Regulation of the Heavy Fuel Oil modification process for Medium-Low temperature coal tar pitch aromatic depolymerization-recombination and design of the derived carbon microcrystalline structure

Abstract

This research addresses the challenge of heterogeneous mosaic carbon structures encountered when directly thermally converting Medium-Low temperature coal tar pitch (MLP) to prepare high-performance carbon materials, by introducing Heavy Fuel Oil (HFO) as a molecular-level modification medium. Directed design of derived carbon microcrystalline structures is achieved by regulating the HFO blending ratio to induce selective depolymerization and reorganization of MLP's aromatic system during low-temperature copolymerization. Studies revealed that HFO, characterized by hydrogen-rich alkyl branches, is capable of efficiently extracting oxygen elements from MLP in low-temperature copolymerization and can guide the polymerization of substituent sites beyond the aromatic rings in the pitch, resulting in the formation of broader sheet-like molecular formations. As a result, there's a notable rise in the toluene-insoluble (TI) levels in the altered pitch to 7.39 %, accompanied by an average molecular weight of 1684 Da, an aromaticity index of 0.394, a branching index of 0.661, and an aromatic degree of 0.89. The altered pitch during thermal conversion-calcination, due to the creation of a uniform miscible/melt state and structural and compositional shifts, stabilizes pitch free radicals through hydrogen supply, leading to a combined effect of “depolymerization-stabilization”. The liquid-phase carbonization setting is significantly enhanced, leading to even breakdown and lamellar reorganization of the pitch. The derived pitch's optical microstructure has evolved from its initial mosaic form to a structured lamellar/fibrous form, concurrently diminishing carbon structural flaws. The derived carbon material's structural organization is greatly improved, achieving an ideal graphite microcrystal concentration of 72.90 %. The research accomplished precise alterations to the optical microstructure of pitch derived from MLP, paving the way for a novel technical route in MLP's high-value use and providing both theoretical groundwork and actionable advice for the regulated creation of high-efficiency carbon materials.