Trabalho10_Overview Biodiesel Production

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Overview on the current trends in biodiesel production

N.N.A.N. Yusuf, S.K. Kamarudin , Z. Yaakub

Department of Chemical and Process Engineering, Universiti Kebangsaan Malaysia, 43600 UKM Bangi, Selangor, Malaysia

a r t i c l e i n f o

Article history:

Received 18 March 2010Accepted 5 December 2010

Available online 29 March 2011

Keywords:

BiodieselBiofuelEconomy

a b s t r a c t

The finite nature of fossil fuels necessitates consideration of alternative fuels from renewable sources. Theterm biofuel refers to liquid, gas and solid fuels predominantly produced from biomass. Biofuels include

bioethanol, biomethanol, biodiesel and biohydrogen. Biodiesel, defined as the monoalkyl esters of vege-table oils or animal fats, is an attractive alternative fuel because it is environmentally friendly and can besynthesized from edible and non-edible oils. Here, we review the various methods for the production ofbiodiesel from vegetable oil, such as direct use and blending, microemulsion, pyrolysis and transesterifi-cation. The advantages and disadvantages of the different biodiesel-production methods are also dis-cussed. Finally, we analyze the economics of biodiesel production using Malaysia as a case study.

2010 Elsevier Ltd. All rights reserved.

1. Introduction

The world is currently facing the worst energy crisis in history.Many countries worldwide are still heavily dependent on petro-leum as their main source of electricity and transportation fuel,and its price has been setting record highs in recent days. Thus,the only possible solution to this crisis is to find a sustainable(renewable) and economically feasible source of alternative en-ergy. There are many alternative energy sources such as wind, so-lar, geothermal and biomass that fulfill the first criterion(sustainability). However, few of these can fulfill the second crite-rion (economic feasibility). The best option, fulfilling both criteria,is biofuel, particularly that made from readily available biomassfeedstock [13]. Biomass refers to all the vegetable matter thatcan be obtained from photosynthesis. The great versatility of bio-mass as a feedstock is evident from the range of materials thatcan be converted into various solid, liquid and gaseous fuels usingbiological and thermochemical conversion processes. Biomass en-ergy is by far the largest renewable energy source, representing10.4% of the worlds total primary energy supply or 77.4% of global

renewable energy supply [4].The concept of using biofuels in diesel engines originated with

the demonstration of the first diesel engine by its inventor, RudolfDiesel, at the World Exhibition in Paris in 1900, using peanut oil asthe fuel. However, due to the then-abundant supply of petroleumdiesel, research and development activities on vegetable-oil fuelswere not seriously pursued. These fuels received attention only re-cently, when it was realized that petroleum fuels were fast dwin-dling and environmentally friendly renewable substitutes mustbe identified [5,6]. Biofuels are liquid or gaseous fuels for the

transport sector that are predominantly produced from biomass.Biofuels can be produced from a variety of bio-feedstocks, theyare renewable, sustainable, biodegradable, carbon neutral for thewhole life cycle and environmentally friendly; they encouragegreen industries and agriculture and are applicable as motor fuels,without or with slight engine modifications. Several biofuels,including bioethanol, biomethanol, biodiesel and biohydrogen, ap-pear to be attractive options for the future of the transport sector.The production of biofuels is expected to rise steadily in the nextfew decades [7]. At present, several countries such Brazil, the Uni-ted States, Germany, Australia, Italy and Austria are already usingbiofuels such as bioethanol and biodiesel. It is expected that thistrend will continue to grow and more countries will use biofuels[8,9].

Bioethanol is an alternative fuel based on alcohol produced bythe fermentation and distillation of raw materials with high sugarsand starch contents. Besides these raw materials, ethanol can beobtained from lignocellulosic biomass from trees and some annualplants. Ethanol can be produced from any organic matter of biolog-ical origin with considerable amounts of sugars and/or materials

that can be converted into sugar such as starch or cellulose. Sugar-cane, sugar beetroot, and sugar sorghum are examples of rawmaterials with high sugar contents which thus can be used for eth-anol production. Wheat, barley, and corn are raw materials con-taining starch, which can easily be converted into sugar usingavailable technologies. A significant part of the woody part of treesand annuals is composed of cellulose, which can also be convertedinto sugar, but the process is more complicated than that requiredfor starch [10].

Biomethanol is another alcohol fuel produced from biomass. Anew study patented in Sweden concluded that methanol can beproduced from biomass via black-liquor gasification at a cost com-petitive with gasoline and diesel [11]. A recent study on oil-palm

0196-8904/$ - see front matter 2010 Elsevier Ltd. All rights reserved.doi:10.1016/j.enconman.2010.12.004

Corresponding author. Tel.: +60 389216422; fax: +60 389216148.E-mail address: [email protected] (S.K. Kamarudin).

Energy Conversion and Management 52 (2011) 27412751

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biomass waste showed that black liquor can be produced from thetrunk of the oil palm, but at present the black liquor is used to pro-duce pulp and paper [12].

Biological hydrogen-generation (biohydrogen) technologiesprovide a wide range of approaches to generate hydrogen andare potentially more environmentally friendly and less energyintensive than thermochemical or electrochemical processes.

There are three types of microorganisms used for hydrogen gener-ation: cyanobacteria, anaerobic bacteria and fermentative bacteria.The cyanobacteria directly decompose water into hydrogen andoxygen in the presence of light energy by photosynthesis. Photo-synthetic bacteria use organic substrates such as organic acids.Anaerobic bacteria use organic substances as the sole source ofelectrons and energy, converting them into hydrogen. Biohydrogencan be generated using bacteria such as Clostridia by controllingtemperature, pH, reactor hydraulic-retention time (HRT), and otheroperating parameters of the fermentation system. Biohydrogen canbe generated by direct biophotolysis, indirect biophotolysis, photo-fermentations and dark fermentation [13].

