Novel Approach for Liquid−Liquid Phase Equilibrium of Biodiesel (Canola and Sunflower) + Glycerol...

Novel Approach for Liquid−Liquid Phase Equilibrium of Biodiesel(Canola and Sunflower) + Glycerol + MethanolMaziar Hakim,† Hamed Abedini Najafabadi,† Gholamreza Pazuki,‡ and Manouchehr Vossoughi*,†,§

†Department of Chemical and Petroleum Engineering, Sharif University of Technology, Tehran 145888-9694, Iran‡Department of Chemical Engineering, Amirkabir University of Technology (Tehran Polytechnic), Tehran 15875-4413, Iran§Institute for Nanoscience and Nanotechnology, Sharif University of Technology, Tehran 145888-9694, Iran

ABSTRACT: In this study, a novel experimental approach was used to overcome the lack of phase equilibrium information toobtain data that is more applicable to industrial situations. Liquid−liquid equilibrium (LLE) data, tie-lines, and phase boundarieswere carried out for two systems of canola oil methyl esters (containing 1 wt % KOH) + glycerol + methanol and sunflower oilmethyl esters (containing 1 wt % KOH) + glycerol + methanol at three different temperatures (303.15, 313.15, and 323.15 K).The quality of data was also ascertained using Othmer−Tobias correlations. The experimental LLE data was also correlated bythe nonrandom two-liquid (NRTL) and the Wilson−NRF Gibbs free energy models. The energy interaction parameters of bothmodels were obtained for both systems. The results indicated that the Wilson−NRF provided an accurate correlation of LLEbehavior with average absolute deviation (AAD%) inferior to 8.78% and 10.80% for canola and sunflower biodiesel systems,respectively. However, the NRTL model presented a more accurate correlation of LLE behavior of both studied systems withAAD% inferior to 6.26% and 7.43% for canola and sunflower biodiesel systems, respectively.

1. INTRODUCTION

Crude oil is the biggest source of energy in today’s worldwhose galloping declining rate is everyone’s concern. Theconsumption of fossil fuels not only has increased greenhousegases but has decreased its resources as well.1 Consequently, inrecent years, the attention of many researchers has been drawnto biodiesel as a replacing source of energy. Biodiesel has quitea few advantages over petroleum-based fuels, of which the mostimportant ones are lower production of greenhouse gases,2 amore favorable combustion profile,3 easier storage as well astransportation,4 biodegradability, and nontoxicity.5

There are several different ways to produce biodiesel, amongwhich the transesterification reaction is the industrially usedapproach and the most preferable one. Through this process,vegetable oil or animal fat reacts with alcohol at an evaluatedtemperature, producing alkyl esters of fatty acids and glycerol.Due to the slow rate of the transesterification reaction, catalystssuch as alkaline catalysts are used to increase the rate andyield.6,7 The unsaturated fatty acid esters content of producedbiodiesel changes depending on the raw materials. For instance,methyl oleate and methyl linoleate are the main products ofsoybean oil.8 Experiments have shown that oleaginous seeds,soybean, sunflower, canola, and rapeseed seeds, have high oilcontent. Accordingly, they have gained much attentionrecently.9,10

The production of high quality biodiesel depends on thepurification process of transesterification products. Theseparation of these products is facilitated by the formation oftwo immiscible liquid phases. The heavier phase almostcontains glycerol; on the other hand, the lighter phase almostcontains biodiesel. The excess alcohol is distributed betweenthe two phases.11 As a consequence, many researchers havestudied different ternary systems (fatty acid methyl esters +glycerol + methanol) to understand the liquid−liquid

