Abstract
The synthesis of DDR-type zeolite membranes faces the problem of cracks that occur on the zeolite membrane due to differences in the thermal expansion coefficient between zeolite and the porous substrate during the detemplating process. In this study, Al-containing ZSM-58 zeolite membranes with DDR topology were prepared by rapid thermal processing (RTP), with the aim of developing a reproducible method for preparing DDR zeolite membrane without cracks. Moreover, we verified the influence of RTP before performing conventional thermal calcination (CTC) on ZSM-58 membranes with various silica-to-aluminum (Si/Al) molar ratios. Using the developed method, an Al-containing ZSM-58 membrane without cracks was obtained, along with complete template removal by RTP, and it had higher CO2/CH4 selectivity. An all-silica ZSM-58 membrane without cracks was obtained by only using the ozone detemplating method. ZSM-58 crystals and membranes with various Si/Al molar ratios were analyzed by using Fourier-transform infrared (FTIR) spectroscopy to confirm the effects of RTP treatment. Al-containing ZSM-58 zeolites had higher silanol concentrations than all-silica zeolites, confirming many silanol condensations by RTP. The condensation of silanol forms results in the formation of siloxane bonds and stronger resistance to thermal stress; therefore, RTP caused crack suppression in Al-containing ZSM-58 membranes. The results demonstrate that Al-containing ZSM-58 zeolite membranes with high CO2 permeance and CO2/CH4 selectivity and minimal cracking can be produced by using RTP.
Highlights
Zeolites have been investigated due to their unique crystal structures
The production of many zeolites requires organic structure-directing agents (SDAs), which eventually need to be removed from the framework using high temperatures, which generates cracks due to differences in the thermal expansion coefficients between zeolite and the porous substrate [9,10]
We examined the synthesis conditions of Al-containing ZSM-58 zeolite membranes as well as the effect of rapid thermal processing (RTP) treatment on ZSM-58 membranes with various Si/Al molar ratios
Summary
Zeolites have been investigated due to their unique crystal structures They can be used in gas separation membranes, in which a porous substrate is covered by a thin zeolite layer. DDR-type zeolites have pore sizes of 0.36 nm × 0.44 nm; their application as a membrane material has been studied for the separation of CO2 (0.33 nm) from natural and digestive gases [1,2,3,4,5,6,7,8]. The production of many zeolites requires organic structure-directing agents (SDAs), which eventually need to be removed from the framework using high temperatures, which generates cracks due to differences in the thermal expansion coefficients between zeolite and the porous substrate [9,10]. The as-made MTI was washed with ethanol and dried at 343 K
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