Silica supported SAPO-34 membranes for CO2/N2 separation

In this work, SAPO-34 membrane was successfully synthesized on silica support by an optimized secondary growth method which combines ageing and rubbing with the use of enhanced synthesis gel. The enhanced synthesis gel was prepared by the addition of SAPO-34 crystals into the synthesis gel. Results of XRD and IR-ATR analysis of SAPO-34 seeds confirmed the formation of SAPO-34 crystal. SEM analysis showed that the crystal has cubic form and the size was about 200-400 nm. The resultant crystals were then used for the preparation of SAPO-34 membrane on the inner surface of the tubular silica support. XRD and XRF analysis showed that SAPO-34 layer was successfully formed on the membrane support with Si/Al ratio of 0.48-0.49. SEM images showed that the optimized secondary growth method could produce continuous and defect-free SAPO-34 membrane (SAPO-34-M2). In contrast, membrane prepared by rubbing method with conventional synthesis gel (SAPO-34-M1) displayed discontinued and defects layer. In single-gas permeation test, SAPO-34-M2 membrane showed two regions of N-2 flux indicating the drastic effect of concentration polarization on N-2 permeation at higher pressure. The concentration polarization phenomenon resulted in a decrease of CO2/N-2 selectivity with increasing transmembrane pressure. It was demonstrated by single-gas permeation test that the SAPO-34-M2 membrane could surpass the Robeson plot (2008) for CO2/N-2 separation (permeance = 2.01 x 10(-6) mol/m(2) s Pa; the highest selectivity = 53). The results showed that the prepared SAPO-34 membrane could be an alternative for CO2/N-2 separation.