Biodiesel production from low cost and renewable feedstock

8/10/2019 Biodiesel production from low cost and renewable feedstock

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Cent. Eur. J. Eng.DOI: 10.2478/s13531-013-0102-0

Central European Journal of Engineering

Biodiesel production from low cost and renewablefeedstock

Research Article

Veera G. Gude 1, Georgene E. Grant 1 , Prafulla D. Patil 2 , Shuguang Deng 2

1 Civil & Environmental Engineering Department,Mississippi State University, Mississippi State, Mississippi 39762

2 Chemical Engineering Department, New Mexico State University,Las Cruces, New Mexico 88003

Received 21 February 2013; accepted 21 May 2013

Abstract: Sustainable biodiesel production should: a) utilize low cost renewable feedstock; b) utilize energy-efficient, non-conventionalheating and mixing techniques; c) increasenet energy benet of the process; and d) utilize renewablefeedstock/energy sources where possible. In this paper, we discuss the merits of biodiesel production followingthese criteria supported by the experimental results obtained from the process optimization studies. Waste cook-ing oil, non-edible (low-cost) oils (Jatropha curcas and Camelina Sativa) and algae were used as feedstock forbiodiesel process optimization. A comparison between conventional and non-conventional methods such as mi-crowaves and ultrasound was reported. Finally, net energy scenarios for different biodiesel feedstock options andalgae are presented.

Keywords: Biodiesel Sustainability Waste cooking oils Algae energy balance Non-conventional techniques Mi-crowaves and ultrasound

Versita sp. z o.o.

1. Introduction

The U.S. consumes over 50 billion gallons of diesel fuel peryear for transportation purposes [1] and about 65% of thesefuels are imported from foreign countries. In 2007, theU.S. Government Accountability Office reported the needto develop a strategy for addressing a peak and decline inoil production [2]. Declining oil production will cause oiland diesel prices to rise sharply creating a strong marketfor replacement fuels. Apart from this, increasing energyuse, climate change, and carbon dioxide ( CO 2) emissions

E-mail: [email protected]

from fossil fuels make switching to low-carbon fuels a highpriority [3]. Biodiesel is an alternative liquid fuel thatcan substantially replace conventional diesel and reduceexhaust pollution and engine maintenance costs. This re-newable fuel can be produced from different feedstock such

as soybeans, waste cooking oil, and algae. Although thebiodiesel production has exponentially increased at na-tional (USA) and global levels in recent years [4,5], cur-rent biodiesel technologies are not sustainable since theyrequire government subsidies to be protable for the pro-ducers and to be affordable by the public. This is mainlydue to: 1) high feedstock cost (up to 75-80% of the totalbiodiesel cost) [6, 7] and, 2) energy intensive process stepsinvolved in their production [8]. Most of the biodiesel inthe U.S. is currently made from soybeans, which will soon


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Biodiesel production from low cost and renewable feedstock

reach a resource limitation of arable land. Use of naturalresources for soybean biodiesel production has resultedin high food costs [9, 10] and deforestation increasing thenet C O 2 emissions to increase the arable land by remov-ing the existing forests. These situations have resultedin hot debates and were termed as "food vs. fuel" and"energy vs. environment" dilemmas [3, 11]. For example:converting rainforests, peatlands, savannas, or grasslandsto produce food crop-based biofuels in Brazil, SoutheastAsia, and the United States creates a "biofuel carbondebt" by releasing 17 to 420 times more C O 2 than theannual greenhouse gas (GHG) reductions that these bio-fuels would provide by displacing fossil fuels. In contrast,biofuels made from waste biomass or from biomass grownon degraded and abandoned agricultural lands plantedwith perennials incur little or no carbon debt and can of-fer immediate and sustained GHG advantages [3]. Also,another example: as fuel demand for corn increases and

