Thermal decompositions of three components of biomass (cellulose, hemicellulose and lignin) were studied using nonisothermal thermogravimetric analysis (TGA) under both oxidative and inert atmospheres at a heating rate of 10 K min(-1). The multi-Gaussian-distributed activation energy model (DAEM)-reaction model was first developed to describe thermal decomposition behaviors of three components. Results showed that the presence of CO₂ enhanced the thermal decompositions of three components in high temperature range, but made little difference in low temperature range. Decomposition behaviors under CO₂ were analyzed by the two-stage reaction mechanism corresponding to the pyrolysis process of original materials and the gasification process of char. During gasification stage, CO₂ was reduced to CO, which provided a possibility of a reduction in greenhouse gas emissions. In addition, more CO was produced, and therefore the thermal value of gas was improved. The findings imply that CO₂ gasification technology of biomass has great research significance.

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To maximize selective condensation of organics that are of known higher commercial value and to investigate the effects of selective condensation on bio-oil characterization, pine sawdust was pyrolyzed in a 1-5 kg/h bench-scale fluidized-bed reactor. In the experiments, the selective condensers and electrostatic precipitator were used to condense the pyrolysis vapors. In addition, the characterization of bio-oils, gases, and biochar was investigated. The results showed that the total bio-oil, gases, and char yields were 41.5, 43.3, and 15.2%, respectively, and 86.2 wt % water steam was condensed in condenser 1. The bio-oil condensed in the later condensers has a lower water content, higher pH value, higher heating value, and higher kinetic viscosity compared to the first one. Analysis of the 1, 4, and 5 bio-oils with gas chromatography-mass spectrometry (GC-MS) showed that 102 types of chemical compounds were detected and most of the compounds were condensed at different condensers. Therefore, the selective condensation is useful to separate the water and chemical compounds from bio-oil compared to direct contacting condensing. The gas products were mainly CO, H 2 , CO 2 , CH 4 , and C 2 -C 4 . Char characteristics were determined by ultimate analysis, Fourier transform infrared (FTIR) spectrometry, and scanning electron microscopy (SEM) methods. A lot of bonds, such as -NH-, -CH-, -CdC-, -CH 3 , and -C-O-C-, were found in the char samples. It was observed that the surface morphology of the pine particle changed after pyrolysis, and it became thinner and shrank. The thermal decomposition of chemical bonds and the melting of some compounds can break the chemical bonds of the original material, and the chemical bonds with lower bond energies break with priority. The research has provided a useful reference for biomass fast pyrolysis.

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This work deals with the pyrolysis kinetics of cellulose, hemicellulose and lignin. Experiments were carried out in a thermogravimetric analyzer (TGA Q5000) in the inert atmosphere of nitrogen at a heating rate of 10 K min À1 . The single Gaussian distributed activation energy model (DAEM) was utilized to study the pyrolysis kinetics. Kinetic parameters such as the pre-exponential factor (k 0 ), mean activation energy (E 0 ) and standard variance (s) were computed by a pattern search algorithm. It was found that the calculated kinetic parameters using the single Gaussian-DAEM-reaction model could reproduce the differential thermogravimetric (DTG) curves of cellulose very well. However, there existed obvious deviations in the whole range of temperatures between the calculated and experimental data for hemicellulose and lignin.In order to describe the thermal decompositions of hemicellulose and lignin more accurately, a novel double Gaussian-DAEM-reaction model consisting of two parallel partial reactions was developed to describe the pyrolysis processes. Calculated results of the fitting procedure using the double Gaussian-DAEM-reaction model showed good agreement with experimental DTG data of hemicellulose and lignin.

The kinetic and energy productions of pyrolysis of a lignocellulosic biomass were investigated using a three-parallel Gaussian distribution method in this work. The pyrolysis experiment of the pine sawdust was performed using a thermogravimetric-mass spectroscopy (TG-MS) analyzer. A three-parallel Gaussian distributed activation energy model (DAEM)-reaction model was used to describe thermal decomposition behaviors of the three components, hemicellulose, cellulose and lignin. The first, second and third pseudocomponents represent the fractions of hemicellulose, cellulose and lignin, respectively. It was found that the model is capable of predicting the pyrolysis behavior of the pine sawdust. The activation energy distribution peaks for the three pseudo-components were centered at 186.8, 197.5 and 203.9kJmol(-1) for the pine sawdust, respectively. The evolution profiles of H2, CH4, CO, and CO2 were well predicted using the three-parallel Gaussian distribution model. In addition, the chemical composition of bio-oil was also obtained by pyrolysis-gas chromatography/mass spectrometry instrument (Py-GC/MS).

a b s t r a c t a r t i c l e i n f oThe pyrolysis of three representative sources of biomass, namely, white ash, switchgrass and corn stover were investigated using a fixed-bed reactor to observe and compare the characterizations of three energy carriers, biochar, syngas and bio-oil. The characteristics of biochar were determined by Fourier Transform Infrared Spectroscopy (FT-IR), X-ray diffractometer (XRD) and Scanning Electron Microscopy Energy Dispersive Spectroscopy (SEM-EDS), Gas Chromatography (GC) and Gas Chromatography Mass Spectrometry (GC-MS).The results showed that the carbon content of biochar increased with the increase of pyrolysis temperature. More than 52 wt.% of the carbon was captured in the biochar. The infrared spectra of char samples illustrated that various bands in the spectra were identified, corresponding to stretches -NH-, aliphatic stretches -CH-, stretches conjugate -C_C-, -CH 3 and stretches -C\ \O-. The surface morphology of biomass sample changed after pyrolysis and carbon fiber can be formed at the temperature of 500°C. The content of combustible gas CH 4 , H 2 and CO was changed from 50% to 70%. The GC-MS analysis of bio-oil showed that most of the chemical compounds detected were phenolic ones. This study provides a useful reference for energy carriers from the pyrolysis of biomass.

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