Paul Sutton

Abstract

Organic matter which is insoluble in common solvents and non-oxidising acids often comprises the quantitatively most important fraction of organic matter in sediments. This operationally defined material is usually simply termed 'insoluble organic matter' (IOM) or 'kerogen' when it is isolated from ancient sediments. Indeed, kerogen is regarded as the most abundant form of carbon on the planet. The molecular character of this generic material has not been fully elucidated, principally because of its insolubility which limits instrumental methods of analysis to those applicable to solid substrates. This thesis describes the quantitative isolation of IOM from lacustrine and marine sediments and two species of methanogenic bacteria using a sequential isolation procedure. A range of synthetic IOMs (melanoidins) was also prepared. The dissolution of IOM and melanoidins obtained in this manner was then attempted using the acidic ionic liquid l-ethyl-3- methylimidazolium chloride-aluminium (III) chloride. Two synthetic dendrimers containing similar functional groups to those observed in sedimentary IOM were used to try and assess the mode of action of the ionic liquid. Ionic liquid treatment of the DCM soluble dendrimers resulted in the formation of 7 - 62 % of material that was no longer soluble in DCM, whilst the soluble components had been substantially altered. The ionic liquid was found to non-quantitatively promote ether cleavage, protonation and rearrangement reactions. IOM was isolated from lacustrine Rostherne Mere, UK, sediments (7 - 3 0 % dry weight), Kimmeridge Clay, Dorset (11 - 12 %) and methanogenic bacteria (Methanococcus jannaschii, 3 %; Methanobacterium thermoaiitotrophicum, 0.1 %) using a time-consuming isolation procedure involving over forty separate chemical manipulations. Monitoring of the sequential isolation of IOM and characterisation of the final isolates was carried out using solid-state NMR, IR, elemental analysis, pyrolysis-gas chromatography-mass spectrometry (Py-GC-MS), scanning electron microscopy, and the newer surface sensitive technique of time of flight-secondary ion mass spectrometry (ToF-SIMS). Less than 1 % of sedimentary IOM and 5 % of Kimmeridge Clay IOM was soluble in DCM following ionic liquid treatment, whilst alkyl chains were lost from the insoluble portion which also increased in aromaticity. The poor yield recovered following ionic liquid treatment of M. jannaschii IOM (5 %) was attributed to loss of volatile material during hydrolysis. Following ionic liquid treatment 93 - 96 % of the melanoidins remained insoluble in DCM although their character had been altered, becoming more condensed. This ionic liquid dissolution procedure has not provided the substantial progress in elucidating the molecular character of IOM promised by earlier reports.

Document Type

Thesis

Publication Date

2000

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