Calcium carbide is a chemical compound with the chemical formula CaC2. Its appearance depends on the grade and ranges from black through to grayish white lumps. Its main use now is as a source of acetylene. In China, acetylene is a feedstock for the chemical industry, in particular for the production of polyvinyl chloride, PVC.
Locally produced acetylene is more economic than using imported oil. Production of calcium carbide in China has been increasing. In 2005
output was 8.94 million tons with capacity to produce 17 million tons. In the USA, Europe and Japan consumption is generally reducing. Production levels in the USA in 1990 were 236,000 tons pa.
Production
Calcium carbide is produced industrially in an electric arc furnace loaded with a mixture of lime and coke at about 2000 °C, this method has not changed since its invention in 1888.Calcium carbide is formed:
CaO + 3C→CaC2 + CO
Calcium carbide synthesis requires an extremely high temperature,
~2000 °C, which 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 a few mm up to 50mm. 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. Impurities present in the carbide include phosphide,
which produces phosphine when hydrolysed.
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