Among all the biofuels, biodiesel has been receiving perhaps themost attention, due to the similarity between biodiesel and con-ventional diesel in terms of chemical structure and energy content.Additionally, no modification of the diesel engine is required, asbiodiesel is compatible with existing engine models and has beencommercially blended with diesel as a transportation fuel in anumber of countries including Germany, Italy and Malaysia [3].

2. Biodiesel

Biodiesel is an alternative fuel for diesel engines produced bychemically reacting a vegetable oil or animal fat with an alcohol.Alcohols are the most frequently used acyl acceptors, particularlymethanol and, to a lesser extent, ethanol. Other alcohols can alsobe used, e.g., propanol, butanol, isopropanol, tert-butanol,branched alcohols and octanol but the cost is much higher. Regard-

ing the choice between methanol and ethanol, the former is cheap-er, more reactive and the fatty-acid methyl esters (FAME) producedare more volatile than fatty-acid ethyl esters (FAEE). However, eth-anol is less toxic and is considered more renewable because it canbe easily produced from renewable sources by fermentation. Incontrast, methanol is currently mainly produced from non-renew-able fossil sources, such as natural gas. Regarding their character-istics as fuels, FAME and FAEE show slight differences; forexample, FAEE have slightly higher viscosities and slightly lowercloud and pour points than the corresponding FAME [14]. The reac-tion requires a catalyst, usually a strong base, such as sodium orpotassium hydroxide, and produces new chemical compoundscalled methyl esters. It is these esters that have come to be knownas biodiesel [15,16].

The physical properties of biodiesel are given in Table 1. Biodie-sel is a clear amber-yellow liquid with a viscosity similar to that ofpetroleum diesel. Biodiesel is non-flammable and, in contrast topetroleum diesel, is non-explosive, with a flash point of 423 K forbiodiesel as compared to 337 K for petroleum diesel. Unlike petro-leum diesel, biodiesel is biodegradable and non-toxic, and it signif-icantly reduces toxic and other emissions when burned as a fuel.

International practice led to the adoption of a single nomencla-ture to identify the concentration of biodiesel in the blends, knownas the BXX nomenclature, where XX is the percentage in volume ofthe biodiesel in the diesel/biodiesel blend. For example, B2, B5, B20and B100 are fuels with a concentration of 2%, 5%, 20% and 100%biodiesel, respectively. Currently, there are four main concentra-tions of biodiesel used in the fuel market, namely, pure (B100),

blends (B20B30), additive (B5) and lubricity-additive (B2). Theblends in volumetric proportions between 5% and 20% are the most

common. The B5 blend does not require any engine modification.Biodiesel is perfectly miscible with, and also physically and chem-

ically similar to, mineral diesel and so can be used in compressionignition engines without significant or onerous adjustments [1,10].Biodiesel can be pumped, stored and handled using the same

infrastructure, devices and procedure usually employed for con-ventional diesel fuel. In fact, as biodiesel does not produce explo-sive vapors and has a relatively high flash point (close to 150 C),transportation, handling and storage are safer than with conven-tional diesel [17].

2.1. Various raw materials used as feedstock

Vegetable oils are becoming a promising alternative to dieselfuel because they are renewable in nature and can be produced lo-cally and in environmentally friendly ways. Edible vegetable oils

such as canola [1822] and soybean oil [2327] in the USA, palmoil [2833] in Malaysia, rapeseed oil [26,3438] in Europe and cornoil [39,40] have been used for biodiesel production and found to begood diesel substitutes [15]. Non-edible vegetable oils, such asPongamia pinnata (Karanja or Honge) [4145], Jatropha curcas(Jatropha or Ratanjyote) [43,44,4648] and Madhuca iondica (Ma-hua) [49,50] have also been found to be suitable for biodieselproduction.

The oil yield from the crop itself is always the key factor indeciding the suitability of a feedstock for biodiesel production.Oil crops with higher oil yields are more preferable in the biodieselindustry because they can reduce the production cost. Generally,the cost of raw materials accounts for about 7080% of the totalproduction cost of biodiesel. Table 2 shows the oil yields in termsof kg/ha and wt.% and also the prices for various types of edible and

Table 1

Physical properties of biodiesel [1].

Common name Biodiesel

Common chemical name Fatty acid (m)ethyl esterChemical formula range C14C24 methyl esters or C1525H28

48O2Kinematic viscosity range (mm2/s, at

313 K)3.35.2

Density range (kg/m3, at 288 K) 860894Boling-point range (K) >457Flash-point range (K) 420450Distillation range (K) 470600Vapor pressure (mm Hg, at 295 K)


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non-edible oils grown worldwide. It is clear that higher oil yield al-ways corresponds to lower cost. Some of the costs of the non-edi-ble oils were not obtained as they are not currently traded on theopen market [2].

From Table 2, it is observed that palm oil has the highest oilyield at 5000 kg of oil per hectare; this value is far higher thanother oils, which are only in the range of hundreds to 2000 kg of

oil per hectare. Among the various non-edible oils shown in Table2, jatropha has the highest yield, followed by P. pinnata and castor.However, the oil yield in P. pinnata is not constant, depending onmany factors such as plantation type and oil-extraction technique[2].

2.2. The production of biodiesel

Considerable efforts have been made to develop vegetable-oilderivatives that approximate the properties and performance ofhydrocarbon-based diesel fuels. The problems with substitutingtriglycerides for diesel fuels are mostly associated with their (i)high viscosity; (ii) low stability against oxidation (and the subse-quent polymerization reactions); and (iii) low volatility, whichinfluences the formation of a relatively high amount of ash dueto incomplete combustion [51]. These can be changed in at leastfour ways, as follows.

