE, the first ever

fully tested, effective topical cream for the safe treatment of male erectile dysfunction (impotence).

Restore" contains 1% nitroglycerin and is "effective within minutes of application of achieving an

erection of up to 45 minutes duration.

Safe sweetener Glycerin is an alcohol (glycerol) and is used as a preservative in the food industry, as well as a

sweetener: it is very sweet, yet it contains no sugar. This makes it an ideal sweetener for patients who

cannot take sugar, such as the increasing number of Candida sufferers. Vegetable glycerin is said to

be the "only acceptable sweetener" for Candida patients.

Health supplement Health supplement for sportsmen -- Glycerin increases blood volume, enhances temperature

regulation and improves exercise performance in the heat, or so it is claimed. It helps "hyperhydrate"

the body by increasing blood volume levels and helping to delay dehydration. Following glycerol

consumption, heart rate and body core temperature are lower during exercise in the heat, suggesting

an ergogenic (performance enhancing) effect. In long duration activities, a larger supply of stored

water may lead to a delay in dehydration and exhaustion.


Preserving plants It is used in preserving foliage, cut sprigs or leaves.

Burning glycerin The glycerin by-product burns well, but unless it's properly combusted at high temperatures it will

release toxic acrolein fumes, which mainly form at between 200 and 300 º C (392-572 º F). At natural

gas prices around 9 €/GJ, crude glycerin will have a natural gas substitution value around 100-140

€/ton. The disadvantage of using crude glycerin as a fuel is that high dust emissions need to be

prevented and thus dust filters need to be used.

Figure 2-9 Bioking 200 kWth glycerin/bio-oil burner and boiler (left), gas turbine duct burner running on

crude glycerin (Heat Power & Ingenia; right)

Glycerin and biogas Approximately 600 m3 of biogas for each ton of crude glycerin can be produced. The addition of crude

glycerin in digestion plants can dramatically increase the gas production. The biogas is used as fuel in

diesel engines which power electricity generators.

Glycerin in poultry and pig diets Crude glycerin is, in compliance with f.i. German animal feed regulations, more and more used as a

cheap 2-5% component in animal diets (see also paragraph 2.6).


Other applications: • Manufacture of paper as a plasticizer, nitroglycerin, humectant and lubricant.

• Humectants for pet foods to retain moisture and enhance palatability.

• Used in lubricating, sizing and softening of yarn and fabric.

• Used in de-/anti-icing fluids, as in vitrification of blood cells for storage in liquid nitrogen.

• Patent applications have been filed for detergent softeners and surfactants based on glycerin (i.e.,

alkyl glyceryl ethers) instead of quaternary ammonium compounds.

• Can be added to solutions of water and soap to increase that solution's ability to generate soap

bubbles that will last a long time.

• Use as antifreeze in cryogenic processes.

• Used in fog machine fluids.

• Used in hookah tobacco mixtures (called "ma'assel" or "shisha" tobacco), often along with molasses

and/or honey.

Glycerin is also a source of lecithin (used in foods as a fat emulsifier, and a vital component of all cell

membranes in the body) and of tocopherols (vitamin E). It is used in skin moisturizers, lotions,

deodorants, makeup, toothpaste, sweets and cakes, pharmaceuticals and patent medicines, in paper

manufacturing, printing ink, in textiles, plastics, and electronic components.

Glycerin market developments and prices From the 1970s until the last few years, high purity natural glycerin had a fairly stable

price from about $1200 per tonne to $1800 per tonne [11]. This was based on stable markets

and production. Prices often surged outside these ranges, but sustained high prices

made it worthwhile for users to reformulate with alternative materials such as sorbitol

and synthetic glycerol, whereas sustained low prices encouraged its use in other

applications, pushing out petrochemical materials.


Figure 2-10 Impact of biodiesel glycerin on the glycerin market prices (99,5%, $/pound)

Figure 2.7 shows the impact of biodiesel derived glycerin on the existing market. Both the year 2006

and 2007 are characterised by low glycerin prices. Current European prices for high-purity glycerin

derived from biodiesel amount to 440-580 €/tonne [12] and seem to have stabilised at this level. In

March 2007, the prices were around 400-450 €/tonne for tallow derived glycerin (99,5%) for delivery in

North West Europe (24-27 $ct/pound; [13]).

The crude glycerin market moves at levels around 0-150 €/tonne depending on a.o. the purity (50-

90%), water and residual methanol content. The refined glycerin market is described as being strong

(with new feed and chemical applications) while the crude glycerin market is described as weak [12].

The combination of high fossil oil prices and historically low glycerin prices have resulted in the

increased application of glycerin as an ideal platform chemical in the chemical and pharmaceutical

industry.

2.6 Quality requirements for high-purity applications It is most common to refine up to a purity of 99,5% before further use. For high-purity, refined glycerin

the following grades or classifications are discerned [4,6]:

• 99,5% technical grade


• 96% USP (vegetable based)

• 99,5% USP (tallow based)

• 99,5% USP (vegetable based)

• 99,5% USP/FCC (Kosher)

• 99,7% USP/FCC (Kosher)

The United States Pharmacopeia (USP) is the official public standards-setting authority for all

prescription medicines, dietary supplements, and other healthcare products manufactured and sold in

the United States.

In Germany, it is allowed to both use crude and refined glycerin as a feed (pellet) ingredient [14]. The

quality demands for the crude glycerin are max. 0,5% methanol and min. 80% glycerin while it is

common to use only 2-5% of crude glycerin in the animal feed mix for poultry and pigs. One significant

drawback however, is that the biodiesel factory itself has to have GMP or GMP+ certification (most of

the biodiesel plants don’t have these certificates).


3 Producing cleaner glycerin at the biodiesel plant

The existing biodiesel-derived crude glycerin is of poor quality and requires expensive refining before

it is suitable for new product technologies. Current glycerin refining technology requires significant

economies of scale to be economical.

The application of heterogeneous catalysts in biodiesel factories results in a much purer crude glycerin

and thus makes smaller scale and low-cost refining at the biodiesel plant viable.

3.1 Biodiesel production with heterogeneous bio-catalysts

3.1.1 Process explanation & literature reviews

Research on the enzymatic trans-esterification process for biodiesel production is still in an early

developmental stage, as this is still a relatively new field of study. Important studies in that field are

done by F. Yagiz, et. al [17] and Y. Shimada, et. al.[19]) while also a lot of progress was made by the

University of Cordoba [47]. Work at the University of Cordoba has shown that up to 100 re-uses of the

immobilised enzymes can take place and a PhD thesis will follow shortly. The well-known supplier of

ion exchange granulates Lanxess also investigated lipase immobilisation for biodiesel production and

claims a lifetime of 1 year using their Lewatit OC 1600 granulate as carrier material for the enzymes

[58 and below]. Lanxess gives several advantages for enzymatic biodiesel production and apparently

does not use any KOH.


Figure 3-1 Advantages & process characteristics of enzymatic biodiesel production according to

Lanxess [58]


Much knowledge has been gained from the research on aspects such as the optimal conditions for the

process, problems associated with enzymatic trans-esterification, the types of materials suitable as

immobilization material for the lipases and the effects of different physical conditions (such as

temperature and pH) on the immobilization of the lipases.

The two studies by Y. Shimada, et. al. and F. Yagiz, et. al. have each focused on the use of a different

lipase for the trans-esterification process, namely Candida antarctica and Pseudornonas cepacia.

Many other lipases remained untested as yet, and will remain to be tested in the future as

development in the field matures.

There is general consensus in the studies that the enzymatic production of biodiesel is a superior

method as compared to conventional chemical trans-esterification, considering the lower complexity of

the reaction process and the absence of waste products, in particular soap (produced due to presence

of free fatty acids in the waste oil), which will create environmental problems if disposal is not handled

appropriately. As is shown in figure 3.1, also a cleaner biodiesel is produced. The enzymatically

produced crude biodiesel does contain less KOH and water washing of the biodiesel could thus be

substituted for a dry washing of the biodiesel. It has also been concluded that generally, the

immobilization of the lipases led to a higher activity of the lipases, which translates into a higher yield

of methyl esters (biodiesel) and a faster rate. However, the enzymatic trans-esterification process is

more time consuming than the chemical trans-esterification and the supercritical trans-esterification

process.

In enzymatic trans-esterification, although the reaction mechanism is similar to that of chemical trans-

esterification, an enzyme, specifically lipase, replaces the chemical catalyst. The lipase [19] catalyzes

hydrolysis1, esterification as well as trans-esterification.

Methanolysis (hydrolysis using methanol instead of water) of vegetable oil with a lipase is reported to

produce more effective results for the biodiesel production using waste oils. Enzymatic trans-

esterification offers a feasible option over the conventional method where the end product is not

1 Hydrolysis is the cleavage of an ester with water back to a carboxylic acid and alcohol


contaminated by the biocatalysts, therefore no waste material is generated [18] that will pollute the

environment.

3.1.2 Types of enzymes and lipases

Types of lipase

Many laboratory experiments have been conducted to determine the effectiveness of enzymes in

replacement of chemical catalysts in trans-esterification production of biodiesel. The most common

and widely used enzyme in this initial trial stage is lipase, due to many of its favorable characteristics.

Lipases are water-soluble enzymes that catalyze the hydrolysis of ester bonds in water–insoluble lipid

substrates. They attack specific positions on the glycerol backbone of the bio-oils to allow the free fatty

acids to react with the alcohols more efficiently. Although there are many different lipases present

around, only a few selected lipases are selected for most of these experiments currently.

The Candida antarctica lipase [19] is a very common type of enzymes used in many experiments. It is

a moderately thermo-stable enzyme that is able to retain most of its activity for many hours when

incubated between 30 – 40°C. However, the enzymatic activity of the lipase is reduced when

temperature increases beyond 40 °C, exposed to higher water concentrations as well as xenobiotic2

compounds.

Another lipase used in the enzymatic trans-esterification of biodiesel is the Pseudornonas cepacia.

According to the experiments carried out by the University of Nebraska, Lincoln in 2004 [18], they

found that this strain of lipase resulted in the highest yield of alkyl esters produced. However, little

information has been known more extensively about the lipase as of now.

Although there are only two examples of lipases discussed here, there are still many other more

lipases suitable for the enzymatic trans-esterification of biodiesel production, but still currently

2 A xenobiotic substance is a foreign chemical not normally found in an organism and is in higher

than expected concentrations


unknown. Each type of lipase is specific and unique; hence the general reaction conditions will vary

according to the types of lipases chosen for the individual reactions. In addition, lipases are very

sensitive micro-organisms to temperature and pH, and will only function optimally at specific range for

each strain.

Lipase immobilization techniques

There are 3 common established lipase immobilization techniques: (i) physical adsorption onto solid

support; (ii) covalent bonding to solid support and (iii) physical entrapment within polymer matrix

support [18].

In the third technique, the lipase is captured within a matrix of polymer. This method is preferred and

has already received considerable attention in recent years. This is because it better stabilizes the

lipase as compared to physical adsorption, and uses a simpler procedure than the covalent bonding

method. In general, the physical entrapment of lipase maintains the activity and stability of the

immobilized lipase.

3.1.3 Factors affecting lipase activity & enzymatic transesterification

Water concentration affecting methanolysis

Waste oil generally contains water (~1980ppm), free fatty acids (~2.5%) and some partial

acylglycerols (~4.6%) [19]. Water concentration greater than 500ppm will decrease the bio-oil

methanolysis, but it does impact the reaction equilibrium. By performing the reaction in cycles using

recycled enzymes in fresh substrates, it is possible to increase the conversion rate and eliminate the

negative effect of water present in waste oils.

