Optimization of the Carbonization Process for the Preparation of High-Grade Needle Coke Based on the Response Surface Method and Microstructure Analysis

Refined coal tar pitch (RCTP) with a quinoline insoluble (QI) content less than 0.01% was obtained from Wuhai coal tar pitch (CTP), which was used as a raw material to prepare needle coke by carbonization and calcination experiments. In this work, the effects of carbonization time, carbonization temperature, and carbonization pressure on the optical structure of green coke and the microstructure of needle coke were investigated. Meanwhile, the microstructure changes of products were characterized by polarizing microscopy, XRD analysis, Raman analysis, and SEM. The reliable transfer functions between the green coke mesophase content and the investigated factors, as well as the graphitization degree of needle coke, were established based on the response surface analysis method. Furthermore, we provide an operable window for carbonization temperature, time, and pressure, guaranteeing that the content of the green coke mesophase is greater than 90% and the graphitization degree of needle coke is greater than 80%. It can be found that the carbonization temperature has the most significant effect on the mesophase content and graphitization degree of coke. Prolongation of carbonization time is helpful for mesophase molecules to fully grow up, and the directional arrangement, which results in the structure of the coke, is regular. The appropriate carbonization pressure not only ensures that the carbonization reaction system has a certain viscosity but also provides hydrogen free radicals, which is conducive to the formation of drainage optical structure.