Template-free synthesis of low-silica chabazite zeolite aggregates in K+/Sr2+ system by in situ hydrothermal growth

Separating CO 2 and N 2 from CH 4 is crucial for energy production and environmental protection. This study showed the rapid synthesis of CHA zeolites with different morphologies using an in situ growth method, without the assistance of organic structure directing agents (OSDA) or fluoride media. The crystallization behavior of CHA zeolites was studied in terms of synthesis gel composition (including water content, silicon and aluminum content, alkalinity and Sr 2+ concentration), synthesis temperature and duration. The results suggested that pure phase CHA zeolite nano-aggregates could be synthesized with broad precursor conditions at 150 °C for only 4 h. Then, K-CHA zeolite was ion-exchanged to Na-CHA and Ca-CHA and the adsorption properties of CHA zeolites with different morphologies and ions were studied. The results suggested that Na-CHA exhibited highest CH 4 , CO 2 and N 2 adsorption capacity and showed higher ideal selectivity for N 2 /H 2 ; Although Ca-CHA zeolites exhibited relative lower CO 2 and CH 4 adsorption capacity, it exhibited the highest ideal selectivity for CO 2 /CH 4 ; Simultaneously, K-CHA zeolite exhibited high CH 4 adsorption capacity and high adsorption separation ability of CH 4 /N 2 . Furthermore, breakthrough experiments have confirmed the practical feasibility of separating CO 2 from CH 4 .