J. Chem. Eng.

Data 2005, 50, 1631-1634 1631

Experimental Determination of the Solubility of Thiophene in

Carbon Dioxide and in Carbon Dioxide + Ethanol

Verónica Serrano-Cocoletzi, Luis A. Galicia-Luna,* and Octavio Elizalde-Solis

Instituto Politécnico Nacional, ESIQIE, Laboratorio de Termodinámica, Edif. Z, Secc. 6, 1ER piso,
UPALM Zacatenco, C.P. 07738, Lindavista, México, D.F., México

The solubility of thiophene (1) in CO2 (2) and in CO2 (2) + ethanol (3) mixtures were measured from (313
to 363) K using a static-analytical method connected on-line to a gas chromatograph. The solubility of
thiophene in CO2 was obtained at (314.53, 334.12, and 363.55) K. Isothermal solubilities of thiophene in
CO2 + ethanol mixtures with mass fractions of ethanol (w3) on a solute-free basis of 0.0245, 0.0548, and
0.0820 were obtained at (333 and 363) K. The solubility of thiophene was not greatly enhanced when
ethanol was added to CO2 at any composition. The experimental results were compared with those
calculated values from Peng-Robinson equation of state using classical mixing rules.

Introduction obtained from Merck, México, with a stated purity of 99.8

%. These compounds were used without any further
New efforts have been applied to obtain low-sulfur
purification. Thiophene and ethanol were degassed and
fuels.1-5 Extraction of sulfur compounds using ionic
vigorously stirred under vacuum before they were used.
liquids,1-3 the use of zeolites as selective sorbents for the
desulfurization of fuels,4 and the formation of sulfur salts Apparatus and Procedure. The apparatus and ex-
from the reaction of sulfur compounds5 are some of the perimental procedures have been described previously.6,11
recent investigations conducted to reduce sulfur content The apparatus is based on the static-analytical method. An
in commercial fuels. The extraction of sulfur compounds equilibrium cell with a volume of about 100 cm3 is the main
using supercritical solvents is another possible process. Its component of this apparatus, and the temperature of the
development requires previous study of phase equilibria6 cell was regulated by air bath. Two platinum probes Pt100
and thermophysical properties. CO2 is the most used and (Specitec, France) immersed in two thermometric wells at
attractive supercritical fluid.7 However, the solvent power the top and bottom of the cell body were used for temper-
of pure CO2 is not sufficient to dissolve light and high polar ature measurements. The Pt100 were calibrated against
compounds;7 therefore, some liquid solvents have been a 25-Ω reference probe (model 162CE, Rosemount) con-
added in small quantities to improve the capacity and nected to a calibration system (model F300S, Automatic
selectivity of CO2.7,8 The success of a SFE strongly depends Systems Laboratories). A thermoregulated pressure trans-
on choosing of the right cosolvent. On the other hand, ducer (model PDCR, Druck) recorded the pressure of the
thiophene is one of the principal sulfur compounds present system. This sensor was calibrated against a dead weights
in commercial fuels.6 This compound can be used as model gauge (model 5304 Class S2, Desgranges & Huot). Esti-
sulfur compound as in previous papers.1-4 Information mated uncertainties were within ( 0.03 K for temperature
about phase equilibria involving sulfur compounds, CO2 and within ( 0.04 % for pressure.
and liquid solvents reported in the literature are scarce. A movable capillary takes samples from the cell, and
Triday9 reported the vapor-liquid equilibria of thiophene these are sent to a gas chromatograph (HP-5890 II) for
+ light alcohols binary systems at low pressures. Recently, composition analyses by means of a thermoregulated
we have reported the solubility of thiophene in CO2 and transferring circuit using helium as carrier gas. The gas
CO2 + 1-propanol.6 The addition of 1-propanol did not chromatograph was equipped with a thermal conductivity
improve significantly the solubility of thiophene. In this detector (TCD). The carrier gas was set to 30 mL/min
work, ethanol was used as cosolvent in order to investigate through a packed column (Porapak Q 80/100, Alltech) with
its influence on the solubility of thiophene. We chose a length of 1.2 m and an external diameter of 0.32 cm. The
ethanol at mass fractions up to 0.0820 due to the critical TCD was calibrated by introducing known amounts of each
properties for the CO2 + ethanol are lower than those for component through calibrated syringes in the injector of
the CO2 + 1-propanol and are near the critical point of the the analytical equipment. Experimental composition un-
CO2 as reported by Yeo et at.10 certainties were estimated to be within ( 1 %. The TCD
calibration for thiophene is shown in Figure 1, and the
Experimental Section uncertainty did not exceed ( 0.8 %, as is demonstrated in
Figure 2. Similar results were obtained for CO2 and
Materials. Air Products-Infra, México, supplied CO2 and
ethanol.
helium with a minimum purity of 99.995 mol % and 99.998
mol %, respectively. Aldrich Chemical Co., USA, supplied After the calibrations of the TCD detector, temperature
thiophene with a minimum purity of 99+ %. Ethanol was probes, and pressure transducer,12 the measurements were
carried out. Thiophene was fed into the equilibrium cell
* To whom correspondence should be addressed. Tel: (52) 55 5729- followed by degassing under vacuum and stirring. Then
6000, ext 55133. Fax: (52) 55 5586-2728. E-mail: lgalicial@ipn.mx. the solvent (CO2 or CO2 + ethanol) was introduced into
10.1021/je050097a CCC: $30.25 © 2005 American Chemical Society
Published on Web 07/29/2005
1632 Journal of Chemical and Engineering Data, Vol. 50, No. 5, 2005

