Commercialization of Calcium Carbide and Acetylene

Uses for Calcium Carbide and Acetylene

In , while experimenting with a voltaic cell, Humphry Davy produced the first arc light by passing an electric current between two carbon rods, which touched each other, and then drawing them apart. When an electric current meets with resistance, its energy is transformed into heat, and because the carbon vapor in the arc offers high resistance to the electric current, temperatures as high as ° C are attainable, high enough to melt or vaporize any known substance.

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The carbon-arc furnace, which dates from when it was battery operated, was of no practical value until after the development in of the electrical dynamo for converting water or steam power into electricity. Not until the work in Spray did the arc furnace become an industrial reality.

Improved Lighting

Over the half century following its discovery in by Edmund Davy, a cousin of Humphrey Davy, acetylene was only a laboratory curiosity. After Thomas L. Willson's discovery of a cheap commercial process for making acetylene in , massive quantities of the gas were in demand for lighting.

A newly developed acetylene burner, designed to bring adequate air to the flame to eliminate smoke and soot, gave a brilliant white light, 10 to 12 times brighter than that of any commercial fuel then in use. By , acetylene generators and compressed acetylene were successfully competing with the fledgling electric light industry to provide excellent lighting, particularly in country homes and those not accessible to gas utilities.

Portable acetylene generators, which worked simply by dropping water on calcium carbide, provided a practical way for lighting railways, mines, bicycles, and automobiles. Acetylene lighting was used in transportation for a decade or more until electrical generation systems and shock-resistant light bulbs were developed. Miners continued to use carbide lights on their caps until long-lasting, dry-cell electric batteries were perfected in the s.

Acetylene also replaced oil in marine buoys because it provided a far brighter light. The automatic carbide acetylene generators used at first were not very reliable and were replaced by compressed acetylene. Swedish engineer Gustaf DalÉn received the Nobel Prize in physics for his discovery of techniques that allowed safe compression of acetylene. A few of the acetylene buoys were still in operation in the s.

High-Quality Alloy Steels

In , Thomas Willson began experiments at Spray with smelting metals in the carbon-arc furnace. After , this work was carried on by Guillaume de Chalmot. The high temperature of the arc furnace provided a more efficient means for alloying iron with chromium, manganese, and other metals.

As a group, these low-iron alloys, called ferro-alloys, can be readily dissolved in steel to impart predictable properties according to the type and amount of metal added. For the first time, steels could be tailor-made for such properties as toughness, impact strength, high strength at high temperatures, and corrosion resistance. Improved armor plate for battle ships, high-speed tool steels, and stainless steels are just three of the hundreds of specialized steel products now in use.

Rapid Welding and Cutting of Metals

During the 19th century, the only means of continuously joining two pieces of iron or steel was to heat them in a forge and hammer them together. In , electric welding was introduced, but it was of no practical value because the electric power industry was not sufficiently developed to sustain it. Oxyhydrogen and thermite welding were known but had not been perfected.

When burned with oxygen instead of air, acetylene gave a flame temperature of °C compared with °C for the Bunsen burner flame. This high flame temperature was reported in but not exploited until about , when a commercial oxyacetylene welding apparatus was developed in France. The first oxyacetylene welding shop in the United States was set up in , and in the technique was adopted at the Brooklyn Navy Yard. There, oxyacetylene torches could cut a porthole in 3-inch armor plate in 30 minutes, a task that formerly had required five men working for two weeks to complete. The sudden, great demand for oxygen for welding launched oxygen as a commodity product.

Nitrogen Fixation and Fertilizer Manufacture

Henri Moissan observed in that calcium carbide absorbed atmospheric nitrogen. In , Fritz Rothe of Germany found that the compound formed by this absorption was calcium cyanamide. In the soil, calcium cyanamide decomposes to yield urea and ammonium carbonate, both potent fertilizers. A commercial process patented by Adolf Frank and Nikodem Caro for making calcium cyanamide from carbide was perfected in Germany in and was widely adopted almost immediately. This was the first commercial process that was used worldwide to fix atmospheric nitrogen. World output of calcium cyanamide increased from 1,700 tons in to an estimated peak production of 1.5 million tons in .

