(568d) Microwave Assisted Preparation of SAPO-34 Crystals and Membranes

SAPO-34, a type of silicoaluminophosphate zeolite, is of particular interest because of its applications in gas separations, catalysis and adsorption, owing to their unique functional properties such as mechanical, chemical and thermal stability, shape selectivity, molecular sieving properties, and surface properties. SAPO-34 has been successfully employed in separation of CO₂ from CH₄, methanol transformation to olefin, trapping of hydrocarbon and thermo-chemical storage of heat. Synthesis of zeolites under microwave (MW) heating has several advantages over conventional hydrothermal synthesis methods, such as fast crystallization, phase selectivity, narrow particle size distribution, abundant nucleation, morphology and size control and rapid and uniform heating, leading to homogeneous thinner membranes.

In this work, SAPO-34 was synthesized under microwave (MW) heating. Homogeneous hexagonal crystals of pure SAPO-5 were formed after the gel was treated for 30 min and transformed to pure cubic SAPO-34 crystals after 500 min under MW heating. The synthesized SAPO-34 displayed small (~0.5 µm) and narrow particle size distribution. The prepared SAPO-34 by phase transition of SAPO-5 displayed CO₂/CH₄ adsorption ratios as high as ~29, making it highly attractive for CO₂/CH₄ gas separations. The small crystals with narrow particle size distribution of the synthesized SAPO-34 and short synthesis time make the MW heating an attractive approach for the preparation of zeolite membranes for CO₂ separation. The resultant SAPO-34 seeds synthesized under microwave heating were used for the preparation of membranes on porous γ-Al₂O₃ supports and tested in the separation of CO₂/CH₄ mixtures.