Sorption of vapour mixtures of methanol and dimethyl carbonate in PTMSP: Cooperative and competitive sorption in one system

Abstract

Equilibrium sorption of vapour mixtures of methanol and dimethyl carbonate in poly[(trimethylsilyl)propyne], PTMSP, is reported. The experiments were conducted at 40°C and at atmospheric pressure using an apparatus that combined the sorption gravimetry in a carrier gas and the analysis of the desorbate by Fourier transform infrared spectroscopy (FT-IR). An unusual combination of competitive and cooperative sorption effects of dimethyl carbonate on methanol was observed. The cooperative sorption occurred at small methanol vapour activities, at which the sorption of pure methanol vapour is anomalously, and advantageously, small. The sorption isotherms of pure vapours and vapour mixtures were plausibly parameterized using Guggenheim, Anderson, De Boer (GAB) model and its semi-empirical extension for vapour mixtures, respectively. While the ideal separation factor of sorption, observable from the pure component sorption data, ranged 2–248, the real separation factor was significantly lowered by the co-sorption effects to 1–20. Overall, the highest real separation factors were observed for the higher dilutions of the binary feed mixtures with the inert gas and, advantageously, for methanol rich feed mixtures (i.e. in the vicinity of the composition of the azeotropic mixture).