How can oxygen be prepared? What are the commercial production and commercial uses of oxygen? Information about distribution of oxygen.
Preparation.
Oxygen can be prepared in small quantities from many of several compounds wherein it occurs in chemical combination. Generally one of three methods is used to isolate small quantities of oxygen for laboratory or demonstration purposes :
(1) The electrolysis of water to which a small amount of sulphuric acid or an alkali has been added furnishes high-purity oxygen liberated at the anode (positive pole). At the same time twice the volume of hydrogen is liberated at the cathode (negative pole).
(2) A convenient laboratory method for the preparation of pure oxygen is to treat “oxone” (a convenient form of sodium peroxide) with water. This compound is prepared specially for this purpose.
(3) Under proper conditions the application of heat causes oxygen to be liberated from many compounds, including oxides of mercury, silver, gold, and platinum; peroxides of hydrogen, barium, lead, and manganese; and many chlorates, nitrates, and bichromates of potassium and some other metals.
- (a) Niter, when ignited, gives up approximately one third of its oxygen. Priestley first obtained impure oxygen by this method in 1771.
- (b) Ignition of mercuric oxide was used by Priestley on August 1, 1774 to isolate the first pure oxygen on record.
- (c) Heating manganese dioxide was formerly one of the cheapest methods of commercial preparation of oxygen This was one of the methods used by Scheele.
Commercial Production.
Oxygen was generated first for commercial use by the potassium chlorate laboratory process. Later commercial oxygen was produced by the Brin barium oxide process; and (after 1895) was obtained from the electrolysis of water. Prior to 1907 the production of commercial oxygen was limited. Small quantities were used for oxyacetylene and oxyhydrogen heating and lighting.
The European development of the liquid air process for producing high-purity oxygen was pioneered by Karl P. G. ton Linde (1842-1934). This eminent physicist of Munich, who designed the first ammonia compression machine in 1876, made the first continuous machine for liquefying air in 1895. This machine was the forerunner of today’s oxygen, nitrogen, and rare gas industries. In 1902, Georges Claude of France also devised machines, independently of Linde, for liquefaction and fractional distillation of air.
The first major liquid air installation in the United States was made for Linde Air Products Company in 1907. This equipment, installed at Buffalo, N. Y., had a capacity of 750,000 cubic feet of gaseous oxygen per month. In 1915 there were approximately 50 liquefaction type oxygen plants operating in Europe and 5 in the United States. Oxygen plants are now found in every industrial region of the United States and in nearly every industrial area of the world.
The majority of the enormous volume of commercial oxygen produced is obtained from the air by the liquid process. By this physical method (air is not a chemical compound) air is liquefied and the main components (nitrogen and oxygen) are separated by fractional distillation. In addition to this process a relatively small amount of oxygen is obtained from the electrolysis of water.
According to the Survey of Manufacturers, approximately 2,058,000,000 cu. ft. of commercial oxygen were produced in the United States in 1923. By 1939 production of commercial oxygen increased to about 4,562,000,000 cu. ft. According to the Bureau of the Census, approximately 18,495,000,000 cu. ft. of commercial oxygen were produced in the United States in 1944. In 1966 almost 215,000,000,000 cu. ft. were produced. In addition, some 1,750,000 short tons of lower-purity oxygen (less than 99.5% oxygen) were also manufactured. Commercial oxygen comes from the distillation of liquid air and the electrolysis of water. Oxygen production exceeds that of any other inorganic gas in the United States.
Liquid Air
In the liquid air process for producing oxygen air is first cooled until it becomes partially liquefied. The liquid air is then rectified, boiling off the nitrogen and leaving the oxygen as a liquid. Oxygen then can be withdrawn from the apparatus either as a liquid or as a gas, depending upon the specific design of the plant.
A variety of cycles have been developed to accomplish air liquefaction. Some use the Joule-Thompson effect exclusively and others combine this principle with the use of expansion engines or turbines. In some cycles external refrigeration is also used.
In one cycle for the production of liquid oxygen air is first compressed to from 2,000 to 3,000 pounds per square inch. This compressed air is cooled by countercurrent heat exchange with waste nitrogen gas coming from the fractionating column. After some cooling, the compressed air is divided into two portions. One portion is further cooled and partially liquefied by expansion through a throttling valve. The partially liquefied air is then fed into the high-pressure section of a double-column fractional distillation unit. The second portion of the compressed air is expanded in an expansion engine and is also delivered to the high-pressure section of the rectification column.
Any cycle for the production of liquid or gaseous oxygen from the air can be divided into three fundamental steps: (1) purification of the air, (2) partial liquefaction of the air by refrigeration, (3) separation of oxygen from nitrogen by fractional distillation of the partially liquefied air.
