The Ideal Vegetable Oil-based Biodiesel Composition a Review of Social Economical & Technical Implications

8/11/2019 The Ideal Vegetable Oil-based Biodiesel Composition a Review of Social Economical & Technical Implications

1/17

The Ideal Vegetable Oil-based Biodiesel Composition: A Review of Social, Economical and Technical Implications

S. Pinzi, I. L. Garcia, F. J. Lopez-Gimenez, M. D. Luque de Castro, G. Dorado, | andM. P. Dorado* ,

Department of Chemical Physics and Applied Thermodynamics, EPS, Edicio Leonardo da Vinci;

Department of Agricultural Engineering, ETSIAM, Edicio Leonardo da Vinci; Department of AnalyticalChemistry, Edicio Marie Curie; and Department Bioqu mica y Biologa Molecular, Campus Rabanales,C6-1-E17, Uni Versidad de Cordoba, 14071 Cordoba, Spain

Recei Ved December 15, 2008. Re Vised Manuscript Recei Ved April 6, 2009

Though a considerable number of publications about biodiesel can be found in literature, several problemsremain unsolved, encompassing economical, social, and technical issues. Thus, the biodiesel industry has comeunder attack by some environmental associations, and subsidies for biofuel production have been condemnedby some governments. Yet, biodiesel may represent a truly competitive alternative to diesel fuel, for whichfuel tax exemption and subsidies to energetic crops are needed. Biodiesel must increase its popularity amongsocial movements and governments to constitute a valid alternative of energy source. In this sense, the use of nonedible oils to produce biodiesel is proposed in the present review. Moreover, the compromise of noninterference between land for energetic and food purposes must be addressed. Concerning technical issues,it is important to consider a transesterication optimization, which is missing or incomplete for too manyvegetable oils already tested. In most cases, a common recipe to produce biodiesel from any raw material hasbeen adopted, which may not represent the best approach. Such strategy may t multifeedstock biodiesel plantneeds but cannot be accepted for oils converted individually into biodiesel, because biodiesel yield will mostlikely fail, increasing costs. Transesterication optimization results depend on the chemical composition of vegetable oils and fats. Considering sustainable vegetable oils, biodiesel from Calophyllum inophyllum , Azadirachta indica , Terminalia catappa , Madhuca indica , Pongamia pinnata , and Jatropha curcas oils tsboth current biodiesel standards: European EN 14214 and US ASTM D 6751 02. However, none of them canbe considered to be the ideal alternative that matches all the main important fuel properties that ensure thebest diesel engine behavior. In search of the ideal biodiesel composition, high presence of monounsaturatedfatty acids (as oleic and palmitoleic acids), reduced presence of polyunsaturated acids, and controlled saturatedacids content are recommended. In this sense, C18:1 and C16:1 are the best-tting acids in terms of oxidativestability and cold weather behavior, among many other properties. Furthermore, genetic engineering is aninvaluable tool to design oils presenting the most suitable fatty acid prole to provide high quality biodiesel.Finally, most published research related to engine performance and emissions fails in using a standardmethodology, which should be implemented to allow the comparison between tests and biofuels from differentorigin. In conclusion, a compromise between social, economical, and technical agents must be reached.

1. Introduction

Nowadays, the depletion of fossil fuel reserves and thenecessity to reduce CO 2 emissions in order to limit globalwarming are leading the research on alternative sources of energy. Among these alternatives are biofuels for internalcombustion engines. 1

In recent years, biofuel research has been directed mainly toexplore plant-based fuels: that is, fatty acid methyl esters(FAME) of seed oils, and in some cases, fats. 2 FAME, alsoknown as biodiesel, is environmentally less contaminating,

nontoxic, and biodegradable compared to diesel fuel. 3 The usualraw materials being exploited commercially to produce biodieselconsist of edible fatty oils derived from rapeseed, soybean, palm,sunower, and other plants. However, biodiesel from edible oilsis controversial. Some nongovernmental organizations (NGO)and social movements (e.g., the Global Forest Coalition, amongothers), pinpoint the making of biofuels from edible rawmaterials as the main cause of increased global food marketprices. Another claim against the use of biofuels is the depletionof ecological resources due to the intensive agricultural practicesin the crop cultivation. Although international authorities suchas the Food and Agriculture Organization of the United Nations(FAO) and the Austrian Biofuels Institute (ABI), among others,provide gures to demonstrate the small and nonsignicantaftereffect of biofuels in global economy, 4 the focus must be

* Corresponding author. Phone: + 34 957 218332; fax: + 34 957 218417;e-mail: [email protected].

Department of Chemical Physics and Applied Thermodynamics. Department of Agricultural Engineering. Department of Analytical Chemistry.| Department Bioqumica y Biolog a Molecular.(1) Luque, R.; Herrero-Davila, L.; Campelo, J. M.; Clark, J. H.; Hidalgo,

J. M.; Luna, D.; Marinas, J. M.; Romero, A. A. Energy En Viron. Sci. 2008 ,1, 542564 .

(2) Dorado, M. P. In Biofuels Rening and Performance ; Nag, A., Ed.;McGraw Hill Professional: 2008; pp 107 - 148.

(3) Azam, M.; Waris, A.; Nahar, N. M. Biomass Bioenergy 2005 , 29 ,293302 .

(4) Bergsma, G.; Kampman, B.; Croezen, H.; Sevenster, M. Biofuelsand their global inuence on land a Vailability for agriculture and nature ;Delft: CE, 2006.

Energy & Fuels 2009, 23, 23252341 2325

10.1021/ef801098a CCC: $40.75 2009 American Chemical SocietyPublished on Web 04/29/2009


2/17

put on nonedible oils instead of edible ones, to gain socialacceptance of biodiesel.

These arguments are not contradictory to the last annual reporton the state of food and agriculture (2008), where FAO warnsthat policies concerning biofuels production should aim at theequal distribution of benets between rich, developing, and poorcountries. 5 In this way, an increase in biofuels demand couldhelp the rural development of less-favored countries. The FAOreport concluded that both farm subsidies of biofuels and tradebarriers that create articial markets that benet producersbelonging to the Organization for Economic Co-operation andDevelopment (OECD) countries at the expense of producers indeveloping countries should be removed.

Another main concern in further usage of biodiesel is theeconomic viability. Several studies have identied that the priceof feedstock oils is by far one of the most signicant factorsaffecting the economic viability of biodiesel manufacturing. 6- 8Approximately 70 - 95% of the total biodiesel production costarises from the raw material. 7 Therefore, to produce a competi-tive biodiesel, the feedstock price is a key factor that needs tobe taken into consideration. 2

It has been shown that biodiesel quality depends on fatty acidcomposition of raw materials (oils or fats). A biodiesel reactionis depicted in Scheme 1. Among the main fuel specicationsrelated to chemical composition are cetane number; kinematicviscosity; oxidative stability; cold-ow properties in the formof cloud point (CP), pour point (PP), and cold-lter pluggingpoint (CFPP); exhaust emissions; lubricity; and heat of combus-tion.9 Other parameters inuenced by fatty acid compositionare conversion rate of FAME and optimal amount of reagentsinvolved in the transesterication reaction. Those parametersare also important in terms of economic viability of biodieselproduction. 2

According to these reasons, the use of nonedible, low-cost,and sustainable feedstocks compatible with a good quality of biodiesel should become a primary research target for thescientic community, thus facilitating the acceptance of biodiesel

by both customers and vehicle manufactures. For this reason,the aim of this work is to provide a review about the mainachievements concerning the inuence of the chemical com-position of biodiesel on several fuel topics (i.e., fuel properties,engine performance, etc.), focused on low-cost and nonedibleoils. An approach to the biodiesel ideal chemical compositionis also proposed. The ideal chemical structure of vegetable oils-

based biodiesel, together with some ethical, social, and eco-nomical considerations is presented. According to the conclu-sions of these sections, some nonedible low-cost vegetable oilswith high potential to be used to produce biodiesel arerecommended. Because of the limitations of the proposedvegetable oils, the inuence of free fatty acids (FFA) contentin biodiesel production are discussed, as well as potentialmodications by genetic engineering. Finally, a comparativestudy concerning the best-tting raw materials to produce

biodiesel is presented.

2. The Ideal Chemical Structure of Biodiesel

The inuence of the chemical structure of fatty acids onbiodiesel quality has been demonstrated. 9- 13 In this section, theoptimal fatty acid prole of low-cost and nonedible vegetableoils, to be considered suitable and sustainable raw materials forbiodiesel production, is discussed. According to this, main fuelproperties are provided and analyzed, as shown in Table 1.

2.1. Iodine Value (IV). This parameter reects total unsat-uration regardless of the relative proportion of mono-, di-, tri-,and polyunsaturated compounds. In this sense, several authorshave determined IV as a function to fatty acid prole. 3,14 Resultsreveal that a high IV has been linked with low oxidationstability, causing the formation of various degradation products,which can negatively affect engine operability by formingdeposits on engine nozzles, piston rings, and piston ring grooves.The effects of oxidative degradation represent a legitimateconcern in terms of maintaining fuel quality of biodiesel. 15Biodiesel may oxidize more rapidly than conventional dieselfuel, particularly when the former is produced from highlyunsaturated sources.

