Determination of Various Properties of Biodiesel Fuels Based on Methyl Ester Composition

Jason Freischlag

Chem 403 Dr. Porter

4/30/2014

Abstract-

Biodiesel is an alternative fuel source produced from vegetable oil, animal fat oil, or

used cooking oil. In theory the usage of biodiesel seems to have tremendous advantages

however it does not come without its disadvantages; including a higher cloud point which leads

to engine filters becoming clogged at temperatures around 0 oC. This leads to biodiesel/diesel

blends that reduce the dependency on fossil fuels while maintaining some of the advantages of

biodiesel.

Using simple separatory techniques on a feedstock yields organic oil comprised of a

triglyceride mixture. Many methyl esters may result from this process with the only difference

being the length of the carbon chain and the degree of unsaturation in this chain. Although

there are many molecules the four most predominant are palmitic acid, stearic acid, lineolic

acid, and oleic acid.1

This research compared biodiesel synthesized from waste vegetable oil, rapeseed oil,

canola oil, and regular petroleum diesel. The main properties examined in order to determine

fuel efficiency were heat of combustion and cloud point. The results support the notion that

biodiesel fuel made from canola oil is the best form of biodiesel2 among those tested due to its

high heat of combustion and theoretical low cloud point.

Introduction-

Biodiesel is different from diesel in that biodiesel is produced from renewable

resources while diesel is produced from petroleum oil, a fossil fuel. Biodiesel fuel has great

potential as it is much cleaner than typical diesel fuel and can reduce the huge dependence of

the world on fossil fuels.3 Biodiesel is composed of multiple different methyl esters, most

notably palmitic acid, stearic acid, lineolic acid, and oleic acid.1

Figure 1. Structures of Methyl Esters Composing Biodiesel

Biodiesel can be synthesized from feedstocks by their transesterification with an

alcohol. Transesterification, is the process of exchanging the R group of an ester with the R

group of an alcohol; thereby resulting in a different ester and a different alcohol. This process

is an Sn2 reaction that can be catalyzed with either an acid or a base.3 Acid catalyzing results

in a protonated carbonyl of the ester which makes it a better electrophile for attack by the

alcohol whereas base catalyzing deprotonates the alcohol making it an excellent nucleophile.

Transesterification is a useful process in that it allows for bulk quantities of biodiesel to be

easily produced from triglycerides with minimal lab preparation.2

Biodiesel fuel has been receiving major attention as a potentially viable green

alternative to gasoline and traditional fossil fuels. While biodiesel is unlikely to completely

replace traditional gasoline there is no doubt in its potential to lessen the dependence of

industrialized societies on fossil fuels. Because biodiesel simply refers to diesel made from

renewable vegetable oil or animal fat it follows that there are many forms of biodiesel. Each

form of biodiesel is a mixture of various hydrocarbons and methyl esters which causes the

chemical properties of each form to vary. In order to evaluate the applications of biodiesel it is

essential to first establish which properties accurately describe a mixtures efficiency as a fuel.

Figure 2. Transesterification

Another possible method for producing biodiesel is the pyrolysis reaction.

Pyrolysis is the thermochemical decomposition of organic compounds in the absence of

oxygen. This process has gained increasing attention as an efficient method for the creation of

biofuels. Pyrolysis is useful because it can convert different feedstocks into useable fuels in a

simple process that is the same regardless of stock, thereby wasting as little energy as

possible. Pyrolysis of feedstock into biodiesel is similar to the epoxide chemistry that is used to

convert crude oil into petroleum. Both processes require a final reduction step in order to

create the diesel or biodiesel fuel.1

The determination of biodiesel can be made using gas chromatography with a flame

ionization detector because biodiesel consists mostly of carboxylic acids and their methyl ester

derivatives.3 A flame ionization detector is suitable because it is extremely sensitive to organic

molecules and also offers the advantage of not being destructive.3

Several properties can be used to determine the efficiency of biodiesel as a fuel

but some important properties include cetane index, cloud point, pour point, heat of

combustion, acid value, and iodine value. The cetane index of a fuel is a measure of its ignition

quality and indicates the ability to ignite spontaneously in the combustion chamber. The higher

the cetane index, the shorter the ignition delay and the easier the fuel is to ignite; the higher

the cetane index, the better the ignition quality of the fuel. The cloud point is the temperature at

