Organic template-free synthesis of K-SAPO-34 zeolite for efficient CO2 separation

Silicoaluminophosphate (SAPO) zeolites as one of the most important members of zeolitic materials, providing equally high adsorption capacity of CO 2 as aluminosilicate zeolites, can be used as promising candidate materials for selective adsorption and separation of CO 2 . In this work, desirable from both economic and environmental viewpoints, a green and cost-effective one step synthesis strategy of K-SAPO-34 zeolite was developed in a wholly inorganic system under hydrothermal conditions. The pure K-SAPO-34 crystals can be obtained in a wide range of initial gel compositions. The as-synthesized K-SAPO-34 has high proportion of framework Si (Si / (Si + Al + P) = 0.37) and framework charge density ((Al – P) / (Si + Al + P) = 0.36). Because the presence of silica islands in K-SAPO-34 framework leads to a decrease in the number of extra framework cations per unit cell, the K-SAPO-34 in this work has a high CO 2 adsorption capacity (64.1 cm 3 /g) than the conventional K-SAPO-34 prepared by ion-exchange (1.9 cm 3 /g). Moreover, the K-SAPO-34 in this work has a superior separation performance for CO 2 /N 2 and CO 2 /CH 4 .