Calcium carbide is a chemical compound with the chemical formula of CaC2. Its main use industrially is in the production of acetylene and calcium cyanamide.
The pure material is colorless, however 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), etc.). In the presence of trace moisture, technical-grade calcium carbide emits an unpleasant odor reminiscent of garlic.
Applications of calcium carbide include manufacture of acetylene gas, and for generation of acetylene in carbide lamps; manufacture of chemicals for fertilizer; and in steelmaking.
Calcium carbide is produced industrially in an electric arc furnace from a mixture of lime and coke at approximately 2200 °C. This method has not changed since its invention in 1892:
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 temperature). Impurities present in the carbide include phosphide, which produces phosphine when hydrolysed.
This reaction was an important part of the industrial revolution in chemistry, and was made possible in the USA as a result of massive amounts of inexpensive hydroelectric power produced at Niagara Falls before the turn of the 20th century.
The method for the production in an electric arc furnace was discovered in 1892 by T. L Willson and independently by H. Moissan in the same year
Production of acetylene
The reaction of calcium carbide with water, producing acetylene and calcium hydroxide, was discovered by Friedrich Wöhler in 1862.
CaC2 + 2 H2O → C2H2 + Ca(OH)2
This reaction was the basis of the industrial manufacture of acetylene, and is the major industrial use of calcium carbide.
At high temperatures, CaC2 reacts with water vapor to give calcium carbonate, carbon dioxide and hydrogen. 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.
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. Production of calcium carbide in China has been increasing. In 2005 output was 8.94 million tons, with the capacity to produce 17 million tons.
In the USA, Europe, and Japan, consumption of calcium carbide is generally declining. Production levels in the USA in 1990s were 236,000 tons per year.
Production of calcium cyanamide
Calcium carbide reacts with nitrogen at high temperature to form calcium cyanamide:
CaC2 + N2 → CaCN2 + C
Commonly known as nitrolim, calcium cyanamide is used as fertilizer. It is hydrolysed to cyanamide, H2NCN.
Calcium carbide is a powerful and effective chemical reducing agent, and can also be used as a source of energy. Nowhere is this more evident than in the field of metallurgy, where it is used in several ways to reduce costs.
In modern steelmaking operations, the need for lower sulfur steels demanded by modern continuous casting operations and specialty applications has increased calcium carbide's appeal as a hot metal desulfurizer or as a modifier to the slag to increase desulfurization efficiency. In addition, the reaction of carbide with oxides produces a large amount of heat that is highly retained in the process. This has efficiency implications for ladle metallurgy, but moreover carbide provides major cost savings as a source of energy and productivity improvement in the steelmaking furnace.
Calcium carbide is used:
- In the desulfurisation of iron (pig iron, cast iron and steel)
- As a fuel in steelmaking to extend the scrap ratio to liquid iron, depending on economics. -As a powerful deoxidizer at ladle treatment facilities.
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 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, although they are increasingly being replaced in this use by LED lights.
Carbide lamps were also used extensively as headlights in early automobiles, motorcycles and bicycles, but have been replaced entirely by electric lamps.
In the artificial ripening of fruit, calcium carbide is sometimes used as source of acetylene gas, which is a ripening agent similar to ethylene. However, this is illegal in some countries because consumption of fruits artificially ripened using calcium carbide can cause serious health problems in those who eat them.
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.
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.
Production of Calcium Carbide in India
In India there is only one unit, DCM Shriram Alkalies & Chemicals making Calcium carbide with the installed capacity of 112,000-tons. The company uses more than 90% of its production of calcium carbide for making PVC. It is the only unit in the country making PVC from Calcium Carbide.
Table below gives the data on calcium carbide production, Imports and consumtion during last few years.
Table: Production, Imports and Consumption of calcium carbide in India (Th. Tons)
Production of calcium carbide in India in the year 2016-17 was 85 thousand tons. Imports during the same year were 55.69 thousand tons valued at Rs. 236.52 crores. The consumption of calcium carbide in India has grown from 74,000-tons in 2009-10 to 166,000-tons in 2014-15. The total consumption of calcium carbide in 2016-17 is estimated at 140 thousand tons. Consumption has registered CARG of around 9 to 10% per annum.
