不同结构分子筛的甲醇制丙烯催化性能

在常压、空速为1.5 h^-1、反应温度为450℃条件下,考察了4种具有不同拓扑结构的分子筛(SAPO-34、ZSM-48、ZSM-5和beta)在甲醇转化制丙烯(MTP)反应中的催化性能,并对催化剂的积炭失活行为进行了研究。结果表明,从8元环到12元环,分子筛孔口尺寸越小,低碳烯烃(乙烯+丙烯)选择性越高,积炭失活速率也越快。孔道尺寸越大,丙烯/乙烯(P/E)比越高,但产物分布向C₄以上组分偏移,丙烯选择性降低。10元环分子筛具有较高的丙烯选择性,但催化剂的积炭失活速率随孔道体系的不同有很大差异。一维直通孔道的ZSM-48容易积炭失活,而具有三维交叉孔结构的ZSM-5表现出了优异的抗积炭失活性能。不同结构分子筛在MTP反应中催化性能的差异主要归因于分子筛的过渡态择形和产物择形作用的不同。

Methanol to propylene reaction over zeolite catalysts with different topologies

Conversion of methanol to propylene(MTP)was comparatively studied over four zeolites with different topologies,em.e.SAPO-34,ZSM-48,ZSM-5 and beta at atmospheric pressure,450℃ and WHSV=1.5 h^-1.The correlations between product selectivity,catalyst stability and zeolite topology were investigated.Besides,coking behavior of the four zeolite catalysts during the reaction was also discussed.Among the studied catalysts,SAPO-34 with narrow 8-member ring openings showed the highest selectivity to light olefins(ethylene and propylene).However,it seems that the high density of acid site and the large cages of SAPO-34 resulted in an extremely fast coking deactivation.Beta zeolite with wide pore structure exhibited high propylene/ethylene(P/E)ratio,but the propylene selectivity was somewhat low due to the product distribution shifting towards heavier hydrocarbons.In contrast,ZSM-48 and ZSM-5 zeolite with 10-member ring openings gave higher propylene selectivity,but their deactivation rates were quite different.ZSM-48 zeolite with symmetrical straight channels underwent fast deactivation after a few hours on stream,while ZSM-5 zeolite with intersecting channel system presented superior resistance to coke deactivation.The significant difference in catalytic performance of the four zeolites could be mainly ascribed to the combined effect of shape selectivity for intermediates and products controlled by zeolites topology.