Where Found (Encyclopedia of Global Resources)
Oxygen is the most abundant element in the Earth’s crust (46.6 percent by weight), occurring mainly as oxides and silicates of metals. The earth’s waters are 85.8 percent oxygen by weight, and the atmosphere is 23.0 percent oxygen. The combined weight of oxygen in the crust, hydrosphere, and atmosphere is about 50 percent.
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Primary Uses (Encyclopedia of Global Resources)
In addition to its importance in the combustion of food for energy by living organisms, oxygen has many commercial applications. It is used in the iron and steel industry, in rocket propulsion, in chemical synthesis, and to hasten the aerobic digestion of sewage solids.
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Technical Definition (Encyclopedia of Global Resources)
Oxygen (abbreviated O), atomic number 8, belongs to Group VI of the periodic table of the elements. Its chemical properties are somewhat similar to those of sulfur. It has an average molecular weight of 15.9994 and six naturally occurring isotopes, three of which are radioactive with half-lives on the order of seconds and minutes. At ordinary temperatures, oxygen is a colorless, odorless gas. Its liquid form is pale blue. Oxygen melts at -218° Celsius and boils at -183° Celsius. Oxygen can form compounds with all other elements except the low-atomic-weight elements of the helium family.
(The entire section is 93 words.)
Description, Distribution, and Forms (Encyclopedia of Global Resources)
The total content of oxygen in the Earth’s air, crust, and oceans is approximately 50 percent by weight. In chemically combined form, it is found in water and in the clays and minerals of the lithosphere. Despite the fact that it is an active element, forming oxides easily by the process of combustion, elemental oxygen makes up about 23 percent of the atmosphere. Dissolved gaseous oxygen is found in the waters of the Earth, where it provides for the respiration of most marine animals and for the gradual oxidation of waste materials in lakes and rivers.
Elemental oxygen is found in three allotropic forms: the ordinary diatomic molecule found in the atmosphere (O2), ozone (O3), and the unstable, nonmagnetic, and rare pale blue O4 form, which decomposes easily to O2. Unstable atomic oxygen is a short-lived species that results from the absorption of ultraviolet radiation by ozone in the upper atmosphere or from electrical discharges.
The solvent properties of water are attributable to the great difference in the strength of attraction for the bonding electrons between hydrogen and oxygen, which makes the resulting molecule very polar. The H2O molecules are attracted to both cations and anions, surrounding them by the attraction of the negative oxygen or the positive hydrogen, respectively. Water also dissociates slightly into H+ and OH- ions. These processes allow water to form hydrates with, and to...
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History (Encyclopedia of Global Resources)
Most chemists agree that the discovery of oxygen was made independently by Carl Scheele in Sweden and Joseph Priestley in England at about the same time. In 1774, Priestley heated mercuric oxide and collected the liberated gas over water. He showed that the “dephlogisticated air” (oxygen) was capable of supporting burning and was respirable. Scheele prepared oxygen in 1771-1772 by heating various carbonates and oxides. Although his experiments were performed earlier than those of Priestley, the latter published his results first. The great French chemist Antoine-LaurentLavoisier was the first to recognize that oxygen is an element, and he was able to explain the combustion process correctly. This explanation revolutionized the field of chemistry and provided the stimulus for the discovery of many new elements.
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Obtaining Oxygen (Encyclopedia of Global Resources)
For many years the only means of obtaining oxygen was by the fractional distillation of liquid air. A variation of this basic process is still used when high-purity oxygen is needed. In 1971, an ambient temperature process was introduced by the Linde Division of Union Carbide Corporation. The process uses a pressure cycle in which “molecular sieves” are used to selectively absorb nitrogen from the air. The resulting product contains about 95 percent oxygen and about 5 percent argon and is economically preferable in situations where the argon will not interfere.
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Uses of Oxygen (Encyclopedia of Global Resources)
The greatest consumers of oxygen are the steel, chemical, and missile industries. The oldest use of oxygen is in the welding of steel by means of a hot acetylene-oxygen torch. Thicknesses of steel of up to 0.6 meter can be cut by a high-pressure oxygen stream after heating with an acetylene torch. An oxygen stream passed through molten iron can remove carbon impurities by means of combustion to carbon dioxide.
