Study on the influence of the free volume of hybrid membrane on pervaporation performance by positron annihilation spectroscopy

To improve the pervaporation separation performance, an organic–inorganic hybrid membranes were prepared by adding zeolite 13X into the polyimide (BAPP–BODA), which was synthesized using one-step polycondensation polymerization of 2,2-bis(4-(4-aminophenoxy)phenyl)propane (BAPP) with bicyclo[2.2.2]oct-7-ene-2,3,5,6-tetracarboxylic dianhydride (BODA). The influence of the zeolite 13X content on the free volume and pervaporation performance of hybrid membranes were systematically analyzed by positron annihilation spectroscopy (PAS). The trend of ortho-positronium (o-Ps) lifetime and free volume holes changes consistently well with the permeation rate variation of aqueous isopropanol mixtures dehydration. The BAPP–BODA/13X hybrid membrane morphology was characterized by AFM and SEM. Compared with the BAPP–BODA membrane, the BAPP–BODA/13X hybrid membrane had good pervaporation performance for aqueous alcohol solution dehydration. The sorption selectivity dominates the behavior of pervaporation while adding zeolite 13X into the polyimide matrix.