Molecular condensation of ethylene tar for producing impregnating pitch by gas-blowing process

Abstract

Ethylene tar can be converted into high-value functional solid-phase pitches through heat treatment; however, the intrinsic mechanism of its thermal reaction remains insufficiently studied. In this work, the thermal reaction of ethylene tar during gas-blowing was systematically investigated and the synergistic effects of temperature/duration/gas atmosphere were compared using a stirred autoclave. The fundamental properties, molecular structures, and composition of the obtained pitches were analyzed. The results demonstrated that both air and nitrogen blowing promoted the conversion of ethylene tar into solid pitches, with air proving more efficient. Oxidative crosslinking during air-blowing effectively increased the molecular weight, carbon content, aromaticity and condensation degree of the pitches, thereby significantly improving the key parameters of softening point, toluene insoluble, and coking value. In addition, it was observed that an increase in temperature and duration favored the thermal reaction of ethylene tar. Higher conversion temperatures facilitated molecular dealkylation and aromatization, shifting the feedstock composition toward large molecules with high condensation degree and increased structural order. This process formed macromolecular polycyclic aromatic hydrocarbons, including asphaltenes and toluene insolubles. The oxidation kinetics of ethylene tar were analyzed and the possible mechanisms were proposed to illustrate the thermal reaction behavior for the conversion of liquid ethylene tar into solid pitches during gas-blowing.