Study On The Hydro-liquefaction Property Of Solvent Pretreated Coal

In order to study the effects of the macromolecular structure relaxation and small molecular phase separation on the liquefaction preformance of coal,Shenfu subbituminous coal(SF coal)and Xilingele lignite(XL coal)were pre-treated by soxhlet extraction with tetrahydrofuran solvent,room extraction with N-methylpyrrolidone/carbon disulfide(NMP/CS2)mixed solvent,and dissolution at high temperature in methanol/toluene mixed solvent,respectively.Structural characterisitics of raw coals and their pretreated coals were characterized by FTIR spectroscopy,elemental analysis and thermogravimetric analysis,and the influences of pretreatment condition on the structures of pretreated coals were discussed.Then,hydro-liquefaction performances of pretreated coals under different conditions were investigated.By the characterization of the hydro-liquefaction products,the influences of the relaxation of macromolecular structure and the separation of small mobile phase on the hydro-liquefaction performance of low-rank coal was studyed.The experimental results indicated that SF and XL coals mainly consist of macromolecular network structure,in which there is a little of small molecular compounds,resulted of low solvent extraction yields.By comparison with XL coal,SF coal is a higher rank coal and shows lower reactivities in pyrolysis and hydro-liquefaction.The pretreatments,whichever the mild extraction by THF and NMP/CS2 mixed solvents or thermal dissolution by toluene/methanol solvents,all can remove small molecular mobile phase from coal at different degree,reduce the cross-linking density of macromolecules to relaxate coal macromolecular network,so that the hydro-liquefaction performance of pretreated coals were improved at a certain degree.Especially,the mild extraction treatment promoted the hydroliquefaction activity of SF coal,and showed obvious increasing coal conversion and oil+gas yield.Thermal dissolution treatment by toluene/methanol mixed solvent improved obviously properties of hydro-liquefaction of SF and XL coals.With the increase of temperature of thermal dissolution,their liquefaction conversions and oil+gas yields increased,and the yield of APA heavy products decreased.However,significant decreased hydro-liquefaction conversion and oil+gas yield were observed when these thermal dissolved coals were further extracted by THF or NMP/CS2 mixed solvents before hydro-liquefaction.Therefore,the relaxation and configuration rearrangementof coal macromolecular structure and the in-situ hydrogen donoration of small molecular compounds should be the important factor to affecting hydro-liquefaction properties.