Gasoline Processing and Production

Summary

About one-quarter of the crude oil extracted globally is processed to produce gasoline, the fuel for the internal combustion engine that powers most cars, light trucks, motorcycles, and piston-engine aircraft. Refineries perform several processing steps to meet the world's demand for quantity and quality of gasoline, beginning with desalting and distilling crude oil into separate fractions. Selected fractions undergo desulfurization, cracking, reforming, and other processes. The different components gained are blended with further additives to produce various grades of gasoline. Gasoline can also be made as synthetic fuel from coal, oil sands, natural gas, and biomass.

Definition and Basic Principles

Gasoline is the most effective fuel for the internal combustion engine, and it powers most automobiles, light trucks, and piston-engine aircraft. It is generally gained from processing crude oil at a refinery. The gasoline sold to consumers is a complex blend of hydrocarbons with boiling ranges from about 38 to 205 degrees Celsius (100 to 400 degrees Fahrenheit).

The first step in processing at a refinery is generally desalting crude oil. Then, the oil is heated, partially vaporized, and sent to a distillation tower operating at atmospheric pressure. There, it condenses into separate fractions that are extracted. The yield of light straight-run (LSR) gasoline from crude oil after atmospheric distillation generally consists of only up to 10 percent. This is much too low to satisfy the global gasoline demand. Therefore, different fractions from distillation are processed into suitable components of gasoline.

Heavy straight-run (HSR) naphtha gained from atmospheric distillation and vacuum distillation, followed by thermal, catalytic, or hydrocracking, is fed into a catalytic reformer to become a reform desalting component. To boost the octane rating of the final gasoline blend, which is a key indicator of its quality as engine fuel, gasoline components also undergo chemical processes such as isomerization, polymerization, and alkylation. Special additives gained in other refining processes are mixed in to form high-quality gasoline.

Gasoline can also be produced by processing feedstock such as coal, oil sands, oil shale, natural gas, and often biofuels. These processes are far more expensive than producing gasoline from crude oil. They are usually undertaken only in exceptional circumstances, such as periods of abundance of alternative feedstock and lack of crude oil, during wars, or due to a political commitment to alternative fuels.

Background and History

In 1856, the first refineries were built in Poland and Romania to process crude oil into more valuable products through distillation into different fractions. The first refinery opened in the United States in 1861. What would later be known as gasoline in the United States, a naphtha-based hydrogen compound called petrol in Great Britain, was one of the different refinery products. The rise of the internal combustion engine in the late nineteenth century, particularly as the motor of the newly invented automobile, led to a tremendous increase in the demand for gasoline as its fuel.

To satisfy this demand, methods of increasing gasoline yield from crude oil were developed. Thermal cracking of other distillation fractions was invented separately by Vladimir Shukhov in Russia in 1891 and William Merriam Burton in the United States in 1913. Thermal cracking doubled the yield of gasoline in the United States.

In 1930, the invention of thermal reforming boosted the octane rating of gasoline and lessened the stress on engines burning gasoline. In 1932, hydrogenation came into use to lower the undesirable sulfur content of gasoline, and coking created additional base stocks for gasoline out of heavier distillation fractions. In 1935, catalytic polymerization further boosted octane ratings.

The big breakthrough in producing more gasoline with higher octane ratings came with the invention of catalytic cracking in 1937 and fluid catalytic cracking (FCC) in 1942. French engineer Eugene Jules Houdry is generally credited for the first and a consortium of American university scientists and oil industry researchers for the second. Other necessary steps were the introduction of visbreaking in 1939, alkylation and isomerization in 1940, catalytic reforming in 1952, and hydrotreating in 1954. Research to improve refinery processes to optimize gasoline yield and quality and to make processes and products more environmentally friendly continues into the twenty-first century.

Producing gasoline synthetically from coal using direct coal liquefaction (DCL) was invented in 1913 by German chemist Friedrich Bergius. This method was inspired by Franz Fischer and Hans Tropsch's 1920s process of indirect coal liquefaction (ICL), the Fischer-Tropsch synthesis (FT). These methods gained popularity in 1950s South Africa, providing energy security. DCL and ICL were researched, improved, and used in World War II.

How It Works

Gasoline is processed and produced from crude oil at a refinery. Refineries are very complex installations that process a wide variety of crude oils. Each refinery follows its own customized process. However, the following are the most common processes.

Desalting. When crude oil arrives at a refinery, it is generally desalted to remove suspended salt and solid contaminants. Crude oil is heated and mixed with hot water between 100 and 150 degrees Celsius (212 and 302 degrees Fahrenheit). Salt and contaminants are washed out by adding chemicals or applying an electric field. Another method is to filter heated crude oil through diatomaceous earth. Another method is to filter heated crude oil through diatomaceous earth.

