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pyrobitumen
Pyrobitumen is a type of solid, amorphous organic matter. Pyrobitumen is mostly insoluble in CS2 (and other organic solvents) as a result of molecular cross-linking which renders previously soluble organic matter (i.e., bitumen) insoluble.,〔B. P. Tissot and D. H. Welte (1984) Petroleum Formation and Occurrence, 2nd ed., Springer-Verlag, pp. 460-463.〕〔J. M. Hunt, Petroleum Geochemistry and Geology, 2nd ed., Freeman, 1996, p. 437.〕 Not all solid bitumens are pyrobitumens, in that some solid bitumens (e.g., gilsonite) are soluble in common organic solvents, including CS2, dichloromethane, and benzene-methanol mixtures.
==Other related hydrocarbons==
While the primary distinction between bitumen and pyrobitumen is solubility, the thermal processes driving the molecular cross-linking also decrease the atomic ratio of hydrogen to carbon from greater than one to less than one and ultimately to approximately one half. It should also be understood that both solubility and atomic H/C ratios form a continuum, and most solid bitumens have both soluble and insoluble components. The distinction between pyrobitumen and residual kerogen in a mature source rock is based on microscopic evidence of fluid flow within the rock fabric and is usually not determined.
The terms bitumen and pyrobitumen have related definitions in the earth’s crust and in the laboratory. In geology, bitumen is the product of deposition and maturation of organic matter, and the extractable organic material (EOM) by organic solvents in petroleum source rocks and reservoir rocks is defined as bitumen. Upon exposure to high regional temperatures over geological time, bitumen is converted to pyrobitumen as a result of the thermally activated reactions that drive off lighter oil and gas products and leave an insoluble, carbon-rich residue. Pyrobitumen represents a significant fraction of the ultimate fate of petroleum liquids formed from kerogen during catagenesis. In the laboratory, experiments on organic-rich rocks (oil shales and petroleum source rocks), decomposition of the initially insoluble organic matter (defined as kerogen) produces gaseous and liquid products. The soluble fluid that remains in the heated rock is defined as bitumen. Upon further thermal exposure, the bitumen continues to evolve and disproportionates into pyrobitumen and more oil and gas.
The terms bitumen and asphalt are often used interchangeably to describe highly viscous to solid forms of petroleum that have been used in construction since the fifth millennium B.C.〔Asphalt, downloaded January 2, 2014.〕 Bitumen is distinct from tar, which properly describes a product formed by pyrolysis (destructive distillation) of coal or wood. Pitch recovered from petroleum by distillation is also sometimes called bitumen or asphalt.〔Pitch (resin), downloaded January 2, 2014.〕
抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』
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