J. of Supercritical Fluids 76 (2013) 24 31

Contents lists available at SciVerse ScienceDirect

The Journal of Supercritical Fluids

jou rn al h om epa ge: www.elsev ier .com

Biodies ia tsuperc

S.M. GhoDepartment of

a r t i c l

Article history:Received 14 DReceived in reAccepted 27 Ja

Keywords:BiodieselTransestericaSupercritical mWaste vegetabOptimizationResponse surf

) wasion tel (SCMas perze thanol5.27%entaergy

1. Introdu

Biodiesel is an alternative fuel for diesel engines which is denedas a fuel comprised of mono alkyl ester of long chain fatty acids pro-duced by chemically reacting a vegetable oil or animal fat with analcohol such as methanol. It is a non-toxic, biodegradable, relativelyless inammalso essentexhaust em

Becausesoybean, anproductionwhile usingthan edibletion [5]. In athe environwaste oils [

Transestwith an alcestericatiosimilar to nterication catalyst. Trafaster and rprocess [7,8

CorresponE-mail add

ce Wor water, homogeneous alkaline catalysts processes leads to sideformation of soap and reduces the yield of biodiesel production.So homogeneous alkaline and acidic catalyst processes have com-plex and energy-consuming separation and purication steps. Inaddition, the recovery of glycerol is difcult due to the solubility of

0896-8446/$ http://dx.doi.oable fuel compared to the normal diesel. Biodiesel isially free of sulfur and aromatics that produces lowerissions than normal diesel [14].

of high cost of edible vegetable oils such as canola,d corn it seems that commercialization of biodiesel

from edible vegetable oil is not economically favorable, of WVO as the feedstock, which is much less expensive

vegetable oil, can reduce the costs of biodiesel produc-ddition, the conversion of WVO into fuel also eliminatesmental impacts caused by the harmful disposal of these6].erication or alcoholysis is the reaction of a fat or oilohol to form esters and glycerol. The purpose of trans-n reaction is to reduce the viscosity of oils to a valueormal diesel. The reaction is shown in Fig. 1. Transes-reaction can be performed with alkali, acid or enzymensesterication reaction with alkali and acid catalysts isequires lower costs as compared to the enzyme catalyst].

ding author. Tel.: +98 311 3915604; fax: +98 311 3912677.ress: ghoreshi@cc.iut.ac.ir (S.M. Ghoreishi).

excessive methanol and catalyst [9].Supercritical methanol (SCM) is a method of transesterica-

tion reaction without the presence of catalyst in the process. Inthis method the temperature and pressure of the reactants reachup to the critical temperature and pressure of alcohol (239 C and8.1 MPa for methanol). In these conditions the solubility parameterof alcohol is reduced to a value near to triglycerides which leadsto formation of a single phase solution [10]. In addition, absence ofcatalyst in the process, leads to simpler separation and puricationsteps of biodiesel [11].

SCM method has a drawback toward commercialization of theprocess with the high cost of apparatus due to the high temperatureand pressure. The addition of co-solvents, such as carbon diox-ide, propane and hexane can decrease the operating temperature,pressure and the amount of alcohol. Co-solvents with increasingthe miscibility of oil and alcohol aid the mixture of alcoholoil tobecome a single phase [1214]. The gaseous co-solvents such as CO2and propane, can be separated easily from the products by expan-sion and be recycled directly while the liquid co-solvents suchas n-hexane and tetrahyrdrofuran require additional separationsteps [15]. Carbon dioxide is non-toxic, nonammable, inexpen-sive, environmentally benign, has a low critical temperature of304.4 K and a moderate critical pressure of 73.9 bar. CO2 also is a

see front matter 2013 Elsevier B.V. All rights reserved.rg/10.1016/j.supu.2013.01.011el synthesis from waste vegetable oil vritical methanol

reishi , P. Moein Chemical Engineering, Isfahan University of Technology, Isfahan 84156-83111, Iran

e i n f o

ecember 2012vised form 26 January 2013nuary 2013

tionethanolle oil

ace methodology

a b s t r a c t

Response surface methodology (RSM(molar ratio of methanol to oil, reactproduction via supercritical methanorial and transesterication reaction wrotatable design was used to maximidetermined by RSM to be 33.8:1 (methfor the maximum predicted yield of 9successfully correlated to the experimthe frequency factor and activation en

ction Sin/ locate /supf lu

ransesterication reaction in

applied to analyze the effect of four independent variablesmperature, pressure and time) on the yield of the biodiesel) method. Waste vegetable oil (WVO) was used as raw mate-formed in a supercritical batch reactor. The central compositee yield of the biodiesel. The optimal values of variables were/oil molar ratio) 271.1 C, 23.1 MPa and 20.4 min reaction time

