Gasoline is a volatile, flammable liquid obtained from the refinement of petroleum, or crude oil. It was originally discarded as a byproduct of kerosene production, but its ability to vaporize at low temperatures made it a useful fuel for many machines. The first oil well in the United States was struck by Edwin L. Drake near Titusville, Pennsylvania, in 1859 at a depth of almost 70 feet (21 m). With the development of the four-stroke internal combustion engine by Nikolaus Otto in 1876, gasoline became essential to the automotive industry. Today, almost all gasoline is used to fuel automobiles, with a very small percentage used to power agricultural equipment and aircraft.
Petroleum, a fossil fuel, supplies more energy to the world today than any other source. The United States is the world's leading consumer of petroleum; in 1994, Americans used 7,587,000 barrels of oil per day. Petroleum is formed from the remains of plants and animals that have been held under tremendous pressure for millions of years. Ordinarily, this organic matter would decompose completely with the help of scavengers and aerobic bacteria, but petroleum is created in an anaerobic environment, without the presence of oxygen. Over half of the world's known crude oil is concentrated in the Persian Gulf basin. Other major areas include the coasts of Alaska and the Gulf of Mexico.
Petroleum products, including gasoline, are primarily a mixture of hydrocarbons (molecules containing hydrogen and carbon molecules) with small amounts of other substances. Crude oil is comprised of different lengths of hydrocarbon chains, with some short chains and some very long chains. Depending on how much the oil is broken down, or refined, it may become any number of products. In general, the smaller the molecule, the lower the boiling point. Therefore, gas, with very small chains of one to five carbons, boils at a very low temperature. Gasoline, with 6-10 carbons, boils at a slightly higher temperature. The heaviest oils may contain up to 25 carbon atoms and not reach their boiling point until 761°F (405°C).
Gasoline is one of the products derived from distilling and refining petroleum. Compounds of organic lead were added to gasoline in the past to reduce knocking in engines, but due to environmental concerns this is no longer common. Other chemicals are also added to gasoline to further stabilize it and improve its color and smell in a process called "sweetening."
1 The first step in the manufacture of gasoline is to find its parent
ingredient, petroleum. Crude oil is trapped in areas of porous rock, or
reservoir rock, after it has migrated there from the area of its origin.
Possible areas of oil concentration may be pinpointed by looking for
rock types that are commonly found in those areas. Explorers may examine
the surface features of the land, analyze how sound waves bounce off
- 2 After a possible oil reservoir is found, the area must be test drilled. Core samples are taken from test wells to confirm rock formations, and the samples are chemically analyzed in order to determine if more drilling is justified. Although the methods used today are more advanced than any of the past, there is still no certainty in oil exploration.
- 3 Crude oil is recovered through wells that can reach over 1,000 feet (305 m) into the rock. The holes are made by rotary drillers, which use a bit to bore a hole in the ground as water is added. The water and soil create a thick mud that helps hold back the oil and prevent it from "gushing" due to the internal pressure contained in the reservoir rock. When the reservoir is reached, the mud continues to hold back the oil while the drill is removed and a pipe is inserted.
- 4 To recover the oil, a complicated system of pipes and valving is installed directly into the drilling well. The natural pressure of the reservoir rock brings the oil out of the well and into the pipes. These are connected to a recovery system, which consists of a series of larger pipes taking the crude oil to the refinery via an oil (liquid) and gas (non-liquid) separator. This method allows the oil to be recovered with a minimum of waste.
- 5 Eventually, the natural pressure of the well is expended, though great quantities of oil may still remain in the rock. Secondary recovery methods are now required to obtain a greater percentage of the oil. The pressure is restored by either injecting gas into the pocket above the oil or by flooding water into the well, which is far more common. In this process, four holes are drilled around the perimeter of the well and water is added. The petroleum will float on the water and come to the surface.
6 Crude oil is not a good fuel, since it is not fluid and requires a
very high temperature to burn. The long chains of molecules in crude oil
must be separated from the smaller chains of refined fuels, including
gasoline, in a petroleum refinery. This process is called
A fractional distillation tower is a huge unit that may hold up to 200,000 barrels of crude oil. The oil is first pumped into a furnace and heated to over 600°F (316°C), causing all but the largest molecules to evaporate. The vapors rise into the fractionating column, which may be as tall as 150 feet (46 m). The vapors cool as they rise through the column. Since the boiling points of all the compounds differ, the larger, heavier molecules will condense first lower in the tower and the shorter, lighter molecules will condense higher in the tower. Natural gases, gasoline, and kerosene are released near the top. Heavier compounds used in the manufacture of plastics and lubricants are removed lower in the tower.
