Study On Catalytic Hydrothermal Liquefaction And Co-liquefaction Of Municipal Sludge To Produce Bio-oil

At present,with the rapid development of social economy and the rapid process of urbanization,the output of municipal sludge is increasing year by year,which is characterized by high water content and a large amount of organic matter.Hydrothermal liquefaction method is suitable for the treatment of such high moisture content materials.In this paper,sludge catalytic hydrothermal liquefaction and sludge/biomass（rice bran,chlorella,waste oil）co-hydrothermal liquefaction were studied with sludge as the main research object to clarify the liquefaction mechanism.Co and Co-Mo heterogeneous metal-supported catalysts were prepared using Al₂O₃ and attapulgite（ATP）as supports,and were characterized to explore the influence of catalyst on the distribution and characteristics of sludge hydrothermal liquefication products.The results showed that Co-Mo/Al₂O₃ increased the bio-oil yield from 19.37%to 28.93%at 350℃for 15 min.Co-Mo/ATP had the best effect,increasing to 31.36%,and O content in bio-oil decreased by 2.36%.The selected catalysts all promoted the formation of phenols and hydrocarbons.Co-Mo/ATP,Co-ATP and Co/Al₂O₃ inhibited the formation of amide,while Al₂O₃ and ATP increased the contents of pyrazine and indole in bio-oil by promoting the Maillard reaction.The results of co-liquefaction of sludge and biomass（rice bran,chlorella,waste oil）showed that the synergistic effect was good when the ratio of sludge to rice bran was 3:1 at 350℃for 15 min,and the bio-oil yield was 27.52%,which was 2.37%higher than the theoretical oil yield.The model substances were selected to simulate sludge and rice bran（3:1）,and it was found that there was synergistic effect among all the selected model substances,among which the synergistic effect of egg-carbon group was the most obvious.The actual bio-oil yield was 14.33%higher than the theoretical yield,and the caloric value was 33.24 MJ/kg.Elements,variance,principal component,nuclear magnetic resonance spectroscopy（NMR）and gas chromatography-mass spectrometry（GC-MS）were used to analyze the bio-oil and explore the hydrothermal liquefaction mechanism of the model compound.The yield of bio-oil was positively correlated with lipid content and the yield of solid phase was positively correlated with carbohydrate content by principal component analysis.In the egg-carbon group,new nitrogen-containing compounds such as 2,5-dimethylpyrazine and 2,3,5-trimethylpyrazine were formed by maillard reaction.In addition,in the lipid-egg group,we found a reaction pathway between fatty acids and nitrogenous compounds,in which long chain fatty acids reacted with piperidine from lysine to form 1-（piperidine-1-yl）-1-decone.