(g/g). Moreover, an irreversible rst order kinetic model wasl transesterication data with 3.37 (s1) and 31.71 (kJ/mol) as

of the process. 2013 Elsevier B.V. All rights reserved.

VO contains a high proportion of free fatty acids (FFAs)

S.M. Ghoreishi, P. Moein / J. of Supercritical Fluids 76 (2013) 24 31 25

Nomenclature

Ea activation energy (kJ/mol)k kinetic rate constant (1/S)k0 pre-exponential factor (mol/dm3 s)m mass (g)M molecular weight (g/mol)P pressure (MPa)r reaction rate (mol/dm3 s)R the universal gas constant (8.314 J/mol K)R2 condence levelT temperature (C)X1 methanol to oil molar ratioX2 reaction temperature (C)X3 CO2 pressure (MPa)X4 reaction time (min)[]

AbbreviaANOVA FAMERSM SCMWVO TG

Greek let0iiiij

Subscript0 exp

good solvenand essentiating condiin Table 1, tyield via SC

In this sWVO in susimultaneoeffect of foture, pressuinvestigatedware and s

Fig. 1. Transesterication reaction of triglycerides and alcohol.

for biodiesel (fatty acid methyl ester: FAME) yield as a functionof operating variables via response surface methodology (RSM).

erimental

ateri

ste vrant. rbonent.thyle (C1ethymethrd. n

Table 1Reported oper

Oil type

RapeseedHazelnut/coSunower Waste oil Castor/linseeSoybean Soybean Soybean SoybeanPalm

a N/R, not reconcentration (mol/dm3)

tionsanalysis of variancefatty acid methyl esterresponse surface methodologysupercritical methanolwaste vegetable oiltriglyceride

tersconstantlinear coefcient

2. Exp

2.1. M

Warestauand caco-solving mestearatand mN,N-distandaquadratic coefcientinteractive coefcient

sinitialexperimental value

t for the non-polar compounds, such as hydrocarbonsal oils [1619]. Table 1 shows a list of reported oper-tions for production of biodiesel using SCM. As shownhe co-solvent utilization can lead to the high biodieselM at moderate operating conditions.tudy, RSM optimization of biodiesel production frompercritical methanol and CO2 as the co-solvent andusly pressure enhancement factor was carried out. Theur variables, mole ratio of methanol to oil, tempera-re and time of the reaction on the biodiesel yield was. The experiments were designed with Minitab 16 soft-ubsequently an empirical correlation was developed

solvent.

2.2. Equipm

The scheestericatioco-solvent tor was maabout 8 cmrequired re

Filtered specied mthe silica oithrough thwas chargetor (5). The water and etor (7) was increased uto the reactbut also acof reactants

ating conditions for production of biodiesel via SCM.

T (C) P (MPa) MeOH/oil molar ratio Reaction time (min)

350 45 42:1 4 ttonseed 350 N/Ra 41:1 5

400 20 40:1 30 287 N/R 41:1 30

d 350 20 40:1 40 320 N/R 33:1 10 280 12.8 24:1 10 288 9.6 65.8:1 10 280 14.3 24:1 10 280 15 30:1 20

ported.als

egetable oil used in this study was supplied from a localMethanol (99.9%) was purchased from Sigma Aldrich

dioxide (Zamzam Co.) with 99% purity was used as The standards of methyl esters of fatty acids includ-

myristate (C14:0), methyl palmitate (C16:0), methyl8:0), methyl oleate (C18:1), methyl linoleate (C18:2)l linolenate (C18:3) were purchased from Supelco.ylanilin (99% purity, Merck) was used as an internal-Hexane (99% purity, Merck) was used as an analytical

