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Extreme Oil
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The Journey The History The Science
Exploration Production Transportation Refining
Early Prospecting - Modern Exploration Always a Messy Business - Modern Production Pipelines, Tankers, Trains, and Trucks Turning Crude Into Commodities

Excavation Feature
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Refining

Though many think of oil primarily as a source of gasoline, it in fact provides much more. Crude contains other fuels, such as heating oil, jet fuel, and diesel. Other components feed into industries like tires, plastics, or synthetic textiles. Still other refining products become fundamental building blocks for the chemical industry, particularly fertilizers. Even hydrogen gas, a much-touted energy "source" of the future is, for the most part, not a source at all but rather a product of crude-oil refining.

Regardless of origin, crude oil consists overwhelmingly of hydrocarbons -- hundreds and hundreds of configurations of carbon and hydrogen atoms, linked together in chains of varying length and complexity. Natural substance that it is, crude oil comes from particular batches underground, with varying physical and chemical traits. The somewhat colorful names used in the oil business -- like "Nigerian sweet" or "Hamaca Blend" -- generally refer to the oil's place of origin, the level of impurities, or the predominant size of its hydrocarbon constituents.

Photo of oil complex
Complexes like this one are necessary to process oil near the site of extraction.
Refining involves a number of physical and chemical processes. One key step is fractional distillation, which works much like an old-time whiskey still: a liquid mixture is heated, and vapors are drawn off into separate batches, or "fractions," as they rise, then condense into liquid in a vertical column. Hydrocarbons vary in their volatility; they evaporate and condense at different temperatures based primarily upon molecular size. The shortest of these -- methane, ethane, and propane -- are very volatile, and usually require compression to form liquids. Others, like hexane and octane, are intermediate and can be vaporized, then retrieved as liquid relatively high in the column. Thicker, but still fluid, constituents may become diesel fuel, lubricating oil, or fuel oil. Finally, the most tar-like substances, which do not boil even at greater than 600 degrees Celsius, may be processed to create fluids, leaving behind coke (a type of carbon) and residual solids much like asphalt.

Once the fractions are separated, many are chemically modified, cleaned, or treated. Heavy and complex molecules may be broken apart in a process known as "cracking." Some undergo chemical rearrangement or recombination to create fuels or chemical feedstocks. Many impurities are removed by "scrubbing" and other processes. Ultimately, these products are blended into often finely calibrated mixtures -- such as higher and lower "octane" gasoline -- with a range of uses.

Photo of facilities in forest
Oil processing in South America takes place among many rain forests located throughout the continent.
Though it is generally preferable for petroleum products to be as close as possible to pure hydrocarbons, there are exceptions, one being the need for "oxygenates" in gasoline. This class of oxygen-rich compounds helps to prevent "knocking" as well as inefficiencies and pollution from incomplete combustion. A widely-used oxygenate, MTBE (methyl tertiary-butyl ether), has been in the headlines in recent years due to its leakage and spreading from local gasoline storage tanks into groundwater, with potentially adverse health and environmental consequences. In response, some have advocated the use of less toxic oxygenates, such as ethanol.

Oil refining has also crept into the headlines recently due to the widespread opinion among oil-business analysts that constraints in refining capacity -- alongside geopolitical and supply factors -- are a key contributor to summer spikes in prices at corner gas stations around the U.S. This occurs because refining is a technically complex undertaking, requiring great investments and time to open new facilities. Rapidly changing supply of crude and seasonal demand from drivers can create a mismatch between the market demand for oil, and the existing refineries' ability to process it quickly.

It is telling that the dominance of the Standard Oil monopoly was, in the early stages, almost synonymous with its refining capacity. Refining, then, as now, is a relatively slow and stable, and often low margin business -- an essential, but not attention-grabbing, part of the oil-supply chain.

-- Edwin Adkins

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