Experimental Liquid− Liquid Equilibrium of (Lube Cut+ Furfural+ 2, 2

Ind. Eng. Chem. Res. 2009, 48, 9325–9330

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Experimental Liquid-Liquid Equilibrium of (Lube Cut + Furfural + 2,2,4-tri-Methyl Pentane) Ternary System from T ) 323.15-343.15 K and Simulation with NRTL S. M. Fakhr Hoseini, M. S. Hatamipour,* T. Tavakkoli, and A. Montahaee Chemical Engineering Department, UniVersity of Isfahan, Isfahan, Iran

The use of 2,2,4-tri methyl pentane as a cosolvent for extraction of aromatic hydrocarbons from lube cut is studied. Optimized values of extraction temperature and amount of 2,2,4-tri methyl pentane are determined. The liquid-liquid equilibrium between {lube oil + furfural + cosolvent} is examined with the NRTL equation. The binary interaction parameters for the NRTL model are obtained by minimization of an objective function. General binary interaction parameters are computed and reported for estimating the liquid-liquid equilibrium products between 323.15 and 343.15 K. Also, a generalized model is presented for calculation of the refractive index and specific gravity of lube-oil fractions. The calculated results are in good agreement with the results of the experiments. 1. Introduction Solvent extraction is an effective method for the reduction of the aromatic content of lube oil. For many years, several works have been focused on finding selective solvents for extraction of aromatics. Minimization of properties, such as aromatic content, pour point, and viscosity index, is the most important reason for selecting a good extraction solvent. Solvent + lube-oil cut is a complex system because of the high number of components in the system. In order to manufacture lubricating base stokes, it is required to remove aromatic hydrocarbons from the lube cut. A lubricating oil feed stoke has been prepared from a vacuum distillation unit.1 A good solvent is needed for extraction of aromatics from the lube oil. Basically, a good solvent must have high capacity (solvent power) and selectivity toward aromatic hydrocarbons. These properties vary with extraction temperature and solute composition.2 One single solvent cannot always have all properties required for the implementation in an optimized extraction process. Particularly if the solvent power of the solvent is too high, extraction is either impossible or is not very selective. By adding a cosolvent, i.e. a compound whose solvent power is low, a combination solvent is obtained whose solvent power and selectivity are better suited to the separation under consideration.2 Use of cosolvents in liquid-liquid extractions is a common method for increasing the selectivity of extraction and increasing the aromatic content of the extract. The lube cut is a complex mixture that has various complex components. Extraction of aromatic hydrocarbons from the lube cut is one of the most important subjects in separation processes. Aromatic hydrocarbons are the undesired components in the lubricating oil because of their high activity and low viscosity index. Furfural is used frequently for removal of these components from lube oil, because of its high selectivity toward aromatics.3 In the existing literature, data are hardly found on liquid-liquid equilibrium (LLE) with cosolvent, but for systems without cosolvent, there is a remarkable wealth of literature available.4-9 LLE data are required for design of extraction units. Obtaining a data bank for liquid-liquid equilibrium is an important tool * To whom correspondence should be addressed. Tel.: 0098-3117934047. Fax: 0098-311-7934031. E-mail: [email protected].

for researchers and design engineers. On the basis of the previous works, adding paraffinic hydrocarbon solvents as cosolvent in the mixture of {lube oil + furfural} can increase the purity of the raffinate.3,9 This increase can be explained as follows: Use of some hydrocarbons as cosolvents increases the quality of extraction through producing a {paraffinic hydrocarbon + cosolvent} solution. This solution has lower density, and the mixture reaches equilibrium at lower settling times. In other words, a {lube oil + solvents} system reaches a higher purity level at the same settling time.3 Researchers have proved that, in an extraction unit, prediction of liquid-liquid equilibrium products is of great importance.10-17 An equation is reliable when the binary interaction coefficients of equation could be obtained for the system in question. In this study, the liquid-liquid equilibrium in {lube oil + furfural + 2,2,4-tri methyl pentane} is investigated at three different temperatures, i.e. (323.15, 333.15, and 343.15 K) and three different ratios of cosolvent/feed. For this purpose, the

