Structure of anisotropic spheres obtained in the course of needle coke formation

Abstract

Three kinds of spheres obtained from the heat-treated pitches which gave needle-like cokes were examined by means of an X-ray diffractometer (Diamond's method), an electron microscope and a magnetic balance to get their structural information. The precise chemical analyses were also obtained for spheres solubilized by the method of reductive alkylation. The planar condensed-ring compounds of relatively small size (6 ~ 15 Å) were revealed to align with preferred orientation to form the anisotropic sphere by these instrumental analyses. The molecular weight measurement showed that the sphere contained the molecules of molecular weight distributed from 400 to 3000 or more, and that the average molecular weight remained constant through the stages of their appearance, growth and initial coalescence in spite of the enlargement of the anisotropic domains. These results indicated that the smaller molecules are anchored to the larger ones by the π-π van der Waals forces to form the insoluble sphere. It can be also assumed that the growth of the spheres is not attained by their coalescence but by incorporation of smaller molecules in the matrix into the sphere at an adequate rate to increase their diameter as large as possible for the formation of a needle-like coke. The structural model of the sphere component was tried to be described by the chemical terms based on the results.