Experimental Vapor–Liquid Equilibrium for the Quaternary Carbon

Article pubs.acs.org/jced

Experimental Vapor−Liquid Equilibrium for the Quaternary Carbon Dioxide + Ethanol + Thiophene + Pentane/Nonane Systems Verónica Serrano-Cocoletzi,† Luis A. Galicia-Luna,*,† and Octavio Elizalde-Solis‡ †

Laboratorio de Termodinámica, SEPI-ESIQIE, Instituto Politécnico Nacional, UPALM, Ed. Z, Secc. 6, 1ER piso, Lindavista, C.P. 07738, México, D.F., México ‡ Departamento de Ingeniería Química Petrolera, ESIQIE, Instituto Politécnico Nacional, UPALM, Edif. 8, 2° piso, Lindavista, C.P. 07738, México, D.F., México ABSTRACT: In this study, experimental vapor−liquid equilibrium (VLE) behavior for two quaternary carbon dioxide + ethanol + thiophene + (pentane or nonane) systems was measured by means of a static−analytic apparatus with online sampling. The VLE data was obtained at (∼334.2 and ∼363.8) K. Carbon dioxide + ethanol was used as a solvent + cosolvent mixture prepared in a solute-free basis of 0.033 mass fraction ethanol. The solute mixture, constituted by the sulfur compound + linear alkane, was used to determine the feasibility to extract the sulfur compound in the studied range. Standard uncertainties (u) for the measured properties are estimated to be p ± 0.02 MPa, T ± 0.04 K, and x1 ± 0.0028, y1 ± 0.0015 mole fraction for these last two values. According to the results, the vapor phase is enriched with pentane compared with the sulfur compound. On the other hand, high separation factors for thiophene over nonane are obtained at low pressures.

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INTRODUCTION

In the petroleum industry, information about the phase behavior of multicomponent mixtures containing hydrocarbons and other fluids is necessary for process design especially for enhanced oil recovery. The development of new thermodynamic models and algorithms to predict multiphase equilibria of complex mixtures depends on accurate experimental data which have to be measured with a suitable apparatus. Several papers about equilibrium data of binary carbon dioxide + hydrocarbon systems have been reported in the literature. Although the number of papers about the phase behavior for multicomponent mixtures has increased during the last few years, those containing carbon dioxide + multicomponent mixtures are scarce.1−5 This work constitutes part of a project focused on the study of the phase behavior of solute sulfur compound + alkane mixtures in carbon dioxide as a solvent.6,7 Information about the phase behavior of carbon dioxide + sulfur compound + hydrocarbon systems is scarce even with other compounds.8 Therefore, the vapor−liquid equilibrium (VLE) for the quaternary carbon dioxide + ethanol + thiophene + alkane systems was obtained at (∼334.2 and ∼363.8) K from (2.5 to 12.7) MPa. The good trend of equilibrium ratios demonstrates an internal consistency of the experimental data. The feasibility of separating the sulfur compound from model fuel systems was performed from binary mixtures of thiophene + pentane or nonane in the presence of carbon dioxide + ethanol as the solvent mixture. Separation factors for thiophene over nonane indicate higher quantities of thiophene in the vapor phase. © 2012 American Chemical Society

EXPERIMENTAL SECTION

Materials. Carbon dioxide and helium were provided by Air Products-Infra. Ethanol was purchased from Merck Chemicals. Sigma-Aldrich supplied thiophene, pentane, and nonane. Water content was quantified using a Karl Fischer coulometer (831, Metrohm). All chemicals were used as received with no further purification; their certified purities and water content are listed in Table 1. Apparatus. Experimental VLE measurements for the quaternary systems CO2 + ethanol + thiophene + alkane were carried out using a static−analytic setup. This apparatus has been already used in previous multicomponent phase equilibrium measurements and is capable to operate up to 60 MPa and 673 K.6,9 Isothermal phase equilibrium conditions are reached in a high-pressure view cell. A vapor or liquid sample of 1 μL from the cell is withdrawn with the ROLSI sampler− injector10 and sent online to a gas chromatograph (5890 Series II, Hewlett-Packard) for the sample quantification. The thermal conductivity detector (TCD) from the gas chromatograph was previously calibrated using each compound. Temperature conditions for the analytical equipment in the calibrations and VLE quantifications were (491 and 513) K for the injector port and TCD detector, respectively. A temperature gradient had to be used to separate compounds in the packed column (Porapak Q, Alltech; 1/8 in × 4 ft of length); the initial temperature was set to 423 K and reached a final Received: July 25, 2012 Accepted: September 19, 2012 Published: September 26, 2012 2896

