甲醇制烯烃反应工艺、反应机理及其动力学研究进展

Progresses in reaction processes,mechanism and kinetics of methanol to olefins

甲醇制烯烃工艺近年来已成为煤化工领域的研究热点。不同的甲醇制烯烃催化剂将导致不同的反应过程,以SAPO-34为催化剂时,甲醇主要遵循烃池机理,通过快速的平行反应直接生产乙烯和丙烯(MTO)等低碳烯烃;以ZSM-5为催化剂时,甲醇主要遵循双循环机理中的烯烃循环机理,通过甲基化-裂解等多步反应间接生产丙烯(MTP)。这种反应特征的不同也决定着反应器类型和工艺条件的不同:SAPO-34催化剂易失活的特性决定了工业MTO过程通常采用易再生的流化床反应器从甲醇一步生成乙烯和丙烯,而具有良好抗结焦能力的ZSM-5催化剂使得工业MTP过程通常选择易放大的固定床反应器,通过大量烯烃循环与分离逐步获得丙烯。针对SAPO-34催化剂上MTO过程以及ZSM-5催化剂上MTP过程的不同反应情况,综述了近年来甲醇制烯烃代表性的反应工艺、反应机理以及反应动力学等方面的研究进展,并根据其存在的问题提出了相应的发展方向。

Methanol to olefins process has recently been a hot research topic in modern coal chemical industry.However,reaction mechanism and kinetic behavior differ greatly in case of different catalysts.Methanol-to-Olefins(MTO)over SAPO-34 catalyst is a direct conversion process following hydrocarbon pool mechanism,with methanol mainly transforming to ethylene and propylene rapidly through parallel reaction steps.On the contrary,Methanol-to-Propene(MTP)over ZSM-5 catalyst is a complex interconversion process and the propene comes mainly from methylation and cracking processes via the alkene cycle of dual-cycle mechanism.Hence,suitable reactors and different operating conditions must be chosen for commercial MTO or MTP processes.Ethene and propene can be produced over easily deactivated SAPO-34 catalyst in the commercial MTO process by one step in fluidized bed reactor,whereas fixed bed reactor is generally applied in the commercial MTP process over ZSM-5 catalyst with better anti-coking capability,and olefins should be separated and recycled for the maximum production of propene.In order to give a comprehensive understanding of methanol transformation over the SAPO-34 and ZSM-5 catalysts,advance in typical commercial reaction processes,mechanism and kinetics research of methanol to olefins(MTO/MTP)process would be reviewed in this paper.According to the existing problems and challenges,the prospective tendencies of methanol to olefins process are also proposed.