Preparation Of Mesophase Pitch From The Co-liquefaction Residue Of Coal And Catalytic Cracking Slurry Oil

Mesophase pitch is a quality precursor for preparation of functional carbon and graphite materials, and the structure of mesophase pitch directly determines the performance of carbon materials. In this paper, asphaltine and heavy oil were extracted by Soxhlet extraction from the coliquefaction residue obtained from the coliquefaction process of Yanzhou coal and Shijiazhuang catalytic cracking slurry oil. The temperature range during the preparation of mesophase pitch was confirmed by hot-stage microscopy. The influences of temperature, soaking time and initial gauge pressure on the formation of mesophase pitch were explored systematically in the confirmed temperature range. The optimum formation condition of mesophase pitch with good performance was determined ultimately. In order to optimize the performance of the mesophase products, the asphaltine was carbonized with different proportions of heavy oil in this optimum condition. The co-carbonization effect of asphaltine and heavy oil in mesophase development process was investigated. This paper reaches the following results:(1) Based on SEM result, mesophase microspheres present a globe structure, they grow and coalesce obeying the mechanism of homogeneous nucleation.(2) Based on the result of hot-stage polarized microscopic test, the transformation from asphaltine to mesophase pitch can only be conducted in a certain temperature range(308~510 oC), and the temperature range is chosen at 350~500 oC in this paper. With the increase of temperature, mesophase pitch content initially increases and then decreases, the yield and H/C atomic ratio gradually decline while insolubles content, softening point, aromaticity index and condensed degree gradually increase. Only at a lower temperature(~400 oC) can the extension of soaking time promote the formation, growth and coalescence of mesophase. Increasing the initial gauge pressure appropriately promotes the coalescence and rearrangement of mesophase microspheres, but too high pressure hinders microspheres to coalesce.(3) The optimum formation condition of large wide-area mesophase pitch with lower softening point(~270 oC) is determined by the temperature at about 400 oC, initial gauge pressure at about 1 MPa, and a soaking time of about 10 h.(4) The co-carbonization research of asphaltine and heavy oil was conducted in the aforementioned optimum condition. With the increase of heavy oil content in the precursor blend, the H/C atomic ratio and alkyl group of polymerized samples gradually increase while insolubles content and softening point of polymerized samples gradually decrease.(5) With about 20 wt% of heavy oil, a large number of orderly mesophase flow domains with low softening point(~210 oC) can be obtained and the polymerized sample yield reaches the maximum of 76.68 wt%. Furthermore, the mass fraction of polymerized sample soluble part is relatively high, therefore, the polymerized sample is likely to possess high spinnability, and it is interesting for the potential application of the polymerized sample as precursor of carbon fiber.(6) When the percentages of heavy oil are higher than about 20 wt%, the mesophase nucleation rate of the system is relatively slow due to the higher H/C ratio, lower aromaticity and molecular weight of raw materials, therefore, the mesophase is insufficiently developed. Moreover, when the percentage of heavy oil is about 80 wt%, discrete mesophase microspheres with relatively uniform size(~9 μm) and good sphericity can be generated.(7) This paper indicates that it is indispensable to extract the asphaltine and heavy oil from the coliquefaction residue, and then adjust the ratio of asphaltine to heavy oil for the purpose of preparing mesophase flow domains and mesophase microspheres, which both have good performances.