2.2.1. Direct use and blending

Vegetable oil can be mixed with diesel fuel and used directly forrunning an engine. The successful experimental blending of vege-table oil with diesel fuel has been done by various researchers. Adiesel fleet was powered with a blend of 95% filtered used cookingoil and 5% diesel in 1982. In 1980, Caterpillar Brazil Company usedpre-combustion chamber engines with a mixture of 10% vegetableoil to maintain total power without any modification to the engine.A blend of 20% oil and 80% diesel was found to be successful [52].

Pramanik [53] found that a 50% blend of Jatropha oil can beused in diesel engines without any major operational difficulties

but further study is required to determine the long-term durabilityof the engine. The direct use of vegetable oils and/or the use of oilblends have generally been considered to be unsatisfactory andimpractical for both direct and indirect diesel engines. The highviscosity, acid composition, free fatty-acid content, gum formationdue to oxidation, polymerization during storage and combustion,carbon deposits and lubricating-oil thickening are the obviousproblems (see Table 3).

It has been proven that the use of 100% vegetable oil was alsopossible with some minor modifications to the fuel system. Major

problems have been associated with the use of pure vegetable oilsas fuels in compressionignition engines, mainly due to the in-creased viscosity. Micro-emulsification, pyrolysis and transesterifi-cation have been used as remedies to solve the problemsencountered due to high fuel viscosity [54].

2.2.2. Microemulsion

Microemulsions are isotropic, clear or translucent, thermody-namically stable dispersions of oil, water, surfactant, and often asmall amphiphilic molecule, called a cosurfactant. The dropletdiameters in microemulsions range from 100 to 1000 . A micro-emulsion can be made of vegetable oils with an ester and disper-sant (cosolvent), or of vegetable oils, an alcohol and a surfactant,with or without diesel fuels. Because of their alcohol contents,microemulsions have lower volumetric heating values than dieselfuels, but these alcohols have high latent heats of vaporizationand tend to cool the combustion chamber, which reduces nozzlecoking. A microemulsion of methanol with vegetable oils can per-form nearly as well as diesel fuels. The use of 2-octanol as an effec-tive amphiphile in the micellar solubilization of methanol intriolein and soybean oil has been demonstrated; the viscosity

was reduced to 11.2 cSt at 25 C. The reported engine tests on amicroemulsion consisting of soybean oil:methanol:2-octa-nol:cetane improver (52.7:13.3:33.3:1) indicated the accumulationof carbon around the orifices of the injector nozzles and heavydeposits on exhaust valves [55].

Wellert et al. [56] studied the phase behavior of a microemul-sion and a bi-continuous phase was identified using small-angleneutron scattering (SANS) and freeze-fracture electron microscopy(FFEM); the influence of choice of co-surfactant on the structuralparameters was also studied. Jesus et al. [57] introduced the useof a microemulsion method for the determination of sodium andpotassium in biodiesel using a water-in-oil emulsion process forbiodiesel produced from different sources such as soybeans, castor,sunflower oil, animal fat and other vegetable oils.

2.2.3. Thermal cracking (pyrolysis)

Pyrolysis is the conversion of one organic substance into an-other by means of heat or by heat in the presence of a catalyst.The pyrolyzed material can be vegetable oil, animal fat, naturalfatty acids or methyl esters of fatty acids. The pyrolysis of fatshas been investigated for more than 100 years, especially in thoseareas of the world that lack deposits of petroleum. Many investiga-tors have studied the pyrolysis of triglycerides to obtain productssuitable for diesel engines. Thermal decomposition of triglycerides

Table 3

Problems and potential solutions for using vegetable oils as engine fuels [53].

Problem Probable cause Potential solution

Short-term

1. Cold-weather starting High viscosity, low cetane, and low flash point of vegetable oils Preheat fuel prior to injection; chemically alter fuel to an ester2. Plugging and gumming of

filters, lines and injectorNatural gums (phosphatides) and ash in vegetable oil Partially refine the oil to remove gums; filter to 4 lm

3. Engine knocking Very low cetane of some oils. Improper injection timing Adjust injection timing; preheat fuel prior to injection; chemicallyalter fuel to an ester

Long-term

4. Coking of injectors andcarbon deposits onpiston and head ofengine

High viscosity of vegetable oil, incomplete combustion of fuel;poor combustion at partial load

Heat fuel prior to injection; switch engine to diesel when operatingat part load; chemically alter the vegetable oil to an ester

5. Excessive engine wear High viscosity, incomplete combustion of fuel, poor combustion atpartial load; possibly free fatty acids in vegetable oil; dilution ofengine-lubricating oil due to blow-by of vegetable oil

Heat fuel prior to injection; switch engine to diesel when operatingat partial load; chemically alter the vegetable oil to an ester;increase frequency of lubricating-oil changes; lubricating-oiladditives to inhibit oxidation

6. Failure of engine-lubricating oil due to

polymerization

Collection of poly-unsaturated vegetable oil blow-by in crank-caseto the point where polymerization occurs

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produces alkanes, alkenes, alkadienes, aromatics and carboxylicacids [53,68].

2.2.4. Transesterification

Transesterification is a process of reacting a triglyceride such asvegetable oil with an alcohol in the presence of an alkaline catalystto produce fatty-acid esters and glycerol. Among the alcohols,

methanol and ethanol are used commercially because of theirlow cost and their physical and chemical advantages. They are eas-ily dissolved in and react quickly with tri-glycerides and NaOH. Acatalyst is used to improve the reaction rate and yield. An alka-line-catalyzed transesterification process is normally adopted forbiodiesel production because alkaline metal alkoxides and hydrox-ides are more effective than acid catalysts. Sodium and potassiummethoxide are much more effective catalysts for the base-cata-lyzed transesterification of triglycerides [5861].

