inio

.

, Uerin

sed

27

used with a homogenous alkali catalyst. Acid catalysts canalso be used to facilitate reaction [7e16]. However, recent

studies, largely still at the laboratory stage, have exploredthe use of the enzyme lipase as a biological catalyst

that, currently, there are no industrial-scale processes for bio-diesel based on enzymatic esterification. An outcome of thisstudy is to identify the scientific and technical barriers to over-come for a biological route to be competitive with establishedinorganic routes.

* Corresponding author. Fax: 27 21 650 5501.E-mail address: kevin.harding@uct.ac.za (K.G. Harding).

Available online at www.sciencedirect.com

Journal of Cleaner Production 16Biodiesel is a generic term for alkyl esters of fatty acids,produced by esterification of vegetable oils with an alcohol(usually methanol, but also ethanol). It is blended with dieselfuel derived from crude oil to reduce the proportion of CO2 at-tributed to the fossil-fuel when the mixture is burnt. Biodieselcan also decrease other emissions characteristic of normal die-sel fuel, such as particulates and SOx. The advantages of bio-diesel combustion over petroleum diesel are well documented[1e6].

Both virgin and waste vegetable oils can be converted toform the renewable fuel biodiesel. Industrially, methanol is

[17e34]. Other methods of preparation have also been pro-posed. These include using supercritical fluids [35,36], orzeolites and metal catalysts [37e42]. The latter two processalternatives are not considered here.

The purpose of this study is to compare the environmentalimpacts of various flowsheets which could be proposed for theproduction of biodiesel at the industrial scale. These includethe use of alkali or enzyme catalysts, the use of alcohols meth-anol and ethanol in reaction and varied recovery levels of ex-cess alcohol (Table 1). An LCA based methodology such asISO 14040: 2006 is used [43]. It should be borne in mind1. IntroductionAbstract

Life cycle assessment (LCA) has been used to compare inorganic and biological catalysis for the production of biodiesel by transesterifica-tion. The inorganic route, using catalysis by sodium hydroxide, has been compared with a conceptual biological one using enzymatic catalysisby the lipase produced by Candida antarctica. Although biological catalysis has not been used for industrial production of biodiesel to date,results from laboratory experiments suggest that it could have distinct advantages over the inorganic route, particularly with regard to a simplifiedflowsheet for purification and concomitant energy savings. Five flowsheet options have been included in the study to investigate the alkali andenzyme catalysed production routes from rapeseed oil, use of methanol or ethanol for transesterification and the effect of efficiency of alcoholrecovery. The LCA shows that the enzymatic production route is environmentally more favourable. Improvements are seen in all impact cate-gories. Global warming, acidification, and photochemical oxidation are reduced by 5%. Certain toxicity levels have more than halved. Theseresults are mainly due to lower steam requirements for heating in the biological process. 2007 Elsevier Ltd. All rights reserved.

Keywords: Biodiesel; Life cycle assessment (LCA); Biological catalysts; Candida antarctica lipaseA life-cycle comparison betweenfor the product

K.G. Harding a,*, J.S. Dennis b, Ha Department of Chemical Engineering

b Department of Chemical Engine

Received 8 February 2007; received in revi

Available online0959-6526/$ - see front matter 2007 Elsevier Ltd. All rights reserved.doi:10.1016/j.jclepro.2007.07.003organic and biological catalysisn of biodiesel

von Blottnitz a, S.T.L. Harrison a

niversity of Cape Town, South Africag, University of Cambridge, UK

form 16 July 2007; accepted 30 July 2007

September 2007

(2007) 1368e1378www.elsevier.com/locate/jclepro

2. Biodiesel production process

2.1. Introduction

In order to determine the environmental impacts of biodie-sel production through life cycle assessment, process flow-sheets giving material and energy inputs and outputs arerequired. Simulation models for each process option havebeen developed using Aspen Plus. Flowsheets were devel-oped for each case, using NaOH for chemical catalysis andthe enzyme lipase from Candida antarctica for biologicalcatalysis.

