Study On Preparation Of Bio-Based Methyl Levulinate

With the continuous depletion of fossil resource petroleum oil and environmental problems,it is urgent to seek renewable resource which can be used to replace fossil oil.Currently,biomass is the only renewable resource that can derive liquid fuel and fine chemicals to replace the petroleum-based chemicals.It can be used to synthesize various energy products and chemicals through biological or chemical transformation,such as levulinate esters.Levulinate ester is a kind of important intermediates and energy chemicals having high reactivity and widespread application in many fields.Recently,the development of bioenergy concerning the synthesis of levulinate ester from biomass also has attracted more and more concerns.In this thesis,a series of solid acid catalysts were designed and prepared.Catalytic conversion of corncob,microcrystalline cellulose and lignin-removing biomass with solid acid catalysts to produce high value-added methyl levulinate?ML?was studied with the aim of improving the yield of ML,which is in order to explore the rules of different sources of biomass catalytic liquefaction and to provide a theoretical basis for the efficient and directional transformation of biomass.The main contents and results are summarized as follows:1.Solid acid catalysts were prepared in our laboratory and then used for the catalytic liquefaction of corncob in methanol.The effects of different reaction conditions on corncob conversion and ML yield were investigated.The feasibility of direct alcoholysis of corncob with solid acid as catalyst to prepare ML was discussed by analyzing the distribution of compounds in bio-oil.The results indicated that SO₄^2-/TiO₂-ZrO₂ was found to have the best catalytic activity among the catalysts used and the target product ML was detected in bio-oil by GC-MS.The optimal conditions of liquefaction were as follows:1 g corncob with 4 wt%SO₄^2-/TiO₂-ZrO₂ at250?for 90 min,the ratio of methanol to cyclohexane was 2:1?v/v?and the solid-liquid ratio was 1:15?m/v?.Under the conditions the liquefied rate of corncob reached 76.67%.The main components of the liquefaction product were phenols and ester compounds.Ester compounds contained ML,but the selectivity of ML was very low and the relative content of ML was 1.52%.2.Catalytic liquefaction of model compound microcrystalline cellulose in methanol was studied in this part.The effects of catalyst type,catalyst dosage,reaction temperature,reaction time and solid-liquid ratio on the conversion of microcrystalline cellulose and the yield of ML were investigated.The results showed that the conversion of microcrystalline cellulose and the yield of ML were highest when SZM5 was used as catalyst.The optimal conditions were as follows:1 g microcrystalline cellulose with 20 wt%SZM5 at 200?for 60 min when the ratio of microcrystalline cellulose to methanol was 1:25?m/v?.Under the conditions,a liquefaction conversion rate of 96.48%and ML yield of 32.11%were obtained.When the catalyst SZM5was repeatedly used for 5 times,the yield of ML was still higher than 10%,indicating that SZM5had good catalytic activity and catalytic stability.The combination of atmospheric distillation and vacuum distillation could effectively separate and purify the liquefaction product with 95.46%ML.In addition,the separated methanol and the recovered dodecane could be recycled.3.Six kinds of lignin-removed biomass such as rice straw,wheat straw,corn stover,corncob,poplar and bamboo,were used as raw materials,to prepare ML.It was found that lignin-removed corncob was a much better raw material for the preparation of ML.The effects of reaction conditions such as catalyst dosage,reaction temperature,reaction time,and solid-liquid ratio on the conversion of the raw material and the yield of ML were investigated by a single factor method.The results showed that the optimal reaction conditions were 40 wt%catalyst loading,200?reaction temperature,60 min reaction time,and solid-liquid ratio 1:25?m/v?.Atmospheric distillation combined with vacuum distillation could roughly purify the resultant products to obtain crube extract of 82.83%ML and 8.27% furfural.