Study On The Pyrolysis Characteristics And Coke Structure Evolution Behavior Of Rubber Wood

Rubber trees are widely planted in tropical regions,and its derivative rubber wood is the main source of raw materials for the wood industry in China and Southeast Asia.About 80%rubber wood wastes are generated in the industrial production process.Because of the low economic value,rubber wood wastes are difficult to treat,a considerable part of the waste is simply burned,resulting in energy waste and ecological environment pollution,and is not fully utilized.Based on the above reasons,the pyrolysis characteristics of rubber wood were systematically studied by using elemental analyzer,industrial analyzer,thermogravimetric analyzer,tubular furnace,scanning electron microscope,specific surface area meter,Fourier transform infrared spectrometer and Raman spectrometer,and the pyrolysis kinetic model of rubber wood was established,the changes of element composition,surface functional groups and carbon skeleton structure of rubber wood pyrolysis coke were analyzed to provide guidance for the efficient and clean utilization of rubber wood.The main conclusions of this paper are as follows:(1)The pyrolysis process of rubber wood includes dry preheating,rapid pyrolysis and carbonization stages,and the corresponding weight loss rates of each stage are 6.9%,65.9%and 7.3%,respectively.Due to the difference between the content of hemicellulose and cellulose,the DTG peak of rubber wood pyrolysis has a main peak and a shoulder peak.The maximum weight loss rate during the pyrolysis process of rubber wood increased significantly with the increase of the heating rate,and the temperature range of the main pyrolysis stage increased with the increasing heating rate.In addition,the increase of the heating rate will promote the release of rubber wood volatiles and continuously weaken the shoulder peak,thus,the higher the heating rate,the more conducive to the pyrolysis of rubber wood.The pyrolysis activation energy of rubber wood is about 175 kJ/mol.The calculation results of the CoatsRedfern method show that the pyrolysis process of rubber wood is more accurately described by the four-stage reaction series model.(2)This study uses tube furnace to make coke,and investigates the influence of pyrolysis temperature and heating rate on the evolution characteristics of the physical structure of rubber wood coke.The results show that the heating rate has little effect on the micromorphology of the rubber wood coke at 400?,and the surface of coke is smooth without obvious pore structure.At 800?,pyrolysis coke has a more developed pore structure and a larger specific surface area.With the increase of pyrolysis temperature,the release of volatiles under fast pyrolysis conditions is more intense than slow pyrolysis,destroying the raw material structure and forming a denser pore structure,resulting in an increase in surface roughness and specific surface area.The rapid pyrolysis coke has a large number of micropores and mesopores,and the specific surface area is significantly increased.However,the specific surface area of slow pyrolysis coke increases significantly at 900?.(3)Based on the experimental results in Chapter 2,this study uses elemental analysis,Fourier infrared transform spectroscopy and Raman spectroscopy to analyze the evolution characteristics of the chemical structure of rubber wood pyrolysis.The research results show that with the increase of temperature,the degree of aromatization and carbonization of rubber wood coke increases.Below 500?,the pyrolysis of rubber wood is mainly dehydration,decarboxylation and decarbonylation reactions to generate H2O,CO2,CO and hydrocarbons;above 500?,dehydrogenation and demethanation reactions dominate.With the increase of pyrolysis temperature,the contents of CH,-CH3,-OH and other functional groups continuously decreases,the C=C bond strength increases first and then decreases,the absorption peak of aromatic C=O increases,the aromatization degree of rubber wood pyrolytic coke was enhanced.At a lower pyrolysis temperature,the relative content of small aromatic ring structures in rubber wood coke under fast pyrolysis conditions is greater than that of large aromatic ring structures,while the content of large aromatic ring structures is relatively high during slow pyrolysis.At a higher coking temperature,the heating rate has the same effect on the pyrolysis of rubber wood,and the relative content of the large aromatic ring structure is greater than that of the small aromatic ring structure.Under the conditions of rapid pyrolysis,with the increase of residence time,the strength of functional groups such as C=C and C=O decreases.The strength of functional groups such as C-H,-CH3,and C-O tends to increase first and then decrease,and the coke structure tends to be stable.In addition,under the conditions of rapid pyrolysis,as the residence time increases,the content of small aromatic ring structures in rubber wood pyrolysis coke first decreases and then increases,the degree of aromatization of rubber wood pyrolysis coke decreases,and the content of coke bridge bond structure increases with the increase in residence time.Decrease,the reactivity of pyrolysis coke improves with the increase of residence time.This is due to the rapid pyrolysis of coke with increasing residence time,along with the polycondensation of a large number of aromatic rings,the active sites formed by the breakage of side chains,etc.,further form a more stable cross-linked structure such as C-C.