Study On Solvent Extraction Of High Sulfur Coal And Pyrolysis Characteristics Of Residues

Direct liquefaction,gasification,low temperature pyrolysis are the clean and efficient technologies for coal utilization.The structure of coal is complex and this limited the further development of coal direct liquefaction and gasification technology.Low temperature pyrolysis and solvent extraction of coal are the effective ways to understand the molecular structure of coal.In this paper,Xin Zhou bituminous high-sulfur coal was selected as the research object.The high-sulfur coal was extracted with organic solvents(n-hexane,acetone,carbon disulfide,tetrahydrofuran,and pyridine)and ionic liquids([Bmim]BF4,[Bmim]HSO4,[Bmim]Br,and[Bmim]Cl).The extraction characteristics of different components in high-sulfur coal by different solvents were determined by extraction yield and the analysis of extracts composition and content.The high-sulfur coal and different solvent residues were pyrolyzed in a fixed bed reactor.The gas-liquid-solid product distribution of residues with different solvent was investigated.The effect of different solvent pretreatment on pyrolysis gas composition,tar composition and carbon number of high sulfur coal were analyzed.The element distribution of the pyrolysis chars of different solvent was also investigated.The effect of solvent pretreatment on pyrolysis characteristics of high sulfur coal was obtained.The main conclusions of this study were as follows:(1)Among the organic solvents,pyridine has strong electronegativity,and the extraction yield was up to 10.10%,and it had certain selective extraction ability on nitrogen-containing compounds.Tetrahydrofuran obtained the maximum relative content of oxygenated compounds.All solvents did not exhibit selective extraction capabilities for sulfur-containing compounds.The distribution of pyrolysis gas-liquid-solid products could be improved by solvent extraction pretreatment significantly.The volume fraction of CH4 and C2+in the pyrolysis gas of the residues decreased,while the volume fraction of CO,CO2 and H2 increased.Compared with raw coal tar,the relative content of tricyclic and larger PAHs in tar obtained from residues of tetrahydrofuran and pyridine decreased,and the relative content of phenols increased.There was no significant change in the content of sulfur-containing compounds in the tar.The maximum carbon number of the raw coal pyrolysis tar was 97,and the maximum carbon number of tar from residues of pyridine was 69.Organic solvent extraction leaded to a reduction in high carbon number components in the tar,and organic solvent extraction pretreatment could increase oil yield,the oil phase yield of the pyridine residue was up to 17.63%.(2)Among the four imidazolium-based ionic liquids of[Bmim]Cl,[Bmim]Br,[Bmim]HSO4,and[Bmim]BF4,[Bmim]Cl had a higher extraction yield than other ionic liquids,and it was up to 20.82%.All ionic liquids exhibited selective extraction ability for oxygenated compounds.The main oxygenated compounds in the extracts were furan and ether compounds.[Bmim]Cl had a selective extraction ability for sulfur-containing compounds,and the relative content of sulfur-containing compounds in the light oil of[Bmim]Cl extract was 5.10%.Compared with pyridine residue pyrolysis tar,the relative content of tricyclic and larger PAHs,sulfur-containing compounds and oxygenated compounds in[Bmim]Cl and[Bmim]Br residues pyrolysis tars showed an increasing trend,while the relative content of phenols showed a decreasing trend.The high carbon number component of the ionic liquid residues tar was further reduced,which could promote the upgrade of the tar.Ionic liquid pretreatment could promote the release of S and O in the char and increase the char aromaticity.Compared with organic solvent pretreatment,the ionic liquid pretreatment had further improved the yield of oil phase products.The oil phase yield after[Bmim]Cl extraction pretreatment was up to 24.89%.