The oxidation rate of biodiesel can be inuenced by manyfactors, including temperature and chemical composition. Theinuence of fatty acid composition on biodiesel oxidation rateis higher than the inuence of environmental conditions such

as air, light, and the presence of metals. 16 Monounsaturated fattyacid methyl esters (such as C18:1) are considered to be betterthan poly unsaturated ones (such as methyl linoleate (C18:2)and C18:3) in terms of oxidation stability, without any adverseeffect on fuel cold properties. 17 In particular, the number andposition of double bonds in fatty acid esters affect the rate of oxidation. 18 According to literature, the rates of oxidation havea relative value of 1 for oleates like methyl esters (ME) andethyl esters (EE), 41 for linoleates, and 98 for linolenates. Smallamounts of more highly unsaturated fatty compounds containingbis-allylic carbons have a signicant strong effect on oxidativestability. In the case of lubricating oil dilution, highly unsaturatedesters present in engine oil are suspected of forming high-

molecular compounds, which may reduce the lubricating qual-ity. 19The IV limit of 120 set by the European biodiesel standard

(EN 14214) excludes several promising oil sources such as

(5) FAO The state of food and agriculture (SOFA) 2008 ; Food andAgriculture Organization of the United Nations (FAO): Rome, 2008.

(6) Dorado, M. P.; Cruz, F.; Palomar, J. M.; Lopez, F. J. Renewable Energy 2006 , 31 , 12311237 .

(7) Krawczyk, T. In International News on Fats, Oils and Related Materials ; American Oil Chemists Society Press: Champaign, IL, 1996;Vol. 7, p 801.

(8) Zhang, Y.; Dube, M. A.; McLean, D. D.; Kates, M. Bioresour.Technol. 2003 , 90 , 229240 .(9) Knothe, G. Energy Fuels 2008 , 22 , 13581364 .

(10) Knothe, G. Fuel Process. Technol. 2005 , 86 , 10591070 .(11) Canakci, M.; Sanli, H. J. Ind. Microbiol. Biotechnol. 2008 , 35, 431

441.(12) Harrington, K. J. Biomass 1986 , 9 , 117 .(13) Ramos, M. J.; Fernandez, C. M.; Casas, A.; Rodr guez, L.; Perez,

A. Bioresour. Technol. 2009 , 100 , 261268 .(14) Schober, S.; Mittelbach, M. Lipid Technol. 2007 , 19 , 281285 .(15) Dunn, R. O. J. Am. Oil. Chem. Soc. 2002 , 79 , 915920 .(16) Knothe, G.; Dunn, R. O. J. Am. Oil. Chem. Soc. 2003 , 72 , 1155

1160 .(17) Imahara, H.; Minami, E.; Saka, S. Fuel 2006 , 85 , 16661670 .

(18) Durrett, T. P.; Benning, C.; Ohlrogge, J. Plant J. 2008 , 54 (4),593607 .(19) Knothe, G. Fuel Process. Technol. 2007 , 88 , 669677 .

Scheme 1. Transesterication Process

2326 Energy & Fuels, Vol. 23, 2009


3/17

T a b l e 1 . I n u e n c e o f O

i l F a t t y A c i d P r o l e o n B i o d i e s e l P r o p e r t i e s

d e g r e e o f u n s a t u r a t i o n

p r o p e r t y

s t a n d a r d

m o n o u n s a t u r a t e d

f a t t y a c i d s ( F A )

d i u n s a t u r a t e d a n d

t r i u n s a t u r a t e d F A

p o l y u n s a t u r a t e d F A

c h a i n l e n g t h

o t h e r f a c t o r s

i n t e r a c t i o n b e t w e e n

b i o d i e s e l p r o p e r t i e s 1

r e f

i o d i n e v a l u e ( I V )

E N 1 4 2 1 4 ;

E N 1 4 1 1 1

d i r e c t l y d e p e n d e n t ( + + ) e a c h d o u b l e b o n d c a n a d d 2 5 3

. 8 g o f i o d i n e

3 ,

1 4

o x i d a t i o n s t a b i l i t y

( O S )

E N 1 4 2 1 4 ;

E N 1 4 1 1 2

O S ( - ) d e c r e a s e s w i t h

u n s a t u r a t i o n

O S d e c r e a s e s m o r e

t h a n p r e s e n c e o f


F A d o ( -

- -

)

D r a m a t i c a l l y d e c r e a s e

s t a b i l i t y ( -

- -

)

1 7 -

1 9

c e t a n e n u m b e r

( C N )

E N 1 4 2 1 4 ;

E N 5 1 6 5

M o s t i m p o r t a n t f a c t o r : d e c r e a s e C N

. ( - - -

)

I t i n c r e a s e s w i t h t h e

n u m b e r o f s e q u e n t i a l

C H

2 ( + + )

C N )

4 6 . 3 +

5 4 5 8 / S N -

0 . 2 2 5 I V

.

I t d e p e n d s o n d e n s i t y

( + ) i n a s e c o n d o r d e r

p o l y n o m i a l f u n c t i o n

1 4 1

L o w C N ( - -

)

N O

x e m i s s i o n s

i t i n c r e a s e s (

+ + )

i t i n c r e a s e s m o r e

t h a n w i t h t h e p r e s e n c e o f


F A ( + + + )

i t d e c r e a s e s ( - -

)

i n v e r s e l y p r o p o r t i o n a l

t o C N

2 6

, 4 0

P M e m i s s i o n s

t h e r e i s n o n p r o p o r t i o n a l

r e l a t i o n

i t d e c r e a s e s w i t h C 1 2 : 0

a n d C 1 6 : 0

2 7

l o w - t e m p e r a t u r e

o w p r o p e r t i e s

( C P a n d P P )

i t i n c r e a s e s (

+ + + )

i t i n c r e a s e s l e s s

t h a n t h e p r e s e n c e o f


F A d o ( + + )

l o w i n c r e a s e ( + )

i t d e c r e a s e s ( - )

1 0

, 1 7

k i n e m a t i c

v i s c o s i t y ( )

E N 1 4 2 1 4 ;

E N I S O 3 1 0 4

n o n l i n e a r d e c r e a s e w i t h

u n s a t u r a t i o n . F i r s t d o u b l e

b o n d p r e s e n t s h i g h e r e f -

f e c t

i t d e c r e a s e s l e s s

t h a n t h e p r e s e n c e o f

m o n o u n s a t u r a t e d F A d o

p o l y n o m i a l s e c o n d o r d e r

r e l a t i o n s h i p 1

) 1

. 1 6 E

-

4 M 2

- 0 . 0 2 6 4 M +

2 . 2 8

f a t t y a c i d w i t h h y d r o g e n

g r o u p s i n c r e a s e s

3 5

, 1 4 2

h e a t o f c o m b u s t i o n

( H H V )

H H V ) 4 9 . 4 3 -

0 . 0 4 1 S N

-

0 . 0 1 5 I V

H H V )

7 9 . 0

1 4 -

4 3 . 1

2 d 1

2 9

, 1 4 3 , 1 4 4

m e t h y l e s t e r

c o n t e n t

E N 1 4 2 1 4 ;

E N 1 4 1 0 3

r e a c t i v i t y s l i g h t l y d e c r e a s e s d u r i n g e s t e r i c a t i o n u s i n g s u p e r c r i t i c a l m e t h a n o l ( - )

R e a c t i v i t y d e c r e a s e s

u s i n g h e t e r o g e n e o u s

c a t a l y s t ( - -

)

3 6

, 3 7

1 S N : s a p o n i c a t i o n n u m b e r ;

d : d e n s i t y ; M : m

o l e c u l a r w e i g h t ( g / m o l ) ; + : l o w d i r e c t c o r r e l a t i o n b e t w e e n b i o d i e s e l p r o p e r t y a n d f a t t y a c i d p r o l e ;

+ + : m e d i u m d i r e c t c o r r e l a t i o n ;

+ + + : s i g n i c a n t d i r e c t

c o r r e l a t i o n ; - : l o w i n v e r s e c o r r e l a t i o n ; - - : m e d i u m i n v e r s e c o r r e l a t i o n ; - - - : s i g n i c a n t i n v e r s e c o r r e l a t i o n .

ReViews Energy & Fuels, Vol. 23, 2009 2327


4/17

sunower and some nonedible low-cost oily crops. In fact,Schober and Mittelbach state that this limit cannot be arguedas a suitable limit to describe or avoid the initial concerns aboutproblems resulting from oxidative degradation. 14 They state thatIV itself is not the most suitable parameter to express biofuelstability, because it cannot weigh the signicant difference inoxidative stability between mono-, di- and triunsaturated esters.As a matter of fact, it seems that parameters such as oxidationstability, linolenic acid ester content, and polyunsaturated esters

content are better indicators of degradation tendencies. 202.2. Cetane Number (CN). This parameter gives a measure-

ment of the combustion quality during ignition. It providesinformation about the ignition delay (ID) time of a diesel fuelupon injection into the combustion chamber. Fuels with lowCN tend to cause diesel knocking and show increased gaseousand particulate exhaust emissions (PM), due to incompletecombustion. 21 Moreover, excessive engine deposits are reported.In general, biodiesel has higher CN values than fossil fuel, whichis considered to be a signicant advantage in terms of engineperformance and emissions, allowing biodiesel-fuelled enginesto run more smoothly and with less noise. 22

Long ID times, with low CN s and subsequent poor combus-tions have been associated to FAME with highly unsaturatedcomponents such as linoleic (C18:2) and linolenic (C18:3) acidesters. High CN values have been observed in saturated fattyacid esters, such as palmitic (C16:0) and stearic (C18:0) acidesters. Generally, the higher the chain length, the higher theCN value. 12,23 Also, the more sequential CH 2 groups in the fattycompound, the higher the CN. Knothe et al. 24 studied the effectof the structure (branching, unsaturation, and length) of the fattyacid chain and the alcohol moiety on the CN of biodiesel. Suchauthors stated that the level of unsaturation of the fatty acidchains is the most signicant factor causing lower CN. Also,results have shown that one saturated, long straight chain in afatty ester sufces to provide a high CN.

