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INTRODUCTION
Life is but a continuous process of energy conversion and transformation. The
accomplishments of civilisation have largely been achieved through the increasingly efficient
and extensive harnessing of various forms of energy to extend human capabilities and
ingenuity. Lately there has been a growing concern about the negative environmental impacts
of fossil energy which drawn significant attention to renewable liquid biofuels as a way to
replace petroleum-based fuels (Krohn, McNeff, Yan, & Nowlan, 2010).Biomass is one of the
better sources of energy, large-scale introduction of biomass energy could contribute to
sustainable development on several fronts, environmentally, socially and economically
(hossain, Salleh, Boyce, chowdhury, & Naqiuddin, 2008). Biodiesel, a common term for long
chain alkyl esters, is a renewable, biodegradable, and non-toxic biofuel that shows great
promise to the environment (Lu, Zhai, Liu, & Wu, 2009). Biodiesel is derived from the
transesterification of mono-, di- and tri-acylglycerides (TAGs) and the esterification of free
fatty acids (FFAs) that occur naturally in biological lipids, such as animal fats and plant oils.
As a result, biodiesel has the potential to be a carbon neutral fuel (Krohn, McNeff, Yan, &
Nowlan, 2010). Furthermore, in comparison to petroleum diesel which is a major source of
greenhouse gas (GHG) (hossain, Salleh, Boyce, chowdhury, & Naqiuddin, 2008), biodiesel
emits lower levels of environmental pollutants including volatile organic compounds,
particulate matter, and sulphur-compounds during combustion (Krohn, McNeff, Yan, &
Nowlan, 2010). In this perspective, considerable attention has been given towards the
production of biodiesel as a diesel substitute.
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Biomass Energy Biomass resources are agricultural and forest residues, algae and grasses, animal
manure, organic wastes, and biomaterials. The supply is dominated by traditional biomass
used for cooking and heating, especially in rural areas of developing countries. World
production of biomass, mostly wild plant growth, is estimated at 146 billion metric tons a
year worldwide (Demirbas, Chapter 9 Global Renewable Energy and Biofuel Scenarios,
2008). For fuels produced from biomass, various conversion routes are available that follow
from the different types of biomass feed stocks. These routes include direct conversion
processes such as extraction of vegetable oils followed by esterification (biodiesel),
fermentation of sugar-rich crops (ethanol), pyrolysis of wood (pyrolysis oil derived diesel
equivalent), and hydrothermal upgrading (HTU) of wet biomass (HTU-oil-derived diesel
equivalent). Another possibility is to produce liquid biofuels (methanol, DME, Fischer-Tropsch
liquids) from synthesis gas, which results from the gasification of biomass. In the future,
biomass has the potential to provide a cost-effective and sustainable supply of energy while at
the same time aiding countries to meet their greenhouse gas reduction targets.
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Biodiesel
Properties of biodiesel
Biofuels are expected to reduce dependence on petroleum with its associated political
and economic vulnerability, reduce greenhouse gas emissions and other pollutants, and
revitalize the economy by increasing demand and prices for agricultural products.
Although most attention focuses on ethanol, interest in biodiesel is also increasing
(Demirbas, Chapter 9 Global Renewable Energy and Biofuel Scenarios, 2008) Biodiesel is the monoalkyl esters of long-chain fatty acids derived from renewable
feedstocks, such as vegetable oil or animal fat (Kakali Mukhopadhyay, 2005). It contains
very little sulfur, polycyclic aromatic hydrocarbons, and metals. Petroleum-derived diesel
fuels can contain up to 20% polycyclic aromatic hydrocarbons. For an equivalent number
of carbon atoms, polycyclic aromatic hydrocarbons are up to three orders of magnitude
more soluble in water than straight chain aliphatics. The fact that biodiesel does not
contain polycyclic aromatic hydrocarbons makes it a safe alternative for storage and
transportation (Palligarnai T. Vasudevan, 2008).
Advantages of biodiesel
Biodiesel can be used as a fuel for vehicles in its pure form, but it is generally be used
as a petroleum diesel additive to reduce levels of particulates, carbon monoxide,
hydrocarbons and air toxics from diesel-powered vehicles. Biodiesel is made from
biomass oils, mostly from vegetable oils.
It appears to be an attractive energy resource for several reasons. First, biodiesel is a
renewable resource of energy that could be sustainably supplied. It is understood that the
petroleum reserves are to be depleted in less than 50 years at the present rate of
consumption. Second, biodiesel appears to have several favourable environmental
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properties resulting in no net increased release of carbon dioxide and very low sulfur
content. The release of sulfur content and carbon monoxide would be cut down by 30%
and 10%, respectively, by using biodiesel as energy source.