The process flowsheets developed are continuous modelsconverting rapeseed oil (assumed to be pure triacylglycerole C57H104O6), via a transesterification reaction, to biodiesel(Eq. (1)). The alkali catalysed process is based on the ap-proach of Zhang et al. [15], including supportive and alterna-tive conditions described by others (Table 2).

2.2. Alkali catalysed process

As shown in Fig. 1, in the base case (case 1), methanol(stream 101) enters at a 6:1 molar ratio with respect to theoil (stream 105) (twice the stoichiometric requirement) allow-ing the equilibrium to be shifted towards biodiesel production(Fig. 1). The catalyst (NaOH) is present at a 0.01 mass fractionwith respect to oil. An assumption is made that dehydrogen-ated vegetable oil with less than 0.5 wt.% free fatty acid, an-hydrous alkali catalyst and anhydrous alcohol are used aswater and free fatty acids can lead to soap formation[44,45]. If waste cooking oils were used, a purification stepis needed before the reactor to ensure a low free fatty acidand water content.

The oil, catalyst and alcohol are fed (stream 102) into reac-tor R-101. The reactor is maintained at a temperature of 60 Cand a pressure of 4 bar. After a 2 h residence time, a 95% con-version of oil to biodiesel and a glycerol co-product is assumed.The reactor products (stream 106) are fed to a methanol recov-ery unit (distillation column, T-201) where 94% of the metha-nol is separated by distillation and recycled back to R-101.

Biodiesel from the transesterification reaction (stream 202)is separated from glycerol by counter current water washing(T-301). Zhang et al. [15] recommended 11 kg of wash waterper 1050 kg fresh oil feed and the use of a second unspecifiedpurification unit. The amount of water used was increased to260 kg to achieve separation in a single step. The majority

Table 1

Specifications of the different biodiesel production process flowsheets

investigated

Flowsheet 1 2 3 4 5

Catalyst Alkali Lipase Alkali Alkali Lipase

Alcohol used Methanol Methanol Methanol Ethanol Ethanol

Alcohol recovery (%) 94 e 50 94 e

La

Ra

sun

Alcohol used Methanol Methanol, Methanol Me

2-p

6:1

KO

me

O

O

O

iese

1369K.G. Harding et al. / Journal of Cleaner Production 16 (2007) 1368e1378Catalyst used NaOH NaOH or NaOCH3in THF

NaOHbutanol

Alcohol to oil ratio 6:1 6:1e30:1 6:1Table 2

Literature process conditions for transesterification of oils (alkali catalysts)

Karaosmanoglu

et al. [12]

Boocock

et al. [11]

Vicente et al.

[10,16]

Oil used Rapeseed Soybean Sunflower

OOC R 3CH2

OOC R 2CH

CH2 OOC R 1 R 1 CO

R 2 CO

R 3 CO

3 R'OH+Catalyst

Oil 3 (Biod3 (Alcohol)+Catalyst wt. fraction 0.016 0.002e0.01 0.013 0.0

Reactor temperature 65 C 20e60 C 20e65 C 25Reactor pressure 1 atm 1 atm 1 atm 1 a

Residence time 38e50 min 10e15 min 8 h 40

Oil conversion 97.4e99.7%

(50 min)

70e95% 100% 98

Methanol recovery w100%

Wash water (kg/kg oil) Inc

aci

Neutralising acid

THF e tetrahydrofuran.d or brine

H3PO4 HClludes tannic Includes H3PO4 0.01 0.26ng et al. [13] Antolin

et al. [14]

Zhang et al. [15] This study

peseed, linseed,

flower

Sunflower Waste cooking oil,

triacylglycerol

Triacylglycerol

(rapeseed oil)

thanol, ethanol,

ropanol, 1-butanol

Methanol Methanol Methanol, ethanol

9:1 6:1 6:1

H, sodium

thoxide

KOH NaOH NaOH

1e0.02 0.0028e0.0055 0.01 0.01

e110 C 60e70 C 60 C 60 Ctm 1 atm 4 bar 4 bar

mine3 h 2 h

% (1 h) 96% 95% (2 h) 95% (2 h)

