Study On The Chemical Structure And Thermo-chemical Characteristics Of Hemicellulose

To solve the problem caused by energy shortage and environmental pollution, the exploitation and utilization of biomass energy has been paid more attentions during these years. Pyrolysis is not only an independent process for biomass conversion, but also a key mechanism of biomass pyrolysis. Study on biomass pyrolysis is essential to develop and improve the advantage of bio-energy. Cellulose, hemicellulose and lignin are the main components of biomass and research on hemicellulose is less because it is difficult to get from nature and has a complex structure. In this paper, the structural and thermal characteristics of hemicellulose isolated from sugarcane bagasse are studied, which help to provide useful reference to biomass liquefaction and gasification.The structure characterization of hemicellulose was performed by FT-IR,1H-NMR,13C-NMR and ion chromatogramThe results showed that hemicellulose were composed mainly of L-arabino-D-xylans, and uronic acid were also identified in these fractions,which were the representative structure of straw hemicellulose.The pyrolysis characteristics and kinetic of hemicellulose at different heating rates were studied by thermogravimetric analysis (TG).The pyrolysis process of hemicellulose can be divided into four stages, and the major reaction stage was within 200℃~ 315℃. TG-FTIR and PY-GC/MS analysis were introduced to examine reaction products from the pyrolysis of uncatalyzed and catalyzed hemicellulose. CO2, hydrocarbons, alcohols, aldehydes, acids and phenol are found to be the main products. K+ promoted complete decomposition of polyssachloride and glucosidic units at lower temperatures, and Mg2+ enhanced the cracking and rearrangement process of molecules and increased the char yields.The fast pyrolysis of wheat straw hemicellulose was conducted in the tubular furnace at 550-850℃to research pyrolysis products distribution and the mechanism of hemicellulose fast pyrolysis. The result showed that the gas yield was the highest of those three phase products and increased with the increasing of temperature. The gas was mainly consisted H2, CO, CO2, CH4 and hydrocarbon. The liquid products included acids, alcohols, furan, cyclopentenes and other aromatic compounds, and its relative yield changed slightly. The relative yield of char had contrary trend to that of gas. The isopropanol-extracted components remaining in the char were alcohols and other compounds of larger molecular weight.