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Table 1. Chemicals Used in This Work

CO2 ethanol thiophene pentane nonane a

purity

water content

Tca/K

pca/MPa

ωa

CAS

supplier

mole fraction

mole fraction

304.12 513.92 580.00 469.70 594.60

7.374 6.148 5.660 3.370 2.290

0.225 0.649 0.197 0.252 0.445

124-38-9 64-17-5 110-02-1 109-66-0 111-84-2

Air Products-Infra Merck Chemicals Sigma-Aldrich Sigma-Aldrich Sigma-Aldrich

0.99995 0.99993 0.998 0.9931 0.996

6.7·10−5 3.6·10−4 1.0·10−4 2.3·10−4

Properties reported in ref 15, except for acentric factor (ω) of thiophene taken from ref 16.

value of 493 K with a temperature rate of 25 K·min−1 for the system containing pentane; the final temperature for the system where nonane is contained was 513 K with increments of 70 K·min−1. Helium flow was established to 30 cm3·min−1 in the column and 45 cm3·min−1 in the reference for TCD. Estimated uncertainties for the composition of each phase at equilibrium did not exceed 0.0028 for xCO2 and 0.0015 for yCO2 in the whole range of equilibrium measurements. For better precision in the equilibrium measurements, calibrations of temperature and pressure instruments were previously performed; the corresponding procedure has been already described in detail in previous works.7 Uncertainties were evaluated following the National Institute of Standards and Technology (NIST) Technical Note 1297.11 The pressure transducer (PDCR 4010-A093, DRUCK) had a standard uncertainty within 0.02 MPa. The uncertainty for the temperature platinum probes (100 Ω Specitec) was calculated to be less than 0.04 K. Procedure. Isothermal VLE was obtained using the following stages: (1) Each system was separately loaded in the 100 cm3 equilibrium cell (EC). The solute mixture composed by sulfur compound + alkane was used as based model fuels and loaded to the cell with half of its volume capacity. The solutes thiophene + pentane were fed with a volume relation of 6:1. The second system was charged with a volume relation of 4.5:1 for the thiophene + nonane mixture. (2) Carbon dioxide and ethanol were used as the solvent + cosolvent mixture and previously prepared in a loading cell at 3.3 wt % of ethanol in a solute-free basis.12 The known composition was obtained by successive loadings of each compound as follows: The empty cell was first weighed; ethanol was aggregated into the loading cell and degassed to calculate the mass of ethanol. Then, carbon dioxide was added to the cell at a pressure higher than the critical point of this gas and weighed again. Weight measurements were performed in a mass comparator balance (MCA 1200, Sartorius) within an uncertainty of 4·10−6 mole fraction of carbon dioxide. (3) The equilibrium cell loaded with the solute mixture and all of the circuit of the static apparatus was carefully degassed with a vacuum pump. Pressure in the system was increased by adding the homogeneous carbon dioxide + ethanol mixture taken from the loading cell. After the four components were contained into the equilibrium cell, the mixture was stirred along the measurements to ensure the correct mixing of chemicals in both phases. Equilibrium cell temperature is regulated in an air bath (France Etuves) and was initially set to ∼334 K.