Using biodiesel as energy source, the gas generated during combustion could be
reduced, and the decrease in carbon monoxide is owing to the relatively high oxygen
content in biodiesel. Moreover, biodiesel contains no aromatic compounds and other
chemical substances which are harmful to the environment. Recent investigation has
indicated that the use of biodiesel can decrease 90% of air toxicity and 95% of cancers
compared to common diesel source. Third, biodiesel appears to have significant economic
potential because as a non-renewable fuel that fossil fuel prices will increase
inescapability further in the future. Finally, biodiesels better than diesel fuel in terms of
flash point and biodegradability (Moser, 2009). Sources of biodiesel
Crude Palm Oil (CPO)
Based on few criteria, palm oil is the most potential vegetable oil which can be used as raw
material to manufacture biodiesel (Surawidjaya & colleagues, 2003), and on the other hand the usage
of CPO consider to be the most wanted palm oil products for its cheap price and readiness for
downstream processing.
CPO is meant to anticipate oversupply. In the year of 2005, oversupply of CPO in Malaysia
reached 0.40 million tons. It is estimated that this amount will keep rising reaching 1.3 million tons in
2010. The data of 2007 shows that from about 3 million hectares of palm tree plantations, 6.7 million
tons of CPO is produced. Besides that, if the fuel subsidy is no more available, PAME (palm oil
methyl ester ± processed CPO which can be used as 100% biodiesel or a blend with other fuels) can
be able to substitute diesel oil that is readily available to be marketed with a competitive price. Figure
1 shown the average prices of the 4 quarters of the year 2006 and also the total average price of
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di
¡ ¢ ¡ £ t¤
¡ ¥
¡ ¢ ¦ l § ¦ l¨ © il ¢ ¦
§ ¢ © duct¤
i £ compare to ot
er t pes of oil and fats in t
e nor t
estern
Europe market; C
recorded t
e lowest value af ter tallow wit
sli
t difference between t
em (478
and 451, respectivel
It is to be noted t
at t
e average pr ices of t
e 4t
quar ter increased rapidl
especiall
in
November it might due to the beginning of the winter in which the dependency on oil and fats as diet
and fuel for heat that increases the demand against the supply or it might be related to the end of the
economical year of the oils and fats market; in any case, the C
did not show rapid increase and
decrease in its value which show high sustainability with higher percentage for pr ice prediction and
this another advantage for C
along with its low pr ice and high yield which is not seen only in the
European region but also in the Malaysian region which is consider the leader in producing,
processing and expor ting palm oil & C
(Figure 2 and 3).
Figure 1: Average Pr ices of Selected Oils & Fats for 2006
(Nor th West Europe Market ± US$/Ton)
Note: R BD: Ref ined, Bleached & Deodorized.
Figure 2. Production of CPO for Malaysian Sates Year 2006 & 2007 (Year ly)
ource: MPOB
0200400600800
10001200
1st Quar ter Average
2nd Quar ter Average
3rd Quar ter Average
4th Quar ter Average
Total Average
Crude Palm OilRB! Palm OilRB
"
Palm OleinRB
! Palm Stear inPalm Kernel OilSoyabean OilCotton Oil
# roundnut Oil
Sunf lower Oil
T
ons
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Talk ing about another aspect of CPO; fresh fruit bunches have to be harvested and
transpor ted to factor ies and have to be extracted within 24 hours. Otherwise the quality of extracted
palm oil will deter iorate. Given this fact, the factor ies have to be located close to the palm growing
areas. Crude palm oil (CPO) supplied by extracting factor ies has to be ref ined to obtain pure palm oil
suitable for consumption or for use as raw mater ial by the downstream industry. The palm oil, which
has undergone the ref ining process, is called RB$
oil (ref ined, bleached and deodor i% ed oil).
The requirement of petroleum in the country increased due to economy development, increase
population, and also the selling pr ice of petroleum product, which is relatively cheap. For that, if CPO
has to be used as diesel substitute, pr ice of the CPO should be considered along with the pr ices of the
Figure 3:
Production of
CPO for
Malaysian
Sates Year
2006 & 2007
(Monthly)
&
ource: MPOB
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operational factors and material used in the process in comparing with the ones of the conventional
diesel.
Properties of CPO
The properties of the CPO alkyl ester (Table1) are found to be comparable with those of
petroleum diesel. The densities at 40ºC of methyl, ethyl and isopropyl esters of CPO were 0.855±
0.857 kg/L and, therefore, slightly higher than petroleum diesel, which slightly exceeds 0.820 kg /L.
This, however, is not important, as this would only cause a slight increase of fuel consumption.
