Thermal-Decomposition Products of Hexane-Insoluble Asphaltenes from Coal Pitch

Abstract

The thermal-destruction products of hexane-insoluble asphaltenes from coal pitch and petroleum asphaltenes are compared. The volatile thermal-decomposition products of the asphaltenes are studied by thermal analysis and gas–liquid chromatography and mass spectroscopy. The morphology and structure of the solid residue is investigated by scanning electron microscopy and X-ray phase analysis. By that means, the analysis of the thermal-decomposition products permits assignment of the asphaltenes to known structural types and prediction of the coke residue’s morphology. The volatile thermal-decomposition products from coal pitch are aromatic polycondensed compounds with 3–7 aromatic nuclei, including N- and S-bearing compounds. The thermal decomposition of petroleum asphaltenes is accompanied by the liberation of alkanes, alkenes, and O-bearing compounds, with chain length from C₁₁ to C₃₀. The content of arenes and polyaromatic hydrocarbons in the volatile thermal-decomposition products from petroleum asphaltenes is considerably less than the content of aliphatic hydrocarbons. Morphological data indicate that the solid thermolytic residues of the asphaltenes differ in structure. For petroleum asphaltenes, the structure is porous and, according to X-ray phase analysis, shows no signs of graphite-like structure. For the asphaltenes from coal pitch, the residue contains graphite-like structure and has a distinctive luster.