Experimental Study On Lignin Pyrolysis Characteristics Of High-temperature In Different Atmosphere

With the growing shortage of fossil fuel and severity of environmental pollution, the exploitation and utilization of biomass energy has caused public concerns widely. Biomass pyrolysis technology is a kind of independent and efficient way of using biomass, lignin as an important component of biomass.It can improve the efficiency of biomass energy’s transition and utilization and explore the laws of biomass pyrolysis/steam to study the pyrolysis characteristics in different atmosphere of lignin.This paper got great support of the National Natural Science Foundation Project which named "Reaction Mechanisms research of Biomass Gasification using High Temperature Air/Steam based on Theoretical of Quantum Chemistry" (NO.51276023), and was engaged in systemic studying the pyrolysis behavior of lignin in different atmosphere.The main topics of this paper are as follows:(1) Research the structure of lignin. Micro-structure of lignin with fourier transform infrared spectroscopy were analyzed. The results show that:C-H planar deformation of guaiacol-type aromatic nucleus at 1138cm-1, C-O、C-C、C=O stretching vibration of lilac aromatic at 1217cm-1, unique aromatic functional groups at 735cm-1～873 cm-1, and corresponding to methoxy functional groups at 1266cm-1 and 3432cm-1,all this have done preparation for revealing the pyrolysis characteristics of lignin in different atmosphere.(2) Research characteristics of lignin pyrolysed in helium atmosphere. A new insight for TG-GC/MS combined were proposed, the non-isothermal pyrolysis of (kraft) lignin, in an helium atmosphere, had been studied by thermo-gravimetric analyzer (TGA)-coupled with a gas chromatograph/mass spectrometry analyzer (GC/MS). The results show that:corresponding temperature of the maximum weight loss rate of three stages were turn lags with the increase of heating rate, there were 2 main weight loss peaks, at 315℃ and 690 ℃, respectively. The heating rate had no effect on the selection of mechanism model when lignin pyrolysis in the stage of volatiles dissolved out. The mechanism in that stage belonged to the first-order reaction control mechanism. What’s more, the average sparent activation energy of lignin showed no obvious regularity with the increase of heating rate, and its values were about from 54kJ/mol to 63.1kJ/mol. The produced laws of CO and CO2 were different in this atmosphere, reached the peaks at different temperatures, respectively. Each gas generation mechanism was also not identical in different temperature stage. The generation of CH4 could be divided into low and high temperature stages, and H2 mainly derived from aromatic ring’s breakage and restructuring of lignin.(3) Research characteristics of lignin pyrolysed in oxygen atmosphere. The pyrolysis characteristics of lignin had been studied by thermo-gravimetric analyzer in different oxygen concentrations, the results show that:the pyrolysis of lignin can be divided into dehydration, oxidative pyrolysis and char oxidation three stages in an oxygen atmosphere. Oxygen can promote the precipitation of volatiles. It was help for pyrolysed reaction that accelerating oxidative pyrolysis and char oxidation rate. Corresponding temperature of the maximum weight loss rate of each stage were turn ahead with the increase of oxygen concentrations. Oxygen can change the reaction heat of lignin, the endothermic and exothermic peaks were not obvious in nitrogen atmosphere, and there were 2 endothermic peaks and 3 exothermic peaks in oxygen atmosphere, and the total heat of pyrolysis was increased with the increasing of oxygen concentration. The activation energy of three stages was gradually increased in the same oxygen concentration, the activation energy of the char oxidation stage increases with increasing oxygen concentration, but the stage of dehydration and oxidative pyrolysis did not have the rules. Based on Caots-Redfern integral method, combined with domestic and foreign research achievements, the equation of theoretical conversion rate and the theoretical reaction rate were obtained. In different oxygen concentration, the root mean square error of theoretical and experimental conversion rate are within 2,50%, and the average deviation of that are at around 10%, which proved that the three components parallel and consecutive reactions kinetic model has a better adaptability with the behavior of lignin pyrolysis in oxygen atmosphere.