Experimental Study On Preparation Of Methyl Levulinate By Alcoholysis Of High-solid Cellulose

Lignocellulose is a by-product of agriculture and forestry.As a raw material for sustainable development,it can be used to produce fuel or chemicals to meet the strategic needs of human society for sustainable development.Cellulose is the main component of lignocellulose.Because of its special result unit and abundant annual output,it is an important raw material for the production of levulinate.As an important biomass-based platform compound,methyl levulinate is used in solvents,fuels,medicine and other fields.However,the research on the kinetics and mechanism of alcoholysis of high-solid cellulose to prepare methyl levulinate is still insufficient.Studying high-solid cellulose alcoholysis to directly prepare high-concentration levulinate esters can reduce product separation costs,save downstream processing costs,and improve production efficiency.It has important research significance in theoretical research and actual production.In this paper,cellulose is used as raw material and aluminum sulfate is used as catalyst to produce methyl levulinate,and the preparation process and reaction mechanism are explored.Firstly,the catalyzed conversion of high-solid cellulose alcoholysis to methyl levulinate was studied under different process conditions.The kinetics of high-solid cellulose alcoholysis was further studied by the shrink core model,finally using Gaussian 16W software through the density functional theory B3LYP/6-31G+G（d）method,the cell monosaccharide alcoholysis mechanism was studied by quantum chemical theory calculations.The main research contents are as follows:1.First,the effects of different metal salts in the methanol system on the catalytic high-solid cellulose preparation of methyl levulinate were studied,the catalytic performance and reusability were examined,and Al₂（SO₄）₃was selected as the catalyst for the subsequent reaction,and then investigated The effect of solid content on the alcoholysis of high-solid cellulose was investigated.Under the condition of 15%solid content,the mass yield of methyl levulinate was 36.59%.The effect of catalyst addition on alcoholysis of high-solid cellulose was further investigated.When cellulose is 7.5g,Al₂（SO₄）₃is 1.6g,and the reaction time is 1 h,the yield of methyl levulinate is 38.67%.Then,the influence of the amount of water added on the yield of methyl levulinate was investigated.When the amount of water added was 5%,the yield of methyl levulinate was 38.59%,and the reaction temperature and reaction time were investigated.The effect of alcoholysis of solid cellulose,the reusability of Al₂（SO₄）₃was finally explored.The yield of methyl levulinate after 5 times of repeated use was 33.95%,indicating that Al₂（SO₄）₃has good reusability.Sex.2.The application of core shrinkage kinetic model in the process of cellulose degradation to methyl glucoside was studied.The application of core shrinkage kinetic model in high solids,low solids,and different particle sizes was investigated,and the high solids 90μm was obtained.During the alcoholysis of cellulose,the reaction rate constants at different reaction temperatures（160℃,170℃,180℃）were further obtained,and the activation energy was 151.6 k J/mol,and the activation energy of the high-solid 250μm cellulose alcoholysis process was 163.7,respectively.k J/mol.In addition,FTIR,XRD,SEM,and laser particle size analyzer were used to characterize the solid residue after the reaction,and the microscopic changes during the alcoholysis of cellulose were studied.3.The conversion of cellulose alcoholysis to prepare methyl levulinate is embodied into two steps from cellulose to 5-methoxymethylfurfural and5-methoxymethylfurfural to methyl levulinate.The specific reaction path of each step is verified by density functional theory（DFT）in the B3LYP/6-31G+G（d）method,and the reactants,intermediates,and transition states involved in the path are verified by the B3LYP/6-31G+G（d）method.The structure was optimized,the SCAN and QST2 methods were used to find the transition state.The transition states were verified by IRC and optimized by TS.Finally,the thermodynamic and kinetic parameters of the cellulose alcoholysis reaction at 180°C and 3.5 MPa were calculated.The results showed The limiting reaction step of the process from cellulose to 5-methoxymethylfurfural is the first dehydration process of methyl glucoside,the reaction energy barrier is 288.3 kcal/mol,5-methoxymethylfurfural to methyl levulinate The limiting reaction step of the process is the5-methoxymethylfurfural demethanolization process,and the reaction energy barrier is 422.5 kcal/mol.