According to engine exhaust emissions, higher CN is cor-related with reduced nitrogen oxides (NO x ),25 although this maynot always hold for all types of engine technologies. 24 Theconnection between the structure of fatty acid esters and exhaustemissions was investigated by studying enriched fatty acid alkylesters as fuel and using different vegetable oil esters with a widerange of iodine numbers. 26 The NO x exhaust emissions report-edly increase with lower saturation and decreasing chain length,which can also lead to a connection with the CN of thesecompounds. 27 Peterson et al. 28 found that fatty acids with twodouble bonds had more effect on increasing NO x emissions thanthose with one double bond. On the other hand, PM was notinuenced by chain length, but the higher reductions were foundusing methyl laurate and methyl palmitate. 27 Changes in carbon

monoxide (CO) and hydrocarbons (HC) could not be linearlycorrelated with unsaturation. 28

2.3. Gross Caloric Value (Higher Heating Value) andNet Caloric Value (Lower Heating Value). These fuelproperties indicate the suitability of fatty compounds as dieselfuel. Due to higher oxygen content, FAME exhibit lower heatingvalues than fossil diesel. So, to achieve adequate engine torqueand power, an increasing of injection volumes is needed. 21However, this leads to higher specic fuel consumptions.Caloric value is not included in most fuel standards, but it isa limiting parameter within the European standard for FAME

used as heating fuels (EN 14213). Freedman and Bagby 29developed a model to predict heating values from different fattyacids composition. Generally, the higher the chain length(number of carbons and hydrogens in FAME molecules), thehigher the heating value. 10 The increase in the ratio of theseelements relative to oxygen also results in a heat contentincrease. A decrease in heat content is the result of fewerhydrogen atoms (i.e., higher unsaturation) in the fuel molecule.Therefore, from this point of view, oil sources with a highproportion of long-chain saturated compounds should be selectedfor transesterication. 21

2.4. Brake-specic Fuel Consumption. BSFC is the ratiobetween mass fuel consumption and brake effective power,

being inversely proportional to break thermal efciency (BTE).Biodiesel-specic fuel consumption is expected to increasearound 10 - 20% in relation to diesel fuel, since the loss of heating value of biodiesel must be compensated with higherfuel consumption. An indicator of the loss of heating value isthe oxygen content in the fuel. 30 Several researchers found acorrelation between BSFC and oxygen content, concluding thatthe increase in BSFC is due to the oxygen enrichment from thefuel, but not from the air intake. 31,32

2.5. Cold Weather Performance. One of the major prob-lems associated with the use of biodiesel is poor ow propertiesat low temperatures. 10 Partial solidication in cold weather maycause blockages of fuel lines and lters, leading to fuel starvationand problems during engine start-up. 21 Provided that long-chainsaturated fatty esters signicantly increase CP and PP, reducingsaturated fatty acid content of vegetable oils can improve coldtemperature ow properties of biodiesel.

To improve cold temperature ow characteristics of biodiesel,several proposals have been suggested, including winterization,additives, esterication with branched alcohols, and modicationof oil chemical composition. Several authors have stated thatthe cheapest and more effective way to improve the low-temperature ow properties of biodiesel is the optimization of fatty acid composition of the raw material. 18,33,34 With this aim,Imahara et al. 17 developed a prediction model to estimate CPof biodiesel from various oils/fats, providing a useful tool todetermine optimal fatty acid methyl ester composition. They

observed that CP depends mostly on saturated ester content,while the effect of unsaturated ester composition could benegligible.

2.6. Kinematic Viscosity. Fuel viscosity impacts on bothinjection and combustion efciency. Higher viscosity leads to

(20) Mittelbach, M. Bioresour. Technol. 1996 , 56 , 711 .(21) Mittelbach, M.; Remschmidt, C. Biodiesel: The Comprehensi Ve

Handbook; Martin Mittelbach: Graz, Austria, 2004.(22) Knothe, G.; Matheaus, A. C.; Ryan, T. W. Fuel 2003 , 82, 971

975.(23) Klopfenstein, W. J. Am. Oil. Chem. Soc. 1985 , 62 , 10291031 .(24) Knothe, G.; Matheaus, A. C.; Ryan, T. W. Fuel 2003 , 82, 971

975.(25) Ladommatos, N.; Parsi, M.; Knowles, A. Fuel 1996 , 75 , 814 .(26) Peterson, C. L.; Taberski, J. S.; Thompson, J. C.; Chase, C. L. Trans.

ASAE 2000 , 43 , 13711381 .(27) Knothe, G.; Sharp, C. A.; Ryan, T. W. Energy Fuels 2006 , 20,

403408 .

(28) Peterson, C.; Reece, D. Trans. ASAE 1996 , 39 , 805816 .(29) Freedman, B.; Bagby, M. O. J. Am. Oil. Chem. Soc. 1989 , 66 , 16011605 .

(30) Lapuerta, M.; Armas, O.; Rodr guez-Fernandez, J. Prog. EnergyCombust. Sci. 2008 , 34 , 198223 .

(31) Rakopoulos, Ct. D.; Hountalas, D. T.; Zannis, T. C.; Levendis, Y. A.SAE Paper 2004 - 01 - 2924 ; 2004 .

(32) Graboski, M. S.; Ross, J. D.; McCormick, R. L. SAE Paper 961166 ;1996 .

(33) Lee, I.; Johnson, L. A.; Hammond, E. G. J. Am. Oil. Chem. Soc.1996 , 73 , 631636 .

(34) Lee, I.; Johnson, L. A.; Hammond, E. G. J. Am. Oil. Chem. Soc.

1995 , 72 , 11551160 .(35) Allen, C. A. W.; Watts, K. C.; Ackman, R. G.; Pegg, M. J. Fuel1999 , 78 , 13191326 .



5/17

a higher drag in the injection pump, causing higher pressuresand injection volumes, especially at low engine operatingtemperatures. As a direct consequence, the timing for fuelinjection and ignition tends to be slightly advanced for biodiesel,which might in turn lead to increased NO x emissions due tohigher maximum combustion temperatures. 21 Allen et al.35

developed a method for predicting the kinematic viscosity of biodiesel from its fatty acid composition. Results showed thatfor saturated fatty acid esters, viscosity increased with carbonnumber in a curvilinear trend, rather than linear. Indeed, forunsaturated C18 esters, they observed a nonlinear decrease inviscosity, while increasing number of double bonds. The mostsignicant effect was found for the rst unsaturation. Contami-nation with small amounts of glycerides signicantly increasedbiodiesel viscosity. 35

2.7. Mono-, Di-, and Triglycerides (TG) or Triacylglycer-ols (TAG) Content. Fuel exceeding the limits of mono-, di-,and triglycerides dened in the EN 14214 standard may causeformation of deposits to injector nozzles, pistons, and valves.Indirect hints at high glycerides contents in biodiesel arecorrespondingly increased values for viscosity and carbon

residue.21

There are only few studies about the inuence of fattyacid composition of vegetable oils on transesterication yield.Abreu et al. 36 studied the effect of heterogeneous catalysts andfound that the activity of metal complexes increases for shortchains. It is worthy to highlight that their results indicated thatboth the saturation degree and the alkyl-chain length aredeterminant factors in the catalytic activity. Stavarache et al. 37

established the relationship between yield of FAME duringultrasound-assisted transesterication and the composition of fatty acids from different vegetable oils. In fact, they found thatsaturated fatty acids that have a natural preference for rst andthird positions in triglycerides were transesteried mostly at thebeginning of the reaction, while the amount of unsaturated fattyacids esters increased as the reaction progressed. 38 Warabi etal.39 studied the alkyl esterication in supercritical alcohol andobserved that saturated fatty acids, including palmitic and stearicacids, had slightly lower reactivity than unsaturated fatty acids(i.e., oleic, linoleic, and linolenic acids).

In conclusion, given the antagonistic requirements betweenlow-temperature ow characteristics and the oxidative stability,NO x emissions, and CN, there is strictly no fatty acid proleproviding a fuel for which all these parameters are optimal. 18

However, various studies have suggested that biodiesel withhigh levels of methyl oleate may have excellent, if not optimal,characteristics with regard to ignition quality, NO x emissions,

fuel stability, ow properties at low temperature, and iodinenumber according to the standard EN 14214. 10,13 Furthermore,it is expected that biodiesel with an average of 1.5 double bondsper molecule will produce an equivalent amount of NO x toconventional diesel fuel. 40 Lastly, given that polyunsaturatedfatty acids have a disproportionably large effect on the auto-

oxidation of biodiesel, 16 it is recommended to avoid theirpresence in TG to be used as raw material for biodieselproduction.

3. Considerations about Biodiesel Produced fromVegetables Oils

3.1. Ethical Issues. The major obstacle for large-scaleadoption of biodiesel from vegetable oils is the production of sufcient amounts of oilseed crops without signicantly affect-ing food supply and cost. To reach this goal, researchers andindustry have put a lot of effort proposing and developingalternative sources to produce biofuels. Although a largeproportion of these efforts are focused on conversion of lignocellulosic feedstocks to ethanol (second-generation fuels),some strategies to design new crops to produce biodiesel areoutlined below. 18 It must be noted that there is currently a socialcontroversy over biofuels produced from energy crops that areprimarily used for feeding purposes. Yet, even in case thescientic community eventually nds an efcient technologyto produce alcohol from agricultural pruning and forest residuesthat denitely will not compete with food, this will provide uswith an insufcient quantity of biofuels. Plantations of trees toprocess biomass into alcohol may be needed, leading to the samesocial alarm caused by the use of energy crops (rst-generationfuels) instead of crops for food.

