Constitution of Organic Acids Prepared from Colorado Oil Shale - Based on n-Butyl Esters

Abstract

KNOWLEDGE of the principal chemical structures in the mixture of organic material, commonly called kerogen, in Colorado oil shale would be of value as a basis for the selection of favorable reactions and processing conditions for converting oil shale to liquid fuels. Only about 15% of the kerogen is soluble in common organic solvents. Consequently, to determine the constitution of the major portion of the kerogen, it is necessary to convert, or degrade, the material to soluble products which are more amenable to analysis. Heating in the presence or absence of hydrogen and oxidation has been used extensively to degrade polymers, cellulosic materials, and the fossil fuelspetroleum, coal, and oil shale.This paper describes a study of the constitution of organic acids degraded from Colorado oil shale by oxidation with alkaline potassium permanganate. The oxidation conditions were selected to obtain acids containing some of the structures present in the original kerogen. The acids were then converted to ra-butyl esters for characterization. Based upon these esters, two general types of acids were derived from the kerogen-diearboxylic acids of the alkane series ranging principally from oxalic to adipic acid, and a series of dicarboxylic acids of higher molecular weight which were not identified. The latter acids appear to consist predominantly of saturated cyclic structures rather than aromatic or paraffinic structures.Degradation of kerogen by oxidation with alkaline potassium permanganate has several advantages. The method has been studied extensively as a means of degrading compounds of known composition and type (2, 6, H, 20), and for characterizing complex materials of unknown composition (1, 3-5, 7, 8, 12, 13).Based upon this background of published information, the oxidation reactions are believed to be predominantly degradative and are not complicated by secondary reactions, such as polymerization, which may occur in pyrolytic degradations. The degree of oxidation can be controlled to obtain products within different ranges of molecular weight. Thus, kerogen in Colorado oil shale is oxidized almost completely to carbon dioxide and oxalic acid by treatment for 100 hours with a boiling solution of potassium permanganate, but yields variable amounts of organic acids by brief treatments with small amounts of the reagent Bureau of Mines, Laramie, Wyo.(15). The organic acids formed by the oxidation are soluble in the alkaline solution and can be separated from the oil-shale minerals.The organic materials in oil shales from different deposits may vary in composition, but only minor variations are observed for organic materials in various grades of oil shale within a given deposit. Thus, the kerogens in oil shales of the Green River formation in the vicinity of Rifle, Colo., exhibit minor physical variations, but their over-all compositions are very uniform and average 76.1% carbon, 10.5% hydrogen, 2.6% nitrogen, 1.3% sulfur, and 9.5% oxygen (19).

Composition of Low-Temperature Thermal Extracts from Colorado Oil Shale.

“…Based upon the composition of the extracts, the kerogen structure appears to be predominantly of a saturated heterocyclic nature with smaller amounts of cyclic paraffins, straight-chain paraffins, and aromatic portions constituting the remainder of the structure. These conclusions supplement those reported earlier (7,8) from oxidation studies.…”

“…where loss of resin sulfur occured. (7) The pentane-insoluble material produced at higher temperatures contained less hydrogen and more nitrogen than the resins.…”

Nature of Oil-Shale Kerogen. Oxidations with Potassium Permanganate in Acetone Solution.

“…In a few cases the presence of succinic acid has been reported in the oxidation products. Flowever, by performing the oxidation of oil shale in several steps, higher yields of intermediate acids were obtained: "regenerated humic acids" (30), a mixture of dicarboxylic acids ranging from oxalic to adipic acid, besides complex acids of higher molecular weight which were not identified (29) and volatile monocarboxylic acids, dicarboxylic acids ranging from oxalic to azelaic acid and some viscous acids of unknown composition (70).…”

Western oil-shale development: a technology assessment. Volume 4. Solid waste from mining and surface retorts

“…Numerous studies have investigated the products of the controlled oxidation and low temperature thermal. degradation of kerogen, with the assumption that these components represent original structural features (Robinson et ale 1953, 1956, 1963, Robinson and Lawlor 1961, Burlingame 1969, Djuricic et ale 1971, Hubbard and Fester 1958, Fester and Robinson 1966. These experiments have suggested that kerogen exists as a complex polymeric assemblage composed of linear networks of cyclic rings of methylene groups with associated long chains and aromatic structures.…”