equilibrium (LLE). Negi et al.12 determined experimentaldata for the glycerol + methanol + methyl oleate and glycerol+ monoolein + methyl oleate ternary systems and evaluatedthe ability of two models, the UNIFAC and UNIFAC−Dortmund models, to predict the experimental data. Rostamiet al.13,14 studied phase behavior of four ternary mixtures(glycerol + methanol + palm, soya, sunflower, and canola oilbiodiesel) at three different temperatures (293.15, 303.15,and 313.15 K) and predicted the experimental data, usingthe UNIQUAC model. Felice et al.15 correlated the Wilsonactivity coefficient based on thermodynamic data availablein the literature including mixtures of two (biodiesel andglycerol), three (biodiesel, glycerol, and methanol), and four(biodiesel, glycerol, methanol, and water) components, with-out the addition of any empirical fitting parameter. Oliveiraet al.16,17 measured LLE data for the ternary system of canolaoil biodiesel + ethanol + glycerol, evaluated the performanceof commonly used excess Gibbs energy (gE) models, andshowed the capability of cubic-plus-association (CPA) EoSto predict the phase equilibrium used for the design andoptimization of biodiesel production plants. Mesquita et al.18

reported experimental LLE data for two systems of soybeanand sunflower oil biodiesel + ethanol + glycerol at twodifferent temperatures (293.15 and 323.15 K) and correlatedthe experimental data using the nonrandom two-liquid(NRTL) model. Machado et al.19 investigated the influenceof temperature and catalyst on a ternary LLE system ofcastor oil biodiesel, ethanol, and glycerol, as well as a qua-ternary LLE system that consisted of castor oil biodiesel,

Received: September 25, 2013Revised: November 22, 2013Accepted: November 26, 2013

Article

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ethanol, glycerol, and NaOH. Nevertheless, in all theseworks, pure components were mixed to evaluate the phaseequilibrium, making the situations different from real indus-trial conditions.In the present study, liquid−liquid phase equilibrium of

two pseudoquaternary systems of canola biodiesel (containing1 wt % KOH) + glycerol + methanol and sunflower biodiesel(containing 1 wt % KOH) + glycerol + methanol are studiedexperimentally at 303.15, 313.15, and 323.15 K. Data areobtained by experiments directly done on the two phase,resulting from the transesterification reaction, to simulate con-ditions closer to industrial production of biodiesel. Accordingly,in this study, the effect of the presence of KOH in both phasesis not neglected, and the experimental LLE data are obtained

under this circumstance. Furthermore, a modified version of theWilson model proposed by Pazuki et al.,20 so-called theWilson−NRF, and the NRTL models were used to correlatethese systems.

2. EXPERIMENTAL SECTIONMaterials. The chemicals used in this work included

glycerol (mass purity > 99% GC, Merck), methanol (masspurity > 99.5%, Merck), distilled water, canola refined oil(Mohsen Oil Company), sunflower refined oil (Mohsen OilCompany), and H3PO4 (99%, Merck). Biodiesel samples usedin the present study were produced in the laboratory via thetransesterification reaction of both oils, and KOH (99%,Merck) was used as the catalyst. To produce the samples, the

Table 1. Canola and Sunflower Oil Fatty Acid Methyl Esters Composition

canola biodiesel sunflower biodiesel

trivial name fatty acids composition (% mass) trivial name fatty acids composition (% mass)

myristic acid C14 0.00 myristic acid C14 0.00palmitic acid C16 4.27 palmitic acid C16 12.72palmitoleic acid C16:1 0.00 palmitoleic acid C16:1 0.40stearic acid C18 1.92 stearic acid C18 2.77oleic acid C18:1 68.43 oleic acid C18:1 29.69linoleic acid C18:2 24.08 linoleic acid C18:2 53.05linolenic acid C18:3 0.90 linolenic acid C18:3 1.14arachidic acid C20 0.00 arachidic acid C20 0.00

Others 0.40 Others 0.23

Figure 1. Phase diagram and liquid−liquid results for system containing canola oil biodiesel (containing 1 wt % KOH) + methanol + glycerol at303.15 K. Experimental (• and ), NRTL (▲ and •••), and Wilson−NRF (■ and ---) results.

