Study On Preparation And Carbonylation Of Dimethyl Ether Of Zeolites

Zeolites have wide application prospect,even though its hydrothermal synthesis is still a"black box"and the impact factors are numerous and complex.Therefore,the researches of optimizing synthesis conditions on the basis of theoretical experience to get suitable catalysts for catalytic reaction are worth exploring more and more.Carbonylation of dimethyl ether to methyl acetate is the technical core in the process of syngas to ethanol.The scientific problem involved in this reaction is that CO is inserted into CH3-O to achieve C-C bond coupling at acidic sites in zeolite channels.In this paper,considering that zeolites with different structures and properties have different degrees of influence on the carbonylation of dimethyl ether,by synthesizing zeolites with different topological structures and acid distributions,the carbonylation performance of the catalyst has been greatly improved.（1）The synthesis of aluminosilicate zeolites by using piperazine as the organic structure directing agent（OSDA）was studied.Zeolites ZSM-4（MAZ）,Mordenite（MOR）,ZSM-35（FER）,ZSM-5（MFI）and ZSM-12（MTW）,these five different zeolites with different topological structures were obtained as SiO₂/Al₂O₃ ratio in the initial gel composition changed,of which piperazine fits best with the FER structure.The obtained FER zeolite has a hierarchical micro/mesopore texture with micropores inside the plate zeolite crystals and mesopores formed by interplate assembling,and this kind of hierarchical structure is thought to be beneficial for the reduction of molecule diffusion limitation.The ZSM-4,mordenite and ZSM-35 zeolites（in acidic form）which contain eight-ring channel（8MR）were tested for the dimethyl ether carbonylation reaction,the essential role of 12MR pore in mordenite for molecule transportation to the 8MR pore and the relatively higher stability of ZSM-35 were proved.（2）H-ZSM-35 zeolites were synthesized with different kinds of templates,including piperazine,pyrrolidine and tetrahydrofuran.It was found that compared with piperazine and pyrrolidine templates,the activity and stability of carbonylation reaction of dimethyl ether catalyzed by ZSM-35 zeolites prepared with tetrahydrofuran templats were significantly improved.The conversion of the former was¹7%at the highest,and decreased to¹2%after20 hours of reaction;the highest conversion of the latter was³0%,which was reduced to¹5%after 200 h of continuous reaction,and the selectivity of the two kinds of zeolites remained above 95%.Ammonia temperature-programmed desorption（NH₃-TPD）and pyridine adsorption infrared spectrum（Py-IR）analysis showed that the ZSM-35 zeolites obtained by tetrahydrofuran templates had more and stronger Br?nsted acid sites,and they tended to be distributed in small pore channels inaccessible to pyridine.