Study On Catalytic Conversion Of Pyrolysis Oil Water-Soluble Fraction To High Value-Added Chemicals

Biomass is an alternative energy which has been paid great attention due to its rich resource,wide distribution and renewability.Pyrolysis oil is a liquid intermediate produced by fast pyrolysis of lignocellulose biomass.Pyrolysis oil has attracted much attention because of its low cost,easy access,convenient storage and transportation.Catalytic upgrading of pyrolysis oil to transport fuel is a widely studied approach for its valorization.However,the composition of pyrolysis oil is complex,and catalytic upgrading usually requires harsh reaction conditions.From the view of economy and practice,catalytic conversion of pyrolysis oil（or its fraction）to high value-added chemicals seems to be a feasible alternative strategy.In this thesis,based on the study of the polymerization mechanism of pyrolysis oil water-soluble fraction,the processes of some key components and water-soluble fraction conversion to different high value-added chemicals were studied.The polymerization rates of pyrolysis oil water-soluble and water-insoluble fractions were compared by accelerated aging experiments.The thermogravimetric and differential thermogravimetry analysis results showed that water-soluble fraction polymerized much more rapidly than water-insoluble fraction.Additionally,the polymerization mechanism of water-soluble fraction was investigated by evaluating the changes in its physical properties（water content,viscosity and element content）and chemical compositions（gas chromatography and liquid chromatogram）before and after aging.The results showed that hydroxy aldehydes and ketones（especially glycoaldehyde,acetol and levoglucosan）,dicarbonyl compounds andα,β-unsaturated carbonyl compounds were mainly responsible for water-soluble fraction polymerization.The reaction process and reaction pathway of levoglucosan conversion to methyl lactate at different temperatures with different m（H-Beta）:m（Sn-Beta）ratios were investigated.The results showed that the yield of methyl lactate was mainly affected by the conversion degree of methyl-glucoside and the competitiveness degree of the dehydration pathway.The relatively higher temperature and appropriately lower m（H-Beta）:m（Sn-Beta）ratio were favorable for the production of methyl lactate.Under the optimal conditions,the highest yield of 35%could be obtained.H-Beta mainly catalyzed the methanolysis of levoglucosan and the hydrolysis of methyl glucoside,whereas Sn-Beta mainly catalyzed the retro-aldol of fructose.The reaction process of model compounds（glycoaldehyde,levoglucosan）and pyrolysis oil water-soluble fraction oxidation to glycolic acid and formic acid over H₃PMo₁₂O₄₀·n H₂O was investigated.The product distribution of the two single model compounds oxidation and the reaction path of their conversions to two acids were determined.The optimal reaction condition for the model mixture oxidation was determined.The oxidation of pyrolysis oil water-soluble fraction under the optimal process condition was negatively affected by phenols,cyclopentanone and furans.After removing the above three types of chemicals by activated carbon adsorption,satisfactory results could be obtained.The yields of glycolic acid and formic acid were31.7%and 23.6%（based on the carbon moles of main substrates）,respectively.The reaction process of model compounds（glycoaldehyde,acetol and levoglucosan）and pyrolysis oil water-soluble fraction hydrogenation to diols over（Ni+H₂WO₄）was investigated.The product distribution of levoglucosan hydrogenation at different temperatures and times was determined and analyzed.The process of the model mixtures hydrogenation under different catalyst compositions was investigated and the optimum condition was determined.The total yield of diols obtained from the water-soluble fraction hydrogenation under the optimal condition was much less than that obtained from the model mixture hydrogenation.Various other types of chemicals in the water-soluble fraction tended to polymerize during reaction,and then deactivated Ni.After removing the other types of chemicals by activated carbon adsorption and subsequent reactive extraction,the yields of ethylene glycol and 1,2-propylene glycol could be increased to 40.4%and 42.0%（based on the carbon moles of main substrates）,respectively.The thesis can provide reference for the formulation of measure for stabilizing pyrolysis oil,the development of process for converting pyrolysis oil（or its fraction）to high value-added chemicals and the improvement of catalyst for retro-aldol reaction.