Industrial & Engineering Chemistry Research Article

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international standard method of ISO 5501978 (E) for bio-diesel preparation was used.21

After production, The methyl ester content of producedbiodiesels was analyzed by gas chromatography (GC) using aVarian gas chromatograph system equipped with a flam ion-ization detector (Tdetector = 523.15 K), automated split injector(Tinjector = 513.15 K), and the split ratio considered as 100:1.The temperature program applied to the column was thefollowing: an initial temperature of 323.15 K was held for 1 minand then raised to 453 K at 15 K/min, 503.15 K at 7 K/min,and finally to 613.15 K at 30 K/min with a total analytical runtime equal to 20 min. The profiles of studied biodiesels arereported in Table 1.A 50 mg sample of biodiesel was mixed with 1 mL of a

standard solution of methyl heptadecanoate and n-hexane(5 mg/1 mL). The yield of biodiesel was determined by ana-lyzing 1 μL of the mixture by a GC test.Methods. 1. Saturation Curve of the Pseudoquaternary

System of Biodiesel (Containing 1 wt % KOH) + Methanol +Glycerol. The determination of phase boundaries for eachpseudoquaternary system was carried out at three differenttemperatures of 303.2, 313.2, and 323.2 K by a titration methodunder isothermal conditions. In this method, so-called“turbidimetric analysis”, for the biodiesel-rich phase, a mixtureof a certain amount of biodiesel containing 1 wt % KOH andmethanol was added to a flask that was immersed in a constant-temperature water bath with a temperature uncertainty of±0.2 K. The mixture was titrated by glycerol, while stirring with

a magnetic stirrer, until the mixture changed from transparentto turbid. This is, in fact, a transition point from a one-phaseregion into a two-phase region, which is considered the sat-uration point of glycerol in a biodiesel + methanol mixture.Similarly, in the case of the glycerol-rich phase, a mixture ofglycerol and methanol was titrated with biodiesel, containing1 wt % KOH, until the mixture turned cloudy. The cor-responding solubility curve was calculated on the basis of theamount of each component added. Uncertainties in the massfraction of each component were calculated to be less than10−3.

2. Tie-Line Determination of the TransesterificationReaction Products. For tie-line determination, a newprocedure was devised and applied to create conditions moresimilar to industrial ones. First, methyl ester biodiesel wasprepared by transesterification of canola and sunflower oil withmethanol in the presence of KOH as a catalyst. Throughthis step, oil and methanol reacted with a mole ratio of 1:6 at333.15 K for 60 min. A sample of the produced biodiesel waswashed three times with deionized water containing 1 wt %H3PO4. The biodiesel phase was collected and mixed withNa2SO4 to remove the remaining water. The mixture wascentrifuged, and the liquid phase was collected. The treatedbiodiesel sample was analyzed by gas chromatography (GC),and the results proved the nearly complete conversion of oil tomethyl esters (>99%) by the use of this molar ratio. Theobtained mixture of transesterification products was kept in anisothermal incubator at constant temperature for 24 h to



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provide an adequate time for complete separation into twophases. Samples were carefully taken from the biodiesel-richphase and the glycerol-rich phase using syringes. The sampleswere weighed and then kept in an oven at 348.15 K for 3 h toevaporate the whole methanol. According to the phase rule,at a fixed temperature and pressure, only one component canindependently change. Thus, the points, which represent thecomposition of each phase, were determined by measuring theamount of removed methanol with uncertainties less than 10−3

g and using the binodal curves obtained in the previous section.Later, since the higher content of methanol was proved by GCanalysis to result in the complete conversion of oil, the pro-cedure was repeated for a higher amount of methanol to obtainother tie-lines.Thermodynamic Section. In this study, to model the

experimental data of both canola and sunflower biodiesel sys-tems, two Gibbs free energy-based models are selected.First, the NRTL model22 was used due to its high accuracy

and applicability to strongly nonideal mixtures. The NRTLactivity coefficient is as follows:

∑γτ

ττ

=∑

∑+

∑−

∑

∑=

= = =

=

=

⎛⎝⎜⎜

⎞⎠⎟⎟

G x

G x

x G

G x

x G

G xln i

j ji ji j

l li l j

j ij

l lj lij

r r rj rj

l lj l

13

13

1

3

13

13

13

(1)

where γi and xi are the activity coefficient and molar fraction ofcomponent i. Gij and τij are calculated by eqs 2 and 3:

α τ= −G exp( )ij ji ij (2)

τ =Δg

RTijij

(3)