One of the largest plants in the United States for the production of high-purity (99.5 per cent) liquid oxygen has a capacity of about 400 tons per day (9,640,00 cu. ft. gaseous equivalent at standard pressure and temperature).
Whether the product is withdrawn from a plant as liquid or gas, it is fed into a storage container. This is a type of gas holder or, in the case of liquid, a special storage tank that is well enough insulated to hold a liquid which boils at nearly —300°F.
Since World War II a demand has grown for oxygen of only 95 or so per cent purity for chemical and metallurgical purposes. At the time of its construction in 1946, the largest known single unit for producing low-purity gaseous oxygen in the United States could produce about 4,800,000 cu. ft. (about 200 tons) per day of 90 per cent oxygen from a single fractional distillation unit. Since 1946 larger units have been built. The cycle used for this unit was designed for most efficient production of 90 to 95 per cent oxygen.
Electrolysis of Water
A process used to a very minor extent for commercial oxygen production is the electrolytic separation of water to give off hydrogen and oxygen, both as gaseous products. Two volumes of hydrogen are released for each volume of oxygen. Since power consumption and other costs are high, large-scale electrolytic installations for obtaining oxygen are not practical.
Distribution
The oldest and probably most familiar method for distribution of oxygen is in the form of compressed oxygen (gaseous) in standard steel cylinders holding 244 cu. ft., 122 cu. ft., or 80 cu. ft. at 2,200 pounds per square inch pressure and 70° F. The cylinder distribution system is the only practical means of oxygen supply for use at temporary or widely scattered points or where consumption is not large or consistent.
When demand is greater than can be handled conveniently by single cylinders, cylinders are manifolded together to supply pipeline distribution to use points. High-pressure receivers manifolded together and mounted on trailers are also used commonly for transporting gaseous oxygen to large users to supply pipeline distribution systems.
To meet the ever-growing demand for large-quantity distribution, in 1932 a method of transporting and storing high-purity oxygen in liquid form was introduced in the United States. The ratio of volume of oxygen as a liquid at its boiling point and normal pressure to gas at normal temperature and pressure is about 1 to 862. Liquid oxygen is delivered by railroad tank car or by truck and stored as a liquid on the user’s property. As needed, the oxygen is converted to gas and delivered to use points through a pipeline system.
Generally only those who consume about 1,000,000 or more cu. ft. of oxygen per month are supplied by this system. Storage tanks with a capacity of the equivalent of 1,500,000 cu. ft. each are installed to give sufficient reserve. When stored as a liquid, oxygen is maintained at normal pressure and —297° F. Specially designed insulation keeps daily evaporation down to about 0.5 per cent of capacity. Any evaporation from the storage tank is also piped into the distribution system.
Advantages of liquid distribution can be realized in meeting demands of from 50,000 cu. ft. (2 tons) to 1,000,000 cu. ft. (40 tons) per month by a variation of the system. Liquid oxygen is brought to the storage point as a liquid in a tank truck. At that point it is converted into gaseous form by equipment on the truck and is charged into receiver tubes on the user’s property.
The capacity of a railroad tank car is approximately 6,500 or 8,700 gallons of liquid (or the equivalent of about 750,000 or 1,000,000 cu. ft. of oxygen gas at standard pressure and temperature) . If distributed as a gas in standard 244 cu. ft. cylinders, 14 railroad cars would be required to transport the 4,100 cylinders necessary to contain 1,000,000 cu. ft. of compressed gaseous oxygen. Trucks vary from 520 to 2,600 gallons in capacity of liquid oxygen (gaseous equivalents: 60,000 to 300,000 cu. ft.)
Commercial Uses.
Oxygen is often used with combustible substances, such as acetylene or hydrogen, to produce an extremely hot flame. As early as 1895, Henri Chatelier, a French chemist, noted the very high temperature of the oxyacetylene flame. Not until 1901, however, did Edmond Fouche announce the first welding and cutting apparatus utilizing this^ flame. When oxygen and acetylene are combined in suitable apparatus, the hottest flame temperature currently available to industry is produced—approximately 5,800 to 6,300° F. This is the only gas flame hot enough to melt all commercial metals.
Iron and Steel Industry
If one thing can be singled out as being the most important factor in the growth of the oxygen industry, it is probably the many processes that the availability of low-cost, bulk oxygen has made practical. The uses of oxygen in the iron and steel industry, for instance, begin with the extraction of iron ore and end with the production of finished metal parts. The modern Linnz and Donnewitz (LD) process produces high-purity steel by directing jets of pure oxygen into molten iron in a furnace.