Increased demand for the production of edible oils for feedingpurposes has put limitations on the use of these oils for biodieselproduction. Some voices claim that edible oils are too importantfor human feeding to run vehicles. 2 However, the FAO hascalculated that 41.88 million km 2 of land are available foragriculture, although just 15.06 million km 2 are in use, and only0.11 million km 2 are used for biofuels production today, whichis no more than 1% of that area. The FAO estimates that in2030, 0.325 million km 2 will be used for biofuels production,which is no more than 2% of total agricultural land use. 41

Nevertheless, to avoid the use of edible crops to produce fuel,and the supposed subsequent increase of food price, nonediblecrops developed in marginal lands could provide a sustainableoption as biodiesel feedstocks. Biodiesel technology should notcause starvation in underdeveloped countries. In fact, it can havethe opposite effect: it should be focused to help poor anddeveloping countries to decrease their dependence to fossil oilimports, thus enhancing their Balance of Payments (BOP) andgeneral welfare.

However, it is important to mention again that either energycrops grown in marginal lands or biomass from forests toproduce biofuels cannot nowadays provide the total amount of fuels required for the current high energy-dependent life.Therefore, to reduce the impact on climate change and otherrelated problems including pollution, a change in the consump-tion habits is strongly recommended.

3.2. Economical Issues. One main concern in further usageof biodiesel is the economic viability of its production. A fewyears ago, biodiesel unit price was 1.5 - 3.0 times higher thanthat of petroleum-derived diesel fuel. 11 But currently, due tothe dramatic increase of crude mineral oil price, cost of biodieselis not too far from diesel price (Table 2). Remarkably, indifferent countries, biodiesel price has always shown the sameprice as diesel fuel, even after the increase of fossil fuels price.The reason for this linearity is not clear, as other interests seemto control the market.

(36) Abreu, F. R.; Lima, D. G.; Hamu, E. H.; Wolf, C.; Suarez, P. A. Z. J. Mol. Catal A: Chem. 2004 , 209 , 2933 .

(37) Stavarache, C.; Vinatoru, M.; Maeda, Y. Ultrason. Sonochem. 2007 ,14 , 380386 .

(38) Richards, A.; Wijesundera, C.; Palmer, M.; Salisbury, P. AOCSAustralian Workshop: Sydney, 2002; p 29.

(39) Warabi, Y.; Kusdiana, D.; Saka, S. Bioresour. Technol. 2004 , 91 ,

283287 .(40) McCormick, R. L.; Graboski, M. S.; Alleman, T. L.; Herring, A. M.;Tyson, K. S. En Viron. Sci. Technol. 2001 , 35 , 17421747 .

(41) Konandreas, P.; Smithuber, J. Global Biofuel Production Trendsand Possible Implication of Swaziland; Food and Agricultural Organizationof United Nations: 2007 .



6/17

Manufacturing costs and raw feedstock prices are the maineconomic criteria to take into account for biodiesel productionto compete with diesel fuel. Manufacturing costs include directcosts for oil extraction, reagents, operating supplies, andmanpower, as well as indirect costs related to insurance and

storage. For a complete analysis, xed capital costs involvedin the construction of processing plants and auxiliary facilities,distribution, and retailing must also be taken into consideration. 6In this sense, several studies have identied that the price of feedstocks is by far one of the most signicant factors affectingthe economic viability of biodiesel manufacture. 6- 8,42 In fact,approximately 70 - 95% of total biodiesel production cost arisesfrom the cost of the raw material. 42,43 Thus, to produce acompetitive biodiesel, the feedstock price is a factor that needsto be taken into consideration.

Several authors have found that a key factor to make biodieseleconomically feasible is the application of tax credits. 44,45 Topromote biodiesel consumption, several countries have exemptedbiodiesel from their fuel excise tax. According to this, theEuropean Union (EU) approved the biodiesel tax exemptionprogram in May 2002 (Art. 21, Finance Law 2001). 2 Despitethis, some European countries, including Germany (consideredone of the fathers of biodiesel), have started removing taxexemption. On Oct 22, 2008, the German federal governmentratied the law entitled Gesetz zur A nderung der Forderungvon Biokraftstoffen (Energy Tax Law). 46 According to this,starting in January 2009, the German government will receivenine cents on the dollar more per liter of biodiesel (increasingfrom 0.18 to 0.21 Euros). Such a tax will increase to more than65 cents on the dollar in 2012, putting obstacles to thedevelopment of German biofuel reneries, constituting astimulus for the importation of cheaper biodiesel. Taxes remove

the price advantage of biodiesel over conventional diesel fueland should result in a massive decline in biodiesel output.A lower-cost biodiesel production can also be achieved by

the optimization of the process. Because biodiesel chemicalproperties determine its feasibility as fuel, the optimization of reaction parameters can be exploited to maximize the yield of ester, thus achieving a low-cost chemical process and ensuring

appropriate chemical properties to guarantee adequate engineperformance and appropriate exhaust emissions. In this sense,it is important to characterize the oil (i.e., fatty acid composition,water content, and other signicant parameters) to determinethe feasibility to convert the oil into biodiesel.

3.3. Ecological, Political, and Agronomical Issues. Therenewed interest in the use of vegetable oils to produce biodieselis due to its less polluting and renewable nature, compared toconventional petroleum-based diesel fuel. Biodiesel could bebenecial for environment, local population job creation,provision of modern energy carriers to rural communities,mitigation of human migration, and reduction of CO 2 and sulfurlevels in the atmosphere. 47

Current biodiesel energy originates from the sun, throughphotosynthesis of biomass. However, to keep the main benetof its use (i.e., to be an environmentally friendly energy),limiting factors such as the extensive use of land, irrigation,and labor practices (such as fertilizing, weed control, etc.) mustbe taken into consideration and reduced to minimal levels.Implementation of efcient farming practices to preserve soilfertility and to reduce the use of valuable inputs, such asfertilizers and water, gain special interest.

The increasing development of biodiesel opens new chal-lenges to the scientic community, including the production of renewable energy respecting natural ecosystems. Genetic en-gineering can nowadays be carried out in a clean, environmen-tally friendly, and cost-effective way, thus becoming an efcientapproach to achieve such ecological, political, and agronomicalgoals, as discussed below. Another way to increase globalvegetable oil production without harming ecosystems is to usemarginal or nonarable wasteland. 18 In addition, the set-asiderules of the EU Agricultural Policy specify a minimum area of obligatory set-aside (10% in 2001) of the total arable land, butalso allow up to 50% of the total claimed area to be put into

voluntary set-aside. Nevertheless, an exception has been intro-duced into the rules for managing set-aside land, allowingfarmers to cultivate crops for nonfood purposes. 48,49 It shouldbe noted that increasing the set-aside area could lead to erosionproblems, and may have an impact on arable land. Related tothat, in response to the increasingly tight situation on the cerealmarket, the EU agriculture ministers recently approved aCommission proposal to remove the obligatory set-aside ratefor autumn 2007 and spring 2008 sowings. Furthermore, theabolition of the compulsory set-aside from 2009 onward is partof the Common Agricultural Policy (CAP) Health Check proposal, which was adopted by the Commission on 20th May2008 and it is currently under discussion in the Council, the

European Parliament and other European Institutions.50

For all these reasons, another approach is the use of nonediblecrops and trees, which have several advantages, such as growingin arid or less favored regions, requiring very little manpowerand care, having high oil content, being resistant to plagues anddrought, etc. The foliage could be used as manure, giving anadded value to the crop. As an example, most trees and crops

(42) Connemann, J.; Fischer, J. The International Liquid BiofuelsCongress. US National Biodiesel Foundation: Brazil, 1998, p. 15.

(43) Haas, M. J.; McAloon, A. J.; Yee, W. C.; Foglia, T. A. Bioresour.Technol. 2006 , 97 , 671678 .

(44) Bender, M. Bioresour. Technol. 1999 , 70 , 8187 .(45) Peterson, C. L. Transactions of the ASAE 1986 , 29, 14131422 .(46) Vorblatt Entwurf eines Gesetzes zur A nderung der Frderung von

Biokraftstoffen. Federal Ministry for the Environment, Nature Conservationand Nuclear Safety, Oct. 20, 2008; pp 38. (http://www.bmu.de/les/pdfs/ allgemein/application/pdf/entw_foerderung_biokraftstoff.pdf).

(47) Demirbas, A. Energy Con Vers. Manage. 2008 , 49 , 21062116 .(48) Dorado, M. P.; Ballesteros, E.; Lopez, F. J.; Mittelbach, M. Energy

Fuels 2004 , 18 , 7783 .(49) Graciani, A. L., Amores, A. G., Arnal Almenara, J. M., Chico

Gaetan, J. M., Dorado, M. P. In 1st World Conference and Exhibition on Biomass for Energy and Industry ; James & James (Science Publishers) Ltd.:

London, 2001; pp 1560-

1561.(50) Europa s Press Releases; EU: Brussels, 2008; Vol. IP/08/1069.Available at: http://europa.eu.

Table 2. Price of Biodiesel from Different Raw Materials andDiesel Fuel

fuel price (USD/t), Sept 2007 price (USD/t), Sept 2008 ref

diesel fuel 733 1017 145RME (B100) a 1020 - 1060 1415 145SME (B99) b 850- 865 1185 145PME (B99) c 780- 850 990 145

a RME: rapeseed oil methyl ester, pure and without additives,matching EN 14214 standard and typically reaching - 10 or - 12 Cquoted in USD/MT on a free on board (FOB) Northwest Europe (NorthGerman ports, North France, Benelux and South-East UK) basis. b SME:soybean oil methyl ester, with a minimum of 99% biodiesel (B99),typically not matching the EN 14214 and reaching a 0/ - 5 C CFPP,quoted in USD/MT on a cost, insurance, freight (CIF) ARA with the6.5% duty paid included (T2). c PME: palm oil methyl ester, with aminimum of 99% biodiesel (B99), typically not matching the EN 14214and reaching a + 11/ + 15 C CFPP, quoted in USD/MT on a cost,insurance, freight (CIF) ARA with the 6.5% duty paid included (T2).



