Crude oil or petroleum is a flammable liquid and is a complex
mixture of organic and some inorganic materials, varying
with its geologic origin. API defines it as “a complex
combination of hydrocarbons. It consists predominantly of
aliphatic, alicyclic, and aromatic hydrocarbons. It may also
contain small amounts of nitrogen, oxygen, and sulfur compounds.
This category encompasses light, medium, and
heavy petroleum, as well as the oils extracted from tar
sands. Hydrocarbonaceous materials requiring major chemical
changes for their recovery or conversion to petroleum
refinery feedstocks such as crude shale oils, upgrade shale
oils, and liquid coal fuels are not included in this definition.”
Crude oil contains hundreds, perhaps even thousands, of
aliphatic or other hydrocarbon compounds ranging from C1
to greater than C50 and boils in the range of 32 to 2000 F
range (-1 to 565℃ at 1013 hPa); however, In practice,
atmospheric distillation of crude oil is not practiced above
275-300 ℃, to avoid thermal decomposition of the residue
(114, 115). It may vary in chemical composition and appearance
from an almost clear liquid to a viscous tar-like material
(20), depending on the geologic and geographical
source.
Depending on the composition that varies among geologic sources, it is used to manufacture gasoline, jet and diesel fuels, kerosene, heating oil, naphtha solvents, greases, waxes, lubricating oils, asphalt, and various singly isolated compounds such as alicyclic hydrocarbons (cycloalkanes and cycloparaffins), butene, propene, benzene, toluene, cumene, dicyclic alkanes (e.g., decalin), alkanes (e.g., pentane, hexane, heptane, octane, dodecane, and undecane), and naphthalene.
Crude oil varies in distillate type, which is directly fractionable, through extraction, distillation, and cracking, into gasoline and accompanying products to highly viscous asphalts. The basic processes used in petroleum refining include distillation, cracking, and finishing operations. In distillation procedures, materials are separated according to the boiling range. In a variety of cracking operations using heat, catalysts, and/or hydrogen, molecules may be split (“cracked”) into smaller units or rearranged into different or larger molecules. Combinations of distillation and cracking processes are used as needed to fill the demand for various products from the available crude oils. The properties of the crude products are modified or improved by finishing treatment to make them acceptable for use.
Petroleum oil was one of many agents associated with scrotal cancer in Sweden and in an older study. No evidence of leukemia, CNS, or biliary passage/liver cancers was found in a follow-up study of petroleum refinery workers, but the mortality rate from lymphopoietic cancers, especially lymphoreticulosarcoma, increased with the duration of employment of those hired before 1946. Crude oil or its fractions have caused tumors when painted on the skin of mice. It has been judged an equivocal tumor agent. It was a less potent carcinogen than coal or shale oil. However, the carcinogenic potency may increase with the boiling point and sulfur content. A fraction boiling in the range of 700–1070F was highly active, as were all fractions that contain aromatic compounds. Presumably, the potency of crude oil in inducing cancers in experimental animals (or humans) may also vary with the geologic origin of the material. Crude oil can contain up to 0.2% benzene, a confirmed human carcinogen.
