Solubility of thiophene in carbon dioxide and carbon dioxide + 1-propanol mixtures at temperatures from 313 to 363 K
Introduction
Phase equilibrium data are of great significance in the petroleum industry for development and validation of thermodynamic models. Separation processes, design, and supercritical fluid extraction, in particular, strongly depend on accurate vapor–liquid and vapor–liquid–liquid equilibrium data.
Sulfur compounds extraction from oil fractions is very important in the petroleum refining industry, especially the extraction of thiophene and benzothiophene from gasoline and diesel fuel. In Mexico, the Maya oil has about 4% of total sulfur; therefore an economical process without environmental impact for sulfur removing is required. The most common process for sulfur removal from gasoline uses a metal catalyst in the presence of hydrogen at high temperature (≈600 K), where the supercritical extraction might be a competitive option to eliminate these compounds at lower temperature.
An analysis of sulfur compounds from a Mexican commercial premium gasoline is presented in Fig. 1. This was done using a pulsed flame photometric detector (PFPD) in a gas chromatograph HP 6890 equipment. It is shown that thiophene and benzothiophene are the major sulfur compounds in this gasoline. Based on these results, a systematic experimental study of solubility of thiophene and benzothiophene in supercritical CO2 and CO2 + alcohol is being carried out. In this work, experimental solubility data of thiophene in carbon dioxide and carbon dioxide + 1-propanol mixtures from 313 to 363 K are presented. These systems have not been reported in literature.
Section snippets
Experimental method and apparatus
Measurements were made in an apparatus showed in Fig. 2 and previously described by Elizalde-Solis et al., based on static–analytic method [1]. It is based on the same principle described by Galicia-Luna et al. [2]. The equilibrium cell can be used up to 60 MPa and 673.15 K. This apparatus allows studying systems in one, two or three phases.
A gas chromatograph (HP 5890 II) with a thermal conductivity detector TCD and a 4-ft by 1/8-in. diameter packed column packed (Chromosorb 101) was used for
Experimental results and discussion
Experimental VLE data for CO2 + ethanol system at 333.15 K were measured in order to test experimental methodology. CO2 + ethanol system was compared with those reported by Galicia-Luna et al. [2] and both data sets are in good agreement. These results are reported in Table 1 and are plotted in Fig. 3.
Solubility data of thiophene in pure CO2 were determined at 314.47, 334.28, 363.53 and 383.03 K and they are reported in Table 2. At constant pressure, the solubility of this sulfur compound increased
Modeling
The isothermal VLE data were correlated using the Peng–Robinson (P–R) EoS [5] combined with classical mixing rules. This kind of EoS is not suitable to predict VLE at critical point region. Binary interaction parameters (kij) were fitted to VLE experimental data reported in literature [4], [6] and in this work using data points at lower temperatures. VLE data at the highest temperature was well predicted. kij values for binary systems are reported in Table 5. Critical properties were taken from
Conclusions
In this work, new experimental solubility data are reported for thiophene in CO2 and CO2 + 1-propanol mixtures at temperatures from 313 to 363 K. These mixtures contained 2.3 and 6.5 mol% of 1-propanol as co-solvent. The addition of small amounts (up to 6.5 mol% fraction) of 1-propanol as co-solvent did not improve the solubility of thiophene against pure CO2, this implies that 1-propanol is not a good co-solvent for extraction. On the other hand, the solubility of thiophene was improved as more
Acknowledgments
The authors are grateful to reviewers for their useful comments and thank CONACYT and IPN for their financial support.
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