Hydro-liquefaction Of Coal Asphaltenes And Preliminary Characterization Of Its Products

The raw material used in this study is the heavy thermal extraction product,coal asphaltenes,obtained by catalytic hydro-thermal dissolution of Xilinguole?XL?lignite at temperatures between 420?and 430?.The structure and property of coal asphaltenes was investigated by elemental analysis,FTIR,and TG-DTG characterization and extraction performance evaluation.The experimental results show that coal asphaltenes are mainly consisted of aromatic structures;it contains a large amount of aliphatic hydrocarbons and a small amount of oxygen-containing functional groups.Coal asphaltenes contain high carbon,low oxygen,low sulfur,and no ash content,and is almost completely soluble in tetrahydrofuran.The solubility of coal asphaltenes in cyclohexane is higher than that in hexane,and its pyrolysis activity is high at 360? to 400?.Through the direct hydro-liquefaction of coal asphaltenes,the influences of catalysts such as Cu-Ni/?-Al₂O₃,Ni/ZSM-5,Ni-Mo-S/?-Al₂O₃,SO₄^2-/ZrO₂ solid acid on the conversion and the product yield of hydro-liquefaction were examined.The effects of reaction temperature,reaction time and solvent on the catalytic hydrogenation activity of Ni-Mo-S/?-Al₂O₃ were also investigated.The results show that the suitable liquefaction condition is reaction temperature 400?,reaction time 60 min,THN as solvent,feedstock-solvent ratio 1:4,initial hydrogen pressure 5MPa,Ni-Mo-S/?-Al₂O₃as a catalyst.The gas and oil yields reached 1.8%and 73.5%respectively,and TS and TI yields were 11.07%and 13.64%respectively at the suitable liquefaction condition.In the meantime,the gas and oil yields decreased to 6.4%and 60.4%,respectively without catalyst.The characterization analyses of the liquefaction products show that high active catalyst,prolonging reaction time and strong hydrogen donation solvent are beneficial to the hydrocracking of macromolecular structures in coal asphaltenes,thus promoting the cleavage of hydroxyl groups,C-O bonds,ether bonds,resulting in high yield of light oil product,which is mainly composed of aromatic structure with low content of oxygen-containing functional groups,high H/C atomic ratio.However,as the temperature of the reaction increased,the content of cycloalkanes in the oil decreased,so that the production of jet fuels which are rich in cycloalkanes and hydrogenated aromatic rings can be appropriately reduced in temperature.In addition,the aromaticity of the oils obtained at different liquefaction conditions hardly changed.Recycling utilizations of the catalyst studies on the hydro-liquefaction of coal asphaltenes show that the oil yield from the liquefaction of the third cycle of Ni-Mo-S/?-Al₂O₃ gradually decreased from 73.5%to 62.7%,and the gas yield increased from1.8%to 5.0%.And through the results of the characterization analyses of the catalyst and the liquefaction products found that with the increase in the number of cycles,the surface of the catalyst adsorbs a large amount of macromolecules deposited in the coal asphaltenes,blocking the pores of the catalyst.As a result,the activity of the catalyst gradually decreases,the aromatic structure and oxygen-containing functional groups of the oils gradually increased,and the content of cycloalkanes gradually decreased.