soybean and wheat lands switch to corn, prices increaseby 40%, 20%, and 17% for corn, soybeans, and wheat, re-spectively. As more American croplands support ethanolor biodiesel production, U.S. agricultural exports declinesharply (compared to what they would otherwise be at thetime - corn by 62%, wheat by 31%, soybeans by 28%, porkby 18%, and chicken by 12%). All of this will result inincreased land use in other parts of the world to balancethe supplies [12]. For biodiesel to substitute conventionalgasoline as an alternative transportation fuel should ( i )have superior environmental benets ( ii ) be economicallycompetitive, (iii ) have meaningful supplies to meet energydemands, and (iv) have a positive net energy balance ra-tio (NER) [13,14]. Biofuels are a potential low-carbonenergy source, but whether biofuels offer carbon savingsdepends on how they are produced as explained earlier[3]. Figure 1 shows potential pathways for sustainablebiodiesel production. Utilizing low cost edible or non-edible feedstock such as waste cooking oils, jatropha curcas and camelina sativa oils can be an attractive alterna-tive to reduce overall biodiesel cost. Waste cooking oilsare often available at free of cost. They will need to bedisposed properly or they will pose environmental threat.Camelina Sativa, Jatropha curcas and other non-ediblecrops are known as low maintenance and low cost crops.

Few examples of non-edible oils are Jatropha oil, Karanjaor Pongamia oil, Neem oil, Jojoba oil, Cottonseed oil, Lin-seed oil, Mahua oil, Deccan hemp oil, Kusum oil, Orangeoil, and Rubber seed oil [15, 16]. Algae, on other hand,is very high oil yielding biodiesel feedstock. The objec-tive of this research is to study and optimize the biodieselproduction process from waste cooking oils, Jatropha Cur- cas and Camelina Sativa oils and compare the benetsof utilizing non-conventional techniques (microwaves and

ultrasonics). The research also attempts to provide anoverview of net energy scenarios for biodiesel productionoptions from different feedstock with a special emphasison algae as renewable feedstock.

Figure 1. Potential pathways for sustainable biodiesel production

2. Materials and methods2.1. Oils to biodiesel conversion (reactionscheme)

The carbon chains (triacylglycerides) in vegetable andother plant oils (including algae) are too long and tooviscous for good ow and combustion. They have to beconverted into low viscous fuels to serve as transporta-tion fuels. Transesterication is the most commonly usedmethod which involves addition of alcohol-catalyst mix-ture to convert the triglycerides into smaller hydrocarbonchains. Glycerol is formed as by-product which can beused in many chemical industries as raw material. Theend product of the oil conversion using methyl alcohol isfatty acid methyl ester (FAME) which is called "Biodiesel".Biodiesel fuels must meet stringent chemical, physical andquality requirements imposed by the US EPA as speciedin ASTM standard D6751.

2.2. Waste cooking, Jatropha Curcas andCamelina Sativa oils

Waste cooking oil was collected from local restaurants inLas Cruces, NM, and Starkville, MS, U.S.A. Cold-pressed

Camelina Sativa oil was obtained from Marx Foods Com-pany, New Jersey, U.S.A. Jatropha Curcas oil was ob-tained from Purandhar Agro & Biofuels (Pune, India).Potassium hydroxide akes, methanol (AR Grade), andchloroform were procured from Fisher Scientic. The fer-ric sulfate catalyst was obtained from MP Biomedical.Heterogeneous metal oxide catalyst (BaO) was purchasedfrom Alfa Aesar. To test the physio-chemical properties of oil, ethanol (95% v/v), hydrochloric acid and diethyl etherwere purchased from Fisher Scientic. A round-bottom


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V.G. Gude, G.E. Grant, P.D. Patil, S. Deng

ask with reux condenser arrangement was used as lab-oratory scale reactor for the experimental studies in thiswork, and a hot plate with magnetic stirrer was used forheating the mixture in the ask. For transesterication of oil, the mixture was stirred at the same agitation speed of 1000 rpm for all test runs. A domestic microwave unit (800W power) and Sonic dismembrator (Model 550 from FisherScientic, 500W and 20 kHz) were used for microwave andultrasonic based transesterication reactions. Jatropha Curcas and waste cooking oils conversion con-sists of two steps namely, acid esterication and alkalitransesterication. For a successful reaction, the wastecooking oils must be heated above 100 C for 1 hour toremove the water and other impurities. Its free fatty acid(FFA) content was determined by a standard titrimetrymethod. After the reaction, the mixture was allowed tosettle for eight hours in a separating funnel. The acidvalue of the pretreated oil from step 1 was determined.The pretreated oil having an acid value less than 2 0.25mg KOH/g was used for the main transesterication re-action.For Jatropha Curcas oil, in acid esterication, 25 mL of oil was poured into the ask and heated to about 45 C.Then 8 mL of methanol was added and stirred at low stir-ring speed for 10 minutes followed by 0.5% (v/v) of sulfuricacid. The reaction mixture was then poured into a sepa-rating funnel to remove excess alcohol, sulfuric acid andimpurities. The experimental set-up for alkali catalyzedtransesterication was the same as that used for the acidesterication. 0.45 g (2 %) of KOH was dissolved in 10 mL

