| The thiophene and its derivatives are major component of total sulfur content in petroleum products, therefore, the removal of thiophene has a great significance for environmental protection. Removal of thiophene using green solvent is a potentially important method. Ionic liquids and supercritical carbon dioxide as a widely used solvent emerging in recent years, were applied to the extraction study on desulfurization in this work. Although some researchers investigated the solubility, invasive, selective and desulfurization efficiency for thiophene in these solvents with experiments, microstructure of these systems is not very clear so far. In order to understand the microstructure and intermolecular interactions from molecular level, molecular simulation method is used to study these systems.Monte Carlo simulation method is performed to discuss the microstructure and phase behavior of thiophene in [Bmim][PF6,[Bmim][BF4], ScCO2and [Bmim][PF6]/ScCO2. The force field parameters for each component used in this work are reasonable. In thiophene-ionic liquid systems, we have predicted that the molar fractions of thiophene and temperature have an important effect on the microstructure of fluids. In addition, we analysed the phase behavior of these systems in detail. In thiophene-supercritical CO2system, we have studied the effect of temperature and pressure on fluid structure. In [Bmim][PF6]-ScCO2-thiophene ternary system, we have studied the effects for pressure changes on the microstructure of the system. The results shows that fluid structure of thiphene in [Bmim][PF6] is similar with that in [Bmim][BF4]. Thiophene is easy to gather in the cone and terminal of the alkyl chain of the cation, and uniformly distribute around the anion. Compared with the cation, thiophene tend to distribute around the anion. The vapor pressure of thiophene in [Bmim][PF6] is lower than that in [Bmim][BF4J, and the affinity is stronger between [Bmim][PF6] and thiophene than [Bmim][BF4] and thiophene. Compared with the sulphur removal efficiency of the two ionic liquids, as we observed that [Bmim][PF6] is more appropriate for the removal of thiophene. In thiophene-ScCO2system, thiophene distributes around carbon dioxide in an orderly partern. In contrast to the distribution of oxygen atom of carbon dioxide, the thiophene molecure distributes more orderly around carbon atoms of CO2. According to the changes of solubility of thiophene in carbon dioxide with temperature and pressure, it is much favorable for extraction and separation of thiophene with supercritical carbon dioxide. In [Bmim][PF6]-ScCO2-thiophene ternary system, CO2and thiophene distribute around [Bmim][PF6], however, CO2more easily distributes round the anions. CO2mainly spread in the void between imidazole ring and which attached to the alkyl chain of cation, also the cone carbon atom of cation. At the same time, joining of ionic liquid has an effect on the spatial structure of thiophene in supercritical carbon dioxide. |
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