Gasoline

In 1859 Edwin Drake and E. B. Bowditch of the Seneca Oil Company drilled the first commercial oil well in the United States in Titusville, Pennsylvania. The well produced about 400 gallons of crude oil, less than ten barrels a day. Soon, similar wells all over western Pennsylvania were providing crude oil for kerosene production that was needed to fuel the nation's streetlights and house lamps. The lighter boiling component, gasoline, was discarded, since it had no market. There are historical reports that "waste" gasoline, which had been dumped into rivers, sometimes caught fire. In 1892 the first gasoline-powered engines, for both car and tractor, were developed: This soon provided a market for the once useless substance, gasoline.

Today gasoline is the most important product of a typical oil refinery: The entire refinery process is designed to maximize its production. Gasoline is a complex mixture of molecules with a boiling range of 40–200°C (104–392°F). To produce various grades, there is a blending of many refinery components, each of which promotes specific fuel qualities such as desired octane rating, volatility, and minimization of engine deposits.

Octane Quality

The most important quality parameter for gasoline is the octane quality. Octane number is a measure of the antiknock properties of the fuel. Knocking in a gasoline engine is a metallic clattering noise (pinging), which indicates excessive intensity in preflame reactions. Severe knocking can damage the engine.

Preflame reactions occur in the engine cylinders when portions of the fuel self-initiate combustion prior to the advancing flame from the spark plug. This additional combustion causes an excessive rate of energy release, which is knock. The tendency of a fuel to engage in preflame reactions is dependent upon the structure of its component molecules (see Figure 1);

the tendency for preflame reactions is high for straight chain hydrocarbons, medium for branched hydrocarbons, and low for aromatics.

The octane number for a test gasoline represents the percentage by volume of isooctane (2,2,4-trimethylpentane) in a reference fuel consisting of the mixture of isooctane and heptane that would be necessary to match the test fuel's knocking tendency. Isooctane burns with a minimal knocking and is given an octane rating of 100. This is in contrast to heptane, which burns with much knocking and is given an octane rating of 0. Thus, a gasoline that burns with the same amount of knocking as a mixture of 92 percent isooctane and 8 percent heptane is classified as a 92 octane gasoline.

The octane ratings of gasoline can be increased by the addition of small amounts of antiknock agents. The first commercially successful antiknock agent, tetraethyllead (TEL), was developed in the 1920s. TEL was used to promote the development of higher efficiency, higher compression engines. However, TEL is highly toxic and poisons catalytic converters. Since 1974 all new U.S. automobile engines have used catalytic converters in order to reduce exhaust emissions.

Methyl t -butyl ether (MTBE) has been the antiknock agent of choice for unleaded gasoline. MTBE provides high-octane quality along with low volatility and is readily soluble in gasoline. However, leakage of gasoline from underground storage tanks has resulted in the detection of MTBE in the drinking water of several urban areas. This prompted the state of California to order the removal of MTBE from California gasoline by 2003.

Alcohols also have found use as octane enhancers. At higher concentration alcohols can be used as gasoline extenders, thus decreasing our dependency upon imported crude oil. A significant portion of all U.S. marketed gasoline is believed to contain ethanol.

Gasoline Additives

Trace amounts of olefins and diolefins found in gasoline are prone to reaction with oxygen dissolved in the gasoline. This process is referred to as autoxidation and involves a radical chain reaction that can incorporate oxygen

into the olefin and also can promote a molecular size increase via polymerization reactions. The end result of this complex process is the formation of deposits and gums that can block fuel filters and interfere with the metering of fuel and air in the carburetor. This can result in adverse engine performance. Additives are frequently added to gasoline to address oxidative stability and other issues; they include antioxidants, metal deactivators, and detergents.

Antioxidants are additives that minimize autoxidation reactions. They function as hydrogen atom donors that stop the chain oxidation process of the olefins. The two different types of antioxidants used in gasoline are phenylenediamines (PDA) and hindered phenols (such as BHT).

Trace levels of soluble metal compounds, particularly copper, catalyze the oxidative degradation of gasoline by promoting the formation of gums and deposits. Metal deactivators overcome this problem by chelating the metal and rendering it inactive. The most widely used metal deactivator is N, N′-disalicylidene-1,2-propanediamine, the copper complex of which is shown in Figure 3.

