甲醇制乙烯和二甲醚反应机理研讨

Reaction Mechanism of Methanol to Ethylene and Dimethyl Ether

以杂化轨道理论和关于含Si、Al元素催化剂酸中心认识为理论依据和研究方法,以甲醇分子中C、H原子与催化剂B酸中心中Al原子相互作用为切入点,分析催化剂B酸中心中Al原子外层电子轨道变化与甲醇分子中C原子外层电子轨道变化间的相互关系,探讨甲醇制乙烯、二甲醚的反应机理。结果发现:中间体H-form C↑↓〇H2是构成乙烯、二甲醚的基本结构单元;甲醇制乙烯、二甲醚反应机理分3步:(1)B酸中心释放H+攻击甲醇分子中C-O键,C-O键断裂生成甲基碳正离子(CH3+),B酸中心失去活性;(2)失活B酸中心从CH3+中获得H+恢复活性,CH3+失去H+生成中间体C↑↓〇H2;(3)2个中间体C↑↓〇H2结合生成乙烯和二甲醚。

Based on the hybrid orbital theory,knowledge of acid center of silicon and aluminum-containing catalysts and the mutual interaction between the reactant and catalyst B-acid center,the molecular structure of methanol and B-acid center in the interaction process are investigated.Through the above studies,the natures of reaction mechanisms of methanol to ethylene and dimethyl ether are understood.It is found that methanol to ethylene and dimethyl ether under the action of B-acid center can be divided into three steps:In the first step,B-acid center provides hydrogen proton(H+)to attack C-O bond in methanol molecular,and C-O bond breaks to form methyl carbocation(CH3+)and water molecule.The outer layer of carbon atom of CH3+has an empty orbit,but B-acid center after releasing hydrogen proton(H+)loses its activity.In the second step,inactivated B-acid center obtains hydrogen proton(H+)from CH3+,and the reaction produces a new intermediate H-form C↑↓〇H2(the double arrow represents the lone pair e-,and circle represents empty orbit)which has a pair of lone pairs of electrons(e-)and an empty orbit.Thus,inactive B-acid center recovers the activity after obtaining hydrogen proton(H+).H-form C↑↓〇H2 is the basic structural unit of ethylene and dimethyl ether.In the third step,two C↑↓〇H2 form ethylene,and two C↑↓〇H2 and one water molecule form dimethyl ether.