Study of carbonization using a tube bomb: evaluation of lump needle coke, carbonization mechanism and optimization

The carbonization of three representative feedstocks derived from petroleum and coal tar was studied using a tube bomb, where the carbonization temperature and pressure are freely set up and carbonization progress is pursued at the desired stages. The coke lumps produced in the bomb are evaluated by optical anisotropy defined through a montage technique and coefficient of thermal expansion, which are semi-quantitatively correlated. The carbonization into needle coke follows the three major stages: the formation and growth of liquid crystal spheres; their coalescence into bulk mesophase; and the uni-axial rearrangement of mesophase molecules into a solid coke. The nature of bulk mesophase and gas evolution for the rearrangement define the quality of the needle coke. These factors are sharply influenced by the reactivity of feedstocks, carbonization temperature and pressure. Chemical analyses of the feedstocks and the carbonization intermediates describe the chemistry of the carbonization reaction, providing a structural basis for the reactivity. Based on such a mechanistic understanding of the carbonization, guiding principles to optimize the carbonization conditions of respective feedstocks into their best needle coke are proposed according to their structure and reactivity.