Study On The Pyrolysis Behavior Of Cellulose And Hemicellulose In A Fixe-bed Reactor

Micro-scale reactors?such as Py,TG,etc.?have been extensively used to investigate the cellulose and hemicellulose pyrolysis behaviors.However,it is noteworthy that there are some shortcomings for the micro-scale reactors,for example,TG cannot provide high heating rate adopted in fast pyrolysis,the thermal lag for Py,and both of them neglect the effect of heat and mass transfer and cannot provide the production yield,which hinders the industrial application of those findings obtained from the micro-scale reactors.So,it is necessary to explore the pyrolysis behaviors of cellulose and hemicellulose in a lab-scale reactor prior to the industrialization.In present work,the char evolution,effects of condition parameters?temperature,material thickness and carrier gas flow rate?on the products distribution and bio-oil composition for cellulose and xylan pyrolysis in a fixed-bed reactor were investigated,and the char evolution and bio-oil composition of cellulose building blocks?cellobiose and glucose?and that of xylan?xylose and arabinose?were also examined for a better understanding the cellulos e and xylan pyrolysis.It was found that cellulose evolved from white powders to brown,and became black char finally under 300 and 500? respectivelyy,while the glucose,cellobiose,xylan,xylose and arabinose changed from white powders to porous and puffy char with a evident melting transformation.Cellulose white powders shrunk into black and shiny chip at 700?,which indicates cellulose melting needes enough high temperature or high heating rate.The FTIR analysis of these material residues implied that relative high temperature?500??caused the feedstock violent decomposition,while the dehydration was favored under relative low temperature?300??.The bio-oil yield for cellulose and xylan reached their peaks at 450? and 500?,respectively.And the content of furfural?FF?,cyclopentanones,low molecular weight compounds?such as acetic acid,hydroxyl acetaldehyde,hydroxyl acetone etc.?in cellulose bio-oil and that of hydroxyl acetaldehyde in xylan bio-oil increased with temperature increasing,while high temperature?>450??hindered the formation of levoglucosenone?LGO?and 5-hydroxymethyl-furfural?5-HMF?from cellulose and DAP2?an unknown compound may be produced from pentose by losing two H₂O?from xylan.The cellulose bio-oil yield went downhill when the material thickness exceeds 2 mm,while the content of LGO,5-HMF and FF in bio-oil increased and that of levoglucosan?LG?decreased with the material thickness increasing.It was noted that the xylan bio-oil yield increased monotonically with material thickness?1⁵ mm?,and the char yield almost kept stable,and thicker material layer enhanced the content of FF,DAP1 but decreased that of acetic acid and DAP2 in xylan bio-oil.Carrier gas flow rate posed similar influence on cellulose and xylan products distribution and their bio-oil composition,the bio-oil yield decreased when the carrier gas flow rate was lager than 2.55 L/min,however,fast carrier gas flow favored the recovery of LG and DAP2 in the pyrolysis of cellulose and xylan,respectively.Comparative study on the xylan,xylose and arabinose pyrolysis behavior showed the close relationship among them,both the xylose and arabinose contributed the FF formation in xylan pyrolysis,and the U1 only derived from the arabinose unit,U3 simply produced from the xylose unit and U2 speculatively merely yielded from the glucuronic acid unit.Comparative investigation on cellulose,cellobiose and glucose demonstrated that cellobiose produced the most char,glucose had the highest bio-oil yield.The similar bio-oil composition for cellulose,cellobiose and glucose,but the cellulose bio-oil had more LGO,cyclopentanones and low molecular weight compounds,while cellobiose bio-oil contained more furan compounds and glucose bio-oil had the highest content of 1,6-anhydro-?-d-glucofuranose.The findings of present work could provide guidance for the industrialization of cellulose and hemicellulose pyrolysis to some extent.