In above equations, Δgij is a Gibbs energy parametercharacteristic of the i−j interaction, and αji is related to thenonrandomness in the mixture, which is arbitrarily set to 0.3.Second, the Wilson−NRF model20 was used due to its

simplicity and high accuracy in correlating LLE systems. It ispointed out that the Wilson model cannot be used for liquid−liquid calculations, whereas the Wilson−NRF model has solvedthis problem. The Wilson−NRF model has been previouslyused for the correlation and prediction of amino acids andsimple peptides in aqueous solutions,20 polymer solutions,23

aqueous electrolyte solutions,24 and physical properties ofseveral biodiesels.25 The Wilson−NRF activity coefficient isdefined as follows:

∑ ∑

∑ ∑

γ = − − +∑

− −

= = =

= =

⎡⎣⎢⎢

⎤⎦⎥⎥

C x Hx H

x H

x x H H H

ln ln( ) 1

( ln ln )

ij

j jij

j ij

k k ki

jj

jk kj ij ji

1

3

1

3

13

1

3

1

3

(4)

where C is the coordinate number, which is set to be 10, and Hij

is calculated by following equation:



dx.doi.org/10.1021/ie4031902 | Ind. Eng. Chem. Res. XXXX, XXX, XXX−XXXD

= −Δ⎛

⎝⎜⎞⎠⎟H

h

CRTexpij

ij

(5)

where Δhij is the enthalpy energy parameter characteristic ofthe i−j interaction.The objective function described below was minimized to

obtain the energy interaction parameters of both models

∑ ∑= − + −= =

X X X XOF [( ) ( ) ]i

N

ji j i j i j i j

1 1

3

,I,calc

,I,exp 2

,II,calc

,II,exp 2

(6)

where Xi,j is the mass fraction of component j in each phase, Nis the number of experimental tie-lines, superscripts “I” and “II”stand for biodiesel-rich phase and glycerol-rich phase, andsuperscripts “calc” and “exp” stand for calculated and exper-imental results.The optimization procedure for each model consisted of two

different iterating steps. First, the Newton−Raphson methodwas applied to obtain the values of Xi,j

I,calc and Xi,jII,calc by the

simultaneous solution of eqs 7−11:

γ γ=x x x x x x x x( , , ) ( , , )1I

1I

1I

2I

3I

1II

1II

1II

2II

3II

(7)

γ γ=x x x x x x x x( , , ) ( , , )2I

2I

1I

2I

3I

2II

2II

1II

2II

3II

(8)

γ γ=x x x x x x x x( , , ) ( , , )3I

3I

1I

2I

3I

3II

3II

1II

2II

3II

(9)

= + −Z X B B X(1 )1 1I

1II

(10)

= + −Z X B B X(1 )2 2I

2II

(11)

where x1I , x2

I , and x3I are mole fractions of biodiesel, methanol,

and glycerol in biodiesel-rich phase (I), respectively, and x1II,

x2II, and x3

II are mole fractions of biodiesel, methanol, andglycerol in glycerol-rich phase (II), respectively. γi

I and γiII are

the activity coefficients of component i in the biodiesel-richand glycerol-rich phases. Z1 is the biodiesel mass fractionin the feed, and B is the biodiesel-rich phase mass ratio tototal mass.Second, a genetic algorithm (GA) was applied to minimize

the objective function and converge at the optimized energyinteraction parameters of both models.In our study, the parameter Δgi,j/R, which represents the

energy parameter characteristic of the interaction betweencomponents i and j, was considered as the adjustable parameterfor the NRTL model due to its independency on temperature.Similarly, the parameter Δhi,j/R, which represents the enthalpycharacteristic between components i and j, was considered asthe adjustable parameter for the Wilson−NRF model.

3. RESULT AND DISCUSSION

LLE data at T = (303.2, 313.2, and 323.2) K for system ofcanola oil biodiesel (containing 1 wt % KOH) + methanol +glycerol are shown in Figures 1−3, and for the sunflower oilbiodiesel (containing 1 wt % KOH) + methanol + glycerol dataare presented in Figures 4−6. These diagrams include biodieselcurves and experimental tie-lines as well as calculated tie-linesby the Wilson−NRF and the NRTL models. Experimental LLEresults for canola oil biodiesel and sunflower oil biodiesel arerespectively presented in Tables 2 and 3. In Figures 1−6 as well

Figure 4. Phase diagram and liquid−liquid results for system containing sunflower oil biodiesel (containing 1 wt % KOH) + methanol + glycerol at303.15 K. Experimental (• and ), NRTL (▲ and •••), and Wilson−NRF (■ and ---) results.


