Gas solubilities in ionic liquids using a generic van der Waals equation of state

A family of modified van der Waals equations of state (vdW EOS) is extremely useful for many industrial applications. For example, the generic Redlich–Kwong (RK) EOS or its modification by Soave (SRK EOS) and Peng–Robinson (PR EOS) are still of popular use in industry to the present day. These two most popular (“cubic”) EOSs are based on modifications [1/(V2 + bV), or 1/(V2 + 2bV − b2)] of the volume dependence on the attractive part of the original van der Waals EOS [1/V2] and also modifications of the temperature dependence of the attractive “a(T)” parameter of the original EOS (constant a). It is extremely rare in actual EOS applications to use the volume dependence of the original van der Waals EOS. In the present phase equilibrium calculations, we employ such a generic vdW EOS, P = RT/(V − b) − a(T)/V2, with our well-tested mixing rule for multi-component mixtures. Using the same form of the “a(T)” parameter and the mixing rule, it has been found that all generic RK, PR, and vdW EOSs can present the phase behaviors (temperature–pressure–composition diagrams) equally well. It is shown that experimental gas solubility data (CO2, CF3–CFH2, SO2, and NH3) in room-temperature ionic liquids are well correlated with the present EOS model, and also that the phase behaviors such as LLE (liquid–liquid separations) are satisfactorily predicted.

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