Mechanism Research On The Influence On Yield And Quality Of Tar Derived From Co-pyrolysis Of Biomass And Coal

Open burning straw and direct combustion of coal cause severe environmental pollution recently.Co-pyrolysis of biomass and coal was one of feasible methods to produce liquid fuels and high added-value chemicals through clean conversion of the abundant biomass and low rank coal in China.Study of the co-pyrolysis could be beneficial to protect the environment and facilitate low-carbon development.Moreover,the research was carried out to reveal the inherent relationship between pyrolysis products and influence factors in order to improve the yield and quality of pyrolysis tar.The formation mechanism and reaction pathway of co-pyrolysis products were further discussed from the viewpoint of radical regulation theory.Afore mentioned researches will increase the sources of biofuel and promote actually the resource utilization and innocent treatment of carbonaceous solid wastes.Raw matreials including cotton stalk(CS),rice husk(RH),saw dust(SD),green alga(GA) were used as raw biomass.Huainan coal(HN),Shenmu coal(SM),Heishan coal(HS)Daliuta coal(DLT),Inner Mongolia coal(NM)were chosen as raw coals.Co-pyrolysis of biomass andcoal was performed in a tubular furnace under mild condition.Then,the different effects on the product distribution of co-pyrolysis were analyzed by the variation of raw materals and blendings.Comparison with co-pyrolysis of CS/SM and de-ashed CS/SM,the results showed that the inherent minerals of CS had catalytic effects on the co-pyrolysis and increased the yields of tar and n-hexane soluble in the co-pyrolysis of CS/SM.Furthermore,the alkane and aromatic yield in CS/SM co-pyrolysis tar was obviously higher than that of SM pyrolysis tar.The results indicated that the CS addition can accelerate the formation in aliphatic and aromatic hydrocarbon in tar during CS/SM co-pyrolysis.In order to investigate the mechanism of the compound formation derived from n-hexane soluble during co-pyrolysis,microcrystalline cellulose(MCC)was selected as a model compound and the co-pyrolysis tar of MCC/SM was analyzed for comparison with SM pyrolysis,CS pyrolysis and co-pyrolysis of CS/SM.Base on the experimental results,it was indicated that the alkyl radicals generated from pyrolysis were converted to aliphatic hydrocarbons by polymerization.And the benzenes and phenols were generated from mononuclear aromatics radicals by the decomposition of biomass and coal.The mononuclear aromatics radicals also contributed the formation and stabilization of polycyclic aromatic hydrocarbon in co-pyrolysis tar.The GC/MS analyses of water-soluble extracts from co-pyrolysis tar indicated that the alkyl radicals from SM pyrolysis improved the generation of pyridines and prohibited the formation of amides.These radicals simultaneously increased the content of ketones and alcohols while dereased the content of aldehydes during co-pyrolysis of CS/SM.Moreover,the interaction effects of CS/SM co-pyrolysis prohibited the formation of acetic acid and improved the generation and stabilization of esters.The formation of small molecules essentially has competition with the formation of aliphatic hydrocarbon,aromatic hydrocarbon and syngas during co-pyrolysis.Based on these results,the mechanism of aliphatic hydrocarbon formation was discussed during co-pyrolysis.The mechanisms of syngas formation were further discussed.In order to elaborate the effects of carbon structure in coal on co-pyrolysis product distribution.The research results of four coals showed that the yields of pyrolysis tar were correlated with carbon structure and the mechanism was similar to that on coal.The alkyl structure in coal was in direct proportion to the content of aliphatic hydrocarbon in pyrolysis tar.And the aromatic structure had relationship with the formation of aromatic hydrocarbon during co-pyrolysis.Moreover,the oxygen-containing functional group in coal would decrease the n-hexane soluble yield in pyrolysis tar.In addition,a neural network model was built to forecast the product distribution of co-pyrolysis based on the understanding of interaction effects.The physicochemical property of biomass and coal were used in input characteristic variables.Because the maximum value of average generalization error was only 1.41%,the RBF neural network was feasible to forecast the yields of co-pyrolysis products.