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as Tables 2 and 3, quaternary LLE data are represented aspseudoternary systems by calculating the weight fraction ofeach component without considering 1 wt % KOH. The exper-imental results showed good agreement with previouslypublished data on similar systems of methyl oleate + glycerol+ methanol,12 as well as canola and sunflower oil biodiesel +glycerol + methanol.14

As it is observed, biodiesel and glycerol are both completelysoluble in methanol; on the other hand, biodiesel and glycerolare partially miscible in one another. As the slope of tie-linescan present, the solubility of methanol in glycerol is higher thanmethanol solubility in biodiesel, which is due to the highersimilarity between methanol and glycerol than that of methanoland biodiesel.The methanol distribution was also studied by a calculation

of the solute distribution coefficient (K) given by eq 12.

=KXX

2I

2II

(12)

The resulted solute distributions for each biodiesel at allstudied temperatures are presented in Table 4. As it can beobserved, increasing the temperature leads to a small decreasein the K value. This behavior can be explained by an increase ofmethanol solubility in the glycerol-rich phase due to the tem-perature increase. K values data also show that the methanolpartitioning is different for canola and sunflower oil biodieselsystems. K values for the sunflower oil biodiesel system isslightly higher than those for the canola oil biodiesel system.

As it is shown, two main methyl esters of sunflower and canolaoil biodiesels were oleic and linoleic acid. Additionally, Linoleicacid contains two unsaturated bonds, whereas oleic acidcontains one that makes linoleic acid more polar than oleicacid. Consequently, due to the linoleic acid having a highercontent of sunflower oil biodiesel, methanol solubility in thebiodiesel-rich phase in the sunflower oil biodiesel system isslightly higher than that for the canola oil biodiesel system at afixed temperature.The quality of LLE data was proved by two factors. First, the

agreement of tie-lines with feed composition indicated slightmass loss and low experimental error. Second, LLE data wastested by the Othmer−Tobias26 equation, which is described aseq 13:

−=

−+

⎛⎝⎜

⎞⎠⎟

⎛⎝⎜

⎞⎠⎟

XX

aX

Xblog

1log

11I

1I OT

3II

3II OT

(13)

where aOT and bOT are angular and linear coefficients, respec-tively, X1

I is the mass fraction of biodiesel in biodiesel-richphase, and X3

II is the mass fraction of glycerol is glycerol-richphase.An example of the Othmer−Tobias plot of sunflower oil

biodiesel at 303.15 K is presented in Figure 7. The experimentalLLE data of both biodiesels show a good linear fit with theOthmer−Tobias equation, which indicates the consistency ofexperimental tie-lines and binodal. Moreover, the quality ofdata is also shown by R2 > 0.92 achieved for both biodiesels atall temperatures, as presented in Table 5.



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The NRTL and the Wilson−NRF models were used tocorrelate LLE data of both canola oil biodiesel and sunflower oilbiodiesel systems. As previously described, due to the negligibleamount of catalyst, both systems were considered as pseudoternarysystems consisting of biodiesel + methanol + glycerol. Figures 1−6also include the results of both models for each studied system.The NRTL model correlations are shown by blue dashed lines,and the Wilson−NRF modeling results are shown by red dottedlines. The obtained energy interaction parameters of the NRTLmodel and the Wilson−NRF model are presented in Table 6.

The average absolute deviation (AAD%) of tie-lines was

calculated in accordance with eq 14 for both studied systems.

