| As the main product of biomass pyrolysis and liquefaction,bio-oil is expected to alleviate the energy crisis and the climate crisis and has great potential for application.However,it has not been able to achieve large-scale market application because of high moisture content,low calorific value,low fluidity,easy coking at high temperatures and corrosive properties.Some of the undesirable properties of bio-oil can be improved by different separation and refining techniques to meet the needs of certain application scenarios.However,the economics of bio-oil utilization through a single method is currently not guaranteed.Therefore,it is necessary to combine various technologies to separate and transform the components according to their properties and values to achieve high-value utilization of the full components.Based on this,this paper proposed a pathway for the high-value utilization of bio-oil components by combining the technologies of fractional condensation,distillation separation,and electrochemical conversion.After separating the bio-oil into different qualities through fractional condensation,the bio-oil enriched with high value-added chemicals was distilled to obtain fractions and distillation residues.The fractions could be prepared as zerocarbon high-value-added chemicals,while the distillation residue could be converted and utilized by direct combustion,as well as the preparation of biomass carbon and porous carbon materials.The high water content bio-oil could be electrochemically transformed to produce high-value gaseous fuels,while the solid products could then be further utilized as fuels or new materials.To explore and study the pathway of full-component high-value utilization of biooil,the following work was carried out in this paper:Firstly,by analyzing the main components of bio-oil,six principles for selecting the characteristic components in the distillation process of bio-oil were proposed based on factors such as substance category,content,utilization value and interactions involved in the distillation process,and a bio-oil distillation molding system was established.Subsequently,an intermittent distillation model was constructed by Aspen plus,and the distillation characteristics of each characteristic component were simulated at five different pressures of 1.0 bar,0.7 bar,0.5 bar,0.35 bar,and 0.2 bar.The results showed that the total fractionation rate of the molded compounds was the highest at 1.0 bar,reaching 88.6%.At lower operating pressures,the distillation temperatures of the components decreased significantly,and the high value-added products such as phenol and guaiacol were enriched in the high-temperature fraction.According to the results of the simulation,the distillation of the molded compounds was verified at 1.0 bar,0.7 bar,and 0.5 bar using a bio-oil distillation and separation pilot plant.It was found that the total fractionation rate of the molded compounds increased under the reduced pressure environment,and the yield of distillation residue in the tower kettle decreased.Moreover,the fractionation rates of acetic acid,furfural,phenol,and guaiacol at 0.5 bar increased by 10.0%,8.3%,4.7%,and 9.8%,representing the reduced pressure conditions were more favorable for the separation of the high value-added components in bio-oil.Analysis of the distillation residue revealed that the carbon content of it was as high as 74.51%,and the structure was relatively dense with no observable pores present.The infrared analysis showed that the condensation reaction of phenols and aldehydes occurred during the distillation process,and the components involved in the reaction included furfural,phenol,and guaiacol.The distillation characteristics of the crude bio-oil were then investigated and eight characteristic components were selected to trace their contents,including acetic acid,furfural,methylcyclopentenone,phenol,4-ethylphenol,guaiacol,4-methyl guaiacol and 4-ethyl guaiacol.The bio-oil distillation process could be divided into the stable phase,the fast growth phase,and the coking phase.The fast growth stage was the most efficient stage for the distillation of high value-added chemicals and would not lead to swelling and coking of bio-oil.Whereas the bio-oil would swell and coke rapidly in the coking stage,which greatly affected the reactor cleaning and the continuity of the experiment.Some characteristic components,represented by furfural and guaiacol,slowed down or even started to decrease in yield growth at this stage,which indicated that some high value-added compounds might be involved in the coking reaction,leading to a decrease in separation efficiency.In addition,an azeotropic-like phenomenon occurred during the distillation of bio-oil,with a common distillation temperature threshold for most characteristic components including acetic acid,furfural and phenols.This might be due to the formation of molecular forces of different strengths in the components of bio-oil.There was also redistribution of components in different fractions during distillation,such as water and acetic acid.This could be avoided by the separate collection of fractions from different temperature stages with separate preservation of the oil and water phase fractions.To investigate the utilization of fractions obtained from bio-oil distillation,the phenolic substances in bio-oil fractions were extracted by barium ion precipitation method.And the effects of adding NaOH concentration,reaction temperature,and reaction time on the extraction rate of guaiacol were investigated.The results showed that the barium ion precipitation method could effectively separate the phenolic substances in the fraction,and the separation effect was more obvious for guaiacol,and the extraction rates of low-temperature aqueous phase fraction,low-temperature oil phase fraction and high-temperature fraction could reach 34.1%,33.8%and 33.5%,respectively.The structure of the precipitation produced by barium ion and phenolic substances was not stable,and it would start to decompose at a very fast rate at a higher temperature.Considering the material consumption,reaction rate and phenolic extraction rate,adding NaOH solution with a concentration of 5.5 mol/L at 35℃ and continuing the reaction for 20 min was the best operating parameter for the separation.The effects of distillation temperature on the elemental composition,macroscopic properties,microstructure,functional group composition and pyrolysis properties of distillation residues were analyzed.The main characteristics of distillation residues prepared at different distillation temperatures were summarized,and their potential utilization paths were studied.The results showed that the residues prepared at 120℃could be considered for re-separation of components,while the distillation residues from 140 to 220℃ were more suitable for co-pyrolysis with coal or biomass feedstock to achieve high-value utilization.The distillation residue at 240-300℃ could be utilized directly as a fuel due to its high calorific value,or it could be transformed into a highperformance carbon material by preparing porous biomass carbon for high-value utilization.In this paper,after enhancing the electrical conductivity with ammonium carbonate,the bio-oil electrochemical conversion experiments were carried out by an H-type electrolytic cell using the constant current method.The properties of the three types of products,gas,liquid and solid,were analyzed and characterized.The main reactions occurring during the electrochemical conversion of bio-oil were deduced and summarized.The main reactions in the electrochemical conversion of bio-oil included copolymerization of phenols,aldehydes and lignin oligomers,decarbonylation and decarboxylation of unsaturated fatty acids and water cleavage reactions.The copolymerization reaction produced solid products,while the decarbonylation and decarboxylation of unsaturated fatty acids and the cracking of water produced gaseous products such as carbon monoxide,carbon dioxide,hydrogen and some olefins.The total content of flammable gases in the gaseous products was 79.24%,indicating a great potential for application as gaseous fuels.The solid products,on the other hand,might mainly originate from the copolymerization of phenols,aldehydes,and lignin oligomers,which could be subsequently utilized as feedstock for the preparation of new materials. |
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