Study On The Improvement Of Bio-oil Quality By Biomass Pretreatment And Composite Solvent

With the development of economy,the problems of energy shortage and envi-ronmental pollution bring great challenge to sustainable development of the world.Biomass has attracted more and more attention as a kind of renewable energy.The fast pyrolysis is a promising technology for biomass utilization because of its low production cost,short cycle and high efficiency.The bio oil was prepared by biomass pyrolysis,which has advantages of storage,transportation and clean.It was an alter-native to fossil fuel.Nevertheless,the composition of bio oil is complex,and has dis-advantages of strong corrosion,high viscosity and low heat value,which cause many obstacles to application of bio-oil.The research shows that the metal elements in bi-omass can catalyze the reaction during the pyrolysis of biomass,which reduce the quality of bio oil,and bio-oil contains a large number of active oxygen functional groups in the bio oil,which will occur in the storage process,such as polymerization,acetal and other reactions,resulting in the easy stratification of bio oil.Based on this,this paper mainly improves the quality of bio oil through biomass pretreatment and adding composite solvents in bio oil.(1)Influence of pyrolysis products distribution by oil washing pretreatment bio-massThe aqueous phase bio oil obtained by fractional condensation of biomass pyrol-ysis,which has characteristics of acidity and high water content.The quality of py-rolysis products was improved through aqueous phase bio oil water washing pre-treatment(oil washing).Element analyzer,Py-GC/MS and thermogravimetric analyz-er were used to study the pretreatment of walnut shell with oil washing.The results showed that the content of four metal elements of Na,K,Ca and Mg decreased,and because of the strong activity of alkali metals,the content of Na and K decreased most obviously.The walnut shell pyrolysis process mainly goes through four stages:dehy-dration,preheating,fast pyrolysis and carbonization stage.The oil washing pretreat-ment has an effect on the composition and structure of walnut shell,the whole curve is shifted to the right,the identification degree of the two peaks of the curve increases,the maximum weight loss rate increases,and the final residual amount is reduced.The oil washing pretreatment reduces the content of metal elements in the walnut shell,reduces the production of acids and ketones,increases the yield of phenols and sugars in the pyrolysis products,and thus improves the quality of the bio-oil.Under the con-dition of constant pyrolysis time,the type and yield of pyrolysis products first in-creased with the increase of temperature.When the temperature was higher,the types of pyrolysis products remained unchanged.When the pyrolysis temperature is 500?,the target product represented by phenols is the largest.At high temperature,exces-sive pyrolysis time leads to two cracking of phenols.Therefore,when the pyrolysis temperature is 500 500?,the best pyrolysis time is 20s.(2)Adding composite solvent to improve the stability of bio oilThe bio-oil aging was tested under 80?.The viscosity,water content,pH value and chemical composition of bio oil before and after aging were studied.The results showed that the viscosity and water content of bio oil increased,and the phenols,al-dehydes,ketones and furans decreased.This is due to polymerization,acetal,esterifi-cation and oxidation of aldehydes,ketones and other compounds in bio oil.Therefore,based on this,the study of the effects of n-butanol,two methyl sulfoxide and ethyl acetate on the storage performance of bio oil,the bio-oil was physically diluted,re-duced the reactant concentration or changed the microstructure of the bio oil to reduce the rate of bio oil reaction and the reaction with the active components in the bio oil to inhibit the macromolecular polymerization.The com-posite solvent,which consisted of 2.421 wt%n-butanol,2.327 wt%DMSO and 3.252 wt%ethyl acetate,was obtained through simplex lattice of mixture design.A 24 h aging experiment at 80? revealed that composite solvent can improve bio-oil stability,and the effect of the composite additive was superior to that of a single additive.During the long aging process(12,24,36 and 48 h),the increase in viscosity and water content of the blank group was larger than that of the control group.Thermo-gravimetric analysis(TGA)results showed that the residual mass fraction of the bio-oil rose with aging time,and the trend increase of blank was larger than that of control.GC-MS findings showed that the content of phenols was highest in bio-oil samples and decreased with increasing aging duration.The total contents of ketones,aldehyde and furans diminished with aging time.