ent and experimental procedure

matic diagram of batch-type reactor system for trans-n of WVO using supercritical methanol and CO2 asand pressure enhancer is shown in Fig. 2. Batch reac-de from SUS 316 tubing (3/8 in.) and had the volume of3. Silica oil bath was used for heating the reactor up toaction temperature.WVO and methanol were loaded into the reactor withole ratio. Then the batch reactor was submerged intol bath (6). In order to purify and liquefy, CO2 was passede lter (2) and condenser (3), respectively. Then, CO2d to the high pressure pump (4) and to the batch reac-cooling liquid in the condenser was mixture of 50% (v/v)thylene glycol. At this stage the back pressure regula-completely closed and pressure inside the reactor wasp to the prescribed value. In this study adding the CO2ants not only cause to increase in the reactor pressurets as a co-solvent. After the temperature and pressure

were reached to the set values and transesterication

Co-solvent/alcohol molar ratio Yield (%) Reference >95 [20] 95 [21] 97 [22] 99.6 [23] 100 [24] 95 [14]C3H8/MeOH = 0.05 98 [12]C3H8/MeOH = 0.05 99 [25]CO2/MeOH = 0.1 98 [14]Heptane/MeOH = 0.2 66 [11]

26 S.M. Ghoreishi, P. Moein / J. of Supercritical Fluids 76 (2013) 24 31

Fig. 2. A schematic diagram of experimental setup for transesterication of WVO in supercritical meth(5) batch reactor, (6) silica oil bath, (7) back pressure, (8) electrical heater and (9) ice-water bath.

reaction waulator was ice-water bCO2 can beheater (8) weffect for CO

For the sit was evapoto settle fo(biodiesel) and lower o

2.3. Analys

Fatty aciin Table 2.sured to be samples wegraph (GC) 60 m 0.25gen was usfrom 195 C220 C and to 230 C wof the injectively. N,N-methyl estearea peak. Tuct sample was calcula

yield(%) =t

2.4. Experim

In ordertaneously oexperimentlevels for e

Table 2Fatty acid com

Fatty acid

Myristic (C1Palmitic (C1Stearic (C18Oleic (C18:1Linoleic (C18Linolenic (C1Others

nd un

nden

ratio on temactionon tim

les an0 to 5essu

to 25n Tabs 31

and ownized

sev poin

atisti

condodiesles. Tsed a

+4

i=1iXi +

i=1

iiX2i +i=1

i=i+1

ijXiXj (2)

Y is the predicted response, 0 is a constant and i, ii and the linear, quadratic and interactive coefcients, respec-Xi and Xj indicate levels of the variables. In order to estimateefcients of the polynomial by least square tting method,b 16 software was used and validity of the model was inves-

by analysis of variance (ANOVA).s carried out in the selected time, back pressure reg-opened and reactor contents were discharged to theath (9) and cooled rapidly to terminate the reaction.

recycled and used again in the process. An electricalas used on the tubing to prevent the JouleThompson2.

eparation of unreacted methanol from collected sample,rated at 70 C for 60 min. The sample was then allowedr 60 min in order to separate glycerol from FAMEsby gravimetric precipitation. Upper layer is biodieselne is glycerol.

is

ds composition of the WVO was analyzed and indicated The FFA and water content of the WVO were mea-5.67% (w/w) and 0.2% (w/w), respectively. The collectedre analyzed for methyl esters content by gas chromato-equipped with a capillary column (SGE, SOLGEL-WAX,

mm 0.25 m) and ame ionization detector. Nitro-ed as the carrier gas. The temperature program began

and held for 13 min. Then it ramped with 10 C/min toheld for 5 min. Finally after increasing the temperatureith 10 C/min it remained for 10 min. The temperaturestor and detector were set at 250 C and 300 C, respec-dimethylanilin was used as an internal standard andrs content was calculated by calibration curve usinghe gas chromatogram of the methyl esters in the prod-is shown in Fig. 3. The yield of the biodiesel productionted by the following equation:

total weight of methyl estersotal weight of oil in the sample

100 (1)

ental design

to study the effect of various reaction variables simul-n the biodiesel yield, RSM was used to design thes. In this study, the effect of four variables with veach one, on the biodiesel yield was investigated. The

