The effect of the naphthenic ring on the VLE of (carbon dioxide + alkane) mixtures

Abstract

Isothermal (vapour + liquid) equilibrium (VLE) data for the binary systems (carbon dioxide + cyclopentane) and (carbon dioxide + cyclohexane) were determined using a (static + analytical) method with phases sampling by rapid online sample injectors (ROLSI) coupled to a gas chromatograph (GC) for analysis. The VLE behaviour for these systems was also analysed based on the PR and RKPR equations of state (EoS) and different available data from the literature, both critical and subcritical. It is clearly shown how CO 2 is more soluble and miscible with normal alkanes than with the corresponding cycloalkanes. Predictions based on the general correlation of available data in wide ranges of conditions suggest the appearance of double retrograde behaviour at least for (CO 2 + cyclohexane) mixtures with very low contents of the hydrocarbon in CO 2 , being this phenomenon very much related to asymmetry of the system. The existence of this phenomenon has not been experimentally confirmed yet for these systems and should be explored.