7/17

mentioned below grow well on wasteland and therefore cantolerate long periods of drought and dry conditions. 2

4. Nonedible and Low-cost Vegetable Oils with HighPotential to Be Used As Raw Materials to Produce

Biodiesel

In terms of sustainability, provided the previous technical,ethical, economical, and social considerations, potentially suit-able vegetable raw materials for biodiesel production aredescribed below. The selection has been done considering lowinput crops and the most promising ones, according to theirproperties (Tables 3 and 4). 2 In the following sections,potentially suitable low-cost vegetable oils for biodiesel produc-tion are analyzed separately, in terms of fuel properties and theirsuitability to be used as alternative diesel fuel. Finally, acomparison between them facilitates nding out the best ttinglow-cost vegetable oil for biodiesel production.

4.1. Jatropha curcas. J. curcas is a perennial plant, nativeand widely spread throughout many tropical countries. It growsreadily in poor and stony soil. It is drought- and disease-resistant,and its oil yields high-quality biodiesel. 51,52 Biodiesel producedfrom J. curcas oil meets all the requirements stipulated by the

EU standard EN 14214. 53 However, as J. curcas is still a wildplant, the initiation of systematic selection and breedingprograms is a prerequisite for sustainable utilization of this plantfor biodiesel production. 54

The FFA content of J. curcas seed oil (JCSO) variesdepending on the quality of the feedstock. Although Sivaprakasamand Saravanan 55 reached 91% yield on jatropha oil methyl ester(JOME) using alkaline transesterication and jatropha oil pooron FFA, Berchman and Hirata 56 developed a technique toproduce biodiesel from crude JCSO containing high levels(15%) of FFA. Some researchers have proposed the use of immobilized enzymes, such as those from ChromobacteriumViscosum , Candida rugosa , and Sus scrofa porcine pancreas as

catalyst.57,58

In this sense, Modi et al.59

proposed the use of propan-2-ol as an acyl acceptor for immobilized Candidaantarctica lipase B. Additionally, Zhu et al. 60 proposed the useof a heterogeneous solid superbase catalyst (catalyst dosage of 1.5%) and calcium oxide, at 70 C for 2.5 h, with a 9:1methanol:oil molar ratio to produce biodiesel.

Kumar et al. 61 obtained values of brake thermal efciencyof jatropha oil methyl ester comparable to diesel fuel values,higher values of CH and CO emissions, but lower values of NO x exhaust emissions.

4.2. Pongamia pinnata (Karanja Seed Oil). This nonedibleoil tree is drought-resistant, tolerant to salinity, moderately frosthardy, and is commonly found in East Indies, Philippines, and

India.2 Several scientists have investigated and proposed karanjaoil as a potential source of biodiesel. 3,62 - 66 Most researchershave conducted the transesterication of P. pinnata oil by usingmethanol and potassium hydroxide. 64,66,67

Due to its high FFA content, some researchers have proposedthe esterication of the FFA with H 2SO4, prior to transesteri-cation with NaOH. 68 In all cases, karanja oil has shownpromising properties to be used as a raw material to producebiodiesel, saving large quantities of edible vegetable oils. Diesel

engine performance tests have been carried out with karanjaoil methyl ester (KOME) and its blend with diesel fuel from20 to 80% by volume (v/v). 65 Results have revealed a reductionin exhaust emissions together with an increase in torque, brakepower, thermal efciency, and reduction in brake-specic fuelconsumption compared to diesel fuel. Prakash et al. 69 optimizedtransesterication of karanja oil using the Taguchi optimizationmethodology 70 and carried out performance and emission testsusing diesel fuel and biodiesel blends. Among the blends, 20%KME showed better performance characteristics compared toother blends. They observed better BTE, BSFC, and indicatedthermal efciency (ITE). With regard to exhaust emissions, 20%blend slightly increased the NO x due to the higher specicgravity of the fuel. Both the PM emission and smoke densitywere low. 69

4.3. Madhuca indica (Mahua Oil). This is a deciduous treethat belongs to the family Sapotaceae . It can reach up to 21 mhigh. Several approaches to produce biodiesel from this cropcan be found in literature. 2 In this sense, Ghadge and Rahemanhave proposed a two-step pretreatment to reduce high FFAlevels. Transesterication was carried out adding 0.25 (v/v)methanol and 0.7% KOH. Fuel properties were found to becomparable to those of diesel fuel. 71 Other authors haveproposed different successful alternatives to produce biodieselfrom this species: ethanol and sulfuric acid, and methanol andsodium hydroxide. 72- 74 Excepting water content, the fuelproperties of mahua biodiesel are within the limits specied bythe ASTM D 6751 - 02 and EN 14214 standards. 71 Besidescaloric value, all other fuel properties of mahua biodiesel werefound to be higher than high-speed diesel fuel. 75

Raheman and Ghadge 75 measured engine performance andemissions of biodiesel obtained from mahua oil and its blendswith diesel fuel. They observed that BSFC increased while BTEdecreased by increasing the proportion of biodiesel in the blends.Smoke level and CO were reduced, whereas NO x increased with

(51) Becker, K.; Makkar, H. P. S. Lipid Technol. 2008 , 20 , 104108 .(52) Banapurmath, N. R.; Tewari, P. G.; Hosmath, R. S. Renewable Energy 2008 , 33 , 19821988 .

(53) Kumar, A.; Sharma, S. Ind. Crops Prod. 2008 , 28 , 110 .(54) Foidl, N.; Foidl, G.; Sanchez, M.; Mittelbach, M.; Hackel, S.

Bioresour. Technol. 1996 , 58 , 7782 .(55) Sivaprakasam, S.; Saravanan, C. G. Energy Fuels 2007 , 21 , 2998

3003 .(56) Berchmans, H. J.; Hirata, S. Bioresour. Technol. 2008 , 99 , 1716

1721 .(57) Shah, S.; Sharma, S.; Gupta, M. N. Energy Fuels 2004 , 18 , 154

158.(58) Shah, S.; Sharma, S.; Gupta, M. N. Indian J. Biochem. Biophys.

2003 , 40 , 392399 .(59) Modi, M. K.; Reddy, J. R. C.; Rao, B. V. S. K.; Prasad, R. B. N.

Bioresour. Technol. 2007 , 98 , 12601264 .(60) Zhu, H.; Wu, Z. B.; Chen, Y. X.; Zhang, P.; Duan, S. J.; Liu, X. H.;

Mao, Z. Q. Chin. J. Catal. 2006 , 27 , 391396 .(61) Senthil Kumar, M.; Ramesh, A.; Nagalingam, B. Biomass Bioenergy2003 , 25 , 309318 .

(62) Naik, M.; Meher, L. C.; Naik, S. N.; Das, L. M. Biomass Bioenergy ,2008 , 32 (4), 354 - 357.

(63) Meher, L. C.; Dharmagadda, V. S. S.; Naik, S. N. Bioresour.Technol. 2006 , 97 , 13921397 .

(64) Meher, L. C.; Naik, S. N.; Das, L. M. J. Sci. Ind. Res. 2004 , 63 ,913918 .

(65) Raheman, H.; Phadatare, A. G. Biomass Bioenergy 2004 , 27 , 393397.

(66) Karmee, S. K.; Chadha, A. Bioresour. Technol. 2005 , 96 , 14251429 .

(67) Vivek, G. A. K. J. Sci. Ind. Res. 2004 , 63 , 3947 .(68) De, B. K.; Bhattacharyya, D. K. Lipid Fett 1999 , 101 , 404406 .(69) Prakash, N.; Arul Jose, A.; Devanesan, M. G.; Viruthagiri, T. Indian

J. Chem. Technol. 2006 , 13.(70) Rao, R. S.; Kumar, G.; Prakasham, R.; Hobbs, S. P. J. Biotechnol.

J. 2008 , 3 , 510523 .(71) Ghadge, S. V.; Raheman, H. Biomass Bioenergy 2005 , 28 , 601

605.(72) Raheman, H.; Ghadge, S. V. Fuel 2007 , 86 , 25682573 .(73) Ghadge, S. V.; Raheman, H. Bioresour. Technol. 2006 , 97 , 379

384.(74) Puhan, S.; Vedaraman, N.; Sankaranarayanan, G.; Ram, B. V. B.

Renewable Energy 2005 , 30 , 12691278 .

(75) Raheman, H.; Ghadge, S. V. Fuel 2008 , 87 , 26592666 .(76) Nabi, M. N.; Akhter, M. S.; Zaglul Shahadat, M. M. Bioresour.Technol. 2006 , 97 , 372378 .



