Pitches with softening points of about 140°C, 175°C and 210°C were prepared by progressive air-blowing at 300°C of coal-tar pitches from different commercial coke-oven tars. The modification induced by the mild oxidation was monitored using solvent fractionation, elemental analysis and contact angle measurement. The kinetics and mechanism of mesophase formation on isothermal treatment at 450°C and the optical texture of resultant cokes were studied by polarized-light optical microscopy. The air-blowing increases gradually the coking yield and toluene insoluble content of pitch with very little changes in quinoline insoluble content and elemental composition. The modified pitches preserve characteristic structural features of parent materials. Air-blowing accelerates the formation of mesophase on carbonization and modifies to a different extent the mechanism of the transformation. QI particles tend to form large aggregates in the early stage of the transformation and mesophase growth occurs in the practically Ql-free pitch, leading to two-phase optical texture of resultant cokes.
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New technology for obtaining mesophase coal tar pitch in the experimental installation of the continuous run system has been developed. The process involves thermal preparation of the coal tar pitch at 400°C in the installation that is a compact system including typical elements of chemical equipment arranged to allow simultaneous run of a few unit operations. Charge of raw materials and discharge of products proceeded continuously (or semi continuously). The installation yields ca. 0.5 kg/h. The series of investigations have also been performed to analyze the possibilities for the use of the coal tar pitch obtained in the newly developed installation in materials technology.
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