of methanol and half of that was poured into the ask con-taining unheated mixture from acid esterication step andstirred for 10 minutes. After 10 minutes, the mixture washeated and stirred continuously to about 60 C, and thenthe remaining methoxide was added to it. The reactionwas continued for the next 2 hours.For Camelina Sativa oil, a single step alkali transester-ication was conducted with heterogeneous metal oxidecatalyst, BaO. The experimental plan involved ve levelsof methanol to oil ratio varying from 3:1 to 15: 1; velevels of catalyst concentration, 0.25, 0.5, 1, 1.5, 2 (%,w/w,oil); ve levels of reaction time, 0.5,1 ,1.5, 2 , 3 h; and ve

levels of reaction temperature varying from 40 to 130

C.

2.3. Dry Algae

The experimental protocol for single-step microwave-assisted extraction and transesterication process for dryalgal biomass is illustrated in Figure 2 . Wet algalbiomass was allowed to dry in a laboratory vacuum ovenat 50-60 C for 24 h. Dry algal powder was obtained bytreating the algal biomass with liquid Nitrogen and rup-

Figure 2. Algal biomass conversion scheme via microwave process

turing it in the laboratory grinder. Two grams of dry algaepowder were added to the premixed homogeneous solutionof methanol and KOH catalyst. The mixture was then sub- jected to the microwave irradiation with exiting power of 800W (power dissipation level of 50% = 400 W), under amatrix of conditions: reaction times of 3, 6, and 9 min; cat-alyst concentrations in the range 1-3 wt.% of dry biomass;and dry algae to methanol (wt./vol.) ratios of 1:9-1:15. Af-

ter the reaction was completed, the reactor contents weretransferred into a 50 mL round-bottom ask to removemethanol and volatile compounds at a reduced pressure ina rotary evaporator. The remaining products were takenin hexane-water mixture and then centrifuged (3200 rpm)for 5 min to induce biphasic layer. The upper organiclayer containing non-polar lipids was extracted and runthrough a short column of silica (Hyper SPE silica) (Fig-ure 2). Neutral components were eluted with the solvent.An internal standard, methyl heptadecanoate (C17:0) wasadded to the eluted neutral component-solvent solutionand analyzed by gas chromatography-mass spectroscopyGC-MS.The effect of the three factors and their interactions werestudied using response surface methodology. Based onexperience and economic feasibility, a three factorial sub-set design was employed. The following equation is ageneral linear model used in our analysis:

= 0 +3

=1

+3

=1

2 +2

=1

3

= 1

(1)

where 1 , 2 and 3 are the levels of the factors and is the predicted response if the process were to followthe model. The detailed statistical analysis of experiment

design is presented elsewhere [29].

3. Results and discussion

In this section, process parametric optimization studiesfor three different feed stocks [waste cooking, Jatropha Curcas (non-edible) and Camelina Sativa (edible) oils] arepresented. A comparison between three process heatingtechniques (conventional, microwave and ultrasonic) for


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waste cooking oil biodiesel conversion is also presented,followed by biodiesel production from algae, comparison of conventional and non-conventional heating methods andnet energy benet ratio discussion.

3.1. Use of low cost feedstock: waste cook-ing, Jatropha Curcas and Camelina Sativa oils

The main process parameters optimized in this study are:1) methanol to oil ratio; 2) catalyst concentration; 3) re-action temperature and 4) reaction time [18].

3.1.1. Methanol to oil ratio

Transesterication reaction was studied for four differentmolar ratios. The methanol to oil molar ratio was variedfor Jatropha Curcas oil and waste cooking oil within therange of 3:1 to 12:1. The maximum ester conversions for

Jatropha Curcas oil and waste cooking oil were found atthe methanol to oil molar ratio of 9:1. Figure 3a showsthe effect of methanol to oil molar ratio on the conversionof oil. The yield remains the same with further increasein the methanol to oil molar ratio. The excess methanol inthe ester layer can be removed by distillation. Therefore,the methanol to oil molar ratio was kept at 9:1 in the re-maining experiments with Jatropha Curcas oils. For wastecooking, and Camelina Sativa oils similar trend was ob-served. The yield of the process increased with increasein methanol to oil molar ratio up to 9:1.