∑ ∑=−

+−

= =

⎛

⎝⎜⎜

⎞

⎠⎟⎟

N

X X

X

X X

X

AAD1

6 i

N

j

ij ij

ij

ijI

ij

ij

1 1

3 I,exp I,calc

I,exp

I,exp II,calc

II,exp(14)


Table 2. LLE Experimental Data for Canola Oil Biodiesel (1) + Methanol (2) + Glycerol (3) Obtained by New ExperimentalMethod

LLE data

feed biodiesel-rich phase glycerol-rich phase

temperature (K) Z1 Z2 Z3 X1 X2 X3 X1 X2 X3

303.15 0.8459 0.0662 0.0879 0.9624 0.0376 0.0000 0.0100 0.2890 0.70100.7843 0.1342 0.0815 0.9272 0.0728 0.0000 0.0000 0.4587 0.54130.7229 0.2020 0.0751 0.9022 0.0978 0.0000 0.0027 0.6055 0.39180.6554 0.2765 0.0681 0.8797 0.1203 0.0000 0.0150 0.7319 0.2531

313.15 0.8039 0.1126 0.0835 0.9417 0.0583 0.0000 0.0000 0.4158 0.58420.7552 0.1663 0.0785 0.9272 0.0728 0.0000 0.0000 0.5692 0.43080.6909 0.2373 0.0718 0.8940 0.1060 0.0000 0.0000 0.6718 0.32820.6015 0.3360 0.0625 0.8495 0.1505 0.0000 0.0315 0.7667 0.2018

323.15 0.7979 0.1192 0.0829 0.9394 0.0606 0.0000 0.0000 0.4713 0.52870.7528 0.1690 0.0782 0.9222 0.0778 0.0000 0.0000 0.5771 0.42290.6841 0.2448 0.0711 0.9006 0.0994 0.0000 0.0010 0.6799 0.31910.6284 0.3063 0.0653 0.8860 0.1140 0.0000 0.0265 0.7595 0.2140


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The calculated AAD% for each model is presented in Table 7.The Wilson−NRF model with AAD% inferior to 8.78% and10.80% correlated canola and sunflower biodiesel LLE systemswell. Nevertheless, the NRTL model presented a more accu-rate correlation of LLE behavior of both studied systems withAAD% inferior to 6.26% and 7.43% for canola and sunflowerbiodiesel systems, respectively.

4. CONCLUSIONNovel experimental measurements were carried out for the LLEbehavior of two systems consisting of canola oil methyl ester

Table 3. LLE experimental data for sunflower oil biodiesel (1) + methanol (2) + glycerol (3) obtained by new experimentalmethod

LLE data

feed biodiesel-rich phase glycerol-rich phase

temperature (K) Z1 Z2 Z3 X1 X2 X3 X1 X2 X3

303.15 0.8155 0.0998 0.0847 0.9404 0.0596 0.0000 0.0000 0.3760 0.62400.7778 0.1414 0.0808 0.9265 0.0735 0.0000 0.0000 0.4838 0.51620.7529 0.1689 0.0782 0.9115 0.0885 0.0000 0.0000 0.5400 0.46000.6035 0.3338 0.0627 0.8447 0.1553 0.0000 0.0184 0.7432 0.2384

313.15 0.8230 0.0915 0.0855 0.9385 0.0615 0.0000 0.0000 0.3200 0.68000.7750 0.1445 0.0805 0.9243 0.0757 0.0000 0.0000 0.4953 0.50470.6963 0.2313 0.0724 0.9057 0.0943 0.0000 0.0000 0.6838 0.31620.5981 0.3397 0.0622 0.8519 0.1481 0.0000 0.0303 0.7649 0.2048

323.15 0.7811 0.1377 0.0812 0.9302 0.0698 0.0000 0.0000 0.4952 0.50480.7083 0.2181 0.0736 0.9049 0.0951 0.0000 0.0000 0.6654 0.33460.6735 0.2565 0.0700 0.8884 0.1116 0.0000 0.0128 0.7039 0.28330.5820 0.3575 0.0605 0.8493 0.1507 0.0000 0.0484 0.7616 0.1900

