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 CO2 as aluminosilicate zeolites, can be used as promising candidate materials for selective adsorption and separation of CO2. 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 CO2 adsorption capacity (64.1 cm3/g) than the conventional K-SAPO-34 prepared by ion-exchange (1.9 cm3/g). Moreover, the K-SAPO-34 in this work has a superior separation performance for CO2/N2 and CO2/CH4.