| Propylene glycol methyl ether acetate(PMA),which contains many functional groups,is a harmless solvent.It can dissolve not only polar substance but also nonpolar substance,so it is called "almighty solvent".Nowadays,there are three methods to synthesize PMA:epoxy propane one-step method,interesterification method and direct esterification method.Among these routes,the direct esterification method is the only way which achieves commercial production.In this method,propylene glycol monomethyl ether(PM)and acetic acid(HAc)were used as reactive raw materials,the used catalysts were the traditional liquid acids,such as concentrated sulfuric acid,hydrofluoric acid and so on.However,this route exists some drawbacks,such as severe equipment corrosion,difficult separation of catalyst from raw material and reaction product and so on.Therefore,this paper proposed a benign preparation method of PMA via direct esterification from PM and HAc using the solid super acid TiO2/SO42-as catalyst,which was based on the drawbacks of traditional synthetic method.The research focused on the following aspects:(1)The solid super acid catalyst TiO2/SO4-was prepared by impregnation method.The orthogonal test was employed to optimize the synthesis method of solid super caid catalyst and the more suitable synthesis method was obtained:the concentration of sulfuric acid solution lmol/L,the mass ratio of titanium dioxide and sulfuric acid solution 1:2,the calcination temperature 450°C,the drying temperature 120? and the calcination time 4h.Then the structures of above-mentioned catalyst were characterized by BET,pyridine-adsorbed FT-IR,TGQ XRD and ESEM method.The characterization results showed that the surface area was 48.96 m2·g-1,the average pore diameter was 16.40 nn,the inner channel of this catalyst was mesoporous.There were a large number of L acid and a handful of B acid on the surface of catalyst.The tolerant temperature of this catalyst was 4500C and the titanium dioxide molecule existed in the form of anatase type.The particles which can be observed on the surface of catalyst were spherical and uniform,the average diameter of them was approximately 1?m.(2)In the high-pressure reactor,the reaction kinetics of the direct esterification of PM and HAc to synthesize PMA were studied in the presence of solid super acid TiO2/SO42-as catalyst.Under the condition of eliminating external diffusion,the influences of catalyst dosage,reaction temperature and molar ratio of HAc to PM on the esterification were investigated.According to kinetic experiment data,a pseudo-homogeneous kinetic model was established and the model parameters were obtained from kinetic experiment data.The pseudo-homogeneous kinetic model showed good correlation between model values and the experiment values.(3)The batch PMA synthesis process of the direct esterification of PM and HAc was studied in the presence of solid super acid TiO2/SO42-as catalyst.The water-carrying agent,molar ratio of HAc to PM and catalyst dosage were varied,respectively.The results showed that the molar ratio of HAc to PM and catalyst dosage were 1.5:1 and 3wt%,respectively,the conversion of PM could reach 100%.(4)The molding process of solid super acid TiO2/SO42-was studied.The molding scheme was determined based on catalytic performance and the orthogonal test was used to optimize the molding formula of solid super caid catalyst TiO2/SO42-and the more appropriate molding formula was that:binder 7wt%,reinforcing agent 20wt%,pore forming agent 2.5wt%,lubricant 4wt%and the others were solid super acid catalyst TiO2/SO42-.The structures of molded catalyst were characterized by BET,TG and XRD methods.The characterization results showed that the surface area was 30.56 m2·g-1,the average pore diameter was 17.16 nm,inner channel of the catalyst was still mesoporous.The tolerant temperature of molded catalyst was 600 ? and the titanium dioxide molecule still existed in the form of anatase type,the catalytic performance of this catalyst was higher than others. |
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