In the chemical industry, oxygen is used for the production of hydrogen from natural gas or “synthesis gas”:CH4 + 0.5 O2 → CO + H2
Other important industrial processes are the manufacture of hydrogen peroxide, sodium peroxide, ethylene oxide, and acetylene.
Large rockets are propelled from their launch pads by the combustion of a fuel similar to kerosene. The fuel and oxygen are kept in liquid form in separate tanks until ignition. (In some rockets the second stage is propelled by the combustion of hydrogen.)
Oxygen has limited but important uses in the health-care industry in the treatment of pneumonia, emphysema, and some heart problems. Hyperbaric chambers provide high-pressure, oxygen-rich atmospheres for the treatment of both carbon monoxide poisoning and decompression sickness (“the bends”).
(The entire section is 190 words.)
Further Reading (Encyclopedia of Global Resources)
Ardon, Michael. Oxygen: Elementary Forms and Hydrogen Peroxide. New York: W. A. Benjamin, 1965.
Gilbert, Daniel L., ed. Oxygen and Living Processes: An Interdisciplinary Approach. New York: Springer, 1981.
Greenwood, N. N., and A. Earnshaw. “Oxygen.” In Chemistry of the Elements. 2d ed. Boston: Butterworth-Heinemann, 1997.
Hayaishi, O., ed. Molecular Oxygen in Biology: Topics in Molecular Oxygen Research. New York: American Elsevier, 1974.
Jackson, Joe. A World on Fire: A Heretic, an Aristocrat, and the Race to Discover Oxygen. New York: Viking, 2005.
Lane, Nick. Oxygen: The Molecule That Made the World. New York: Oxford University Press, 2002.
Lewis, Bernard, and Guenther von Elbe. Combustion, Flames, and Explosions of Gases. 3d ed. Orlando, Fla.: Academic Press, 1987.
Massey, A. G. “Group 16: The Chalcogens—Oxygen, Sulfur, Selenium, Tellurium, and Polonium.” In Main Group Chemistry. 2d ed. New York: Wiley, 2000.
Scott, Gerald. Atmospheric Oxidation and Antioxidants. New York: Elsevier, 1965.
Weeks, Mary Elvira. Discovery of the Elements. 7th ed. New material added by Henry M. Leicester. Easton, Pa.: Journal of Chemical Education, 1968.
Universal Industrial Gases, Inc.. Oxygen (O2) Properties, Uses and Applications: Oxygen Gas and Liquid Oxygen....
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Oxygen (Chemical Elements)
Oxygen is the first element in Group 16 (VIA) of the periodic table. The periodic table is a chart that shows how chemical elements are related to each other. The elements in Group 16 are said to belong to the chalcogen family. Other elements in this group include sulfur, selenium, tellurium, and polonium. The name chalcogen comes from the Greek word chalkos, meaning "ore." The first two members of the family, oxygen and sulfur, are found in most ores.
Oxygen is by far the most abundant element in the Earth's crust. Nearly half of all the atoms in the earth are oxygen atoms. Oxygen also makes up about one-fifth of the Earth's atmosphere. Nearly 90 percent of the weight of the oceans is due to oxygen. In addition, oxygen is thought to be the third most abundant element in the universe and in the solar system.
The discovery of oxygen is usually credited to Swedish chemist Carl Wilhelm Scheele (1742-86) and English chemist Joseph Priestley (1733-1804). The two discovered oxygen at nearly the same time in 1774, working independently of each other.
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Oxygen (World of Earth Science)
Oxygen is the simplest group VIA element and is, under normal atmospheric conditions, usually found as a colorless, odorless, and tasteless gas. Oxygen has an atomic number of 8 and an atomic mass of 16.0 amu. The liquid and solid forms, which are strongly paramagnetic, are a pale blue color. Oxygen has a boiling point of 97°F (82.8°C) and a melting point of 68.7°F (22.6°C).
Oxygen is the third most abundant element found in the Sun, after hydrogen and helium, and plays an important role in the carbon-nitrogen cycle. Oxygen composes 21% of Earth's atmosphere by volume and is vital to the existence of carbon-based life forms.