(4) Isothermal VLE measurements started after temperature and pressure values are within the reported uncertainty in the indicators. Temperature and pressure readings were observed in the digital indicators F-250 (ASL) and DPI 145 (Druck), respectively. (5) At fixed pressure, the vapor phase was first analyzed with the ROLSI sampler−injector. The sample was sent online to the gas chromatograph through thermoregulated tubing; it was set at a temperature higher than the boiling point of the less volatile compound with the aim of avoiding condensation. At least five consecutive samples with a deviation lower than 1 % in composition were analyzed in the chromatograph to minimize the uncertainty of the equilibrium composition. Afterward, the ROLSI sampler was moved down to the liquid phase to quantify the composition with the same criteria than the vapor phase. (6) Pressure was increased by adding the solvent + cosolvent mixture, and both phases were analyzed at each pressure to accomplish the isothermal phase envelope. (7) Finally, the temperature in the cell was changed to ∼363 K, and the equilibrium compositions were obtained using the above-mentioned procedure.

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MODELING The Peng−Robinson equation of state13 (eq 1) coupled to the classical (eqs 2 and 3) and Wong−Sandler14 mixing rules (eqs Table 2. Binary Interaction Parameters for the Classical Mixing Rule ref

data points

17

33

CO2 + ethanol

9

37

18

40

CO2 + thiophene CO2 + pentane

19

42

20

28

21

38

22

24

a a

binary system

ethanol + thiophene ethanol + pentane CO2 + nonane ethanol + nonane thiophene + pentane thiophene + nonane

T 313.2− 353.2 314.4− 383.0 310.1− 363.1 308.1− 318.1 372.7− 422.6 315.1− 418.8 343.1

%Δp

%ΔyCO2

kij

9.5

2.0

0.1059

4.3

0.2

0.0710

3.6

1.0

0.1481

14.3

18.3

0.1070

8.9

5.6

0.1074

5.9

3.2

0.1527

10.2

2.7

0.0410 0 0

a

Considered as zero due to the absence of VLE data reported in the literature.

2897

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Table 3. Binary Interaction Parameters for the Wong−Sandler Mixing Rules NRTL

a

ref

data points

binary system

%Δp

%ΔyCO2

kij

17 9 18 19 20 21 22 a a

33 37 40 42 28 38 24

CO2 + ethanol CO2 + thiophene CO2 + pentane ethanol + thiophene ethanol + pentane CO2 + nonane ethanol + nonane thiophene + pentane thiophene + nonane

7.3 1.5 3.2 1.4 5.5 4.3 0.5

1.7 0.5 1.2 2.6 3.5 0.5 0.3

0.2670 0.3897 0.5125 −0.4572 0.2826 0.6977 0.4020 0 0

−1

τ21/kJ·mol−1

τ12/kJ·mol 28.4045 5.6999 44.1026 5.4861 48.4469 8.2741 3.8707 0 0

2.4139 −1.4139 2.8090 10.6402 5.1764 −2.0510 7.1189 0 0

Considered as zero due to the absence of VLE data reported in the literature.

Table 4. Vapor−Liquid Equilibria for the Carbon Dioxide (1) + Ethanol (2) + Thiophene (3) + Pentane (4) Systema p/MPa

a

x1

x2

x3

x4

3.09 4.08 5.19 6.32 7.28 7.73

0.2336 0.3208 0.4237 0.5691 0.6971 0.7581

0.1944 0.1719 0.1423 0.1058 0.0693 0.0538

0.0761 0.0676 0.0597 0.0431 0.0293 0.0215

0.4959 0.4397 0.3743 0.2820 0.2043 0.1666

2.54 3.57 4.46 5.73 6.55 7.54 8.45 9.26 9.77 9.98

0.1746 0.2379 0.2907 0.3679 0.4181 0.4831 0.5475 0.6244 0.6945 0.7359

0.0564 0.0611 0.0643 0.0692 0.0710 0.0731 0.0717 0.0687 0.0620 0.0580

0.1263 0.1135 0.1014 0.0852 0.0741 0.0601 0.0470 0.0365 0.0295 0.0261

0.6427 0.5875 0.5436 0.4777 0.4368 0.3837 0.3338 0.2704 0.2140 0.1800

y1 T = 334.24 K 0.9272 0.9400 0.9495 0.9530 0.9515 0.9477 T = 363.80 K 0.7805 0.8288 0.8485 0.8619 0.8682 0.8673 0.8623 0.8476 0.8326 0.8199

y2

y3

y4

U(x1)

