Refining Petroleum
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Refining Petroleum Last month's Historical Note described crude oil and the techniques used over the centuries to extract it from the ground. An average sample of crude oil is a greasyfeeling, greenish-brown liquid with a strong odor. The crude can be thick and tarry, such as in oil sands, or light and bubbly if it contains a high percentage of dissolved natural gas. Crude oil serves as the raw material for some 3000 different products—but first the petroleum must be refined. Near a producing oil field, crude petroleum is stored in large tanks until it can be shipped by tankers or over pipelines to the nearest refinery. Preliminary small-scale tests on samples of the crude initially determine the rough percentages of gasoline, kerosene, fuel oil, lubricating oil, and wax that can be recovered from it. Petroleum refining techniques have been developed to separate out the useful components of crude oil. Any particular sample contains a large number of separate hydrocarbon compounds, many of them in very small percentages. Chemists at the National Bureau of Standards (now the National Institutes of Standards and Technology) began work in 1927 to determine all the constituents of a typical gasoline obtained from one part of the central United States; they eventually identified over 60 different hydrocarbons in a single sample, ranging from methane (CH4, which boils at -161 °C) to mesitylene (an aromatic hydrocarbon with a boiling point of 176 °C). In the mid-19th century, James Young in England found a way to obtain oil from coal as a substitute for expensive whale oil; shortly afterward, chemist Abraham Gesner developed an improved coal oil specifically for use in lamps. By 1859—the same year Colonel E.A. Drake in Pennsylvania struck the first commercial oil well— some 60 small coal-oil refineries had been established in the United States. Two years later, the first refinery designed specifically to refine petroleum began operation. Early refineries used a process called batch distillation, in which the crude oil was placed in a heated cylinder called a cheesebox still, or a horizontal cylindrical still. When the vapor temperature of the heated crude reached about 38 °C, the light hydrocarbons vaporized and then condensed in a pipe coil immersed in a water tank. These first products had little value in the late 19th century and were often discarded, though some were sold as "petroleum ether" to be used as a solvent.
Next to be distilled from the heated crude was the gasoline fraction, also considered economically unimportant at the time. In fact, the first runnings of gasoline were dumped into Pennsylvania rivers, where they occasionally caught fire and caused enormous pollution problems. When the crude temperature rose to 177 °C, an operator tested the specific gravity of the condensate. If it had reached a chosen value, the output stream was shunted to a new tank. Up to about 260°C, the condensate was considered the kerosene fraction—at the time the most economically important portion because of its broad use in li
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