Synthesis,Characterization Of Solid Acidic Catalysts And Their Applications In The Preparation Of Glycerol Monolaurate

Glycerol monolaurate(GML)is not only an excellent food emulsifier,but also an effective bacteriostatic agent,preservative,mainly found in the breast and Palmetto GML is one of generally recognized as safe(GRAS)food additive,certified by the US Federal Drug Administration(FDA),has been widely used in the fields of food,medicine,cosmetics and so on.GML was prepared by esterification with lauric acid(LA)and glycerol(GL)as raw materials,which is one kind of commonly used method.It is also a promising potential approaches to make greater use of glycerol Moreover,the traditional catalysts for catalytic esterification has some problem about low catalytic efficiency and environmental pollution.Therefore,to achieve the goal of sustainable development,screening the green and highly active catalyst is of great significance for efficient preparation of GMLIn this paper,a series of solid acidic catalysts have been synthesized.and their structures were characterized by various characterization methods.The application of FT-IR,TGA,XRD and solid-state 31P MAS NMR can fully prove the structure of the catalysts.The solid acidic catalysts were applied to the preparation of GML with lauric acid and glycerol,catalytic activity of different types of solid acidic catalysts in the preparation of GML were investigated,and the best catalyst in different types of catalysts was screened.In order to provide reasonable parameter level for response surface experiment,single factor experiments were carried out to study the effects of each reaction factor on lauric acid conversion and GML yield,on the basis of the single factor experiment,the key process parameters were optimized by the response surface analysis(RSM)method,and the kinetic model was established.Finally,the bacteriostasis performance of the crude sample was preliminarily studied.The aim is to provide references for the preparation and application of monoglyceride.In the second chapter,many kinds of rare earth modified silicotungstic acid catalysts MxH4-3xSiW12O40(M=La,Ce,Pr,Nd,Sm;x= 1/3,2/3,1,4/3)were prepared by ion exchange method.The structural characteristics and catalytic esterification activities were investigated.Among them,the catalytic performance of Ce1/3H3SiW12O40 is the most significant,the strong Br(?)nsted acidity,synergistic effect of Br(?)nsted-Lewis acid and the pseudo-liquid phase characteristics of the catalyst are the reasons for its high activity.The best reaction conditions were determined by response surface methodology:GL/LA molar ratio of 4.1,catalyst amount(relative to LA mass)4.6 wt%,reaction temperature 424 K and reaction time 120 min,GML yield is 79.0%.After repeated use for five times,the Ce1/3H3SiW12O40 still maintains good catalytic activity.With an apparent activation energy of 42.07 kJ/mol,the reaction kinetic equation is as follows:r=dcA/dt=589.93 exp(-42.7/RT)cAcB.In the third chapter,a series of catalysts AgxH4-xSiW12O40 with different acid strength were synthesized from metallic silver and silicotungstic acid as raw material,which were insoluble in esters and water.The results show that Ag2H2SiW12O40 has the best catalytic activity for the esterification,the catalytic performance of the catalyst is closely related to its acidity,the synergistic effect of Br(?)nsted-Lewis acid,and the substrate.Using Ag2H2SiW12O40 as catalyst,the optimum conditions of GML synthesis were optimized by response surface methodology.GL/LA molar ratio of 4.4,catalyst amount 4.6 wt%(0.46 g),reaction temperature of 429 K,and reaction time 153 min,an average experimental yield of 80.2%.Additional kinetic studies revealed that synthesis of GML with a activation energy Ea of 38.14 kJ/mol,the kinetic equation for the esterification of GL with LA to GML under the aforementioned optimum conditions may readily be written as:r=-dcA/dt=121.84×exp(-38.14/RT)cAcB.In the fourth chapter,a series of propyl sulfonic acid-functionalized ionic liquids(SAFILs)modified silicotungstic acid(STA;H4SiW12O40)catalysts,were applied to the esterification of GML,their structure and catalytic performance have been also studied.The results show that[DMBPSH]iH3SiW12O40 has prominent catalytic performance,and the self-separation,strong acidity and low space hindrance may be the reason for its good catalytic performance.Under the optimum conditions:GL/LA molar ratio of 3.3,catalyst amount 3.9 wt%,reaction temperature 427 K,reaction time 60 min,the yield of GML reached the maximum value 79.1%.Under these conditions,the apparent activation energy of the reaction Ea was 39.49 kJ/mol,and the kinetic equation was:r=-dcA/dt=399exp(-39.49/RT)cAcBIn the fifth chapter,a series of silica gel supported sulfonated functional ionic liquids catalysts(SSILCs)has been successfully synthesized through sol-gel method.On this basis,their structures and catalytic esterification activity were investigated.The embedded 20%N,N-dimethyl(benzyl)ammonium propyl sulfobetaine hydrosulfate in silica gel(20%[DMBPSH]HSO4/SG)catalyst exhibited the highest catalytic activity in the esterificasion of GML.Process variables were explored and optimized by the response surface methodology(RSM)as follows,GL/LA molar ratio of 4.1,amount of catalyst 2.0 wt%,reaction temperature 418 K,reaction time 45 min,and a highest GML yield of 83.9%was achieved.Further kinetic studies exhibited the esterification of GL with LA followed a second-order reaction with an activation energy of 33.22 kJ/mol,and the kinetic equation was:r=-dcA/dt=78.02×exp(-33.22/RT)cAcA.The bacteriostatic study showed that the crude isolated samples had better inhibitory effects on Staphylococcus aureus,Bacillus subtilis,Escherichia coli and Pseudomonas aeruginosa.Comparatively speaking,the antimicrobial effect of the samples on G bacteria was more obvious.