Figure 1. Schematic diagram of experimental setup. Table 1. Physical Properties of Lube-Oil Cut property

feed

SG 60/60 °F flash point (K) viscosity 311 K (c.St.) viscosity 355 K (c.St.) viscosity 372 K (c.St.) n aromatic (wt %) saturate (wt %)

0.929 531.5 400 29.07 16.03 1.505 25 75

10.1021/ie9003267 CCC: $40.75  2009 American Chemical Society Published on Web 09/29/2009

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Table 2. Experimental Conditions Used with a Constant Solvent/ Feed Ratio and Variable Temperature and Cosolvent/Feed Ratios run no.

lube Cut m3 × 106

furfural m3 × 106

2,2,4-tri-methyl pentane m3 × 106

T (K)

1 2 3 4 5 6 7 8 9 10 11 12

40 40 40 40 40 40 40 40 40 40 40 40

40 40 40 40 40 40 40 40 40 40 40 40

5.0 5.0 5.0 10.0 10.0 10.0 15.0 15.0 15.0 20.0 20.0 20.0

323.15 333.15 343.15 323.15 333.15 343.15 323.15 333.15 343.15 323.15 333.15 343.15 Figure 3. SG vs T50% in the raffinate.

Table 3. Raffinate Properties and Component Distribution for Different Runs of Table 2 run no. n (20 °C) 1 2 3 4 5 6 7 8 9 10 11 12

1.48764 1.48646 1.48735 1.48772 1.48295 1.48464 1.48785 1.48689 1.48794 1.48956 1.48937 1.48964

SG

Mw

wS

XA

XS

0.8701 0.8694 0.8711 0.8701 0.8687 0.8704 0.8716 0.8726 0.8714 0.8721 0.8715 0.8709

552 569 557 571 581 570 548 564 556 512 521 512

1.88 1.81 1.73 1.73 1.72 1.78 1.82 1.78 1.80 1.79 1.76 1.77

12.06 10.88 11.26 11.92 7.27 8.48 11.68 10.03 11.78 13.79 13.72 14.39

87.94 89.11 88.74 88.07 92.73 91.51 88.31 89.96 88.22 86.21 86.28 85.61

2,2,4-trifurfural methyl (wt %) pentane (wt %) 8.3 8.6 9.2 8.1 8.8 8.3 7.9 7.8 8.4 9.1 9.6 10.3

6.80 7.40 8.30 11.27 12.3 9.24 5.96 6.29 5.17 5.11 5.65 5.01

Table 4. Extract Properties and Component Distribution for Different Runs of Table 2

run n no. (20 °C) 1 2 3 4 5 6 7 8 9 10 11 12

1.55621 1.56451 1.57152 1.57562 1.58945 1.58629 1.58592 1.57911 1.56883 1.56878 1.56771 1.55756

SG

Mw

wS

XA

XS

0.9799 0.9899 1.0045 1.0098 1.0278 1.0245 1.0256 1.0165 1.0001 1.0012 0.9945 0.9814

487 479 491 451 448 454 467 469 465 478 492 481

3.95 4.11 3.89 4.95 5.64 5.24 5.11 5.68 4.98 4.56 4.21 3.89

39.73835 44.52206 45.62321 48.43047 55.67153 53.57197 52.47522 49.00476 45.02869 44.28766 45.79593 40.64416

60.26165 55.47794 54.37679 51.56953 44.32847 46.42803 47.52478 50.99524 54.97131 55.71234 54.20407 59.35584

Figure 4. n vs T50% in the extract.

2,2,4-trimethyl furfural pentane (wt %) (wt %) 67.4 69.6 71.4 77.6 80.1 78.2 78.1 77.1 74.6 72.5 69.5 66.2

1.25 1.18 0.95 0.57 0.32 0.48 0.51 0.56 0.76 0.88 0.96 1.12

effect of the addition of cosolvent and temperature difference are primarily studied, and then, the binary interaction parameters for this system are calculated. After calculating the binary interaction parameters, the accuracy of the predictions of the equation is tested with experimental and other reported data.