U(y1)

0.0122 0.0107 0.0100 0.0099 0.0108 0.0115

0.0042 0.0037 0.0035 0.0036 0.0039 0.0041

0.0564 0.0456 0.0370 0.0335 0.0338 0.0367

0.0022 0.0025 0.0021 0.0018 0.0012 0.0017

0.0014 0.0010 0.0011 0.0005 0.0010 0.0008

0.0114 0.0120 0.0126 0.0140 0.0158 0.0188 0.0216 0.0266 0.0314 0.0342

0.0119 0.0095 0.0087 0.0084 0.0083 0.0088 0.0097 0.0115 0.0136 0.0159

0.1962 0.1497 0.1302 0.1157 0.1077 0.1051 0.1064 0.1143 0.1224 0.1300

0.0024 0.0023 0.0013 0.0015 0.0018 0.0011 0.0022 0.0023 0.0016 0.0017

0.0004 0.0006 0.0012 0.0011 0.0009 0.0006 0.0015 0.0015 0.0012 0.0011

Uncertainties: u(T) ± 0.04 K, u(p) ± 0.02 MPa, u(x2) ± 0.0013, u(x3) ± 0.0012, u(x4) ± 0.0022, u(y2) ± 0.009, u(y3) ± 0.005, u(y4) ± 0.009.

The critical values and acentric factor15,16 are presented in Table 1. To predict the VLE data for the quaternary systems, binary interaction parameters for both mixing rules were optimized by correlating the VLE for the binary systems that concern this work reported in the literature;9,17−22 optimized results are summarized in Tables 2 and 3. Calculations were carried out by minimizing the following objective function.

4 to 6) were selected as the base models to predict the experimental VLE of the quaternary systems. p=

a(T ) RT − v−b v(v + b) + b(v − b)

am =

∑ ∑ xixj(aiaj)1/2 (1 − kij) i

bm =

(1)

(2)

j

∑ xibi

(3)

i

(

∑i ∑j xixj b − bm =

2 ⎡ ⎛ calcd 2 ⎛ pcalcd − pexptl ⎞ ⎤⎥ − yijexptl ⎞ ⎢ Nc ⎜ yij j ⎟ +⎜ j ⎟⎥ OF = ∑ ⎢∑ exptl exptl ⎜ ⎟ ⎜ ⎟ yij pj j=1 ⎢ i=1 ⎝ ⎠ ⎝ ⎠ ⎥⎦ ⎣ NP

a

1 − ∑i xi b RTi − i

a RT ij

)

(7)

Gγexc

(4)

CRT

The superscripts calcd and exptl denotes calculated and experimental values, respectively, for the mole fraction y and pressure p. NP denotes the number of data points, and Nc represents the number of compounds. The absolute average deviation of bubble pressure and mole fraction composition in the vapor phase was calculated according to eqs 8 and 9.

with

(

bi − ⎛ a ⎞⎟ ⎜b − = ⎝ RT ⎠ij

ai RT

aj

) + (bj − RT ) (1 − k )

⎛ Gγexc ⎞ a ⎟ am = bm⎜⎜∑ xi i + bi C ⎟⎠ ⎝ i

2

ij

(5)

%Δp = (6)

NP |pi exptl − pi calcd | ⎛ 100 ⎞ ⎜ ⎟ ∑ ⎝ NP ⎠ pexptl i=1

2898

i

(8)

