Chemical structure and hydrocarbon formation of the Huanxian brown coal, China

Abstract

The Huanxian brown coal of the Lower Tertiary of East China is taken as an example for the study of relationships between coal chemical structure and the mechanism of hydrocarbon formation. Maceral examination shows that the brown coal has a high liptinite (up to 20%), which includes alginites, resinites and sporinites. Fatty acids produced from potassium permanganate stepwise oxidation of the brown coal are mainly composed of normal and iso-branched saturated monocarboxylic (up to C 29) and dicarboxylic (up to C 9) acids. All of the aromatic acids are mono- or dibasic, and most have no more than two rings. The Py-GC fingerprint of this brown coal agreed well with the results of the oxidation. XRD and 13C NMR spectroscopic analyses show that the carbon aromaticity of the coal ranges from 0.54 to 0.59. In combination with the chemical analyses of the oxygen-containing functionalities, and 13C NMR measurements, various structural parameters and the carbon, oxygen and hydrogen atomic distributions of the brown coal were assessed. Artificial thermal maturation of the brown coal was carried out both by anhydrous and hydrous pyrolysis under different temperatures and times. Based on systematic analyses of the gaseous, liquid and solid products, a mechanism of oil and gas formation, related to the thermal evolution of the coal structure, is proposed.