Although English chemist Joseph Priestley (1733804) is generally credited with the discovery of oxygen in 1774, many science historians contend that Swedish chemist Carl Scheele (1742786) probably discovered oxygen a few years prior to Priestly. French chemist Antoine Lavoisier's (1743794) contributions to the study of the important reactions, combustion and oxidation, were spurred by the discovery of oxygen. Lavoisier noticed that something was absorbed when combustion took place and that it was obtained from the surrounding air. Lavoisier noted that the increase in the weight of the substance burned was equal to the decrease in the weight of the air used. His studies lead to Lavoisier's oxidation theory, which eventually superseded the phlogistonists' theory (i.e., that every combustible substance was thought to contain a phlogiston, or inherent principal of fire, liberated through burning, along with a residue) that was widely accepted at that time. Lavoisier eventually named the gas he studied oxygen from the Greek oxys meaning acid or sharp, and geinomial meaning forming. Lavoisier named the gas oxygen because he noted that the burned materials were converted into acids.
Although oxygen has nine isotopes, natural oxygen is a mixture of only three of these. The most abundant isotope, oxygen-18, is stable and available commercially. The most common use for commercial oxygen gas is in enrichment of steel blast furnaces and for medical purposes. Large quantities are also used in making synthetic ammonia gas, methanol and ethylene oxide. Oxygen is also consumed in oxy-acetylene welding. Most commercial oxygen is produced in air separation plants. It is estimated that the United States consumes 20 million tons of oxygen in commercial use per year and the demand is expected to increase dramatically.
When oxygen is exposed to ultraviolet light, as from the Sun, or an electrical discharge, as from lightening, ozone (O3) is formed. Although ozone is toxic to breathe, the 0.12 in (3 mm) thick layer of ozone in the earth's atmosphere provides a shield from harmful ultraviolet rays from the Sun. The ozone layer has recently been the subject of intense scientific interest to determine whether, and to what extent, it may be deteriorating, mainly from pollutants in the atmosphere. Unlike pure oxygen gas, ozone has a bluish color and its liquid and solid forms are bluish black to violet-black.
See also Atmospheric chemistry; Atmospheric composition and structure; Global warming; Greenhouse gases and greenhouse effect; Ozone layer and hole dynamics; Ozone layer depletion
Oxygen (How Products are Made)
Oxygen is one of the basic chemical elements. In its most common form, oxygen is a colorless gas found in air. It is one of the life-sustaining elements on Earth and is needed by all animals. Oxygen is also used in many industrial, commercial, medical, and scientific applications. It is used in blast furnaces to make steel, and is an important component in the production of many synthetic chemicals, including ammonia, alcohols, and various plastics. Oxygen and acetylene are combusted together to provide the very high temperatures needed for welding and metal cutting. When oxygen is cooled below -297° F (-183° C), it becomes a pale blue liquid that is used as a rocket fuel.
Oxygen is one of the most abundant chemical elements on Earth. About one-half of the earth's crust is made up of chemical compounds containing oxygen, and a fifth of our atmosphere is oxygen gas. The human body is about two-thirds oxygen. Although oxygen has been present since the beginning of scientific investigation, it wasn't discovered and recognized as a separate element until 1774 when Joseph Priestley of England isolated it by heating mercuric oxide in an inverted test tube with the focused rays of the sun. Priestley described his discovery to the French scientist Antoine Lavoisier, who experimented further and determined that it was one of the two main components of air. Lavoisier named the new gas oxygen using the Greek words oxys, meaning sour or acid, and genes, meaning producing or forming, because he believed it was an essential part of all acids.
In 1895, Karl Paul Gottfried von Linde of Germany and William Hampson of England independently developed a process for lowering the temperature of air until it liquefied. By carefully distillation of the liquid air, the various component gases could be boiled off one at a time and captured. This process quickly became the principal source of high quality oxygen, nitrogen, and argon.
In 1901, compressed oxygen gas was burned with acetylene gas in the first demonstration of oxy-acetylene welding. This technique became a common industrial method of welding and cutting metals.
The first use of liquid rocket propellants came in 1923 when Robert Goddard of the United States developed a rocket engine using gasoline as the fuel and liquid oxygen as the oxidizer. In 1926, he successfully flew a small liquid-fueled rocket a distance of 184 ft (56 m) at a speed of about 60 mph (97 kph).
After World War II, new technologies brought significant improvements to the air separation process used to produce oxygen. Production volumes and purity levels increased while costs decreased. In 1991, over 470 billion cubic feet (13.4 billion cubic meters) of oxygen were produced in the United States, making it the second-largest-volume industrial gas in use.
Worldwide the five largest oxygen-producing areas are Western Europe, Russia (formerly the USSR), the United States, Eastern Europe, and Japan.