94% 94%

50%

OHCH2

OHCH

CH2 OHR'

R'

R'

+

l) Glycerol+

The biodiesel and unconverted oil from the water washing

R-101

T-201 T-401

R-201T-501

T-301

X-302

OIL (WASTE)

WATER

ALCOHOLCATALYST

OIL

ACID

SALT

BIODIESEL

GLYCEROL

METHANOL (WASTE)

WATER (WASTE)304

101

103

101A 102

106

201

202

301

401

401A

401B401C

402 402A402B

105

105A

H2O

ACID

H2OA

302 501 501B

501C

502

306

305

tran

on);

1370 K.G. Harding et al. / Journal of Cleaner Production 16 (2007) 1368e1378of the glycerol and sodium hydroxide is taken out with the wa-ter stream (302), while the unreacted oil and biodiesel productremain in stream 301.

Sodium hydroxide in stream 302 is neutralised in a secondreactor (R-201). Zhang et al. [15] suggest phosphoric acid. Asthe thermodynamics of the resulting salt were unknown,hydrochloric acid (HCl) was chosen to replace it. Acid enters(acid stream) stoichiometrically so that all the alkali is treated.The products from the reactor (stream 304) were further puri-

Fig. 1. Biodiesel process flowsheet to be used in LCA e alkali catalyst. R-101:

counter current water washing; T-401: distillation column (biodiesel purificati

glycerol/salt); X-302: crystalliser (salt removal from glycerol).fied in distillation column T-501 to remove water (stream 501)which is split and recycled or discarded. The salt is removedby a crystalliser (X-302), leaving 105 kg of 85% purityglycerol (stream 305).

R-101

T-301

WATER

ALCOHOL

OIL

101 102

106

401C

402B105

105A

H2O

H2OA

302

50

Fig. 2. Biodiesel process flowsheet to be used in LCA e biological catalyst. R-101tillation column (biodiesel purification); T-501: distillation column (water removaunit (T-301) proceed to distillation column T-401 (stream 301)for separation. Oil is removed in the bottoms and recycled toreactor R-101 via stream 402B. A liquid/vapour mixture is ob-tained from the distillate of column containing 99.6 wt.% liq-uid biodiesel product (stream 401) and a vapour methanol(68%) stream (401A) which is split and recycled to reactorR-101 or discarded.sesterification reactor; T-201: distillation column (methanol recovery); T-301:

R-201: alkali neutralisation; T-501: distillation column (water removal from2.3. Biologically catalysed process

Using the flowsheet model for biodiesel production with analkali catalyst outlined above, relevant changes were made to

T-401

T-501

OIL (WASTE)

BIODIESEL

GLYCEROL

METHANOL (WASTE)

WATER (WASTE)

301

401

401A

401B

402 402A

501 501B

1C

502

: transesterification reactor; T-301: counter current water washing; T-401: dis-

l from glycerol/salt).

accommodate an enzyme catalyst (case 2). Where possible,features were kept unchanged to facilitate comparison throughlife cycle analysis. Lipase from C. antarctica (immobilized onpolyacrylate polymer beads as supplied by Novo Nordisk eNovozym 435) was used as the enzyme catalyst.