Darnoko and Cheryan [62] studied the kinetics of palm-oiltransesterification in a batch reactor. Their study illustrated thatwhile the overall conversion of the process did not change withtemperature, the rate of the transesterification process was in-creased with temperature. The overall reaction kinetics is depen-

dent on the individual rate constants for the conversion oftriglycerides to diglycerides, monoglycerides and alcohol esters.Based on the rate constants obtained, the conversion of triglycer-ides to diglycerides was the slowest reaction in transesterification.The time needed for the mass transfer to occur is shortened as tem-perature is increased, leading to a higher rate of transesterificationat higher temperatures.

Figs. 13 represent the different transesterification reactions.Fig. 1 shows the production of biodiesel via an alkaline catalyst.The commonly used catalysts are sodium and potassium hydrox-ides. These reactions are operated at 25125 C. Fig. 2 presentsthe production of biodiesel using an acid catalyst. The reaction issimilar to the alkaline reaction but the alcohol reactants are fedin excess in order to increase the conversion rate. This reaction is

operated at 5580 C. The other type of reaction for transesterifica-tion is enzymatic, using lipase in hydrolysis, alcoholysis and acid-olysis reactions. The advantage of this reaction is the ease ofproduct separation; however, the cost of the biocatalyst is veryexpensive compared to other catalysts and so it is not yet a viableprocess for commercial biodiesel production. Lastly, Fig. 3 presentsthe production of biodiesel via a supercritical reaction with alco-

hol. This reaction uses methanol as alcohol and is capable of pro-ducing high conversions in a short period of time. However theoperating temperature is very high, around 350 C [63,64]. Table4 summarizes the advantages and disadvantages of the differenttransesterification reactions.

2.3. Advantages of biodiesel

2.3.1. Availability and renewability of biodiesel

Biodiesel is the only alternative fuel with the property that low-concentration biofuelpetroleum fuel blends will run well inunmodified conventional engines. It can be stored anywhere petro-leum diesel fuel is stored. Biodiesel can be made from domesticallyproduced, renewable oilseed crops such as soybean, rapeseed andsunflower. The risks of handling, transporting and storing biodieselare much lower than those associated with petroleum diesel. Bio-diesel is safe to handle and transport because it is as biodegradableas sugar and has a high flash point compared to petroleum dieselfuel. Biodiesel can be used alone or mixed in any ratio with petro-leum diesel fuel. The most common blend is a mix of 20% biodieselwith 80% petroleum diesel, or B20 in recent scientific investiga-tions; however, for future commercial applications in Europe thecurrent regulation foresees a maximum of 5.75% biodiesel [66].

2.3.2. Lower emissions from biodiesel

The European Transportation Policy for 2010 created by theEuropean White Paper Commission projects an increase in carbondioxide emissions from vehicles of about 50% from the years 2000

Fig. 1. Production of biodiesel via alkaline catalysis.

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Fig. 2. Production of biodiesel via acidic catalysis.

Fig. 3. Production of biodiesel via supercritical-alcohol transesterification.

Table 4

Comparison of transesterification reactions [65].

Technique Biodiesel (%) Advantage Disadvantage

Acidic-catalysttransesterification

99% after 4 h ofreaction

High production of biodiesel Acidic catalyst

Alkaline-catalysttransesterification

99% after 2 h ofreaction

High and rapid production of biodiesel in a shortperiod of time

Formation of calcium foam at initial stage oftransesterification

Lipase-catalyst

transesterification

95% after 105 h of

reaction

Can be operated at room temperature Slow reaction



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to 2010. The White Paper states that the only way around thisproblem is to develop clean alternative fuels so that the green-house effects can be decreased [67]. The best potential future en-ergy source in the transportation sector is biodiesel.

Biodiesel mainly emits carbon monoxide, carbon dioxide, oxi-des of nitrogen, sulfur oxides and smoke. Combustion of biodieselalone provides over a 90% reduction in total unburned hydrocar-

bons (HC) and a 7590% reduction in polycyclic aromatic hydrocar-bons (PAHs). Biodiesel further provides significant reductions inparticulates and carbon monoxide over petroleum diesel fuel. Bio-diesel provides a slight increase or decrease in nitrogen oxidesdepending on engine family and testing procedures [66].

Currently, global warming caused by CO2 is the main climaticproblem in the world. Therefore, environmental protection isimportant for the future of the world. Because biodiesel is madefrom renewable sources, it presents a convenient way to providefuel while protecting the environment from unwanted emissions.Biodiesel is an ecological and non-hazardous fuel with low emis-sion values, and therefore it is environmentally useful. Using bio-diesel as an alternative fuel is a way to minimize global airpollution and in particular reduce the emission levels of potentialor probable carcinogens [68].

Carraretto et al. [69] investigated the emission of unburnedhydrocarbons, carbon dioxide, carbon monoxide, sulfates, polycy-clic aromatic hydrocarbons, nitrated polycyclic aromatic hydrocar-bons and particulate matter from biodiesel; the net emission ofCO2 was considerably lower than that of diesel oil. Kegl [70]stressed the importance of fuel-injection system to reduce engineemissions as well as fuel consumption. The author suggested thatpressure squareness (ratio of mean to maximum injection pres-sure) should be at a maximum, and fuelling in the first part ofthe injection should be reduced to reduce NOx emission. Simulta-neously, the fuelling in the last part of the injection should be low-ered to reduce smoke emissions.