Table 3Coded a

Indepe

MolarReactiCO2 reReacti

variabfrom 1tion prfrom 5listed irequirepointsare shrandomformedcenter

2.5. St

A sedict bivariabexpres

Y = 0

whereij aretively. the coMinitatigatedposition of WVO used in this study.

wt.%

4:0) 0.656:0) 27.79:0) 4.57) 38.82:2) 24.928:3) 0.96

2.30

3. Results

3.1. Regres

The estiyield of biorespectivelof the interhave signition (condis 0.409 whanol: (1) CO2 tank, (2) lter, (3) condenser, (4) high pressure pump,

coded levels of variables for RSM central composite design.

t variable Symbol Coded levels

2 1 0 1 2of methanol to oil X1 10 20 30 40 50perature (C) X2 240 250 260 270 280

pressure (MPa) X3 10 15 20 25 30e (min) X4 5 10 15 20 25

d their ranges were: molar ratio of methanol to oil (X1)0, reaction temperature (X2) from 240 to 280, CO2 reac-re (X3) from 10 to 30 MPa and time of the reaction (X4)

min. The coded and uncoded independent variables arele 3. The central composite rotatable design (CCRD) that

experiments for four variables (16 factorial points, 8 star7 central points) and the obtained yields (responses)

in Table 4. The experiments were carried out in a order and in duplicate. But the central point was per-en times to consider reproducibility. The error value oft experiments was calculated and presented in Table 4.

cal analysis

-order polynomial regression model was used to pre-el yield (response) as a function of four independenthe general form of this quadratic polynomial can bes:

4 3 4and discussion

sion model and analysis of variance

mated regression coefcients of Eq. (2) and ANOVA fordiesel production in SCM are shown in Tables 5 and 6,y. Since the p-values of all the linear, quadratic and twoaction coefcients are less than 0.05, these coefcientscant inuence on biodiesel yield in SCM transesterica-ence level is 95%). The p-value of the lack-of-t analysisich is greater than 0.05. The determination coefcient of

S.M. Ghoreishi, P. Moein / J. of Supercritical Fluids 76 (2013) 24 31 27

Fig. 3. Gas chromatogram of methyl esters in the product sample.

regression is calculated to be 0.986, which indicates the quadraticpolynomial model can adequately describes the experimental data.

3.2. Effect of process variables

The surface and contour plots of the biodiesel yield versus inter-actions of two variables are presented in Figs. 47. In each graph,the two remaining variables are set constant at their center points.The interaction effect of alcohol to oil molar ratio and temperatureon the biodiesel yield is indicated in Fig. 4. Molar ratio of alcoholto oil from 10 to around 34 has a positive effect on the yield, butbeyond 34 has a negative effect. Higher alcohol to oil molar ratiosrather than stoichiometric value can increase contact area betweenalcohol and oil and so the reversible transesterication reactionshifts to forward and subsequently the yield of biodiesel increases.Two factors can reduce biodiesel yield in higher molar ratios. Oneof them is the reverse reaction between FAMEs and glycerol and

Table 4Central composite rotatable design and responses.

Runorder

Methanol/oilm

Temperature CO2 pressure Time Yield (%)

1 2a

34a

5 6a

7a

8 9

10 11 12 13 14a

15 16 17 1819 20 21 22 2324 25 26 27 28a

29 30a

31

a Seven reption + coefcie

decomposition of FAMEs, and another one is the reduction of criticaltemperature of reactant/product mixture by increasing the molarratio of alcohol to oil. As shown in Fig. 4 at high levels of methanol tooil molar ratio (>34:1) and temperature (>271 C), decomposition ofFAME and reduction of yield occur. By increasing the temperatureabove the reactant/product mixture critical temperature, decom-position of FAMEs decreases the yield of biodiesel [26]. The effectof temperature and time of the reaction is shown in Fig. 5. Theyield of the biodiesel increases with higher temperature up toaround 271 C, but in upper temperatures beyond 271 C a grad-ually reduction occurs in the biodiesel yield. The main reason forthis phenomenon is decomposition of unsaturated fatty acid alkylesters. Decomposition of FAMEs in high temperature and pressureis due to isomerization of carbon double bonds from cis-type intotrans-type that is naturally unstable fatty acids [27]. The reactiontime is a signicant variable that has a direct effect on the biodieselyield. FAMEs yield increases in longer reaction times due to theextent of transesterication reaction progress. The side degradation