Table 4. Solute Distribution Coefficient of Canola andSunflower Oil Biodiesel

distribution coefficient K

temperature (K) canola oil biodiesel sunflower oil biodiesel

303.15 0.1301 0.15850.1587 0.15190.1615 0.16390.1694 0.2090

313.15 0.1402 0.19220.1279 0.15280.1578 0.13790.1913 0.1936

323.15 0.1286 0.14090.1348 0.14290.1462 0.15850.1501 0.1979

Table 5. Othmer−Tobias Correlated Constants for Canola Oil Biodiesel and Sunflower Oil Biodiesel Systems

canola oil biodiesel sunflower oil biodiesel

temperature (K) aOT bOT R2 aOT bOT R2

303.15 0.6398 −1.1206 0.9438 0.0648 −1.0646 0.9963313.15 0.6340 −1.1375 0.9775 0.4376 −1.0675 0.9268323.15 0.4933 −1.1487 0.9688 0.5849 −1.1323 0.9894

Table 6. Obtained Energy Interaction Parameters of NRTL and Wilson−NRF Models

Wilson−NRF model NRTL model

parameters canola oil biodiesel sunflower oil biodiesel parameters canola oil biodiesel sunflower oil biodiesel

Δh12/R 1944.293 3802.296 Δg12/R −795.708 −798.833Δh13/R 3390.798 4851.177 Δg13/R 1884.381 2483.285Δh21/R 1737.542 1823.828 Δg21/R 2277.450 2345.375Δh23/R 4891.088 5887.057 Δg23/R 1219.732 1569.897Δh31/R 1391.600 3938.215 Δg31/R 2596.237 2456.78Δh32/R −480.242 −70.218 Δg32/R −879.097 −901.118

Figure 7. Othmer−Tobias plot of sunflower oil biodiesel at 303.15 K.


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biodiesel (containing 1 wt % KOH) + methanol + glycerol +KOH and sunflower oil methyl ester biodiesel (containing1 wt % KOH) + methanol + glycerol + KOH at 303.2, 313.2,and 323.2 K. Moreover, experimental tie-lines were determinedthrough a new experimental approach. The agreement of tie-lineswith feed composition and linearity of Othmer−Tobias plotsproved the reliability of experimental tie-lines obtained in this study.The experimental data was correlated using the NRTL and

the Wilson−NRF models. The energy interaction parameters ofboth models were obtained for each studied system. Despitethe fact that the corrolated results of both models proved suit-able for modeling such systems with AAD% inferior to 10.80%,the NRTL model provided a more precise correlation withAAD% inferior to 7.43%.

■ AUTHOR INFORMATIONCorresponding Author*M. Vossoughi. Tel: +98-021-66164104. E-mail: [email protected] authors declare no competing financial interest.

■ NOMENCLATUREa = angular coefficient in Othmer−Tobias equationAAD = average absolute deviationB = biodiesel-rich phase mass ratio to total massb = linear coefficient in Othmer−Tobias equationC = coordinate numberGij = parameter of the NRTL modelHij = parameter of the Wilson−NRF modelK = solute distribution coefficientN = number of experimental tie-linesOF = objective functionR = universal gas constantT = temperature (K)X = mass fractionx = mole fractionZ = mass fraction in feed

Greek Lettersγ = activity coefficientΔgij = interaction energy between i−j pair in the NRTLmodelΔhij = interaction energy between i−j pair in the Wilson−NRF modelτij = parameter of the NRTL modelαij = nonrandomness parameter in the NRTL model

Subscriptsi = tie-linej = componentOT = Othmer−Tobias

Superscriptscalc = calculatedexp = experimentalI = biodiesel-rich phaseII = glycerol-rich phase

