Commonly called ˜rare gases due to their presence at extremely low levels in the atmosphere, neon, krypton and xenon form an important area within the special gases industry. The recent history of rare gases, and krypton and xenon in particular, which this article will focus on, is related not only to supply and demand, but also international politics and the highs and lows of the steel industry. Coupled with some novel new applications,these factors combine to ensure that this area of the special gas industry is undoubtedly, one of the most fascinating.
With the exception of the radioactive isotope krypton85, which is produced in nuclear fission, neon, krypton and xenon are obtained by fractional distillation of air in an air separation unit(ASU). Krypton is present in the atmosphere at approximately 1.1ppm and xenon at only 0.08 ppm, which means that only very large ASUs (generally larger than 800 tonnes /day) fitted with rare gas recovery units can economically produce the ˜crude gas, which is normally 90 per cent krypton and 10 per cent xenon and which has to be further purified by distillation in special rare gas purifiers.
Even at 800 tpd less than 500kg of pure xenon is produced per year, which explains its extremely high price and also reveals that an ASU is never run solely to produce rare gases “ they are always a by-product of the air separation process.
War games raise demand
Prior to President Reagans ˜Star Wars programme in 1984 the rare gas sector was generally stable with lighting being the main application for all three products. The world-wide ASU capacity in the west was generally sufficient to meet the demand and due to the relatively high cost, many large ASUs were not even fitted with rare gas recovery units.
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