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Table 5. Vapor−Liquid Equilibria for the Carbon Dioxide (1) + Ethanol (2) + Thiophene (3) + Nonane (4) Systema p/MPa

a

x1

x2

x3

x4

3.01 4.03 4.95 5.73 6.50 7.36 8.33 9.12 9.34

0.2127 0.2874 0.3595 0.4224 0.4846 0.5683 0.6685 0.7500 0.7781

0.0770 0.0712 0.0648 0.0590 0.0536 0.0448 0.0345 0.0267 0.0246

0.1605 0.1453 0.1312 0.1189 0.1063 0.0904 0.0708 0.0538 0.0477

0.5498 0.4961 0.4445 0.3997 0.3555 0.2965 0.2262 0.1695 0.1496

2.87 4.11 6.02 7.00 8.01 9.06 10.19 11.09 11.75 12.31 12.75

0.1518 0.2194 0.3236 0.3791 0.4388 0.5013 0.5712 0.6301 0.6720 0.7240 0.7680

0.0084 0.0144 0.0195 0.0219 0.0241 0.0251 0.0256 0.0260 0.0261 0.0252 0.0233

0.2040 0.1843 0.1586 0.1438 0.1288 0.1134 0.0966 0.0822 0.0722 0.0595 0.0506

0.6358 0.5819 0.4983 0.4552 0.4083 0.3602 0.3066 0.2617 0.2297 0.1913 0.1581

y1 T = 334.27 K 0.9786 0.9816 0.9827 0.9829 0.9828 0.9816 0.9795 0.9758 0.9742 T = 363.81 K 0.9655 0.9693 0.9704 0.9693 0.9679 0.9652 0.9606 0.9545 0.9478 0.9395 0.9166

y2

y3

y4

U(x1)

U(y1)

0.0103 0.0087 0.0080 0.0077 0.0075 0.0074 0.0073 0.0075 0.0078

0.0077 0.0067 0.0063 0.0062 0.0062 0.0065 0.0070 0.0080 0.0084

0.0034 0.0030 0.0030 0.0032 0.0035 0.0045 0.0062 0.0087 0.0096

0.0021 0.0028 0.0024 0.0015 0.0017 0.0025 0.0021 0.0014 0.0017

0.0009 0.0010 0.0014 0.0014 0.0011 0.0015 0.0007 0.0012 0.0008

0.0053 0.0061 0.0074 0.0080 0.0087 0.0093 0.0101 0.0107 0.0116 0.0125 0.0151

0.0210 0.0169 0.0143 0.0139 0.0136 0.0138 0.0146 0.0158 0.0169 0.0186 0.0226

0.0082 0.0077 0.0079 0.0088 0.0098 0.0117 0.0147 0.0190 0.0237 0.0294 0.0457

0.0014 0.0025 0.0021 0.0017 0.0011 0.0018 0.0021 0.0018 0.0015 0.0017 0.0023

0.0009 0.0011 0.0015 0.0007 0.0007 0.0011 0.0013 0.0012 0.0015 0.0014 0.0008

Uncertainties: u(T) ± 0.04 K, u(p) ± 0.02 MPa, u(x2) ± 0.0014, u(x3) ± 0.0010, u(x4) ± 0.0025, u(y2) ± 0.005, u(y3) ± 0.004, u(y4) ± 0.008.

%Δy =

■

NP yi exptl − yi calcd ⎛ 100 ⎞ ⎜ ⎟ ∑ ⎝ NP ⎠ y exptl i=1

i

Table 6. Equilibrium Ratios for the Carbon Dioxide (1) + Ethanol (2) + Thiophene (3) + Pentane (4) System and Separation Factor for Thiophene over Pentane

(9)

p/MPa

RESULTS AND DISCUSSION Experimental VLE for the quaternary system carbon dioxide + ethanol + thiophene + pentane was measured at (334.24 and

