Pyrolysis Law Of Wheat Straw And Its Three Main Components

Biomass has been recognized as a potential source for the renewable energy to substitute the declining fossil fuel resources. With the depletion of fossil fuel and the concern of environmental protection, the utilization of biomass resources has attracted increasing worldwide interest. Pyrolysis is a vital thermochemical conversion route for energy and transport fuel production. In this experiment, wheat straw as the research object, theoretical guidance is supplied with studying pyrolysis law of the straw and its three major components in the different pyrolysis conditions to achieve reasonable regulation and control of the target products.In the work, the structural characterization of hemicellulose, cellulose and lignin from was investigated, separately. Hemicellulose isolated in the experiment preserved theβ-D-Xylp andα-L-Araf units as well as a little of glucuronic acid existed, cellulose mainly contained cellulose Iα, cellulose Iβand a few quasi-crystalline cellulose, The lignin was a GSH-lignin withβ-O-4' structures and several condensed units (β-5',β-β',β-1', 5-5') and vinyl ether moieties.The thermal decomposition characteristics of the wheat straw and its three major components at different heating rates were explored, which showed that the degradation of hemicellulose was easier than cellulose, both their decomposition focused on different range and only two weight loss peaks appeared in DTG profiles. At pyrolysis temperatures over 400℃, the influence of lignin in wheat straw on wheat straw was obvious during pyrolysis, lignin pyrolysis dominating over that of wheat straw. The pyrolysis products of wheat and its major three components at four phases were analyzed through Py-GC-MS, the pyrolysis pathway of furfura and some kinds of phenol compounds from hemicellulose and lignin, respectively, were also researched. The thermal degradation of hemicellulose, cellulose and lignin in wheat straw was not carried out independently, but there could be interactions, nonetheless the mechanism was not very clear according to the releasing orderliness of volatile gas produced by wheat and its major three components at slow heating rate with TG-FTIR technique.The active energy of wheat straw and its major three components in pyrolysis was determined by Kissinger, Ozawa and DAEM methods, respectively. The activation energy and frequency factor of reckoned by Kissinger and Ozawa formulas were similar and the result of Ozawa method was slightly higher than Kissinger one, while the fitting degree of the Kissinger technique which deduced the active energy of hemicellulose and lignin was better than of the Ozawa one. Distribution of activation energy (DAEM) model did not apply to the thermal decomposition kinetic of lignin. The pyrolysis of wheat straw and its major three components at 400,500,600,700,800 and 900℃was tested on a laboratory-designed tubular furnace.The pyrolysis gas mainly included H₂, CO, CO₂, and CH₄, C₂H₄ and C₂H₆ existed only at certain temperature with GC analysis. The major components of pyrolysis tar from wheat straw and its major three components were detected at 400, 600 and 800℃. As the pyrolysis temperature increased, with the exception of lignin, the pyrolysis tar of wheat straw, hemicellulose and cellulose composition was quite diverse and the sorts of pyrolysis tar gradually reduced. A comparative analysis of coke from wheat straw and its three major components was performed in the case of solid products in pyrolysis at 600℃. Solid residues of pyrolysis from lignin dominated over the main mixture of coke in wheat straw.Benzene series decreased and low molecular weight compounds increased in the pyrolysate after hot water pretreatment of wheat straw were proved by comparing the three kinds of pretreatment methods on fast pyrolysis characteristics of wheat straw.