正己烷催化裂解制低碳烯烃:ZSM-5分子筛催化剂酸性的影响

Catalytic cracking of n-hexane to light olefins:effects of acidity of ZSM-5 catalyst

在小型固定床装置上,以ZSM-5分子筛为催化剂,研究不同硅铝物质的量比对合成的ZSM-5分子筛织构性能以及酸性对正己烷催化裂解性能的影响。采用XRD、SEM、N2吸附-脱附和NH3-TPD等方法对不同硅铝物质的量比的ZSM-5分子筛进行表征,结果表明,硅铝物质的量比的改变对ZSM-5分子筛的形貌和结构没有影响;随着硅铝物质的量比的增加,分子筛的酸量减少,酸强度减弱,正己烷催化裂解活性逐渐降低。同时,随着酸量减少和酸强度减弱,高硅ZSM-5分子筛上氢转移反应得到明显抑制,丙烯选择性提高。

Effects of SiO2/Al2O3 molar ratio on textural characteristics and acidity of ZSM-5 zeolite on catalytic cracking of n-hexane to light olefins were investigated in a fixed bed reactor. ZSM-5 zeolites with different SiO2/Al2O3 molar ratio were characterized by XRD, SEM, BET and NH3-TPD. It was found that SiO2/Al2O3 molar ratio had little effect on morphology and structure of synthesized ZSM-5 zeolites. Acidity and strongly acidic sites decreased with increasing SiO2/Al2O3 molar ratio. Correspondingly, activity of the ZSM-5 catalysts for conversion of n-hexane to olefins declined. Hydrogen transfer reactions on the catalysts with higher SiO2/Al2O3 molar ratio were obviously restrained with the decreasing acidity and strongly acidic sites, resulting in high selectivity to propylene.