| Biomass is an abundant and environment friendly source of renewable energy which has attracted a wide spread attention.Pyrolysis which converts biomass into gas,solid and liquid products is a promising utilization of biomass energy.However,to date,pyrolysis technology has not yet come to industralized application,because,as the main products of pyrolysis,bio-oilhas many disadvantages,such as high moisture content,low calorific value,corrosive and unstability.In addition,bio-oil is complex which contains more than 300 kinds of compunds,such as acids,aldehydes,ketones,furans,phenols.Separation and purification of bio-oil is very difficult,which limits its use as chemical raw materials.Currently,a series of condensers with different temperatureswere set to condense pyrolysis gas,thus,various kinds of bio-oils can be obtained,which reduces the complexity of a single bio-oil and improves the quality of bio-oil.Based on this background,the work carried out in this papercan be divided into two sections as the following.1.The composition and properties of biomass pyrolysis gas and bio-oil,as well as the establishment of pyrolysis gas model.Pyrolysis of rice husk,walnut shell,pine needle and phyllostachys pubescen were analyzed by Py-GC/MS,and the effects of pretreatment and experimental conditions on the pyrolysis products were also studied.The results show that the pyrolysis products containing a variety of high value-added compounds,such as furfural,2-(5H)-furanone,methyl cyclopentenolone,guaiacol,4-vinyl guaiacol.The pyrolysis products of the four biomass materials were similar,but the product contentswere certain difference.Pyrolysis of rice husk obtained high contents of2,3-dihydrobenzofuran and 4-vinyl guaiacol;phenolic products of walnut shell pyrolysis possessed high content,such as guaiacol,4-methyl guaiacol,4-vinyl guaiacol and isoeugenol;the contents of acetic acidand hydroxyl acetone were higher for the pyrolysis of pine needle;the mainpyrolysis products of phyllostachys pubescens were acetic acid,hydroxy acetone and 2,3-dihydrobenzofuran.It is necessary to point out that the pyrolytic products of pinus massoniana needle containedseveral unique compunds,such as pyrrole and limonene.Pretreatment can significantly affect the composition of biomass pyrolysis products.Water leaching decreased the yield of acetic acid and hydroxyacetone and increased the yiled of phenolic products.Acid leaching promoted the dehydration reaction and increased the content of furfural and levoglucosan.Alkali leaching promotes the pyrolysis of lignin and increase the content of phenols.The pyrolysis productswere simpleat low pyrolysis temperature and high pyrolysis temperature promoted cracking reaction which results in the more complex products.Extending the pyrolysis time was beneficial to the production of productsandrequired time was shorterata higher temperatureThe main components of bio-oil and accelerated aging bio-oil were analyzed by GC/MS and Py-GC/MS.Meanwhile,the main physicochemical properties of bio-oil were measured and analyzed.In addition,the thermogravimetric characteristics of bio-oil were analyzed by TG-FTIR.The results show that compunds of bio-oil were different by different detection methods.Components of bio-oils were comprehensive by GC/MS,while Py-GC/MS is less effective for the detection of volatile components and effective for the test of phenols.The components of bio-oil and pyrolysis gas were obviously different.The contents of aldehydes and ketones in bio-oil were relatively low,whereas the acetal contents were high.Contents of several aldehydes,ketones and furans in bio-oil decreased and contents of phenols and esters increased after accelerated aging procedure.The thermogravimetric process of bio-oil and aged bio-oil can be divided into three stages,namely the evaporationof the small molecules such as methanol and water,the volatilization and pyrolysis of heavy components such as phenols and anhydrosugar and the formation of coke.What's more,methanol addition has a good effect on the stability of bio-oil.According to the components identification of pyrolysis gas and bio-oil,several compounds were selected through a series of principles and a characteristic component model of the walnut shell bio-oil was established.In addition,a three chemical compounds model was built by the analysis of the non-condensable gas.At last,a 29 component model of pyrolysis gas of the walnut shell was established and the measurement and estimation of its physicochemical propertieswere analyzed.2.Fractional condensation of pyrolysis gas chemical model and biomass pyrolysis gas.A model of phenol,furfural,acetic acid,water,methanol and nitrogen was used for the study of fractional condensation.The results showed that the condensable components were condensed in the condensers according to their boiling point,but the condensation temperature was smaller than the corresponding boiling point.Highcondensation temperature was beneficial to the enrichment of the high boiling point products such as phenol and furfural and Low condensation temperature was beneficial to the enrichment of methanol.The effect of condenser structure on the component enrichment was different.A straight tube condenser has better effect on the enrichment of low boiling point components such as methanol and water,while a spherical tube condenser had better effect on the enrichment of furfural and phenol.A set of fixed-bed biomass pyrolysis reactor incorporated with three-stage condensers was constrcucted and rice husk and walnut shell were used for the tests.The results show that pyrolysis temperature significantly affectedthe liquid yield and composition.Increasing the pyrolysis temperature can increase the content of phenolic products,whereasa high pyrolysis temperature will reduce the guaiacol products.The fractional condensation temperature significantly affected the distribution of bio-oil and the carrier gas flow rate indicated minimal effects on the yields of products.The properties of the fractions seemed independent on the tests of the two feedstocks.Phenols and anhydrosugars are enriched at high condensation temperatures,whereas acids,alcohols,and ketones are concentrated at medium condensation temperatures,and furans and hydrocarbons reach the maximum yield at low condensation temperatures.A four-stage condenserattached to a pilot-scale pyrolysis apparatus was established andthe physicochemical properties of the bio-oils obtained in the fractional condensers were studied for pyrolysis of rice husk and walnut shell.The results show that when the temperature of the four-stage condensers were 220?,105?,70?,20? for pyrolysis of rice husk,the first fraction is viscous black substance andsolidification at room temperature;thesecond fraction had a high calorific value,high viscosity and high phenolic content,which was a promising intermediate for platform chemicals,for example,phenols;the three fraction had the most moisture contentandthe strongest acidity,whichcan be used as wood vinegar or extraction for acetic acid;the last fraction had a low water content,high calorific value and the weakest acidity,as well asseveral content of aromatic hydrocarbon,which can be used as liquid fuel.Moreover,when the temperature of the four-stage condensers were 70?,30?,20?,20? for pyrolysis of walnut shell,the first fraction contained the most moisture content,whichaccounted for more than 80%of the total water in liquid products;the physicochemical properties,composition and elements of the second and third fractions weresimilar,which can be usedas liquid fuels.The last fraction had the lowest moisture,the highest calorific value,the weakest acidity and the highest concentration of the phenols,which can be used as liquid fuel or chemicals. |
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