| Energy is the basic material resource for maintaining stability and promoting development in modern human society.With the acceleration of social development,the demand for energy is increasing day by day.The development and utilization of biomass energy and other renewable energy sources have attracted wide attention due to their non-renewable nature and destructive effect on the environment.Biomass energy has the characteristics of low carbon emission,renewable and environmentally friendly.At present,the bio-oil obtained from biomass by fast pyrolysis is easy to store,has many kinds of organic components and is widely used.Therefore,the separation and extraction of bio-oil to produce high quality liquid fuel and high value-added chemicals is a new way to solve energy and environmental problems.Atmospheric distillation is an industrial technology with the most mature industrial equipment in the current bio-oil separation methods.However,due to the disadvantages of bio-oil such as high water content,strong acidity,complex organic composition and low actual content of each compound,it is difficult to separate and purify the bio-oil directly by distillation.Aiming at this problem,this paper puts forward the idea of combining extraction technology,distillation technology and additives to improve the quality of downstream bio-oil products.The effects of the combination of extraction and distillation on the quality of downstream bio-oil products were investigated.Ethyl acetate,methylene dichloromethane,ethyl ether and toluene were mixed with the bio-oil in accordance with the same mass ratio of 0.8:1,and the extraction solution was separated by atmospheric distillation.The experimental results show that the distillate obtained by distillation of pre-extracted bio-oil is of high quality,and the water content in the oil layer decreases obviously,and the lowest water content is 0.91%.For example,among the four solvents of toluene,ethyl acetate,ethyl ether and dichloromethane,the extraction rate of toluene to biological oil was relatively low,resulting in that most of its fractions were extraction solvents,and the absolute peak area of phenols was relatively small.The extraction efficiency of ethyl acetate and ethyl ether was high,but the content of phenols in the distillate was very low because they contained ether bonds and were easy to react with bio-oil.Methylene dichloromethane has a high extraction efficiency for bio-oil,especially for phenolic compounds.The guaiacol and its derivatives in the fraction obtained after distillation have a high degree of enrichment,with a relative content of 34.11%.It is the most suitable for extraction-distillation among the four solvents to improve the quality of downstream products of bio-oil.The quality of bio-oil downstream products was improved by the combination of additive pretreatment and distillation technology,the physical and chemical properties of fractions were optimized,and guaiacols compounds were separated from bio-oil effectively.Six nitrogen compounds including urea,ammonium acetate,ammonium carbonate,ammonium bicarbonate,ammonium sulfate and ammonium dihydrogen phosphate were added into bio-oil in the same mass ratio before the bio-oil distillation.The results showed that all additives,except for ammonium sulfate,increased the pH value of fractions by facilitating the conversion of acidic compounds to salts.Adding additives could decrease the content of ketones and furfural in the fraction and increase the stability of fraction.Meanwhile,the moisture content of fractions was decreased and the content of high-value guaiacols compounds was increased.Among these additives,the minimum moisture content(7.48%),the maximum pH(5.10)of fraction and the maximum yield of high-value guaiacols compounds(increased by 85.89%)all were obtained by adding urea.Therefore,urea can be used as an additive to improve the quality of downstream products of bio-oil by means of atmospheric distillation.This paper also used different concentrations of additives and distillation technology to improve the bio-oil downstream products quality,from the yield,water content,pH value,elemental analysis,NMR,GC-MS,FID and so on methods to analysis the physical and chemical properties of bio-oil fractions and the enrichment influence of the organic composition compound.The concentration of urea was set at 1%,2%,3%,4%and 5%,and the distillation temperature was 280?.The results showed that with the increase of urea concentration,the quality of the oil layer gradually improved,and reached a better state at 4%concentration.Therefore,adding 4%urea into the bio-oil and combining with atmospheric distillation can improve the quality of the downstream products of bio-oil.In conclusion,the method of combining extraction or additives with distillation technology is highly feasible and simple.It has obvious effect on the quality improvement of bio-oil downstream products,which can provide a new approach and data reference for the separation method of high-value chemicals in bio-oil. |
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