Study On The Mechanism Of High-quality Bio-oil Prepared By High-efficiency Catalysis Of Microalgae Hydrothermal Liquefaction

Due to the decipitation of traditional fossil fuels and the increasing environmental problems caused by utilization of fossil fuels,renewable energy sources have attracted worldwide interests.Among them,bio-energy is recognized as a promising alternative of fossil fuels due to its green and carbon neturialization properties.Microalgae have the advantages of high photosynthesis efficiency,fast growing rate,high lipid yield,and no competition of land with food.Accordingly,they are recognized as the third-generation biomass energy raw material.Among the microalgal biofuel production strategies,hydrothermal liquefaction（HTL）is a promising technology that can convert algal biomass into bio-oil under high temperature and pressure.In order to improve the conversion efficiency of hydrothermal liquefaction and remove the content of heteroatoms as much as possible,this paper developed two different types of catalysts and used them to product bio-oil by hydrothermal liquefaction of microalgae.The specific research content and conclusions are as follows:The Keggin type（Mo-V-P）heteropolyacids was used as a catalyst to catalyze the preparation of low-nitrogen biocrude oil from microalgae HTL.Under the optimal conditions of 300℃,2h,5wt%H₄PMo₁₁VO₄₀,the yield of bicrude oil is 29.95%,which is an increase of19.66%compared with non-catalytic HTL.The nitrogen content is 1.09%,and nitrogen compounds are reduced by 71.17%.According to the detailed characterization of biomass oil and water phase（including GC-MS,TGA,elemental analysis,etc.）,possible catalytic mechanisms are proposed.Heteropolyacids increase the yield of biocrude oil by catalyzing the hydrolysis of cellular compounds,and reduce its nitrogen content by avoiding Maillard reactions between carbohydrates and protein hydrolysis intermediates.Mg Al-LDHx/LDOx was used as a catalyst to catalyze the production of low-oxygen biomass oil from microalgae HTL.Under the optimal conditions of 300℃,2 h,5 wt%Mg Al-LDH2,the yield of biocrude oil is 32.8%,which is 16.29%higher than that of non-catalytic HTL.Mg Al-LDH3 with higher acid sites has higher hydrolysis efficiency than Mg Al-LDO3catalyzing cellular compounds;Mg Al-LDO3 has higher basic sites,catalyzes the decarboxylation and decarbonylation of fatty acids more effectively than Mg Al-LDH3.Finally,a possible catalytic mechanism was proposed based on the detailed characterization of the biomass oil and water phase（including GC-MS,TGA,elemental analysis,etc.）.