Figure 5. SG vs T50% in the extract.

For describing the liquid-liquid equilibrium, the NRTL (nonrandom two liquid) equation was used. This equation gives good results for strong nonideal mixtures.17 On the basis of the rmsd values, results are in good agreement with experimental values and those calculated using new binary interaction coefficients. Table 5. Values of Constants for Correlation between Pseudocomponent Properties and T50% pure raffinate property (P )

a × 10

SG n

0.14 0.256

a

Figure 2. n vs T50% in the raffinate.

a

P ) aT50% + b.

3

pure extract

b

a × 103

b

0.7622 1.2898

1.824 1.188

-0.3857 0.6677

Ind. Eng. Chem. Res., Vol. 48, No. 20, 2009 Table 6. Experimental and Calculated n and SG for the Raffinate Phase with Generalized Correlationa run no.

T50% (K)

experimental n

calculated n

experimental SG

calculated SG

1 2 3 4 5 6 7 8 9 10 11 12

768.25 763.55 766.35 770.75 753.35 757.75 772.05 765.25 772.55 777.25 775.55 777.45

1.48764 1.48646 1.48735 1.48772 1.48295 1.48464 1.48785 1.48689 1.48794 1.48956 1.48937 1.48964 average error %

1.486472 1.485269 1.485986 1.487112 1.482658 1.483784 1.487445 1.485704 1.487573 1.488776 1.488341 1.488827 -0.08387

0.8701 0.8694 0.8711 0.8701 0.8687 0.8704 0.8716 0.8726 0.8714 0.8721 0.8715 0.8709 average error %

0.869055 0.868124 0.870014 0.869125 0.867669 0.869405 0.870287 0.871162 0.870357 0.871015 0.870777 0.869923 -0.10823

a

T50% is the temperature when 50% of the sample was distilled.

Table 7. Experimental and Calculated n and SG for the Extract Phase with Generalized Correlationa run no.

T50% (K)

experimental n

calculated n

experimental SG

calculated SG

1 2 3 4 5 6 7 8 9 10 11 12

748.65 752.15 762.15 764.95 772.15 775.55 771.25 768.35 759.55 758.25 754.55 751.45

1.55621 1.56451 1.57152 1.57562 1.58945 1.58629 1.58592 1.57911 1.56883 1.56878 1.56771 1.55756 average error %

1.557096 1.561254 1.573134 1.576461 1.585014 1.589053 1.583945 1.580500 1.570045 1.568501 1.564105 1.560423 -0.01648

0.9799 0.9899 1.0045 1.0098 1.0278 1.0245 1.0256 1.0165 1.0001 1.0012 0.9945 0.9814 average error %

0.979838 0.986222 1.004462 1.009569 1.022702 1.028903 1.021060 1.015770 0.999719 0.997348 0.990599 0.984945 -0.12137

a

T50% is the temperature when 50% of the sample was distilled.

2. Material and Methods 2.1. Materials. Furfural and the lube-oil cut were provided by Sepahan Oil Refinery located at Isfahan, Iran. The physical properties of the lube-oil cut are shown in Table 1. In order to characterize the lube-oil cut, it was assumed that it consisted of two pseudocomponents named as follows: saturated and aromatic hydrocarbons. The aromatic pseudocomponent consists of cyclic nonsaturated hydrocarbons, and it must be removed from the lube-oil cut. The saturated pseudocomponent is a mixture of {saturated cyclic hydrocarbons + saturated linear hydrocarbons}. In other words, saturated combinations are hydrocarbons without free electrons. Furfural was distilled before use in order to remove the oxidation products formed due to its contact with air, and then, the distilled furfural was analyzed through gas chromatography. 2,2,4-triMethyl pentane with a purity of 99% was prepared from Merck agent in Iran. 2.2. Experimental Setup. The experimental setup used for the extracting process is illustrated in our previous work,3 and a schematic diagram of it is shown in Figure 1. For measuring the refractive index (n), an index instrument (GPR-11-37E) was used. Viscosity and density were measured according to ASTM D-704218 with an Anton Paar SVM3000 instrument. The molecular weight of each pseudocomponent was determined by using ASTM D-2504 that is described in our previous work.3 The amount of sulfur in samples was determined with a Perkin-Elmer Optima-5300 V analyzer. The uncertainty in measurement of viscosity was (0.01 Pa · s; density (0.0001 g · cm-3; sulfur mass fraction (1; and that of the refractive index was (0.0001. A Herzog vacuum distillation instrument HDV632 was used for determination of the mass percents of furfural and 2,2,4-tri-methyl pentane.