Table 5Estimated reg

Co

891207

000200

00

10

0%, R lue < 0olar ratio X1 X2 X3 X4

1 1 1 1 77.160 0 0 0 87.681 1 1 1 76.430 0 0 0 89.841 1 1 1 87.920 0 0 0 90.260 0 0 0 90.611 1 1 1 96.320 2 0 0 90.261 1 1 1 92.800 0 2 0 85.021 1 1 1 68.531 1 1 1 89.630 0 0 0 89.132 0 0 0 88.270 0 0 2 91.641 1 1 1 90.630 0 2 0 86.122 0 0 0 83.321 1 1 1 80.91

Term

0X1X2X3X4X21X22X23X24X1X2X1X3X1X4X2X3X2X4X3X4

R2 = 98.6* p-Va1 1 1 1 68.850 0 0 2 63.141 1 1 1 83.741 1 1 1 92.931 1 1 1 72.371 1 1 1 93.971 1 1 1 78.660 0 0 0 88.431 1 1 1 92.110 0 0 0 87.490 2 0 0 82.36eated runs in center point for reproducibility (standard devia-nt of deviation = 0.468 0.014).

Table 6Analysis of var

Source

Regression Linear SquareInteraction Residual errLack-of-tPure error Totalression coefcients for biodiesel yield in coded units.

efcient SE coefcient t-Value p-Value Signicant*

.0629 0.5038 176.768 0.000 Yes

.5650 0.2721 5.751 0.000 Yes

.7425 0.2721 10.079 0.000 Yes

.7508 0.2721 2.759 0.014 Yes

.7775 0.2721 28.583 0.000 Yes

.7888 0.2493 3.164 0.006 Yes

.6601 0.2493 2.648 0.018 Yes

.8451 0.2493 3.390 0.004 Yes

.8901 0.2493 11.594 0.000 Yes

.3475 0.3333 1.043 0.313 No

.4975 0.3333 1.493 0.155 No

.8025 0.3333 2.408 0.028 Yes

.1225 0.3333 0.368 0.718 No

.1600 0.3333 3.481 0.003 Yes

.0200 0.3333 0.060 0.953 No Sq(pred) = 93.92%, R Sq(adj) = 97.37%..05: signicant; p-value > 0.05: insignicant.iance for biodiesel yield.

Degree offreedom

Sum ofsquares

Meansquare

f-Value p-Value

14 1997.18 142.66 80.28 0.0004 1704.57 426.14 239.81 0.0004 254.64 63.66 35.82 0.0006 37.97 6.33 3.56 0.020

or 16 28.43 1.7810 19.21 1.92 1.25 0.4096 9.22 1.54

30 2025.61

28 S.M. Ghoreishi, P. Moein / J. of Supercritical Fluids 76 (2013) 24 31

Fig. 4. The effects of methanol/oil molar ratio and reaction temperature on the biodiesel yield at CO2 pressure of 20 MPa, and reaction time of 15 min (a) response surfaceplot and (b) contour plot.

Fig. 5. The effects of reaction time and temperature on biodiesel yield at methanol/oil molar ratio of 30, and CO2 pressure of 20 MPa (a) response surface plot and (b) contourplot.

Fig. 6. The effects of methanol/oil molar ratio and reaction time on biodiesel yield at reaction temperature of 260 C, and CO2 pressure of 20 MPa (a) response surface plotand (b) contour plot.

