Molecular Structure Analysis And Basic Application Of Medium-low-temperature Coal Tar Pitch

The proportion of coal production and consumption in the primary energy structure has been maintained at more than 70%due to coal resources being rich in China.More than 55%of the proven coal reserves are low-rank coal,which produces 6%～10%of medium-low temperature coal tar products in the process of gasification and medium-low temperature dry distillation.What’s more,about 30%of medium-low-temperature coal tar pitch will be produced during the preliminary processing of medium-low-temperature coal tar.In recent years,with the increasing scale of low rank coal retorting processing in our country,a large number of low-cost medium-low-temperature coal tar pitch has also been produced.At present,most of the medium-low-temperature coal tar pitch is burned as fuel,which results in a waste of resources and environmental pollution.Therefore,it is greatly significant to conduct a basic research on the deep processing of medium-low-temperature coal tar pitch.This paper takes medium-low-temperature coal tar pitch（MLP）as the research object and the heptane soluble component（HS）,heptane insoluble toluene soluble component（HI-TS）and toluene insoluble component（TI）were obtained by solvent extraction of MLP.The average molecular structure of MLP and its family components are analyzed by means of Fourier transform infrared spectroscopy（FTIR）,elemental analysis,vapor pressure osmometry（VPO）,ultraviolet spectroscopy（UV）and nuclear magnetic resonance spectroscopy（¹H-NMR）.The results show that aromatic structure units exist in the molecules of MLP and its family components,and there are alkylsubstituents in the aromatic rings with the different chain length and the relatively more side chains,as the heteroatom oxygen mainly exists in AR-OH structure.The average molecular structure of MLP is four-membered fused ring with linear arrangement as the main and planar arrangement as the auxiliary;the average molecular structure of HS is linear linking of two single benzene ring structure;the average molecular structure of HI-TS is five-membered fused ring with mainly planar array.The pyrolysis characteristics of MLP and its family components have been systematically analyzed in detail by Flynn-Wall-Ozawa,Kissingr-Akahira-Sunose and Satava-Sastak methods.The results show that the pyrolysis mechanism of HS,HI-TS and MLP conforms to the random nucleation and subsequent growth model,and the corresponding model functions are G（α）=-ln（1-α）of HS and HI-TS and G（α）=[-ln（1-α）]^2/3of MLP.The mesophase coke was prepared by pressurized thermal polymerism-liquid phase carbonization process.The aromatic structure of thermally modified pitch is studied by FTIR.The variations of optical microstructure,carbon microcrystalline structure and microstrength of mesophase coke was studied by polarizing light microscope（PLM）,scanning electron microscope（SEM）,X-ray diffraction（XRD）and Raman spectrometer,respectively.The results showed that the aromaticity index of thermal-modified pitch increases from 0.1167 to 0.1886 after thermal polymerizing under pressure.The aromaticity of thermal-modified MLP increases gradually;the functional groups,hydrogen substitution types and aromaticity of MLP are changed after thermal modification.With the increase of modification temperature,the content of graphite microcrystalline I_g increases from 66.74%to 74.60%,and the content of amorphous carbon I_D3/I_ALL decreases from 9.75%to 9.17%.The microcrystalline structure of mesophase Coke tends to be more ordered,and the micro strength of mesophase coke is higher than 80.59%,which displayed the better strength of carbon skeleton.Medium-low-temperature coal tar pitch resin（MLPR）has been prepared by chemical crosslinking modification method.The results show the aromaticity of MLPR intensifies and the functional groups,hydrogen substitution types and aromaticity all have changed.The average molecular structure of MLPR is six-membered fused ring with mainly surface arrangement.The pyrolysis reaction mechanism of MLPR is matched to the model of random nucleation and subsequent growth,and its model function is G（α）=[-ln（1-α）]^3/4.Porous carbon materials have been synthesized by carbonizing and activating with MLPR as carbon precursor and KOH as activator.The results of electrochemical test show that,the porous carbon of MLPR-PC-750 which activation temperature is 750 ^oC presents the highest specific capacitance of 281.6 F·g^-1 at the current density of 0.5 A·g^-1.When the current density increased to 10 A·g^-1,78.3%of original specific capacitance still remained.The porous carbon of MLPR-PC-750 presents excellent performance in terms of high rate,electrical conductivity and cycling stability.The porous carbon which prepared from MLPR displays outstanding performance electrochemically.