Investigation of separation of Mixtures of Supercritical Carbon Dioxide and Ionic Liquids

Ionic liquids are organic salts that are liquid at room temperature [1, 2].They are generally composed of a large organic cation and organic or inorganic anions [2]. The applications of ionic liquids have generated number of discussions in the past decade. This is mainly because of their physico-chemical properties, which are able to be adjusted through combination of cations and anions. This phenomenon allows the researchers to design specific solvents for the development of more efficient processes and products. Having no vapor pressure, no flammability, high thermal stability, a wide liquid range, and electric conductivity are among the other elements that make ionic liquids become interesting more and more[1-3]. Due to the difficulties of experimental measurements and also time-consuming and costly nature of such techniques, it is desirable to develop predictive methods for evaluating the phase behavior of these kinds of systems. Furthermore, in order to efficiently design the processes dealing with mixtures of CO2 in ionic liquids, one needs to know the operational conditions to reach a desired CO2 solubility in the applied ionic liquid solvent. In recent years, several attempts have been done regarding this concept. The Peng-Robinson (PR) [4] cubic equation of state (CEoS) was applied by Shariati and Peters [5] to model the solubility of CHF3 in [C2mim][PF6] from 309.3 to 367.5 K and 1.6 to 51.6 MPa. Breure et al. [6] used the Group The First National Conference of Novel Technologies in Oil & Gas Industries, 3 and 4 March 2011, Islamic Azad University, Omidiyeh Branch Contribution (GC) equation of state (EoS) to model the phase behavior of binary systems of ionic liquids and supercritical carbon dioxide. In addition, Yokozeki and Shiflett [7] used successfully a generic Redlich-Kwong (RK) [8] EoS in order to understand the global phasebehavior of trifluoromethane and room-temperature ionic liquid [bmim][PF6] mixtures. They gained satisfactory results for vapor-liquid-equilibria (VLE) and vapor-liquid-liquidequilibria (VLLE) in such systems at wide ranges of pressures. So far, several industrial applications of ionic liquids have been proposed including as solvents in organic synthesis, homogeneous and biphasic transfer catalysts, In this communication, we focus on investigating the capability of the well-known two-parameter cubic equations of state (the PR and the SRK) accompanied with three mostly-used mixing rules applied in modeling of supercritical fluids including the Wong-Sandler (WS) , the van der Waals one (vdW1) , and the van der Waals two (vdW2) for calculating/predicting the phase behaviors of the mixtures of supercritical carbon dioxide in classical ionic liquids.

Keywords:

Cubic equation of state , Ionic liquid , Supercritical CO2 , Phase behavior , Separation