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