The Applied Fundamental Research On The Pyrolysis Of Mallee Wood

With the deterioration of environment and the increasing crisis of fossil fuel,the sustainable biomass,which was regarded as the potential fuel resource,has attracted much attention.Fast pyrolysis/gasification are the main thermo-chemical technologies converting the biomass to drop-in fuels or syngas.However,the commercialisation of pyrolysis was restricted by several factors,such as grinding of biomass,the energy supply,low quality of crude bio-oil,the usage of large amount of inert gas and the formation of tar.From the view of these points,the pyrolysis properties of mallee wood grown in Australia were systematically investigated in this study.Polycyclic aromatics are important components in bio-oil from pyrolysis or tar from gasification,which would significantly strict the upgrading(cracking or hydrotreating)of bio-oil or removal of tar.The mallee wood cylinders with the diameter of 8 mm and the length of 10 mm were used as feedstock and thermal treated at a temperature range of 150-260 ? in a fluidized-bed reactor.The pyrolyzing products trapped in the treated biomass were extracted with organic solvents and characterized with GC-MS,UV-fluorescence and FT-IR.The results revealed that polycyclic aromatics were formed even at temperatures as low as 150 ?.These aromatics could not be released and were mainly trapped in the resultant chars due to the mass transfer limitation in the big biomass particles.The formation and release of aromatics were enhanced with the increase in the temperature.It indicated that the temperature is the main factor influencing the formation and release of aromatics,which could be attributed to the mass transfer limitation.UV-fluorescence characterization of aromatics extracted by different solvents showed that these polycyclic aromatics contained polar functionalities(e.g.hydroxy groups,carbonyl groups or carboxylic groups)on the aromatic rings.From the view of grinding pyrolysis,understanding and controlling how the grinding and pyrolysis affect the formation and release of aromatics in a pyrolyzing and shrinking biomass particle would be essential to optimizing the condition parameters.In order to achieve fast pyrolysis of large biomass particles and minimize the capital input,Curtin University proposed a new pyrolysis technology,grinding pyrolysis,which could be used for carbonaceous materials including biomass and coal.Based on this technology,the further investigations on the influencing mechanism of ex-situ grinding pyrolysis for big biomass particles were performed in this study.Mallee wood cylinders were firstly thermal treated at 150-380 ? and were then crushed into small particles before further pyrolysis at 500 ? in the fluidized-bed reactor.The results indicated that the thermal treatment alone for wood cylinders could not enhance the formation of bio-oil,while controlled thermal treatment coupled with ex-situ grinding obviously promoted the yield of heavy bio-oil from the pyrolysis of wood cylinders.As well,the thermal treatment temperature significantly affected the distributions of pyrolyzing products.Compared with the direct pyrolysis of wood cylinders and small particles(90-300 ?m),combined thermal treatment at low temperatures(< 200 ?)with ex-situ grinding promoted the formation of bio-oil.Also,the formation of polycyclic aromatics and active hydroxy unsaturated acetone/aldehydes in bio-oil was suppressed.With increasing the thermal treatment temperature to 230 ?,the yield of heavy bio-oil began to decrease,but the polycyclic aromatics and bio-char formation were increased.However,as the further increase in the thermal treatment temperature(? 320 ?),the yield of bio-oil decreased and the yield of biochar increased due to the cross-linking and charring reactions.These charring reactions compromised the beneficial effects of grinding,leading to decreases in the yield of heavy bio-oil.Thus,the balance between thermal pretreatment and grinding needed to be delicately managed to maximise the formation of bio-oil.Oxidative pyrolysis is an important method to supply energy for the whole pyrolysis process of biomass.In addition,oxygen would be carried into reactor with continuous feeding of biomass in both grinding pyrolysis and traditional fast pyrolysis.Correspondingly,the research about the effects of oxygen on the pyrolysis of biomass was necessary.Meanwhile,oxidative pyrolysis is an important method to supply energy for the whole pyrolysis process of biomass.Oxidative pyrolysis of mallee wood,lignin and cellulose were performed at 500 ? in a fluidized-bed reactor.The oxidation mechanism between oxygen and pyrolyzing products were studied through controlling the reactions invving oxygen.The results indicated that,oxygen concentration,gas-phase oxidation of pyrolysis vatiles and particle size of feedstocks played an important role in the distribution of products from pyrolysis of biomass.At low oxygen concentration(< 1.0 v%),the gas-phase oxidation of vatiles would improve the yields of phenol,levoglucosan,syringaldehyde and furfural as well as the unsaturated hydroxyl ketones/aldehydes for wood particles through the oxygeninduced radical reactions.Although oxygen could facilitate the production of some compounds in bio-oil through the gas-phase reactions,it did lead to the decrease of heavy bio-oil yield due to the over-oxidation of some pyrolysis products.In addition,effects of oxygen on the pyrolysis of wood cylinders were more complicated due to the secondary reactions of vatiles and the diffusion of oxygen to particle surface.By comparing the oxidative pyrolysis of biomass and its components,the data showed that the yield of bio-oil from the pyrolysis of lignin was not affected by the gas-phase oxidation of vatiles.Pretreatment of biomass prior to pyrolysis/gasification is an important way to modify the yield and quality of bio-oil or tar from the pyrolysis or gasification of biomass.Mallee wood particles were pretreated with water extraction of crude bio-oil and light bio-oil fraction and then were pyrolyzed or gasified at 500 ? and 800 ?,respectively.The results showed that the contents of inorganic metals such as K?Na?Mg and Ca decreased after pretreatment.The pretreatment prior to pyrolysis facilitated the formation of heavy bio-oil and levoglucosan during pyrolysis,while the yields of acetic acid and other carbonyl groups decreased after leaching.For the gasification at 800 ?,although the pretreatment process led to tiny increases in the tar yields,it did decrease the concentrations of polycyclic aromatics in tar,which was beneficial for the tar reduction.Leaching biomass with pyrolysis fractions from biomass itself was a potential method to improve the production of bio-oil and levoglucosan.Also,no extra minerals and chemical components were introduced into the pyrolyzing products during this process.