The water, initially present in the waste oil, is transferred onto the polar glycerol and subsequently

removed from the system. Hence water concentration drops with repeated reactions, thereby

increasing methanolysis and hence the conversion rates. The diagram in fig. 3.2 shows the reaction in

cycles, coupled with a three-step methanol addition.


Figure 3-2 Reactions with three-step methanol addition. 1,2,3, storage tanks for step-wise addition of

methanol; 4,5, fixed-bed reactor with immobilized lipase; 6, pump; 7, receiver of reaction mixture [19]

Alcohol concentration

As mentioned earlier, the insoluble methanol can inhibit the lipase activity, and is an irreversible

reaction, therefore resulting in a lower alkyl ester yield.

In an experiment performed by Osaka Municipal Technical Research Institute [19], methanol is

consumed completely in methanolysis when less than one-third molar equivalent of stoichiometric

methanol is added. When the alcohol is added in more than half molar equivalent ratios (Fig. 3-3), the


activity of the lipase, Candida Antarctica, decreased substantially. The activity was not restored even

in subsequent reactions with one-third molar equivalent methanol; hence it can be concluded that

enzymatic inactivation is irreversible when in contact with large amounts of insoluble methanol.

Figure 3-3 Methanolysis of vegetable oil with varying amounts of methanol using immobilized

Candida antarctica lipase. Conversion is expressed as the amount of methanol consumed.

This inactivation problem can be overcome by pre-treatment with higher order alcohols or the step-

wise addition of methanol into the mixture, as methanol is more soluble in alkyl esters than in oil [18].

In this way, there will be minimal methanol present to inhibit the enzyme activity. Results [19] have

shown that the Candida antarctica lipase can be used repeatedly for more than 100 days without

showing effects of inactivation using both three-step and two-step methanolysis.

Temperature A joint research study [16] by 3 institutions in Turkey, Kocaeli University, University of Marmara and

the Marmara Research Center, showed the effects of temperature on lipase immobilized onto


hydrotalcite, a form of zeolite used as immobilization material. The immobilization technique used was

chemical adsorption rather than physical adsorption or entrapment. They found that for single batch

reactions, optimum temperature for enzymatic activity (100%) was 45°C. For temperatures greater or

lower than the optimum, activity of the immobilized enzymes were not affected too much, e.g. 89.6%

and 86.8% activity at 30°C and 60°C respectively.

On the other hand, for more practical and cost-effective reasons, immobilized lipases are usually used

in repeated batch processes due to their high costs. A continuation to the single step process

experiment carried out by the 3 institutions in Turkey, they investigated the activity of the enzymatic

activity at different temperatures.

According to their results, at 45°C the immobilized lipases displayed little or no loss of enzymatic

activity for the first 2 repeated cycles, and following 7 cycles, they retained about 36% of their initial

activity. At a higher temperature 55°C, the enzymatic activity was significantly different. Just after one

cycle, the activity of the immobilized lipases dropped almost 40%; and after 7 cycles, the remaining

activity was only 14% that of the initial activity.

From the above experiments, it is clear that for single processes, temperature does not have

significant effect on the activity of the lipases. However, after repeated usages, the higher the reaction

temperatures, the faster the rate of inactivity will occur. Thus, for practical reasons, temperatures

should be maintained at 45°C so that maximum activity of the lipases can be sustained.

pH

The 3 Turkish Institutions [16] further varied the pH values of the system to determine its effect on the

resulting yields. At different pH values, the amount of lipases chemically adsorbed onto the supporting

structure differs. Experiments showed that the highest lipase adsorption occurs at pH 8.5, and the

amount absorbed decreased more drastically when pH increases, than it decreases. As a rule of

thumb, enzymatic trans-esterification should not be operated at pH values higher than 8.5. However,

we should bear in mind that the results obtained from this literature are based on chemical adsorption

of lipase immobilization. Recently experiments at the University of Cordoba has shown that

immobilization methods through covalent bonding makes higher optimal pH values possible.


3.1.4 Comparison with chemical trans-esterification

Although enzymatic trans-esterification produces a less contaminated biodiesel and by-product and is

considered a feasible alternative, the chemical catalyzed reaction is more commonly used and

recognized due to their shorter reaction time and lower overall costs [20].

As enzymes are costing at least 30 €/kg, it is necessary to re-use and immobilise the enzymes. The

University of Cordoba claims successful re-uses of the immobilised enzymes for up to 100 times while

a company like Lanxess claims a lifetime of up to 1 year while still retaining good enzyme activity.

More research is needed in order to develop cheap mass production of granulates containing

immobilised enzymes.

As previously mentioned, enzymes are very sensitive to the methanol concentration in the reaction

system; hence to ensure a minimum activity of the enzymes low concentrations of methanol should be

maintained at the initial stage of reaction. Some studies [20] have shown that it took 34 hours to

convert 97.3% of bio-oil in the refined vegetable oil to fatty acid methyl ester (FAME), in a two-step

methanol addition enzymatic process. When the refined vegetable oil is replaced by waste oil, the

conversion dropped to about 90.4%, taking a total of 48 hours.

The conventional trans-esterification is very sensitive to the purity of the bio-oil feedstock. Only well-

refined vegetable oil with less than 0,5-1,0% free fatty acid and less than 0,1% water can be used as

the feestock for conventional biodiesel production. The enzymatic process is also capable to convert

used cooking oil, waste animal fats and crude bio-oils [16, 47]. These lower quality feedstocks have

lower prices and thus the feedstock versatility may well be the most important economic advantage of

enzymatic biodiesel.

3.1.5 Relationship between bio-catalyst and purity

As was shown in table 2-1, conventional crude glycerin is polluted with 3,5-7 w-% of salt residue (ash).

Because the enzymatic process requires no homogeneous catalyst, only a high pH (8,5-11) the

amount of NaOH or KOH can be reduced by a factor of four compared to the conventional process.


This means that the formation of soap due to the presence of water will also be reduced with a factor

four. Moreover the enzymatic reaction is very selective, meaning that the presence of free fatty acids

(FFA’s) is no problem, because they are converted also into alkyl esters reducing also the amount of

organic side products. These effects result in a much cleaner glycerin of probably 90-95% reducing

the process costs of glycerin purification.

3.1.6 Critical points of biodiesel production with bio-catalysts

Although significant progress has been made by a.o. the University of Cordoba, the trans-esterification

of bio-oils using lipases as catalysts is not completely without challenges. Two major challenges faced

by this alternative process are: the effects of the reactant [16] methanol and the product glycerol [18] on the lipase activity. Both of the compounds lower the enzymatic performance and thus giving poorer

yields.

Fig. 3-3: Negative effect on lipase activity by methanol and glycerol

1. Low solubility of methanol Methanol is commonly used as the reactant alcohol mainly because it costs less than ethanol.

However, it is less soluble in oils due to its short hydrocarbon chain, resulting in a thin liquid film

appearing in the reaction system that inactivates the lipases, giving a lower alkyl ester yield [16].


2. Low solubility of glycerol One of the end products generated is glycerol and it is not soluble in the biodiesel (alkyl esters)

produced. It poses a huge problem to the lipase activity because the insoluble glycerol can coat the

immobilized lipase surfaces, reducing their activity and performance. This problem is almost absent in

the beginning of the reaction but is aggravated as conversion ratio increases, when more glycerol is

produced.

Solutions for these problems are given by the study conducted by D. Royon, et. Al [16]. He showed

that addition of some alcohols, which have 3 or more carbons, significantly increases the conversion

yields of biodiesels. When these alcohols are added in replacement of the methanol in the system, the

blank experiment showed no significant conversion of the oils to esters. Thus the higher alcohol

chains are not suitable substrates for the lipases used and do not interfere with the transesterification

process. Pretreatment of the enzymes with these higher alcohols reduces the inhibitory effects on the

enzymes of methanol and glycerol, because the higher alcohols increase the solubility of both reactant

methanol and product glycerol.

An example of a suitable higher order alcohol is the t-butanol (C4H9OH). Experimental results showed

that when sufficient t-butanol is present, an increase in methanol concentration increases the initial oil

consumption. The highest methyl-ester yield obtained occurs at a methanol-to-oil ratio of 3.6:1 in the

presence of t-butanol; when without this pre-treatment, any ratio greater than 1 inhibits lipase activity.


3.2 Biodiesel production with heterogeneous metallic catalysts

Some biodiesel equipment manufacturers like Axens and BDI are now experimenting with the

application of solid re-usable catalysts.

In the heterogeneous [15] transesterification process used by Axens the solid metal oxides such as

those of tin, magnesium, and zinc are known catalysts but they actually act according to a

homogeneous mechanism and end up as metal soaps or metal glycerates. In this new continuous

process, the transesterfication reaction is promoted by a completely heterogeneous catalyst. This

catalyst consists of a mixed oxide of zinc and aluminum, which promotes the transesterification

reaction without catalyst loss. The reaction is performed at higher temperature and pressure than

homogeneous catalysis processes, with an excess of methanol. This excess is removed by

vaporization and recycled to the process with fresh methanol.

Figure 3-4: Simplified [15] flow sheet of the new heterogeneous process


The desired chemical conversion, required to produce biodiesel at European specifications, is reached

with two successive stages of reaction and glycerol separation in order to shift the equilibrium of

ethanolysis. The catalyst section includes two fixed bed reactors, fed with vegetable oil and methanol

at a given ratio. Excess of methanol is removed after each reactor by partial evaporation. Later the

esters and glycerol are separated in a settler. Glycerol outputs are gathered and the residual methanol

is removed by evaporation. In order to obtain biodiesel in European specifications, the last traces of

methanol and glycerol have to be removed. The purification section of methyl ester output coming

from decanter 2 consists of finishing methanol vaporization under vacuum followed by a final

purification in an adsorber for removing the soluble glycerol.

3.3 Conclusions Preventing contamination of the glycerin fraction is the best way of reducing cost of purification of

glycerin and increasing the use of crude glycerin. Enzymatic biodiesel production with immobilized

enzymes looks very promising in this respect. Critical points of the enzymatic route are the relative

slow reaction compared to the conventional, homogeneous process and the number of times that the

enzymes can be used.

The heterogeneous catalytic process is also a promising way of producing glycerol fractions with high

purities. Critical points of this route are that the input oil has to be more pure and the stability of the

catalysts which has to sufficient justifying the higher investment costs.

Overall it can be concluded that it is possible to reach crude glycerin purities of 90-95% and thus

reducing purification costs.


4 Existing and new glycerin purification technologies

There are different processes for refining glycerol. However, all of them involve soap splitting followed

by two main separation steps: salt removal and methanol removal. Some of the separation techniques

should involve vacuum because glycerol is a heat sensitive compound that splits into water and

decomposes at 180°C 3 .

Generally speaking, the following technologies may be used to further purify glycerin (after the soap

splitting step): fractional distillation, ion-exchange, adsorption, precipitation, extraction, crystallisation,

dialysis. The glycerin soap splitting followed by a combination of methanol recovery/drying, fractional

distillation, ion-exchange (zeolite or resins) and adsorption (active carbon powder) seems to be the

most common purification pathway.

Well-known companies who deliver crude glycerin purification plants are Desmetballestra and Buss-

SMS Canzler (ion exchange equipment). Chemical companies like Rohm & Haas and Lanxess supply

ion-exchange granulates while a company like Norit supplies powder and granulated activated carbon.

3 Brockmann, R., Jeromin, L., Johannisbauer, W., Meyer, H., Michel, O. and Plachenka, J.(1987).Glycerol distillation process.