Distillation. Desalted crude oil is heated for fractional distillation between 343 and 399 degrees Celsius (650 to 750 degrees Fahrenheit). The resulting vapor and liquid mix is sent to the first distillation tower that operates at atmospheric pressure. Because of the different boiling points of the different hydrocarbon molecules of crude oil, the hydrocarbons can be separated into different fractions (also called cuts). This occurs at the distillation tower, which can be as tall as 50 meters (164 feet). The heaviest hydrocarbons remain at the bottom, while the middle and lighter ones are extracted.

From the lightest hydrocarbons collected from distillation, light straight-run (LSR) gasoline (sometimes called light naphtha) is extracted at a gas separation plant that commonly contains a hydrodesulfurization unit. Among the lighter gases, butane is used for blending into the final gasoline products or as feedstock for the alkylation unit.

Atmospheric distillation also yields lower-boiling heavy straight-run (HSR) gasoline (or HSR naphtha). Often, after hydrotreating, this fraction is processed further at the catalytic reformer.

Cracking. Distillation also yields residue. Among its fractions is what is commonly called gas oils, middle distillate, or wax distillate. After hydroprocessing, these gas oils are sent to a cracker at the refinery to convert them into more valuable products, including gasoline components. If a hydrocracker is used, no prior hydroprocessing occurs.

Cracking is the chemical conversion process used to break down longer-chain hydrocarbon molecules into shorter-chain ones that are more valuable. The naphtha gained from various cracking processes is used for further processing into gasoline components with high octane ratings.

The mildest form of thermal cracking is visbreaking. It breaks the longest hydrocarbon molecules to eventually yield also more gasoline. Delayed coking is severe thermal cracking, heating the gas oil feedstock to 500 degrees Celsius (930 degrees Fahrenheit). The product gained for gasoline processing is called coker naphtha.

Fluid catalytic cracking (FCC) is a key process to gain components for gasoline blending from the heavier feedstocks processed at an FCC unit. Fluid catalytic cracking converts nearly half of the heavy feedstocks into naphtha for gasoline production. It accounts for 35 to 45 percent of the volume of gasoline produced at US refineries in the early twenty-first century. The naphtha gained from cracking is typically divided. The light fraction is used directly for gasoline blending. The heavy fraction is sent to the catalytic reformer and functions as an octane booster.

Hydrocracking is the most sophisticated, flexible, and expensive form of cracking. Hydrocrackers are less common at American refineries than at European and Asian ones. This is because gasoline is the most in-demand product in the United States, and a hydrocracker's maximum yield of gasoline components is only 8 percent more than that of a much cheaper fluid catalytic cracker. Hydrocracking combines catalytic cracking with the insertion of hydrogen. Light and heavy naphtha is gained for gasoline blending and processing.

Catalytic Reforming. To improve the octane rating of the blended gasoline, HSR naphtha and naphtha gained from cracking are sent to a catalytic reformer. During catalytic reforming, the feedstock naphtha has its hydrocarbon molecules restructured by light cracking in the presence of a platinum-based catalyst. Catalytic reforming creates a desirable high-octane gasoline stock. Its aromatics, which are responsible for its high octane rating, have come under environmental scrutiny.

Isomerization, Polymerization, and Alkylation. There are some further processes to increase the octane rating of gasoline. LSR gasoline often has at least some of its components isomerized so that it consists of some molecules with a different structure but with the same number of atoms. Polymerization is a cost-effective way to boost octane ratings by combining the very light gases propane and butane into longer-chain olefin molecules. Alkylation is an effective but expensive process to increase the octane rating of light components of the gasoline blending pool. It refers to adding an alkyl group to isobutene at low temperatures of 5 to 38 degrees Celsius (41 to 100 degrees Fahrenheit) with a sulfuric or hydrofluoric acid catalyst.

Blending and Additives. In the end, all gasoline components are blended together. At a modern refinery, this is done in a computer-controlled process. Additives are used primarily to boost octane ratings. Lead was widely used once but was banned in 1996 in the United States, as well as in many other nations. With the increasing prohibition of methyl tert-butyl ether (MTBE) in many US states, the use of alternatives such as tertiary amyl methyl ether (TAME) or ethyl tert-butyl ether (ETBE) increased. Many governments mandate the blending of ethanol, which is done after gasoline leaves the refinery.

Gasoline from Synthetic Fuels. Gasoline can be produced from oil shale, coal, biomass, or natural gas. These processes are invariably more expensive than processing and producing gasoline from crude oil. They are employed in specific locations such as South Africa for coal and Canada and Venezuela for massive oil sand deposits.

