Alcoholysis Mechanism Of Wheat Stalk Catalyzed By CaO/Al₂O₃/Fe₃O₄

Catalytic alcoholysis of biomass at high pressure is an effective way to prepare bio-oil andchemicals, which has greatly practical significance for comprehensive utilization of biomass.According to the product yields and components of bio-oil, this study investigated the influenceof solvents (methanol and ethanol) and catalysts (CaO, Al2O3, Fe3O4, CaO/Al2O3, CaO/Fe3O4,Al2O3/Fe3O4and CaO/Al2O3/Fe3O4) on supercritical alcoholysis of wheat stalk power,respectively. Cellulose, hemicellulose and lignin were as model compounds to study thealcoholysis mechanism of wheat stalk over the above catalysts.On the supercritical conditions, cellulose and hemicellulose depolymerize, open loop andfracture becoming small molecule compounds at first. Then parts of small molecule compoundscondense into long-chain compounds and the rest dehydrate and cyclize to generatecyclopentanones, alcohols, phenols as well as hydrocarbon and so on. Lignin fractures intoalkyloxybenzenes, arenols and side chain intermediates. Parts of side chain intermediatescondense into aliphatics, while the others dehydrate and cyclize to alcohols and ring ketones.Alcohols can react with acids from the products and come into being methyl or ethyl esters. Therelative percentage of ethyl esters in ethanol is lower than methyl esters in methanol becausesteric hindrance of ethanol is bigger than methanol. In the process of catalytic alcoholysis ofcelluloses, hemicelluloses and lignin, CaO induces releasing of hydrogen from alcohols anddecarboxylization of acids. Al2O3shows the same properties as CaO in the process of catalyticalcoholysis of three compounds and due to its weak acid in the ethanolysis of cellulose andhemicellulose, Al2O3restrains the releasing of hydrogen from alcohols. The catalytic effect ofAl2O3on lignin in ethanol is the same with methanol. When CaO/Al2O3was used, CaO andAl2O3act synergistically on three model compounds while only CaO promots ethanol producinghydrogen in the celluloses and hemicelluloses ethanolysis. The catalysts CaO/Fe3O4,Al2O3/Fe3O4and CaO/Al2O3/Fe3O4show the catalytic function of CaO, Al2O3and CaO/Al2O3inthe alcoholysis process, respectively, and Fe3O4is only as magnetic carrier.