US Patent No. 4,655,879


Figure 4-1 Process flow charts of integrated biodiesel production and glycerin purification by Buss-

SMS-Canzler (top) and MEGTEC (bottom)


Figure 4-2 Laboratory test with vacuum glycerin distilling & 80% glycerin (left) and 95% glycerin (right)

Figure 4-2 shows laboratory set-up for distilling the crude glycerin resulting in a 90-95% glycerin purity.

4.1 Soap splitting as a glycerin pre-treatment step As was described earlier in paragraph 2.1, and according to the biodiesel handbook [5], three steps

can be distinguished in the purification process. The first step involves neutralization using an acid to

remove catalyst and soaps. The reaction of an acid with soap will give FFA and salt while its reaction

with the base catalyst gives salt and water. Since the FFA’s are insoluble in the glycerol they will rise

to the top so that they can be skimmed off. Some salts which are insoluble in the glycerol will also

precipitate out. The second step involves removal of methanol. The methanol stream in the glycerol

can be removed with flash evaporation or using falling film evaporators. Falling film evaporators have

an advantage of keeping the contact time short and are best suited for our process because of the

temperature susceptibility of glycerol which can result in its decomposition. After removal of methanol

the purity of glycerol will be approximately 85%. In the third step, glycerol can be further be purified to

99.5% using a combination of adsorption, vacuum distillation and ion exchange processes4 (see also

next paragraph).

4 Knothe, G., van Gerpen, J. & Krahl, J. (2005). The biodiesel handbook. Illinois: AOCS Press.


4.2 Conventional processes for glycerin purification The conventional process for glycerol purification comprises of the following steps: pretreatment,

concentration, purification and refining. The pretreatment step is used to remove colour and odour

matters as well as any remaining fat components from crude glycerol. In the pretreatment step sodium

hydroxide is used for the removal of fat components by saponification reaction where as activated

carbon is used for bleaching purpose. The concentration step involves the removal of ionic substances

using ion exclusion chromatography. In this process a bed filled with strongly acidic exchange resins is

charged with a glycerol stream. The principle used for the separation is Donnan exclusion. Ionic

substances are repelled from the resin surface remain in the liquid volume due to their charge while

the non-ionic ones can be accommodated in the pores of the resins. Afterwards the column is rinsed

with water which removes the ionic substances in the liquid first and the non-ionic ones later. In some

cases when the concentration of ionic substances in the glycerol stream is very high, ion exchangers

both cationic and anionic are used and they are exchanged for wash water. The next step is

purification which uses ion-exchangers. As mentioned before the exchangers are used in pairs

(cationic and anionic). In cationic exchangers positive ions are exchanged for hydrogen ion while in

anionic exchangers negative ions are exchanged for hydroxide ions. This purification step will remove

inorganic salts, fat and soap components, colour and odour causing matters. The subsequent step is

treatment of glycerol in multiple vacuum flash evaporators (10-15kPa vacuum) which results in 90-

95% concentration (Figure 4-3). An alternative way to do the same job is to use thin film distillation

(Figure 4-4). In thin film distillation the glycerol stream is distributed as a thin film on the wall of the

evaporator and heated externally. The glycerol will fall down to the bottom as a residue while high

volatile components like methanol and water are evaporated and collected at the top. The final

concentration of glycerol to 99.5% is carried out in vacuum (0.5-1kPa) in forced circulation

evaporators5

5 R. Christoph, B.Schmidt, U.Steinberner, W. Dilla, R.Karinen. (2006). Glycerol, Ullmann’s Encyclopedia of Industrial Chemistry: electronic release, 6th ed.


Figure 4-3: Continuous glycerol Concentration: a) Feed heater: b) Evaporator: c) Separator with

demister: d) Water Condenser: e) Glycerol heater: f) Glycerol heater/final product cooler: g) Falling film

evaporator: h) Glycerol condenser [7].


Figure 4-4: Continuous glycerol distillation (Cognis):a)Economizer: b)End heater: c) Thin-film

distillation: d) Fractionating Column: e) Reboiler: f) Reflux Condenser: g) Glycerol condenser h) water

condenser [7]

4.3 Recent development in glycerol purification processes John E. Aiken6 has made some improvements in glycerol purification process. He proposed five

separation steps, which can be conducted in either batch or continuous mode (Figure 4-5). This

process is claimed to be able to produce glycerol of higher than 99.5% purity from typical crude

glycerol, which contains a mixture of mono-, di- and triglycerides, excess methanol, water, fatty acid

alkyl esters, residual catalyst and salt.

6 Aiken, J.E. (2006). Purification of glycerin. US Patent No.7,126,032 B1


i) First reactor

Crude glycerol, whose purity is typically 86-92%, is preheated then fed to the first reactor. The first

reactor is used to recover triglycerides by reacting entrained methyl esters and glycerol to produce

glycerides and methanol (reversed biodiesel production reaction). Nitrogen is sparged to provide

agitation and to remove methanol and water; thus, the reaction is shifted to glycerides formation. The

temperature inside the reactor is maintained at 120-160°C. Gas effluent stream is then passed

through a condenser. After separated from condensed methanol and water in a condenser, nitrogen is

recycled to the reactor.

ii) Second reactor

Liquid effluent stream from the first reactor is heated to maintain the second reactor at 120-160°C. In

this reactor, unreacted methyl esters are reacted to produce methanol and triglycerides. Wash water,

which contains glycerol, is also added to the second reactor. Similarly, sparging nitrogen is used to

agitate the mixture inside the reactor and to remove methanol and water. Entrained methanol and

water are condensed. After being separated from nitrogen, wash water is recycled. The operating

conditions are adjusted in such a way that glycerol effluent stream contains maximum 0.5 wt% of

methanol and approximately 5 wt% of water.

iii) Decanter

A decanter is placed after the second reactor. It serves as a feed tank for the flash distillation column

and a separator to remove oil layer of the glycerol stream by lowering the pH below 7 and skimming it

from the glycerol layer. The recycle stream from the bottom of the flash distillation column is mixed

with the glycerol stream in this tank.

iv) Flash distillation column/stripper

The flash distillation column consists of a packed bed column with a steam-heated reboiler. This

column operates at a temperature of 185°C and a pressure of 5-20 mmHg. There is no reflux returned

to the top of the column. About 80-90% of glycerol in the feed stream is drawn as overhead product,

which is then condensed in two condensers in series. The first condenser is used to condense

glycerol, while the second one is used to condense water which will be sent to waste water stream.


The bottom product of the column, which contains glycerol and heavy compounds, is pumped back to

the decanter. Some of it is purged continuously or intermittently to prevent salts and glycerin buildup in

the decanter.

Figure 4-5. Simplified flow sheet of the recent development process, based on US 7,126,032 B1

v) Adsorption columns

The last step of glycerol refining is the removal of colour and trace impurities. There are lots of

material that may be used as adsorbent, such as activated carbon, ion exchange resins and molecular

sieves. The purified glycerol is then pumped to a storage tank.


4.4 Chromatography and regenerative column adsorption

Separation of glycerin by applying adsorption techniques is a proven technology. Some biodiesel

equipment vendors7 purify glycerin using activated carbon powder from suppliers like f.i. Norit. The

main components to separate are:

• Glycerol (key component)

• Water

• Ions (like K+)

• Saponification residues

• Methanol traces

Activated carbon powder is, with surface areas between 500-1500 m2/g and sizes <150 micron, a very

suitable adsorption medium to adsorb organic molecules, but is rather expensive to regenerate the

carbon. Operational costs will be high when using a column adsorption, because of the high viscosity

of the crude glycerin and the high pressure drop. Activated carbon is applied because of its good

properties in waste water cleaning.

New developments in adsorption techniques are mostly based on chromatography separation.

Originally this technique is applied to separate small amounts of samples in a laboratory. Nowadays

capacities and applications are increased. The next table shows some possible chromatography

techniques and its properties.

7 Megtec USA


Table 4-2. Summary of chromatography separation processes 8

Method Separation parameters Important parameters

Gel permeation Particle size Column length

Ion exchange chromatography Charge pH, ionic strength

Hydrophobic interaction Hydrophobicity Polarity, ionic strength

Reversed phase Hydrophobicity Polarity, ionic strength

Affinity chromatography Biospecific interaction Ligand, eluent

The companies Rohm & Haas and Lanxess sell granular ion exchange resins which are also used for

glycerin purification (a.o. salts, colour and odour removal). But most important is the separation of

water and glycerin molecules based on affinity and particle size. Water molecules that are bound to

glycerin molecules are difficult to separate. It is therefore important to find a suitable type of adsorbent

with respect to high separation efficiency (resolution) at a high volume flow capacity and low pressure

drops. Next table summarises some chromatographic techniques with their resolutions and volume

flow capacities.

Table 4-3 Summary of chromatography separation processes 8

Chromatographic technique Resolution Capacity

Gel permeation Moderate Moderate

Ion exchange Low/moderate Very high

Hydrophobic interaction High High

Reversed phase Very high High

Affinity Very high High

It should be possible to design new type of adsorbent media specific for glycerin that meet more or

less of the mentioned criteria. The first process set-up can be an ion exchange column with a second

column added. This column could be based on affinity properties adsorbent and (gel) permeation

principle. This principle is shown in the following figure:

8 Adapted from Biotol, Product Recovery in Bioprocess Technology (1992)


Figure 4-3 Gel permeation principle

Typical properties of gel permeation are:

• Particle size: 0.1 – 0.2 mm

• Column length: up to 1 meter

• Liquid flux: up to 5*10-5 m/s

These characteristics are rather bad to apply on large scale, but new developments show potential for

higher fluxes at stable pressure drops, however these are far from economical feasible applications.

The figure below shows typical pressure drop calculations for continuous flow ion exchange granulate

columns [58].

Enzymatically produced crude glycerine will probably have a purity of 90-95%. Both soap splitting and

fractional distillation of the 90-95% glycerine can probably be eliminated. It seems likely that the use of

activated carbon powders and/or ion adsorption (zeolites or resins) techniques will probably be

sufficient to obtain a glycerine purity of 99,5%.

Regeneration of the granulates of activated carbon may typically be performed with methanol, acids,

steam or water.


Figure 4-4 Pressure drop calculations for an ion exchange column by Lanxess [58].

The figure below shows a technical feasible column adsorption process on laboratory scale

(batch process). The resolution of the process is rather good but only possible at high retention times

and high pressure drop. Actual laboratory tests of column purification of enzymatic glycerine are

necessary to gain a further understanding about the process, possible absorbents (f.i. wood powder,

carbon, clay minerals), regeneration, retention times and purities that can be obtained.


Figure 4-5 Column adsorption of enzymatically produced glycerine on laboratory scale (using ordinary

clay minerals)

4.5 Energy Comparison

4.5.1 Energy balance calculation Tables 4-1 and 4-2 show the energy balance calculations for the patent of Aiken and the convectional

process respectively. From these tables it can be concluded that the evaporation of glycerol consumes

most of the energy. The conventional process consumes around 0.314 MJ/kg of glycerol. This is

around 2% of the heat of combustion of glycerol and < 1% of the combustion energy of biodiesel

produced. The Aiken process consumes 0.55 MJ/kg (around 100 % of the heat of evaporation of

glycerol) resulting in only 3.5 % of the heat of combustion of glycerol.


Table 4-1. Energy balance Summary for Process based on Patent of Aiken

Equipment Duty Energy supplied ,J/gram of

glycerol

Preheater 1 Feed heater 103

Compressor Increase N2 pressure 8

Preheater 2 Increase N2 temperature 8.1

Reboiler Heat need in distillation

column

430

Total energy required 550

Table 4-2. Energy balance summary for a conventional process

Equipment Energy supplied , J/gram of glycerol

First Effect Evaporator 297

Last Effect Evaporator 17

Total energy required 314

This means that most of the costs are not involved in the energy but in the investment of equipment.

