Silica sol gel assisted defect patching of SSZ-13 zeolite membranes for CO2/CH4 separation

Abstract

• Silica sol post-treatment effectively patched defects of SSZ-13 zeolite membrane. • Ethanol content of silica sol is a significant parameter in defect patching process. • More than 6-fold increase in selectivity is achieved for CO 2 /CH 4 mixed gas test. • The modified SSZ-13 membrane has superior performance in Robeson plot of CO 2 /CH 4. Intercrystalline defects are commonly present in zeolite membranes formed during membrane synthesis and calcination process. Therefore, the selection of a suitable post-treatment method is of particular importance. In this work, SSZ-13 membrane defects were significantly reduced by dipping in the different ethanol/TEOS molar ratios of the silica sol solutions. Characterizations including FTIR, FESEM, EDX, BET, and gas adsorption isotherms of CO 2 and CH 4 revealed that silanes groups were properly placed on the surface of the zeolite while the crystal structure and zeolitic pores remained intact. Permporometry analysis was also carried out to find the effectiveness of the applied patching method. Permeation of CO 2 and CH 4 and CO 2 /CH 4 ideal and mixture selectivity through the fresh and improved membranes was investigated. The results showed that ethanol/TEOS molar ratio of 95.5 increased the single gas selectivity from 33 to 176 at 30 °C and the pressure difference of 100 kPa, while the permeation of CO 2 declined by 15%. In the mixed gas conditions, the selectivity of CO 2 /CH 4 reached a really high value of 660, proving that this post-treatment modification is very effective in SSZ-13 zeolite membrane.