Applications and Products

Fuel Gasoline. According to the US Energy Information Administration (EIA), gasoline demand is expected to decline through 2050 as countries worldwide produce fuel using renewable sources. Over 90 percent of gasoline produced in the United States is used to fuel automobiles and light trucks, with Texas and California historically consuming more than other states. Worldwide, gasoline as fuel is essential for transportation in any industrial and industrializing society. Its desired qualities are strong resistance to premature ignition in the engine, facilitating easy start, warm-up, and engine acceleration. Further desirable qualities include high mileage for the fuel consumed, prevention of vapor lock and deposit build-up in the engine, and as few polluting emissions as possible.

Gasoline Components. To optimize its quality as fuel for the internal combustion engine, gasoline is blended from different components. National governments often regulate the composition of gasoline out of concern for the environment and for protection from cancer-causing components. An example is the prohibition of lead as an additive for fuel gasoline in the United States, the European Union, and increasingly in many other nations.

In the United States, gasoline sold to consumers consists primarily of naphtha gained from catalytic cracking at 38 percent of the total, reformate from catalytic reforming at 27 percent, alkylate at 12 percent, and light straight-run gasoline and its isomeric form at 7 percent. Smaller contributors are the light component normal butane at 3 percent, light naphtha from hydrocracking at 2.4 percent, light coker naphtha at 0.7 percent, and polymers at 0.4 percent. Other additives, especially ethanol, account for the remainder.

Out of environmental concerns in the United States, the concept of reformulated gasoline (RFG) has been developed. This refers to a blend of gasoline that burns at least as cleanly as high-methanol-content alternative fuels. As a result of federal and state regulations, most of the gasoline produced by US refineries is blended with ethanol to become reformulated gasoline. The typical ethanol content in US gasoline is up to 10 percent.

Measuring Gasoline Quality. The most important indicator of gasoline quality for the consumer is its octane rating. The higher the octane rating, the less likely the gasoline blend will ignite prematurely in the engine, damaging it in an event commonly called knocking. There are many different ways to calculate the octane rating. The research octane number (RON) is derived from testing the gasoline blend in a laboratory engine. The gasoline's ability to burn by controlled ignition and not ignite prematurely is related to the respective quality of a mix of iso-octane and heptane. A RON rating of 95, for example, indicates that this gasoline burns, as well as a blend of 95 percent iso-octane and 5 percent heptanes. The motor octane number (MON) uses the same comparison but places the test engine under more stress to simulate actual driving situations. For this reason, the MON octane rating is between 8 to 10 points lower than the RON. Different nations use different octane ratings. In the United States, an average of RON and MON is used and posted at gas station pumps. It can be called PON (posted octane number) or (R+M)/2 and is also called the antiknocking index (AKI).

In the United States, gasoline is typically available as regular unleaded gasoline, with a PON of generally 85, and premium gasoline ranges from a PON of 89 to 93. California typically offers three grades—87, 89, and 91 PON. Premiums are branded under different names. Because lower atmospheric pressure at high altitudes reduces pressure in the engine's combustion chamber and lessens the danger of premature ignition, gasoline sold at high elevations in the Rocky Mountains states typically has a PON of 85 up to 91, signifying that gasoline has to be blended to account for the environment where it is burned as fuel. Particular gasoline for automobile racing in the United States can have a PON of 100 or higher.

Two other indicators of gasoline quality are as important but less visible to consumers than the octane rating. They are the Reid vapor pressure (RVP) and boiling range of the blended gasoline. Low RVP, or low volatility, and higher boiling ranges mean the gas is less likely to evaporate too quickly, causing a vapor lock in the engine. They also prevent higher evaporation losses than lower mileage gained from gasoline. A high RVP, or high volatility, and lower boiling ranges make the engine start easier and warm up more quickly. Outside temperature influences gasoline behavior. As a result, gasoline is blended differently for use during the summertime, with an RVP of about 7.2 pounds per square inch (psi), or 49.6 kilo Pascal (kPA), and during the wintertime with an RVP of about 13.5 psi (93.1 kPa).

E85. Ethanol, flex fuel, or grain alcohol, is blended into gasoline before sale to consumers because it is a clean-burning fuel from renewable resources. However, it gets only 70 percent of the mileage of undiluted gasoline. Several states have mandated a blend of at least 5.9 percent ethanol in gasoline, and many gas pumps state that the gasoline sold may contain up to 10 percent ethanol. An alternate fuel, marketed as E85, contains 85 percent anhydrous ethanol to only 15 percent gasoline. Its lack of fuel efficiency is made up by a federal tax subsidy trying to encourage consumption. To encourage the use of E85, the US Environmental Protection Agency (EPA) suggested using it in flex-fuel vehicles. The production of E85 flex vehicles steeply increased in the first quarter of the twenty-first century.

