Pyrolysis Process And Thermodynamic Characteristics Of Lignocellulosic Biomass Components

Biomass is the only renewable energy which could provide fuels in solid, liquid andgaseous. However, due to the complexity structure of biomass, its pyrolysis behavior is also acomplex procedure with chemical and physical changes. In order to reveal the regulations ofendothermal or exothermal during biomass pyrolysis and interaction between components, thepyrolysis process of biomass and its components had been investigated by thermal analysis andthermogravimetric analysis methods. The main contents of the work are summarized asfollows:The pyrolysis characteristics of microcrystalline cellulose, xylan, lignin and their mixtureshad been investigated by Thermogravimetric analyzer （TG） and Simultaneous thermal analyzer（STA）. The results showed that both cellulose and xylan were fast pyrolyzed in a narrowtemperature ranges, in which an obvious endothermic peak has been observed with theabsorbed heat of547.98J/g and45.01J/g. Lignin was with a wide pyrolysis temperature region,with two heat releasing trends in the range of320⁵00℃. There were two weight loss peaks indifferent ratios of xylan and cellulose mixed components, and the two weight loss peaks wereinversely proportional to the ratio of xylan and cellulose. In addition, the pyrolysis of cellulosewas inhibited grater by xylan and the weight loss peak was shifted to higher temperature, andthe maximum weight loss rate was decreased sharply. While the xylan pyrolysis was lessaffected by cellulose. Two independent endothermic peaks had been detected in correspondingDTG peaks temperature region. The peak of xylan is less impacted by ratio of xylan, however,the peak of cellulose decreased largely when the ratio of cellulose decreased either in DTG orin DSC curves. There was only one weight loss peak in cellulose-lignin mixtures pyrolysiswhich main caused by the degradation of cellulose. The addition of lignin, the weight lossstarting temperature of cellulose was forward, the peak temperature was increased and themaximum weight loss rate was decreased largely. On DSC curve, the endothermic peak was only been detected in sample C2L1（ratio of cellulose and lignin is2:1）. There was only oneweight loss peak caused by xylan during the pyrolysis of the mixtures of xylan and lignin, andthe peak temperature is higher than that of xylan pyrolysis individually. There was anendothermic peak when the ratio of xylan was higher than that of lignin.Thermogravimetric analyzer coupled with a fourier transform infrared spectroscopy andthermogravimetric analyzer coupled with a mass spectrometry were utilized to analyze thepyrolysis process and on-line analyze the product evolved out during pyrolysis process. H₂O,CH₄, CO₂, CO and other organic compounds were the mainly pyrolysis products. H₂O wasalmost released during the whole pyrolysis procedure and the released temperature of otherproducts was corresponding to weight loss area. The pyrolysis products of the mixedcomponent was the superposition of each biomass components, and the yields of CH₄, acids,aldehydes, phenols and CO were increased while the release of CO₂decreases drastically. Theresults of TG-MS showed that the pyrolysis products of xlyan and cellulose were mainlyreleased in the rapid weight loss phase, and the lignin pyrolysis products was less and had abroader release area. The results of TG-MS analysis of mixed components are similar to that ofTG-FTIR analysis.Accelerating Rate Calorimeter （ARC） had been utilized to investigate the pyrolysis ofbiomass components and several types of biomass. The results showed that in the process ofslow heating rate pyrolysis, xylan had a sharp exothermic peak at204.5²32.2℃, and thereleased heat was566.205J/g; cellulose exothermic peak was in the range of242.3²60.5℃and generated655.225J/g heat; lignin pyrolysis showed a endothermic trend between133.3²92.2℃; the extractives also showed a similar tendency between98.1¹86.1℃. Themixed components of xylan and cellulose had two exothermic peaks between180²77℃.Compared to the pyrolysis of single component, the start exothermic temperature of xylan andcellulose were all declined. The exothermic reaction of cellulose was distinctively depressed inthe mixed components. There was an exothermic peak had been detected during thexylan-lignin mixtures pyrolysis. The addition of lignin had distinct prevented the heat release of xylan. With the lignin proportion increased, the exothermic peak of xylan became morefaint. The cellulose exothermic peak also depressed by the addition of lignin. There were twoconsequent exothermic peaks during the pyrolysis of each lignocellulosic biomass, and thesetwo peaks came from hemicellulose and cellulose respectively. The endothermic trend of ligninhas also been detected as well. Each biomass released different amount of heat, and the initialtemperature of was around190℃, the first peak was around220℃, the second peak wasconcentrated around255℃.Inert solvent was selected to extract beech and poplar sawdust, the correspondingextractives and extracted biomass were obtained. The structure of extractives, extractedbiomass and original biomass had been characterized by Fourier transform infaredspectrometer （FT-IR）. TG-FTIR and tube furnace were used to carry out pyrolysis. The resultshowed that the structure of extractives contains hydroxyl, carbonyl, benzene ring and esterbelt, and the removal of extractives did not change the basic structure of biomass and had lesseffect to the behavior of biomass pyrolysis. The mainly weight loss of extractives between227⁴50°C and a shoulder at227³00°C. DTG peak was362.9°C, the maximum weight lossrate was4.28%/min and the residue was30.82%. The mainly products detected by FTIR werewater, CH₄, CO₂, CO, acids, aromatics, phenols and alkenes. The pyrolysis of tube furnaceshowed that the main liquid products constituents of extractives were aromatic compounds,alkenes, esters, phenols, and ketones. Compared to original biomass, there were more totalcontent and type phenols for extracted biomass pyrolysis. However, the other competitionspecies were less than that of original biomass.Thermogravimetric analysis of cellulose was conducted in pressurized thermogravimetricanalyzer. TG curves under different heating rates （5,10,20K/min） and different pressures （0.1,0.5,1,1.5,2MPa） were obtained. Pyrolysis kinetic parameters were gained by thermalanalysis mathematical methodology. The results indicated that when heating rate was raised,the main pyrolysis region shifted to the higher temperature; pressure was enhanced, the mainpyrolysis region moved to the lower temperature, paralysis time became shorter and the ratio of residue raised. The activation energy increased along with the increase of pressure or heatingrate. There was a good compensation effect between preexponential factor and the pyrolysisactivation energy under all kinds of conditions.