Manipulation of the surface microstructure and its effects on the flux of NaA zeolite membranes in pervaporation

Abstract

NaA membranes with different microstructures are synthesized on macroporous alumina tubes with the addition of crystallization improving agents (CIAs) which have the same composition with the synthesis hydrogel but are aged for a longer time (e.g., 24 h). The as-synthesized membranes are characterized by SEM, contact angle measurement and pervaporation test. It is found that the addition of the CIAs in the synthesis hydrogel has significant influence on the surface roughness of zeolite membrane, resulting in the change of the hydrophilicity and thus flux of the zeolite membrane. Dense NaA membranes with high flux of 4.53 kg m−2 h−1 can be obtained at 100 °C for 3 h with the addition of 10 wt% CIAs in the synthesis hydrogel. The flux is increased by 14% compared with the membrane synthesized at the same condition without CIAs. The surface roughness of the membranes can also be changed by the method of polishing and re-synthesizing with the assist of nano-seeds. After polishing, the flux decreases to 3.83 kg m−2 h−1; however, the flux can be recovered to 4.45 kg m−2 h−1 after re-synthesizing. This study provides a good method to enhance the separation efficiency and indicates that the surface microstructure of membranes influences their pervaporation performance.