3.1.2. Catalyst concentration

For Jatropha Curcas and waste cooking oils, acid esteri-cation was performed using sulfuric acid and ferric sulfateas catalysts respectively, followed by alkali transester-ication reaction using KOH as catalyst. The effect of alkali catalyst (KOH) was studied in the range of 0.3% to2.5% and 0.5% to 2% by weight for waste cooking oil and Jatropha Curcas oil, respectively. Figure 3b shows the in-uence of the amount of ferric sulfate on biodiesel yield forwaste cooking oil. The yield was quite low for small quan-tities of catalyst. The amount of catalyst required dependson the amount of free fatty acid content. In this study, thecatalyst concentration of ferric sulfate to waste cooking oil

was varied within a range of 0.5-2.5 %. Similarly, sulfuricacid catalyst amount was varied in the range of 0.3-2% for Jatropha Curcas oil. These percentages are based on thevolume of the oil used for the acid esterication reaction.The catalyst amount also affects the yield of the processas shown in Figure 3b. The acid-catalyst process attainedmaximum yield for jatropha oil at 0.5% catalyst concentra-tion. For Jatropha Curcas oil, it was observed that theyield started to decline when the catalyst concentrationwas increased above 0.5%. For Camelina Sativa oil, a het-

erogeneous catalyst (BaO) was employed. Biodiesel yieldincreased initially with increased BaO concentration (0.5-1%) and remained unchanged with further increase in thecatalyst concentration (>1%).

3.1.3. Reaction temperature

In order to study the reaction temperatures, some alkalitransesterication experiments were conducted at temper-atures close to the boiling point of methanol [19]. Asshown in Figure 3c, the reaction temperature effect onthe yield was studied in the temperature range of 40 to100 C for Jatropha Curcas oil at atmospheric pressure.The maximum yield was obtained at a temperature of 60 C for Jatropha Curcas oil. A decrease in yield was ob-served when the reaction temperatures were above 60 C.Although other researchers have achieved optimum yieldat temperatures above 60 C and 70 C while using renedlinseed oil and brassica carinata oil, respectively [20, 21].The reaction temperature for processing Jatropha Curcas soil should be maintained below 60 C because saponica-tion of glycerides by the alkali catalyst is much faster thanthe alcoholysis at temperatures above 60 C. For wastecooking oil, the reaction temperature was studied in therange of 60 to 120 C. The maximum biodiesel yield wasobtained at 100 C.

3.1.4. Reaction time

As shown in Figure 3d, the optimum reaction times weredetermined as 120, 120 and 180 minutes for Jatropha Cur- cas , waste cooking and Camelina Sativa oils respectively[18, 22, 23]. Camelina Sativa oil was transesteried us-ing heterogeneous metal oxide catalyst which generallyrequires longer reaction times [22]. However, heteroge-neous catalysts allow for successive recovery and recy-cling for many times without affecting the biodiesel yieldand quality.

3.1.5. Previous studies

For waste cooking oils, optimum reaction conditions of methanol to oil ratios of 4.8:1-9:1 were reported in theprevious studies with catalyst concentrations between 0.5-1% (wt.) and reaction temperatures in the range 48-120 C

(higher temperatures for pretreatment) and reaction timescommonly around 1 hour [47, 48]. For Jatropha Curcas oil,the optimum conditions are reported as 1.43% v/v H 2SO 4acid catalyst, 0.28 v/v methanol-to-oil ratio and 88-minreaction time at a reaction temperature of 60 C as com-pared to 0.16 v/v methanol-to-pretreated oil ratio and 24min of reaction time [49]. In another study, the acid valueof the oil was reduced from the initial 14 mg-KOH/g-oil tobelow 1.0 mg-KOH/g-oil in 2 h with 12 wt% methanol, 1wt% H 2SO 4 in oil at 70