The non-captive merchant market for calcium carbide in India is estimated at 55,000-tons, which is expected to reach 75,000-tons in the next five years at CARG of 8%.
60% of the total carbide consumption goes for production of PVC and acytylene gas, followed by 20% in steel and gas industry, 5% in carbide lamps and the balance 15% in other uses.
Illegal use of Calcium Carbide in India in Fruit Ripening
In India large quantities of calcium carbide are used in speeding up the ripening process of fruits though its use for this application is banned in India.
While some states in India have banned the use calcium carbide by fruit vendors, many are still to follow suit. As per the Food Safety and Standards (Prohibition and Restriction on Sales) Regulations 2011, use of Calcium Carbide for ripening of fruits is prohibited. The Union Ministry of Health & Family Welfare in December 2016 has also asked the state health authorities to conduct frequent inspection of fruit and vegetable markets.
Calcium carbide is an inorganic compound with the following primary commercial applications: generation of acetylene, production of calcium cyanamide (a nitrogen fertilizer), and use in the iron (foundry) and steel industries as a desulfurization reagent in the production of ductile iron and steel and as a slag modifier/conditioner (reducer) in steel production. In the United States, Japan, and China, the largest end use is the production of acetylene, both for cutting and welding and for chemicals. In Europe, metallurgical use and calcium cyanamide each have a share of over 36% of the market for calcium carbide.
China is the dominant player in the calcium carbide market, representing about 96% of total supply and consumption.
The following pie chart shows consumption of calcium carbide by major region:
Because of its large reserves and recent capacity rationalizations, and with the rapid development of chemical production, especially for the production of VCM, VAM, and BDO from acetylene, Chinese consumption of calcium carbide increased at an average rate of 8.5% per year between 2011 and 2016. During the next five years, calcium carbide will continue to play an important role as a raw material in the production of acetylene-based chemicals. Although China's economic growth may further moderate, it is expected that demand growth for calcium carbide will continue to sustain healthy rates. China is the world’s largest exporter of calcium carbide.
The production of acetylene is the largest end use for calcium carbide, amounting to about 90% of total consumption in the major regions. China’s sizable share of the global calcium carbide market is linked to the country’s strong economic growth, large coal reserves, and ever-increasing acetylene demand for chemicals. Calcium carbide to PVC, considered an antiquated process in developed parts of the world, represents over 80% of China’s total PVC production. As a result of continued development, China is projected to experience just over 4% per year growth in the consumption of calcium carbide to 2021. Although supply/demand for calcium carbide in some other regions/countries will increase in the future, the limited growth in volume will not change the world's supply/demand pattern in the forecast period.
Japan is a small producer and consumer of calcium carbide. Japanese calcium carbide consumption is estimated to be mainly for acetylene production (87%); calcium cyanamide and use as a desulfurization reagent accounted for 8% and 5%, respectively, in 2016. Overall calcium carbide demand is expected to decrease slightly through 2021.
In the United States, calcium carbide demand for acetylene in chemical applications, metallurgical uses, and industrial acetylene will show small increases.
Asia-Pacific region dominated the calcium carbide markets by geography in 2016 and the scenario is expected to remain the same in the next decade. This dominance is mainly due to the Chinese market. Chinese calcium carbide industry is highly fragmented with more than 300 producers of calcium carbide. China is the world largest producer and also the consumer of calcium carbide in the world. Asia-Pacific region is being followed by Europe accounts for 2.51% share of global calcium carbide market revenue.
Some of the major players for this chemical are: AlzChem AG, American Elements, Carbide Industries LLC., DCM Shriram Ltd., Hudson Chemicals Corp., KC Group, Metaloides, SA de CV, Mil-Spec Industries Corp., NGO CHEMICAL GROUP LTD., and Regency Carbide Pvt. Ltd.
The non-captive merchant market for calcium carbide in India is estimated at 55,000-tons, which is expected to reach 75,000-tons in the next five years at CARG of 8%. Globally, China will continue to be the dominant player, as a global supplier and global consumer.