Modelling sorption thermodynamics of gases, vapors and gas mixtures in glassy polymers using a non-equilibrium version of PC-SAFT accounting for specific interactions and volume change

Glassy polymers are among the materials of choice for membrane -based separations of gas and vapor mixtures. Sorption thermodynamics plays an important role in determining the separation performances of these materials. In this context, a general model which can deal with multicomponent sorption thermodynamics in glassy polymer/penetrants systems represents a theoretical challenge due to the possible complex interactional scenario characterized by the occurrence of cross and self- hydrogen bonds and/or by penetrant induced dilation of the glassy matrix. To this aim, the Dry Glassy Reference Perturbation Theory (DGRPT) framework has been implemented here, for the first time, in conjunction with the standard Perturbed Chain Statistical Associating Fluid Theory (PC-SAFT) model incorporating an association term that accounts for possible specific interactions. In particular, a modification of the standard DGRPT framework, based upon a self-consistent estimation of the free volume, is proposed to minimize the number of adjustable parameters of the DGRPT-PC-SAFT model. In the present contribution we first validate the theoretical approach by addressing the modelling of sorption thermodynamics of Poly(1-trimethylsilyl-1-propyne) (PTMSP), a high glass transition temperature polymer, with the aim of elucidating the solubility data of CO2/CH4 binary gas mixtures at high pressure, available in literature. In addition, the capability of the model to predict penetrant induced dilation has been tested against literature volumetric data of PTMSP/ CH3OH and PTMSP/DMC binary mixtures. Then, the case of polyimides, a class of materials of interest for applications in the field of dehydration of alcohols and separation of polar/non-polar azeotropic mixtures, is considered. In this case, the theoretical approach has been used to interpret not only the overall sorption thermodynamics but also to provide quantitative predictions of different populations of interacting penetrant sorbed into the polymers. Experimental outcomes of in situ FT-IR, previously obtained by our research group for two binary polyimides/CH3OH systems of technological interest, have been analyzed: polyetherimide (PEI)/CH3OH and 6FDA-ODA/CH3OH. The proposed case studies provide evidence for the efficacy of the DGRPT-PC-SAFT approach in describing the multicomponent sorption thermodynamics of gases mixtures at high pressures as well as of interacting vapor penetrants within amorphous glassy polymers.