■ REFERENCES(1) Subramaniam, R.; Dufreche, S.; Zappi, M.; Bajpai, R. Microbiallipids from renewable resources: production and characterization. J.Ind. Microbiol. Biotechnol. 2010, 37, 1271−1287.(2) Monyem, A. H.; van Gerpen, J. The effect of biodiesel oxidationon engine performance and emissions. Biomass Bioenergy 2001, 20,317−325.(3) Demirbas, A. Political, economic and environmental impacts ofbiofuels: A review. Appl. Energy 2009, 86, 108−117.(4) Kralova, I.; Sjoblom, J. Biofuels−Renewable Energy Sources: AReview. J. Dispersion Sci. Technol. 2010, 31, 409−425.(5) Gerpen, J. V. Biodiesel processing and production. Fuel Process.Technol. 2005, 86, 1097−1107.(6) Ma, F.; Hanna, M. A. Biodiesel production: a review. Bioresour.Technol. 1999, 70, 1−15.(7) Meher, L. C.; Vidya Sagar, D.; Naik, S. N. Technical aspects ofbiodiesel production by transesterificationa review. RenewableSustainable Energy Rev. 2006, 10, 248−268.(8) Abo El-Enin, S. A.; Attia, N. K.; El-Ibiari, N. N.; El-Diwani, G. I.;El-Khatib, K. M. In-situ transesterification of rapeseed and costindicators for biodiesel production. Renewable Sustainable Energy Rev.2013, 18, 471−477.(9) Basiron, Y. Palm oil production through sustainable plantations.Eur. J. Lipid Sci. Technol. 2007, 109, 289−295.(10) Barnwal, B. K.; Sharma, M. P. Prospects of biodiesel productionfrom vegetable oils in India. Renewable Sustainable Energy Rev. 2005, 9,363−378.(11) van Gerpen, J.; Shanks, B.; Pruszko, R.; Clements, D.; Knothe,G. Biodiesel production technology; Report NREL/SR-510-36244;National Renewable Energy Laboratory: Golden, CO, 2004.(12) Negi, D. S.; Sobotka, F.; Kimmel, T.; Wozny, G.; Schomacker,R. Liquid−Liquid Phase Equilibrium in Glycerol−Methanol−MethylOleate and Glycerol−Monoolein−Methyl Oleate Ternary Systems.Ind. Eng. Chem. Res. 2006, 45, 3693−3696.(13) Rostami, M.; Raeissi, S.; Mahmoudi, M.; Nowroozi, M. Liquid−Liquid Phase Equilibria of Systems of Palm and Soya Biodiesels:Experimental and Modeling. Ind. Eng. Chem. Res. 2012, 51, 8302−8307.(14) Rostami, M.; Raeissi, S.; Mahmoodi, M.; Nowroozi, M. Liquid−Liquid Equilibria in Biodiesel Production. J. Am. Oil Chem. Soc. 2013,90, 147−154.(15) Di Felice, R.; De Faveri, D.; De Andreis, P.; Ottonello, P.Component Distribution between Light and Heavy Phases in BiodieselProcesses. Ind. Eng. Chem. Res. 2008, 47, 7862−7867.(16) Oliveira, M. B.; Barbedo, S.; Soletti, J. I.; Carvalho, S. H. V.;Queimada, A. J.; Coutinho, J. A. P. Liquid−liquid equilibria for thecanola oil biodiesel + ethanol + glycerol system. Fuel 2011, 90, 2738−2745.(17) Oliveira, M. B.; Ribeiro, V. t.; Queimada, A. n. J.; Coutinho, J. o.A. P. Modeling Phase Equilibria Relevant to Biodiesel Production: AComparison of gE Models, Cubic EoS, EoS−gE and Association EoS.Ind. Eng. Chem. Res. 2011, 50, 2348−2358.(18) Mesquita, F. M. R.; Feitosa, F. X.; Sombra, N. E.; de Santiago-Aguiar, R. S.; de Sant’Ana, H. B. Liquid−Liquid Equilibrium forTernary Mixtures of Biodiesel (Soybean or Sunflower) + Glycerol +Ethanol at Different Temperatures. J. Chem. Eng. Data 2011, 56,4061−4067.

Table 7. Average Absolute Deviation of Calculated Data byNRTL and Wilson−NRF Models

calculated AAD%

canola biodiesel sunflower biodiesel

phasetemperature

(K) NRTLWilson−NRF NRTL

Wilson−NRF

biodiesel-rich 303.15 4.626 6.372 3.676 3.957313.15 6.601 14.105 11.966 15.687323.15 9.105 14.313 6.925 15.316

glycerol-rich 303.15 6.837 4.326 7.172 7.275313.15 4.240 6.952 9.110 11.609323.15 6.110 6.558 6.670 10.955

average 6.253 8.771 7.425 10.800


dx.doi.org/10.1021/ie4031902 | Ind. Eng. Chem. Res. XXXX, XXX, XXX−XXXI

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Novel Approach for Liquid−Liquid Phase Equilibrium of Biodiesel (Canola and Sunflower) + Glycerol...

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