![]() ![]() Recently, we reported that all-silica ZSM-58 zeolites can be used to afford high-purity DDR-type zeolite membranes with CO 2/CH 4 and CO 2/N 2 separation performances equivalent to those previously reported for DD3R membranes. Therefore, we speculated that RTP treatment would result in crack suppression of Al-containing DDR-type zeolite membranes due to the concentration of silanol in the zeolite increasing with the Al concentration, and ZSM-58 zeolite has DDR topology. ![]() On the other hand, ZSM-58 has the DDR topology of Al-containing zeolites and is reported to have a Si/Al molar ratio of 20–∞. reported that RTP did not affect DD3R zeolite membranes because of the low concentration of surface silanols in all-silica zeolite. RTP has been applied to some membranes, such as CHA and MFI. RTP is a preprocessing method in which the zeolite membrane is rapidly heated and then cooled, and cracks can be suppressed during high-temperature calcination by increasing the bonding strength among zeolites during this process. The ozone detemplate method has been applied not only to DDR-type zeolite (DD3R, ZSM-58) membranes but also to other zeolite membranes. The ozone detemplate method can remove SDAs at lower temperatures than the conventional thermal detemplate method. Possible approaches in suppressing crack formation include the ozone detemplate method and rapid thermal processing (RTP). Therefore, inhibiting the occurrence of cracks to obtain membranes with a high gas separation performance is necessary. In fact, some researchers have reported that cracks form on DDR-type zeolite membranes during high-temperature calcination. Moreover, 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. Various phases might be generated from the target zeolite when the zeolite is synthesized on a porous substrate. However, producing these membranes is challenging. For example, DDR-type zeolites have pore sizes of 0.36 nm × 0.44 nm therefore, their application as a membrane material has been studied for the separation of CO 2 (0.33 nm) from natural and digestive gases. They can be used in gas separation membranes, in which a porous substrate is covered by a thin zeolite layer. Zeolites have been investigated due to their unique crystal structures. ![]() The results demonstrate that Al-containing ZSM-58 zeolite membranes with high CO 2 permeance and CO 2/CH 4 selectivity and minimal cracking can be produced by using 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. Al-containing ZSM-58 zeolites had higher silanol concentrations than all-silica zeolites, confirming many silanol condensations by RTP. 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. An all-silica ZSM-58 membrane without cracks was obtained by only using the ozone detemplating method. 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 CO 2/CH 4 selectivity. 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. 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. 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. ![]()
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