Optimized rapid thermal processing for the template removal of SAPO-34 zeolite membranes

Abstract

The synthesis of defect-free zeolite membrane remains a big challenge due to the fact that thermal expansion mismatch between the zeolite film and the porous support can generate thermal stress and cracks during template removal process. Rapid thermal processing (RTP) for the template removal of SAPO-34 zeolite membrane was systematically studied and an optimized procedure was provided. A short RTP at 973 K led to substantially increased selectivity and permeance. The higher selectivity is the result of bonding between zeolite crystals generated during the rapid heating, which reduced cracking during the flowing slow calcinations. Moreover, RTP also facilitated the decomposition of template molecules which resulted into higher permeance. Long exposure at high temperature and thermal cycling may lead to the formation of defects in SAPO-34 membranes. The integration of RTP and conventional calcination, using a 1 min RTP at 973 K, fast cooling to 673 K, then 4 h calcination and slow cooling to room temperature, led to significantly improved selectivity and permeance. This optimized template removal procedure inherited the advantage of RTP treatment and also reduced the exposure time at high temperature, thus led to membranes with both high permeance and selectivity. Permporometry analysis confirmed the reduced defect size and area caused by RTP treatment. The best membrane exhibited CO2 permeance of 6.1 × 10−7 mol/(m2 s Pa) and CO2/CH4 selectivity of 88 at 4.0 MPa pressure drop, which were improved by 49% and 80% respectively, compared with membranes calcined by conventional template removal procedure.