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On the basis of the measured values for refractive index (n), specific gravity (SG), and sulfur content, the values of aromatic, saturated content were determined via ASTM D-323819 the method which is explained in our previous work.3 2.3. Experimental Method. For extracting by furfural, different conditions are reported in the literature. Lucas et al.9 used 2 h for agitation at 280 rpm and 15 min for settling. Coto et al.4 used 1 h for agitation at 430 rpm and 1 h for settling. In this work, agitation was maintained at 450 rpm for 1 h, followed by settling for 1 h to achieve a good separation of two phases.3 Table 2 shows the experimental conditions. At the end of each run, furfural was removed from extract and raffinate phases by vacuum distillation. 3. Generalized Correlation As it was mentioned, the system could be specified by using its measured values of SG and n. Since the measurement of these properties is expensive and time-consuming, it should be useful if they could be determined by using a simpler and easy to measure parameter of the system. For this purpose, the experimental values of SG and n were plotted against T50% (temperature of the mixture when 50% of sample was distilled). It was found that these two properties for the extract and raffinate phases could be correlated by a linear relation with T50% (eq 1). P ) aT50% + b

(1)

The values of constants and the validity of correlation for extract and raffinate is discussed in section 5.2. 4. Calculation of Liquid-Liquid Equilibrium The NRTL equation gives good results for heavy petroleum mixtures.4,9 The NRTL equation for the activity coefficient is given by Poling et al.20 and Prausnitz et al.21 c

ln γi ) (

∑

c

xjτjiGji/

j)1

∑

c

xkGki) + (

k)1

k

ki

ji

j

ji

j)1 c

c

∑ x G )(τ

∑ [(x G /

-(

k)1

c

∑ x τ G )/ ∑ x G )) k kj

k)1

kj

k

ki

(2)

k)1

Gji ) exp(-Rijτij)

(3)

τij ) Rij + bij /Text

(4)

τij is temperature dependent (related to extraction temperature; Text) according to eq 4, for which the binary parameters aij and bij are defined as τii ) 0, aij * aji, bij * bji, and Rij ) Rji. Rij can be calculated from the following equation which is reported by Coto et al.4 Rij ) a′T50% + b′

(5)

a′ and b′ values have been reported in previous works.4 The NRTL model is used to correlate the experimental data by minimizing the following objective function15 by using the Nelder-Mead Simplex (direct search) method at each extraction temperature: RMSD )

∑ ∑ ((x

exp ij

i

2 1/2 - xcal ij ) /6M)

(6)

j

Where, “M” is the total number of tie lines in the extraction process, which consists of three tie lines at any temperature in this work. Obtained binary interaction parameters are examined

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Table 8. Experimental Values in the Raffinate and Extract Phases for 2,2,4-tri-Methyl Pentane Cosolvent raffinate phase

extract phase

run no.