The dependent on the application and pricing of the glycerol it is interesting to invest in this system or

not. Cleaner crude glycerol can in this respect reduce the number of evaporating steps and thus

reduce the purification steps.

4.5.2 Investigation of energy consuming step The rough energy balance calculations of the previous section have indicated that the recent

development for glycerol purification based on US patent consumes higher energy than the

conventional one. One reason could be the reverse transesterification reactions need high

temperature to start which necessitates preheating of the feed streams. The calculations also indicate

a significant contribution from this step for the overall energy requirement of the process. However the

most important source of energy consumption on this process is the flash distillation column which

represents approximately 75% of the total energy consumption. The multiple effect evaporator system

is a more efficient way of utilizing energy from steam and the results from our calculation are also


implying that. With all sorts of energy integration in this system like utilizing the condensates from the

multiple effects to preheat the glycerol rich stream to the boiling temperature in the evaporators, one

can get a lower energy and steam requirement as compared to other systems such as in distillation

column. In a nutshell our calculations indicate that the multiple effect evaporator system used in the

conventional purification process is more energy efficient and a viable alternative as compared to the

one based on patent of Aiken.


5 Economical comparison of enzymatic biodiesel production and glycerin purification

The glycerine applications and market prices in dependence of purity are described in chapter 2.

A challenge faced for enzymatic trans-esterification is the high costs associated with lipases as

catalysts [16]. Much progress has been made with the successful immobilization of the enzymes and

re-use up to 100 times [47]. The well-known supplier of ion exchange granulates Lanxess also

investigated lipase immobilisation for biodiesel production and claims a lifetime of 1 year using their

Lewatit OC 1600 granulate as carrier material for the enzymes [58].

Enzyme costs depend strongly on their purity starting from 30 €/kg up to more than 10.000 €/kg. For

enzymatic biodiesel production it is not necessary to use high grade expensive enzymes [47] and thus

a price of 100 €/kg of enzymes (including immobilisation) was taken. In contrast, KOH costs only 0.6

€/kg.

For this economic evaluation it was assumed the enzymatic process reduces the amount of KOH used

with a factor of 4 (from f.i. 1,8 wt%/kg oil to 0,45 wt%/kg oil). This may be conservative. The

consumption of enzymes was set at 0,1 wt % of immobilised enzymes/ kg oil and 100 re-uses. In table

5.1 it was conservatively assumed that glycerine purification costs for enzymatically produced glycerin

(input 90-95% purity) are 100 €/tonne while for conventionally produced glycerine (75%-85% purity)

this was assumed to be 150 €/tonne. The difference in purification costs follows from the elimination of

a soap splitting and fractional distillation step when purifying enzymatically produced glycerine.

Table 5.1 shows that enzymatic biodiesel production may easily result in significantly lower operating

costs (excl. pure plant oil purchases). Table 5.1 only aims to display the main differences (differential

costs) between the conventional and enzymatic biodiesel process.

From table 5.1 it may also be concluded that the biggest economic advantage when applying

enzymatic biodiesel production processes may not result from decreased glycerine purification costs

but from drastically decreased feedstock oil costs. As the enzymes are able to also convert FFA’s and


are less sensitive towards water, lower qualities of pure plant oils (less refined), used cooking oils and

waste animal fats may be purchased which could easily lower the feedstock oil cost with 100 €/tonne.

Conventional production input data Enzymatic production input dataBiodieselproduction 100.000 tonnes/yr Biodieselproduction 100.000 tonnes/yrBio-oil price 700 €/tonne Bio-oil price 600 €/tonneBiodieselprod. efficiency 98% Biodieselprod. efficiency 98%KOH consumption 1,8% KOH consumption 0,45%KOH cost 600 €/tonne KOH cost 600 €/tonneCrude glycerin production 15.000 tonnes/yr Enzymes consumption 0,1%Glycerine purification cost 150 €/tonne Immob. enzymes cost 100.000 €/tonne

Number of re-uses 100 timesCrude glycerin production 13.000 tonnes/yrGlycerine purification cost 100 €/tonne

Cash flows (excl. bio-oil) Cash flows (excl. bio-oil)KOH purchasing 1.080.000 €/yr KOH purchasing 270.000 €/yrGlycerine purification costs 2.250.000 €/yr Enzymes purchasing 100.000 €/yr

Glycerine purification costs 1.300.000 €/yrOperating cost 3.330.000 €/yr Operating cost 1.670.000 €/yr

Cash flows for bio-oil purchasing Cash flows for bio-oil purchasingBio-oil purchasing 71.428.571 €/yr Bio-oil purchasing 61.224.490 €/yr

Table 5-1 Economic comparison of conventional versus enzymatic biodiesel production


6 Transformation of glycerin into high-quality products

6.1 Investigation of alternative high-quality products from glycerin.

The following processes can be utilized in obtaining useful derivatives from glycerol:

Esterification, Etherification, Oxidation, Reduction, Amination, Halogenation, Phosphorylation,

Nitration and Sulfaction.

The complete schematic flow sheet is given for the production [36] [40] and utilization routes for glycerin

(R&D Potential for biodiesel, NREL 2003).


• Esterification


• Oxidation

• Reduction

The specialty chemicals from glycerin are due the fact that Glycerol provides a C3 building block for

complex structures. It is easily modified by reacting –OH functional groups and it can produce water

soluble, nontoxic, and nonflammable products.


6.2 Conversion of glycerol to methanol

The glycerin [2] recovered from the transesterification reaction is etherified with methanol, ethanol or

butanol using another proprietary heterogeneous catalyst. The former methanol plant at Delfzijl

acquired in 2006 from the joint owners DSM, Akzo Nobel and Dynea by BioMethanol Chemie Holding

(a consortium of Ecoconcern, the NOM, the investor OakInvest, and the process technologists Sieb

Doorn and Paul Hamm) produces fossil methanol and plans to use glycerin as a raw material for

producing bio-methanol. The bio-methanol is intended for use in the first instance as a petrol additive

but at a later stage it could power fuel cells. The plant formerly produced methanol from natural gas

but was closed down because this process was no longer profitable. The plant [1] will use a new

process to make bio-methanol from glycerin.

For the biodiesel process this can eliminate the role of methanol:

C57H104O6 ) + 3 CH3OH → 3 C19H36O2 + C3H8O3

C3H8O3 + 2H2 → 3 CH3OH ∆H reaction = -49 KJ/Mol

Total overall theoretically:

C57H104O6 + 2H2 → 3 C19H36O2

6.3 Conversion of Glycerol to Hydrogen

6.3.1 Virent’s APR (Aqueous-Phase Reforming) process

Virent [26] has developed the novel APR (Aqueous-Phase Reforming) process and has shown that it is

effective for generating hydrogen from aqueous solutions of glycerol. The APR process is a simple

one-step reforming process that can generate easily purified hydrogen and as such is especially cost

effective.


The APR process:

1) Generates hydrogen without the need to volatilize water, which represents a major energy saving.

2) Occurs at temperatures and pressures where the water-gas shift reaction is favorable, making it

possible to generate hydrogen with low amounts of CO in a single chemical reactor.

3) Occurs at pressures (typically 15 to 50 bar) where the hydrogen-rich effluent can be effectively

purified using pressure swing adsorption technology.

4) Takes place at low temperatures that minimize undesirable decomposition reactions typically

encountered when carbohydrates are heated to elevated temperatures.

5) Utilizes agricultural derived feedstocks.

Process Overview – Biodiesel to Hydrogen Raw glycerol is refined to remove contaminants such as KOH and alcohols, and the resultant pure

material is used in many applications including food and personal products. Raw glycerol can be

mixed with water and the resulting aqueous solution can be fed to the APR process that generates

hydrogen in a single reactor. The effluent gas from the APR process can be purified to produce high

purity hydrogen.

The APR process generates hydrogen by reacting a carbohydrate, in this case glycerol, with water to

form carbon dioxide and hydrogen as follows:

C3H8O3 + 3H2O → 3CO2 + 7H2`

∆H reaction =-+341 KJ/Mol

APR process runs at low temperature, an alternative method of providing process energy will be to

utilize waste heat streams from other associated processes. Thermal efficiencies of the process can

be maintained via proper heat exchange (i.e. preheating feed to the reactor by exchanging with the

reactor effluent). Alkanes such as methane, ethane, and propane are also formed in low

concentrations in the APR reactor. The alkane formation is an exothermic process, and while alkane

formation lowers the hydrogen yield, the formation of these compounds provides heat for the

endothermic hydrogen generation process.


Figure 6-1 Overview [26] of the production of hydrogen from biodiesel waste

The non-condensable gas stream leaving the APR contains predominately CO2 and H2. Hydrogen can

easily be purified from this gas stream utilizing pressure swing adsorption (PSA) technology.

Importantly, the gas stream that exits the APR is at desired feed pressures for the PSA unit (between

16 and 40 bar). Accordingly, the PSA unit does not need an expensive and energy consuming

compressor to provide the necessary feed pressure. This results lower capital costs and increased

system energy efficiency. Another important feature is that the PSA technology will generate a waste

hydrogen stream (typically 10 to 20 percent of the feed) due to the pressure swing and purging cycles.

This waste stream would also contain the alkanes produced in the APR process. Combustion of the

waste hydrogen and alkanes would provide much of the necessary processing heat for the reactor.


The gas stream leaving the APR could be utilized directly as a high energy fuel gas to power internal

combustion engines, gas-fired turbines, and solid oxide fuel cells. The high temperature waste heat

from such devices could be recycled back to provide the necessary process heat for the APR process.

In such a configuration, the APR process could generate a fuel gas stream that contains over 100% of

the heating value of the feed glycerol. In addition to fuel, purified hydrogen from the waste stream

could be used as a chemical reactant for hydrogenation reactions. It also is possible to efficiently

purify the CO2 from the high-pressure effluent stream of the APR process. This purified CO2 could be

used either as a chemical or sequestered making the process of generating hydrogen from corn a

consumer of the greenhouse gas CO2.

6H2 + 2CO2 → 2CH3OH + 2H2O

Finally, the waste stream could provide a starting reactant for the production of biodiesel. Hydrogen

and CO2 reacted over a catalyst of copper and zinc is converted to methanol by the reaction

Preliminary Cost Model The following assumptions are made in this analysis:

1) APR reforming unit that generates 530 kg of hydrogen per day.

2) Capital cost which includes the cost of precious metal catalyst.

3) Operation and maintenance expenses are included.

4) 10% return on investment with a depreciation over 15 years.

With Virent’s targeted efficiency of 70% for the APR process, output of 2 Watts/gm catalyst, and a raw

glycerol cost of 11.4 euro cent per lb, it is expected that hydrogen can be generated at approximately

3.04 euros per kg.


Figure 6-2 Preliminary [24] cost model for APR production of H2 from glycerol

A comparable steam reformer utilizing non-renewable natural gas is expected to be 56% efficient and

could generate hydrogen at a cost of 2.66 euros per kg of hydrogen (National Research Council,

2004). Furthermore, a comparable unit that generates hydrogen via the electrolysis of water would

generate hydrogen at a cost of 4.94 euros per kg of hydrogen (1 kg equals a heating value of 121 MJ).

.

