| As a green renewable energy source,biomass has received more and more concern and attention.Microalgae,which is the third generation biofuel,has attracted great attention of current research.Chemical conversion technology is a common technology for microalgae to produce biocrude oil.Especially,as a kind of efficient liquefaction technology,solvolysis liquefaction of microalgae has attracted the attention of researchers.At present,the foreign and domestic researches still have poor understanding of the liquefaction mechanism of solvolysis liquefaction of microalgae in ethanol-water solvent.The synergy effect between ethanol and water,and the interaction between protein and carbohydrate,have not been deeply explored.Therefore,Chlorella pyrenoidosa was chosen as the research object.And then this study in-depth investigated the effect of reaction parameters and model components on the biocrude oil yield and the composition of liquefied products.Through adjusting the component proportion of microalgae,the improvement of biocrude oil yield and quality was also studied.Thus,this study could provide deep understand of the reaction mechanism of solvolysis liquefaction of microalgae.Moreover,it has an improtant practical significance.Firstly,the influence of reaction temperature,retention time,solid/liquid ratio and ethanol content on biocrude oil yield was investigated.Moreover,the energy evaluation of solvolysis liquefaction technology was studied.The results showed that the reaction temperature,solid/liquid ratio and ethanol content obviously improved the biocrude oil yield.Instead,the influence of retention time on biocrude oil yield was negligible.When the reaction temperature was below 260 °C,there existed a black product which was insoluble in dichloromethane(DCM)during the extraction process.The yield of this insoluble product was less than 1%.After dried in the air,it became fragile solid.Comprehensively considering the energy consumption of microalgae cultivation step,harvesting step,dewatering step,ethanol production step and conversion step,the net energy ratio of solvolysis liquefaction technology was higher than the pyrolysis technology when the reaction temperature was 300 °C,retention time was 60 min,solid/liquid ratio was 18.8/75 g/m L and ethanol content was less than 40%.Secondly,this paper investigated the composition of liquefied products from solvolysis liquefaction of microalgae through various analysis equipments,which achieved the effect of ethanol content on the composition of liquefied products.The results showed that the addition of ethanol contributed to the decomposition of solid residue,and decreased the aromaticity of solid residue.However,when the ethanol content exceeded 60%,the repolymerization of solid residue occurred,resulting in the generation of solid particles with compact structure.The DCM-insoluble solid products had a flat smooth surface and dense matrix.With the increasing of reaction temperature,the aromaticity of DCM-insoluble solid product decreased.The ethanol-water cosolvent contributed to the generation of nitrogen-containing compounds in aqueous product,and decreased the content of toxic nitrogenous organic compounds with two or more methyl groups in aqueous product.The esters content of biocrude oil and light oil increased with the increasing addition of ethanol.The biocrude oil obtained from 60% ethanol content had the highest content of kerosene and diesel oil,and performed the best thermal stability.Thirdly,the kinetic behavior and evolution characteristics of gaseous products during the combustion of biocrude oil were investigated by TG-FTIR.The results showed that the combustion process of biocrude oil could be divided into three stages,the light compounds combustion stage,the heavy compounds combustion stage and porous char combustion stage.The ethanol-water solvent contributed to the generation of cenosphere,which resulted in higher burnout temperature of biocrude oil.In combustion stage 2,the activation energy of biocrude oil from ethanol-water solvent was higher than that from sole water.Compared to other biocrude oil samples,the biocrude oil obtianed from 40% ethanol content had the highest absorbance of C-H,C=O and C=C in combustion stage 1,and the lowest absorbance of CO in combustion stage 3,which performed better combustion characteristic.Fourthly,model compounds,such as soya protein,corn starch and their mixture,were liquefied in water,ethanol and ethanol-water solvents to investigate the synergistic effect between ethanol and water and the interaction between protein and starch.The results showed that starch contributed less to the biocrude oil yield(2.71%)in sole water solvent compared with protein(27.95%).However,in the ethanol-water solvent,the addition of starch into protein could enhance the Maillard reaction,which promoted the conversion of protein into biocrude oil.Based on the optimal mixed ratio of protein/starch(2/1),14 wt% of starch was added into the microalgae.As a result,the biocrude oil yield increased from 42.93% to 45.79%,and the energy recovery reached up to 80.50%.The esters content of biocrude oil increased from 38.81% to 52.91%.And the pyrazines content of light oil increased from 6.32% to 41.76%,which indicated that the Maillard reactions were promoted greatly after adding appropriate amount of starch into the microalgae.Based on the above component analysis of biocrude oil and light oil from different feedstock in different reaction solvents,a possible reaction pathway of solvolysis liquefaction of microalgae in ethanol-water solvent was proposed.Subsequently,adopting sweet potato residue with high starch content replaced the pure starch.The effect of different microalgae/sweet potato residue ratio on biocrude oil yield from hydrothermal liquefaction was investigated.Through the composition analysis of biocrude oil and biochar,the interaction between microalgae and sweet potato residue was explored.The results showed that the biocrude oil yield from hydrothermal liquefaction of microalgae(38.06%)was higher than that from sweet potato residue(12.94%).However,the excess amount of sweet potato residue would inhibit the decomposition of microalgae.However,3/1 of microalgae/sweet potato residue ratio achieved the highest energy recovery of biocrude oil and biochar.When the microalgae/sweet potato residue ratio was below 1/1,the biochar occurred demethanation reaction,resulting in lower calorific value.With the increasing addition of sweet potato residue,the hydrocarbons content of biocrude oil performed decline tendency.The combustion activation energy of biochar was lower than microalgae and sweet potato residue.The biocrude oil from co-liquefaction had lower comprehensive combustion index than microalgae biocrude oil.Finally,the effect of different reaction solvent(water,ethanol-water and ethanol)and microalgae/sweet potato residue ratio on the products distribution,chemical composition of liquefied products and combustion performance of biocrude oil and biochar was investigated.The results showed that ethanol solvent achieved the highest biocrude oil yield for microalgae,while ethanol-water solvent achieved the highest biocrude oil yield for sweet potato residue and the mixture of microalgae/sweet potato residue.In the ethanol-water solvent,with the increasing addition of microalgae,the esters and ethers content of bicochar increased gradually.In the ethanol-water solvent,3/1 of microalgae/sweet potato residue ratio achieved the highest content of esters and hydrocarbons in biocrude oil.Co-liquefaction of microalgae and sweet potato residue in ethanol-water solvent effectively improved the kerosene content and decreased the lubricating oil content in biocrude oil.Moreover,it contributed to the decrease of combustion activation energy of biochar.In the ethanol-water solvent,with the increasing addition of microalgae,the comprehensive combustion index of biocrude oil decreased,and the activation energy of combustion stage 3 increased gradually.Based on the Maillard reaction between protein and carbohydrate,adopting ethanol-water solvent and adding appropriate amount of starch or sweet potato residue into microalgae,were effective ways to improve the yield and quality of biocrude oil. |
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