Crude Oil
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Crude Oil
The world consumes 1.5 billion gallons of petroleum every day, whether as fuel, petrochemicals, lubricants, or uncounted other uses. This enormous demand makes crude oil the single most important raw material to our civilization. When it emerges from the ground, crude oil is a mixture of thousands of hydrocarbons in solid, liquid, and gaseous form. This mixture is practically useless until it is refined into fuels, lubricants, petrochemicals, asphalts, solvents, plastics, waxes, and a large number of other materials. Petroleum-based fuels alone account for more than half the world's total supply of energy (and on the down side, account for much of the pollution in industrialized countries). Crude oil comes from concentrations of aquatic plants and animals that died hundreds of millions of years ago, buried under mud and sand in layered deposits that slowly decayed. Through heat and pressure over the millennia, these concentrations were geologically transformed into petroleum. Because new petroleum requires a geological age to be created, it is obviously not being replenished as fast as we are using it. Much of the work in the petroleum industry is involved in estimating the world's reserves of crude oil. The components of crude oil can be categorized by molecular size. Small molecules (containing 1-4 carbon atoms) are usually gases; larger molecules (four to about ten carbon atoms) are used as gasoline; hydrocarbons with about 50 carbon atoms are the source of light fuels and lubricating oils, while giant molecules of up to several hundred carbon atoms are the waxes, asphalts, and heavy fuels. With the extreme pressures underground, both gases and heavy wax are dissolved into the liquid crude, but on reaching the surface these components separate out. Though they are all made up primarily of hydrocarbons with small traces of sulfur, oxygen, and nitrogen, crude oils vary a great deal in their actual compositions and material properties. Black tarry asphalts are found in Trinidad and the Athabasca tar sands of Canada. Light, volatile oils which can be used directly as gasoline, are found in the Kettleman hills of California. Some crude oil smells like turpentine or camphor; other crude smells light and pleasant, while still others have a sulfur smell. Crude oil can be black, dark brown, reddish brown, cherry red, amber, green, or yellow; some fluoresce green or purple in reflected light. Physical properties such as specific gravity, volatility, and viscosity MRS BULLETIN/SEPTEMBER 1992
also vary according to the hydrocarbon mixture. Crude oil pooling up from natural seeps in the ground has been used for more than 6,000 years, as evidenced by Mesopotamian inscriptions (dated at 4000 B.C.) that describe uses for asphalt and oil, such as setting jewels and mosaictilesor fastening the blades of implements and weapons to their handles. In Egypt, crude oil was used as a wound dressing, a liniment, and a laxative, as well as for embalming mummies. People settling around the Black and Caspian Seas used oil skimme
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