Methyl Levulinate Production From Direct Conversion Of Biomass In Methanol Medium

Biomass is the only renewable resources on the earth that can derive liquid fuel and finechemicals to replace the petroleum-based chemicals. Carbohydrate, is the most plentifulelement in biomass resources, can be converted into a variety of interesting bulk chemicalsvia biological or chemical pathways, which is one of the focuses in the field of biomassenergy today. Recently, the development of bioenergy concerning the synthesis of levulinateester from biomass has attracted more and more concerns. Levulinate ester is a kind ofimportant intermediates and energy chemicals having high reactivity and widespreadapplication in many fields. Up to now, there are four developed potential pathways for thesynthesis of levulinate esters from biomass conversion, including the direct acid-catalyzedalcoholysis of biomass, the esterification of levulinic acid that from hydrolysis of biomass, thealcoholysis of5-（chloromethyl）furfural derived from biomass, and the alcoholysis of furfurylalcohol that from hydrogenation of furfural. Among these, the direct acid-catalyzedalcoholysis of biomass is considered the most promising pathway for the synthesis oflevulinate ester, however, high cost production caused from low conversion efficiency, seriousside reaction and trouble post-treatment is the obstacle that restricts progress and large-scaleapplication of this technology.To develop green chemistry for the purpose, aiming at present research situation andmain existing scientific problems for the direct alcoholysis of biomass to levulinate ester, aseries of innovation studies were performed in this dissertation. For example, development oflow cost and green efficient catalyst system, exploration of biomass alcoholysis mechanismand kinetics, resource utilization of paper sludge for levulinate ester synthesis, separation andcharacterization of the products. Specifically, conversion of cellulose and glucose into methyllevulinate in methanol medium was selected as the representative route for detailed study.Firstly, some different types of solid acid catalysts were obtained from company and ownsynthesis, which were employed for the catalytic conversion of carbohydrate to methyllevulinate in methanol medium. Among these catalysts used, sulfated metal oxides (especiallySO₄^2–/TiO₂) were found to be a type of potential catalysts for prospective utilization, whichshowed remarkably high yield of methyl levulinate and had negligible undesired dimethyl ether formation from the dehydration of methanol. After reaction, the catalyst is recoverablefrom the resulting product mixture and reused multiple times after calcination. In the case ofSO₄^2–/ZrO₂–TiO₂, Zr/Ti molar ratio and calcinations temperature are two factors that stronglyaffected its surface properties and glucose reactivity in methanol medium. The resultssuggested that the moderate acid sites were responsible for the formation of methyl levulinateand the catalytic activity for methyl levulinate production from glucose almost increaseslinearly with the catalyst acid site density.Secondly, extremely low sulfuric acid （≤0.01mol/L） was selected as acid catalyst for theconversion of carbohydrate to methyl levulinate in methanol medium. It found that extremelylow sulfuric acid offer enough acid site for the completion of reaction. Based on the detectedcompounds, a plausible reaction pathway for the acid-catalyzed conversion of cellulose andglucose to methyl levulinate in methanol medium was proposed. Compared with the first solidacid, extremely low sulfuric acid exhibited more catalytic activity with high methyl levulinateyield and good material adaptability. Compared to the conventional dilute sulfuric acidcatalysis, an advantage of extremely low sulfuric acid catalyst system is that methyl levulinateyield is high, negligible undesired dimethyl ether formed from the side reaction for thedehydration of methanol, the equipment corrosion was slight, and less spent acid need to beaddressed after reaction. In summary, this technology can provide a great help to acceleratethe development of the industrial production of levulinate ester from carbohydrate.Based on the above findings, kinetic investigation on the conversion of cellulose tomethyl levulinate in methanol medium catalyzed by extremely low sulfuric acid wasperformed. During the methanolysis of cellulose, a key and stable intermediate product ofmethyl glucoside was produced, so a simplified kinetic model of first-order reaction for thegeneration of methyl levulinate from cellulose via methyl glucoside was developed, and thecorresponding activation energy and reaction order of H+were evaluated using the method ofnon-linear least squares regression analyses. The kinetic results can provide theoretic basis forthe development and improvement of novel process.Primary sludge from a toilet paper mill was used as biomass material to produce methyllevulinate in methanol medium, technical conditions for the acid-catalyzed methanolysis ofpaper sludge were optimized by response surface analysis （RSA）. The results indicated that about seventy percent of the paper sludge was liquefied, the major liquid phase productsincluded methyl glucoside, methyl levulinate, methyl formate and2-（dimethoxymethyl）furan.Under the optimum conditions, the yield of methyl levulinate is around60%of the availablecarbohydrate on the initial substrate, corresponding to methyl levulinate yield of290g/kg ofdry paper sludge. This conversion technology can provide new reference for the resourceutilization of paper sludge.After the methanolysis of glucose, the products were isolated and purified by adistillation technique that combines an atmospheric distillation with a vacuum distillationwhere n-dodecane was added to help distil the heavy products. The chemical structure ofmethyl levulinate was confirmed using FTIR,1H-NMR and13C-NMR, respectively. Thepurity of isolated methyl levulinate was about95%and the separation efficiency of methyllevulinate reached95%with this method.In conclusion, the present study developed two novel, green and efficient strategies forthe conversion of carbohydrate to levulinate ester, especially extremely low sulfuric acidcatalyst system, which can effectively overcome many disadvantages of the conventionaltechnology with low production cost. A plausible reaction pathway for the alcoholysis ofcarbohydrate was proposed and a convictive kinetic model was developed. Efficient resourceutilization of paper sludge for the synthesis of levulinate ester and the multi-componentsseparation of products were realized. The findings of this dissertation can provide theoreticalguidance and technical reference for further research and industrial scale production ofbiomass-based levulinate ester.