Thermal Disollution Of Medium/High-sulfur Bituminous Coals And Isolation And Analyses Of Their Soluble Species

There exist abundant medium/high-sulfur bituminous coal resources in China,therefore,it is crucial to study the occurrence formsand dissoluble characteristics of soluble organic species in them during thermal depolymerization for their clean transformtion and value-added utilization.In this paper,thermal dissolution?TD?depolymerization behaviors of three medium/high-sulfur bituminous coals,including Linfen coal?LF?,Xinyu coal?XY?and Guxiancoal?GX?,were investigated,then the compositon and structural charateristics of gas,soluble portions?SPs?and residues was systematically characterized by gas chromatography?GC?,Fourier transform infrared?FTIR?spectrometer,gas chromatograph/mass spectrometer?GC/MS?,direct analyze in real time direct analysis time-of-flight mass spectrometer?DART/TOF-MS?and ¹³C solid-state nuclear magnetic resonance(¹³C NMR)to deeply under stand the dissolution profile of soluble organic species in medium/high-sulfur bituminous coal.The dissolution profile of soluble organic species in LF at 220-300 ^oC was investigated,and the difference in the thermal dissolution behavior of LFinfive solvents including methanol?MET?,ethanol?ETH?,n-propanol?PRO?,benzene?BEN?and toluene?TOL?was compraed.The yields of gas and SPs of LF increase with the increase of thermal dissolution temperature,and the gas is the main product.CH₄,H₂ and CO accounts for80-90%of gas yield.FTIR and GC/MS analyses of SPs indicate that soluble organic species in LF are mainly composed of aliphatic hydrocarbons and arenes,and souble organic oxygen-containing compounds are dominated by ethers,alcohols and phenols.The n-paraffins in the SPs concentrates on C₁₆-C₁₉,and 2-3 rings polycyclic aromatic hydrocarbons?PAHs?are the dominated arenes.TD in low carbon alcohols are conducive to the production of gas products,therein,aliphatic hydrocarbons of C₁-C₄ maybe are originated from the reforming reaction of low carbon alcohols.XPS analyses indicate that the relative contents of C-O and pyridine nitrogen on the surface of TD residues in alcohols solvents are less than those in benzene and toluene.¹³C NMR analyses show that there exist larger peaks at 13.4 ppm?terminal-CH₃?and 149-164 ppm?aromatic carbon attached to heteroatom?in the ¹³C NMR spectra of alcohols solvent residues,which is possibly ascribed that the alkoxy of the alcohol solvent bounded to the condensed aromatic rings of coal to form C_ar-OR groups.The thermal dissolution behavior,the compositon and structural charateristics of products from LF,XY and GX at 300 ^oC in alcohol solvents were systematically compared.The yields of both gas and SPs from LF are higher than those of XY and GX,which are possibly ascribed to its lower coalification and good thermal dissolution reactivity.The soluble PAHs of three coals are dominated by 2-3 rings PAHs,including naphthalene,acenaphthene,fluorene,phenanthrene,anthracene and fluoranthene,while the concentration of over tetracyclic PAHs,such as pyrene,benzo[a]anthracene and chrysene,is low.Comparing the TD results in these three alcohol solvents,the order of the yields of gas and SPs is MET>PRO>ETH.Quantitative analyses of n-paraffins and PAHs indicate that ETH is more favorable for the dissolution of n-paraffins and PAHs.Compared with raw coals,the sulfur content of residues is obviously lower,while the nitrogen and oxygen contents are higher,implying that the TD in alcohol solvents are favor to the dissolution of OSCs in coals,and the order of desulfurization effect is PRO>ETH>MET.GC/MS and DART/TOF-MS analyses indicate that detected OSCs in the SPs include thiols,thioethers,thiones,disulfides,sulfones,sulfoxide and thiophenes,therein,thiophenes are most abundant.With the increase of coalification degree,the amount of dibenzothiophenes with tricyclic structure decreases,while the contents of four or five ring thiophenecompounds?suchasthiophanthrenes,benzonaphthothiophenes phenanthrenothiophenes?and the OSCs with stable methyl substitutions increase.In addition,MET is conductive to dissolute more thiophenes compounds compared with other four solvents.SP_LF-PRO was elueted with different ratio of petroleum ether?PE?and ethyl acetate?EA?mixed solvents in a medium pressure preparation chromatography affording to six fractions.GC/MS analyses indicate that n-paraffins of even carbon are the main components in allfractions.With the volume ratio of PE/EA decreasing,the concentration of even carbon n-paraffins gradually decreases and the carbon number of them gradually increases.DART/TOF-MS analyses indicate that pure PE was favorable for the elution of OSCs with low carbon number and low DBE value.With the radio of polar component EA in the mixed solvent increasing,more OSCs with high carbon number and high DBE value were eluted.By the gradient elution of PE/EA mixed solvent,a number of OSCs with high DBE were detected which are difficult to detect before the seperation.