Kerogen structural studies-oxidations with alkaline permanganate and with ferric chloride

Abstract

Two oxidizing agents were used for structural studies of the kerogen from Aleksinac shale (Yugoslavia), namely: (1) alkaline potassium permanganate, and (2) acidic ferric chloride. (1) The main goal with alkaline permanganate was to obtain optimum yields of identifiable oxidation products with preserved kerogen structural characteristics. In order to find optimal conditions, experiments were carried out at various temperatures (20-100°C) with varying amounts of permanganate per step. The best total yield of isolable degradation products (92,25%) was obtained at 75°C. At the same reaction temperature the best yield of ether-soluble acids was obtained (39% of the total organic matter). Kerogen degradation products obtained in high yields provide a better basis for more reliable structural interpretations than the products obtained in minor yields, which may represent small undefined portions of the original kerogen. (2) Ferric chloride is an oxidant of relatively high oxidation potential, although it is more gentle and more specific (e.g., dehydrogenation and decarboxylation) than most oxidation reagents containing oxygen used in kerogen structural studies. In oxidation of the Aleksinac shale kerogen concentrate with acidic ferric chloride solution, the pyrite content decreased (38-75%), and the kerogen content increased (7-15%). A small portion of the kerogen (∼8%) was degraded into soluble products. The chemical nature of the kerogen was considerably changed. In addition to a decrease in the atomic H C ratio and an increase in the O C ratio, changes in the content of aliphatic, aromatic, carbonyl and quinoid structures were observed.