Vapor-phase Aldol Condensation Of Methyl Acetate With Formaldehyde Over Solid Acid-base Catalysts

Methyl acrylate is a kind of unsaturated carbonyl compounds,as the intermediate of organic synthesis and the monomer of macromolecule synthesis,widely used in the Pharmaceutical,leather,papermaking,adhesive,paint,et al.Currently,the production of methyl acrylate mostly include the acetylene process,acrylonitrile process,propylene oxidation method,propane oxidation method and aldol condensation of methyl acetate with formaldehyde.The first four methods rely on the production of petrochemical industry.While the energy structure of our country is more coal and less oil,which restrain these production processes.There are vast coal resources in our country,possessing the surplus of acetic acid production and large number of methyl acetate discharge as the waste liquid which pollute the environmental.The aldol condensation of methyl acetate with formaldehyde is the promising produce route,which gets rid of the petroleum process,low the cost and gain more benefit;at the same time,it can fully utilize the resources,reduce the waste and achieve high value-added product.The catalysts for aldol condensation of methyl acetate with formaldehyde include solid acid catalysts and solid base catalysts.Solid acid catalysts are the acidic properties compounds,PbO,MnO2,Al2O3,metal phosphate,metal borates,multicomponent oxides containing V?Nb?W and Mo.Solid acid catalysts have the problem:complex preparation process,difficulty to control the active component(V4+,V5+)and differences of the surface acid-base property.Solid base catalysts include alkali and alkaline earth metal supported on a support such as silica gel,aluminosilicate or molecular sieve,mixed metal oxides and hydrotalcite.Solid base catalysts have the advantage of easily producing and high catalytic activity.Therefore,it is meaningful to prepare the efficient,renewable and stable solid base catalysts.The condensation of methyl acetate with formaldehyde has been investigated over the solid base catalysts.The structures and surface properties of the catalysts are studied by different characterizations,and associated with the catalytic activity.The main experimental results and conclusions are as follows:1.The Cs/KIT-6 catalysts for the condensation of methyl acetate withformaldehydeThe solid base catalysts of alkali metal and alkaline earth metal supported silicon carrier are prepared by the incipient wetness impregnation method and applied to the aldol condensation of methyl acetate with formaldehyde.The experimental results show the optimal activate component is Cs species and the optimal support is silicon material.Calcination temperature 723K,reaction temperature 663K,Ma/FA=1/2,the 8Cs/KIT-6 catalyst shows the best catalytic activity:Ma conversion is 35.7%,and MA selectivity is 94.0%.The samples were characterized by XRD,FT-IR,N2 physisorption,ICP-MS,TEM,XPS and TPD.The results indicated that the cesium nitrate was highly dispersed on the KIT-6 support,and the formation of the Cs-O-Si species make the KIT-6 gaining more weak base sites.The catalytic activity probably associates with the weak base sites,and the 8Cs/KIT-6 catalyst shows the largest numbers of weak base sites for the best catalytic activity.2.Cs/SAB-15 catalysts for the aldol condensation of methyl acetate withformaldehydeA cesium ion-containing catalyst,on an SBA-15 mesoporous molecular sopport,was prepared by the impregnation method and applied to the aldol condensation of methyl acetate with formaldehyde.Calcination temperature 723K,reaction temperature 663K,Ma/FA=1/2,the 5Cs/SBA-15 catalyst demonstrated the highest(48.4%)conversion of methyl acetate reported and 95.0%selectivity for methyl acrylate.Characterizations indicated that the cesium nitrate below 5wt%loading was highly dispersed on the SBA-15 support,and the surface of catalysts is mostly weak base sites;the cesium nitrate above 5wt%loading was existed as the CsNO3 species on the SBA-15 support,and the surface of catalysts is mostly medium base sites;The 5Cs/SBA-15 catalyst shows the best catalytic activity.The deactivated catalyst was completely regenerated by calcination.The catalyst was regenerated 29 times with a total operation time of more than 300 h,and the initial conversion of methyl acetate was decreased with the time of regeneration.The decreasing of catalytic activity was mainly due to reduce of BET area and the Cs species content.3.B/AO catalysts for the aldol condensation of methyl acetate withformaldehydeThe solid base catalysts of alkali metal and alkaline earth metal supported AO carrier are prepared by the incipient wetness impregnation method and applied to the aldol condensation of methyl acetate with formaldehyde.The experimental results show the optimal activate component is B species and the optimal support is AO.Calcination temperature 550?,5wt%Bloading,reaction temperature 390?,Ma/FA=1/2,the 5 B/AO catalyst shows demonstrated the highest(41.4%)conversion of methyl acetate reported and 91.0%selectivity for methyl acrylateCharacterizations Show that when the calcination temperature is below 750?,the active component is B-M species and the surface of catalysts is mostly weak base sites;when the calcination temperature is above 730?,the active component is B-M2 species and the surface of catalysts is weak base sites and most of strong base sites;The 5B/AO catalyst shows the largest numbers of weak base sites,it is the reason for the best catalytic activity.Under the optimal reaction conditions,the life testing and regeneration of the 5B/AO catalyst was studied.With the increasing of reaction time,the conversion of Ma decrease from 41.7%to 20.5%in the life testing.The result of regeneration show the catalytic activity can be regenerated by calcinations.Characterizations Show the activate component of the catalyst after reaction is same to the fresh and the content is almost no change.Therefore,the 5B/AO catalyst is suitable to this condensation.In summary,a series of solid base catalysts(Cs/SiO2,Cs/KIT-6,Cs/SBA-15,B/AO)are prepared and applied to the aldol condensation of methyl acetate with formaldehyde.The optimal catalytic activity of solid base catalyst is obtained,and associated with the activate sites and reaction mechanism.We hope to provide a reference for the aldol condensation over the solid base catalysts.