Prior to the late 1940’s it was not economically feasible to mine ore from the eastern end of the vast Mesabi iron range in Minnesota. The reason for this was the difficulty of drilling the very hard, tough ore deposit. In 1949 the jet-piercing process was developed for drilling blastholes in the ore or the rock. This flame process uses oxygen, fuel, and water to get such high temperatures and gas velocities that rock is disintegrated. In 1951 it was estimated that the jet-piercing process would make it possible to mine 30 to 40 million tons of iron ore per year from the hard, massive beds of magnetic taconite of the Mesabi.
When scrap iron and steel, pig iron, and hot iron from the blast furnace are loaded into huge open-hearth furnaces to be melted and refined, oxygen-enriched air is often used instead of ordinary air to support combustion. In this way the melt-down and refining periods are shortened considerably.
When steel has been refined and is ready for rolling or forging, surface defects are removed by a process known as deseaming, scarfing, or conditioning. This process uses a nozzle designed to deliver a relatively large jet of oxygen at low velocity. In mechanized steel conditioning, the entire surface of the billet, bloom, or slab is removed by a scarfing machine set into the rolling-mill line. The machine can remove a thin layer containing surface defects from one, two, or four sides simultaneously and the operation can be performed while the metal is still hot and without interrupting the rolling operation.
Cutting Applications
The principle of oxygen steel conditioning and other cutting applications is fundamentally simple. When heated to the kindling temperature, iron or steel can be cut (actually burned) by a jet of pure oxygen. With this process iron or steel can be shaped under close control. Tolerances of Yie inch are easily maintained. By introducing an iron-rich powder into the cutting oxygen stream, oxyacetylene cutting has been further expanded, so that it can be used effectively for cutting stainless steel and cast iron. Whereas scrap-metal sections which were too heavy for handling had been discarded by burying these in slag dumps, hundreds of thousands of tons of steel and iron scrap now are cut easily and economically and are reclaimed as heavy melting scrap. Pieces as large as six feet thick can be cut with accuracy at a rate of two to three inches per minute.
Oxyacetylene cutting by hand- or machine-guided blowpipes is indispensable to United States industry. This method of severing and shaping steel plates, bars, and slabs has proved more efficient than older methods in performing many cutting and trimming operations. It also has been a key factor in the creation of new techniques for fabricating steel. With suitable apparatus the oxyacetylene flame can perform straight-line cutting, circle cutting, shape-cutting of 20 to 40 stacked sheets of steel, and beveling or grooving the edges of steel plate in preparation for welding. Oxyacetylene cutting is also useful in repairing and reclaiming old, worn equipment.
Welding Applications
Metal production, fabrication, and repair, as it is known today, would be impossible without the oxyacetylene processes. Oxyacetylene welding permits the fabrication of many structures and parts which could not be built before welding was developed. Welding also has provided a means of repairing broken or damaged structures with large savings in time and money. With the oxyacetylene blowpipe practically any metals—similar or dissimilar-can be joined, so that the weld is as strong as the base metal. There are many closely allied applications for the oxyacetylene flame.
Heating Applications
Oxyacetylene flame-hardening is used to impart a hard, wear-resistant case to quench-hardening steel and iron parts. The oxyacetylene flame can be used also to anneal metal parts after welding or cutting.
Flame-priming utilizes the quick heat of oxyacetylene flames to remove loose scale, rust, and surface moisture from steel prior to painting.
Oxyacetylene blowpipes provide a convenient source of controllable heat for bending, straightening, or shaping operations on steels. Another process, flame-spinning, uses the oxyacetylene flame and a shaping tool to shape tubing. This process is especially effective for making end closures.
Medicine
The oxygen supplied for welding and cutting has a purity of 99.5 per cent. This same oxygen is used by hospitals for oxygen therapy. Patients suffering from want of oxygen are supplied with any required concentration of oxygen, up to 99.5 per cent, by a nasal catheter, face mask, or oxygen tent. To provide proper concentrations for specific needs, special pressure-reducing regulators control the flow of oxygen.
Patients suffering from asphyxia, asthma, pulmonary diseases, heart diseases, and anemia are often treated with oxygen concentrations. Oxygen is often prescribed as part of standard post-operative treatment also. It has been found that patients who breathe extra oxygen for a short time following an operation are frequently more comfortable.
The aviator flying at high altitudes has difficulty getting enough oxygen from the “thin air” of the rarified atmosphere. In such instances, unless the airplane’s cockpit or cabin is pressurized, he requires extra oxygen. Oxygen from cylinders is also used in submarines to replace the oxygen consumed by the crew.
Rocket Engineering
One of the newest uses of commercial oxygen—and one that promises to be of increasing importance in the years to come —is in the field of rocket and jet propulsion. Experiments were begun in this field prior to 1929. In World War II, Germany developed a liquid oxygen-alcohol rocket bomb. Rocket engineering depends on the use of liquid oxygen as the principal rocket fuel oxidant.
