| The purpose of this research was to manufacture the modified mesophase pitch, as well as needle coke, by co-carbonization of toluene soluble of coal tar pitch (TS) and waste polystyrene (WPS), ethylene tar pitch (ETP) and WPS, respectively. The mechanism of co-carbonization and modification were investigated. The eutectic effect and its influence on the resultant product were also discussed.The properties of mesophase pitches were characterized using polarized light optical microscope, apparent viscometer, FT-IR, 1H NMR and X-ray diffractometer. And the characteristics of needle cokes derived from co-carbonization were examined using polarized light optical microscope, FT-IR, X-ray diffractometer, co-efficient of thermal expansion (CTE), scanning electron microscope.The toluene soluble of coal tar pitch (TS) was co-carbonized with waste polystyrene (WPS). The contents of soluble mesophase were increased from 10% to 52% and the anisotropic contents of mesophase pitches were developed from 65% with coarse mosaic texture to 100% with flow domain texture by TS added with WPS. During the co-carbonization of ethylene tar pitch and waste polystyrene, the content of soluble mesophase was increased from 5% to 56%, the mesophase content was increased from 32% to 100% and the optical texture was developed from incomplete coalescence to flow domain after adding waste polystyrene into ethylene tar pitch. During the co-carbonization of WPS with TS and ETP, the mesophase pitch was changed from thixotropy to unthixotropy, suggesting a better rheological behavior. The increased alkyl groups, which were mainlyαmethylene, improved the molecule assembly of mesophase pitch and resulted in the eutectic effect. The properties of the mesophse pitch were greatly improved due to eutectic effect.During co-carbonization, crosslinking of radicals derived from WPS and the pitches brought someαmethylene group and naphthenic structure to polymerized aromatic hydrocarbons (PAH). The fluidity and solubility of the mesophase pitches were improved by increasing alkyl groups in the pitch molecule. The naphthenic structure availed the slipping of aromatic planar molecule without destroying the stacking of the crystal. Although the arrangement of the crystal was disturbed a little, the other alkyl groups were able to improve the fluidity and solubility of the mesophase pitch. As a whole these alkyl in the mesophase showed positive effect in mesophase formation. The eutectic effect consisted in two aspects: one was intermolecule hydrogen transfer and alkyl transfer, the other was interaction of intramolecule and intermolecule in the pitch matrix. The former was the inherent reason and the latter was extrinsic one. During the early stage of co-carbonization, WPS availed the crosslink of pitch molecule and the earlier formation of mesophase. In the middle and latter stage, methylene groups improved the coalescence of the mesophase and kept a lower viscosity for a longer time. The rigorous reaction was inhibited during the middle and latter co-carbonization stage due to hydrogen transfer.The mechanism of modification of the mesophase pitch derived from co-carbonization was able to be interpreted by a newly introduced solutions theory. The formation of mesophase was in response to two primary driving forces: one was poor solubility of high molecular weigh aromatic molecules in the lower molecular weight fractions, promoting liquid/liquid phase separation, the other was lowering of the system free energy by molecular orientation of the large, disc-like molecules and expulsion of some of the smaller, less orientated molecules to a separate (isotropic) phase. The characteristics of mesophase pitch were able to correlate with the degree of condensed structure and alkyl content of the mesophase pitch. The molecule weight distribution and structure were improved by co-carbonization during different stage of carbonization, leading to increasing molecule volume and irregular structure of molecule. Based on the model of solutions theory, the chemical potential of mesophase was depressed by the alkyl structure, availing the development of mesophase.Co-carbonization properties of toluene soluble of coal tar pitch and waste polystyrene were studied in a tube bomb to correlate the content of alkyl groups in the mesophase pitches with CTE and anisotropic orientation. The more alkyl contents improved the properties of resultant needle coke in terms of optical texture and CTE value. The anisotropic indices of average length of vectors parallel to the CTE axis and average length of anisotropic unit vectors increased from 20.8μm to 28.4μm and 23.4μm to 28.8μm, respectively, and CTE value decreased from 0.8×10-6 /℃to 0.1×10-6 /℃. Ethylene tar pitch was co-carbonized with waste polystyrene to prepare needle coke. The anisotropic indices (average length of vectors parallel to the CTE axis and average length of anisotropic unit vectors) increased from 10.8μm to 28.4μm and 12.6μm to 28.8μm, respectively. The anisotropic indices of average length of vectors parallel to the CTE axis and average length of anisotropic unit vectors increased from 20.8μm to 28.4μm and 23.4μm to 28.8μm, respectively. The CTE value was decreased from 3.2×10-6 /℃to 0.3×10-6 /℃and the optical texture of the coke was changed from coarse mosaic of incompleteness coalescence to flow domain with high uniaxial orientation after adding WPS into ETP. Due to the increasing alkyl groups, the lower viscosity of the carbonization system favored the development of flow texture and uniaxial orientation. And the sufficient gas evolution of good timing in co-carbonization forced the uniaxial arrangement of bulk mesophase molecules at the solidification stage.The enormous difference of carbonization behavior of CTP and ETP, when carbonized singly, was vanished when mesophase pitch and needle coke were manufactured through co-carbonizing. And the characteristics of the mesophase pitch and needle coke were greatly improved, suggesting WPS being an excellent additive of co-carbonization.
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