S.M. Ghoreishi, P. Moein / J. of Supercritical Fluids 76 (2013) 24 31 29

Fig. 7. The eff olar r(b) contour plo

reactions anof reaction shows the ethe biodiesthan 20 MPbut for highstudy becauenhancer sigradually reing the precauses dilutent reduceratio of memethanol totent. On thelonger timeof methanotherefore yia positive emost nonpodissolved inof methanohydrophobimum condias: the molture and COreaction timoptimal con

4. Kinetic

In orderRSM data oreaction temThe molar rand 20 MPaterication

TG + 3MeO

Becausereaction wa

tratireactction

d[d

reac

] = k

calcunedexp

=1(X

X is c

[TG[TG

rderonce

molects of CO2 pressure and reaction temperature on biodiesel yield at methanol/oil mt.

d losses of unsaturated FAMEs appear in a higher leveltime that can reduce the biodiesel yield [28,29]. Fig. 6ffect of temperature and CO2 pressure on the yield ofel. It was reported that for the system pressures lowera, FAMEs content is affected signicantly by pressure,er pressures yield variation is negligible [2830]. In thisse of using CO2 as a co-solvent and system pressuremultaneously, for the pressures up to around 23 MPa, aduction in biodiesel yield was observed. With increas-ssure the amount of the co-solvent increases too andtion and obstruction of the reactants; so FAMEs con-s slightly [31]. Fig. 7 shows interaction between molarthanol to oil and reaction time. In the higher levels of

oil molar ratio, reverse reaction can reduce FAMEs con- other hand, side degradation reactions that occur in thes can reduce FAMEs content too. So in the higher levelsl to oil molar ratio and time, FAMEs decomposition andeld reduction occurs. The existing water in the WVO hasffect on the FAMEs yield in SCM transesterication. Thelar organic compounds such as hydrocarbons can be

the water at temperatures above 250 C. The mixturelwater in high temperatures has both hydrophilic andc properties that accelerate the reaction [32]. The opti-

concenSo the the rea

rTG =

The

d[TGdt

Forwas de

OF =nn

where

X = 1

In oeride cthat TGtions for this process obtained by RSM are indicatedar ratio of methanol to oil of 33.8, reaction tempera-2 pressure of 271.1 C and 23.1 MPa respectively ande of 20.4 min. The maximum yield of biodiesel in theditions was 95.27%.

of the reaction

to investigate transesterication reaction kinetics, thebtained from quadratic model (Eq. (1)) was used. Theperature was varied from 240 C to 280 C in 01200 s.

atio of methanol to oil and CO2 pressure were set at 30, respectively. The stoichiometric equation of transes-reaction with methanol is as follows:

HK1K2

3FAME + glycerol (3)

of high molar ratio of methanol to oil, the reverses ignored and it can be assumed that the methanol

rewritten a

X = [FAME3[TG]0

Eq. (4) wwith initialXkinetic. A cminimizati(k) in variouminations w

Table 7Reaction rate SCM.

Temperatur

240 250 260270280 atio of 30, and reaction time of 15 min (a) response surface plot and

on is approximately constant throughout the reaction.ion will be a pseudo rst-order reaction that the rate of

is a function of triglyceride only as indicated below:

TG]t

= k[TG] (4)

tion rate can be rewritten via Arrhenius equation as:

[TG] = k0 exp(Ea

RT

)[TG] (5)

lation of the reaction constant (k), an objective function as:

exp Xkinetic)2 (6)

onversion of triglyceride and is expressed as:

]]0

= 1 [TG]0 [FAME]/3[TG]0

= [FAME]3[TG]0

(7)

to calculate conversion without analyzing the triglyc-ntration in the product sample and considering the factecular weight is three times of its FAMEs, Eq. (7) can be

s:

] = mFAME/MFAME3mTG,0/MTG

= mFAME/3MFAMEmTG,0/MTG

mFAMEmTG,0

(8)

as solved by 4th-order RungeKutta numerical method condition: [TG] = [TG]0 at t = 0 and was used to calculateomputer program was developed and applied for theon of OF (Eq. (6)). The obtained reaction rate constants reaction temperatures and their coefcients of deter-ith comparison to RSM data are presented in Table 7.

constant in various temperatures for transesterication of WVO via

e (C) k (s1) R2

0.001934 0.99320.002326 0.99120.002715 0.99050.003057 0.98970.003297 0.9869

30 S.M. Ghoreishi, P. Moein / J. of Supercritical Fluids 76 (2013) 24 31

Fig. 8. Conve(methanol/oil 23.1 MPa and

-6.3

-6.2

-6.1

-6

-5.9

-5.8

-5.7

-5.6

0.0018

Ln

(k

)

Fig.