Pradeep and Sharma [71] studied the use of hot-exhaust-gasrecirculation for the control oxides of nitrogen in a compression

ignition engine fuelled with biodiesel from Jatropha oil. Exhaust-gas recirculation was shown to be an effective method for NOx con-trol. The exhaust gases mainly consist of inert carbon dioxide andnitrogen and possess a high specific heat. When recirculated to theengine inlet, they reduce oxygen concentration and act as a heatsink. This process reduces oxygen concentration and peak combus-tion temperature, which results in reduced NOx. Exhaust-gas recir-culation is not free from demerits. It can significantly increasesmoke and fuel consumption and reduce thermal efficiency unlesssuitably optimized.

2.3.3. Biodegradability of biodiesel

The biodegradability of biodiesel has been proposed as a solu-tion for the waste problem. Biodegradable fuels such as biodiesels

have an expanding range of potential applications and are environ-mentally friendly. Therefore, there is growing interest in degrad-able diesel fuels that degrade more rapidly than conventionalpetroleum fuels. Biodiesel is non-toxic and degrades about fourtimes faster than petroleum diesel. Its oxygen content improvesthe biodegradation process, leading to an increased level of quickbiodegradation [72].

Vegetable-oil methyl esters are reported to be non-toxic andeasily biodegradable in an aquatic environment. It was determinedthat during a 21-day period, 98% of pure rapeseed oil methyl ester(RME) was biologically decomposed, while only 60% of pure fossildiesel fuel decomposed. This means that RME fully meets the mainrequirements of international standards for biological degradation(more than 90% degraded within 21 days for biofuels) [73]. Pasqua-

lino et al. [74] reported more than 98% degradation of pure biodie-sel after 28 days in comparison to 50% and 56% for diesel fuel and

gasoline respectively. Also, the time taken to reach 50% biodegra-dation was reduced from 28 to 22 days in 5% biodiesel mixtureand from 28 to 16 days in the case of a 20% biodiesel mixture atroom temperature. The biodegradability of the mixture was re-ported to increase with the addition of biodiesel.

2.3.4. Higher lubricity

Biodiesel has good lubricant properties compared to petroleumdiesel oil, in particular very-low-sulfur diesel. This is very impor-tant to reduce wear in the engine and the injection system [69].

Demirbas [68] stated that the oxygen content of biodiesel im-proves the combustion process and decreases its oxidation poten-tial. The structural oxygen content of a fuel improves combustionefficiency due to the increase of the homogeneity of oxygen withthe fuel during combustion. Due to this, the combustion efficiencyof biodiesel is higher than petroleum diesel, and the combustionefficiency of methanol/ethanol is higher than that of gasoline. A vi-sual inspection of the injector types would indicate no differencebetween the biodiesel fuels when tested on petroleum diesel.The overall injector coking is considerably low. Biodiesel contains11% oxygen by weight and contains no sulfur. The use of biodiesel

can extend the life of diesel engines because it is more lubricatingthan petroleum diesel fuel.The higher heating values (HHVs) of biodiesels are relatively

high. The HHVs of biodiesels (3941 MJ/kg) are slightly lower thanthat of gasoline (46 MJ/kg), petroleum diesel (43 MJ/kg) or petro-leum (42 MJ/kg), but higher than coal (3237 MJ/kg). Table 5shows a comparison of the chemical properties and HHVs of bio-diesel and petroleumdiesel fuels.

2.3.5. Engine-performance evaluation using biodiesel

Cetane number (CN) is widely used as a dieselfuel qualityparameter. It is related to the ignition-delay time and combustionquality; a higher cetane number indicates better ignition proper-ties [16]. CN is measured by the ISO 5156 test method. This test

method is recommended for diesel and biodiesel and the passinglimits are 46 and 51, respectively. However, there are reports ofthe theoretical estimation of cetane numbers without runningextensive engine tests. The cetane number of biodiesel from vari-ous sources has been estimated to vary from 48 (grape biodiesel)to 61 (palm biodiesel) [75]. The CN of biodiesel is generally higherthan for conventional diesel. The longer the fatty-acid carbonchains and the more saturated the molecules are, the higher theCN is. The CN of biodiesel from animal fats is higher than thoseof vegetable oils [76].

Altn et al. [77] studied a single-cylinder engine fueled with var-ious types of vegetable oils. The results obtained gave a very goodcomparison of engine performance when various vegetable oils areused as fuel. The engine was operated at 1300 rpm and a torque of35 Nm. Petroleum dieselfuel performance was used as a refer-ence. The observed maximum torque differences between the ref-erence value and peak values of the vegetable-oil fuels were about10% with raw sunflower oil, raw soybean oil and opium-poppy oilfuels. The maximum power differences between the reference

Table 5

Comparison of chemical properties and higher heating values (HHVs) of biodiesel and

petroleumdiesel fuels [63].

Chemical property Biodiesel (methyl ester) Diesel

Ash (wt.%) 0.0020.036 0.0060.010Sulfur (wt.%) 0.0060.020 0.0200.050Nitrogen (wt.%) 0.0020.007 0.00010.003Aromatics (vol.%) 0 2838Iodine number 65156 0

HHV (MJ/kg) 39.240.6 45.145.6



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value and peak values of the vegetable-oil fuels were about 18%with raw cottonseed oil and raw soybean oil. The minimum torqueand power difference was about 3% between the reference valueand the oils. These results may be due to the higher viscosity andlower heating values of vegetable oils. The specific fuel consump-tion of petroleum diesel was very low in comparison with all veg-etable oils and their esters. Specific fuel-consumption values of

methyl esters were generally less than those of the raw oil fuels.The higher specific fuel-consumption values of vegetable oils aredue to their lower energy contents. Relatively low CO emissionswere obtained with the esters in comparison with raw vegetableoils. Maximum CO2 emissions were about 10.5% with petroleumdiesel fuel and slightly lower with vegetable oil. This was due tothe better spraying qualities and more uniform mixture prepara-tion of these esters. NOx emissions with vegetable-oil fuels werelower than those with petroleum diesel fuel and the NOx valuesof the methyl esters were higher than those of the raw fuels. NOxformation is related to maximum combustion temperature. Asthe injected particle size of the vegetable oils was greater thanwith petroleum diesel fuel, the combustion efficiency and maxi-mum combustion temperatures with each of the vegetable oilswere lower and NOx emissions were reduced. Smoke-opacity per-centages during each of the vegetable-oil operations were greaterthan that with petroleum diesel fuel. The opacity values of methylesters were between those of diesel fuel and raw vegetable-oilfuels. The greater smoke-opacity percentages of the vegetable-oilfuels were mainly due to the contents of heavier hydrocarbon mol-ecules. Acceleration tests indicated that maximum engine-poweroutput depended on the biodiesel content in the fuel and de-creased as the biodiesel concentration increased.

