Americans consume more gasoline than any other petroleum product – some 360 million gallons a day. More than 40 percent of the crude oil refined in the United States becomes gasoline.
So how does it actually get made? What’s the secret recipe? Here’s something to ponder as you fill your tank at Circle K.
Refining
Crude oil is transformed into a variety of petroleum products inside a refinery. Often these are huge complexes in which the crude oil undergoes several different processes before emerging as final products ready to ship to consumers. Depending upon the markets they serve and the type of crude oil they are processing, some refineries may emphasize the production of gasoline, while other may focus on making heating oil or other petroleum products. However, there are limits to how much gasoline “yield” can be obtained from a barrel of crude. In general, yields vary between 35 and 50 percent.
Processing
The basic refining processes are separation, conversion and treatment. Separation is most commonly accomplished by heating the oil in tall distillation towers. Vapors form as the oil is heated, and at various levels in the tower, the vapors condense and are drawn off for further processing. Gasoline vapors tend to be the lightest and are drawn off at the top. Heating oil and diesel are toward the middle, while heavy fuel oil and asphalt-like materials condense at the bottom. Following distillation, the molecular structure of the separated fractions may undergo conversion in reformers, catalytic cracking units, alkylation units and other refinery equipment. Here heat, pressure and chemical catalysts break heavier oil elements into lighter ones (such as gasoline) or combine several light molecules into a few heavy ones for fuels such as high-octane aviation gas.
Finally, many petroleum products undergo treatment processes of some kind in order to remove chemical impurities. Sulfur is a common impurity found in most crude oil, which with advanced treatment methods, can be reduced to near-zero levels in gasoline and distillates. Removing sulfur significantly lessens the amount of polluting sulfur dioxide that is formed when heating oil, diesel fuel and gasoline are consumed. Since 1995, air emission regulations in several major metropolitan area have made it necessary for refiners to adjust gasoline components in order to produce “reformulated” gasoline (RFG). This fuel, which contains less benzene and more oxygenate and has a lower evaporation rate than normal gasoline, is intended to help reduce air pollution during the hot summer months.
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