Organic Chemicals and Macromolecules

Following Willson's synthesis of chloroform and aldehydes from acetylene in , acetylene soon became the starting material in the synthesis of a host of organic substances, particularly for the solvent, plastics, and synthetic rubber and fiber industries. By , work in Germany led to chlorinated solvents by partial or complete chlorination of acetylene, and in to a full-scale plant producing 1,1,2-trichloroethene. These solvents were used extensively after for degreasing metals in preparation for electroplating or painting. By , Germany was producing polyvinyl acetate for use in varnishes. Subsequently, polyvinyl acetate was used in adhesives, paints, paper, textiles, glue, and flooring materials.

During World War I, commercial processes for the production of acetaldehyde, acetic acid, and acetone (by passing acetic acid over a hot catalyst) were installed in Canada; acetone in particular was needed for making explosives. Similar processes in the United States in the s served the cellulose acetate industry for the production of fibers and film. In the same decade, the synthesis of vinyl acetylene by Julius Nieuwland led to the development in of the synthetic rubber, neoprene, by DuPont. Its annual output reached 120,000 tons by .

In Germany after World War I, butadiene made from acetylene was the basis of a rubber substitute that made the country self-sufficient in rubber. Also in Germany, beginning in , J. Walter Reppe pioneered the study of acetylene chemistry at pressures as high as 200 atmospheres. This opened up a vast new field, often known as "Reppe chemistry." Reppe even managed to form cyclooctatetraene by linking four acetylene molecules in a ring, confirming Richard Willstïtter's much contested claim that he had made the same compound in .

With hydrocyanic acid, acetylene forms acrylonitrile, which can then be polymerized and spun into acrylic fibers. World production of acrylic fibers in was 2,523,000 tons.

In the past 40 years or so, acetylene has increasingly been derived from petroleum, but if petroleum reserves dwindle sufficiently to raise the price above that of coal, industry might return to coal, and calcium carbide would again become a main path to organic chemicals.

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Chemical compound

Chemical compound

Calcium carbide, also known as calcium acetylide, is a chemical compound with the chemical formula of CaC2. Its main use industrially is in the production of acetylene and calcium cyanamide.[3]

The pure material is colorless, while pieces of technical-grade calcium carbide are grey or brown and consist of about 80&#;85% of CaC2 (the rest is CaO (calcium oxide), Ca3P2 (calcium phosphide), CaS (calcium sulfide), Ca3N2 (calcium nitride), SiC (silicon carbide), C (carbon), etc.). In the presence of trace moisture, technical-grade calcium carbide emits an unpleasant odor reminiscent of garlic.[4]

Applications of calcium carbide include manufacture of acetylene gas, generation of acetylene in carbide lamps, manufacture of chemicals for fertilizer, and steelmaking.

Production

Calcium carbide is produced industrially in an electric arc furnace from a mixture of lime and coke at approximately 2,200 °C (3,990 °F).[5] This is an endothermic reaction requiring 110 kilocalories (460 kJ) per mole[6] and high temperatures to drive off the carbon monoxide. This method has not changed since its invention in :

CaO + 3 C &#; CaC2 + CO

The high temperature required for this reaction is not practically achievable by traditional combustion, so the reaction is performed in an electric arc furnace with graphite electrodes. The carbide product produced generally contains around 80% calcium carbide by weight. The carbide is crushed to produce small lumps that can range from a few mm up to 50 mm. The impurities are concentrated in the finer fractions. The CaC2 content of the product is assayed by measuring the amount of acetylene produced on hydrolysis. As an example, the British and German standards for the content of the coarser fractions are 295 L/kg and 300 L/kg respectively (at 101 kPa pressure and 20 °C (68 °F) temperature). Impurities present in the carbide include calcium phosphide, which produces phosphine when hydrolysed.[7]