The sulfur content of these esters are very low; a 0.04 wt% maximum as compared with 0.2
wt% presently found in Malaysian petroleum diesel. The exhaust emissions will therefore contain
very little SO2. The viscosities at 40ºC of alkyl esters of CPO were in the range of 4.4x10-6
± 5.2x10-6
m2/s, slightly higher than petroleum diesel fuel (4.4x10-6 m2/s). However, they are still in an
acceptable range and able to flow under warm weather conditions.
The pour points of alkyl esters of CPO range from 6 to 18.8 ºC. Pour point is defined as the
lowest temperature that the product still can be poured by gravity. Ethyl and isopropyl esters provide
better cold flow properties when compared to methyl esters.
Table1: Typical Fatty Acid Composition
of Alkyl Esters of CPO
Fatty acid composition (%) Alkyl esters of CPO
C12 0.3
C14 0.8
C16:0 44.3
C16:1 0.2
C18:0 5.0
C18:1 39.1
C18:2 10.1
C18:3 0.1
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Production of Biodiesel Two major steps are necessary in order to produce biodiesel from microalgae. The
first step entails extraction of oil from microalgal cells, while in the second step the extracted
oil is transformed through reaction into biodiesel (hossain, Salleh, Boyce, chowdhury, &
Naqiuddin, 2008)
Oil Extraction Extracting oil from microalgae requires drying as the first step to reduce the water
content. Several methods have been employed to dry microalgae where the most common
include spray-drying, drumdrying, freeze-drying and sun-drying. Because of the high water
content of algal biomass sun-drying is not a very effective method for algal powder
production and spray-drying is not economically feasible for low value products, such as
biofuel or protein. After drying it follows the cell disruption of the microalgae cells for release of the
metabolites of interest. Several methods can be used depending on the microalgae wall and
on the product nature to be obtained either based on mechanical action (e.g. cell
homogenizers, bead mills, ultrasounds, autoclave, and spray drying) or non-mechanical
action (e.g. freezing, organic solvents and osmotic shock and acid, base and enzyme
reactions). Although different methods have been studied the best results were obtained from
autoclaved and mechanically disrupted biomass, with yield 3 times higher than with other
methods (Mata, Martins, & Caetano, 2010). Solvent extraction can be used along with expeller /press method, in which case more
than 95% of total microalgal oil can be extracted. According to Lu, Zhai, Liu, & Wu (2009)
the supercritical fluid extraction is more efficient than the other methods being able to extract
100% of microalgal oil
In supercritical fluid extraction method liquefied CO2 is used as the solvent for oil
extraction. The liquefied CO2 fluid is prepared by liquefying CO2 under pressure, and heating
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it to the point that it has properties of both a liquid and a gas (Halim, Gladman, Danquah, &
Webley, 2011)
Patil, et al (2010) were able to directly convert wet algae paste (10% solids) to
biodiesel under supercritical methanol conditions. The single-step process favours the energy
requirements for biodiesel production by eliminating the needs for drying and extraction of
algal biomass and has the potential to provide an energy efficient and economical route to
algal biodiesel production.
Conversion of Oil to Biodiesel There are a number of ways to produce biodiesel from animal fat and vegetable oil.
Direct conversion, micro-emulsification, pyrolysis transesterification are the four techniques
applied to solve the problems encountered with the high fuel viscosity (Demirbas,
Comparison of transesterification methods for production of biodiesel from vegetable oils
and fats, 2008) Direct conversion The direct usage of the oils as biodiesel is possible by blending it with conventional
diesel fuels in a suitable ratio and these ester blends are stable for short term usages. The
blending process is simple which involves mixing alone and hence the equipment cost is low.
But direct usage of these triglyceric esters is unsatisfactory and impractical for long term
usages in the available diesel engines due to high viscosity, acid contamination, and free fatty
acid formation resulting in gum formation by oxidation and polymerization and carbon
deposition.
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Pyrolysis Pyrolysis refers to chemical change caused by application of heat to get simpler
compounds from a complex compound. The process is also known as cracking. Vegetable
oils/animal oil can be cracked to reduce viscosity and improve cetane number. The products
of cracking include alkanes, alkenes, and carboxylic acids. Soyabean oil, cottonseed oil,
rapeseed oil and other oils are successfully cracked with appropriate catalysts to get biodiesel.
According to Milford & Fangrui (1999) using this technique resulted in good flow
characteristics because of the reduction in viscosity. Disadvantages of this process include
high equipment cost and need for separate distillation equipment for separation of various
fractions. In addition, the products obtained are similar to gasoline containing sulfur which
makes it less eco-friendly (Milford & Fangrui, 1999). Microemulsification Microemulsification is another technique that has been reported to produce biodiesel
and the components of a biodiesel microemulsion include diesel fuel, vegetable oil, alcohol,
surfactant and cetane improver in suitable proportions (Milford & Fangrui, 1999). Alcohols
such as methanol, ethanol and propanol are used as viscosity lowering additives, higher
alcohols are used as surfactants and alkyl nitrates are used as cetane improvers. Viscosity
reduction, increase in cetane number and good spray characters encourage the usage of
microemulsions but prolong usage causes problems like injector needle sticking, carbon
deposit formation and incomplete combustion ( (Milford & Fangrui, 1999) Transesterification The triacylglycerols are esters of long chain carboxylic acids combined with glycerol.
