| With the rapid development of social economy and rapid population growth,the annual output of sludge in China has been increasing.Due to its high energy density,sludge is a potential raw material for the preparation of liquid biofuels,but a large amount of harmful and toxic substances in it have brought huge problems to its disposal and resource utilization.At present,the treatment of municipal sludge by hydrothermal liquefaction method has attracted more and more attention due to its incomparable advantages.The sludge contains a large amount of nitrogen-containing compounds such as protein,which results in a high content of nitrogen in bio-oil and restricts the burning and utilization of bio-oil.Therefore,it is necessary to study the migration and transformation pathways of nitrogen in the liquefaction process.Based on research progress,this article takes municipal sludge and its model compounds as the research object,systematically studies the effects of reaction conditions and catalysts on sludge hydrothermal liquefaction,bio-oil physical and chemical properties,and nitrogen migration and transformation,as well as on liquefaction technology and the large-scale utilization of bio-oil has important reference value.Based on the methanol-water mixed solvent liquefaction,in order to improve the yield of bio-oil produced by sludge liquefaction,the two-stage liquefaction technology provides a new research direction for bio-oil production from sewage sludge.Studies have shown that the two-stage continuous hydrothermal liquefaction of a methanol-water mixed solvent at medium and low temperatures has a greater impact on sludge liquefaction.When the reaction conditions were 260℃-40 min-340℃-40 min,the bio-oil yield is the highest 42.2%,the highest ester content is 41.8%.Two-stage continuous liquefaction has a great influence on the distribution of nitrogen in each phase product.The nitrogen content in bio-oil and solid products increased,but most of the nitrogen still exists in the water phase product.A series of metal-supported HZSM-5 catalysts with different loadings were prepared by impregnation method,and the influence of Ni and Co content in HZSM-5 catalyst on the performance of sludge hydrothermal liquefaction was studied.The metal-supported HZSM-5 catalyst combines the catalytic performance of metal and molecular sieve,and the specific surface area and acidity of the catalyst were increased.When the loading of Ni and Co were 1%and 0.5%,the yield of bio-oil reached the highest value,which was 26.16%and 28.55%,respectively.The bio-oil obtained by catalytic liquefaction has higher hydrogen content and lower nitrogen and oxygen content.Ni,Co modified HZSM-5 showed a similar nitrogen transfer tendency.Under the action of the bifunctional catalyst,the transfer of nitrogen in the sludge to the water phase and solid products is enhanced,and the conversion of polycyclic nitrogen-containing compounds in the bio-oil to amines and amides is promoted.The model compounds were further used to clarify the transformation mechanism of organic matter and the migration and transformation path of nitrogen in the hydrothermal liquefaction process.Lysine,glucose and oleic acid were selected as the typical organic components of sludge.When the liquefaction feedstock contained lysine,the type of nitrogen element in the nitrogen-containing components of bio-oil was emphasized.Lipids are the main contributor to the yield of bio-oil,and the contribution rate of the yield of bio-oil is arranged in the order of lipid>protein>carbohydrate.There was a synergistic effect between protein and carbohydrate in the liquefaction process,and the interaction between the two could significantly improve the yield of bio-oil.Part of the nitrogen and oxygen heterocycles in the reaction system can react with the long-chain fatty acids generated by the cleavage of oleic acid to form fatty acid amides.In the presence of lipids,the formation of amides competes with the formation of nitrogen-containing heterocycles. |
PDF Full Text Request