C. The FFAs conversion of higher


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Figure 3. Process optimization for waste cooking, Jatropha Curcas and Camelina Sativa oils

than 97% at 90 C in 2 h using 4 wt% solid acid and amolar ratio of methanol to FFAs of 20:1 were reported[50]. In another study, the rst step was carried out with0.60 w/w methanol-to-oil ratio in the presence of 1% w/wH2SO4 as an acid catalyst in 1-h reaction at 50 C. Thesecond step used 0.24 w/w methanol to oil and 1.4% w/wNaOH to oil as alkaline catalyst to produce biodiesel at65 C. The nal yield of methyl esters was around 90%in 2 h [51]. For Camelina Sativa oils, 1.8 g KOH/33.5ml methanol (Method 1) or 2.5 g KOH/24 ml methanol(Method 2) was added to 120 g of oil with 1 h reactiontime at room temperature by Frohlich et al. [52].

3.2. Use of renewable feedstock

Algae Biodiesel feedstock can be separated into threegenerations. First generation feedstock such as corn andsoybeans cannot meet all the transportation fuel needsdue to limitations in production capacity. Additionally,food vs. fuel issues, requirement of intensive agriculturalinputs, land use, and freshwater use are some of the lim-itations for large scale production of the rst generationof biofuels. Second generation feedstocks, using cellulosein nonedible plant biomass, address some of the concernssuch as food vs. fuel. Though (ligno) cellulosic feed-

stocks do not use human food resources, they still requirearable land, freshwater, and some agricultural and nu-trient inputs for their production [24]. Algae and othermicroorganism (such as cyanobacteria) based feedstockare termed as third generation feedstock. Algae are anideal example of renewable feedstock since they are pro-duced in very short periods of time. Microalgae are verysmall aquatic plants that produce natural vegetable oilssuitable for biodiesel production. Algae have the poten-tial for yields 50-100 times greater than biodiesel fromsoybeans and other feedstock [25]. Algal cultivation canbe enhanced by the direct addition of waste CO 2 fromfossil-fueled power plants and other high carbon emittingfacilities thus recycling and reducing environmental CO 2emissions [1]. In addition, algal biodiesel is a carbon-neutral fuel, which means it assimilates about as muchC O 2 during algal growth as it releases upon fuel combus-tion.

3.3. Use of non-conventional technologies

3.3.1. Waste cooking oil-biodiesel conversion via conventional, microwave and ultrasonic methods

Three different heating methods to process waste cookingoil were tested. As observed in other studies., the conven-


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tional heating method takes the longest reaction time (105minutes). Microwaves reduce the reaction time signi-cantly to as low as 6 minutes. The reasons for enhancedreaction rates for non-conventional heating are comparedwith conventional heating and summarized in Table 1. Wehave also tested direct transesterication of waste cook-ing oils to biodiesel by using ultrasonic irradiation. Whendirect sonication was applied, we noticed that the reac-tion mixture temperature has increased without any ex-ternal heat addition. Similar effects were observed undermicrowave conditions as well. Reaction mixture tempera-tures as high as 85 C were recorded under 2 minutes of reaction time. This depends on the catalyst ratio and thereaction mixture volume [26].

Figure 4. Comparison of waste cooking oil conversion byconventional/non-conventional methods

As shown in Figure 4, increased reaction times result inincreased energy expenditures. As shown in Figure 4,conventional heating on a laboratory hot plate requires

about 3150 kJ of energy to perform transestericationwhile microwave and ultrasonic processes required 288and 60 kJ of energy. This shows that with appropriate re-actor design, non-conventional techniques have potentialto reduce the process energy requirements signicantly.Another observation made among these studies is that mi-crowave process provides high quality biodiesel productcompared to other two methods of biodiesel conversion.Convectional and ultrasonic based transesterication in-volves intense mixing of reaction mixture thus resulting

in increased separation times, and reduced product yieldand quality.