Avgas. For use as fuel for aircraft with piston engines, refineries produce relatively small quantities of aviation gasoline, called avgas. This is very different from jet fuel. In 2014, US refineries produced about 188 million gallons of avgas, down from 261 million gallons in 2004. This decline occurred because avgas, most commonly of the 10011 variety, contains a small amount of lead in the form of tetraethyl lead (TEL). As public pressure increases to completely phase out leaded gasoline, scientists have looked for an alternative to lead in aviation gasoline. Avgas must have a high octane rating and cannot lead to engine vapor lock at the low pressure encountered during flight. By 2010, there had been some promising experiments with nonleaded aviation gasoline called G100UL. In 2014, General Aviation Modifications, Inc. (GAMI)’s unleaded Avgas G100UL passed the required tests. GAMI also tried to get the Supplemental Type Certificate (STC) for its unleaded avgas in 2017, but it was only approved by the FAA in 2021. In 2022, the FAA approved widespread STCs for G100UL use in all piston-engine aircraft. With this approval, GAMI began preselling and producing the fuel. In April 2024, GAMI announced the successful production of 1 million gallons (3,785,412 liters) of G100UL to roll out beginning at airports in California, Oregon, and Washington.

Careers and Course Work

Students interested in a career in the gasoline processing and production industry should take courses in science, mathematics, and economics in high school. Refineries employ many skilled technicians for their operations and need laboratory analysts, occupations for which a two-year associate degree is helpful. A refinery also has positions for firefighters and employs members of the medical profession, from paramedics to physicians.

A bachelor's degree in chemistry, physics, computer science, mathematics, or environmental science is very useful for a career in the actual processing and production field. The same is true for an engineering degree, whether at the undergraduate or postgraduate level, especially in chemical, electrical, mechanical, or computer engineering. Such degrees create good employment prospects. For a career in the purchasing department of a refineryselecting different crude oils for processing, for instance business major or master of business administration is helpful and can also lead to a higher management position.

Any master of engineering or doctoral degree in chemistry or chemical engineering serves as good preparation for a top-level career. A doctorate in a science field can lead to an advanced research position either with a company or a government agency. A research career linked to gasoline production, whether at a university, institute, or corporation, also benefits from postdoctoral work in chemistry or materials science. Universities, including the University at Buffalo in New York and Duke University in North Carolina, offer courses related to gasoline production.

Particularly for a career in private industry, the cyclical nature of the oil industry does not guarantee employment during industry downturns. As many new refineries are built outside the United States and many operate in different places of the world, global mobility is of significant advantage when pursuing an advanced career. Aspirants can work as production engineers, geophysicists, drilling engineers, and reservoir engineers.

Social Context and Future Prospects

As the most efficient fuel for the internal combustion engine, gasoline has vastly increased the private and public mobility of the world's people, especially in industrialized societies. The nineteenth century increased humanity's mobility through the steam engines of railroad trains, and the twentieth century saw the rise of gasoline to enable private automobile transportation. As such, gasoline significantly affects the lives of almost every person in a developed country.

However, the emissions caused by the production of gasoline and its use as fuel have had a negative impact on the environment, which has been fiercely debated and publicly discussed. Carbon dioxide emissions and the side effects of many gasoline additives are of particular concern. The wide availability of gasoline also promotes the manufacture of automobiles and other vehicles, which generates more greenhouse gases and sometimes hazardous wastes, especially during the vehicle disposal process. Oil, gasoline, and automobiles have been attacked by some activists as the main causes of human-made environmental degradation, although they have granted freedom of mobility to a vast number of people on a scale unthinkable in the nineteenth century.

Because of environmental concerns, research seeks to minimize the aromatics content of gasoline, as additives such as benzene are particularly harmful if handled carelessly. Research is ongoing to make gasoline burn cleaner and increase the cost efficiency of its production. To improve the economics of gasoline production, large world-class capacity refineries have been built to use economies of scale and take advantage of proximity to raw materials or markets.

Twenty-first-century research focuses on alternative fuels to gasoline that may offer similar fuel efficiency at a lesser environmental cost. The rise of the petrochemical industry as a competitor for gasoline's raw material, crude oil, led to more refineries increasing their output of ethane, a very light gaseous hydrocarbon, at the expense of gasoline production, as ethane is a prime and valuable petrochemical feedstock.

The Federal Aviation Administration (FAA) and EPA, in partnership with researchers in Atlantic City, New Jersey, developed unleaded aviation fuel in 2020. In 2022, the FAA officially approved the limited use of 100-octane aviation gasoline (G100UL AvGas) for use in piston-engine planes. In April 2024, one million gallons of the fuel had been produced.

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