Kerogen

In the classical theory of geopolymer formation, kerogen was believed to derive from humic substances 

The selective preservation of resistant biomacromolecules (with the possibility of minor microbial alteration) is likely to be an important process in the formation of most kerogens, and particularly those formed at very early stages of diagenesis (Tegelaar et al. 

The algaenans from most algae contain long -alkyl chains, such as that from the chlorophyte Tetraedron, 

Fig 4 10 Proposed structures for (a) cutan (from Agave americana n is large but unknown, and the central carbonyl link has yet to be confirmed after McKinney et al. 1996) and (b) algaenan (from freshwater species Tetraedron minimum, Scenedesmus communis and Pediastmm boryanum x + y = 27, 29, 31 andx + z = 28, 30, 32 after Blokker et al. 1998). 

The potential pathways to kerogen formation are combined in the scheme shown in Fig. 4.11, in which kerogen is seen to be the combination of resistant biomacromolecules, geomacromolecules, sulphur-rich macromolecules and incorporated LMW biomolecules. The extent to which humic material contributes to kerogen is uncertain. Partial alteration of biomacro- 

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Their chemical compositions are very complex and depend essentially on their age, that is, the phase of development of the kerogene, regardless of the origin of the crude (Speight, 1991) (see Chapter 1). 

Oil Shale. Oil shale (qv) is a sedimentary rock that contains organic matter, referred to as kerogen, and another natural resource of some consequence that could be exploited as a source of synthetic natural gas (67—69). However, as of this writing, oil shale has found Htde use as a source of substitute natural gas. 

Oil shale deposits were formed in ancient lakes and seas by the slow deposition of organic and inorganic remains. The geology and composition of the inorganic minerals and organic kerogen components of oil shale vary with deposit locations throughout the world (1) (see also Fuel RESOURCES Petroleum). 

Kerogen Decomposition. The thermal decomposition of oil shale, ie, pyrolysis or retorting, yields Hquid, gaseous, and soHd products. The amounts of oil, gas, and coke which ultimately are formed depend on the heating rate of the oil shale and the temperature—time history of the Hberated oil. There is Htde effect of shale richness on these relative product yields under fixed pyrolysis conditions, as is shown in Table 5 (10). 

Numerous kinetic mechanisms have been proposed for oil shale pyrolysis reactions (11—14). It has been generally accepted that the kinetics of the oil shale pyrolysis could be represented by a simple first-order reaction (kerogen — bitumen — oil), or... 

Synthetic fuels derived from shale or coal will have to supplement domestic suppHes from petroleum someday, and aircraft gas turbine fuels producible from these sources have been assessed. Shale-derived fuels can meet current specifications if steps are taken to reduce the nitrogen levels. However, extracting kerogen from shale rock and denitrogenating the jet fuel are energy-intensive steps compared with petroleum refining it has been estimated that shale jet fuel could be produced at about 70% thermal efficiency compared with 95% efficiency for petroleum (25). Such a difference represents much higher cost for a shale product. 

Oil Shale Oil shale is nonporous rock containing organic kero-gen. Raw shale oil is extracted from mined rock by pyrolysis in a surface retort, or in situ by steam injection after breaking up the rock with explosives. Pyrolysis cracks the kerogen, yielding raw shale oil... 

General scheme of kerogen evolution from diagenesis to metagenesis in the van Krevelen diagram. 

Geochemists tiy to determine where hydrocarbons begin to be liberated and how their quantity and composition may vaiy with increasing maturity. This is equivalent to evaluating the amount and type of kerogen present m the rocks as well as the maturity... 

One important measurement made by geochemists is the Total Organic Carbon (TOC) measurement. The results are expressed as a weight percentage. When the TOC is less than 0.5 percent, the rock is considered unlikely to have enough kerogen to produce oil or gas. 

Oil shale is a low-permeahle rock made of inorganic material interspersed with a high-molecular weight organic substance called Kerogen. Heating the shale rock produces an oily substance with a complex structure. 

The recovery of petroleum from sandstone and the release of kerogen from oil shale and tar sands both depend strongly on the microstmcture and surface properties of these porous media. The interfacial properties of complex liquid agents—mixtures of polymers and surfactants—are critical to viscosity control in tertiary oil recovery and to the comminution of minerals and coal. The corrosion and wear of mechanical parts are influenced by the composition and stmcture of metal surfaces, as well as by the interaction of lubricants with these surfaces. Microstmcture and surface properties are vitally important to both the performance of electrodes in electrochemical processes and the effectiveness of catalysts. Advances in synthetic chemistry are opening the door to the design of zeolites and layered compounds with tightly specified properties to provide the desired catalytic activity and separation selectivity. 

The method by whieh erude oils are expelled from souree kerogen also influences oil group eomposition. In the case of hydrothermal oils or hydrothermal bitumens, hot water ean enhanee the content of lighter aliphatie and aromatic hydrocarbons (benzene, toluene, ethylbenzene, and xylenes). Typieal hydrothermal oils have a... 

As much as two-thirds of conventional crude oil discovered in U.S. fields remain unproduced, left behind because of the physics of fluid flow. In addition, hydrocarbons in unconventional rocks or that have unconventional characteristics (such as oil in fractured shales, kerogen in oil shale or bitumen in tar sands) constitute an enormous potential domestic supply of energy. 

The isotopic composition of carbon in carbonaceous organic material (kerogen) from ancient sedimentary rocks gives information on whether photosynthetic organisms were present during rock formation or not. It can also provide information on biological activities if cellular structures had already been destroyed. Sulphur can be used in a similar way (Schopf, 1999). 

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