Preparation And Electrochemical Performance Of Coal Liquefaction Residue Based Composite Carbon Fiber

It is an important way to reduce and reuse coal-based solid wastes as advanced materials.Coal liquefaction residue based composite carbon fibers（CLR-CCFs）were prepared by electrostatic spinning,carbonization and subsequent activation of mixture solution,consisting of coal direct liquefaction residue（main carbon source）and polyacrylonitrile（PAN）.The morphologies and properties of CLR-CCFs were characterized by several analytical instruments,and the electrochemical properties of CLR-CCFs were investigated by electrochemical workstation.In addition,the influence of quality ratio of the coal liquefaction residue and PAN on its properties was also explored and the“Constructing skeleton-Filling substrate”method was preliminarily established,which means using the PAN as the skeleton to build fiber skeleton and coal liquefaction residues as substrate to fill the skeleton inside so as to assemble into CLR-CCFs.Firstly,the direct coal liquefaction residues were separated by the ultrasonic assisted extraction technology using the equal volume acetone/carbon disulfide mixed solution（IACM）as the extractant to obtain IACM soluble fraction（IACM-SF）and IACM insoluble fraction（IACM-ISF）.IACM-SF yields up to 86.5%and carbon content is up to 90.18%without ash.The compositions and structures of IACM-SF and IACM-ISF were directly characterized by various analytical instruments,and the fragment structure of IACM-SF was studied by ruthenium ion catalytic oxidation combined with gas chromatography-mass spectrometry.The typical structural characteristics of IACM-SF are substituted aromatic structure,unsubstituted condensation and biphenyl aromatic structure,alkyl bridge bond,hydrogenated aromatic structure and heteroatom containing structure,which makes itself a good raw material for the carbon materials preparation.IACM-SF was extracted by n-hexane to remove the heavy oil component to obtain the extract（E）.Different mass fractions of E and PAN were mixed and dissolved in dimethylformamide（DMF）to prepare different mass fractions of spinning solution.Fiber non-woven fabric precursor was prepared by electrospinning technology,then CLR-CCFs was prepared.By adjusting the spinning voltage,receiving distance,advancing speed and spinning solution preparation conditions,the fiber non-woven fabric precursor with 70%E mass fraction can be obtained.After post-treatment,the extract/polyacrylonitrile based composite carbon fibers（P-E-CCFs）can be obtained.When the parameters of preoxidation and carbonization were optimized,it was found that the composite carbon fibers obtained by HNO₃impregnation,staged preoxidation and carbonization at 850℃show good flexibility.The cyclic voltammetry and constant current charge discharge performance test of P-E-CCFs show that the specific capacitance and flexibility of P-E-CCFs decrease with the increase of E mass fraction.P-E10-800 has 186 F·g^-1 specific capacitance at the current density of 0.5 A·g^-1,and P-E70-800 has a specific capacitance of 149 F·g^-1.The specific capacitance of P-E70-800 was improved obviously after adding Fe Cl₃or Ni Cl₂.The specific capacitance was increased to 163 F·g^-1 and 169 F·g^-1 respectively at the current density of 0.5 A·g^-1.Compared with PAN based carbon fiber,P-E-CCFs sacrifice a certain specific capacitance,but significantly reduce the amount of PAN,and find a suitable way for the utilization of coal-based solid wastes.In addition,the composite carbon fiber was prepared by mixing the IACM-ISF with PAN.The IACM-ISF was oxidized by 30%H₂O₂solution at 60℃for 3 h to obtain oxidation extraction residue（OER）.The precursor fiber nonwovens with 80%OER mass fraction were obtained by adjusting the spinning voltage,receiving distance,advancing speed and spinning solution preparation conditions.The oxidation raffinate/polyacrylonitrile based composite carbon fibers（P-OER-CCFs）were obtained by subsequent treatment.The results show that the specific surface area of P-OER-CCFs decreases gradually with the increase of the content of oxidation extraction residue.The specific surface area of sample P-OER40-800 is 275 m²·g^-1,while the specific surface area of sample P-OER80-800 decays to 93 m²·g^-1.At the current density of 0.5 A·g^-1,the highest specific capacitance of P-OER-CCFs is 97 F·g^-1.In conclusion,the CLR-CCFs were successfully prepared by the“Constructing skeleton-Filling substrate”method with PAN as the skeleton and E and OER as the substrate.The addition ratio of E and OER was as high as 70%and 80%respectively,and showed good electrochemical performance.Although the performance of composite carbon fibers is weaker than that of PAN based carbon fiber,the amount of PAN in composite carbon fibers is significantly reduced.At the same time,the research of this paper provides a reference way for the complete utilization of coal liquefaction residues solid wastes.