Oxygen can be produced from a number of materials, using several different methods. The most common natural method is photo-synthesis, in which plants use sunlight convert carbon dioxide in the air into oxygen. This offsets the respiration process, in which animals convert oxygen in the air back into carbon dioxide.
The most common commercial method for producing oxygen is the separation of air using either a cryogenic distillation process or a vacuum swing adsorption process. Nitrogen and argon are also produced by separating them from air.
Oxygen can also be produced as the result of a chemical reaction in which oxygen is freed from a chemical compound and becomes a gas. This method is used to generate limited quantities of oxygen for life support on submarines, aircraft, and spacecraft.
Hydrogen and oxygen can be generated by passing an electric current through water and collecting the two gases as they bubble off. Hydrogen forms at the negative terminal and oxygen at the positive terminal. This method is called electrolysis and produces very pure hydrogen and oxygen. It uses a large amount of electrical energy, however, and is not economical for large-volume production.
The Manufacturing Process
Most commercial oxygen is produced using a variation of the cryogenic distillation process originally developed in 1895. This process produces oxygen that is 99+% pure. More recently, the more energy-efficient vacuum swing adsorption process has been used for a limited number of applications that do not require oxygen with more than 90-93% purity.
Here are the steps used to produce commercial-grade oxygen from air using the cryogenic distillation process.
Because this process utilizes an extremely cold cryogenic section to separate the air, all impurities that might solidifyuch as water vapor, carbon dioxide, and certain heavy hydrocarbonsust first be removed to prevent them from freezing and plugging the cryogenic piping.
- 1 The air is compressed to about 94 psi (650 kPa or 6.5 atm) in a multi-stage compressor. It then passes through a water-cooled aftercooler to condense any water
- 2 The air passes through a molecular sieve adsorber. The adsorber contains zeolite and silica gel-type adsorbents, which trap the carbon dioxide, heavier hydrocarbons, and any remaining traces of water vapor. Periodically the adsorber is flushed clean to remove the trapped impurities. This usually requires two adsorbers operating in parallel, so that one can continue to process the air-flow while the other one is flushed.
Air is separated into its major componentsitrogen, oxygen, and argonhrough a distillation process known as fractional distillation. Sometimes this name is shortened to fractionation, and the vertical structures used to perform this separation are called fractionating columns. In the fractional distillation process, the components are gradually separated in several stages. At each stage the level of concentration, or fraction, of each component is increased until the separation is complete.
Because all distillation processes work on the principle of boiling a liquid to separate one or more of the components, a cryogenic section is required to provide the very low temperatures needed to liquefy the gas components.
- 3 The pretreated air stream is split. A small portion of the air is diverted through a compressor, where its pressure is boosted. It is then cooled and allowed to expand to nearly atmospheric pressure. This expansion rapidly cools the air, which is injected into the cryogenic section to provide the required cold temperatures for operation.
- 4 The main stream of air passes through one side of a pair of plate fin heat exchangers operating in series, while very cold oxygen and nitrogen from the cryogenic section pass through the other side. The incoming air stream is cooled, while the oxygen and nitrogen are warmed. In some operations, the air may be cooled by passing it through an expansion valve instead of the second heat exchanger. In either case, the temperature of the air is lowered to the point where the oxygen, which has the highest boiling point, starts to liquefy.
- 5 The air streamow part liquid and part gasnters the base of the high-pressure fractionating column. As the air works its way up the column, it loses additional heat. The oxygen continues to liquefy, forming an oxygen-rich mixture in the bottom of the column, while most of the nitrogen and argon flow to the top as a vapor.
- 6 The liquid oxygen mixture, called crude liquid oxygen, is drawn out of the bottom of the lower fractionating column and is cooled further in the subcooler. Part of this stream is allowed to expand to nearly atmospheric pressure and is fed into the low-pressure fractionating column. As the crude liquid oxygen works its way down the column, most of the remaining nitrogen and argon separate, leaving 99.5% pure oxygen at the bottom of the column.
- 7 Meanwhile, the nitrogen/argon vapor from the top of the high-pressure column is cooled further in the subcooler. The mixed vapor is allowed to expand to nearly atmospheric pressure and is fed into the top of the low-pressure fractionating column. The nitrogen, which has the lowest boiling point, turns to gas first and flows out the top of the column as 99.995% pure nitrogen.
