甲醇耦合轻烃反应制芳烃/烯烃研究进展与经济性分析

Advances and economical analysis in the coupling reaction of methanol with hydrocarbons for aromatics/olefins

近年来,利用廉价易得的甲醇与低附加值轻烃进行耦合反应制烯烃或芳烃,赢得了许多研究学者的关注。经过研究证实了耦合反应过程不仅存在热量耦合互供情况,而且反应物之间也发生了耦合作用。本文首先从催化剂研究、工艺技术开发及反应机理等方面介绍了甲醇耦合轻烃反应的研究进展,到目前为止,甲醇耦合轻烃反应研究大多处于实验室基础研究阶段,反应主要以ZSM-5、ZSM-5/ZSM-11、ZSM-11分子筛及对上述三种分子筛进行改性后的分子筛为催化剂;其工艺技术主要利用固定床和流化床反应工艺技术;同时反应机理研究得到耦合反应中单分子反应机理和双分子反应机理可能同时存在,在低转化率和较高反应温度时,反应通过单分子进攻B酸性位的C—H键或C—C键,生成五配位碳正离子,在这种反应机理中高能量过渡态决定了高活化能,单分子反应机理占主导;而当转化率较高和低反应温度时,双分子反应机理占主导,反应过程中被吸附的化合物将发生异构化、β断裂和烯烃的烷基化反应。最后,在实验基础上进行了甲醇耦合轻烃经济性分析。

In recent years, the coupling reaction of cheap, accessible methanol and low value-added light hycarbons for olefins or aromatics has won the attention of people. It has been proved that the reaction had coupling heat and interaction in the reaction. In this paper, the research of methanol coupled light hydrocarbon reaction was introduced from the aspects of the catalyst research, technology development and reaction mechanism, which was in the stage of laboratory, and the main catalysts of coupling reaction were ZSM-5, ZSM-5/ZSM-11, ZSM-11 zeolites and their modification forms. The technology included fixed bed and fluid bed. The possible reaction mechanism was as follows: there are two kinds of reaction mechnism in the coupling reaction of methanol and light hydrocarbons, including monomolecular and bimolecular mechanism. Usually, under conditons of low conversion and high temperature, the initial reaction occurred by a monomolecular attacked by the Bronsted acid site on C-H or C-C bonds. This attack resulted in an adsorbed high-energy pentacoordinate carbonium ion, which decomposes toa smaller alkane(or H2) and an adsorbed carbenium ion. At higher conversion and low temperature, the bimolecular mechanism became the prevailing pathway involving the transfer of a hydride ion between the reactant alkane and an adsorbed carbenium ion derived from decompose of carbonium ion or the adsorption of an alkene on a Bronsted acid site. These adsorbed species then undergo isomerization, β-scission, and alkylation of alkenes.