| Chemical products from oil refinery, such as ethylene, benzene, are the foundation of modern chemical industry, but with exhaustion of fossil resources, biomass resources that are renewable, carbon neutral, and remarkably massive in amount are becoming more important as alternatives to fossil resources. Various conversion processes, such as acid hydrolysis, enzymatic hydrolysis, have been developed to obtain platform chemicals like ethanol, levulinic acid, furfural and 1,3-propanediol, which are feedstocks for chemical production. However, these methods have many issues such as low conversion efficiency, difficultly comprehensive utilization of cellulose and lignin, serious pollution and high production cost. It's still a challenge to accelerate the utilization of biomass resources.Due to the specific properties, such as high ionization constant and low dielectric constant, near critical water (NCW) and near critical methanol (NCM) are regarded as promising technology for organic chemical reactions, biomass resource and depolymerization of polymer. Foucsing on the green and efficient conversion of biomass in near critical medium, the research works were summarized as below:The laboratory had carried out that the catalytic effects of different metal chlorides on decomposition of cellulose model compounds in near critical water, but did not in-depth study of the catalytic effects of anions. Therefore, decomposition kinetics of glucose, fructose and 5-hydroxymethylfurfural catalyzed with anions in near critical water were determined at 180℃.15 types of anions were selected, and their cation was potassium ion. The results indicated that addition of anions could not increase the yield and selectivity of the target products 5-HMF and levulinic acid in NCW, but it promoted the degradation of glucose greatest, then fructose and 5-HMF. Organic acid anions had greater impact on the degradation of glucose and fructose than inorganic anions, which inhibited the degradation of 5-HMF. Addition of anions increased the dielectric constant, thereby enhancing the reaction rate, such as chloride ion, bromide ion; Physical properties and structure of anions also affected the catalytic effects of anions, the pOH values of anions were less than 14, which were in favour of the degradation of glucose and fructose, on the contrary, the pOH values more than 14 could promote the degradation of 5-HMF. In addition, when OH groups of sugar were hydrogen bonded to anions, the catalytic effects of anions was better.To achieve the comprehensive utilization of biomass resources, the non-catalytic decomposition of lignin in near critical water was carried out. Anisole, diphenyl ether, benzyl phenyl ether and phenethyl phenyl ether were selected as the model compounds for ether linkages in lignin. The kinetics studies on non-catalytic decomposition of model compounds were carried out. As a result, ether bonds of lignin could be selectively broken in NCW,4-O-5 type structure (diphenyl ether) were stable,β-O-4 type structure (phenethyl phenyl ether) and methoxy structure (anisole) converted slowly, on the other hand,α-O-4 lignin model compound was cleaved rapidly, these lignin compounds decomposed to some monomeric phenolic compounds. The kinetics data at different temperatures were fitten by the first-order equation, and the activation energies obtained by Arrhenius plot, were 149.8±16.4 kJ.mol-1,150.3±12.5 kJ.mol-1,143.2±21.0 kJ.mol-1, respectively. Based on products distribution, the reaction mechanisms for decomposition of lignin model compounds were proposed. Finally, comparing conversion data of other ethers in the literature, the law of decomposition of ether in NCW was discussed.Finally, in order to explore the feasibility of efficient preparation of new compounds from biomass in near critical methanol, the kinetics studied on methyl levulinate (MLA) production from glucose and cellulose were carried out. Acids bearing SO3H groups were proved to be effective for catalytic alcoholysis to MLA, and synthesis of dimethyl ether could also be accelerated. The kinetics of MLA production from glucose and cellulose were systematically investigated, the results showed that reaction temperature had more significant impact on the alcoholysis reaction and yield of MLA than acid concentration, and higher yield of MLA was obtained at higher temperature. With the first-order kinetic equations, the activation energies evaluated were 107.5 kJ.mol"1 and 68.4 kJ.mol"1 for main and side alcoholysis reactions of glucose, respectively. One-pot preparation of MLA from biomass in near critical methanol was a promising process, with glucose as raw material,38.9 wt% yield of MLA was achieved in the experimental conditions, and 38.7 wt% yield of MLA from cellulose was obtained.
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