Figure 1. TCD calibration curve for thiophene.

Figure 3. Mole fraction solubility of thiophene (1) in CO2 (2) at

b, 314.53 K; ∇, 334.12 K; 9, 363.55 K; and s, P-R EoS.

Table 1. Mole Fraction Solubility of Thiophene (1) in

CO2 (2)
P/MPa y1 P/MPa y1 P/MPa y1
T ) 314.53 K T ) 334.12 K T ) 363.55 K
2.049 0.0148 3.033 0.0192 3.055 0.0473
3.047 0.0098 3.998 0.0161 4.024 0.0370
4.058 0.0085 5.027 0.0155 5.027 0.0343
4.969 0.0085 5.964 0.0160 5.993 0.0336
6.013 0.0098 7.289 0.0183 7.074 0.0346
6.387 0.0102 8.423 0.0225 7.996 0.0361
7.142 0.0113 9.584 0.0317 8.850 0.0385
7.662 0.0122 10.024 0.0493 9.357 0.0404
8.112 0.0152 9.915 0.0431
Figure 2. Uncertainty for the experimental mole number of 11.050 0.0507
thiophene. 11.696 0.0580
12.173 0.0672
12.732 0.0922
12.990 0.1210
the cell. CO2 was introduced by means of a syringe pump
(100DM, Isco). A volume variable cell (∼80 cm3) was used Table 2. Mole Fraction Solubility of Thiophene (1) in
to feed the CO2 + ethanol mixture to the equilibrium cell. CO2 (2) + Ethanol (3)
The samples with the desired compositions were prepared T/K P/MPa y1 y2 T/K P/MPa y1 y2
by successive loadings of the pure compounds. The amounts
w3 ) 0.0245
of the compounds were determined by weighing carried out
333.90 2.527 0.0232 0.9714 363.29 2.034 0.0667 0.9328
with an uncertainty of ( 10-7 kg with a comparator balance 3.001 0.0205 0.9748 3.548 0.0473 0.9506
(CC1201, Sartorius), which was periodically calibrated with 3.899 0.0173 0.9789 5.131 0.0399 0.9590
a standard mass of 1 kg of class E1. The resulting 5.035 0.0164 0.9802 7.039 0.0372 0.9597
uncertainty for the mass fraction composition of the 6.048 0.0173 0.9794 8.027 0.0390 0.9575
mixtures was lower than ( 10-4. Equilibrium measure- 7.081 0.0191 0.9776 8.854 0.0408 0.9554
7.744 0.0211 0.9763 9.764 0.0442 0.9515
ments were performed when temperature and pressure
8.392 0.0234 0.9733 10.792 0.0508 0.9441
were kept constant. At this point, five consecutive samples
for each phase were taken to check for the reproducibility
and perform mole fraction error analysis. Liquid and vapor obtained deviations were within the experimental uncer-
were sampled within a volume of 1 µL from the equilibrium tainty.
cell. Once liquid and vapor compositions were determined, The solubility of thiophene (1) in CO2 (2) + ethanol (3)
at constant temperature, the next measurement was mixtures was measured for three different loadings of the
achieved by adding more solvent into the cell. Isothermal cosolvent on a solute-free basis of w3 ) 0.0245, 0.0580, and
solubility curves were obtained by consecutive increments 0.0820. The solubility measurements for w3 ) 0.0245 were
of pressure. obtained at (333.90 and 363.29) K. These results are listed
in Table 2. For w3 ) 0.0580, measurements were carried
Results and Discussion out at (333.84 and 363.17) K and for w3 ) 0.0820,
Experimental Data. The solubility of thiophene (1) in measurements were made at (334.30 and 363.64) K. For
CO2 (2) was determined at (314.53, 334.12, and 363.55) K. these last loadings the vapor-liquid equilibrium is reported
The obtained solubilities are reported in Table 1 and in in Table 3. Ethanol was added as cosolvent to determine
Figure 3. The solubility values of this system were com- the influence of this polar component on the enhancement
pared with those reported by Elizalde-Solis and Galicia- of the solubility of thiophene in supercritical CO2. No more
Luna6 in order to check for the experimental consistency solubility data could be obtained at higher pressures than
and methodology. It is important to point out that no more the studied range due to the restriction of the small volume
phase equilibrium data are reported in the literature for of the loading cell where the solvent mixtures (CO2 +
this system. These sets of data were in agreement, and the ethanol) were prepared.
 Journal of Chemical and Engineering Data, Vol. 50, No. 5, 2005 1633

