Microwave-assisted Seeded Growth Of SAPO-34Membranes And Their Applications For CO₂/CH₄Gas Separation

SAPO-34with satisfactory thermal, hydrothermal and mechanical stabilities andgood erosion resistance performance has been widely used for methanol to olefins(MTO) and CO2/CH4gas separation process due to its medium acid strength,uniform-sized pores of molecular dimensions and unique molecular sieveperformance. Much work has been reported about SAPO-34molecular sieves andSAPO-34membranes. In this work, some reports on SAPO-34were summarized andwhat we have done is mainly demonstrated as follows:Randomly oriented SAPO-34membranes were prepared on porous α-Al2O3substrates by seeded growth method under microwave irradiation. Synthesisconditions including seed layer, substrate setting, synthesis time, aging time andheating method were optimized for seeded growth to get ultra-thin and defect freeSAPO-34membranes. Well intergrown SAPO-34membranes can be obtained withseeds smaller than1μm and the seeded supports facing upwards under microwaveheating for4h and aging time for24h. Membrane synthesis time was significantlyshortened by microwave heating for4h as compared to conventional heating for24h.The membrane was about1.5μm thick for microwave heating, while it was5μmthick for conventional heating. The gas-mixture separation tests which were carriedout at303K gave the average CO2/CH4selectivity of81and CO2permeance of6.6×10-7mol m-2s-1Pa-1for138kPa pressure drop.Microwave irradiation was used to prepare SAPO-34membranes on α-Al2O3substrates using seeded growth method at180°C for4h. SAPO-34membranes withdifferent orientations were obtained by optimizing synthesis parameters includingwater content, aging time and synthesis procedure, which were confirmed by thecharacterization using scanning electron microscopy (SEM) and X-ray diffraction(XRD). The1.7μm thick and preferentially oriented SAPO-34membrane wassynthesized and the1.5μm thick and randomly oriented SAPO-34membrane wasalso prepared. The CO2/CH4gas separation results indicated that CO2permeance ofthe preferentially oriented SAPO-34membrane was much larger than that of therandomly oriented SAPO-34membrane, while comparable CO2/CH4separationselectivity was obtained. Orientation can improve CO2permeance largely with little effect on CO2/CH4separation selectivity. The CO2permeance was as high as1.2×10-6mol m-2s-1Pa-1and CO2/CH4separation selectivity was reached to89by performingthe thin and preferentially oriented SAPO-34membrane at303K and138kPapressure drop.