which a fuel begins to form wax crystals. A lower cloud point is a good property in a fuel

because it can withstand colder environments before crystals start to form which very easily

clog up filters. Cloud point is directly attributed to the saturated methyl ester content because

saturated fats solidify faster than unsaturated fats. The pour point is the temperature at which a

fuel loses its flow characteristic. A lower pour point indicates a better fuel for similar reasons to

that of the cloud point. As the temperature of a fuel approaches the pour point it will no longer

be able to flow. The Heat of combustion is defined as the energy released per mol of fuel when

the fuel is burned. This value is one of the most important properties of fuel and is the basis for

defining fuel efficiency. A large heat of combustion means more energy is released and thus a

more efficient fuel source than that with a lower heat of combustion. Acid value refers to the

mass of potassium hydroxide, in milligrams, that is required to neutralize one gram of a

chemical substance and is useful in determining the number of carboxylic acid functional

groups on a molecule. Acid value is measured by dissolving a known amount of sample in an

organic solvent and titrating it with a solution of known concentration of KOH with

phenolphthalein indicator. The Iodine value is the mass of iodine in grams that can be

consumed by 100 g of a substance. This is a way to measure unsaturation of a molecule as

the carbon carbon double bonds react with the iodine compounds. The higher the iodine value

the more double bonds present in a molecule.**

This research will address many topics involved in the determination of biodiesel fuel

efficiency including which properties best describe a viable fuel, how these properties relate to

fuel efficiency, which methods are best to determine the quantitative values of these properties,

and which feedstocks are most currently used in biodiesel production.

One similar study used several chemical properties to determine a best fuel

between sewage sludge and canola oil.1 The properties compared included cloud point, pour

point, specific gravity, viscosity, distillation range, cetane index, flash point, heat of combustion,

water and sediment, ash, carbon residue, and elemental analysis. Pyrolysis products were

also analyzed using gas chromatography, IR spectroscopy, and 13C NMR. The cloud point,

spectra, and chromatograms all suggested that these sources may be able to provide a

capable replacement to diesel fuel.All fuel properties were determined using the American

Society for Testing and Materials (ASTM) standard methods including cetane index (D 976),

cloud point (D 2500), pour point (D 97), and heat of combustion (D 240). Each test was run on

sludge lipid and canola oil biodiesels as well as regular diesel fuel.1

The cetane index of both the biodiesels were found to be higher than that of regular

diesel indicating that biodiesel is actually better at igniting than diesel fuel. The cloud point of

both biodiesels was higher than the diesel counterpart which indicates that biodiesels are not

as applicable for colder weather climates. The pour point of both biodiesels was greater than of

regular diesel. The heats of combustions for both biodiesels were comparable to that of

biodiesel and indicate either could be used as an efficient alternative. IR of both biodiesels

showed a weak carbonyl peak at 1720 cm-1 which is indicative of a carboxylic acid. 13C NMR of

both products showed exclusively hydrocarbon signals with a touch of residual solvent toluene.

No carbonyl signal was seen for either biodiesel NMR confirming that both biodiesel reactions

were run to completion. Gas chromatography of the both biodiesels resulted in a fairly uniform

hydrocarbon chain length distribution of chains of 7 to 17 carbons. The Chromatogram of

diesel shows a similar distribution to that of the biodiesels, only lacking the 7 to 9 carbon length

chains.1 This research shows that all the physical properties associated with biodiesel are

intertwined and that the difficulty in interpreting these results comes mostly in understanding

the relationships between the values. According to this experiment biodiesel shows great

potential as an alternative fuel source as it mirrors many of the key chemical properties of

diesel. Furthermore, the differences between sewer sludge and canola oil biodiesels were

negligible in most cases.1

One thermodynamic study used various fatty acid methyl esters to establish a prediction

model for the cloud point of actual biodiesel made from different feedstocks based on their

chemical composition.3 This study found that the cloud point of a biodiesel mixture could be

determined by the amount of saturated fatty acid methyl esters regardless of composition of

unsaturated esters. Biodiesel naturally borrows chemical characteristics from the oils and fats

it was made from. Saturated fats have high melting points which means the biodiesel produced

from these fats would likewise have a high melting point. This is a severe concern during cold

weather as freezing gas could destroy an engine. Unsaturated fats have a lower melting point

but at the same time are more likely to undergo oxidation. This oxidation of fuel can cause

engine damage as well so a balance between these two properties is desired; for this reason

biodiesel is usually synthesized from semi-drying oils like rapeseed and soybean oils.