Fractional distillation itself does not produce gasoline from crude oil, it just removes the gasoline from other compounds in crude oil. Further refining processes are now used to improve the quality of the fuel.
7 Catalytic cracking is one of the most important processes in oil
refining. This process uses a catalyst, high temperature, and increased
pressure to affect chemical changes in petroleum. Catalysts such as
aluminum, platinum, processed clay, and acids are added to petroleum to
break down larger molecules so that it will possess the desired
compounds of gasoline.
Another refining process is polymerization. This is the opposite of cracking in that it combines the smaller molecules of lighter gases into larger ones that can be used as liquid fuels.
- 8 Once gasoline is refined, chemicals are added. Some are anti-knock compounds, which react with the chemicals in gasoline that burn too quickly, to prevent "engine knock." In leaded gasoline, tetraethyl lead is the anti-knock additive. (Unleaded gasoline is refined further so the need for anti-knock additives is minimal.) Other additives (antioxidants) are added to prevent the formation of gum in the engine. Gum is a resin formed in gasoline that can coat the internal parts of the engine and increase wear.
- 9 Gasoline is primarily a mixture of two volatile liquids, heptane and isooctane. Pure heptane, a lighter fuel, burns so quickly that it produces a great amount of knocking in an engine. Pure isooctane evaporates slowly and produces virtually no knocking. The ratio of heptane to isooctane is measured by the octane rating. The greater the percentage of isooctane, the less knocking and the higher the octane rating. For example, an octane rating of 87 is comparable to a mixture of 87% isooctane and 13% heptane.
On average, 44.4% of petroleum becomes gasoline. There really are no waste products from petroleum. The lighter chemicals are natural gas, liquified petroleum gas (LPG), jet fuel, and kerosene. The heavier products are used for the manufacture of lubricants, plastics, and asphalt. In addition, many less valuable products can be chemically converted into more saleable compounds.
Gasoline, though widely used in many applications today, is destined to become a fuel of the past because petroleum is a nonrenewable resource. Current technology centers on making the most of the remaining petroleum reservoirs and exploring alternative energy sources. New methods to accurately determine the extent of oil reservoirs, automated systems to control oil recovery, and ways of enabling workers to recover more oil from known reservoirs are all being investigated to fully utilize the oil stores available today.
The newest methods in oil field exploration measure the physical size of the reservoir and its volume of oil. Frequently, the pressure inside the well is measured over a period of time as the oil is recovered. Using this data, scientists can determine the size of the reservoir and its permeability. An echo meter, which bounces sound waves off the sides of the reservoir, can also be used to discover the well's characteristics.
Modern oil recovery methods are most often controlled, at least in part, by computerized systems. SCADA (Systems for Supervisory Control of Data Acquisitions) use specialized software to monitor operations through one or more master terminals and several remote terminals. These systems increase efficiency, help prevent mishaps that could harm the environment, and reduce the number of laborers with increased safety.
Enhanced oil recovery methods increase the percentage of oil that can be obtained from a reservoir. In the past, workers were able to extract less than half of the oil contained in a reservoir. New methods involve injecting gases or foams into the well to force out the oil, drilling horizontally into the well, and using more geophysical information to accurately predict the characteristics of the reservoir.
Because gasoline is produced from a limited supply of petroleum, scientists are looking for clean, renewable sources of energy to power machines of the future. Steam power, used in the steamboats of the past, is an energy source that is receiving renewed attention. Electric vehicles have been developed, and solar and wind energies are also powering cars and homes.
Where To Learn More
Shilstone, Beatrice. The First Book of Oil. Franklin Watts, Inc., 1969.
Gibbs, L.M. "The Changing Nature of Gasoline." Automotive Engineering, January 1994, pp. 99-102.
Langreth, Robert. "Less Smog, More Buildup?" Popular Science, April 1995, p. 36.
"Getting the Lead Out." Motor Trend, April 1992, pp. 106-107.
— Barry Marton /
Kristine M. Krapp