The silicoaluminophosphate molecular sieves have been the subject of great interest because of their high thermal resistance, mechanical strength, chemical stability, shape selectivity, chemical inertness, and uniform-sized pores of molecular dimensions. SAPO-34 with the composition of SixAlyPzO2 (x = 0.01-0.98, y = 0.01-0.6 & z = 0.01-0.52) is a representative type of silicoaluminophosphate zeolite displaying chabazite structure with uniform microporous channels and cages. SAPO-34 with pore size of ~0.38 nm is an ideal material for carbon dioxide (kinetic diameter of ~0.33 nm) separation from light gases. Also, it is widely used as catalyst in methanol to olefin reaction in petrochemical industries.

Here, we present the synthesis of SAPO-34 crystals using various crystal growth inhibitors (PEG, C12E6 & MB) and several structure directing agents (TEAOH, DPA, Morpholine, TEA & CTAB). Crystal growth inhibitors play an important role in changing the alkalinity of the synthesis of gel and during phase transition of SAPO-34. They also interact with reactive sites of the precursors suppressing the crystal growth. The resultant SAPO-34 crystals were characterized by BET, XRD, SEM, Raman, FTIR, TGA and CO2/CH4 adsorption. The incorporation of crystal growth inhibitors during synthesis led to a remarkable decrease in crystal size from ~2 µm to ~0.5 µm. The surface area of the SAPO-34 crystals was significantly improved from ~450 m2/g to ~700 m2/g. The crystallinity of SAPO-34 was confirmed by XRD and FTIR. These ~0.5 µm SAPO-34 crystals can be potentially used as seeds to prepare the thin membranes on porous supports to separate the CO2 from CH4 ¬to increase the energy content of the natural gas.