Study On The Modification Of Coal Tar Pitch And The Impaction On Semi-coke Structure

Coal tar pitch was modified with different modifiers.The properpties、semi-coke microstructure of modified coal tar pitch and mechanism of modification was investigated.In the prencence of p-toluene sulfonic acid(PTS),medium temperature coal tar pitch were modified,respectively,using benzaldehyde(BA)、diphenyl Ketone(DK)and cyclohexanone(CH)、lauryl alcohol(LA)、1,4-butylenediol(BE)、polyethyrtene glycol-200(PG-200)and polyethyrtene glycol-400(PG-400).The influence to the performance of preparation carbon materials were analyzed,that was the thermal stability,rheological properties and structure(optical microstructure,crystal structure and chemical structure)of the different modified coal tar pitch(MCTP).Finally,the molecular structure of MCTP and possible modification reaction mechanism and kinetic equation was designed.The composition of MCTP analysis found that,modification of coal tar pitch C percentage content decreased,increased of H percentage content and H/C ratio increased,which provided a theoretical basis for the later carbonization process the formation of free radicals of aromatic compounds and the occuring of electrophilic substitution reaction.The value of CV increased of MCTP,that is carbon yield increased.The value of p increased,that is the decrease of porosity.Modification prompted that aromatic molecule aggregate into larger aromatic molecules,increased the degree of ρpolymerization of aromatic compounds,especially β resin percentage content of MCTP increased and SP value increased,which provided corporeal safeguard and theoretical basis in the preparation of ordered carbon fiber structure for the later stages of carbonizing and calcining process.MCTP viscosity were measured using NDJ-79.As the temperature increased,the viscosity of MCTP was dramatically reduced.MCTP viscosity tended to be stablely when the temperature was higher than 150℃.Modified coal tar pitch still had the ideal liquidity.The chemical structure of MCTP were analysed through using FT-IR and 1H-NMR analysis.FT-IR analysis in 1594 cm-1～1611 cm-1 the aromatic ring C=C absorption peak and the strong absorption peak in 813 cm-1～744 cm-1,explained that the conjugation degree aromatic ring of modified coal-tar pitch increased,modified reaction was mainly substituted reaction in the aromatic ring.1H-NMR analysis showed reduction of HA percentage in MCTP illustrated that the modified reaction mainly occurred in the aromatic ring of HA,which provided the theoretical basis for the following design of modified reaction mechanism.Crystal structure and optical microstructure of MCTP-C and CTP-Csemi-coke were analyzed respectively through XRD and optical microscope.The XRD data showed that the crystal structure of MCTP-C had certain enhancement compared to that of CTP-C,and they also had varying degree increase compared with CTP-C.The crystal plane spacing d002 of diffraction peaks of MCTP-C semi-coke microcrystalline,average diameter La,aromatic ring intergranular degree of order Lc and aromatic clusters in the aromatic nucleus layer number M were increased invarying degrees.The modified coal tar pitch semi-coke showed the large grain medium mosaic texture,incompletely fibrous texture and the complete fibrous texture structure characterization.These confirmed that the modification enhanced the intermediate phase micrite crystallinity,also advantageous the order intermediate phase small spheroid formation and the small spheroid growth and melts in the later period carbonization process to form the great intermediate phase small spheroid.These promoted the small spheroid to transform to the aeolotropic small spheroid and formed the order the middle phase structure,which improved the crystal ordered fiber structure of MCTP-C semic-coke after calcination.The’apparent energies(AE).frequency factor(A)and kinetic mechanism of different MCTP was diacussed during dehydration reaction.TG curves analysis determined the kinetic equation of thermal dehydration reaction for ln-ln(1-α)/T2=lnAR/β△E(1-2RT/△E)-△E/RT.With benzaldehyde as the modifier as example,this research mainly analysised the possibly reaction mechanism.The FT-IR and 1H-NMR spectrum analysis for CTP and different MCTP inferred that in the prencence of p-toluene sulfonic acid(PTS)the free radical reaction occurred between the free radical produced by the coal tar pitch and the free radical aromatic ring compounds during the modified process.Moreover,in the prencence of p-toluene sulfonic acid(PTS)the rich electron’s multi-core aromatic hydrocarbon is attacked by the proton transformed to the kiss electrophilic reagent.The electrophilic reagent occurred electricity substitution reaction with modifier benzaldehyde.The products still transformed to electrophilic reagent in the precence of acidic medium.The electricity substitution played mesningful role to the coal tar pitch molecular modified and modification.