High pressure phase behavior in systems containing CO2 and heavier compounds with similar vapor pressures |
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Affiliation: | 1. División de Materiales Avanzados, IPICYT, Instituto Potosino de Investigación Científica y Tecnológica, Camino a la Presa San José 2055 Col. Lomas 4a. sección C.P. 78216, San Luis Potosí, S.L.P., México;2. Centro de Ciencias Aplicadas y Desarrollo Tecnológico, Universidad Nacional Autónoma de México, Circuito Exterior S/N, Ciudad Universitaria, A. P. 70-186, Delegación Coyoacán, C.P. 04510, México D. F., México;1. State Key Laboratory of Advanced Processing and Recycling of Non-ferrous Metal, Lanzhou University of Technology, No. 287 Langongping Road, Lanzhou, 730050, People’s Republic of China;2. School of Materials Science and Engineering, Jiangsu University of Science and Technology, Zhenjiang, Jiangsu 212003, People’s Republic of China;1. University of Sfax, Faculty of Science, LSME, BP1171-3018 Sfax, Tunisia;2. Unité de recherche Toxicologie – Microbiologie Environnementale et Santé, University of Sfax, Faculty of Science, Tunisia;3. CQFM-Centro de Química-Física Molecular from IN and IBB, Instituto Superior Técnico, Universidade de Lisboa, Av. Rovisco Pais, 1049-001 Lisboa, Portugal;4. Laboratoire de Génie Enzymatique et de Microbiologie, Université de Sfax, Ecole Nationale d’Ingénieurs de Sfax, B.P. 1173, 3038-Sfax, Tunisia;5. ITODYS, UMR7086 CNRS, Université Paris Diderot, Sorbonne Paris Cité, Rue Jean Antoine de Baïf, 75205 Paris Cedex 13, France |
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Abstract: | The separation of the para and ortho isomers of xylene as well as the azeotropic mixture of butyl ether/o-xylene using carbon dioxide at high pressure was investigated. The phase behavior of carbon dioxide and each of these compounds along with the ternary systems; CO2/p-xylene/o-xylene and CO2/butyl ether/o-xylene were experimentally determined. The relative volatilities of p-xylene to o-xylene in the CO2/p-xylene/o-xylene system compared favorably with those obtained in distillation. The results also indicated a substantial shift in the butyl ether/o-xylene azeotrope to higher butyl ether concentrations in the presence of carbon dioxide thus indicating a potential for the separation of these mixtures using carbon dioxide at low temperatures. Thermodynamic models using the Peng—Robinson equation of state were developed and better predictions of the bubble point pressures were obtained when the interaction parameter, δij, was allowed to vary with phase density. This approach results in an analytically solvable quartic equation in volume and gives different δij's for the vapor and liquid phases. In this model, the temperature dependence of the binary interaction parameter is contained within its density dependence and, δij's obtained from fitting VLE data at a single temperature could be used for accurate prediction of equilibrium data at other temperatures. The results of such predictions were better than predictions obtained by fitting the actual data using the conventional VDW-1 mixing rules. |
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