T (K)

XA

XS

XF

Xi

XA

XS

XF

Xi

1 4 7 10 2 5 8 11 3 6 9 12

323.15 323.15 323.15 323.15 333.15 333.15 333.15 333.15 343.15 343.15 343.15 343.15

0.104777 0.099900 0.102668 0.120742 0.093872 0.060024 0.087950 0.119041 0.095806 0.072175 0.103697 0.124815

0.764033 0.737828 0.775603 0.754837 0.768197 0.765739 0.788551 0.748638 0.755257 0.778598 0.776817 0.742412

0.072110 0.067856 0.069383 0.079678 0.074138 0.072667 0.068367 0.083298 0.078298 0.070614 0.073963 0.089324

0.059079 0.094412 0.052345 0.447421 0.063793 0.101569 0.055132 0.049024 0.070638 0.078611 0.045522 0.043339

0.235626 0.271822 0.293798 0.255437 0.260698 0.308566 0.275834 0.268661 0.264712 0.299821 0.256778 0.242913

0.373180 0.289440 0.266081 0.321331 0.324850 0.245696 0.287038 0.317987 0.315502 0.259838 0.313476 0.354744

0.399644 0.435539 0.437265 0.418157 0.407541 0.443964 0.433975 0.407720 0.414273 0.437653 0.425411 0.395649

0.007412 0.003199 0.002855 0.005075 0.006909 0.001773 0.003152 0.005632 0.005512 0.002686 0.004333 00.006693

Table 9. Binary Interaction Parameters binary interaction parameter

aromatic (i) saturated (j)

aromatic (i) furfural (j)

saturated (i) furfural (j)

aromatic (i) 2,2,4-tri-methyl pentane (j)

saturated (i) 2,2,4-tri-methyl pentane (j)

furfural (i) 2,2,4-tri-methyl pentane (j)

aij aji bij bji aij

63.1 41.5 -0.3 1.8 0.21

-2.4 8062 0.0 -4.2 0.29

400.6 157.6 -0.3 0.9 0.28

159.9 29.7 2.5 1.2 0.22

8.9 -3765.5 3.1 9.3 0.0

-663.4 269.8 8.6 -0.2 0.28

Table 10. Experimental Values in the Raffinate and Extract Phases for n-Hexane Cosolvent raffinate phase

extract phase

run no.

T (K)

XA

XS

XF

Xi

XA

XS

XF

Xi

1 4 7 10 2 5 8 11 3 6 9 12

323.15 323.15 323.15 323.15 333.15 333.15 333.15 333.15 343.15 343.15 343.15 343.15

0.109073 0.096782 0.097445 0.109936 0.066684 0.041812 0.059944 0.075308 0.076136 0.075363 0.081117 0.085564

0.764213 0.736829 0.786807 0.763960 0.797184 0.787705 0.817623 0.792382 0.797990 0.762847 0.805408 0.787873

0.070824 0.070023 0.065435 0.050314 0.073076 0.071346 0.065824 0.083290 0.070804 0.068740 0.064716 0.081170

0.05589 0.096365 0.050314 0.045705 0.063056 0.099137 0.056609 0.049020 0.055070 0.093051 0.048759 0.045456

0.213738 0.208805 0.207728 0.201908 0.233494 0.229624 0.229345 0.228632 0.206305 0.212655 0.204711 0.203528

0.383549 0.348398 0.357155 0.378585 0.797184 0.787705 0.817623 0.792382 0.371095 0.355333 0.365560 0.392706

0.396034 0.439677 0.432179 0.414392 0.403207 0.441438 0.437483 0.403945 0.417461 0.429399 0.425508 0.396413

0.00663 0.003121 0.002938 0.005115 0.007310 0.001893 0.003077 0.005551 0.005139 0.002613 0.004221 00.007354

Table 11. Calculated Values in the Raffinate and Extract Phases for the n-Hexane System by Using Calculated Binary Interaction Parameters raffinate phase

extract phase

run no.

