Ester- and ether bond cleavage in immature kerogens

Abstract

Quaternary ammonium salt Aliquat 336 and 18-Crown-6 enhance hydrolysis of Timahdit-M kerogen when used as a phase transfer catalyst. The yield of hydrolysis products was higher with Aliquat than with 18-Crown-6, but the identified products were found in lower concentration, the difference being soluble heavy parts from kerogen which cannot be analyzed directly. Both reactions afforded series of aliphatic mono- and dicarboxylic acids, alkylsuccinic acids and alkanols, but differences in distributions were observed. The range of monocarboxylic acids was shorter with Aliquat than with 18-C-6, C 14C 18 compared to C 12C 32, but palmitic and stearic acids were dominant in the two cases. C 10 and C 12 alkyl succinic acids were identified in Aliquat products. Aromatic acids were the major hydrolysis products (59%) with crown ether; only one aromatic acid was found with Aliquat. Hydrocarbons and tertiary amines were obtained from both reactions, they were obviously present in the kerogen as trapped molecules. Many tertiary amines arising from the decomposition of the reagent were obtained with Aliquat. The results give evidence of an important reticulation involving ester groups in the Timahdit-M kerogen. Series of n-, iso- and anteisoalkanes were obtained through HI/LAD treatment of Irati and Aleksinac kerogens, originating probably from glycerol-ether lipids. C 27C 34 α,β-hopanes were also found to be linked to kerogen (Irati) by ether bonds. Reaction with CF 3CO 2H (Irati) afforded seven series of branched alkenes, indicating that branched saturated alkyl chains were bound to aromatic moieties of kerogen by ether groups. Acetates of cholesterol and 24-ethylcholesterol were identified in the BF 3-Et 2O/Ac 2O products. Esters of fatty acids (max C 16, C 18) were also identified. Only alkanes were produced on AII 3 reaction. Each reaction afforded the same series of n-alkanes. This would reflect modifications in the kerogen matrix during these various treatments, resulting in the release of tightly trapped molecules.