8/17

T a b l e 3 . C h e m i c a l P r o p e r t i e s o f N o n e d i b l e V e g e t a b l e O i l s a n d T r a n s e s t e r i c a t i o n C o n d i t i o n s

f a t t y a c i d c o m p o s i t i o n ( % )

r a w

m a t e r i a l ( o i l )

C 1 6 : 0

C 1 8 : 0

C 1 8 : 1

C 1 8 : 2

C 1 8 : 3

o t h e r a c i d s

F F A ( % )

o i l c o n t e n t

( w / w % )

y i e l d F A M E

( w / w % )

t r a n s e s t e r i c a t i o n

c o n d i t i o n s

t r a n s e s t e r i c a t i o n

o p t i m i z a t i o n

r e f

J a t r o p h a c u r c a s

1 3 . 4

- 1 5

. 3 6 . 4 - 6 . 6

3 6 . 5

- 4 1

4 2 . 1

- 3 5

. 3 0 . 3

C 1 6 : 1 ( 0

. 8 )

1 5

5 8 1

9 0 -

9 1

a c i d p r e t r e a t m e n t c a t a l y z e d w i t h

H 2 S

O 4 ,

M e O H 9 : 1 ( M ) , K O H

,

M e O C H

3 0 . 8 %

, 4 5 C

, 1 2 0 m i n

o n e - s t e p a l k a l i c a t a l y z e d : M e O H

1 8 %

, N a O H 1 . 6 %

, 7 0 C

, 6 0 m i n

d o n e

5 1 ,

5 5 ,

5 6 ,

1 4 6

P o n g a m i a p i n n a t a

3 . 7 - 7 . 9

2 . 4 - 8 . 9

4 4 . 5

- 7 1

. 3 1 0

. 8 -

1 8 . 3

C 2 4 : 0 1 ( 1 -

3 . 5 ) 8 . 3

2 7 -

3 9 2

9 0 . 4

M e O H 6 : 1 ( M ) , N a O H 1 - 1 . 5 %

( w / w ) , 6 5 C

, 4 0 -

1 8 0 m i n

d o n e

6 4 ,

6 5 ,

6 7 ,

6 9

M a d h u c a i n d i c a

1 6 -

2 8 . 2

2 0 -

2 5 . 1

4 1 -

5 1

8 . 9 - 1 3

. 7

C 1 4 : 0 ( 1 )

C 2 0 : 0 ( 3 -

3 . 3 )

4 0 1

9 8

P r e t r e a t m e n t a c i d c a t a l y z e d

( H 2

S O 4

) , M e O H 6 : 1 ( M ) , N a O H

0 . 7 % ( w / w ) , 6 0 C

, 1 8 0 m i n

d o n e

3

3 , 7 1

, 7 3

A z a d i r a c h t a i n d i c a

2 0

2 0

4 2

1 5

C 2 0 : 0 ( 1

. 3 )

4 0 -

5 0

8 3

M e O H 6 : 1 ( M ) , N a O H 0 . 6 % ( w / w ) ,

6 5 C

, 6 0 m i n

3 , 7 6

, 1 4 7

H e V e a

b r a s i l i e n s i s

1 0 . 2

8 . 7

2 4 . 6

3 9 . 6

1 6 . 3

1 7

4 0

8 4 . 4

6

M e O H 6 : 1 ( M ) , N a O H 1 % ( w / w ) ,

6 0 C 6 0 m i n +

e t h e r p e t r o l e u m

5 2 ,

7 9 -

8 1

B r a s s i c a c a r i n a t a

4 - 6

1 . 3

1 0 -

1 7

1 7 -

2 5

1 0 -

1 7 E r u c i c : 4 5 . 4 ;

G a d o l e i c : 1 0 . 3

1 0 . 8

9 8 . 2

7

8 2


( l o w

e r u c i c )

5 . 5

0 . 5

4 2 -

4 4

3 5 -

3 7

1 5 -

1 6

2 . 2

9 1 . 9

M e O H 4 . 6 : 1 ( M ) , K O H 1 . 4 %

,

4 5 C

, 3 0 m i n

d o n e

4 8

C a m e l i n a s a t i V a

5 - 6

2 - 3

1 4 -

1 6

1 5 -

1 6

3 6 -

3 7 C 2 0 : 1 ( 1 5 - 1 6 )

C 2 2 : 0 ( 1 -

2 )

C 2 2 : 1 ( 3 )

0 . 0 5 4

- 6 . 1 2 9

. 9 -

3 8 . 3

9 7 . 4

4

M e O H 6 : 1 ( M ) , N a O H 1 . 5 % ( w / w ) ,

2 5 C

, 6 0 m i n

2 t e s t s

8 6 ,

8 9 ,

1 4 8

T e r m i n a l i a c a t a p p a

3 5

5

3 2

2 8

0 . 5

4 9

9 3

M e O H 6 : 1 ( M ) , C H

3 C H

2 O N a

0 . 2 : 1 ( M )

c a t a l y s t

9 3

A s c l e p i a s s y r i a c a

5 . 9

2 . 3

3 4 . 8

4 8 . 7

1 . 2

C 1 6 : 1 ( 6

. 8 )

0 . 0 1 9

2 0 -

2 5

> 9 9

M e O H 6 : 1 ( M ) , C H

3 O N a - K O H

1 . 1 % ( w / w ) , 6 0 C

, 6 0 m i n

c a t a l y s t

9 0 ,

9 2

C a l o p h y l l u m i n o p h y l l u m

1 7 . 9

1 8 . 5

4 2 . 7

1 3 . 7

2 . 1

C 1 6 : 1 ( 2

. 5 )

C 2 4 : 0 ( 2

. 6 )

2 2

6 5 2

8 5

P r e t r e a t m e n t a c i d c a t a l y z e d

( H 2

S O 4

) , M e O H 6 : 1 ( M ) , K O H

1 . 5 %

, 6 5 C

, 4 h

d o n e

3 , 7 8

C y n a r a c a r d u n c u l u s

1 1

4

2 5

6 0

3 2 . 4

7

9 5

c a t a l y s t

2 , 1 0 4 , 1 4 9

1 F r o m s e e d . 2

F r o m k e r n e l . 3

S u r f a c e r e s p o n s e p r e t r e a t m e n t . 4 R e n e d o i l . T r a n s e s t e r i c a t i o n y i e l d f r o m r e n e d c a m e l i n a o i l r e a c h e d 8 9 %

( a c i d v a l u e o f 6 . 0 )

.



9/17

an increase of biodiesel percentage from mahua oil in the blends.They considered that mahua oil methyl esters were safelyblended with diesel fuel up to 20%, without signicantlyaffecting engine performance (BSFC, BTE) and emissions(smoke, CO, and NO x ), and thus it was recommended as asuitable alternative fuel for diesel engines.

4.4. Azadirachta indica (Neem Oil). This large tree growsin almost all types of soils. It thrives well in arid and semiaridclimate with maximum shade temperature as high as 49 C,

bearing rainfalls as low as 250 mm/year. 3Nabi et al. have produced biodiesel from neem oil by using

20% methyl alcohol and 0.6% anhydrous NaOH catalyst.Reaction temperature was kept at 55 - 60 C. Compared withconventional diesel fuel, exhaust emissions including smoke andCO were reduced, whereas NO x emissions were increased withdiesel fuel- biodiesel blends, except when the exhaust gasrecirculation (EGR) was applied. According to their results, theyrecommended it as an environment-friendly alternative fuel fordiesel engines. 76

4.5. Calophyllum inophyllum (Nagchampa/Polanga Oil).This tree thrives in xerophytic habitats. It grows best in deepsoil or exposed sea sands. The rainfall requirement is just

750-

5000 mm/year.3

Polanga oil contains 24.96% saturated and72.65% unsaturated acids. 77 Saturated fatty acid alkyl estersincrease cloud point, cetane number, and stability. The free fattyacid content of unrened ltered nagchampa oil was found tobe 22%, with an acid value of 44 mg KOH/g. 78

Sahoo et al.78 obtained a comparatively higher ash pointthan petroleum diesel fuel for nagchampa oil methyl ester(NOME), indicating better safety conditions during storage. Allcharacterization tests of biodiesel demonstrated that the mostimportant properties are very close to those of diesel fuel. Theperformance of diesel engines was slightly better in terms of BTE, BSFC, smoke opacity, and exhaust emissions includingNO x for the entire range of operations. 78

4.6. He Wea brasiliensis (Rubber Seed Oil). This rubber treeoriginates from the Amazon rain forest (Brazil). Although thereare variations in the oil content from different countries, theaverage oil yield is 40% 2 and contains 17 - 20% saturated and77- 82% unsaturated fatty acids. 79 To check its feasibility as asource to produce biodiesel, several studies have been under-taken. Ikwuagwu et al. 79 prepared methyl esters of rubber seedoil using excess of methanol (6 M), containing 1% NaOH as acatalyst. The biofuel properties showed similar values comparedto those of diesel fuel, with the exception of the oxidativestability. Ramadhas et al. 80 performed a prior acid-catalyzedesterication to reduce the high FFA content, followed by analkaline esterication. The lower blends of biodiesel with dieselfuel increased BTE and reduced both BSFC and exhaustemissions. 80,81

4.7. Brassica carinata (Ethiopian Mustard Oil). This is anadequate oil-bearing crop that is well-adapted to marginalregions. It is drought-resistant and grows in arid regions.Ethiopian mustard presents up to 6% saturated hydrocarbonchains. B. carinata oil from wild species presents high erucicacid content (which is toxic), although cultivars with low erucicacid are used as food by Ethiopians.

B. carinata adapts better and is more productive in adverseconditions than B. napus ., offering the possibility of exploitingthe Mediterranean marginal areas for energetic purposes. 82

(77) Hemavathy, J.; Prabhakar, J. V. J. Am. Oil. Chem. Soc. 1990 , 67 ,

955957 .(78) Sahoo, P. K.; Das, L. M.; Babu, M. K. G.; Naik, S. N. Fuel 2006 ,86 , 448454 .

