Effect Of Chemical Structure Evolution During Catalytic Pyrolysis On Combustion Kinetics Of Cellulose

Microcrystalline cellulose(MC)was loaded with KC1,NaCl,K2SO4 and Na2SO4 by impregnation,and was pyrolyzed in a tube furnace at different pyrolysis temperatures(200?1000 C).Thermogravimetric coupled with Fourier transform infrared spectroscopy(TG-FTIR)was used to analyze the pyrolysis characteristics and gas product release characteristics of the sample,and the pyrolysis gas product was analyzed by pyrolysis-gas chromatography-mass spectrometry(Py-GC/MS).Fourier transform infrared spectroscopy(FTIR)and X-ray diffraction(XRD)were used to characterize the evolution of char chemical structure with pyrolysis temperature.Finally,the combustion characteristics and kinetics of cellulose chars were investigated by Thermogravimetric analysis(TGA).TGA pyrolysis analysis show that all four catalysts can affect the pyrolysis characteristic parameters of cellulose,especially for KCl and NaCl.The addition of alkali metal salt reduce the initial temperature Ti of the pyrolysis reaction by 37.9-44.4?,and the termination temperature Tp increase by 110.1-140.4?.KCl and NaCl inhibite the formation of gas products,while K2SO4 and NaaSo4 promote the release of gas products during pyrolysis.The activation energy of MC-KC1,MC-NaCl,MC-Na2SO4,and MC-K2SO4 samples is higher than that of MC sample by 121.8,128.9,181.7,and 191.6 kJ mol-1.Py-GC/MS analysis shows that the catalyst greatly promoted the formation of furfural product,especially for K salt.The metal salt promotes the cracking of aromatic hydrocarbon compounds in char into small molecular gas products,facilitates the dehydration reaction between organic acid molecules to form anhydrides,and facilitates the esterification reaction between organic acids and alcohol phenols to produce esters.Na salt has a greater influence on the esterification reaction.The catalyst also promotes the increase of furan products.TG-FTIR analysis indicate that KC1 and NaCl increase the yield of CO2 and promote the cracking reaction of COOH and C=O during pyrolysis.K,Na metal salts have little effect on methoxy functional groups.FTIR analysis shows that the temperature has a significant effect on the chemical structure of the cellulose char during the pyrolysis process.The numbers of organic functional groups in the cellulose decrease with the increase of pyrolysis temperature.The catalyst promotes the release of compounds containing C=O functional groups,the depolymerization of the glucose ring structure and the cleavage and reforming reaction of aromatic cyclic hydrocarbons.XRD analysis shows that the characteristic peaks of catalyst disappeared at 900?.The increase in the intensity of the 002 and 10 diffraction peaks indicates that the number of ordered carbon atoms in the chars gradually increases as the pyrolysis temperature increases,indicating that the higher the pyrolysis temperature,the better the aromaticity of coke.However,the aromatic nucleus is still not converted to a graphitized microcrystalline structure.When the pyrolysis temperature is lower than 600?,the catalyst inhibits the lateral growth of the aromatic nucleus and promotes the longitudinal growth of the aromatic cores.When the pyrolysis temperature is higher than 700?,the catalyst has the opposite effect on the aromatic nucleus.In addition,the aromaticity of the celluloses loading KC1,NaCl,K2SO4,and Na2SO4 decreased at 700,900,800,and 700?,respectively,related to the fact that the catalyst promoted secondary cracking of tar.The TGA combustion analysis shows that the catalyst reduces the release and the combustion temperature of volatiles,leading to the movement of char combustion temperature to the low temperature region.The comprehensive combustibility index S of chars decreases with increasing pyrolysis temperature,which is related to the decrease of highly active macromolecules and the increase of aromatic ring structure in chars.The activation energy required for char combustion reaction increases with the release of volatile matter in cellulose.Compared to the cellulose chars without catalyst,the combustion temperature range of cellulose chars loading KC1 and NaCl move to the low temperature region,and the activation energy and the pre-exponential factor of the reaction decrease.The effect of K salt is more obvious.When the pyrolysis temperature is higher than 500?,the activation energy of the combustion reaction of the cellulose char loading the catalysts is reduced,indicating that the K,Na catalyst can promote the sample combustion,and can improve the combustion reactivity of the char.The K salt catalyzes stronger than the Na salt.