- 8 The argon, which has a boiling point between the oxygen and the nitrogen, remains a vapor and begins to sink as the nitrogen boils off. As the argon vapor reaches a point about two-thirds the way down the column, the argon concentration reaches its maximum of about 7-12% and is drawn off into a third fractionating column, where it is further recirculated and refined. The final product is a stream of crude argon containing 93-96% argon, 2-5% oxygen, and the balance nitrogen with traces of other gases.
The oxygen at the bottom of the low-pressure column is about 99.5% pure. Newer cryogenic distillation units are designed to recover more of the argon from the low-pressure column, and this improves the oxygen purity to about 99.8%.
- 9 If higher purity is needed, one or more additional fractionating columns may be added in conjunction with the low-pressure column to further refine the oxygen product. In some cases, the oxygen may also be passed over a catalyst to oxidize any hydrocarbons. This process produces carbon dioxide and water vapor, which are then captured and removed.
About 80-90% of the oxygen produced in the United States is distributed to the end users in gas pipelines from nearby air separation plants. In some parts of the country, an extensive network of pipelines serves many end users over an area of hundred of miles (kilometers). The gas is compressed to about 500 psi (3.4 MPa or 34 atm) and flows through pipes that are 4-12 in (10-30 cm) in diameter. Most of the remaining oxygen is distributed in insulated tank trailers or railroad tank cars as liquid oxygen.
- 10 If the oxygen is to be liquefied, this process is usually done within the low-pressure fractionating column of the air separation plant. Nitrogen from the top of the low-pressure column is compressed, cooled, and expanded to liquefy the nitrogen. This liquid nitrogen stream is then fed back into the low-pressure column to provide the additional cooling required to liquefy the oxygen as it sinks to the bottom of the column.
- 11 Because liquid oxygen has a high boiling point, it boils off rapidly and is rarely shipped farther than 500 mi (800 km). It is transported in large, insulated tanks. The tank body is constructed of two shells and the air is evacuated between the inner and outer shell to retard heat loss. The vacuum space is filled with a semisolid insulating material to further halt heat flow from the outside.
The Compressed Gas Association establishes grading standards for both gaseous oxygen and liquid oxygen based on the amount and type of impurities present. Gas grades are called Type I and range from A, which is 99.0% pure, to F, which is 99.995% pure. Liquid grades are called Type II and also range from A to F, although the types and amounts of allowable impurities in liquid grades are different than in gas grades. Type I Grade B and Grade C and Type II Grade C are 99.5% pure and are the most commonly produced grades of oxygen. They are used in steel making and in the manufacture of synthetic chemicals.
The operation of cryogenic distillation airseparation units is monitored by automatic instruments and often uses computer controls. As a result, their output is consistent in quality. Periodic sampling and analysis of the final product ensures that the standards of purity are being met.
In January 1998, the United States launched the Lunar Prospector satellite into orbit around the moon. Among its many tasks, this satellite will be scanning the surface of the moon for indications of water. Scientists hope that if sufficient quantities of water are found, it could be used to produce hydrogen and oxygen gases through electrolysis, using solar power to generate the electricity. The hydrogen could be used as a fuel, and the oxygen could be used to provide life support for lunar colonies. Another plan involves extracting oxygen from chemical compounds in the lunar soil using a solar-powered furnace for heat.
Where to Learn More
Brady, George S., Henry R. Clauser, and John A. Vaccari. Materials Handbook, 14th Edition. McGraw-Hill, 1997.
Handbook of Compressed Gases, 3rd edition. Compressed Gas Association, Inc., Van Nostrand Reinhold Co., Inc., 1990.
Heiserman, David L. Exploring Chemical Elements and Their Compounds. TAB Books, 1992.
Kent, James A., editor. Riegel's Handbook of Industrial Chemistry, 9th edition. International Thomson Publishing, 1997.
Kroschwitz, Jacqueline I., executive editor, and Mary Howe-Grant, editor. Encyclopedia of Chemical Technology, 4th edition. John Wiley and Sons, Inc., 1993.
Stwertka, Albert. A Guide to the Elements. Oxford University Press, 1996.
Allen, J.B. "Making Oxygen on the Moon," Popular Science (August 1995): 23.
Air Products and Chemicals, Inc. .
(This website contains a summary of the history, sources, properties, and uses of oxygen.)