As with the alkali catalysis scenario, enzyme catalysis con-

s theains

Table 3

Process conditions for biodiesel production used to compare alkali catalysed and biocatalysed biodiesel production

Case 1 Case 2 Case 3 Case 4 Case 5

Oil used Triacylglycerol

(rapeseed oil)

Triacylglycerol

(rapeseed oil)

Triacylglycerol

(rapeseed oil)

Triacylglycerol

(rapeseed oil)

Triacylglycerol

(rapeseed oil)

Catalyst used NaOH Immobilized enzyme

from Candida antarcticaNaOH NaOH Immobilized enzyme

from Candida antarctica

Catalyst fraction 0.01 (molar) 0.04 (mass) 0.01 (molar) 0.01 (molar) 0.04 (mass)

Alcohol used Methanol Methanol Methanol Ethanol Ethanol

Alcohol to oil ratio 6:1 3:1 6:1 6:1 3:1

Alcohol recovery 94% (None required) 50% 94% (None required)

Oil conversion 95% 90% 95% 95% 90%

Reactor temperature 60 C 25 C 60 C 60 C 25 CReactor pressure 4 bar 1 bar 4 bar 4 bar 1 bar

Residence time 1.5 h 16 h 1.5 h 16 h

1371K.G. Harding et al. / Journal of Cleaner Production 16 (2007) 1368e1378sists of a continuous reactor feeding methanol (stream 101) andoil (stream 105) to reactor R-101 (Fig. 2). The enzyme loadingis kept at 4 wt.% (biomass and support) as recommended byShimada et al. [22]. Methanol is fed such that the concentrationis kept low. A concentration higher than half the stoichiometricamount will denature the catalyst [21,22]. Reaction is main-tained at 25 C and 1 bar with a residence time of 20 h.

Since 90% of the methanol reacts (no excess was added),there is little need for methanol recovery by distillation; henceunit T-201 is omitted. Also, since no alkali is present in thesystem, there is no need for neutralisation by acid and reactorR-201 and crystalliser X-302 are omitted.

Table 4

Mass and energy values obtained from flowsheets for each case to be used in

life cycle analysis

Case 1 Case 2 Case 3 Case 4 Case 5ProductsBiodiesel (kg) 1000 1000 1000 1000 1000

Glycerol (kg) 106 106 106 101 101

FeedRapeseed oil (kg) 991 991 991 947 947

Methanol (kg) 112 111 146 e e

Ethanol (kg) e e e 149.82 0.23

NaOH (kg) 10.4 e 10.4 10.0 eHCl (kg) 37.9 e 37.9 36.2 e

Steam (kg) 1820 1540 2060 1820 1490

Electricity (kWh) 8.6 34.1 12.4 9.9 35.4

Water (process) (kg) 29.8 56.4 28.8 30.6 55.9

Water (cooling) (tons) 117 97.4 132 114 92.6

Waste

Salt (kg) 15.2 e 15.2 14.5 eMethanol (kg) 2.9 2.4 36.1 e e

Ethanol (kg) e e e 0 0.23

Water (kg) 57.5 50.9 57.8 57.4 51.0be removed, forming a salt by-product that contaminateglycerol product. In contrast, the immobilized lipase rem2.4. Additional process flowsheets

Further process alternatives in this study include modifica-tion of the original alkali catalysed process (case 1) to allowfor a lower methanol recovery in T-201 (case 3). The alkalicatalysed (case 1) and biologically catalysed (case 2) pro-cesses have also been modeled using ethanol instead of meth-anol (cases 4 and 5, respectively) (Table 3). The mass andenergy balances obtained (Table 4) are then used for the lifecycle assessment (LCA) study.

3. Production alternatives

Even though conversion rates are generally slower in theenzyme catalysed route, interest in the process is justified bythe resultant simplifications and lower reaction temperatures.Advances in the technology have also resulted in a decreasein catalyst price which had been a previous concern [46].The lipase catalyst does not impose restrictions on the watercontent or level of free fatty acids in the oil, and is able toyield similar conversions to the alkali catalysed option. Thereis a high ester yield and no saponification reaction occurs [4].Chemical catalysts need to be neutralised before glycerol canTable 5

