Preliminary analysis of Monterey kerogen by mild stepwise oxidation with sodium dichromate in glacial acetic acid

Abstract

Kerogen from Monterey shale was degraded by a controlled, mild stepwise oxidation with sodium dichromate in acetic acid. The products of each step were examined by capillary gas chromatography and combined gas chromatography-mass spectrometry analyses of their methyl esters. Major oxidation products were saturated normal monocarboxylic acids (C 6-C 34), saturated normal α,ω-dicarboxylic acids (C 4-C 34), and isoprenoid acids (C 14-C 21, except C 18). Less dominant were aromatic acids, branched monocarboxylic acids (C 6-C 16), cyclic structures, heterocyclic compounds, as well as some unidentified compounds. On the basis of the evidence obtained from the qualitative and quantitative variation of the products with duration of oxidation, the following results were obtained: 1. (a) the kerogen nucleus is mainly composed of long-chain polymethylene, cross-linked aliphatic structure from which protrude n- alkyl chains and minor amounts of isoprenoid and non-isoprenoid branched hydrocarbons; 2. (b) the periphery, compared to the nucleus, contains a greater proportion of n- alkyl and isoprenoid moieties, particularly the C 14, C 16, and C 18 n- alkyl chains as well as the C 15 and C 16 isoprenoid chains; 3. (c) other subordinate structures present include phenyl and tolyl groups as well as alicyclic and heterocyclic compounds.