Study Of Influence On Formative Factors Of Coal Tar Pitch Mesophase And Structure Of Needle Coke

Needle coke has potential application under condition of harshenvironmental due to low thermal expansion coefficient, high density, corrosionresistance, good conductivity, high mechanical strength and excellentcomprehensive performance, especially apply for the high and ultra high powerelectrode in high-temperature electric arc furnace steelmaking. The researchesshow that the needle coke electrode can reduce half of the energy consumption,compared with the original ordinary carbon electrode. In addition, needle cokealso has important applications in anode materials for lithium ion batteries andsuper capacitors etc. China is a power country of coal production andconsumption. About2~3wt.%coal tar pitch will be in the deep processing ofcoal such as coking process. The coke production was an estimated4.76millions tons in2013, so, it would give rise to a fairly substantial amount of coaltar pitch production. It can realize the use of science and effective allocation ofresources via high efficient utilization of coal tar pitch. It is most important tostudy on modification of coal tar pitch and influence of external conditions on the formation of the mesophase, in order to improve the structure of needle cokeand the utilization rate of coal resources, which has important significance forextending industry chain of coalprocessing and changing changing industrystructure of coking processing.In this paper, the medium temperature coal tar pitch were selected as rawmaterial for investigation. By means of carbonizing the coal tar pitch removedquinoline insolubles in different condition, Influences of temperature, pressure,time and electric field intensity on the structure and properties of mesophase,semi-coke and needle coke were studied. On this basis, The further researcheswere carried out about influences of solvent pretreatment of coal tar pitch,extraction of MCMB, adding grapheme, modification of coal tar pitch onstructure of mesophase and needle coke and the electrochemical properties.Scanning electron microscopy (SEM), X ray diffraction (XRD) analysis,polarizing microscopy, infrared spectroscopy (FT-IR), cyclic voltammetry (CV)and electrochemical impedance spectroscopy (EIS) and other methods wereadopted to characterize and analyze structure and properties of the refined coaltar pitch, mesophase, semi-coke and needle coke.The research results are as follows:1. Mesophase microbeads were of perfect uniform and the conversion ratereached52.3%under pressure0.5MPa, electric field intensity300kV/m,heated at470℃for3h. Semi-coke structure was of the most perfect heated at600℃for2h with heating rate of0.5℃/min. The calcination treatment could improve the crystal structure of needle coke, which perform increasing thestacking height of molecules enlarging the molecular layer arrangement andimproving the fiber structure and graphitization degree of needle coke.2. The heteroatom of refined coal tar pitch was removed by extraction withdifferent polarity and structure solvent. The extraction effect was analyzed indifferent solvent. The results showed that the removal effections of hetero atomswas different in different solvents. The heteroatom O, N and S of coal tar pitchcould be decreased obviously using heptanes and carbon tetrachloride solventextraction. These hetero atoms were not conducive to the increase of aromaticmolecular conjugate degree. In contrast, the effect of sulfur atom was the mostsignificant, and influence of N and O on orientation degree of fiber was weak.3. Extracted mesophase microsphere is used as the next crystal seed forpreparation of mesophase. Effects of extraction on mesophase structure havebeen systematically studied. The results showed that the microspheres numberof mesophase microspheres by multiple extraction MCMB preparationincreased rapidly along with the increase of extraction times and then slowlyincrease. Mesophase pitch was prepared using the seeds got at the second times,the third times and the forth times, and the proportion of microspheres isrespectively45.4%,69.8%and71.2%. Needle coke was prepared using thethird times and the forth times seed, and the proportion of optical fibermicrograph is respectively89%and80%. Under the stirring conditions, needlecoke showed better capacity better and more clear and perfect crystal structure. 4. The influences of coal tar pitch adding grapheme as crystal nucleus onmesophase formation process and structure of semi coke and needle coke hasbeen discussed. The results showed that with the increase of the quality ofgraphene, the number of microspheres gradually increased. Appropriate addingamount is about0.2wt%even the amount is more than0.2wt.%, the change ofmicrospheres number is no longer significant. The optical fiber structure wasmore perfect and capacitive was greater, compared with the semi-coke andneedle coke without the addition of grapheme.5. Using alkylation reagents like n-butyl bromide and n-propyl bromide asmodifier, the influence of modification on the fiber structure of coal tar pitchmesophase and structure and electrochemical properties of needle coke wasstudied. The results showed that the softening point of MCTP-7B modified byn-butyl bromide was reduced to64℃, char yield was increased by24%. Whilethe softening point of MCTP-7P modified by n-propyl bromide was reduced to63℃, char yield was increased by15%. Moreover, the morphology of needlecoke, prepared from coal tar pitch modified by7wt%of n-propyl bromide,presented long fibrous texture. The electrochemical tests showed that thestability and reversibility of needle coke were all improved.