Peculiarities of the transport properties of chitosan films. 1. Concentration prehistory of pervaporation

Abstract

Chitosan films prepared by the thermal method from molding solutions containing ethanol as a chitosan precipitant have been used as separating membranes for pervaporation of an aqueous isopropanol solution. The flux density and permeate composition have been determined as functions of the composition of a molding solution and a solution to be separated, as well as the concentration prehistory of the separation process. The concentration prehistory reflects the specific features of swelling polymer sorbents, which are distinguished by a labile structure and macroscopic sorption deformations. The existence of a concentration prehistory implies that, at a fixed concentration of an initial solution, parameters characterizing the transport properties of a polymer depend on the process route in which this concentration has been achieved. The composition of a molding solution and the route of variations in the initial concentration of a solution to be separated that correspond to the highest value of our criterion for the process efficiency have been determined. It has been shown that, in the case of films formed from a solution containing 20 wt % ethanol, the water flux density reversibly increases by more than 100 times as compared with the flux density of a water-alcohol solution.