| Summary: | The polycrystalline CHA-type zeolite layer with Si/Al = 18 was formed on the porous α-Al<sub>2</sub>O<sub>3</sub> tube in this study, and the gas permeation properties were determined using single-component H<sub>2</sub>, CO<sub>2</sub>, N<sub>2</sub>, CH<sub>4</sub>, <i>n</i>-C<sub>4</sub>H<sub>10</sub>, and SF<sub>6</sub> at 303–473 K. The membrane showed permeation behavior, wherein the permeance reduced with the molecular size, attributed to the effect of molecular sieving. The separation performances were also determined using the equimolar mixtures of N<sub>2</sub>–SF<sub>6</sub>, CO<sub>2</sub>–N<sub>2</sub>, and CO<sub>2</sub>–CH<sub>4</sub>. As a result, the N<sub>2</sub>/SF<sub>6</sub> and CO<sub>2</sub>/CH<sub>4</sub> selectivities were as high as 710 and 240, respectively. However, the CO<sub>2</sub>/N<sub>2</sub> selectivity was only 25. These results propose that the high-silica CHA-type zeolite membrane is suitable for the separation of CO<sub>2</sub> from CH<sub>4</sub> by the effect of molecular sieving.
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