It was observed that with pure biodiesel the acceleration timeincreased by approximately 8% compared to the baseline petro-leum diesel fuel, while B50 led to an increase of 4.1%. These differ-ences were expected due to the lower energy content of the blends.Poorer atomization may also explain reductions in maximum en-gine-power output [78].

2.4. Disadvantages of biodiesel

The main problem associated with the use of biodiesel, espe-cially that prepared from palm oil, is its poor low-temperature flowproperties, measured in terms of cloud point, pour point and CFPP.The low-temperature properties are very critical for the use of bio-fuels in aviation applications. The low-temperature properties canbe improved by blending with biodiesel from unsaturated feed-stocks [79].

Other major disadvantages of biodiesel are its higher viscosity,lower energy content, higher nitrogen-oxides (NOx) emissions,lower engine speed and power, injector coking, engine compatibil-ity, high price and higher engine wear. Table 6 shows the ASTM

fuel standards for biodiesel and petroleum-diesel fuels. Importantoperating disadvantages of biodiesel in comparison with petro-leum diesel include cold-start problems, the lower energy content,higher copper-strip corrosion and fuel-pumping difficulty due tothe higher viscosity. This increases fuel consumption when biodie-sel is used, in comparison with pure petroleum diesel and inblends, in direct proportion to the share of the biodiesel content.Taking into account the higher production costs of biodiesel com-pared to petroleum diesel, this increase in fuel consumption com-pounds the overall increased cost of application of biodiesel as analternative to petroleum diesel [63].

As more than 95% of biodiesel is made from edible oil, therehave been many claims that this may give rise to further economicproblems. By converting edible oils into biodiesel, food resources

are being used as automotive fuels. It is believed that large-scaleproduction of biodiesel from edible oils may bring about a global

imbalance in the food supply-and-demand market. Recently, envi-ronmentalists have cited the negative impact on the planet of bio-diesel production from edible oils, especially deforestation and thedestruction of ecosystems. EEB, claimed that the expansion of oil-crop plantations for biodiesel production on a large scale hascaused deforestation in countries such as Malaysia, Indonesia andBrazil because more and more forest has been cleared for planta-tion purposes. Furthermore, the line between food and fuel econo-mies is blurred as both of the fields are competing for the same oilresources. In other words, biodiesel is competing with the foodindustry for limited land availability for the plantation of oil crops.Arable land that would otherwise have been used to grow foodwould instead be used to grow fuel [80].

There has been significant expansion in the plantation of oil

crops for biodiesel in the past few years in order to fulfill the con-tinuously increasing demand for biodiesel. Fig. 4 shows the trendin global vegetable-oil blending stocks due to the production ofbiodiesel in the years 19912010 [2]. Although there is continuousincrease in the production of vegetable oil, the blending stocks ofvegetable oils are continuously decreasing due to increasing pro-duction of biodiesel. Eventually, with the implementation of bio-diesel as a substitute fuel for petroleum-derived diesel oil, thismay lead to the depletion of edible-oil supply worldwide.

3. Current trends in biodiesel

The international biofuel market is still at an early and very

dynamic stage. Future conditions for an international biofuel mar-ket in Europe will largely be decided by the European Union (EU)

Table 6

ASTM standards of biodiesel and petroleumdiesel fuels.

Property Testmethod

ASTM D975(petroleum diesel)

ASTM D6751(biodiesel, B100)

Flash point D 93 325 K min 403 KWater and sediment D 2709 0.05 max vol.% 0.05 max vol.%Kinematic viscosity

(at 313 K)D 445 1.34.1 mm2/s 1.96.0 mm2/s

Sulfated ash D 874 0.02 max wt.%Ash D 482 0.01 max wt.% Sulfur D 5453 0.05 max wt.% Sulfur D

2622/129

0.05 max wt.%

Copper-strip corrosion D 130 No. 3 max No. 3 maxCetane number D 613 40 min 47 minAromaticity D 1319 35 max vol.% Carbon residue D 4530 0.05 max mass%Carbon residue D 524 0.35 max mass% Distillation temp. (90%

volume recycle)D 1160 555 K min

611 K max

Fig. 4. Global vegetable-oil blending stock and biodiesel production [2].



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policies on renewable energy and their interplay with national en-ergy policies. So far, the Commission has indicated that biomasswill play an important role in the future. In that context, the biofueltrade seems to be a plausible scenario for Europe. It is likely thatnovel trade flows will appear and disappear as this new fuel mar-ket evolves [81].

European research and testing indicate that, when used as a die-

sel fuel substitute, biodiesel can replace petroleum diesel. Fig. 5shows the world biodiesel capacity between 1991 and 2010. Inthe EU, biodiesel is by far the biggest biofuel and represents 82%of the biofuel production.

