Synthesis of mesophase pitch with high anisotropic content from heavy petroleum fractions

Abstract

Aromatic compounds and resins are key constituents of heavy petroleum fractions, influencing the synthesis of mesophase pitch (MP) via thermal condensation. This study explores MP formation from two distinct feedstocks: an aromatic-rich lubricant extraction oil (LEO) and a resin-rich deoiled asphalt (DOA). Despite their compositional differences, both feedstocks produced nearly 100% anisotropic content. LEO, containing 79% aromatic compounds, generated MP with a wide-area, streamlined texture, while DOA, with 62% resin, resulted in a mosaic texture. These textural differences are attributed to the distinct compositions of the two feedstocks. Average molecular structure models were constructed using the improved Brown-Ladner method, based on FTIR, MALDI-TOF-MS, and NMR analyses. The models indicate that LEO contains more aromatics, smaller molecular size, shorter branched chains, and richer methylene-bridged structures than DOA. Aromatic oligomerization is the primary reaction occurring during thermal condensation. Variations in molecular structure lead to significant differences in the properties of the resulting MP. MP synthesized from LEO was dominated by ordered hexamers, while MP from DOA was predominantly composed of disordered heptamers. Finally, an oligomerization mechanism for aromatic compounds is proposed, providing insights into the selection of raw materials for high-quality MP production.