6.4 Conversion of glycerol to useful chemicals via bacteria 6.4.1 Hydrogen and Ethanol Production from Bacteria Enterobacter

aerogenes HU-101

The microbial [25] conversion of glycerol to various compounds has been investigated recently with

focus on the production of H2 and ethanol from glycerol. H2 is expected to be a future clean energy


source and ethanol can be used as a raw material and a supplement to gasoline. The microorganism

used in this study was E. aerogenes HU-101 isolated from methanogenic sludge. The biodiesel

wastes should be diluted with a synthetic medium to increase the rate of glycerol utilization and the

addition of yeast extract and tryptone to the synthetic medium which accelerates the production of H2

and ethanol. The yields of H2 and ethanol decreased with an increase in the concentrations of

biodiesel wastes and commercially available glycerol (pure glycerol). Furthermore, the rates of H2 and

ethanol production from biodiesel wastes were much lower than those at the same concentration of

pure glycerol, partially due to a high salt content in the wastes. In continuous culture with a packed-

bed reactor using self-immobilized cells, the maximum rate of H2 production from pure glycerol was

80mmol/l/h yielding ethanol at 0.8mol/mol-glycerol, while that from biodiesel wastes was only

30mmol/l/h. However, using porous ceramics as a support material to fix cells in the reactor, the

maximum H2 production rate from biodiesel wastes reached 63mmol/l/h obtaining an ethanol yield of

0.85mol/mol-glycerol.

To ferment biodiesel wastes to H2 and ethanol using E. aerogenes, it would be desirable not to add

any supplements that support cell growth to reduce the cost of fermentation and wastewater treatment

after fermentation. Therefore, batch fermentation was first carried out with biodiesel wastes diluted

with deionised water. When biodiesel wastes were diluted to 80 mM glycerol with deionised water,

glycerol was not completely consumed even after 48 h and no growth was observed after 48 h. This

indicated that some nutrients should be added to ferment glycerol in biodiesel wastes. Therefore, the

synthetic medium was used for dilution of biodiesel wastes. The rate of glycerol utilization further

increased using the synthetic medium. When biodiesel wastes were diluted to 80 mM glycerol with the

synthetic medium, glycerol was completely utilized after 24 h, yielding H2 at 0.89 mol/mol-glycerol and

ethanol at 1.0 mol/mol-glycerol respectively. To minimize the reactor size and running cost, it is

desirable that the concentration of biodiesel wastes is as high as possible. Therefore, batch

fermentation was carried out with biodiesel wastes diluted with the complex medium, which consisted

of the synthetic medium containing 5 g/l yeast extract and 5 g/l tryptone to 1.7, 3.3, 10 and 25 g/l as

glycerol concentrations. Although the yields of H2 and ethanol were 1 mol/mol-glycerol using 5 g/l

glycerol, they decreased with the increase in glycerol concentration, as observed in biodiesel wastes.

The result indicated that a higher concentration of glycerol decreased the

yields of H2 and ethanol. It is necessary to increase glycerol concentration used in the production of H2

and ethanol because an excessive dilution of biodiesel wastes using the medium increases the cost

for the recovery of ethanol and wastewater treatment. Although H2 and ethanol production from


biodiesel wastes was demonstrated using the wild strain of E. aerogenes HU-101 in this study, it is

necessary to further optimize culture conditions and to breed mutants with a high tolerance to a high

concentration of glycerol or salts by conventional breeding methods or genetic engineering.

6.4.2 Glycerol catabolism by Bacteria Pediococcus pentosaceus Among the lactic acid bacteria [27] isolated from beer at different stages of elaboration, Pediococcus

pentosaceus was the predominant species and the only that used glycerol as sole carbon source. Its

utilization was studied in CAg strain growing on glycerol or on glycerol and limited concentration of

glucose. Glycerol kinase and glycerol dehydratase pathways were responsible for glycerol

degradation. On glycerol alone, the enzymatic activities of both pathways were expressed

simultaneously and after glycerol consumption, the main products were acetate, 2,3-butanediol (2,3-

BD) and 1,3-propanediol (1,3-PD). When the carbon source was glycerol and glucose the glycerol was

firstly degraded by the reductive pathway and after glucose consumption the activities of the glycerol

kinase pathway were expressed. In this condition, glycerol was transformed into lactate, acetate, 2,3-

BD and 1,3-PD.

6.4.3 Microbial Conversion of Glycerol to 1,3-Propanediol The [41] biological production of 1,3-propanediol from glycerol was demonstrated for several bacterial

species, e.g., Lactobacillus brevis, Lactobacillus buchnerii, Bacillus welchii,Citrobacter freundii,

Klebsiella pneumoniae, Clostridium pasteurianum, and Clostridium butyricum. Among these

microorganisms, C. butyricum is to the authors knowledge the best “natural producer” in terms of both

the yield and the amount of 1,3-propanediol produced. Moreover, unlike the case with other bacteria,

the production of 1,3-propanediol by this microorganism is not a vitamin B12-dependent process,

which is clearly an economical advantage for an industrial application. The B12-independent pathway

converting glycerol to 1,3-propanediol in C. butyricum has been recently characterized from a

biochemical and a molecular point of view. To develop an economical process of 1,3-propanediol

production, it is necessary to further improve the process by a metabolic engineering approach with

the strain. No genetic tools are currently available for C. butyricum. Among the clostridia, Clostridium

acetobutylicum is a microorganism of choice, as it has already been used for the industrial production

of solvent and the genetic tools for gene knockout or gene over expression are currently available.

Engineering of C. acetobutylicum DG1 for the production of 1,3-propanediol. The conversion of

glycerol to 1,3-propanediol in C. butyricum occurs in two steps. First, glycerol is dehydrated to 3-


hydroxipropionaldehyde in a reaction catalyzed by the B12-independent glycerol dehydratase. Next, 3-

hydroxipropionaldehyde is reduced to 1,3-propanediol by 1,3-propanediol dehydrogenase, consuming

1 mole of NADH. Both the pSPD5 plasmid carrying the 1,3-propanediol from C. butyricum and the

control pIMP1 plasmid were introduced into the C. acetobutylicum DG1 mutant, which is cured of the

pSOL1 megaplasmid and is thus unable to produce solvents and to sporulate. While C.

acetobutylicum DG1 (pIMP1) was unable to grow on glycerol, C. acetobutylicum DG1 (pSPD5) could

grow and consume glycerol to produce 1,3-propanediol as the main fermentation product .

6.5 Glycerol hydrogenolysis to glycols

Glycerol [30] is first adsorbed and dehydrogenated reversibly on the metal catalyst to form

glyceraldehyde. The glyceraldehyde then desorbs from the catalyst and can react through four

different paths in the basic media: the retro-aldol mechanism to form the precursor of ethylene glycol

(glycolaldehyde), oxidation and subsequent decarboxylation to also form glycol aldehyde, dehydration

to the precursor of propylene glycol (2-hydroxypropionaldehyde) or degradation to unwanted side

products. The two glycol precursors could potentially also degrade to unwanted side products. Finally,

the respective glycol precursors are hydrogenated by the metal function to the product glycols.

The flow scheme below gives the reaction pathway for the production of glycols from glycerol.


6.6 Pyrolysis of glycerol

Experimental results of the decomposition of glycerol in near and supercritical water are presented

considering measurements in the temperature range of 622–748 K, at pressures of 25, 35, or 45 MPa,

reaction times from 32 to 165 s, and different initial concentrations. The reaction was carried out in a

tubular reactor and a conversion between 0.4 and 31% was observed. The main products of the

glycerol degradation [42] are methanol, acetaldehyde, propionaldehyde, acrolein, allyl alcohol, ethanol,

formaldehyde, carbon monoxide, carbon dioxide, and hydrogen.

The fact that the measured composition of the product mixture at constant temperature is depended

on the density was taken as an indication, that these products could be formed by competing ionic and

free radical reaction pathways. Usually in gas kinetics, the product composition changes with

temperature. This is due to the different activation energies, the concentration effect on bimolecular

elementary reaction steps and in a minor extent with pressure. In water, the drastic dependence on

pressure is likely a consequence of the competition between reactions with different polarity.

Figure 6-3 Experimental [42] setup of the tubular reactor


The main products obtained from the reaction mechanisms are:

Methanol: Is formed only by the radical mechanism from the radicals CH2OH and CH3O in a hydrogen

transfer reaction. These radicals are formed directly (or indirectly if an isomerization is included) from

the primary radicals (formed by metathesis from glycerol) by radical decomposition. There is no

methanol formed by the ionic mechanism although the experiments show a small amount of methanol

at ionic conditions. Therefore, the ionic mechanism should be completed by a reaction sequence

consisting of glycerol decomposition: glycerol is protonated at the primary O-atom and may

decompose to methanol and two formaldehydes.

Allyl alcohol: Is the second frequent product at high temperatures, is also formed only by the free

radical mechanism. Allyl alcohol can formally be considered as a glycerol, where two neighboring OH-

groups have been removed. Ionic reaction steps can hardly do this. In the radical mechanism, the first

OH-group is removed by the reaction of glycerol with H-atoms. From the resulting radical, the second

OH is then removed by a radical decomposition.

Acetaldehyde: Is the main product at nearly all conditions. It is formed by an ionic and a free radical

pathway. In the ionic mechanism, it is formed by the primary protonated glycerol, followed by water

abstraction to form the primary carbonium ion. Deprotonisation is followed by formaldehyde

abstraction forms the enol-form of acetaldehyde. More than one pathway to form acetaldehyde exists

in the radical mechanism. All of them start with one of the C3-radicals (from glycerol) and the

decomposition to C1 and C2 fragments. From the C2-substances, acetaldehyde is formed by

isomerization or decomposition.

Acrolein: again is formed by ionic and by radical reaction steps. When glycerol is protonated at the

secondary OH-group and the secondary carbonium ion is formed by water elimination, only the

formation of acrolein as a simple reaction step remains. The same is true for the primary carbonium

ion. A simple H2O-elimination and deprotonation leads to acrolein. But for the primary carbonium ion

competitive reactions exist, which lead to acetaldehyde and formaldehyde. In the radical mechanism,

a hydrogen abstraction from glycerol leads to a radical, which eliminates an OH-radical and also water

and finally forms acrolein.


Figure 6-4 Formation [42] of acetaldehyde, acrolein and formaldehyde

Formaldehyde: In the ionic mechanism is formed by the same reactions as acetaldehyde. In the

radical mechanism, nearly all reaction paths, in which a decomposition of C3-radicals to C1 and C2-

fragments take place, lead to CH2O formation. Formaldehyde is here only an intermediate product,

because it is oxidized to CO or CO2 by a sequence of reactions with OH-radicals.

Carbon monoxide: Is formed by the reaction of CH2O with an OH-radical to water and the CHO-

radical, which consecutively decomposes to CO and H-atom.

Carbon dioxide: Is formed by oxidation of CO with OH to form CO2 and an H-atom.

Hydrogen: Is formed by all metathesis reactions (mostly with glycerol) of the H-atoms. The H-atoms

can also react with the OH-groups of a substance (mostly glycerol) to form water and a radical.

Propionaldehyde: Is a product measured only at low concentration. There is no formation in a simple

ionic pathway imaginable. The radical pathway to propionaldehyde is also rather complicated. One of

the paths starts from allyl alcohol (which can be considered as an isomer of propionaldehyde). A

radical addition (e.g. H-atom) followed by a combination of radical isomerization (enol-type) and

radical elimination can yield the propionaldehyde. A lot of other minor products were measured during

the experiments, which are only partially included in the reaction mechanism: ethanol, acetone,

ethane, ethene, propene, propane, butenes, butanes, methyl-hydroxy-dioxanes and other products of

higher molar masses. Most of the minor products are only found at higher temperatures and are most

likely formed via radical reaction pathways decomposing the main products.


