Effect of Crystallization Growth Inhibitors in the Synthesis of Sapo-34

Surendar Reddy Venna and Moises A Carreon. Chemical Engineering Department, University of Louisville, Ernst hall, Chemical Engineering Department, Belknap campus, Louisville, KY 40292

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 Ám to ~0.5 Ám. 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 Ám SAPO-34 crystals can be potentially used as seeds to prepare the thin membranes on porous supports to separate the CO2 from CH4 Čto increase the energy content of the natural gas.