Insight into the Molecular Structure and Pyrolysis Kinetics of Green Petroleum Coke Extracts and Their Implications for Carbon Block Properties

Abstract The self-sintering of green petroleum coke (GPC) offers a promising route for preparing carbon blocks with a short production cycle and high structural homogeneity. However, the complex chemical composition of GPC complicates the understanding of the self-sintering mechanism, posing challenges in controlling the carbonization-induced volume changes and preventing the formation of defects and cracks, which are key barriers to the controllable fabrication of high performance self-sintering carbon blocks. Herein, the GPC is divided into toluene soluble (TS), toluene insoluble-quinoline soluble (TI-QS-90), and toluene insoluble-quinoline insoluble (TI-QI-90) fractions. Compared with TS counterparts, the heavier fraction, TI-QS-90, demonstrates obviously higher aromatic degree, carbonyl group concentration, molecular weight, and thermal stability. After calcination at 1000 °C, the TS fraction displays a typical highly ordered graphite morphology, whereas the TI-QS-90 tends to form a more disordered structure. In addition, two isoconversional methods, i.e., Kissinger–Akahira–Sunose (KAS) and Flynn–Wall–Ozawa (FWO), were employed to investigate the kinetics and thermodynamics of the self-sintering process. Both TS (109.79 kJ/mol) and TI-QS-90 (203.54 kJ/mol) show significantly lower average activation energies (Ea) than the pristine GPC (387.79 kJ/mol), indicating easier occurrence of carbonization. The higher Ea of TI-QS-90 and the toluene insoluble fraction (TI, 401.26 kJ/mol) indicate that the heavier fractions promote the formation of a denser structure as less gases are being released. Finally, all insoluble fractions were used as starting materials for carbon block preparation. The carbon block derived from the TI fraction (TI-C) exhibits flexural and compressive strengths of 18.88 and 60.73 MPa, respectively, which is 1.70 and 2.19 times higher than the GPC-based carbon block (GPC-C).