T (K)

XA

XS

XF

Xi

XA

XS

XF

Xi

rmsd

1 4 7 10 2 5 8 11 3 6 9 12

323.15 323.15 323.15 323.15 333.15 333.15 333.15 333.15 343.15 343.15 343.15 343.15

0.11085 0.111728 0.083643 0.076968 0.098360 0.070798 0.076566 0.082845 0.099033 0.054392 0.077758 0.087387

0.77667 0.776413 0.788070 0.759096 0.758839 0.826370 0.805615 0.792563 0.799632 0.796306 0.814987 0.804655

0.07197 0.071164 0.066502 0.051134 0.077585 0.075748 0.069885 0.084681 0.072312 0.070204 0.066094 0.082899

0.05680 0.097936 0.051134 0.046450 0.066947 0.985254 0.060102 0.049839 0.056243 0.095033 0.049798 0.046424

0.217222 0.205199 0.226681 0.207185 0.222209 0.228518 0.232450 0.219071 0.211114 0.235915 0.210699 0.207863

0.38980 0.384756 0.351900 0.362902 0.354077 0.368848 0.347944 0.373346 0.362977 0.351858 0.378999 0.401071

0.402489 0.446844 0.439224 0.421147 0.428085 0.468675 0.464476 0.410691 0.426353 0.438545 0.434571 0.404857

0.006738 0.003172 0.002986 0.005198 0.007761 0.002010 0.003267 0.005644 0.005248 0.002669 0.004311 0.007511

0.0163

0.0617

0.0213

5. Results and Discussion

On the basis of the experimental values for extract and raffinate phases, the aromatic and saturate content of each mixture are calculated based on ASTM standards. 5.1.1. Effect of Cosolvent/Feed Ratio. With regard to the results given in Tables 3 and 4, for raffinate, using 11.11% of the second solvent at 333.15 K (run 5 in Table 2) resulted in lower contents of aromatic than other cosolvent/feed ratios.

5.1. Experimental Results. Tables 3 and 4 indicate the properties of the raffinate and extract phases at different ratios of cosolvent/feed and different temperatures, respectively.

Increasing cosolvent above 11.11% decreases the yield of the extraction. This is due to the production of {cosolvent + aromatic hydrocarbons} solution as a result of the solubility of

with the rmsd function. A lower value of rmsd represents a higher confidence level for calculated values. According to eq 4, the values of τij and τji are temperature dependent variables. In this study, values of τij and τji were obtained for 323.15, 333.15, and 343.15 K.

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Figure 6. Pseudocomponent distributions in raffinate and extract phases at 323.15 K with n-hexane used as cosolvent: (9) saturated fraction in raffinate phase, (×) saturated fraction in extract phase, (2) aromatic fraction in extract phase, (() aromatic fraction in raffinate phase.

hydrocarbons can be obtained in the extract phase, which leads to a lower percentage of aromatics in the extract. Studies on extraction temperatures show that the highest amount of aromatic extraction is obtained at 333.15 K; therefore, this temperature is an optimum temperature for extraction. 5.2. Modeling Results. 5.2.1. Generalized Correlation Results. Several experiments are carried out for checking the accuracy of a generalized correlation. Results of n and SG can be correlated with a linear model. Figures 2-5 are in good agreement with the scattering of n and SG values and a linear model. On the basis of the n and SG scattering data vs T50%, a linear correlation is proposed for the extract and raffinate phases. The parameters of pseudocomponent properties are calculated at T50%. The constants of the generalized model are presented in Table 5. Pure extract and raffinate are the same two phases but without solvent. The results of calculations are shown in Tables 6 and 7. On the basis of the previous studies,4 n and SG have a linear dependency on T50% as shown in this work. For ensuring the accuracy of linear model, the following definition is used: average error % ) [(

Figure 7. Pseudocomponent distributions in raffinate and extract phases at 333.15 K with n-hexane used as cosolvent: (9) saturated fraction in raffinate phase, (×) saturated fraction in extract phase, (2) aromatic fraction in extract phase, (() aromatic fraction in raffinate phase.

