Synthesis,Characterization Of Supported Heteropoly Acid Catalysts And Their Applications In The Preparation Of Glycerol Monolaurate

Monoglyceride laurate(GML)is an excellent food additive that can be used as an emulsifier,antibacterial agent,and preservative in the food,pharmaceutical,and other industries.Proton acids are commonly used in industry to catalyze the preparation of GML from lauric acid(LA)and glycerol(GL).However,there are many problems in the catalytic reaction of proton acids,such as low catalytic efficiency,strong corrosivity,serious environmental pollution,and low product selectivity.Therefore,developing green and efficient catalyst research has important theoretical and practical significance for the clean preparation of GML.In this thesis,a series of supported heteropoly acid catalysts were prepared by chemical bonding of the lone pair electrons of the nitrogen atoms on the carrier with hydrogen in silicotungstic acid,using the strongly acidic green catalyst silicotungstic acid(H4SiW12O40)as the structural unit.The structure and performance of the catalysts were characterized by BET,XPS,FT-IR,XRD,FE-SEM,EDS,31P MAS NMR,TGA-DTG,and n-butylamine potentiometric titration.The catalytic performance of the catalyst was investigated through a selective esterification process model for the preparation of GML.Based on single factor analysis,response surface analysis was used to optimize the process conditions and establish a kinetic model.The enzymatic preparation of GML in the microemulsion system was investigated to compare the chemical preparation methods,providing a reference for the green synthesis of GML.In chapter 2,piperazine modified chlorosphere supported silicotungstic acid catalysts were prepared,and their catalytic properties were investigated using the selective esterification process to prepare GML as a model.Studies have shown that the[CPPI]2H2SiW12O40 catalyst has a good conversion of lauric acid and the best yield of monoglyceride.The uniformly distributed active centers,suitable Br?nsted acidity,and"pseudo liquid phase" characteristics make the[CPPI]2H2SiW12O40 catalyst exhibit excellent catalytic activity.The optimal process conditions for synthesizing GML optimized by combining single factor and response surface analysis were:amount of catalyst was 4.6 wt%,GL/LA molar ratio was 5.8:1,reaction temperature was 426 K,and reaction time was 1.9 h.Under this condition,the yield of GML was 80.2%,and the apparent activation energy of this secondary reaction was 41.38 kJ/mol,and the kinetic equation was:r=dCA/dt=2.77 × 103 exp(-41.38/RT)CACB.In chapter 3,supported heteropoly acid catalyst Fe3O4@void@PMO-NH2-STA was prepared using amino functionalized magnetic yolk-shell nanomaterial as carrier.The catalytic property was investigated using GML preparation as a model.Studies have shown that the large specific surface area of yolk-shell nanomaterials promotes the exposure of active sites,and the high catalytic activity of this catalyst was related to its strong Br?nsted acidity,uniformly distributed active sites,and "pseudo liquid phase" characteristics.The optimal preparation conditions for monoglyceride optimized by response surface analysis were as follows:amount of catalyst was 4.1 wt%,GL/LA molar ratio was 7.4:1,reaction temperature was 426 K,and reaction time was 2.0 h.Under these conditions,the average yield of the monoglyceride was 83.8%,and the reaction activation energy was 33.81 kJ/mol,and the kinetic equation was:r=dCA/dt=427.48 exp(-33.81/RT)CACB.In Chapter 4,using renewable resource rice straw as raw material,a rice straw based carbon silicon material supported silicotungstic acid catalyst was prepared by carbonization,amino functionalization,and combining with silicotungstic acid.Its catalytic performance was investigated using the selective esterification to GML reaction as a model.The study showed that the carrier calcined at 973 K exhibits the best catalytic performance after immobilizing silicotungstic acid.The large specific surface area and rich pore structure of the carrier material promoted the uniform distribution of active centers.The suitable Br?nsted acidity and "pseudo liquid phase" characteristics of C-Si-NH2-STA enabled it to have the best catalytic performance in catalytic esterification reactions.Response surface analysis was used to optimize the preparation process of GML.The optimal preparation conditions were as follows:GL/LA molar ratio was 5.6:1,catalyst amount was 5.5 wt%,reaction temperature was 428 K,reaction time was 2.1 h.Under these conditions,the average yield of monoglyceride was 82.3%,reaction activation energy 35.59 kJ/mol,and the kinetic equation was:r=dCA/dt=472.48 exp(-35.59/RT)CACB.In chapter 5,the catalytic performance of different lipases in the preparation of GML was investigated using DBSA+TX-100/cyclohexane/EmimBF4 ionic liquid microemulsion system as the reaction medium.The study showed that the presence of microemulsion system avoid the contact between organic solvents and enzymes,and the synergistic effect of lipase and DBSA promoted the esterification reaction.Using Candida antarctica lipase B(CALB)lipase as catalyst,the optimal preparation conditions for monoglyceride by response surface analysis were as follows:GL/LA molar ratio was 3:1,amount of enzyme was 4 wt%,reaction time 2 h,reaction temperature 323 K.Under these conditions,the LA conversion was 93.5%,the average GML yield was 62.1%,and the reaction activation energy was 19.65 kJ/mol.The kinetic equation was as follows:r=-dCA/dt=32.98 exp(-19.65/RT)CACB.