Figure 4. Mole fraction solubility of thiophene (1) in CO2 (2) + Figure 5. Mole fraction solubility of thiophene (1) in CO2 (2) +
ethanol (3) at ∼363 K: ], w3 ) 0.0820; 9, w3 ) 0.0580; 3, w3 ) ethanol (3) with w3 ) 0.0245 at b, 333.90 K; and Ο, 363.29 K.
0.0245; b, w3 ) 0.0 (pure CO2); and s, P-R EoS for w3 ) 0.0580. Mole fraction solubility of thiophene (1) in CO2 (2) + 1-propanol
(3) from Elizalde-Solis et al.6 with w3 ) 0.0231 at 1, 333.89 K; 4,
Table 3. Experimental VLE Data for Thiophene (1) + 363.35 K; and s, P-R EoS.
CO2 (2) + Ethanol (3) Mixtures
T/K P/MPa x1 x2 y1 y2 Table 4. Properties of Pure Compounds14,15

w3 ) 0.0580 component MW Tc/K Pc/MPa ω

333.84 2.009 0.7432 0.1329 0.0307 0.9641 CO2 44.010 304.12 7.374 0.225
3.172 0.6709 0.2153 0.0207 0.9712 ethanol 46.069 513.92 6.148 0.649
4.834 0.5500 0.3465 0.0175 0.9751 thiophene 84.142 580.00 5.660 0.193
6.090 0.4486 0.4645 0.0179 0.9750
7.125 0.3591 0.5710 0.0194 0.9734 Modeling. The Peng-Robinson equation of state (P-R
8.147 0.2689 0.6785 0.0215 0.9712
EoS)13 with classical mixing rules was used to predict
363.17 2.450 0.1043 0.8900
3.995 0.0645 0.9290 ternary systems. The explicit form of this EoS can be
5.455 0.0397 0.9531 written as follows:
7.002 0.0353 0.9571
8.105 0.0365 0.9551 RT a
P) - (1)
9.059 0.0381 0.9531 v - b v(v + b) + b(v - b)
10.038 0.0439 0.9458
11.028 0.0507 0.9370
where P and T are the pressure and temperature, respec-
11.385 0.0536 0.9333
tively; R is the gas constant; and v is the molar volume.
w3 ) 0.0820 The energy (a) and co-volume (b) parameters are related
334.30 2.056 0.7208 0.1392 0.0249 0.9644
3.024 0.6523 0.2162 0.0200 0.9718
to
4.037 0.5840 0.2967 0.0181 0.9748
5.002 0.5084 0.3843 0.0178 0.9756 R2Tc2
5.639 0.4976 0.4382 0.0182 0.9767 a(T) ) 0.45724 R(Tr) (2)
6.347 0.3861 0.5279 0.0182 0.9758
Pc
6.801 0.3605 0.5734 0.0191 0.9752
7.410 0.2941 0.6382 0.0285 0.9639 and
363.64 1.852 0.8797 0.1092 0.0754 0.9206
4.795 0.7363 0.2388 0.0419 0.9528 RTc
6.238 0.6217 0.3458 0.0383 0.9559 b ) 0.07780 (3)
7.700 0.5090 0.4516 0.0386 0.9545 Pc
9.003 0.3926 0.5530 0.0424 0.9474
The subscritpt “c” denotes the critical property for the
In the studied range, the solubility of thiophene in CO2, constituent, and R is the temperature-dependent factor.
and CO2 + ethanol mixtures depended on temperature and The properties of pure compounds were taken from litera-
pressure changes, the solubilities increased as temperature ture data14,15 and are presented in Table 4. The a and b
was increased. At a given temperature and above the parameters for mixtures are defined by
critical pressure of the CO2, the solubility of thiophene
increased greatly with increasing pressure. The solubility
of thiophene in CO2 + ethanol mixtures is plotted in Figure
am ) ∑ ∑x x a
i j
i j ij (4)
4 at ∼363 K. The mole fraction solubility of thiophene was
improved about 6 % for w3 ) 0.0245. However, about the
same solubility values for thiophene were obtained for the
bm ) ∑x b
i
i i (5)

