The Study On Biomass Hydrophobic Property And Pyrolysis Characteristics

As the fourth largest energy source after coal, oil and natural gas, biomass resourceshave been widely used because of its huge quantity, environmentally friendly, renewableand zero CO2emissions. However, there are several problems which severely limit thelarge-scale utilization of biomass, such as strong remarkable seasonality, wide distribution,high water content (10-50%), high hydroscopicitylow energy density, difficult to grind andpoor fluidity. Torrefaction can reduce the moisture content and enhance the energy densitywhich favors to the efficient utilization of biomass.Therefore, This article took the typicalagricultural waste cotton as the research object, studied the torrefaction characteristics andits influence on water absorption properties and the pyrolysis characteristics of torrefiedbiomass.Firstly, cotton straw and cornstalks were torrefied on fixed bed bench at200℃,230℃,260℃,290℃, respectively. And then the changes of the physical and chemicalcharacteristics caused by torrefaction were analyzed by using the fourier raman infraredspectroscopy analyzer, automatic adsorption instrument and, etc. The research showed that:the types and quantity of functional groups decreased, and the pore structure changedobviously, furthermore The surface of the sample particles changed from loose to dense andthen cracked.Then the effects of torrefaction on hydrophobic property were analyzed by usingconstant temperature and constant humidity box with different environmental humidity of50%、60%、70%、80%、90%at30℃, and establish the equilibrium water absorption ratemodel, founding that the water adsorption process of biomass particles could be dividedinto two stages of initial rapid water adsorption and later slow water adsorption untilequilibrium, respectively caused by physical adsorption of the physical pore structure andchemical adsorption of the interactions between the water molecules and superficialoxygenic functional groups; And furthermore, the equilibrium moisture contents decreasedwith the increasing torrefaction temperature, while the ability to resistance to microbialdegradation was strengthened, which favored the long time storage in the moistenvironment. And the factors affecting the water absorption properties of the samplesinclude: surface oxygen-containing functional groups, specific surface area,pore structure and the apparent morphology.Thirdly, the pyrolysis characteristics of torrefied biomass were studied by adoptingTG-DSC-FTIR technology. The thermogravimetric behavior of the torrefied samples couldbe divided into four stages, and the reaction kinetics model were first-order reaction model,and with the pyrolysis temperature increased, the heat absorption of the pyrolysis processincreased, while the activation energy, frequency factor and integrated pyrolysischaracteristics index increased firstly and then decreased, but with the increasingtorrefaction temperature, the starting temperature of pyrolysis gradually increased while theshoulder corresponding to hemicellulose gradually weakened until disappeared. With theincrease of torrefacton temperature, the small molecule gas products and theoxygen-containing organic compounds significantly reduced, the kinds of organic specieswere simplified.Finally, the pyrolysis mechanism and products distribution of torrefied biomass weredeeply studied by a fixed bed bench, founding that the pyrolysis char yield as well as thespecific surface areagradually increased with the increase of torrefaction temperature, butbefore260℃, corn stover pyrolysis gas yield increased slightly, it may be caused by thealkali metal catalysis, while the content of carbon monoxide content showed a downwardtrend. But, the content of methane and hydrogen increased significantly respectively causedby the methoxy group enrichment and intensification of the benzene ring dehydrogenation.The torrefaction leaded to the decreasing of the char yield obviously, but the acid contentand water content decreased a lot,which favored the stability of bio-oil and the reduce ofsubsequent utilization cost.