Fig. 8 showand kinetic tion energyobtained frinversed temkinetic mod

rTG = d[

d

Table 8reported pre-equation.

Oil type

Rapeseed

Soybean

Palm Groundnut P. Pinnata J. Curcas CastorLinseedWVO

Table 8 shows a list of reported pre-exponential factor (k0)and activation energy (Ea) for various operating conditions and oiltypes. The obtained values of pre-exponential factor and activationenergy (3.37 (s1) and 31.71 (kJ/mol), respectively) for this studyare in the raother feedsture sensitiFor instancues of k0 anand J. Curca

5. Conclus

The prodtigated. In level of opas a pressand oil and

biomentted on ir

to of frs for ercreratirsion of TG by RSM and kinetic model in optimum conditionsmolar ratio: 33.8, reaction temperature: 271.1 C, CO2 pressure:

R2 = 0.9898).

95.27%experipredicover, aappliedlation procesthe supmal opy = -3814 .2x + 1.216

R = 0.9814

0.00183 0.00186 0.00189 0.00192 0.00195

1/Tempe rature (1/K)

9. Arrhenius plot for transesterication of WVO via SCM.

s a comparison between the RSM predicted conversionmodel at the optimum operating conditions. The activa-

and pre-exponential value of Arrhenius equation wereom the plot of logarithm of the rate coefcient versusperature as shown in Fig. 9. So the general form of the

el for this study was determined as:

TG]t

= 3.37 exp(

31711.26RT

) [TG] (9)

exponential factor (k0) and activation energy (Ea) for Arrhenius

T (C) P (MPa) k0 Ea (kJ/mol) Reference

200270 712 0.30 38.48 [33]300487 19105 6.87E3 47.09210230 28 514.96 11.22 [30]240280 5.85E3 55.91200400 20 2.60 14.94 [34]

1.30 10.540.82 9.451.68 11.37

200350 20 0.54 35.00 [24]7.80E2 46.50

240280 20 3.37 31.71 This study

engineers f

Acknowled

The naogy (IUT) anacknowledg

References

[1] J.V. Gerpe86 (2005

[2] F. Ma, M.(1999) 1

[3] B. Nas, A. oil: an enPolicy 13

[4] L.C. Meheby transe10 (2006

[5] M.G. Kulbiodiesel290129

[6] Z. Utlu, ESources P

[7] P.R. Munoils and a(1996) 19

[8] M.P. DorcatalyzedEnergy an

[9] J.M. Marction, Ren

[10] K.T. Tan, Methanol iSupercrit

[11] K.T. Tan, co-solvenof Superc

[12] W.L. Cao,supercrit

[13] A. Demircium oxid

[14] H.W. Hansupercrit314831nge of these values for SCM in previous investigation fortocks [24,30,33,34]. According to Table 8, the tempera-vity of the rate constant of various oil types is different.e in the xed temperature range of 200400 C, the val-d Ea for various oil types of Palm, Groundnut, P. Pinnatas were reported to be different [34].

ion

uction of biodiesel in supercritical methanol was inves-this study CO2 was used as co-solvent to reduce theerating temperature and methanol/oil ratio and alsoure enhancer to upgrade the miscibility of alcohol

consequently FAMEs yield. RSM modeling predicteddiesel yield at the optimal operating conditions. Theal biodiesel yield of 94.67% was achieved at the RSMperating conditions which is very compatible. More-reversible rst-order kinetic model was successfullydescribe the transesterication process via the calcu-equency factor and activation energy. The developedbiodiesel synthesis from WVO via transesterication initical medium and the obtained data in regard to opti-ng conditions and kinetic model can be used by processor the design and scale up of the commercial process.

gements

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Biodiesel synthesis from waste vegetable oil via transesterification reaction in supercritical methanol1 Introduction2 Experimental2.1 Materials2.2 Equipment and experimental procedure2.3 Analysis2.4 Experimental design2.5 Statistical analysis

3 Results and discussion3.1 Regression model and analysis of variance3.2 Effect of process variables

4 Kinetic of the reaction5 ConclusionAcknowledgementsReferences