Study Of Catalytic Liquefaction Of Lignocellulosic Biomass In Alcohols And Water As Mixture Solvent And Its Products

In this paper, based on the advantages of the physicochemical property of supercritical alcohols and subcritical water, with the alcohols-water mixed solvent as the medium of liquefaction, autoclave was chosen in the experiment of liquefaction of lignocellulose under subcritical condition to produce the high value-added chemicals. Firstly, the feasibility and impact on the liquefaction of fir sawdust in methanol-water mixed solvent were explored. A series of experiments were conducted to inverstigate the effect of reaction temperature, reaction time, catalyst dosage, ratio of methanol and water, additive amount of fir sawdust on the conversion yield and liquefied products. The results showed that the optimum conditions were the additive amount of fir sawdust with 1 g, methanol/water ratio with 75:75, the catalyst dosage dosage of 0.5 g, reaction temperature of 240℃ and reaction time of 30 min. Under the optimum conditions, the highest conversion yield reached 93.32%. The results indicated that the liquefied products, the residue was comprised of lignin or lignin derivatives. The light oil mainly contained 37 species of compounds, including esters, acids, phenols, aldehydes, especially high content of lactic acid and levulinic acid, while the heavy oil consisted of the products obtained from liquefaction of lignin. This reaction system has the feature of low dependency on the equipment, and high conversion yield of raw material, which can be used as the method to prepare high value-added chemicals.Secondly, the effects of different raw materials and different alcohols on the preparation of high value-added were also explored. A series of reaction parameters were conducted to investigate the effect of reaction temperature, reaction time, catalyst dosage, solid-to-liquid ratio on the liquefaction of raw material. The results indicated slight difference of reaction temperature on the liquefaction of raw materals between borer powder and bagasse. The highest conversion yield of borer powder at 240℃ was 96.32%, while the bagasse was 97.60% at 260℃. Meanwhile, the borer powder of compact structure depends more on the acid environment caused by the catalyst than bagasse, while the conversion yield of bagasse without catalyst at high temperature condition in methanol-water could reach as high as 85.51%. The compositions in the liquified products obtained from liquefaction of two materials in methanol-water consisted of high content of high value-added chemicals such as 5-hydroxymethylfurfural, lactic acid, levulinic acid, etc. Compared with the effects of different alcohols on the liquefaction of cellulose, the results showed that under the optimal conditions of the raw materials amount of 1g, reaction temperature of 240℃, reaction time of 30 min, catalyst dosage of 0.1 g, solid-to-liquid ratio with 30:30, the conversion yield reached more than 98%. Methanol with higher polarity than ethanol provides more hydrogen free radicals, which could promote the polycondensation between the intermediate products. Simultaneously, the liquified produt obtained by methanol/ethanol-water also contained high content of high value-added chemicals such as 5-hydroxymethylfurfural, lactic acid, levulinic acid, and so on.Ultimately, in this paper, the experiments about kinetics and mechanism of liquefaction of cellulose in methanol/ethanol-water were also conducted. The kinetic analysis results showed that the liquefaction reaction of cellulose in alcohols-water was first-order reaction. The kinetics calculation of cellulose catalytic liquefaction in methanol/ethanol-water indicated that the apparent activation energies were 137.06 KJ/mol and 140.56 KJ/mol, respectively, and the pre-exponential factors of these two solvents systems were 5.4761×1012 min-1 and 1.1556×1013 min-1, respectively. The researchs on the reaction mechanism of cellulose liquefaction in alcohols-water were conducted with the pattern of quench the reaction. By various analysis methods, liquefied products were obtained by liquefaction of cellusose at different final temperatures. Based on the analysis results with the conversion yield data, the liquefaction mechanism and the formation routes of main compounds including high value-added chemicals could be speculated, which could offer theoretical basis the for reaction process control and craft optimization.