Laboratory Coking and a New Optical Texture Classification Parameter: Screening of Petroleum Refinery Streams for Premium Needle Coke Production

A new qualitative classification parameter was formulated for ranking optical textures of semi-cokes produced in a laboratory reactor under autogenous pressure from 11 different feedstock samples gathered from conventional and unconventional petroleum refinery streams. This classification can help select the most suitable feedstocks to produce premium needle coke by commercial delayed coking. Like previous studies, the new texture classification method, optical texture parameter (OTP), was formulated based on the population of different texture elements with respect to their apparent anisotropy, as observed by polarized light microscopy. Thus, a high value of OTP reflects a higher degree of carbonaceous mesophase development during coking or a higher degree of anisotropic order in the resulting semi-coke, a critically important property of premium needle cokes. The OTP analysis of the semi-coke samples obtained by laboratory coking at different temperatures suggested that the unconventional feeds have the potential to produce premium needle coke with comparable or higher texture quality to those obtained from conventional feeds. This analysis also showed that unconventional feeds show a relatively high sensitivity to changes in the coking temperature in terms of optical texture development in the resulting semi-cokes; the optimum temperature to obtain the highest degree of anisotropy is lower for the nonconventional feeds compared to that for slurry oils. Trends of mesophase development observed across the entire axial section of the semi-cokes samples provided strong evidence that the results from our coking experiments are relevant to the commercial delayed coking practice. This approach can enable the selection of feedstocks with high potential to produce premium needle coke through laboratory-scale experiments.