three loadings of cosolvent. Moreover, the experimental

solubilities of thiophene (1) in CO2 (2) + ethanol (3) at w3 where aij is defined by
) 0.0245 are compared with those previously reported with
the CO2 (2) + 1-propanol (3) mixture at w3 ) 0.02316 in aij ) (1 - kij)xaiiajj(i * j) (6)
Figure 5. The addition of ethanol improved the solubility
of thiophene in an order of about 5.7 % compares to that kij is the binary interaction parameter that is related to
obtained with the addition of 1-propanol. molecular interactions between each pair of components i
1634 Journal of Chemical and Engineering Data, Vol. 50, No. 5, 2005

+ ethanol mixtures. The solubility of thiophene in CO2 +

ethanol mixtures was compared with the only reported
results for the solubility of thiophene in CO2 + 1-propanol
mixtures.6 The small increase on the solubility of thiophene
(1) in CO2 (2) + ethanol (3) at w3 ) 0.0245 against
1-propanol (3) at w3 ) 0.0231 on a solute-free basis was
caused due to the higher concentration of ethanol. However
the solubility of thiophene in the supercritical solvent was
not greatly increased with the addition of any of these two
cosolvents. It means that they did not enhance substan-
tially the solubility of thiophene in comparison with those
obtained in pure CO2.
Solubility data were calculated with the P-R EoS for
the solvent mixtures at w3 ) 0.0580 and 0.0820. Although
the deviations between calculated and experimental solu-
bilities had higher AAD % values of about 4 % and 6 %,
this simple model predicts with reasonable consistency the
Figure 6. Distribution coefficients for the system thiophene (1) isothermal solubilities.
in CO2 (2) + ethanol (3) at different loadings of the cosolvent: b,
w3 ) 0.0580 at 333.84 K; 1, w3 ) 0.0820 at 363.64 K; and s, P-R Literature Cited
EoS. (1) Huang, C.; Chen, B.; Zhang, J.; Liu, Z.; Li, Y. Desulfurization of
gasoline by extraction with new ionic liquids. Energy Fuels 2004,
Table 5. kij Calculated from Binary Mixtures 18, 1862-1864.
(2) Bösmann, A.; Datsevich, A. J.; Lauter, A.; Schmitz, C.; Wasser-
mixtures kij scheid, P. Deep desulfurization of diesel fuel by extraction with
thiophene (1) + CO2 (2) 0.07508 ionic liquids. Chem. Commun. 2001, 2494-2495.
CO2 (2) + ethanol (3) 0.09589 (3) Zhang, S.; Zhang, Q.; Zhang, Z. C. Extractive desulfurization and
denitrogenation of fuels using ionic liquids. Ind. Eng. Chem. Res.
thiophene (1) + ethanol (3) 0.08660 2004, 43, 614-622.
(4) Yang, R. T.; Takahashi, A.; Yang, F. H. New sorbents for
and j involved in the mixture. The kij values listed in Table desulfurization of liquid fuels by π-complexation. Ind. Eng. Chem.
5 were obtained by correlating VLE data from binary Res. 2001, 40, 6236-6239.
(5) Shiraishi, Y.; Tachibana, K.; Taki, Y.; Hirai, T.; Komasawa, I. A
mixtures reported in the literature.6,9,12 Afterward, the kij novel desulfurization process for fuel oils based on the formation
parameters were used with the same model to predict and subsequent precipitation of S-alkylsulfonium salts. 2. Catalytic-
experimental solubility of thiophene (1) in CO2 (2) and in cracked gasoline. Ind. Eng. Chem. Res. 2001, 40, 1225-1233.
(6) Elizalde-Solis, O.; Galicia-Luna, L. A. Solubility of thiophene in
CO2 (2) + ethanol (3) mixtures. carbon dioxide and carbon dioxide + 1-propanol mixtures at
The absolute average deviation (AAD %) for y1 and P temperatures from 313 to 363 K. Fluid Phase Equilib. 2005, 230,
were within 4 % for w3 ) 0.0580. For the case of w3 ) 51-57.
(7) Perrut, M.; Clavier, J.-Y. Supercritical fluid formulation: process
0.0820, the AAD % was 6.5 % for y1 and 12.3 % for P. These choice and scale-up. Ind. Eng. Chem. Res. 2003, 42, 6375-6383.
deviations were calculated as follows: (8) Dobbs, J. M.; Wong, J. M.; Lahiere, R. J.; Johnston, K. P.
Modification of supercritical fluid phase behavior using polar