T a b l e 4 . F u e l P r o p e r t i e s o f F A M E f r o m N o n e d i b l e V e g e t a b l e O i l s

e x h a u s t e m i s s i o n s r e l a t i v e

t o

p e t r o d i e s e l - b a s e d f u e l ( % )

r u n n i n g c o n d i t i o n s

r a w m a t e r i a l ( o i l )

C N

h e a t o f

c o m b u s t i o n

k J / k g )

o x i d a t i o n

s t a b i l i t y ( h )

C P

( C )

P P ( C )

k i n e m a t i c

v i s c o s i t y

( 4 0 C ; m m

1 / s )

N O

x

P M

H C

C O

m a x i m u m

B T E ( % ) B S F C ( % ) 2

l o a d ( % )

s p e e d ( r p m ) I V ( g l 2 /

1 0 0 g )

r e f

E N 1 4 2 1 4 s t a n d a r d

> 5 1

> 6

> 3 . 5 a n d < 5

> 1 2 0

J a t r o p h a c u r c a s

5 0 -

5 8 . 5

3 7 8 0 0 - 3 8 4 5 0

3 . 2 3

4

4 . 4

- 3 - 7

+ 1 0

+ 8

2 5 . 6

3 - 2 9

+ 1 4

. 5

1 0 0 ( 8 0 f o r B S F C )

1 5 0 0

9 5 -

1 0 7

5 1 ,

5 2 ,

6 1 ,

1 5 0 , 1 5 1

P o n g a m i a p i n n a t a

5 4 . 5

3

3 6 1 0 0

2 . 3 5

5

- 2

4 . 2 - 5 . 5

- 8 . 3

- 2 0

- 7 3

2 9 . 5

1

+ 8

1 0 0

1 5 0 0

8 6 . 5

- 9 0

5 2 ,

6 5 ,

6 9 ,

1 3 8

M a d h u c a i n d i c a

5 6 . 6

1

3 6 8 0 0

6

3 . 9 8

6

- 5

- 8 1

2 1

+ 2 6

1 0 0

1 5 0 0

7 4 . 2

3 , 7 2

A z a d i r a c h t a i n d i c a

5 1 -

5 7 . 8

7 4 0 1 0 0

6 . 8 2

5

- 4

- 4 3

1 0 0

1 5 0 0

7 0 -

7 4

3 , 7 6

H e V e a

b r a s i l i e n s i s

4 3 -

4 4 . 8

1 3 7 5 0 0 - 3 8 6 5 0

8 . 7

0 . 4 - 4 -

8

5 . 8 1

2 4

+ 1 2

1 0 0

1 5 0 0

1 2 1 - 1 4 5

5 2 ,

7 9 ,

8 1


l o w e r u c i c )

5 2

3 6 0 0 0

4 . 5

- 2 7

- 3 5

+ 1 3

1 0 0

1 5 0 0

9 2 -

1 2 8

8 2 ,

8 3

5 6 . 9

3 9 5 5 0

- 9

- 6

4 . 8 3

+ 6 . 4

1 0 0

1 5 0 0

1 3 8

4 8

C a m e l i n a s a t i V a

4 6 4

4 2 2 0 0 4

1 . 9 0

4

- 8

6 . 4 2 5

- 1 0 4

1 0 0

1 5 0 0

1 5 5

8 6 ,

8 9 ,

1 4 8

T e r m i n a l i a c a t a p p a

5 7 . 1

3 6 9 7 0

4 . 3

8 3 . 2

9 3

A s c l e p i a s s y r i a c a

5 0

2 7 7 2 7

- 0 . 9 5 -

6

4 . 6 - 5 . 2

1 5 2 - 1 5 7

9 2

C a l o p h y l l u m i n o p h y l l u m 5 7

. 3

3 9 2 5 0

1 3 . 2

4 . 3

4

- 4

- 3 5 6

- 5 0

0

3 1

+ 2

1 0 0

1 5 0 0

7 1 . 5

7 8

C y n a r a c a r d u n c u l u s

5 9

3 3 0 0 0 - 3 7 2 0 0

- 4

- 1 0 5 . 1

1 1 7

1 0 4 , 1 0 7

1 A t 2 5 C

. 2 P e r c e n t a g e o f b r a k e s p e c i c f u e l c o n s u m p t i o n ( r e l a t i v e t o p e t r o d i e s e l b a s e d f u e l ) . 3 T e s t u s i n g 1 5 % b i o d i e s e l / d i e s e l f u e l b l e n d . 4

C a m e l i n a o i l w i t h o u t t r a n s e s t e r i c a t i o n

. 5 A t 2 0 C

. 6 6 0 % b l e n d w i t h

d i e s e l

f u e l . 7

U n i t s : k g c a l / m o l .



10/17

Dorado et al. 48 described a low-cost transesterication processof B. carinata oil and found negative effects of singular fattyacids (e.g., erucic acid) in the alkali-catalyzed transesterication.Cardone et al. 83 found that B. carinata biodiesel produces lowerlevels of particulate matter but higher levels of NO x concentra-tions with respect to diesel fuel. The soluble organic fractionof biodiesel particulate suggested that the carcinogenic potentialis lower than that of petroleum diesel. 83

4.8. Camelina sati W a (Gold-of-pleasure Oil/False Flax).

Budin et al.84

studied the composition of C. sati Va oil andconcluded that this low-input crop presents food and nonfoodexploitation potential. The oil yield from this species is similarto that of the spring rapeseed; however, lower fertilizer andpesticide requirements lead to a substantial cost reduction, 85being a more environmentally friendly crop. Since productioncost of C. sati Va is relatively low compared to many other oilcrops, including rapeseed, corn, and soybean, it is an attractivepotential crop for biofuels. The free fatty acid content of rawC. sati Va oil is 3.1% (acid value equals to 6.0), whereas renedoil presents a value around 0.05% (acid value is 0.1). The iodinevalue (152- 157), far exceeds the limits of all biodieselstandards, due to very high level of polyunsaturated fatty acidsin the C. sati Va oil (Table 3). However, the high iodine valueof the C. sati Va oil methyl esters does not seem to lead to arapid deterioration of lubricating oil. 86

Frohlich and Rice 86 have investigated the production of methyl esters from C. sati Va oil. Biodiesel was prepared bymeans of a single-stage esterication using methanol and KOH.They compared two methods of transesterication developedby Freedman et al. 87 and by Maurer. 88

Steinke et al. 89 developed both alkali and lipase-catalyzedalcoholeysis of C. sati Va oil. Frohlich and Rice 86 tested biodieselfrom this species in two light transport vehicles. Fuel consump-tion and general vehicle operation resulted to be similar to thoseobserved using rapeseed oil methyl esters. Fuel-specic proper-ties of Camelina sati Va oil methyl esters are largely withinspecication, though low-temperature behavior could be aproblem under certain weather conditions.

4.9. Asclepias syriaca (Milkweed Oil). The common milk-weed is native from the North East and North Central of theUnited States of America, where it grows on roadsides andundisturbed habitat. 90 The seed contains 20 - 25% (dry weight)of triglycerides, composed of over 90% unsaturated fatty acidswith nearly 50% of linoleic acid and less than 2% of linolenicacid (Table 3). 91 On the basis of the fatty acid prole, the oil isexpected to provide an alternative source to biodiesel production.

Milkweed oil contains more than 6% of palmitoleic acid, whichis usually found in smaller amounts in vegetable oils. This is avery interesting fact, because methyl palmitoleate is a strongcandidate to enhance fuel properties, besides methyl oleate. 9

Holser and OKuru 92 analyzed fuel properties of both methyland ethyl esters of milkweed seed oil. Milkweed biodieselexhibits pour and cloud point values that may suggest animproved cold weather performance. Highly unsaturated esterstructures (e.g., linolenate) oxidize more rapidly than saturatedester structures, leading to fuel degradation, reducing its quality.

4.10. Terminalia catappa. This tree is popularly known inBrazil as castanhola. It has been studied by Dos Santos etal.93 The tree is tolerant to strong winds, salt spray, andmoderately high salinity in the root zone. It grows principallyin freely drained, well-aerated, sandy soils. The oil can beobtained from the kernels of the fruit, with yields around 49%w/w. 94

Castanhola oil fatty acid composition is similar to that of theconventional edible oils. Dos Santos et al. 93 compared basicand acid catalysis and observed that basic catalysts are moreefcient than acid ones. In the presence of basic catalysts, anaverage yield of FAME of ca. 93% was obtained. Althoughthe fruit is edible, the kernel is nonedible and is considered awaste. However, it might also be used to produce biodiesel,giving added value to this crop.

4.11. Ricinus communis (Castor Oil). This plant is nativefrom Central Africa, being cultivated in many hot climates. Theoil contains up to 90% of ricinoleic acid, which is not suitablefor nutritional purposes due to its laxative effect. The hydroxy-carboxylic acid is responsible for the extremely high viscosityof castor oils almost a hundred times the value observed in otherfatty materials. 21

Transesterication reactions from this oil have been carriedout mainly by using both ethanol and NaOH, as well as throughenzymatic methanolysis. 95,96 Several authors have studied theinuence of catalyst on biodiesel yield from castor oil. Resultsshowed that the most efcient transesterication of castor oilwas achieved in the presence of sodium methoxide and acidcatalysts. 97

The viscosity of castor oil-based biodiesel is extremely highat low temperatures, and the melting point of methyl ricinoleateis close to 0 C. Furthermore, the cetane number of methylricinoleate, and therefore neat castor oil biodiesel, do not meetthe minimum requirements for biodiesel standard specications.The oxidative stability of methyl ricinoleate is signicantly lowerthan that of its nonhydroxylated counterpart (methyl oleate),and is even lower compared to methyl linoleate. 9 To recommendthis biodiesel as an alternative to diesel fuel, more research isneeded.

4.12. Cuphea ssp. (Cuphea). This genus includes speciessuch as C. carthagenensis, C. painteri, C. ignea, C. Viscosissima ,and C. lla Vea. Cuphea grows in temperate and subtropical

(79) Ikwuagwu, O. E.; Ononogbu, I. C.; Njoku, O. U. Ind. Crops Prod.2000 , 12 , 5762 .

(80) Ramadhas, A. S.; Jayaraj, S.; Muraleedharan, C. Fuel 2005 , 84,335340 .(81) Ramadhas, A. S.; Muraleedharan, C.; Jayaraj, S. Renewable Energy2005 , 30 , 17891800 .

