Study On The Mechanism Of Direct Liquefaction Of The Microalgae Cultured Based On Component Regulation And Optimization Through CO2 Emission Reduction

The global energy demand and environmental pollution issues are the driving force for people to seek alternative energy sources.Alternative sources such as biofuels have attracted the attention of researchers due to their renewable and eco-friendly nature.Microalgae biomass has significant advantages,such as wide distribution,short growth cycle,strong environmental adaptability,no land competition with crops,high photosynthesis and CO₂ fixation efficiency,etc.,which is a powerful boost to the realization of"carbon neutrality".As the third-generation biofuel,microalgae biofuel has become a research hotspot.However,the production cost of raw materials and their energy conversion efficiency are still the main reasons hindering the development of microalgae biofuels.The optimization of microalgae cultivation and the quality of thermochemically transformed bio-oil are key issues that limit its commercial utilization.This study starts from two aspects of microalgae component regulation and liquefaction utilization,and establishes a model of microalgae component regulation,CO₂ reduction,and direct liquefaction to produce bio-oil.The research on the influence of CO₂concentration on the growth of microalgae,the production rate law of liquefaction oil production conditions,and the energy and environmental assessment of system products have been carried out.Meanwhile,the organic combination of microalgae resource utilization,energy saving,and emission reduction has been realized.Therefore,the main work of this thesis is divided into the following points:Based on the selection of CO2 tolerance microalgae,Micractinium sp.YACCYB505,the growth of microalgae is explored,and the Box-Behnken Design response surface method is used to investigate the content of microalgae components（lipids,carbohydrates,and proteins）.Studies have shown that the dry weight and total biomass productivity of Micractinium sp.under 5%and 10%CO2 concentration are significantly increased compared with the control group,and induce a large amount of lipid accumulation.It shows that the addition of CO2 can promote the growth of Micractinium sp.Under the light intensity of 3200 lux,the light energy absorbed by the cells is still not saturated,and it has a higher dry weight and total biomass productivity than 2400 lux.Statistics show that the maximum difference in lipid content can be up to 2 times（14.73-32.98%）.The optimization of microalgae cultivation can help reduce cultivation costs.The Central Composite Design response surface method is used to conduct direct liquefaction experiments on microalgae components under different working conditions（temperature,time,ethanol-water ratio,and material ratio）.The bio-oil yield prediction model related to the microalgae components and various working conditions parameters is established.The model shows that the optimal temperature for Micractinium sp.liquefaction is around 300°C.The alcohol-to-water ratio has a significant effect on the yield of liquefied bio-oil.As the alcohol-to-water ratio increases,the yield of bio-oil increases sharply,which is related to the fact that the addition of ethanol reduces the yield of water phase products.In addition,CO₂ concentration affects the product yield by regulating the structure of microalgae components.The increase in CO₂ concentration is accompanied by the accumulation of lipids resulting in a gradual increase in the yield of bio-oil.Although Micractinium sp.grown under 0%CO2 conditions has a higher carbohydrate content,the lower lipid and protein content results in a lower bio-oil yield.In addition,the study found that he addition of ethanol in the Micractinium sp.liquefaction reaction greatly changed the composition of the product and promoted the esterification reaction.Compared with the 50%ethanol-water co-solvent,the liquefaction reaction of pure ethanol solvent improves the yield of bio-oil and energy on the one hand,and promotes the formation of ester compounds on the other hand.The higher sugar content in the raw materials is not suitable for the production of bio-oil due to the production of more nitrogen-containing compounds.In addition,the evaluation data on the environmental effects of the system show that the large amount of electrical energy input during the cultivation and liquefaction of microalgae directly affects the net input of the functional unit,and the amplified system has achieved good environmental benefits with the advantage of negative carbon dioxide emissions.In this study,the biofuel preparation system that combines microalgae cultivation and liquefaction conversion is a low-cost,sustainable,and high-efficiency system.It has achieved certain ecological and environmental benefits,and confirmed the economic feasibility of microalgae biofuel technology.At the same time,it can provide theoretical and application guidance for the regulation of microalgae components and its thermochemical conversion technology,and it is also of positive significance for the research of greenhouse gas emission reduction.