∑ Nd exptl cosolvents. Ind. Eng. Chem. Res. 1987, 26, 56-65.

i)1|(yi - ycalcd
i )/yexptl
i | (9) Triday, J. O. Vapor-liquid equilibria in binary systems formed
AAD % ) × 100 (7) by thiophene and light alcohols. J. Chem. Eng. Data 1983, 28,
Nd 307-310.
(10) Yeo, S. D.; Park, S. J.; Kim, J. W.; Kim, J. C. Critical properties
of carbon dioxide + methanol, + ethanol, + 1-propanol, +
where Nd is the number of data points. The calculated 1-butanol. J. Chem. Eng. Data 2000, 45, 932-935.
equilibrium ratios (K1) for thiophene had similar trends (11) Elizalde-Solis, O.; Galicia-Luna, L. A.; Sandler, S. I.; Sampayo-
as compared with the experimental sets of data. This Hernández, J. G. Vapor-liquid equilibria and critical points of
comparison is shown in Figure 6. It can be seen that the the co2 + 1-hexanol and CO2 + 1-heptanol systems. Fluid Phase
Equilib. 2003, 210, 215-227.
presence of thiophene in the vapor phase was higher when (12) Galicia-Luna, L. A.; Ortega-Rodriguez, A.; Richon, D. New ap-
the mass fraction of ethanol was increased and with paratus for the fast determination of high-pressure vapor-liquid
increasing temperature. equilibria of mixtures and of accurate critical pressures. J. Chem.
Eng. Data 2000, 45, 265-271.
(13) Peng, D. Y.; Robinson, D. B. New two constant equation of state.
Conclusions Ind. Eng. Chem. Fundam. 1976, 15, 59-64.
(14) Poling, B. E.; Prausnitz, J. M.; O’Connell, J. P. The Properties of
Experimental solubility data of thiophene in CO2 mea- Gases and Liquids, 5th ed.; McGraw-Hill: New York, 2001.
sured in this work were compared with those values (15) Yaws, C. L. Chemical Properties Handbook; McGraw-Hill: New
reported in the literature.6 Deviations were found to be York, 1999.
within the experimental uncertainty. An enhancement on
the solubility values was not obtained when ethanol was Received for review March 12, 2005. Accepted June 20, 2005. The
authors thank CONACYT and IPN for their financial support.
added as cosolvent. Moreover, the solubility of thiophene
had about the same values for the different loadings of CO2 JE050097A