This reaction was an important part of the Industrial Revolution in chemistry, and was made possible in the United States as a result of massive amounts of inexpensive hydroelectric power produced at Niagara Falls before the turn of the 20th century.[8] The electric arc furnace method was discovered in by T. L. Willson, and independently in the same year by H. Moissan.[9][10][11] In Jajce, Bosnia and Herzegovina, the Austrian industrialist Josef Kranz and his "Bosnische-Elektrizitäts AG" company, whose successor later became "Elektro-Bosna", opened the largest chemical factory for the production of calcium carbide at the time in Europe in . A hydroelectric power station on the Pliva river with an installed capacity of 8 MW was constructed to supply electricity for the factory, the first power station of its kind in Southeast Europe, and became operational on 24 March .[12]

Crystal structure

Pure calcium carbide is a colourless solid. The common crystalline form at room temperature is a distorted rock-salt structure with the C22&#; units lying parallel.[13] There are three different polymorphs which appear at room temperature: the tetragonal structure and two different monoclinic structures.[1]

Applications

Production of acetylene

The reaction of calcium carbide with water, producing acetylene and calcium hydroxide,[5] was discovered by Friedrich Wöhler in .

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This reaction was the basis of the industrial manufacture of acetylene, and is the major industrial use of calcium carbide.

Today acetylene is mainly manufactured by the partial combustion of methane or appears as a side product in the ethylene stream from cracking of hydrocarbons. Approximately 400,000 tonnes are produced this way annually (see acetylene preparation).

In China, acetylene derived from calcium carbide remains a raw material for the chemical industry, in particular for the production of polyvinyl chloride. Locally produced acetylene is more economical than using imported oil.[14] Production of calcium carbide in China has been increasing. In output was 8.94 million tons, with the capacity to produce 17 million tons.[15]

In the United States, Europe, and Japan, consumption of calcium carbide is generally declining.[16] Production levels in the US during the s were 236,000 tons per year.[13]

Production of calcium cyanamide

Calcium carbide reacts with nitrogen at high temperature to form calcium cyanamide:[5]

CaC2 + N2 &#; CaCN2 + C

Commonly known as nitrolime, calcium cyanamide is used as fertilizer. It is hydrolysed to cyanamide, H2NCN.[5]

Steelmaking

Calcium carbide is used:

• in the desulfurization of iron (pig iron, cast iron and steel)

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• as a fuel in steelmaking to extend the scrap ratio to liquid iron, depending on economics.
• as a powerful deoxidizer at ladle treatment facilities.

Carbide lamps

Calcium carbide is used in carbide lamps. Water dripping on carbide produces acetylene gas, which burns and produces light. While these lamps gave steadier and brighter light than candles, they were dangerous in coal mines, where flammable methane gas made them a serious hazard. The presence of flammable gases in coal mines led to miner safety lamps such as the Davy lamp, in which a wire gauze reduces the risk of methane ignition. Carbide lamps were still used extensively in slate, copper, and tin mines where methane is not a serious hazard. Most miners' lamps have now been replaced by electric lamps.

Carbide lamps are still used for mining in some less wealthy countries, for example in the silver mines near Potosí, Bolivia. Carbide lamps are also still used by some cavers exploring caves and other underground areas,[17] although they are increasingly being replaced in this use by LED lights.

Carbide lamps were also used extensively as headlamps in early automobiles, motorcycles and bicycles, but have been replaced entirely by electric lamps.[18]

Other uses

Calcium carbide is sometimes used as source of acetylene, which like ethylene gas, is a ripening agent.[19] However, this is illegal in some countries as, in the production of acetylene from calcium carbide, contamination often leads to trace production of phosphine and arsine.[20][21] These impurities can be removed by passing the acetylene gas through acidified copper sulfate solution, but, in developing countries, this precaution is often neglected.

Calcium carbide is used in toy cannons such as the Big-Bang Cannon, as well as in bamboo cannons. In the Netherlands calcium carbide is used around new-year to shoot with milk churns.[22]

Calcium carbide, together with calcium phosphide, is used in floating, self-igniting naval signal flares, such as those produced by the Holmes' Marine Life Protection Association.

Calcium carbide is used to determine the moisture content of soil. When soil and calcium carbide are mixed in a closed pressure cylinder, the water content in soil reacts with calcium carbide to release acetylene whose pressure can be measured to determine the moisture content.[23][24]

Calcium carbide is sold commercially as a mole repellent.[25] When it comes into contact with water, the gas produced drives moles away.[26]

References

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