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The Chemistry and Technology of Petroleum
of the kerogen structure and the models may even allow predictions of properties and behavior.
If the model does not match such behavior and properties, the model must be reworked since it then
becomes of little if any value.
A model derived for kerogen was based on the chromic acid oxidative degradation already discussed (Simoneit and Burlingame, 1974, and references cited therein). Additional information was
provided by studies of the bitumen, again primarily by mass spectrometry, and was incorporated
into the structural model that included regions of undefined structure containing trapped organic
compounds of unknown nature and bearing side chains linked to the main structure by nonhydrolyzable C–C and hydrolyzable ester linkages. Ester linkage was also believed to be present and the
model also includes an alicyclic (naphthene) ring. To understand this model it is important to recall
that the oxidation products (acids and ketones) upon which most of this structure is based, represented only a fraction of the total organic carbon.
Another model for kerogen was developed on the basis of the data derived from the stepwise
alkaline permanganate oxidation of kerogen, which produced high yields of carboxylic acids. Based
on the oxidation results, a cross-linked macromolecular network structure was proposed. The most
striking feature of this model is the predominance of straight-chain groups in the backbone of the
network. The network bears both linear and branched side chains; branching points are indicated in
the model by open circles. This model accommodates many important experimental observations,
including reversible swelling and gel-like rubbery behavior in the swollen state, but does not satisfactorily account for the aromatic carbons observed by carbon 13 magnetic resonance spectroscopy
or the nitrogen and sulfur contents determined by elemental analysis.
Another kerogen model (Schmidt-Collerus and Prien, 1974) was assembled from the subunits
identified by micropyrolysis-mass spectrometry studies. Key features of this model include formulation as a three-dimensional macromolecular network and a very uniform hydrocarbon portion
comprised mostly of small alicyclic and partially hydrogenated aromatic sub-units with few heterocyclic rings. Long-chain alkylene and isoprenoid units and ethers serve as interconnecting bridges
in this structure. Entrapped species (bitumen) include long-chain alkanes and both n-alkyl and
branched carboxylic acids. This model provides a useful view of the types and role of hydrocarbon
units but de-emphasizes heteroatom functional groups and rings, presumably because groups containing these elements would not be detected efficiently by the micropyrolysis technique.
The structure of kerogen has also been probed by a wide variety of techniques, including stepwise alkaline permanganate and dichromate-acetic acid oxidation, electrochemical oxidation and
reduction (in nonaqueous ethylenediamine-lithium chloride), and x-ray diffraction techniques
(Barakat and Yen, 1988, and references cited therein). The following were the findings for that
particular sample of kerogen:
1. Aromaticity was low but isolated carbon–carbon double bonds were possible.
2. The structure largely comprised three-to-four-ring naphthenes.
3. Oxygen was present mostly as esters and as ethers.
4. The kerogen structure comprises a three-dimensional network and ethers serve as crosslinks in this network.
5. Additional linkages were provided by disulfides, nitrogen heterocyclic groups, unsaturated
isoprenoid chains, hydrogen bonding, and charge–transfer interactions.
Using these components as building blocks, a multipolymer network was envisaged (Yen, 1974,
1976). It was also pointed out that the extractable bitumen molecules could reside, more or less
freely depending on their size, within the network.
To further account for the observed variations in the products obtained from the individual steps
of stepwise permanganate oxidation, it was suggested that a core plus shell arrangement existed for
the individual kerogen particles. The core was visualized as a cross-linked region containing most
of the alkyl and alkylene chains and the bulk of the kerogen as naphthenic ring structures. On the
The Chemistry and Technology of Petroleum
of the kerogen structure and the models may even allow predictions of properties and behavior.
If the model does not match such behavior and properties, the model must be reworked since it then
becomes of little if any value.
A model derived for kerogen was based on the chromic acid oxidative degradation already discussed (Simoneit and Burlingame, 1974, and references cited therein). Additional information was
provided by studies of the bitumen, again primarily by mass spectrometry, and was incorporated
into the structural model that included regions of undefined structure containing trapped organic
compounds of unknown nature and bearing side chains linked to the main structure by nonhydrolyzable C–C and hydrolyzable ester linkages. Ester linkage was also believed to be present and the
model also includes an alicyclic (naphthene) ring. To understand this model it is important to recall
that the oxidation products (acids and ketones) upon which most of this structure is based, represented only a fraction of the total organic carbon.
Another model for kerogen was developed on the basis of the data derived from the stepwise
alkaline permanganate oxidation of kerogen, which produced high yields of carboxylic acids. Based
on the oxidation results, a cross-linked macromolecular network structure was proposed. The most
striking feature of this model is the predominance of straight-chain groups in the backbone of the
network. The network bears both linear and branched side chains; branching points are indicated in
the model by open circles. This model accommodates many important experimental observations,
including reversible swelling and gel-like rubbery behavior in the swollen state, but does not satisfactorily account for the aromatic carbons observed by carbon 13 magnetic resonance spectroscopy
or the nitrogen and sulfur contents determined by elemental analysis.
Another kerogen model (Schmidt-Collerus and Prien, 1974) was assembled from the subunits
identified by micropyrolysis-mass spectrometry studies. Key features of this model include formulation as a three-dimensional macromolecular network and a very uniform hydrocarbon portion
comprised mostly of small alicyclic and partially hydrogenated aromatic sub-units with few heterocyclic rings. Long-chain alkylene and isoprenoid units and ethers serve as interconnecting bridges
in this structure. Entrapped species (bitumen) include long-chain alkanes and both n-alkyl and
branched carboxylic acids. This model provides a useful view of the types and role of hydrocarbon
units but de-emphasizes heteroatom functional groups and rings, presumably because groups containing these elements would not be detected efficiently by the micropyrolysis technique.
The structure of kerogen has also been probed by a wide variety of techniques, including stepwise alkaline permanganate and dichromate-acetic acid oxidation, electrochemical oxidation and
reduction (in nonaqueous ethylenediamine-lithium chloride), and x-ray diffraction techniques
(Barakat and Yen, 1988, and references cited therein). The following were the findings for that
particular sample of kerogen:
1. Aromaticity was low but isolated carbon–carbon double bonds were possible.
2. The structure largely comprised three-to-four-ring naphthenes.
3. Oxygen was present mostly as esters and as ethers.
4. The kerogen structure comprises a three-dimensional network and ethers serve as crosslinks in this network.
5. Additional linkages were provided by disulfides, nitrogen heterocyclic groups, unsaturated
isoprenoid chains, hydrogen bonding, and charge–transfer interactions.
Using these components as building blocks, a multipolymer network was envisaged (Yen, 1974,
1976). It was also pointed out that the extractable bitumen molecules could reside, more or less
freely depending on their size, within the network.
To further account for the observed variations in the products obtained from the individual steps
of stepwise permanganate oxidation, it was suggested that a core plus shell arrangement existed for
the individual kerogen particles. The core was visualized as a cross-linked region containing most
of the alkyl and alkylene chains and the bulk of the kerogen as naphthenic ring structures. On the