Biodiesel has become more attractive recently because of itsenvironmental benefits. The cost of biodiesel, however, is the mainobstacle to commercialization of the product. Biodiesel reducescarbon dioxide, carbon monoxide, PAH and nitrated PAH emis-sions. The use of biodiesel decreases the solid-carbon fraction ofPM and reduces the sulfate fraction, while the soluble, or HC, frac-tion stays the same or increases. Emissions of nitrogen oxides in-crease with the concentration of biodiesel in the fuel. Somebiodiesel produces more nitrogen oxides than others, and someadditives have shown promise in moderating the increases. Ger-many produced 1.9 billion liters or more than half the world total.Other countries with significant biodiesel markets in 2005 in-cluded France, the United States, Italy and Brazil. All other coun-tries combined accounted for only 11% of world biodieselconsumption in 2005. In Germany biodiesel is also sold at a lower

price than fossil diesel fuel. Biodiesel is treated like any other vehi-cle fuel in the UK. In February 2006, the European Union set thegoal of fulfilling 5.75% of transportation-fuel needs with biofuelsin all member states by 2010. Many countries have adopted vari-ous policy initiatives. Specific legislation to promote and regulatethe use of biodiesel is in force in Germany, Italy, France, Austriaand Sweden [68]. By 2010, the United States is expected to become

the worlds largest single biodiesel market, accounting for roughly18% of world biodiesel consumption, followed by Germany. Newand large single markets for biodiesel are expected to emerge inChina, India and Brazil [83].

Demand for energy is increasing every day due to the rapidgrowth of population and urbanization. As the major conventionalenergy resources such as coal, petroleum and natural gas are at theverge of becoming extinct; biomass can be considered as one of thepromising environmentally friendly renewable energy options[13]. The biomass-intensive future energy-supply scenario in-cludes 385 million hectares of biomass-energy plantations globallyin 2050, with three quarters of this area established in developingcountries [84].

Based on a study conducted by the 9th National Plan of Malay-sia, the demand for fossil fuel is increasing continuously. In theterm of the 8th National plan of Malaysia, which ranged from2000 to 2005, the demand for energy in the commercial sector in-creased from 1244 PJ to 1632 PJ. The energy intensity increasedfrom 5.9 GJ in the year 2000 to 6.2 GJ in the year 2005. Petroleumis the main source of energy, and, as shown in Table 7a, the per-centage from other energy sources is very low (46%). The increas-ing demand for natural gas (79%) parallels the policy of fuel-source diversity. From Table 7b, it can also be observed that thetransportation sector is the primary energy consumer in Malaysia,accounting for 40.5% of the total energy demand in the commercialsector in the 2005. The industrial sector comprises 38% of the totaldemand while domestic and other sources account for about 13.1%.Based on these figures, Malaysia is predicted to become a net im-porter of fossil fuels by the year 2015. However, the introduction

of alternative fuels such as hydrogen, ethanol and biodiesel, willreduce the dependence on imported fuel sources. Malaysia is capa-ble of generating its own alternative fuels, as mentioned previ-ously, using domestic renewable resources [65]. The potentialfuture use of biodiesel in the transportation sector necessitates ashift in the current energy supply from petroleum products suchas gasoline and diesel, to biodiesel.

Fig. 5. World biodiesel capacity, 19912010 [82].

Table 7a

Final demand of commercial energy by source, 20002010 [65].

Source Petajoules Percentage of the total Average annual growth rate (%)

2000 2005 2010 2000 2005 2010 RMKe-8 RMKe-9

Petroleum products 820.0 1023.1 1372.9 65.9 62.7 61.9 4.5 6.1Natural gas 161.8 246.6 350.0 13.0 15.1 15.8 8.8 7.3Electricity 220.4 310.0 420.0 17.7 19.0 18.9 7.1 6.3Coal 41.5 52.0 75.0 3.4 3.2 3.4 4.6 7.6Total 1243.7 1631.7 2217.9 100.0 100.0 100.0 5.6 6.3

Table 7b

Final demand of commercial energy by sector, 20002010 [65].

Source Petajoules Percentage of the total Average annual growth rate (%)

2000 2005 2010 2000 2005 2010 RMKe-8 RMKe-9

Industrial 477.6 630.7 859.9 38.4 38.6 38.8 5.7 6.4Transportation 505.5 661.3 911.7 40.6 43.5 41.1 5.5 6.6Residential and commercial 162.0 213.0 284.9 13.0 13.1 12.8 5.6 6.0Agricultural 4.4 8.0 16.7 0.4 0.5 0.8 12.9 15.9

Total 1243.7 2217.9 1631.7 100.0 100.0 100.0 5.6 6.3



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The large-scale use of biomass energy in the EU would be facil-itated by a European market for biofuels. Regions rich in biomassresources could become net exporters of biofuels to regions withfewer opportunities for biofuel production, which would increasethe Unions total use of biomass energy. Inter-regional and interna-tional biofuel trade is also a likely consequence of the growing useof biomass energy. At the moment, there is a mounting interest in

the biofuel trade in Europe [81].Kartha and Larson [84] reported that various scenarios havebeen proposed in estimating the yields of biofuels from biomasssources in the future energy system. The availability of resourcesis an important factor in cogenerative use of biofuel in the electric-ity, heat or liquid-fuel market. There are currently two global bio-mass-based liquid transportation fuels that might replace gasolineand diesel fuel, bioethanol and biodiesel. Transport is one of themain energy-consuming sectors. It is assumed that biodiesel willbe used as a fossil diesel replacement and that bioethanol usedas a gasoline replacement. Biomass-based energy sources for heat,electricity and transportation fuels are potentially carbon dioxideneutral and recycle the same carbon atoms. Due to the widespreadavailability of biomass resources, opportunities for biomass-basedfuel technology will potentially employ more people than currentfossil-fuel based technology.