3.3.2. Algal biomass conversion via microwave process

Algae can be processed in both wet and dry forms [27,28]. Wet algal biomass conversion into biodiesel can beprocessed by exploiting the specic characteristics of wa-ter at supercritical conditions. Methanol can be used asa solvent to extract algal oils as well as to achieve trans-esteriction. Algae, in its dry form, can be processed vianon-conventional techniques (like microwaves and ultra-sonics shown in Figure 2). A response surface methodol-

Figure 5. Effect of algae to methanol ratio (wt./vol.), catalyst con-centration (wt.%), and reaction time (min) on the fatty acidmethyl ester (FAME) content using RSM in MW process.

ogy was used to optimize the dry algal biomass conversionunder microwave irradiation. The response contours forthe effect of different process parameters namely algae tomethanol (wt./vol.) ratio, catalyst concentration expressedas wt.% of dry algae, and reaction time (min) on the fattyacid methyl ester (FAME) contents were studied (Figure

5). The effect of methanol on the simultaneous extractionand transesterication reaction is signicant with increas-ing dry algae to methanol ratios up to 1:12 (wt./vol.). Inthis reaction, methanol acts both as a solvent for extrac-tion of the algal oils/lipids as well as the reactant fortransesterication of oils. Methanol is a good microwaveradiation absorption material (loss factor, tan = 0.659at 2.45 GHz) which absorbs most of the microwave ef-fect in its entire spectrum to produce localized superheat-ing in the reactants and assists the reaction to complete


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Table 1. Major advantages and disadvantages in different heating methods

Conventional heating Microwave heating Ultrasonic heatingThermal gradient Inverse thermal gradient Thermal gradient due to mixingConduction and Convection cur-rents

Molecular level hot spots Microbubble formation and col-lapse (compression and rarefactioncycles)

Longer processing times Very short and instant heating Relatively very short reactiontimes, not as quick as microwaves

No or low solvent savings No or low solvent reactions possi-ble

Solvent savings possible

Product quality and quantity canbe affected

Higher product quality and quan-tity possible

Same as conventional heating

Separation times are long Very short separation times Less than conventional heatingHigh energy consumption Moderate to low energy consump-

tionModerate to low energy consump-tion

Complex Process conguration Very simple process Moderate complexity

faster. However, higher volumes of methanol may also re-sult in excess loss of the solvent or aggravated rates of solvent recovery. In addition, excessive methanol amountsmay reduce the concentration of the catalyst in the re-actant mixture and retard the transesterication reaction[28]. Catalyst concentrations up to 2% (KOH, wt.%) showsa positive effect on the transesterication reaction. As thisis two-phase reaction mixture, the oil/lipid concentrationin the methanol phase is low at the start of the reactionleading to mass transfer limitations. As the reaction con-tinues, the concentration of oil/lipid in the methanol phaseincreases, leading to higher transesterication rates withincreased catalyst concentrations [29]. However, higherconcentrations of catalyst above 2% (wt.%) did not showany positive effect on the biodiesel conversion. This maybe due to the interaction of the other compounds resultingin byproducts. Other disadvantages of high basic catalystconcentrations, in general, are their corrosive nature andtendency to form soap which hinders the transesterica-tion reaction [30]. The reaction time has a signicant ef-fect on the FAME content. Generally, extended reactiontimes provide for enhanced exposure of microwaves to thereaction mixture which result in better yields of extractionand biodiesel conversion. Lower reaction times do notprovide sufficient interaction of the reactant mixture with

microwaves to penetrate and dissolve the oils into the re-action mixture. The main advantage of using microwaveaccelerated organic synthesis is the shorter reaction timedue to rate enhancement. The rate of reaction can bedescribed by the Arrhenius equation as: K = A G/RT ,where A is a pre-exponential factor, G is Gibbs freeenergy of activation. The rate of chemical reaction can beincreased through the pre-exponential factor A, which isthe molecular mobility that depends on the frequency of the vibrations of the molecules at the reaction interface

[31] or the pre-exponential factor can be altered by affect-ing the free energy of activation [32, 33]. A reaction timeof 5-6 minutes was found to be sufficient for this methodwith high FAME yields of >80%.Dry, unprocessed (raw) algal samples and residual ma-terial following microwave processing were collected andground into a powder for subsequent analysis by trans-mission electron microscopy (TEM). The dried-rehydrated,unprocessed algal powder contained particles composedalmost entirely of close-packed, roughly spherical algalcells, approximately 1-2 in diameter. Comparableviews of powder particles in thin sections of the residuefrom microwave processing contained intact, very closepacked cell proles with homogeneous and moderate elec-tron dense cytoplasmic contents but no large electron-dense inclusions comparable to the unprocessed algalsamples (Figure 6) suggesting that the lipis were forcedout of the biological matrix without disturbing the otherorganelle in the algae cells. GC chromatogram of algalbiodiesel analysis (Figure 7), shows a major proportion of mono and poly unsaturated fatty acid methyl esters. It wasobserved that the algal biodiesel contains olens, fattyalcohols, sterols and vitamins in minor quantities alongwith saturated and unsaturated FAMEs. The polyunsatu-rated fatty acids (PUFAs) methyl esters (Arachidonic acid;

C20:4, EPA; C20:5, DHA; C20:6) are typically found inNannochloropsis microalgae which differentiate microal-gal oils from most other vegetable oils [25].