(82) Cardone, M.; Mazzoncini, M.; Menini, S.; Rocco, V.; Senatore,A.; Seggiani, M.; Vitolo, S. Biomass Bioenergy 2003 , 25 , 623636 .

(83) Cardone, M.; Prati, M. V.; Rocco, V.; Seggiani, M.; Senatore, A.;Vitolo, S. En Viron. Sci. Technol. 2002 , 36 , 46564662 .

(84) Budin, J. T.; Breene, W. M.; Putnam, D. H. J. Am. Oil. Chem.Soc. 1995 , 72 , 309315 .

(85) Downey, R. K. J. Am. Oil. Chem. Soc. 1971 , 48 , 718722 .(86) Frohlich, A.; Rice, B. Ind. Crops Prod. 2005 , 21 , 2531 .(87) Freedman, B.; Pryde, E. H.; Mounts, T. L. J. Am. Oil. Chem. Soc.

1984 , 61 , 16381643 .(88) Maurer, K. Landtechnik 1991 , 46 , 604608 .(89) Steinke, G.; Schonwiese, S.; Mukherjee, K. D. JAOCS 2000 , 77 ,

367371 .(90) Holser, R. A. Ind. Crops Prod. 2003 , 18 , 133138 .

(91) Adams, R. P.; Balandrin, M. F.; Martineau, J. R. Biomass 1984 , 4,81104 .(92) Holser, R. A.; Harry-OKuru, R. Fuel 2006 , 85 , 21062110 .

(93) Dos Santos, I. C. F.; de Carvalho, S. H. V.; Solleti, J. I.; Ferreirade La Salles, W.; Teixeira da Silva de La Salles, K.; Meneghetti, S. M. P. Bioresour. Technol. 2008 , 99 , 65456549 .

(94) Abdullah, A. H.; Anelli, G. RiVista di Agricoltura Subtropicale eTropicale 1980 , 74 , 245247 .

(95) De Oliveira, D.; Di Luccio, M.; Faccio, M.; Dalla Rosa, C.; Bender,J. P.; Lipke, N.; Amroginski, C.; Dariva, C.; Oliveira, J. V. Appl. Biochem. Biotechnol. 2005 , 122.

(96) Fagundes, F. F.; Garcia, R. B.; Costa, M.; Borges, M. R. J. Biotechnol. 2005 , 118 , 166169 .

(97) Meneghetti, S. M. P.; Meneghetti, M. R.; Wolf, C. R.; Silva, E. C.;Lima, G. E. S.; Silva, L. L.; Serra, T. M.; Cauduro, F.; de Oliveira, L. G. Energy Fuels 2006 , 20 , 22622265 .



11/17

climates. The seeds of these plants contain around 30 - 36% oil.98Fatty acid composition of the oil comprises major quantities of caprylic acid (73% in C. painter and 3% in C. ignea ), capricacid (18% in C. carthagenensis , 24% in C. painteri , 87% in C.ignea , and 83- 86% in C. lla Vea ), and lauric acid (57% in C.carthagenensis ).99 The correlation analysis between fatty acidcomposition of cuphea oil and environmental crop factors aslatitude, elevation, and temperature have been studied byGhebretinsae et al. 100 They observed that environmental factors

contribute signicantly, and in particular, with respect to theratio of lauric/capric and lauric/myristic acids.Genetically modied oil of C. Viscosissima presents relatively

low viscosity, enhancing its performance as an alternative todiesel fuel. 101 Also, the atomization properties suggest betterfuel performance, owing to the presence of short-chain triglyc-erides, compared to traditional vegetable oils comprisingpredominantly long-chain triglycerides. 102

4.13. Cynara spp. This genus includes species such as C.humilis (thistle), C. cardunculus (cardoon), and C. scolymus(artichokes). Although the leaf stalks of these species can beeaten, they are considered weed in many countries. The owerbuds and stems of this genus can also be used for food purposes.The oil to produce biodiesel is extracted from the nonedibleseeds, therefore not competing with food markets and increasingthe value and protability of the plant. Moreover, this genuspresents a high degree of rusticity, is resistant to plagues, dryconditions, and frost, is highly efcient in the use of water andnutrients, and has reduced agrochemical needs.

The low inputs management required, the advantages of increasing biodiversity by including C. cardunculus in agro-ecological systems, and its adaptability to native Mediterraneanregions make this crop a potentially optimum alternative for asustainable agriculture in those regions. 103

The lignocellulosic biomass of cardoon can be used as a solidbiofuel, and seed-oil can be derived to biodiesel production,making its cost lower compared to that of sunower oil. 104

Encinar et al. transesteried C. cardunculus oil by usingmethanol and several catalysts (sodium hydroxide, potassiumhydroxide, and sodium methoxide) to produce biodiesel. 105,106C. cardunculus methyl esters provide a signicant reduction inparticulate emissions, mainly due to reduced soot and sulfateformation. 107

5. The Shortcomings of High FFA Content in Oils toBiodiesel Production

Several nonedible feedstocks exhibit high level of FFA, ascan be seen in Table 3. This represents a key problem duringcommon alkaline transesterication. Alkaline catalyst reacts withFFA and produces soap (saponication reaction), reducing the

biodiesel yield, and preventing the separation of esters, glycerol,and washing water. Soap formation also increases the viscosityand leads to gel formation. 87,108 - 111 In general, the use of alkalinecatalysts in transesterication reactions is not recommended infeedstock with FFA contents above 0.5%. 108,112,113

Homogeneous mineral acids (i.e., H 2SO4) have been used ascatalysts for raw materials with high FFA content. During theesterication step (usually called pretreatment), the acidcatalyst converts the FFA into esters. Triglycerides are then

converted into FAME via transesterication with alkalinecatalyst. During pretreatment, the main factor to monitor is waterformation, due to its inhibiting effects in the transesterication. 11

Di Serio et al.114 showed the possibility to perform asimultaneous esterication and transesterication, using lowconcentrations of homogeneous Lewis acid catalysts (e.g.,carboxylic acids of given metals). However, this process hasalso some associated problems related to the need of separatingcatalysts from products by downstream purication.

Demirbas 115 proposed a supercritical transesterication pro-cess as an alternative method to the previous two-steps catalyzedprocess. The advantages of the supercritical process are thatcatalysts are not required, both esterication and transesteri-

cation reactions happen simultaneously, and the methodologyis neither sensitive to FFA nor water. Nevertheless, thesupercritical process requires a high molar alcohol/feedstock ratio (around 40 - 42:1), involving high-energy consumption(with high reaction pressures, around 35 - 40 MPa, and reactiontemperatures generally higher than 300 C). Side reactionsincluding thermal decomposition and dehydrogenation of un-saturated fatty acid methyl esters may occur in case reactionparameters values exceed the optimal levels. 110,116

Recent studies using heterogeneous catalysts (e.g., acidic andbasic solid resins immobilized lipases) have been reported. Thesecatalysts allow the use of different feedstocks, requiring lowerinvestment costs and less downstream process equipment, ascompared to supercritical processes. Marchetti et al. 117 carriedout a conceptual design of these alternative production plantswith a techno-economical analysis and concluded that thesupercritical approach is not an economically feasible alternative,due to its high operating costs.

Heterogeneous catalysts have some advantages, since theycan be easily separated from the reaction products, and reactionconditions can be less intensive than those required undersupercritical conditions. 118

Most research on the use of heterogeneous catalysts has beenfocused on solid base catalysts. 118,119 Solid acid catalysts havebeen largely ignored for biodiesel synthesis, due to lowerreaction rates and undesired side reactions found for homoge-neous mineral acids. 119 Nevertheless, since acid catalysts can

(98) Kaliangilee, I.; Grabe, D. F. J. Seed Technol. 1988 , 12 , 107113 .(99) Graham, S. A. CRC Crit. Re V. Food Sci. Nutr. 1989 , 28 , 139173 .(100) Ghebretinsae, A. G.; Graham, S. A.; Camilo, G. R.; Barber, J. C.

Ind. Crops Prod. 2008 , 27 , 279287 .(101) Geller, D. P.; Goodrum, J. W.; Knapp, S. J. Ind. Crops Prod.

1999 , 9 , 8591 .(102) Geller, D. P.; Goodrum, J. W.; Siesel, E. A. Trans. ASAE 2003 ,

46 , 955958 .(103) Raccuia, S. A.; Melilli, M. G. Field Crop Res. 2007 , 101 , 187

197.(104) Fernandez, J.; Curt, M. D.; Aguado, P. L. Ind. Crops Prod. 2006 ,

24 , 222229 .(105) Encinar, J. M.; Gonzalez, J. F.; Rodriguez, J. J.; Tejedor, A. Energy

Fuels 2002 , 16 , 443450 .(106) Encinar, J. M.; Gonzalez, J. F.; Sabio, E.; Ramiro, M. J. Ind. Eng.

Chem. Res. 1999 , 38 , 29272931 .(107) Lapuerta, M.; Armas, O.; Ballesteros, R.; Fernandez, J. Fuel 2005 ,84 , 773780 .

(108) Canakci, M.; Gerpen, J. V. Trans. ASAE 2001 , 44 , 14291436 .(109) Haas, M. J. Fuel Process. Technol. 2005 , 86 , 10871096 .(110) Ma, F. R.; Hanna, M. A. Bioresour. Technol. 1999 , 70 , 115.(111) Dorado, M. P.; de Almeida, J. A.; Schellert, C.; Ballesteros, E.;

Lohrlein, H. P.; Krause, R. Trans. ASAE 2002 , 45 , 525529 .(112) Ma, F.; Clements, L. D.; Hanna, M. A. Trans. ASAE

Documents

The Ideal Vegetable Oil-based Biodiesel Composition a Review of Social Economical & Technical Implications