Network engineering of a BTESE membrane for improved gas performance via a novel pH-swing method

Organosilica microporous membranes were fabricated from 1, 2-bis (triethoxysilyl) ethane (BTESE)-derived sols prepared in acidic pH via the pH-swing method. This method includes two steps whereby a specific amount of NH3 was added into the acid sols and switched to acid after a reaction of several minutes. We found that the size of the BTESE-derived sols by pH-swing could be controlled via the H2O/BTESE molar ratio and the reaction time in alkali. Under the same H2O/BTESE ratio of 60, the BTESE-derived sols prepared in the pH-swing method showed an increase sol size in contrast with the acid method, and the sol size was easily controlled by the dominating reaction in alkali pH - the condensation reaction. Gas permeation results showed that some gases (He, H-2, N-2, C3H8, SF6) permeated the membrane that was prepared using the pH-swing sols (pH-swing membrane) at approximately twice the rate shown by the membrane prepared using acid sols (acid membrane); H-2 permeance levels of the pH swing membrane and the acid membrane were 3.4 x 10(-6) and 1.6 x 10(-6) mol m(-2) s(-1) Pa-1 at 200 degrees C, respectively. The pH-swing membrane also maintained similar H-2/C3H8 permeance ratios of ranging from 2600 similar to 5800, confirming that pH-swing processing is an innovative method for improvement in the gas permeance of BTESE-derived organosilica membranes. One possible reason for these results could be that the membranes prepared using the pH-swing sols increased the size of the sols, which reduced the sol penetration into the intermediate layer. Moreover, the high cross-linking that was caused by pH swing increased the thermostability of the BTESE-derived organosilica networks. The CO2/CH4 and CO2/N-2 permeance ratios for the pH-swing membrane were as high as 90 and 28, respectively, at 50 degrees C. (C) 2016 Elsevier B.V. All rights reserved.