3.4. Increase net energy benet ratio (NER)

3.4.1. Overall scenario

Energy is expended in various steps of biodiesel produc-tion including steps: 1) cultivation; 2) feedstock process-


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Table 2. Net energy ratios for different renewable fuel sources

Fuel Type NER ReferencePetroleum diesel 0.83 [35, 36]Corn ethanol 1.34 [37]1st Generation 1.98 (Only RME a) From oilseed rape,bio-diesel 3.45 (RME + meal + glycerin) UK [38]

1.84 (only bio-diesel) From soybean, USA3.2 (Biodiesel + meal) [35, 36]2.42 (Only PME b) From palm, THA3.58 (PME + meal + glycerol) [39]

Algal fuel 1.87c [40]1.50d(2.38e) [34]1.37d(1.82e) [34]

a Rapeseed methyl esterb Palm methyl esterc Lipid productivity=20 ton ha_1 year_1d The base casee Assuming low temperature (


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Table 3. Energy inputs and net energy ratios for algal biodiesel production [40, 41, 43, 44]

Energy required for each operation(GJ/ton)

Sturm&Lamer2011

Batan et al. 2010 Lardon etal.2009

Stephenson etal. 2010

Cultivation 9.7 0.8 5.7 7.2Flocculation 3.0 0.5Centrifugation 15.0 - 2.0Belt lter press 12.2 11.9 -Oil extractionElectricity - 21.8 3.9 0.3Heat - - 10.2 2.3Lipid conversionElectricity - 9.7 - 0.2Heat - - 0.9 1.6Net energy ratio * 0.66 0.88 2.04

* based on 28,800 kJ of energy per kg of algal biomass

3.5. Use of renewable energy sourcesUtilizing renewable energy sources may bring down theGHG emissions as their payback periods are very reason-able (less than 2 years) for both energy and emissions inmany cases [45, 46]. Moreover, the cost of these renew-able energy sources has become competitive with otherconventional fossil fuel based energy. A variety of renew-able energy sources such as solar collectors, geothermalwells and wind turbines can be used to provide for theenergy needs of biodiesel production. However, selectionand application of these resources can be site-specic andthe economics may vary in a wide scope as the economi-cal packages are different for each geographical locationaround the world.

4. Conclusions

This paper illustrated methods for sustainable biodieselproduction from various feedstocks. The optimiza-tion studies for waste cooking oil and jatropha curcas oils followed two-step (step 1-acid esterication andstep 2-alkali transesterication) process with catalystsF 2 (SO 4 )3 /H 2SO 4 (Step 1) and KOH (Step 2). For

waste cooking oils, the optimum conditions are methanolto oil ratios of 9:1, reaction temperature of 100 C, with2% F 2(SO 4 )3 for step 1, and those of 9:1, 100

C, 0.5%KOH for step 2 with biodiesel yield of 96% was deter-mined. For jatropha curcas oil, the optimum conditionsare methanol to oil ratios of 6:1 with 0.5% H 2SO 4 , reac-tion temperature of 40 5 C for step 1 and those of 9:1,2% KOH, 60 C for step 2 are determined. For camelina sativa oil, one-step alkali transesterication with 1% BaOheterogeneous catalyst with the following conditions: 9:1,

1%, 100

C, 180 min was found to be the optimum. For al-gae, reaction times of 5-6 minutes with 2% (wt) catalystand 1:12 algae to methanol (wt/vol) ratio were found tobe sufficient using microwave process with high FAMEyields of >80%. A comparison between the conventionaland non-conventional methods has shown that the reac-tion times, energy requirements can be dramatically re-duced in microwave and ultrasonic irradiated processes.Net energy benet ratios for biodiesel production fromdifferent feedstock suggest that the ratio can be improvedby considering the use of benecial bioproducts derivedfrom the processes.

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