6.7 Conversion of glycerol by Fischer–Tropsch process

The method presented here may allow for economic operation of a small-scale Fischer–Tropsch [45]

reactor by producing an undiluted H2/CO gas mixture. The method reduces the capital cost of the

Fischer–Tropsch plant by eliminating the O2 plant or biomass gasifier and subsequent gas-cleaning

steps. The conversion of glycerol into CO and H2 takes place by Equation (1).

The endothermic enthalpy change of this reaction (350 kJ/mol) corresponds to about 24% of the

heating value of the glycerol (1480 kJ/mol). The heat generated by Fischer–Tropsch conversion of the

CO and H2 to liquid alkanes such as octane (412 kJ/mol) corresponds to about 28% of the heating

value of the glycerol. Thus, combining these two reactions results in the following exothermic process,

with an enthalpy change (63 kJ/mol) that is about 4% of the heating value of the glycerol:

Catalysts consisting of Pt supported on Al2O3, ZrO2, CeO2/ZrO2, and MgO/ZrO2 exhibited deactivation

during time-on-stream, whereas the Pt/C catalyst showed stable conversion of glycerol into synthesis

gas for at least 30 hours. The catalyst with the most acidic support, Pt/Al2O3, showed a period of

apparently stable catalytic activity, followed by a period of rapid catalyst deactivation. The reactor

initially operates at 100% conversion, glycerol is present only in the upstream portion of the catalyst

bed in the tubular reactor and a deactivation front moves from the reactor inlet to the outlet as olefinic

species are formed from glycerol on acid sites associated with alumina, followed by deposition of coke

from these species on the Pt surface sites. The most basic catalyst support, MgO/ZrO2, showed rapid

deactivation for all times-on stream. The most stable oxide-supported catalyst appears to be Pt on

CeO2/ZrO2; however, the performance of this catalyst is inferior to that of Pt supported on carbon. The

different deactivation profiles displayed in Figure 8 for the various catalysts suggest that the support

plays an important role in the deactivation process. Figure 8d shows the rate of formation of C2-

hydrocarbons (ethane and ethylene) normalized to the rate of H2 production for the various supported

Pt catalysts. Negligible amounts of C2-hydrocarbons were formed on the Pt/C catalyst. In contrast,

catalysts consisting of Pt supported on the various oxides formed measurable amounts of C2-

hydrocarbons, and the C2-TOF/H2-TOF ratio (TOF=turnover frequency) increased with time-on-


stream. This behavior suggests that one of the modes of catalyst deactivation is caused by

dehydration on the oxide catalyst supports, which leads to the formation of unsaturated hydrocarbon

species that form carbonaceous deposits on the Pt surface, thereby decreasing the rate of H2

production and increasing the C2- TOF/H2-TOF ratio. The H2/CO ratio for the product stream from the

Pt/C catalyst is approximately 1.3:1 (Table 2), which is in agreement with the stoichiometry of Equation

(1). In contrast, the H2/CO ratios obtained over the other catalysts were higher than 1.5:1, which

indicates some contribution from water–gas shift (WGS). This behavior is demonstrated more clearly

by the CO/CO2 ratio (Figure 8c). The initial CO/CO2 ratio for Pt/C is 12:1, whereas for the other

catalysts it is less than 3:1. Thus, it appears that the WGS reaction is facilitated by the presence of the

oxide support, as reported in other studies of WGS over supported metal catalysts.

(a). Percentage of glycerol conversion to gas phase products.

(b). Hydrogen turn over frequency.

(c). Carbon monoxide and dioxide molar ratio.


(d). C2-TOF/H2-TOF ratio for Pt catalysts supported on Al2O3.

Figure 6-5 Performance [45] of supported Pt catalysts with Variation with time-on-stream.

For these studies of reaction kinetics, 0.060 g of 5 wt% Pt/C was used. [a] Glycerol feed 30 wt%, 623

K, 1 bar. [b] Feed flow rate 0.32 cm3/min, 623 K, 1 bar. [c] Point taken after 2 h time-on-stream. [d]

Glycerol feed 30 wt%, 0.32 cm3/min and 1 bar.


Table 5-1: Experimental [45] data for catalytic processing of glycerol into synthesis gas under various

conditions

Conditions

Conversion into

gas phase [%]

H2-TOF

[min_1]

H2/CO

CO/CO2 CH4/H2

Feed flow rate

[cm3min_1][a]

0.08

68

0.16 71

0.32 64

0.64 39

111

241

373

449

1.6

1.4

1.3

1.3

5.7

8.8

12

17

0.038

0.036

0.045

0.038

Glycerol

concentration

wt%][b]

20 64

30 50

50 26

265

285

267

1.4

1.3

1.2

8.7

14

37

0.025

0.032

0.050

T [K][d]

573 17

623 54

673 100

673[c] 72

723 61

723[c] 43

104

335

600

450

419

300

1.31

1.31

1.33

1.38

1.68

1.83

90

17

11

-

4.6

-

0.037

0.027

0.027

-

0.019

-

The catalytic conversion of polyols to H2, CO2, and CO involves the preferential cleavage of C-C

bonds as opposed to C-O bonds and Pt-based catalysts are particularly active and selective for this

process. Under these reaction conditions, the surface is covered primarily by adsorbed CO species. A

strategy for a catalyst that converts polyols into synthesis gas and is active at low temperatures is to

facilitate the desorption of CO, thereby suppressing the subsequent WGS step and improving the

turnover of the catalytic cycle by regenerating vacant surface sites. Accordingly, we require materials

that possess the catalytic properties of Pt with respect to selective cleavage of C-C versus C-O bonds,

but that have less exothermic enthalpy changes for CO adsorption; Pt–Ru and Pt–Re alloy catalysts fit

this description. These results demonstrate that the conversion of glycerol to synthesis gas can be

accomplished at temperatures well within the ranges employed for Fischer–Tropsch and methanol

syntheses, thus allowing for the efficient combination of these processes at low-temperature catalytic

route for converting glycerol into H2/CO gas mixtures that are suitable for combination with Fischer–

Tropsch and methanol syntheses.


6.8 Selective etherification of glycerol to polyglycerols

Glycerol [32] can be esterified to polyglycerols and especially polyglycerols-esters (PGEs) are gaining

prominence. Esterification of glycerol could be selective to monoglycerides over cationic resins. Never

the less, polyglycerols and polyglycerols esters as well as acrolein were obtained as main by-

products. The schematic representation of the etherification of glycerol to poly glycerols is given

below.

Glycerol etherification is carried out at 533K in a batch reactor at atmospheric pressure under N2 in the

presence of 2 wt% of catalyst; water being eliminated and collected using a Dean-Stark system.

Reagents and products are analysed with a GPC after silylation (It involves the replacement of an

acidic hydrogen on the compound with an alkylsilyl group).

6.9 Glycerolysis–hydrolysis of canola oil in supercritical carbon dioxide

Conventional [33] glycerolysis requires high temperatures (220–260ºC) to increase the solubility of

glycerol in the fat phase, the addition of nitrogen gas to prevent oxidation and the presence of an

inorganic catalyst. The reactants must also be vigorously stirred throughout the reaction and, at the

end of the reaction, the catalyst must be neutralized and reaction mixture must be rapidly cooled to

prevent reversion. Conducting glycerolysis in supercritical carbon dioxide (SC-CO2) simplifies the

conventional process. Under ambient conditions, oil and glycerol are immiscible and the main reason

for conducting glycerolysis reactions at 250ºC is to increase the solubility of glycerol in oil. With the


addition of SC-CO2, it is possible that there may be three phases (liquid–liquid–vapor) inside the

reactor.

6.10 Converting glycerin to propylene glycol

Hydrogenolysis [28] of glycerol to propylene glycol was performed using nickel, palladium, platinum,

copper, and copper-chromite catalysts. The effects of temperature, hydrogen pressure, initial water

content, choice of catalyst, catalyst reduction temperature and the amount of catalyst were evaluated

by the authors. At temperatures above 200 ºC and hydrogen pressure of 200 psi, the selectivity to

propylene glycol decreased due to excessive hydrogenolysis of the propylene glycol. At 200 psi and

200 ºC the pressures and temperaures were significantly lower than those reported in the literature

while maintaining high selectivities and good conversions. The yield of propylene glycol increased with

decreasing water content. Propylene glycol, i.e. 1,2 propanediol, is a three-carbon diol with a

steriogenic center at the central carbon atom. Propylene glycol is a major commodity chemical with an

annual production of over 1 billion pounds in the United States and sells for about 0.53 euro cent per

pound with a 4% growth in the market size annually. The commercial route to produce propylene

glycol is by the hydration of propylene oxide derived from propylene by either the chlorohydrin process

or the hydroperoxide process. There are several routes to propylene glycol from renewable

feedstocks. The most common route of production is through hydrogenolysis of sugars or sugar

alcohols at high temperatures and pressures in the presence of a metal catalyst producing propylene

glycol and other lower polyols. The summary of the overall reaction of converting glycerol to propylene

and ethylene glycols is given below:


In the presence of metallic catalysts and hydrogen, glycerol can be hydrogenated to propylene glycol,

1,3 propanediol or ethylene glycol. Copper-chromite catalyst was identified as the most effective

catalyst for the hydrogenolysis of glycerol to propylene glycol.

6.11 Glycerol conversion in the presence of noble metals as catalysts

Various noble metals (Ru/C, Rh/C, Pt/C, and Pd/C) and acid catalysts [an ion-exchange resin

(Amberlyst), H2SO4 (aq), and HCl(aq)], the combination[29] of Ru/C with Amberlyst is effective in the

dehydration and hydrogenation (i.e. hydrogenolysis) of glycerol under mild reaction conditions (393 K,

8.0 MPa). The dehydration of glycerol to acetol is catalyzed by the acid catalysts. The subsequent

hydrogenation of acetol on the metal catalysts gives 1,2-propanediol. The activity of the metal catalyst

and Amberlyst in glycerol hydrogenolysis can be related to that of acetol hydrogenation over the metal

catalysts. Regarding acid catalysts, H2SO4 (aq) shows lower glycerol dehydration activity than

Amberlyst, and HCl(aq) strongly decreases the activity of acetol hydrogenation on Ru/C. In addition,

the OH group on Ru/C can also catalyze the dehydration of glycerol to 3-hydroxypropionaldehyde,

which can then be converted to 1,3-propanediol through subsequent hydrogenation and other

degradation products.

1,3-propanediol can be formed from dehydration of glycerol to 3-hydroxypropionaldehyde and

subsequent hydrogenation over Ru/C.

The role of OH species on Ru is thought to be important because Ru/C is much more active than other

noble metal catalysts in glycerol hydrogenolysis Another important point is that Ru species can

catalyze dehydration to 3-hydroxypropionaldehyde, although two dehydration routes can be traced to

3-hydroxypropionaldehyde and acetol. When this OH species attacks H linked to terminal carbons, 3-

hydroxypropionaldehyde is produced, which can explain the dehydration selectivity. However, the

reason why OH species do not attack H linked to center carbons remains unclear:


Another product of glycerol dehydration is acetol, the subsequent hydrogenation of which can give

1,2-propanediol.

In the case of the Amberlyst, the active species is a proton. Acetol is formed when the proton attacks

OH linked to terminal carbons:

Given below is the reaction scheme of glycerol hydrogenolysis and degradation reactions.


