Thermodynamic Analysis Of Methyl Methacrylate Synthesis Over Coal-Based Route And Catalytic Behavior Regulation Of Intermediate Products

Methyl methacrylate(MMA)is an important monomer for the production of poly methyl methacrylate,whose synthesis mainly includes acetone cyanohydrin,isobutylene oxidation and methyl acetate method.Among these,the methyl acetate method over coal-based route involves the two-step aldol condensation of formaldehyde and hydrogenation of methyl acrylate.Considering the energy resources structure and distribution of our country,this method has recently attracted extensive attention to produce MMA.On the other hand,in light of methanol as the main product of coal chemical industry,it is highly expected to use methanol as the resource to provide formaldehyde and H2 via direct dehydrogenation.As a result,the direct synthesis of MMA from methyl acetate and methanol could potentially shorten the production process and improve the atom ultilization efficiency.In this thesis,an attempt was made to study the direct synthesis of MMA from methanol and methyl acetate by combining thermodynamic and kinetic studies.Firstly,the feasibility of the process is analyzed by thermodynamic calculation,then the catalytic behavior of the intermediate products is regulated by kinetic experiments,with the aim to developing highly efficient and selective catalysts for dehydrogenation and aldol condensation.The main results are summarized as follows:(1)A reaction network for the direct synthesis of MMA from methanol and methyl acetate is established,in which methyl acrylate and methyl propionate are considered as reaction intermediates.It is found that this route is feasible in thermodynamics,which is mainly limited by the methanol dehydrogenation with a small equilibrium constant.Furthermore,it is found that the reaction temperature and the ratio of methanol to methyl acetate have great influences on the products distribution.Typically,MMA remains as the main product in the temperature range of 300-400℃ and the ratio of more than 2.(2)The support effects of Ce2(MoO4)3-catalyzed direct dehydrogenation of methanol to formaldehyde are explored,in which the regulation mechanism of acid-base sites on the catalytic performance is clarified.It is revealed that the strong acidic sites could promote the activation of methanol to improve methanol conversion,while the strong basic sites lead to the occurrence of side reactions to decrease selectivity.Based on this,TiO2 supported catalyst shows the best catalytic performance because of its involved strong acidic and weak basic sites.(3)The support effects of CS/Al2O3 catalysts with different morphologies and crystal phases for the aldol condensation of formaldehyde and methyl acetate to methyl acrylate are investigated.It is found that too many acidic sites could promote the formation of formaldehyde-activated species and further condensation with methyl acrylate to decrease the selectivity;too many basic sites could inhibit the condensation reaction of methyl acetate when formaldehyde-activated species are insufficient to decrease the conversion.Therefore,it is highly desirable to achieve the synergy between the acidic and basic sites for this reaction,which can further increase the yield of methyl acrylate.