Elsevier

Fluid Phase Equilibria

Volume 236, Issues 1–2, 20 September 2005, Pages 178-183
Fluid Phase Equilibria

High pressure vapor–liquid equilibria for the systems thiophene + nonane + CO2, and thiophene + decane + CO2

https://doi.org/10.1016/j.fluid.2005.06.029Get rights and content

Abstract

The aim of this work was to obtain phase equilibrium data of thiophene in CO2 in the presence of an alkane as cosolute. These data are needed for the design of an extraction process of sulfur compounds from a model fuel. Isothermal vapor–liquid equilibria (VLE) for the thiophene (1) + nonane (2) + CO2 (3), and thiophene (1) + decane (2) + CO2 (3) ternary systems were obtained at temperatures from 333 to 383 K and pressures ranging from 1.9 to 15.3 MPa. The initial loading for the solutes in the equilibrium cell was on a solvent-free basis at volume ratios of 1:4.52 and 1:1.25, for thiophene/nonane and thiophene/decane, respectively. Experimental solubilities of thiophene obtained in these systems were compared with those previously measured for the binary system thiophene + CO2. The distribution coefficients and separation factors for these systems are also reported.

Introduction

The development of a supercritical fluid process that could be applied in the extraction of sulfur compounds from fuels is an interesting option. However, in the process design, it is important to have accurate data on some properties such as phase behavior and physical properties of the compounds involved in the studied system. The presence of thiophene, benzothiophene, dibenzothiophene and their alkyl-derivative compounds in a commercial Mexican gasoline has been already identified by gas chromatograph analysis [1].

The phase behavior for dibenzothiophene + naphthalene + CO2 reported by Mitra et al. [2] has been the unique system that relates the solubility of this sulfur compound in CO2 in the presence of a hydrocarbon. Some studies have started and are focused onto getting solubilities of thiophene in supercritical CO2, and in the presence of a polar cosolvent [1]. Following this study, experimental solubilities of thiophene + nonane, and thiophene + decane binary mixtures in CO2 from 333 to 383 K are reported in this work. The solute mixtures were used as model fuels in order to analyze the separation of thiophene with CO2 as solvent. Therefore, it is necessary to study how nonane and decane modify the distribution of thiophene in the phase equilibrium.

The experimental solubilities were compared with those predicted with the Peng-Robinson equation of state (EoS) [3] and the classical mixing rules for the P  x ternary data. The interaction parameters (kij) used for the calculations of ternary systems were correlated from the VLE for binary systems reported in literature [1], [4], [5]. The calculated solubilities were in agreement with those experimental data.

Section snippets

Materials

CO2 with a minimum purity of 99.995 mol% and helium with a minimum purity of 99.998 mol% were purchased from Infra, México. Thiophene (99+% purity), nonane (99+%, purity) and anhydrous decane (99+% purity) were supplied by Aldrich Chemical Co. Inc, Wisconsin, USA. These substances were degassed and vigorously stirred under vacuum.

Apparatus description

The solubility measurements were performed in an apparatus based on the static-analytical method. It contains an equilibrium cell (ECT) with a volume of ∼100 cm3, which

Experimental data

The reliability of the apparatus to measure phase equilibrium data was previously tested and described [1], [7]. Isothermal VLE for the thiophene (1) + nonane (2) + CO2 (3) system were obtained at 334.31, 363.72, and 383.32 K. These data are presented in Table 1. The experimental VLE for the thiophene (1) + decane (2) + CO2 (3) system were performed at 334.40, 363.78, and 383.27 K, and are reported in Table 2. In both ternary systems, the mole fraction solubilities increased with temperature increasing.

Conclusions

Experimental VLE data were obtained for two different ternary systems. These data were compared to the data for thiophene + CO2 system reported in literature [1], a decrease on the solubility of thiophene in CO2 was observed when nonane or decane was added to the systems. In the system where nonane was added, the solubility of thiophene was higher than that for nonane up to the vicinity of the critical point of the solvent; and above this range the solubility of nonane was higher than the

Acknowledgment

The authors are grateful to CONACYT and IPN for their financial support.

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