Detergents minimize fuel system deposits at low concentrations, and at high concentrations can remove deposits that have already formed. Detergents are molecules that have a highly polar end group and a nonpolar hydrocarbon tail. A conventional amino amide type detergent is shown in Figure 4.

Presumably, the polar groups in the detergent attach themselves to metal surfaces and to polar deposits on these surfaces. The nonpolar tails of these molecules "stick out" into the fuel in such a way that a monomolecular film is formed on the metal surface, preventing deposition and particle aggregation. This process is also believed to solubilize any deposits already on the metal surface. The detergent monolayer is also believed to prevent the buildup of ice on carburetor surfaces during winter. Thus, detergents can also function as anti-icing additives.

Gasoline Production

The production of gasoline begins with desalting the viscous crude oil. Salts and metals in the crude oil promote corrosion and poison processing catalysts. Thus, the crude oil is heated (to decrease viscosity) and extracted with water to remove the salts and metals. Frequently this process results in the formation of an oil/water mixture referred to as an emulsion (suspension). This emulsion is typically broken by the addition of a chemical surfactant (demulsifier) that promotes the separation of discrete oil and water layers. After separation of the aqueous layer, the oil is heated to about 400 ^oC (752^oF): This converts the oil into gaseous products and increases the fluidity of the remaining liquid. In this form, the gaseous mixture enters the fractionating column, where the process of atmospheric fractional distillation separates the crude oil into different components based upon boiling point.

The lightest boiling fractions are molecules that are gases under ambient conditions: methane, ethane, propane, butane, and olefins derived from these compounds. Uses for this distillate stream include burning as a fuel at the refinery; as petrochemical feed stocks; or processing into liquefied petroleum gas (LPG). There are three other major distillate streams collected during atmospheric distillation: the naptha fraction, which has a boiling range of 30 to 180°C (86–356°F); the kerosene fraction, which distills at between 180 and 240°C (356–464°F); and the gas oil fraction, which distills at between 240 and 355°C (464–671°F).

In order to meet current environmental regulations for the sulfur content in fuel products, the three-distillate streams are subjected to the process of hydrodesulfurization. In the presence of a catalyst , distillates are heated in the presence of hydrogen to reduce various organosulfur compounds to simple organic compounds and H₂S. The hydrogen needed for this process is a by-product of the catalytic reforming process. The H₂S product can be readily removed. In this process the refiner can control the octane number of the gasoline blending stock. By heating the naphtha fraction in the presence of an especially designed platinum catalyst, straight-chain hydrocarbons are cyclized, and saturated cyclic hydrocarbons are converted into aromatic compounds. In addition, this process converts straight-chain hydrocarbons into branched hydrocarbons. Catalytic reforming facilitates the production of gasoline blending stocks with octane ratings of from 90 to 100+.

Redistilling the atmospheric residue at a temperature of less than 400°C (752°F) under vacuum produces a vacuum gas oil. Typically, the vacuum gas oil is subjected to fluid catalytic cracking (FCC) to produce lower-boiling liquids that can be blended to make gasoline. This is achieved by breaking large molecules of the vacuum gas oil into smaller, lower-boiling molecules. An important gasoline blending component that can be produced in this manner is alkylate. It is a mixture of highly branched hydrocarbons produced by the acid-catalyzed reaction of isobutene and light olefinic hydrocarbons. Alkylate is a valuable blending component because of its high-octane quality and the absence of aromatics or olefins, which can lead to environmental and oxidative stability problems.

The 1990 Clean Air Act required the Environmental Protection Agency (EPA) to issue regulations that required gasoline to be "reformulated," resulting in significant reductions in vehicle emissions of ozone-forming and toxic air pollutants. This cleaner gasoline is called reformulated gasoline (RFG). RFG is required in the nine major metropolitan areas in the United States having the worst ozone problems. In addition, several other areas with ozone levels exceeding the public health standard have voluntarily chosen to use RFG.

Use of RFG decreases the amounts of volatile organic compounds (VOCs) and oxides of nitrogen (NO_x ) in the atmosphere that react in the presence of sunlight to produce ozone, a major component of smog. Vehicles also release toxic emissions, one of which (benzene) is a known carcinogen.

RFG contains 2 percent by weight oxygen additives (oxygenates), such as MTBE or ethanol. Oxygenates increase the combustion efficiency of gasoline, reducing vehicle emissions of carbon monoxide, a serious public health threat. The appearance of MTBE in some urban water supplies has resulted in legislation pending in the U.S. Congress to phase out the use of MTBE in RFG. Ethanol would then most likely become the primary oxygenate for future RFG.

