Preparation Of Solid Catalysts And It Application In The Synthesis Of Edible Flavor Acetal (Ketone)

Acetal(ketone)is a new type of fragrance.It has the characteristics of stable nature,unique aroma,rich raw materials and simple production process.In recent years,it has been widely used in the pharmaceutical industry,the food industry,and fine chemicals.With the improvement of its quality and demand,the synthesis of acetal flavors has attracted much attention.In the conventional acetal(ketone)production process,proton acids(such as: H2SO4,HCl,phosphoric acid)are commonly used to catalyze the condensation reaction of an aldehyde(ketone)with an alcohol.When protonic acid catalyzed the preparation of acetal(ketone),although it has good catalytic activity,the environmental pollution in the reaction process is serious.When acetal(ketone)is prepared by ion exchange resin,molecular sieve,solid super acid,etc,although the problems of the traditional catalyst in the reaction process are solved to some extent,however,they still have the disadvantages of low relative activity,poor thermal stability,easy carbon deposition,and easydeactivation.Therefore,from the perspective of industrial production and environmental protection,the development of high-efficiency,non-polluting and easily separable catalysts has become a hot spot in this field.Heteropoly acid is a well-recognized environmentally-friendly solid super acid.In this paper,the phosphotungstic acid of Keggin structure is selected as structural unit,and the catalytic activity and recyclability of phosphotungstic acid are improved by metal ion modification or metal oxide immobilization.At the same time,the composite metal oxide and the novel carbon-silicon solid acid catalyst were prepared by sol-gel method,and the structure of the catalyst was characterized by FT-IR,TGA,XRD,BET,SEM,XPS and solid 31 P MAS NMR.The catalytic performance of the benzaldehyde glycol acetal preparation reaction was investigated.The response surface methodology was used to optimize the preparation conditions,and the dynamic model of acetal reaction under optimized conditions was constructed to provide reference for the clean preparation and industrial application of other acetal(ketone)perfumes.In the second chapter,different metal ion modified phosphotungstic acid catalysts were synthesized by ion exchange method,and their structure and catalytic activity were also investigated.Studies have shown that some silver-modified phosphotungstic acid(Ag H2PW12O40)shows the best catalytic performance in the reaction of benzaldehyde withethylene glycol acetal.The strong Br?nsted acidity and the synergistic effect between the Br?nsted and Lewis acid sites are responsible for the high activity of the catalyst.The optimal experimental conditions for the synthesis of benzaldehyde glycol acetal by response surface methodology using Ag H2PW12O40 as catalyst were as follows: molar ratio of aldol was1:1.5,amount of catalyst was 5.7 wt%,reaction time was 3 h,and water dose was 14 m L.Under this condition,the acetal yield reached 92.7 %.Under the optimized conditions,the kinetic equation for the preparation of benzaldehyde glycol acetal is:r=-dC_A/dt=7.5exp(-23.8/RT)C_AC_B.The third chapter investigates the catalytic performance of different metal oxide supported heteropolyacid catalysts in the reaction of benzaldehyde glycol acetal.Studies have shown that 20HPW/Ti O2 catalysts have the best catalytic performance.The large surface area of the catalyst and the synergistic effect between the Lewis acid center(metal oxide)and the Br?nsted acid center(phosphoric acid)are responsible for its high catalytic activity.The optimum conditions for the synthesis of benzaldehyde glycol acetal optimized by response surface methodology were as follows: molar ratio of aldol was 1:1.4,amount of catalyst was 6.8 wt%,reaction time was 3.2 h,and the dose of water was13.7 m L.The aldehyde yield was 93.1 %.Under the optimized conditions,the kinetic equation for the preparation of benzaldehyde glycol acetal is:r=-dC_A/dt=3.96exp(-23.24/RT)C_AC_B.In the fourth chapter,a series of composite metal oxides were synthesized by sol-gel method.The structure and catalytic activity of the composites were investigated.The results show that the Ce Fe Ti O catalyst has the best catalytic performance in the reaction of benzaldehyde glycol acetal.The large surface area of the catalyst and its acid strength are responsible for its high catalytic activity.The optimum conditions for the synthesis of benzaldehyde glycol acetal optimized by response surface analysis based on single factor experiment were as follows: molar ratio of aldol was 1:1.7,amount of catalyst was 6.9 wt%,reaction time was 2.9 h,and water dose was 12 m L.The acetal yield under this condition was96.9 %.Under the optimized conditions,the kinetic equation for the preparation of benzaldehyde glycol acetal is:r=-dC_A/dt=0.97×10~4exp(-46.65/RT)C_AC_B.In the fifth chapter,a series of carbon-silica solid acid catalysts were synthesized by fruct-gel method using fructose as raw material,and the catalytic activity in the acetal reaction was investigated.Studies have shown that the molar ratio of ethyl orthosilicate to fructose is 1:1,and the carbon-silicon solid acid catalyst calcined at 500 °C for 5 h under nitrogen atmosphere has the best catalytic activity.The high catalytic activity is related to the specific surface area and stability of the catalyst.Theoptimum conditions for the synthesis of benzaldehyde glycol acetal optimized by response surface analysis were as follows: molar ratio of aldol was 1:1.6,amount of catalyst was 6.4 wt%,reaction time was 3.3 h,and the dose of water was 11.8 m L.The aldehyde yield was 93.4 %.Under the optimized conditions,the kinetic equation for the preparation of benzaldehyde glycol acetal is:r=-dC_A/dt=20.198exp(-27.7/RT)C_AC_B.