| To clarify the reaction pathways of condensed residues and the structural characterizations of liquefaction products at the stages of decomposition and condensation reaction during wood liquefaction, wood powder(Betula dahurica Pall.) of 40-80 mesh was liquefied at 150℃and 0-180 minites. The ratio of polyhydric alcohols to wood to acid was 3:2:0.03. Liquefying reagents was polyhydric alcohols (PEG400:glycerin=4:1). The catalyst was sulfuric acid (concentration of 72 percent). The methods such as FTIR, XRD, SEM, TGA, GPC, HPLC, GC-MS, NMR and etc, were used to analyze the functional groups, microstructure, theromal weight loss behavior, molecular weight and polydispersity, the content of carbohydrate and molecular structure of liquefied wood residues and products.The main results of this study were as follows,1. When liquefaction time was within 0-180 minites, the content of cellulose decreased firstly and then increased, and the content of lignin increased gradually. Compared with unliquefied wood powder, the contents of cellulose and lignin decreased from 44.54 percent and 19.04 percent before liquefaction to 12.16-24.92 percent and 3.93-15.23 percent after liquefaction, respectively.2. The number of carbonyl, aromatic nucleus from lignin and methoxy group reduced as a function of liquefaction time, respectively. The crystallinity of liquefied wood residues increased by 5.10 percent to 7.38 percent, as was mainly because quasi crystalline region of cellulose was degraded and the molecular structure of condensed residues oriented crystallization. During decomposition reaction, the fiber dimension and the average apparent area of the residues became gradually smaller; during condensation reaction, blocky deposit was found in condensed residues, which resulted in bigger average apparent area. With the prolongation of the liquefaction time, the thermostability of liquefied wood residues was improved.3. Weight average molecular weights of lignin from liquefaction wood residues were mainly distributed in the range from 1160 to 1356, the number of aldehydes group from the lignin increased as a function of liquefaction time. Guaiacyl, syringyl and C-O bond in (3-0-4 position almost desepeard when liquefaction time was 10 minutes. And functional groups of cellulose were changed less.4. For the liquefied wood products, with the prolongation of liquefaction time, the number of carbonyl, phenolic hydroxyl group and methoxy group increased and hydroxyl group reduced. The thermal stability and the contents of hexose and furfural reduced. Average molecular weight decreased significantly, and weight-average molecular weight was distributed in the range from 1103 to 1337. Carbohydrates in the products were mainly degraded into glucoside and leculinic acid, and lignin was degraded and obtained three-group compounds. The compounds having phenol structure were in the first group, they were composed of the basic units of lignin by oxidation and demethylation; the second-group compounds having phenylmethoxy structure were obtained after the first-group compounds removed the hydroxyl in benzene-ring by oxidation and acetylation; the third-group compounds stemed from condensation reaction between the first-and second-group compounds. And liquefying reagents could not be oxidated to carbonyl compounds in the acidic condition at 150℃.In conclusion, at the stage of condensation reaction, there are mainly three formation pathways for condensed residues:(1) Degraded cellulose reacts with polyhydric alcohols, and generats EG-Glucoside and 2-hydroxyethyl levulinate; (2) Lignin or the products from degraded lignin reacts with saccharide compounds, and gives macromolecular phenolic resin and esterification products; (3) Esterification or substitution reaction in Cα, Cβ, Cγand benzene ring positions between the products from degraded lignin and liquefying reagents, generates macromolecular esterification products and alkyl ether compounds. |
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