Coal-based Enol/Vigabatrin Catalytic Reaction Kinetic,Mechanistic And Process Study

Enol/vigabatrin are bothα,β-unsaturated compounds and are an important organic intermediate.Methallyl alcohol（MAA）and acrylic acid（AA）are typical enol/vigabatrin compounds that are used in a wide range of applications including food,pharmaceuticals and fragrances respectively.As a high value-added chemical,MAA and AA are usually synthesized using traditional petroleum routes.With the increasing scarcity of petroleum resources and China’s basic situation of"rich in coal and poor in oil and gas",the development of a new coal-based route for the synthesis of MAA and AA is a green,economic and sustainable synthetic route.The synthesis of MAA through the hydrogen transfer reaction of methacrolein and the synthesis of AA through the aldol condensation reaction of acetic acid and formaldehyde are very economical coal-based synthetic routes,providing an important way for coal chemical companies to enter the field of MAA and AA synthesis technology.In this study,a new process of synthesizing MAA by hydrogen transfer reaction and AA by aldol condensation reaction was proposed,and the kinetics and reaction mechanism of hydrogen transfer reaction and aldol condensation reaction were systematically studied,the effect regulation of catalytic reaction process was investigated,and the mechanism of catalytic action was revealed,the main research contents and results are as follows:（1）The reaction process for the synthesis of MAA by the homogeneous phase catalytic hydrogen transfer reaction of methacrolein with isopropanolic aluminium（Al（OPrⁱ）₃）was investigated.Isopropanol（IPA）was selected as the best hydrogen donor for the hydrogen transfer reaction.The effect of catalyst amount,molar ratio of raw materials,reaction temperature and reaction time on the hydrogen transfer reaction was investigated,and the optimal conditions for the hydrogen transfer reaction were optimized by using response surface analysis（RSM）,and the optimal conditions for the hydrogen transfer reaction were determined as follows:reaction temperature 70℃,reaction time 180 min,n（MAL）:n（IPA）:（catalyst）=1:3:0.1,and the MAL conversion was 89%and the MAA selectivity was 93.1%under these conditions.The effect of reaction temperature and reaction time on the hydrogen transfer reaction was investigated in a tubular reactor,which showed that the hydrogen transfer reaction could be carried out continuously and stably at high temperature,and the reaction time could be shortened and the production efficiency improved.The reaction kinetics of MAA synthesis by MAL and IPA hydrogen transfer reaction was studied,and the reaction kinetic equation was constructed to obtain the hydrogen transfer reaction as a primary reaction with an activation energy of 49.02 k J/mol.The density functional theory（DFT）was used to study the mechanism of hydrogen transfer reaction,explore the catalytic mechanism between reactants and catalysts,and obtain the microscopic mechanism of hydrogen transfer reaction for the synthesis of MAA by MAL.（2）A study of the reaction process of VPO/γ-Al₂O₃-catalyzed aldol condensation reaction of acetic acid and formaldehyde hydroxyl aldehyde for the synthesis of AA.The VPO/γ-Al₂O₃ acid-base bifunctional catalyst was designed and synthesized,and the catalyst was characterized by XRD,SEM,CO₂/NH₃-TPD,FT-IR,etc.The effects of the active component loading and calcination temperature on the catalyst properties were investigated,and the results showed that the calcination temperature was 350℃and the VPO loading was 60%,and the catalyst had excellent active crystalline phase composition,and ball-milledγ-Al₂O₃ support improved the dispersion of the active components and reduced the thermal decomposition temperature of the catalyst.The effect of different reaction conditions（loading,molar ratio of raw materials,reaction temperature and space velocity）on the aldol condensation reaction was investigated,and the optimum conditions for the aldol condensation reaction were determined using RSM:60%loading of VPO,reaction temperature of 350℃,reaction space velocity of 1.2 h^-1,n（acetic acid）:n（formaldehyde）=5:1,and the yield of AA under these conditions was 51.5%.Further study of the reaction kinetics of the synthesis of AA by the aldol condensation reaction of acetic acid and formaldehyde yielded a aldol condensation reaction order of 1.67 and a reaction activation energy of 36.59 k J/mol.