LCIA of biodiesel production (case 1) e CML 2 Baseline 2000 v2.1

Impact category Unit Characterisation Normalisation

Abiotic depletion kg Sbeq 16.0 9.98E14Global warming

(GWP100)

kg CO2 eq 4150 8.97E14

Ozone layer

depletion (ODP)

kg CFC-11eq 0.000827 7.24E16

Human toxicity kg 1,4-DBeq 145 2.41E15Fresh water

aquatic ecotoxicity

kg 1,4-DBeq 14.1 6.82E15

Marine aquatic ecotoxicity kg 1,4-DBeq 277,000 3.66E13Terrestrial ecotoxicity kg 1,4-DBeq 2.71 1.03E14Photochemical oxidation kg C2H2 1.45 1.35E14Acidification kg SO2 eq 30.2 9.65E14Eutrophication kg PO4

3eq 37.6 2.85E13

Values are for 1000 kg of biodiesel product.

in the reactor and does not contaminate reaction products;hence glycerol recovery and purification may be simplified.

Methanol is the most commonly used alcohol in the reac-tion because of its short chain length and low cost. Its use isa possible cause of environmental concern since it requirescrude oil in production, both for energy and as a raw material.Ethanol is renewable and has suggested advantages due to be-ing environmentally based and carbon dioxide neutral [47],making it the most promising alternative. In this study, ethanolis produced from sugar and includes the uptake of CO2 duringsugarcane growth. In alkali catalysed biodiesel production, al-cohol is added in excess to favour the transesterification reac-tion. Alcohol recovery is required to minimise alcohol waste.A high recovery requires a higher energy input for distillation.The relative advantage of minimizing the energy requirementthrough lowering the recovery requires assessment (compari-son of cases 1 and case 3). In the enzyme catalysed route, al-cohol recovery is eliminated completely since a high alcoholconcentration can inactivate the enzyme. Stepwise, stoichio-metric addition is required [21,22,26e28,48].

4. Life cycle assessment (LCA)

Comparison of the different routes of biodiesel productionwas done with the LCA software package SimaPro v6 (PRe

Fig. 3. Process contributions of biodiesel production (case 1) e single score

EPS 2000 v2.1.

Fig. 4. LCA results e chemical vs. biological catalysts (biodiesel production by aduction using lipase as a biocatalyst (case 2)).

1372 K.G. Harding et al. / Journal of Cleaner Production 16 (2007) 1368e1378lkali catalysis assuming 94% methanol recovery (case 1) is compared to pro-

Consultants B.V.), using the CML 2 Baseline 2000 v2.1 as-sessment method. The system was defined as cradle-to-gateproduction of 1000 kg of biodiesel, equivalent to a fuel witha calorific value of 27.1 GJ, or 33.3 MJ/l [49]. The LCA in-cluded all raw materials, agricultural inputs and biodiesel pro-cessing required for the final biodiesel product. The impacts ofprocess plant and equipment construction were not includedin the LCA results. The production includes the useful by-product glycerol which, due to process design and stoichiom-etry, is of equal purity and in equal proportion to biodiesel ineach process. Because of varying costs of glycerol as a func-tion of purity and its stoichiometric yield, burden allocationhas been based on mass ratios of useful end product. Theresults do not include impacts of the biological catalyst sincethe immobilized enzyme is re-used resulting in a very low re-quirement of environmentally benign protein, hence expecta-tions are that such an impact would be low.

5. Results

5.1. Alkali catalyst and methanol (case 1)

Using the CML 2 Baseline 2000 v2.1 method, for 1000 kgof biodiesel produced by alkali catalysis in the presence ofmethanol (case 1), 4150 kg carbon dioxide equivalent is re-leased into the atmosphere, while 30.2 kg SO2eq. and

37.6 kg PO43eq. are emitted. Using the world data set from

the CML method, normalized results show large impacts inmarine aquatic toxicity and, due to rapeseed farming impacts,eutrophication. Abiotic depletion, global warming and acidifi-cation also show significant impacts (Table 5).

The major contributing process in the biodiesel productionis the farming process, including fertilizer production. Furthercontributors include the energy requirements from natural gas,diesel and heat oil, as well as the impacts associated withsteam production. Impacts from methanol production arealso highly rated in the single score of the EPS 2000 impactassessment method (Fig. 3).

