Size Effect of HZSM-5 Zeolite on Catalytic Conversion of Methanol to Propylene

Catalytic conversion of methanol to propylene(MTP) by HZSM-5 zeolite is of great importance in industrial applications.In this paper,a series of HZSM-5 zeolites with different crystal sizes were synthesized by adjusting the initial gel composition,crystallization temperature,and crystallization time.The crystal structure,size,morphology,pore structure,and acidity of HZSM-5 were investigated by X-ray diffraction(XRD),scanning electron microscopy(SEM),nitrogen adsorption,and temperature-programmed desorption of ammonia(NH3-TPD).The catalytic activity and stability of HZSM-5 with different crystal sizes for MTP were evaluated on a continuous flowing fixed-bed reactor.Coke deposited on HZSM-5 was analyzed by thermogravimetric(TG) analyzer.Results indicated that with smaller crystal size,HZSM-5 zeolite had larger surface area and pore volume,higher density of pore openings,and shorter path length of micropore channels that prevent side reactions.For MTP reaction,smaller crystal sizes of HZSM-5 showed a higher resistance and better tolerance to coke,and longer catalytic lifetime.The lowering of both the total and strong acidity on HZSM-5 with smaller crystal size favored a higher selectivity of target product,propylene.