About 60% of current world ethanol production is from sugar-crop feedstocks. Ethanol is a well-established biofuel for transportand industry sectors in several countries, notably in Brazil. TheUnited States has used ethanol produced from maize (corn) in fuelblends since the 1980s. The United States ethanol production, withcorn as the primary feedstock, totaled 2821 million gallons in 2003and is projected to increase to 4544 million gallons in 2025. In2004, 3.4 billion gallons of fuel ethanol were produced from over10% of the corn crop. Ethanol demand is expected to more thandouble in the next ten years. For the supply to be available to meetthis demand, new technologies must be moved from the laboratoryto commercial reality [82].

4. Economic analysis

One of the main limiting factors for the market diffusion of bio-diesel is the high economic cost of production compared to petro-leum diesel oil. Currently, the cost of biodiesel is competitive onlywhen excise tax is not applied. Nevertheless, the promotion of bio-diesel is justified by the fact that the global emission of CO2 isgreatly reduced and that the net energy yield is positive. In addi-tion, the use of biodiesel involves an appreciable reduction of someemitted pollutants. This could be a key solution to reduce urbanpollution [69].

The major economic factor to consider for the input costs of bio-diesel production is the feedstock, which is about 80% of the total

operating cost. Other important costs are labor, methanol and cat-alyst. In some countries, filling stations sell biodiesel more cheaplythan conventional diesel. The cost of biodiesel fuels varies depend-ing on the base stock, geographic area, variability in crop produc-tion from season to season, the price of crude petroleum andother factors. Biodiesel has sold for over twice the price of petro-leum diesel. The high price of biodiesel is in large part due to thehigh price of the feedstock. Biodiesel is becoming of interest tocompanies for commercial-scale production as well as the moreusual home-brew biodiesel user and the user of straight vegeta-ble oil or waste vegetable oil in diesel engines. Biodiesel is com-mercially available in most oilseed-producing countries. Biodieselis a technologically feasible alternative to petroleum diesel, butcurrently biodiesel cost is 1.53 times higher than the fossil diesel

cost in developed countries. Biodiesel is more expensive thanpetroleum diesel, although it is still commonly produced in

relatively small quantities (in comparison to petroleum productsand ethanol). The competitiveness of biodiesel versus petroleumdiesel depends greatly on fuel-taxation approaches and levels.Generally, the production costs of biodiesel remain much higherthan for petroleum diesel. Therefore, biodiesel is not competitiveto petroleum diesel under current economic conditions. The com-petitiveness of biodiesel relies on the prices of biomass feedstockand costs as well as the conversion technology [63].

The price of the feedstock will become a more important factoras it represents 80% of the cost of biodiesel production. Even at cur-rent vegetable oil prices this is an advantage for palm oil whichtrades at a considerable discount compared to rapeseed oil and

soybean oil.Rabobank [85] estimates that the price of palm biodiesel in theEU if produced in Malaysia will be about US$784804/ton (Ta-ble 8). The estimated theoretical production cost for rapeseed bio-diesel is US$1035/tonne and US$840 for soybean biodiesel. Thesefigures are based on the average prices of each vegetable oil,including an approximately 20% cost of production, internationalfreight and domestic distribution charges. The reported consumerbiodiesel price in Germany, based on a three-month average upto January, was US$1332/ton. Palm biodiesel from Malaysia is stillcompetitively priced although this estimate does not consider anypotential excise nor import duty that could be imposed by the EUmember-states on palm methyl ester.

5. Conclusions

The term biofuel refers to liquid or gaseous fuels for the trans-port sector that are predominantly produced from biomass. Biofu-els including bioethanol, biomethanol, biodiesel and biohydrogenappear to be attractive options for the future transport sector. Bio-diesel is better than diesel fuel in terms of sulfur content, flashpoint, aromatic content and biodegradability.

Biodiesel, defined as the monoalkyl esters of fatty acids derivedfrom vegetable oil or animal fat, has demonstrated a number ofpromising characteristics in applications as an extender for com-bustion in compressionignition engines (CIEs), including a reduc-tion of exhaust emissions. Biodiesel is much less polluting thanpetroleum diesel, resulting in much lower emissions of almost

every pollutant: carbon dioxide, sulfur oxide, particulates, carbonmonoxide, air toxics and unburned hydrocarbons. Biodiesel does,

Table 8

Comparison of estimated costs for producing biodiesel from palm, rapeseed and

soybean oils.

Cost component (US$/ ton) Palm oilfromMalaysia

Rapeseedoil from theEU

Soybeanoil fromthe US

Feedstock (FOB at producing country) 547 800 601Biodiesel production cost:

Solvents, acids and chemicals 47 Other costs 35 Adjustment for energy parity with

petroleum diesel (based on 90%of kJ/kg of energy of petroldiesel)

55

Total 137 196 150Cost of biodiesel 684 996 751Estimated freight and insurance cost

to Rotterdam70 50

Total cost in EU 754 996 801Local distribution (approximation) 3050 3050 3050Total cost at petrol kiosk in EU 784804 10291046 831851Price of retail biodiesel (Germany)a 1322

Assuming production plant with capacity > 100,000 ton/annum; other figures basedon pricing as of March 2007.

a FO Licht based on UFOP Marktinformation (three-month average retail pricesfrom November 2006 to January 2007).



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however, have nitrogen oxide emissions that are about 10 percenthigher than petroleum diesel. Blending biodiesel into petroleumdiesel can help reduce emissions. It is well known that transportis almost totally dependent on fossil fuels. Biodiesel is one of thefeasible alternatives. The biodiesel fuels have not been widely ac-cepted in the market because they are more expensive than petro-leum fuels. With recent increases in petroleum prices and

uncertainties concerning petroleum availability, there is renewedinterest in biodiesel fuels for diesel engines [37].

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