Because of the high energy contribution, milder processconditions are expected to improve LCA results as investi-gated in case 2. Reducing methanol recovery should also re-duce the energy needs (case 3). To further improve LCAresults, changing the alcohol used to ethanol allows compari-son with methanol from both the original alkali and enzymeprocesses (cases 1 and 2 for methanol and cases 4 and 5 forethanol).

5.2. Chemical vs. biological catalysts

When comparing biodiesel production (CML 2 Baseline2000 v2.1 method) using inorganic and biological catalystswith methanol as the transesterification alcohol (cases 1 and

1373K.G. Harding et al. / Journal of Cleaner Production 16 (2007) 1368e1378Fig. 5. LCA results e reduced methanol recovery (biodiesel production by alkali cassuming 50% methanol recovery (case 3)).atalysis assuming 94% methanol recovery (case 1) is compared to production

2), all LCA impacts were lower for the enzyme catalysed pro-cess. Fresh water aquatic toxicity was reduced by approxi-mately 12%, while marine aquatic toxicity and humantoxicity were also reduced by almost 10%. Terrestrial ecotox-icity was reduced by over 40% (mainly due to the removal ofhydrochloric acid from the biologically catalysed process).Ozone layer depletion was reduced by 6%, abiotic depletionand acidification by 4%. Reductions in other categories are be-low 5%, but favour biological catalysts in every case (Fig. 4).

5.3. Reduced methanol recovery

When methanol recovery in the alkali catalysed processwas lowered from 94 to 50% (case 1 vs. 3), impacts increasedin all categories. In order to maintain an equal amount of bio-diesel product, flow rates in the product recovery section in-crease when methanol recovery decreases. This results ingreater pumping requirements and higher loads in distillationcolumns. Reducing recovery also increases waste methanol re-leased and the methanol feed.

Reducing methanol recovery to 50% increased all recordedtoxicity levels by at least 20%. Abiotic depletion increased by12%, ozone layer depletion by 8% and global warming, pho-tochemical oxidation and acidification by 5%. The increase ineutrophication is not significant since it is attributed to thefarming component (Fig. 5).

5.4. Alternative alcohol (methanol vs. ethanol)

When methanol is replaced with ethanol (produced biolog-ically from sugarcane) (case 1 vs. 4 (Fig. 6), case 2 vs. 5(Fig. 7)), LCA results are mixed. Human and fresh wateraquatic toxicity and acidification were higher with ethanolthan when using methanol. The changes from methanol useto ethanol use are quantitatively similar in the alkali catalysedand enzymatic routes (Fig. 7). There is a large reduction inabiotic depletion (12.5%) and ozone layer depletion(27.3%), while improvements in photochemical oxidation(2%) and eutrophication (1.3%) are not significant. Despitewhat was expected, the reduction in greenhouse gases(1.4%) is not large when replacing methanol with ethanol,even with the biologically derived ethanol taking up CO2 dur-ing agricultural processes. There is a mixed result for toxicitywith an improvement in marine aquatic and terrestrial ecotox-icity only. Terrestrial ecotoxicity improves to such an extent incase 5 (biological catalyst and ethanol) that it shows a positiveimpact. Negative effects of ethanol use are seen in human tox-icity and fresh water aquatic toxicity. This is partly due to thesugar based-ethanol LCA module used in this study [50]which has an unusually high coal demand compared to othermodels. If directly discharged into water, stillage from sugar(which is not taken into account here) will further increasethe fresh water aquatic toxicity levels.

1374 K.G. Harding et al. / Journal of Cleaner Production 16 (2007) 1368e1378Fig. 6. LCA results e alternative alcohol (methanol vs. ethanol) using alkali cataly(case 1) is compared to production using ethanol at 94% recovery (case 4)).sis (biodiesel production by alkali catalysis assuming 94% methanol recovery

Fig. 8. LCA results for all flowsheeting options (CML 2 Baseline 2000 v2.1 method).