Base catalyzed transesterification was used to synthesize biodiesel fuel from sunflower

oil, coconut oil, rapeseed oil, soybean oil, olive oil, peanut oil, beef tallow, and palm oil. Each of

the products were classified based on weight percent of various fatty acids present. Based on

the data from this experiment it can be seen that these biodiesels consist mostly of palmitic

acid, stearic acid, oleic acid, and linoleic acid. These four methyl esters were chosen to make

standards in various molar ratios for use as a model for predicting the behavior of biodiesel

fuel.3

The range of recorded cloud points went from 270 K to 290 K which is a noticeable

difference in a crucial temperature range when dealing with natural environments.

Furthermore, it was found that cloud point could be predicted based on molar ratios using

known enthalpy values, assuming a eutectic system. The data supports the notion that cloud

point is based primarily on the ratios of saturated esters; unsaturated esters have a negligible

effect on cloud point because once one component of a mixture begins to crystallize the entire

solution becomes cloudy. Oxidation and polymerization of the fuel caused by unsaturation can

be remedied by using mono-unsaturated esters as opposed to those with higher degrees. This

experiment shows that there is a tool to accurately estimate fuel properties and a way to

determine optimal fatty acid methyl ester composition.3

Another study examined the viability of honne oil feedstock as a potential renewable

diesel alternative.4 Based on the information presented in this article honne oil offers a viable

alternative that matches many of the desired properties of diesel fuel when used in a biodiesel-

diesel blend. Cetane number was calculated using the formula CN = 46.3 + (5458)/SV -

0.225*IV where SV is the saponification value and IV is the iodine value.

One study determined new formulas for calculating heating values of fuels by their

proximate analysis data.5 Proximate analysis resulted in values for weight fraction of moisture,

volatile matter, fixed carbon, and ash as set up by ASTM method E870-82. It was also found

that the yield of volatile materials can be increased by increasing the heating rate and the

temperature of the pyrolysis process. Heating values of fuels were measured using a bomb

calorimeter and ASTM method D2015.5

Food industries naturally produce substantial amounts of inedible waste. Processing

these unwanted byproducts can result in a product of value with potential as a biodiesel fuel.

Tomato seed is the major byproduct of tomato paste manufacturing and shows potential as a

raw material capable of producing biodiesel. One study separated tomato seeds from pulp and

dried them using a silica gel desiccant. Oil was then extracted from the seeds using hexane

and a soxhlet extractor and purified by rotary vacuum evaporation. Fatty acid composition was

determined using gas chromatography. A flame ionization detector was used with helium

carrier gas. 16 fatty acids were present in the oil according to GC results but the same four as

previously mentioned were predominant, with linoleic acid comprising 56% of the oil. Iodine

value is the measure of unsaturation of a fuel and the value found for tomato oil (124) is well

within the recommended range (80-145).6

Synthesis-

Methanol was combined with sodium hydroxide to form sodium methoxide. A three

necked round bottom flask was set to stir in a water bath with one neck equipped with a

thermometer, the middle neck a condenser, and the last neck a rubber stopper so that

reactants could be added. Feedstock was added to the round bottom flask then the sodium

methoxide solution was slowly added to prevent emulsion. This solution was heated and

stirred for an hour before being removed and allowed to set overnight. This solution was then

transferred to a seperatory funnel and both layers were extracted. The biodiesel has a lower

density than the glycerol byproduct so it was expected that the bottom layer would have been

the waste glycerol but because the reaction was run with excess methanol which mixed with

the glycerol layer and made the bottom layer in actuality the biodiesel product. This product

was thoroughly filtered. Analysis of each biodiesel product is as follows.