The combination of Ru/C and Amberlyst is effective for glycerol hydrogenolysis under mild reaction

conditions (393 K) compared to Rh/C, Pt/C, and Pd/C as metal catalysts and HCl(aq) and H2SO4(aq)

as acid catalysts. The good performance of Ru/C and Amberlyst in glycerol hydrogenolysis may be

due to the high activity of glycerol dehydration to acetol over Amberlyst and the high hydrogenation

activity of acetol to 1,2-propanediol over Ru/C. The degradation of glycerol proceeded as a side

reaction in glycerol hydrogenolysis, and Ru/C can catalyze the degradation reaction. Ru/C catalyst

can play an important role in the dehydration of glycerol to 3-hydroxypropionaldehyde, which can be

converted to 1,3-propanediol through subsequent hydrogenation and other degradation products. In

particular, the contribution of Ru–OH species is suggested in the dehydration of glycerol

6.11.1 Glycerol tri-butyl ether (GTBE)

In the flow scheme [36] below, the flow scheme describes the conversion of glycerin and isobutlylene

on acid catalysis to give mono, di and tri glycerols.


Glycerol tri butyl ether is a mixture of di and tri butyl ethers of glycerin. This product is particularly

suitable in reducing the emissions of particulate matter, NOx and hydrocarbons when used as a fuel

additive in diesel.

The present state of GTBE is that the synthesis from glycerin and isobutylene has been studied up to

a first plant set up and cost price. The industrial feasibility is positive and process development is

going on. As per the EU directive there’s a production of one million tons of glycerin per annum.

Although the increased production of biodiesel is a positive aspect, the huge quantity of the by product

glycerol needs a proper usage outlet. The world glycerin market cannot take up this additional amount

and the best way to tackle this problem would be to utilize the excess glycerin in making GTBE. This

will not only lower the diesel emissions but also solve the glycerin problem. International cooperation

and funding is required for further product development. Table 4, shows the amount of Nitrous oxides

and particulate matter reduction on using Glycerol tri butyl ether as a fuel additive in diesel. In diesel

engines, changing the fuel composition is an alternative route towards achieving lower emission

levels. The potential of oxygenated fuels to significantly reduce particulate matter emissions has

already been demonstrated. Table 4 shows the Exhaust gas recirculation (EGR) and reduction with

increasing oxygen content (ROSI) on addition of GTBE to diesel.


Table 5-2: Amount [36] of N0x and particulate matter reduction on the usage of GTBE additive in diesel.

In figure 9, the selective analysis of GTBE: diesel ratio is given with isobutene and glycerol as

reactants. The processing costs, NOx reduction and diether selectivity is shown. The variation

percentage of the diesel cost decreases as the use GTBE increases, the NOx however remains more

or less the same.

Figure 6-6 Selective analysis [36] GTBE/diesel ratio for isobutene and glycerol as reactants


6.11.2 Mono-, di-, and tri-tert-butyl ethers of glycerol

In the glycerol ethers synthesis [38], the ethers are excellent oxygen additives for diesel fuel.

Oxygenated diesel fuels are of importance to both environmental compliance and efficiency of diesel

engines. A number of studies on the preparation of glycerol ethers by using different catalytic systems

have been reported. The reaction can be carried out with homogenous or heterogeneous acidic

catalysts. Recently, we developed a procedure of catalytic synthesis of high value glycerol ethers

(primarily di and tri-tert-butyl), obtained directly from glycerol and isobutene contained in the cracking

derived fraction. Several products were obtained in this reaction, the desired ones being: 1,3-di-tert-

butoxy-propan-2-ol (2a), 2,3-di-tert-butoxypropan- 1-ol (2b), 1,2,3-tri-tert-butoxy-propane (3). Efficacy

of 2a, 2b, and 3 for biodiesel fuel results from their decrease of emission of particulate matter,

viscosity, cold filter plugging point, and cloud point. Given below is the flow scheme for tert-Butylation

of glycerol catalysed by ion-exchange resins.

The best [39] results of glycerol tert-butylation by isobutylene at 100% conversion of glycerol with

selectivity to di- and tri-ethers larger than 92% were obtained over strong acid macro reticular ion-

exchange resins. Di- and tri-tert-butyl ethers of glycerol are potential oxygenates to diesel fuel. There

are known some possibilities improving burning characteristics of diesel fuels with oxygenate


additives. Tert- Butyl ethers of glycerol (G) with high content of di-ethers and especially tri-ethers are

known as potential oxygenates to diesel fuels (diesel, biodiesel and their mixtures) for a long time.

These ethers can reduce the emissions and mainly particulate matters (PM). Glycerol tert-butyl ethers

on the basis of natural glycerol as a by-product from transesterification of natural oils by methanol

(production of biodiesel) can be potential alternative for tert-butyl alcohol (TBA), isobutylene (IB) and

preferentially C4-fraction. The tert-butylation of glycerol with isobutylene is a complex of three acid

catalysed consecutive equilibrium reactions with formation of mono-, di- and tri-ethers.

The etherification of glycerol is preferred on primary hydroxyl groups (formation of 1-tert-butyl glycerol

and 1,3- di-tert-butyl glycerol). Di- and tri-tert-butyl ethers of glycerol are usable as potential oxygenate

additives to diesel fuels because of their blending with diesel. Mono-tertbutyl ether of glycerol (MTBG)

has a low solubility in diesel fuel and therefore the etherification of glycerol must be directed to the

maximum formation of di- and tri-ethers. The etherification of glycerol with isobutylene or tertbutyl

alcohol using strong acid ion-exchange resins amberlyst type and two large-pore zeolites H-Y and H

Beta was used. The highest glycerol conversion of 100% was obtained over strong acid macro

reticular ion-exchange resin A 35 at 60ºC. Higher temperature (90 ºC) causes considerable drop in

conversion and yield of desired di- and tri-ethers mainly in the case of acid ion-exchange resins.

6.12 Conclusions

Glycerin is one of the oldest chemicals and the possibilities of use are numerous. For most of the

applications glycerin has to be pure enough in order not to contaminate a catalyst or bacteria. Which

applications are most promising depends on technical and economical criteria in combination with

environmental benefits.

Promising applications from a market point of view are methanol, hydrogen, ethanol, 1,3 propanediol,

propylene glycol and GTBE. From a technical point of view these chemicals can all be made. The


methanol and propylene glycol production are close to commercial operation. The others still have to

be developed further and will become commercial at the earliest stage over 5 years.

One process looks especially useful for glycerin arising from conventional biodiesel production:

making hydrogen via the aqueous phase reforming (APR) process. The APR system generates

hydrogen from aqueous solutions of oxygenated compounds, such as biomass-derived glycerin, in a

single-step reactor process. Sodium hydroxide, methanol and the high pH levels common in low-grade

crude glycerin actually help the process. The producer claims that approximately 5 kg of glycerin can

be converted to 0.75 kg of hydrogen (50% efficiency). With the cheap crude glycerol there is a

possibility to generate gas from glycerol for less than 2 euro per kilogram.

Table 5-3 Indicator score for feasibility of different chemicals from glycerol.

Development phase9

Market Price

Euro/ton

Methanol D / C ο 250

Hydrogen R ++ 2200

Ethanol R ++ 740

1,3 propane diol D + + 1000

propylene glycol C ++ 1500

GTBE D ο 750

Polyglycerols D ο 1000

Conclusion is that all above mentioned chemicals have a great market potential based on glycerol

chemistry.

9 C= Commercial, R=Research, D = Demonstration


7 Conclusions

Enzymatic biodiesel production

Significant progress has been made by researchers at especially University of Cordoba towards the

development of the enzymatic biodiesel process. One doctoral thesis will be published shortly and an

enzymatic pilot plant will be erected in Spain. Enzymatic biodiesel production has the following

advantages:

-not sensitive to lower oil qualities (FFA and water content);

-much purer glycerin (90-95%) not spoiled by catalyst;

-operation at lower temperatures / better energy balance;

-lower chemical catalyst cost;

-much lower glycerin purification costs

-lower biodiesel purification costs.

Drawbacks which can be mentioned are the sensitivity of the process towards reaction conditions

(optimal process step sequences, degradation of enzymes, methanol-enzyme interaction) and the

economic necessity for (cheap) immobilisation and many re-uses of the enzymes. Although some

researchers claim 100 times re-use and/or lifetimes of 1 year much more independent lab-work is

needed to prove the viability of the enzymatic process.

Glycerin purification

The application of heterogeneous catalysts in biodiesel factories results in a much purer crude glycerin

and thus makes smaller scale and low-cost refining at the biodiesel plant viable. It is expected that

enzymatically produced crude glycerine could result in a purity of 90-95% when compared to the

conventional 75-85% purity. This is the result of the much lower KOH quantities used and the much

lower soap concentrations due to the fact that free fatty acids are also converted towards biodiesel.

Both soap splitting and fractional distillation of the 90-95% glycerine can probably be eliminated. It

seems likely that the use of activated carbon powders and/or ion adsorption (zeolites or resins)

techniques will probably be sufficient to obtain a glycerine purity of 99,5%. However, it is highly

recommended to perform actual laboratory tests of column purification of enzymatic glycerine are

necessary to gain a further understanding about the process, possible absorbents (f.i. wood powder,


carbon, clay minerals), regeneration, retention times and purities that can be obtained.

Glycerin market development

The refined glycerin market is described as being strong (with new feed and new chemical

applications) while the crude glycerin market is described as weak. The combination of high fossil oil

prices and historically low glycerin prices have resulted in the increased application of glycerin as an

ideal platform chemical in the chemical and pharmaceutical industry. Large quantities of crude glycerin

are also used the biogas and animal feed industry.

Economic evaluation

The application of enzymatic biodiesel will lead to lower chemical catalyst and much lower glycerine

purification costs. However, our evaluation has shown that the biggest economic advantage when

applying enzymatic biodiesel production processes may not result from decreased glycerine

purification costs but from drastically decreased feedstock oil costs. Attractive conversion routes

towards high value chemicals from glycerin have been identified. Many of these conversion routes

seem economically and technically feasible.

High value applications of glycerin

Glycerin is one of the oldest chemicals and the possibilities of use are numerous. For most of the

applications glycerin has to be pure enough in order not to contaminate a catalyst or bacteria. One

process looks especially useful for glycerin arising from conventional biodiesel production: making

hydrogen via the aqueous phase reforming (APR) process. The APR system generates hydrogen from

aqueous solutions of oxygenated compounds, such as biomass-derived glycerin, in a single-step

reactor process. Sodium hydroxide, methanol and the high pH levels common in low-grade crude

glycerin actually help the process. The producer claims that approximately 5 kg of glycerin can be

converted to 0.75 kg of hydrogen (50% efficiency). With the cheap crude glycerol there is a possibility

to generate gas from glycerol for less than 2 € /kg.


8 Future Outlook

It is clear from the research results that the purification of glycerol produced through normal process

routes needs several steps and is energy consuming. Therefore the current biodiesel research is

focused on developing new ways of producing biodiesel without using base/acid catalyst which can

greatly reduce the downstream processing step.

This report shows that enzymatically produced biodiesel offers huge opportunities which result from

the much lower oil feedstock costs, decreased energy consumption and decreased glycerine

purification costs. We encourage that more research activities are directed towards the development

and commercialisation of the enzymatic biodiesel route.