Gasoline is the most important product of the oil refinery. The most important quality parameter for gasoline is its octane number. Additional quality characteristics for gasoline are controlled by the use of additives, for example, antioxidants, metal deactivators, and detergents. By blending various refinery streams and additives a gasoline formulation can be achieved that minimizes environmental degradation. Such a fuel is called reformulated gasoline.

see also Detergents; Energy Sources and Production; Fossil Fuels; Petroleum.

Bruce Beaver

Bibliography

Marshall, E. L., and Owen, K., eds. (1995). Critical Reports on Applied Chemistry, Vol. 34:Motor Gasoline. Cambridge, U.K.: Royal Society of Chemistry.

Gasoline

Background

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).

Raw Materials

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."

The Manufacturing
Process

Exploration

• 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 the rock, or use a gravity meter to detect slight differences in rock formations.
• 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.

Drilling

• 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.

Recovery

• 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.

Fractional distillation

• 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 fractional distillation.

  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.

Refining petroleum

• 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.

Additives

• 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.

Rating gasoline

• 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.

Byproducts/Waste

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.

The Future

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

Book

Shilstone, Beatrice. The First Book of Oil. Franklin Watts, Inc., 1969.

Periodicals

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

gasoline or petrol, light, volatile mixture of hydrocarbons for use in the internal-combustion engine and as an organic solvent, obtained primarily by fractional distillation and "cracking" of petroleum, but also obtained from natural gas, by destructive distillation of oil shales and coal, and by a process that converts methanol to gasoline using zeolite as a catalyst. Gasoline intended for use in engines is rated by octane number , an index of quality that reflects the ability of the fuel to resist detonation and burn evenly when subjected to high pressures and temperatures inside an engine. Premature detonation produces "knocking" and "pinging" ; it wastes fuel and may cause engine damage. The addition of tetramethyl lead and tetraethyl lead to raise the octane number is no longer permitted in the United States because it leads to dangerous emissions containing lead. New formulations of gasoline designed to raise the octane number contain increasing amounts of aromatics and oxygen-containing compounds (oxygenates), such as alcohols, methyl tertiary butyl ether (MTBE), and methylcyclopentadienyl manganese tricarbonyl (MMT). Automobiles are now equipped with catalytic converters that oxidize unreacted gasoline; the cars are designed to run on newly formulated gasolines as well as on gasohol , which contains 10% ethanol or 3% methanol. In addition, since 1998 a number of American automobiles have been equipped to enable them to run on either gasoline or E85, a mixture of 85% ethanol and 15% gasoline. Some racing cars use pure methanol as fuel.

There are five blends of gasoline marketed in the United States. Conventional gasoline, the most widely available, is sold where air quality is satisfactory; since 1992, it has been formulated to evaporate more slowly in hot weather so as to reduce smog, and it now contains detergent additives to reduce engine deposits. Winter oxygenated gasoline, introduced in 1992, is formulated as conventional gasoline with oxygen-rich chemicals added, such as MTBE or ethanol. The oxygen promotes cleaner burning, reducing carbon monoxide, and is generally sold from November to March because cold engines operate less efficiently and produce more carbon monoxide. Reformulated gasoline (RFG), introduced in Jan., 1995, is mandated in areas where toxins in the air are a constant problem; it contains oxygen-rich chemicals in lesser concentrations than the winter oxygenated gasoline and is formulated to reduce certain toxic chemicals found in conventional and winter oxygenated fuels. Oxygenated reformulated gasoline is a wintertime fuel exclusive to the New York City area, where heavy carbon monoxide pollution occurs. California reformulated gasoline, introduced in 1996, has a different formulation and burns cleaner than regular reformulated gasoline. Because MTBE has been implicated as a pollutant, particularly of groundwater, its use is being curtailed. In 1999, California ruled that the MTBE in California reformulated gas must be phased out by Dec. 31, 2002.

Bibliography: See Society of Automotive Engineers Incorporated, ed., Gasoline and Diesel Fuel: Performance and Additives (1997).

gas·o·line / ˌgasəˈlēn; ˈgasəlēn/ (dated also gas·o·lene) • n. refined petroleum used as fuel for internal combustion engines.

gasoline, gasolene XIX. f. GAS1 + -OL + -INE5, -ENE.

gasoline See petroleum

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