Methods and results-

GC will be used to identify methyl ester composition in the biodiesel. A flame ionization

detector will be used because of cost efficiency as well as specificity to these molecules. A

bomb calorimeter can be used to find the heat of combustion. Based on the information

obtained in the literature review it is estimated that there will be a correlation between the

unsaturation degree and the values of these fuel properties. Biodiesel offers some positive

benefits while regular diesel comes with others. The future of fuel comes in understanding the

best relationship between these two. Also based on these reviews it can be seen that there is a

methodical approach to understanding how the chemical composition of biodiesels affect their

properties and that transesterification is a common mode of synthesis when dealing with

biodiesel. It can be observed that the most common feedstocks used to produce biofuel are

rapeseed oil and olive oil because they produce a good combination of desirable physical

properties. The cloud points of the biodiesel products from rapeseed oil and olive oil are lower

than the competing versions that were tested. Bomb calorimetry is the standard means of

measuring heat of combustion, although there are multiple standard methods available to

follow. HPLC offers a method for determining the chemical composition of the biodiesel fuels.

Titration is a possible means of finding acid value, saponification value, and iodine value. Table

1 below shows the composition of multiple biodiesels.

Table 1. Composition of multiple oils

The HPLC Data, although not complete, shows that the biodiesel formed from waste oil

consists of multiple components but since the waste oil biodiesel is roughly 60% oleic acid it

was expected that the chromatogram from the waste oil biodiesel in figure. 3 should show at

peak at 5.5 minutes similar to the chromatogram for oleic acid in figure 4.

Figure 3. Waste oil Biodiesel Chromatogram

Figure 4. chromatogram of olaic acid

Heat of combustion, ΔH, is defined as the energy released per mole of fuel once burned

and is one of the most important quantities when describing fuel. A large heat of combustion

means more energy is released and thus a more efficient fuel source. A bomb calorimeter was

used in all calculations for ΔH.

Using the fact that the ∆ H reaction = -3230 kJ/mol for benzoic acid and

∆ H reaction≈∆ Ereaction+RT ∆ngases 1)

From the above combustion it can be seen ∆ ngases is five. Considering the two moles of benzoic

in combustion reaction ∆ E reaction=−6472 k . qreaction=−qcalorimeter∧ΔEreaction=qreaction for benzoic acid

ΔT is 2.706.

 qcalorimeter = Ccal ΔT 2)

Using data from benzoic acid Ccal was found to be 2392 kJ/ oC

Table 2. Determination of delta H for multiple feedstocks

Conclusion

These results would indicate that biodiesel synthesized from canola oil would make the

best fuel due to the lower composition of saturated fatty acids that give it a low cloud point and

the high heat of combustion which ensures the combustion is efficient enough to be viable.

These results are far from conclusive though. The composition is not known for each of the

biodiesel products making it difficult to make conclusions about the cloud point without further

analysis. Also the HPLC data was skim as only two trials were run.

1. Bahadur, N., D. Boocock, and S. Konar (1994) Liquid Hydrocarbons from Catalytic Pyrolysis of

Sewage Sludge Lipid and Canola Oil: Evaluation of Fuel Properties. Energy & Fuels

9(1995):248-256.

2. Anderson, Chris. "Count on Canola for Your Biodiesel." Biodiesel Magazine. Biodiesel Magazine, 7

Jan. 2008. Web. 30 Apr. 2014. <http://www.biodieselmagazine.com/articles/2063/count-on-

canola-for-your-biodiesel/>.

3. Imahara, H., E. Minami, and S. Saka (2006) Thermodynamic Study on Cloud Point of Biodiesel

with its Fatty Acid Composition. Fuel 85(2006):1666-1670.

4. Belagur, V., and V. Chitimi (2013) Few Physical, Chemical and Fuel Related Properties of Honne

Oil and its Blends with Diesel Fuel for their Use in Diesel Engines. Fuel 109(2013):356-361.

5. Chemistry Vocabulary - Common chemistry terms explained. (n.d.). Chemistry Vocabulary -

Common chemistry terms explained. Retrieved April 30, 2014, from

http://misterguch.brinkster.net/vocabulary.html

6. Demirbas, A. (1996) Calculation of Higher Heating Values of Biomass Fuels. Fuel 76(1996):431-

434.

7. Giannelos, P.N., S. Sxizas, F. Zannikos, and G. Anastopoulos (2004) Physical, Chemical, and Fuel

Related Properties of Tomato Seed Oil for Evaluating its Direct use in Diesel Engines.

Industrial Crops and Products 22(2005):193-199.

8. Chemistry Vocabulary - Common chemistry terms explained. (n.d.). Chemistry Vocabulary -

Common chemistry terms explained. Retrieved April 30, 2014, from

http://misterguch.brinkster.net/vocabulary.html