Carboxylic acids can be converted to methyl esters by the action of a transesterification
agent. The parameters affecting the methyl esters formation are reaction temperature,
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pressure, molar ratio, water content and free fatty acid content (Georgogianni, Katsoulidis,
Pomonis, Manos, & Kontominas, 2009). Demirbas (2008) observed that increasing the reaction temperature had a favourable
influence on the yield of ester conversion. The yield of alkyl ester increased with increasing
the molar ratio of oil to alcohol. Transesterification consists of a number of consecutive,
reversible reactions. The triglyceride is converted stepwise to diglyceride, monoglyceride
and finally glycerol as shown in equestion 1-4 in which 1 mol of alkyl esters is removed in
each step.
Figure2.1: The Step Stepwise Conversion to Alkyl Ester
The formation of alkyl esters from monoglycerides is believed to be a step that
determines the reaction rate, since monoglycerides are the most stable intermediate
compound. Transesterification of fats and vegetable oils for biodiesel production, free fatty acid
and water always produce negative effects, since the presence of free fatty acids and water
causes soap formation, consumes catalyst and reduces catalyst effectiveness, all of which
result in a low conversion. Demirbas (2008) observed that by increasing the reaction
temperature, especially to supercritical conditions, it has a favourable influence on the yield
of ester conversion. The yield of alkyl ester increased with increasing molar ratio of oil to
alcohol
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Table 3 shows a comparison between several methanolic Transesterification methods Table 3: comparison of various methanolic transesterification methods
Method Reaction Reaction temperature
(K) Reaction time(min) Acid or alkali catalytic
process 303±338 60±360
Boron trifluoride-methanol 360-390 20-50 Sodium methoxide-
catalysed 293-298 4-6 Non-catalytic supercritical
Methanol 523-573 6-12 Catalytic supercritical
Methanol 523-273 0.5-1.5 The transesterification is an equilibrium reaction, and the transformation occurs
essentially by mixing the reactants. In the transesterification of oils, a triglyceride reacts with
an alcohol in the presence of a strong acid or base, producing a mixture of fatty acids alkyl
esters and glycerol. The stoichiometric reaction requires 1 mol of a triglyceride and 3 mol of
the alcohol. However, an excess of the alcohol is used to increase the yields of the alkyl
esters and to allow its phase separation from the glycerol formed.
Alk ali catalytic Transesterification methods
In the alkali transesterification process sodium hydroxide (NaOH) or potassium
hydroxide (KOH) is used as a catalyst along with methanol or ethanol. Initially, during the
process, alcoxy is formed by reaction of the catalyst with alcohol and the alcoxy is then
reacted with any oil to form biodiesel and glycerol. Glycerol being denser settles at the
bottom and biodiesel can be decanted. This process is the most efficient and least corrosive of
all the processes and the reaction rate is reasonably high even at a low temperature of 60 °C.
There may be risk of free acid or water contamination and soap formation is likely to take
place which makes the separation process difficult (Demirbas, Comparison of
transesterification methods for production of biodiesel from vegetable oils and fats,
2008;Milford & Fangrui, 1999).
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Acid catalysed transesterification methods Any mineral acid can be used to catalyze the process; the most commonly used acids
are sulfuric acid and sulfonic acid. Although yield is high, the acids, being corrosive, may
cause damage to the equipment and the reaction rate was also observed to be low (
(Demirbas, Comparison of transesterification methods for production of biodiesel from
vegetable oils and fats, 2008)).
Enzyme catalyzed processes It has been found that enzymes such as lipase can be used to catalyze
transesterification process by immobilizing them in a suitable support. The advantage of
immobilization is that the enzyme can be reused without separation. Also, the operating
temperature of the process is low (50 °C) compared to other techniques. Disadvantages
include inhibition effects which were observed when methanol was used and the fact that
enzymes are expensive (Ranganathan, Narasimhan, & Muthukumar, 2008).
The non-catalytic supercritical methanol transesterification The transesterification process can be carried out even without catalyst but with
considerable increase in temperature. Yield is very low at temperatures below 350°C and
therefore higher temperatures are required. However at temperatures greater than 400 °C
thermal degradation of esters occurred (Demirbas, Comparison of transesterification methods
for production of biodiesel from vegetable oils and fats, 2008). Recently it has been found
that alcohols in their supercritical state produce better yield and researchers have
experimented this process with methanol in its supercritical state.