The effects of solvents on the modification of SAPO-34 zeolite using 3-aminopropyl trimethoxy silane for the preparation of asymmetric polysulfone mixed matrix membrane in the application of CO2 separation

Abstract

SAPO-34 zeolite is the ideal porous filler in Mixed matrix membranes (MMMs) for CO2 separation because it has strong affinity towards CO2 and pore size (0.38nm) which is nearly similar to the molecular sizes of various gasses in natural gas. However, the poor compatibility between zeolite and polymeric matrix causes the formation of non-selective interfacial voids, leading to poor separation of gasses. In this work, 3-aminopropyl trimethoxy silane (APMS) was proposed to modify SAPO-34 zeolite before adding into asymmetric polysulfone (PSf) MMMs prepared via dry–wet phase inversion. The effects of solvent (ethanol or isopropanol) in grafting reaction were studied. The changes in FTIR spectra of both modified SAPO-34 zeolite samples signified that more silane molecules were grafted when ethanol was used. SAPO-34 zeolite dispersed evenly in PSf matrix after modification as shown in EDX analysis. Although showing similar FTIR spectra and morphology, a great improvement in CO2 selectivity and permeance was only shown by PSf/SAPO-34E MMMs with zeolite modified using APMS in ethanol. The highest CO2/N2 selectivity of 28, CO2/CH4 selectivity of 31 and a satisfactory CO2 permeance of 706 GPU were achieved. Besides reduction of filler agglomeration, the improvement could be related to the diminished interfacial voids when SAPO-34 zeolite was modified using APMS in ethanol.