Figure 8. Pseudocomponent distributions in raffinate and extract phases at 343.15 K with n-hexane used as cosolvent: (9) saturated fraction in raffinate phase, (×) saturated fraction in extract phase, (2) aromatic fraction in extract phase, (() aromatic fraction in raffinate phase.

aromatic hydrocarbons in 2,2,4-tri methyl pentane and its transfer to the raffinate phase. 5.1.2. Effect of the Extraction Temperature. Analyzing Tables 3 and 4, it was found that the effect of the ratio of the two solvents is higher than the effect of the temperature as shown in previous works.3,4,15 Tables 3 and 4 show that there is a great difference between the aromatic content of the extract and raffinate phases at 333.15 K as compared to other temperatures. This is because of the higher solubility of paraffinic and naphthenic hydrocarbons in furfural at higher temperatures.2 For this reason, a higher percentage of paraffinic and naphthenic

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∑ (P

exp

- Pcalc))/N] × 100

(7)

Where, “P” in eq 7 is the objective property for pure extract and raffinate phases, i.e. SG or n. The exp and calc subscripts represent experimental and calculated values, respectively. N is the total number of measured data which is 12 in this work. 5.2.2. Liquid-Liquid Equilibrium Results. The NRTL nonrandom parameter (Rij) was calculated by using constant binary parameters that obtained from the linear model proposed by Coto et al.4 for a similar system. In order to generalize the NRTL binary interaction parameters (aij and bij) for any temperature between 323.15 and 343.15 K, NRTL parameters were calculated through minimizing objective function (eq 6) from 323.15 to 343.15 K when 2,2,4-tri-methyl pentane was used. Experimental data for extract and raffinate phases are reported in Table 8. These data are obtained for the {lube cut + furfural + 2,2,4-tri-methyl pentane} system. By using the LLE data shown in Table 9, binary interaction parameters were calculated and are reported in Table 10. In order to examine the obtained binary interaction parameters, liquidliquid equilibrium data of {lube cut + furfural + n-hexane} are checked by these binary interaction parameters. Liquid-liquid equilibrium data for {lube cut + furfural + n-hexane} are reported by Fakhr-Hoseini et al.3 Calculated equilibrium data for extract and raffinate phases are shown in Table 11. These values are calculated by using the obtained binary interaction parameters reported in Table 9. Results show that the NRTL activity coefficient model could predict the liquid-liquid equilibrium between {lube cut + furfural + n-hexane} with good accuracy. Experimental and calculated values for {lube cut + furfural + n-hexane} were plotted in Figures 6-8. These figures show that calculated values were investigated with high accuracy. Results are congruent with this new system with obtained binary interaction parameters and show that the new binary interaction parameters could be used in the systems with similar cosolvent. 6. Conclusions • Equilibrium data for {lube cut + furfural + 2,2,4-tri-methyl pentane} and {lube cut + furfural + n-hexane} systems are reported for raffinate and extract phases.

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• Using 11.11% 2,2,4-tri-methyl pentane as a cosolvent could increase the yield of aromatic extraction at 333.15 K. • Refractive index (n) and specific gravity (SG) could be correlated to T50% with a linear function. The proposed linear function is significantly accurate for predicting n and SG values. • By minimizing the objective function, general binary interaction parameters could be calculated. Using these binary interaction parameters, the component distribution in raffinate and extract phases could be calculated with high accuracy. Acknowledgment The authors wish to acknowledge Sepahan Oil Refinery of Isfahan for providing the materials and test instruments; especially, our thanks go to Mr. Hakim-Davood for his kind assistance in carrying out the experiments as well as providing us with test methods in the laboratory. Nomenclature MW ) molecular weight n ) refractive index SG ) specific gravity T50% ) temperature when 50% of sample was distilled Text ) extraction temperature xexp ) experimental mass fractions xcal ) calculated mass fractions XA ) mass fraction of aromatic hydrocarbon XF ) mass fraction of furfural Xi ) mass fraction of 2,2,4-tri-methyl pentane XS ) mass fraction of saturated hydrocarbon wS ) weight percent of sulfur aij ) NRTL binary interaction parameter bij ) NRTL binary interaction parameter τij ) interaction parameter between pairs of molecules i and j Subscripts i ) designate the component type, like aromatic, saturate, furfural, and 2,2,4-tri-methyl pentane j ) designate the component type, like aromatic, saturate, furfural, and 2,2,4-tri-methyl pentane

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ReceiVed for reView February 26, 2009 ReVised manuscript receiVed September 2, 2009 Accepted September 14, 2009 IE9003267