Fig. 7. LCA results e alternative alcohol (methanol vs. ethanol) using lipase biocatalysis (biodiesel production by lipase biocatalysis using methanol (case 2) is

compared to production by lipase biocatalysis and ethanol (case 5)).

1376 K.G. Harding et al. / Journal of Cleaner Production 16 (2007) 1368e13786. Conclusions

Enzyme catalysed biodiesel production has environmentaladvantages due to avoided use of chemical catalyst and neu-tralising acid. The lower pressures and temperatures obtained

Table 6

LCIA of biodiesel production e CML 2 Baseline 2000 v2.1

Impact category Unit Case 1

Abiotic depletion kg Sbeq 16.0

Global warming (GWP100) kg CO2 eq 4150

Ozone layer

depletion (ODP)

kg CFC-11eq 0.000827

Human Toxicity kg 1,4-DBeq 145

Fresh water

aquatic ecotoxicity

kg 1,4-DBeq 14.1

Marine aquatic ecotoxicity kg 1,4-DBeq 277,000

Terrestrial ecotoxicity kg 1,4-DBeq 2.71

Photochemical oxidation kg C2H2 1.45

Acidification kg SO2 eq 30.2

Eutrophication kg PO43eq 37.6

Fig. 9. Process contributions for all flowsheetihelp to give more favourable LCA results and all environmen-tal impacts considered are reduced (Fig. 8).

The major contributing processes to LCA impacts are sim-ilar in all five processes. Agricultural processes, steam produc-tion, natural gas and diesel are all rated highly on the EPS

Case 2 Case 3 Case 4 Case 5

15.4 18.0 14.0 13.4

4050 4370 4090 3990

0.000777 0.000895 0.000601 0.000555

134 184 162 153

12.4 17.3 42.1 40.6

252,000 352,000 169,000 147,000

1.72 3.58 0.669 0.3021.43 1.52 1.42 1.40

29.3 31.7 31.4 30.5

37.5 37.7 37.1 37.1

ng options e single score EPS 2000 v2.1.

1996;11(1):43e50.

ane[12] Karaosmanoglu F, Cigizoglu KB, Tuter M, Ertekin S. Investigation of the

refining step of biodiesel production. Energy Fuel 1996;10:890e5.[13] Lang X, Dalai AK, Bakhshi NN, Reaney MJ, Hertz PB. Preparation and

characterization of bio-diesels from various bio-oils. Bioresour Technol

2001;80:53e62.[14] Antoln G, Tinaut FV, Brice~no Y, Casta~no V, Perez C, Ramrez AI. Op-

timisation of biodiesel production by sunflower oil transesterification.

Bioresour Technol 2002;83:111e4.

[15] Zhang Y, Dube MA, McLean DD, Kates M. Review paper: biodiesel pro-

duction from waste cooking oil: 1. Process design and technological as-

sessment. Bioresour Technol 2003;89:1e16.

[16] Vicente G, Martnez M, Aracil J. Integrated biodiesel production: a com-

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[17] Mittelbach M. Lipase catalyzed alcoholysis of sunflower oil. J Am Oil

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Technol 1991;13:544e6.2000 v2.1 single score method. The methanol production im-pact is higher than the ethanol production impact and playsa large role in the overall LCA results in these scenarios (cases1, 2 and 3 and cases 4 and 5, respectively) (Fig. 9).

In the alkali catalysed process, lower alcohol recovery re-quires greater flows to give similar product yield and purity.This increases energy needs as well as pollutants and causesa less favourable production route when analysed using lifecycle assessment.

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A life-cycle comparison between inorganic and biological catalysis for the production of biodieselIntroductionBiodiesel production processIntroductionAlkali catalysed processBiologically catalysed processAdditional process flowsheets

Production alternativesLife cycle assessment (LCA)ResultsAlkali catalyst and methanol (case 1)Chemical vs. biological catalystsReduced methanol recoveryAlternative alcohol (methanol vs. ethanol)

ConclusionsReferences