K1

K2

3.09 4.08 5.19 6.32 7.28 7.73

3.9692 2.9302 2.2410 1.6746 1.3649 1.2501

2.54 3.57 4.46 5.73 6.55 7.54 8.45 9.26 9.77 9.98

4.4702 3.4838 2.9188 2.3428 2.0765 1.7953 1.5750 1.3575 1.1988 1.1141

K3

T = 334.24 K 0.0628 0.0552 0.0622 0.0547 0.0703 0.0586 0.0936 0.0835 0.1558 0.1331 0.2138 0.1907 T = 363.80 K 0.2021 0.0942 0.1964 0.0837 0.1960 0.0858 0.2023 0.0986 0.2225 0.1120 0.2572 0.1464 0.3013 0.2064 0.3872 0.3151 0.5065 0.4610 0.5897 0.6092

K4

S3/4

0.1137 0.1037 0.0989 0.1188 0.1654 0.2203

0.4853 0.5278 0.5931 0.7031 0.8045 0.8657

0.3053 0.2548 0.2395 0.2422 0.2466 0.2739 0.3188 0.4227 0.5720 0.7222

0.3086 0.3285 0.3582 0.4071 0.4543 0.5346 0.6475 0.7454 0.8060 0.8435

T−xi − yi) and the expanded uncertainty for the composition in both phases with respect to carbon dioxide are presented in Tables 4 and 5. These isothermal VLE behaviors are shown in Figure 1. In both quaternary systems, the phase envelopes at 363 K cover wider ranges of pressure compared with the data reported at 334 K. The carbon dioxide mole fraction in the vapor phase decreases for 363 K compared with the low temperature and constant pressure; therefore the presence of the solutes in this phase tends to increase at 363 K. Equilibrium ratios (Ki) for each compound and the separation factor between thiophene and alkane are reported in Tables 6 and 7. According to the smoothness of each

Figure 1. VLE for the quaternary systems of carbon dioxide (1) + ethanol (2) + thiophene (3) + alkane (4). Pentane at (●, 334.24; ▼, 363.80) K, and nonane at (○, 334.27; △, 363.81) K.

363.80) K. For the second quaternary carbon dioxide + ethanol + thiophene + nonane system, isothermal data were obtained at (334.27 and 363.81) K. The carbon dioxide + ethanol mixture was used to increase pressure of the system. This mixture was previously prepared at a fixed mass fraction of w2 = 0.033 in a solute free-basis. Experimental data of equilibrium behavior (p− 2899

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Table 7. Equilibrium Ratios for the Carbon Dioxide (1) + Ethanol (2) + Thiophene (3) + Nonane (4) System and Separation Factor for Thiophene over Nonane p/MPa

K1

3.01 4.03 4.95 5.73 6.50 7.36 8.33 9.12 9.34

4.6008 3.4154 2.7335 2.3269 2.0281 1.7273 1.4652 1.3011 1.2520

2.87 4.11 6.02 7.00 8.01 9.06 10.19 11.09 11.75 12.31 12.75

6.3603 4.4180 2.9988 2.5568 2.2058 1.9254 1.6817 1.5148 1.4104 1.2977 1.1935

K2

K3

T = 334.27 K 0.1338 0.0480 0.1222 0.0461 0.1235 0.0480 0.1305 0.0521 0.1399 0.0583 0.1652 0.0719 0.2116 0.0989 0.2809 0.1487 0.3171 0.1761 T = 363.81 K 0.6310 0.1029 0.4236 0.0917 0.3795 0.0902 0.3653 0.0967 0.3610 0.1056 0.3705 0.1217 0.3945 0.1511 0.4115 0.1922 0.4444 0.2341 0.4960 0.3126 0.6481 0.4466

K4

S3/4

0.0062 0.0060 0.0067 0.0080 0.0098 0.0152 0.0274 0.0513 0.0642

7.7579 7.6253 7.1147 6.5132 5.9242 4.7376 3.6072 2.8971 2.7442

0.0129 0.0132 0.0159 0.0193 0.0240 0.0325 0.0479 0.0726 0.1032 0.1537 0.2891

7.9817 6.9298 5.6872 5.0001 4.3992 3.7465 3.1523 2.6475 2.2686 2.0341 1.5452

Figure 3. Equilibrium ratios for the carbon dioxide + ethanol + thiophene + nonane: (●, ○) carbon dioxide; (▼, △) ethanol; (■, □) thiophene; (◆, ◇) nonane. Black and open symbols denote (∼334 and ∼363) K, respectively.

