Polyimide has a high water permeability, water and organic matter also has a high separation factor. The separation coefficient decreases with decreasing temperature. For water - acetic acid system, polyimide and polyamideimide has a higher separation factor than the polyamide. This is because the former has a greater rigidity than the latter. Difficult for the organic material to swell. The introduction of carboxyl groups and sulfuric acid can increase the hydrophilic membrane, so that the transmittance increased several times. With divalent metal, in particular, can reduce swelling after Ca2 + crosslinking can make the separation factor increased tenfold.
A polyimide film pervaporation can be used to remove the water produced in the esterification reaction, the equilibrium shifts in the direction of promoting the ester formation. After the PMDA / ODA polyamic acid obtained asymmetric membrane by thermal imidization as pervaporation membranes have been used by the exchange reaction of phenol and acetone Catalytic Synthesis of bisphenol A in the cation. Since the resulting water is removed in time, not only the reaction time when 1/4 of pervaporation. After the reaction 8h, 70% of the produced water are removed in time, through the membrane and the loss of only 2% acetone. Furthermore, the catalyst can be reused without further treatment after drying.