Rational Synthesis of Chabazite (CHA) Zeolites with Controlled Si/Al Ratio and Their CO2/CH4/N2 Adsorptive Separation Performances

Abstract Separation of CO 2 from CH 4 and N 2 is of great significance from the perspectives of energy production and environment protection. In this work, we report the rational synthesis of chabazite (CHA) zeolites with controlled Si/Al ratio by using N , N , N ‐trimethyl‐1‐adamantammonium hydroxide (TMAdaOH) as an organic structure‐directing agent, wherein the dependence of TMAdaOH consumption on the initial Si/Al ratio was investigated systematically. More TMAdaOH is required to direct the crystallization of CHA with higher Si/Al ratio. Once the product Si/Al ratio is larger than 24, the amount of TMAdaOH consumption remains nearly constant. CHA zeolites with different Si/Al ratios and charge‐compensating cations were then applied for the separation of CO 2 /CH 4 /N 2 mixtures. The equilibrium selectivities predicted by ideal adsorbed solution theory (IAST) and ideal selectivities calculated from the ratio of Henry's constants for both CO 2 /CH 4 and CO 2 /N 2 decrease with the zeolite Si/Al ratio increasing, whereas the percentage regenerability of CO 2 presents the opposite trend. Therefore, there is a trade‐off between adsorption selectivity and regenerability for the adsorbents. There is a weaker interaction between CO 2 molecules and the H‐type zeolites than that on the Na‐type ones, thus a higher regenerability can be achieved. This study indicates that it is possible to design CHA zeolites with different physicochemical properties to meet various adsorptive separation requirements.