Figure 4. Separation factor for thiophene over alkane in the quaternary systems: carbon dioxide (1) + ethanol (2) + thiophene (3) + alkane (4). (●, ○) ∼334 K; (▼, △) 363 K. Black symbols correspond to pentane, and open symbols denote nonane.

Table 8. VLE Predictions for the Quaternary Systems Using the PR EoS

Figure 2. Equilibrium ratios for the carbon dioxide + ethanol + thiophene + pentane: (●, ○) carbon dioxide; (▼, △) ethanol; (■, □) thiophene; (◆, ◇) pentane. Black and open symbols denote (∼334 and ∼363) K, respectively.

classical

isotherm for Ki values presented in Figures 2 and 3, it is assumed that the experimental VLE data are internally consistent. As pressure increases, Ki values for carbon dioxide tend to the unit at the critical pressure. Equilibrium ratios for the other three components are lower than the unit and tend to the unit at the critical pressure. In Figure 2, it is observed that the less volatile solute compound is thiophene due to the low Ki values and the high volatile solute compound is pentane. In Figure 3, for the second quaternary system, nonane represents the less volatile compound, and ethanol takes the function as the high volatile component. The feasibility for separating the sulfur compound over the alkane in the two quaternary systems is presented in Figure 4.

Wong−Sandler

quaternary system

T/K

%Δp

%ΔyCO2

%Δp

%ΔyCO2

CO2 + ethanol + thiophene + pentane

334.24

5.2

2.6

7.7

2.7

363.80 334.27

6.3 11.7

1.1 1.8

8.5 9.7

3.1 0.5

363.81

9.1

0.7

9.2

0.3

CO2 + ethanol + thiophene + nonane

For the thiophene + n-pentane mixture, the separation factor increases as pressure increases. Moreover, it indicates a scarce presence of the sulfur compound than alkane in the vapor phase. In the case of the thiophene + nonane mixture, this phase has higher thiophene quantities compared with nonane. The maximum values are located at low pressures and tend to decrease up to the unit at the critical pressure. No significant 2900

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differences for separation factor values were found between (334 and 363) K. The influence of ethanol in the quaternary system does not increase the separation factor of thiophene over nonane compared with the ternary system carbon dioxide + thiophene + nonane reported by Elizalde-Solis and GaliciaLuna.7 This variable is lower than 8 in both ternary and quaternary systems. Binary interaction parameters from Tables 2 and 3 were used to predict the VLE for the multicomponent systems; these results are summarized in Table 8 with respect to the deviations in pressure and vapor phase composition for carbon dioxide for each temperature. VLE prediction for the CO2 + ethanol + thiophene + pentane system had lower deviations in pressure and composition when the classical mixing rule was used compared against the results from the Wong−Sandler mixing rules. In the system with nonane, a better prediction for the VLE was obtained using the Wong−Sandler mixing rules. This could be attributed to the deviations reported for the binary systems on each case.

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CONCLUSIONS New experimental high-pressure VLE data for two quaternary carbon dioxide + ethanol + thiophene + pentane/nonane systems are reported at (∼334 and ∼363) K. Measurements were carried out in an apparatus based on the static−analytical method taking advantage of the online ROLSI sampler− injector. According to the separation factor, the content of thiophene in the vapor phase is low for the pentane system due to the high volatility of this linear hydrocarbon. In the other hand, the vapor phase is enriched with thiophene and could be separated from nonane at either of the two temperatures.

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AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]. Phone: (52) 55 5729-6000 ext. 55133. Fax: (52) 55 5586-2728. Funding

Authors acknowledge financial support of this research from Mexican Institutions: CONACyT and Instituto Politécnico Nacional. Notes

The authors declare no competing financial interest.

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REFERENCES

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dx.doi.org/10.1021/je300831t | J. Chem. Eng. Data 2012, 57, 2896−2901