Another new biodiesel process uses a two-step supercritical reaction process with adsorption refining

[55]. In this process reaction is carried out at a temperature greater than the critical temperature of

methanol without using base/acid catalyst. Excess methanol is used and fats with any amount of free

fatty acid content can be a raw material for the process. The reaction is carried out in two steps since it

is the most economical way of meeting the energy and pumping requirement of the process [55]. In

contrast to the conventional way of purifying the glycerol stream, the glycerol stream from the reactors

is treated in adsorption beds [55] which later on can be recovered by flashing it with methanol stream

and recycling it back to the reactor. Another process that is tried involves immobilized enzyme

catalysis. In this regard lipase catalyst has been used and it requires the lowest temperature condition

for the reaction and requires less equipment in the purification stage as compared to acid and base

catalysts [48]. The main bottleneck for applying enzymatic production is the cost of catalysts which

makes the process economically less appealing [2]. Another important commercially developed

(Esterfif-HTM process) biodiesel production [45] which is based on heterogeneous catalysis by mixed

oxide of zinc and aluminium allowed reaching glycerol purity level of more than 98% from

transesterification reaction. The reaction in this case is carried out in two successive stages with

excess methanol recycled to the reactor by evaporation. Glycerol is also removed continuously which

favours the forward transesterification reaction. The other important process that has been developed

is microwave irradiation production of biodiesel [49, 56]. The application of microwave energy

selectively energize polar molecules over non-polar and neutral ones thereby enhances selectively the

physical and chemical processes to biodiesel production. The conversion is almost 100% resulting in


high biodiesel yield. It also facilitates separation process and hence the problem of separating glycerol

from other reaction products is mitigated.


APPENDIX A Literature cited

1. Mittelbach, M. (Graz 2004): Biodiesel – the comprehensive handbook

2. UFOP.de, visited 16th March 2007

3. Axens, personal communication, October 2005

4. TU/e, Jayaraj, M.; A review on glycerin

5. ADM, Connemann: Biodiesel in der Welt 2006+

6. Maneely (2006) – Glycerin production and utilisation

7. SRI Consulting, Chemical Economics Handbook (2006)

8. Ingenia company internal information (2007)

9. Van Loo, Procede (2006) – Biodiesel glycerin, the consequences and solution (GTBE)

10. FO Licht, World Ethanol and Biodiesel (Oil World), July 2007.

11. Miller-Klein 2006. Impact of biodiesel on the glycerol market

12. Biodiesel Magazine, September 2007. The glycerin spread, Ron Kotrba

13. ICIS Pricing report March 2007, Glycerin Europe

14. Positivliste fuer Einzelfuttermittel, 5e Auflage. Normenkommission, September 2006

15. New heterogeneous process for biodiesel production: A way to improve the quality and the value

of the crude glycerin produced by biodiesel plants. Catalysis Today, Volume 106, Issues 1-4, 15

October 2005, Pages 190-192 L. Bournay, D. Casanave, B. Delfort, G. Hillion and J.A. Chodorge

Institut Francais du Petrole (IFP), BP3, F-69390 Vernaison, France b Institut Francais du Petrole

(IFP), 1&4 av de Bois Preau, F-92852 Rueil-Malmaison Cedex, France c Axens, IFP Group

Technologies, 89 bd F. Roosevelt, F-92508 Rueil-Malmaison Cedex, France

16. D. Royon, et al (April 2006). Enzymatic Conversion of Vegetable oil to Biodiesel

17. F. Yagiz, D. Kazan, A.N. Akin (March 2007). Biodiesel production from waste oils by using lipase

immobilized on hydrotalcite and zeolites. Chemical Engineering Journal (2007)

18. H. Noureddini, X. Gao, R. S. Philkana (2004). Immobilized lipase for biodiesel fuel production from

soybean oil. Bioresource Technology Vol. 96, Issue 7 (May 2005), pp. 769-777

19. Y. Shimada, Y. Watanabe, A. Sugihara, Y. Tominaga (November 2001). Enzymatic alcoholysis for

biodiesel fuel production and application of the reaction to oil processing. Journal of Molecular

Catalysis B: Enzymatic 17 (2002), pp.133-142.

20. Y. Wang, S. Ou, P. Liu, F. Xue, S. Tang (March 2006). Comparison of two different processes to

synthesize biodiesel by waste cooking oil. Journal of Molecular Catalysis A: Chemical 252 (2006),

pp.107-112


21 http://www.greencarcongress.com/

22 http://www.icbamericas.com

23 http://www.france-chimie.com\

24

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_2.pdf

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manufacturing-process Journal of Bioscience and

Bioengineering, Volume100,Issue3, September2005, Pages,260-265,Society for Biotechnology No. 3,

260–265. 2005 DOI: 10.1263/jbb.100.260 Takeshi Ito, Yutaka Nakashimada, Koichiro Senba,

Tomoaki Matsui and Naomichi Nishio, Department of Molecular Biotechnology, Graduate School of

Advanced Sciences of Matter, Hiroshima University, 1-3-1 Kagamiyama, Higashi-Hiroshima 739-8530,

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Saad,, Facultad de Bioquimica, Quımica y Farmacia, Universidad Nacional de Tucum an and Centro

de Referencia para Lactobacilos (CERELA),Chacabuco 145. Tucum an C.P. 4000, Argentina.

[28] Low-pressure hydrogenolysis of glycerol to propylene glycol,Applied Catalysis A: General, Volume

281, Issues 1-2, 18 March 2005, Pages 225-231 Mohanprasad A. Dasari, Pim-Pahn Kiatsimkul,

Willam R. Sutterlin and Galen J. Suppes. Department of Chemical Engineering, W2028 Engineering

Bldg. East, University of Missouri, Columbia, MO 65211, USA Renewable Alternatives LLC, 410 S. 6th

Street, Suite 203, N. Engineering Bldg., Columbia, MO 65211-2290, USA.

[29] Glycerol conversion in the aqueous solution under hydrogen over Ru/C + an ion-exchange resin

and its reaction mechanism Journal of Catalysis, Volume 240, Issue 2, 10 June 2006, Pages 213-221

Tomohisa Miyazawa, Yohei Kusunoki, Kimio Kunimori and Keiichi Tomishige Institute of Materials

Science, University of Tsukuba, 1-1-1, Tennodai, Tsukuba, Ibaraki 305-8573, Japan.

[30] Biodiesel One-Day Course From Field to Fuel June 15, 2006 Coeur d’ Alene, Idaho Daniel G.

Lahr, Brent H. Shanks Department of Chemical Engineering, Iowa State University, Ames, IA 50011,

USA.

[31] http://journeytoforever.org/biodiesel_glycerin.html#sawdust


[32] Selective etherification of glycerol to polyglycerols over impregnated basic MCM-41 type

mesoporous catalysts Applied Catalysis A: General, Volume 227, Issues 1-2, 8 March 2002, Pages

181-190 J. -M. Clacens, Y. Pouilloux and J. Barrault Laboratoire de Catalyse en Chimie Organique,

UMR 6503, CNRS ESIP ,40 Avenue du Recteur Pineau, 86022 Poitiers Cedex, France.

[33] Kinetic modeling of glycerolysis–hydrolysis of canola oil in supercritical carbon dioxide media

using equilibrium data, The Journal of Supercritical Fluids, Volume 37, Issue 3, May 2006, Pages 417-

424 Paul H.L. Moquin, Feral Temelli, Helena Sovová and Marleny D.A. Saldaña.Department of

Agricultural, Food and Nutritional Science, University of Alberta, Edmonton, AB, Canada T6G 2P5

Institute of Chemical Process Fundamentals AS CR, Rozvojov 135, 16502 Prague, Czech Republic.

[34] Source:M.Heming,OGMR(12-2001), link:http://mlecture.uni-bremen.de/intern/ss2005/fb04/vak-04-

6100108/20050427_a/folien.pdf

[35] Biodiesel in Europa 2005+J.Connemann, J.Fischer, für das Forum industrial ecology 27. April

2005 Uni Bremen.

[36] Families of Possible Glycerol Reactions (source: Biomass oil analysis: research needs and

recommendations)

[37] Glycerin Production and Utilization Liberty Process Technologies University of idaho-college of

cultural and life sciences.

[38] Mono-, di-, and tri-tert-butyl ethers of glycerol A molecular spectroscopic study Spectrochimica

Acta Part A: Molecular and Biomolecular. Spectroscopy, Volume 67, Issues3-4, July2007, Pages980-

988.Małgorzata E. Jamróz, Małgorzata Jarosz, Janina Witowska-Jarosz, Elżbieta Bednarek, Witold

Tęcza, Michał H. Jamróz, Jan Cz. Dobrowolski and Jacek Kijeński. Industrial Chemistry Research

Institute, 8 Rydygiera Street, 01-793 Warsaw, Poland National Institute of Public Health, 30/34

Chełmska Street, 00-725 Warsaw, Poland Faculty of Chemistry, Warsaw University of Technology, 3

Noakowskiego Street, 00-664 Warsaw, Poland.

[39] tert-Butylation of glycerol catalysed by ion-exchange resins Applied Catalysis A: General, Volume

294, Issue 2, 10 October 2005, Pages 141-147 Katarína Klepáčová, Dušan Mravec and Martin Bajus.

Department of Organic Technology, Faculty of Chemical and Food Technology, Slovak University of

Technology, Radlinske´ho 9, SK-812 37 Bratislava, Slovak Republic. Department of Petroleum

Technology and Petrochemistry, Faculty of Chemical and Food Technology, Slovak University of

Technology, Radlinske´ho 9, SK-812 37 Bratislava, Slovak Republic.

[40] J.Mahaffey, WOC05, Athens2005.

link:http://qz.tutech.net/download/bioenergie/Biodiesel_Connemann.pdf


[41] Microbial Conversion of Glycerol to 1,3-Propanediol: Physiological Comparison of a Natural

Producer, Clostridium butyricum VPI 3266, and an Engineered Strain, Clostridium acetobutylicum

DG1(pSPD5) Marıá Gonza´lez-Pajuelo, Isabelle Meynial-Salles, Filipa Mendes, Philippe Soucaille,

and Isabel Vasconcelos

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Journal of Supercritical Fluids, Volume 22, Issue 1, January 2002, Pages 37-53 W. Bühler, E. Dinjus,

H. J. Ederer, A. Kruse and C. Mas W. Bu¨ hler, E. Dinjus, H.J. Ederer *, A. Kruse *, C. Mas Institut fu¨r

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R. Soares, Dante A. Simonetti, and James A. Dumesic*

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of the crude glycerin produced by biodiesel plants. Catalysis Today, Volume 106, Issues 1-4, 15

October 2005, Pages 190-192 L. Bournay, D. Casanave, B. Delfort, G. Hillion and J.A. Chodorge

Institut Français du Pe´trole (IFP), BP3, F-69390 Vernaison, France b Institut Français du Pe´trole

(IFP), 1&4 av de Bois Preáu, F-92852 Rueil-Malmaison Cedex, France c Axens, IFP Group

Technologies, 89 bd F. Roosevelt, F-92508 Rueil-Malmaison Cedex, France.

[46] Source: http://www.purchasing.com/article/CA6450783.html

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2007).

[48] Bournay, L., Casanave, D., Delfort, B., Hillion, G. and Chodorge, J.A. New heterogeneous

process for biodiesel production: A way to improve the quality and the value of the crude glycerin

produced by biodiesel plants. Catalysis Today 106(2005), 190-192

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Ullmann’s Encyclopedia of Industrial Chemistry: electronic release, 6th ed.

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[58] Applications with Lewatit Ion Exchange Resins

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Resinsin.pdf


APPENDIX B Some glycerine market data by ADM Connemann (2003)

Connemann [5] mentions the following market volumes and prices:

Figure 8-1 The glycerin pillow according to Connemann/ADM [5]

Connemann (2006) mentions the following information on the 2003 market:

Figure 8-2 Some market numbers on 2003 by Connemann/ADM [5]

Documents

Glycerine Purification