Commonly called \\$quot;˜rare gases\\$quot; 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 \\$quot;˜crude gas\\$quot;, 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 \\$quot;“ they are always a by-product of the air separation process.

War games raise demand
Prior to President Reagan\\$quot;s \\$quot;˜Star Wars\\$quot; 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.

The Star Wars programme changed all of that due to applications for krypton and xenon in high power fluoride lasers. The huge requirement for rare gases from the US government caused very tight supply situation, and further, a huge increase in pricing with xenon fetching up to $20 / litre ($100,000 for a 10,000 litre cylinder!).

Not to be out gunned, the Soviet Union was playing the same game and using rare gases produced, for the most part, in the Ukraine which was the centre of the Soviet steel making industry and which had a number of huge ASUs all fitted with rare gas recovery.

"... there is no doubt that rare gases will continue to challenge
suppliers and users alike over the coming years"

Two factors combined in the late 80\\$quot;s, which caused an abrupt change in the supply and demand dynamics of rare gases. The signing of the Strategic Arms Limitation Treaty caused a dampening of enthusiasm for high powered lasers (which were rumored never to have been effective) and caused a slackening in world-wide
demand for krypton and xenon.

Using Krypton as a double glazing filler helps reduce noise and heat loss///

Almost simultaneously, the collapse of the Soviet empire caused general economic chaos in that region. Scientists employed in research laboratories, where the Soviet laser research had been conducted, were left with no income but substantial stocks of rare gases. In order to generate income for themselves and their institutes, this inventory was sold to the west at low prices, partially because the quality was generally assumed to be worse but also in order to ensure the income stream. The net result of this supply demand imbalance was that rare gas prices plummeted with xenon being sold as low as $1.00 / litre.

A further disadvantage of former Soviet, krypton in particular is the relatively high level of the radioactive isotope Kr85. Due to the high number of atmospheric nuclear tests carried out by the Soviet Union during the cold war.

Stability in the 90\\$quot;s
For a few years in the early 90\\$quot;s rare gases remained relatively stable. Supply remained relatively fluid and actually decreased slightly. This was partially due to the Soviet inventory being consumed but also the downturn in world
steel consumption and pricing caused the Ukrainian steel units to be mothballed, which meant they required less oxygen from the ASUs and, thus, produced less rare gases. However, as is ever the case with this fascinating part of our industry, change was around the corner in the shape of some novel new applications.

Xenon became the preferred fuel for ion propulsion engines used in geo stationary satellites because of its high molecular weight and ease of ionization. It can be stored as a liquid at near room temperature (but at high pressure) yet easily converts back into a gas to fuel the engine and its inert nature makes it environmentally friendly and less corrosive to the engine then other fuels such a mercury or cesium. These properties caused a major demand for xenon from companies planning to launch satellites for a world-wide, space based cellular telephone system (three separate companies planned to build up to 36 satellites each). However, this was a false dawn as the programme never really took off.

Researching for new applications
The low cost of rare gases encouraged researchers to look for new applications and these applications started to absorb the large quantities of rare gases available. Uses included using krypton as a double glazing filler to reduce noise and heat loss, filling krypton and xenon in high intensity automobile headlamps. At the same time, although xenon had long been known to have anesthetic properties, continuing research showed that it was an ideal gas for anesthesia with virtually none of the side effects of conventional products.

Due to these applications, gas companies, anticipating an increased demand, particularly for xenon started to retrofit larger ASUs with rare gas recovery units \\$quot;“ the largest example being the enormous Sasol complex in South Africa,
which was retrofitted by Air Liquide. As well as this, new projects are now examined much more closely for fitting with rare gas recovery increasing supply and also making the west less dependent on the Russian and Ukrainian supplies.

Filling vehicle headlamps with Krypton and Xenon creates higher intensity lighting///

The future for rare gases?
Undoubtedly, it is xenon that is likely to be greatest demand over the coming years. Although only one of the three satellite phone systems was commissioned, there still remains high demand in ion motors as more and more satellites are launched.

New medical applications are still being discovered including drug treatment therapy and brain imaging as well as its use in anesthesia, which is still to achieve its potential mainly due to cost concerns.

Laser and lighting uses are also contributing to continuing high demand with xenon
headlamps becoming increasingly popular and European law makers introducing daytime running laws, which will see lamps replaced more frequently.

Energy conservation is likely to be the demand driver for future krypton sales. Filling krypton in sealed double glazing units is already common in Europe but much less prevalent in the US. With continuing higher energy costs expect to see this area expand significantly as well as long life light bulbs, which use a krypton mixture and which are predominantly produced in India and China.

Supply is expected to remain relatively stable particularly in the regionally based US market where the few new ASUs being planned will all be smaller units of up to 600 tpd making it uneconomic to produce crude gas. While new giant ASUs are being installed they are in less developed parts of the world including India and China, leading to questions about whether it is practical to purify the crude near the source or transport it to purification centres.

The only exception is the recently announced Air Products (AP) technology, which selectively recovers crude xenon from smaller ASUs of only 400 tpd capacity. Whilst the presence of concentrated xenon in the hydrocarbon off stream in the ASU has been known for some time, it is believed that AP is the first company to actually commercialise this knowledge, and with xenon being the product likely to be in higher demand this new manufacturing technology is well timed.

Whilst the major highs and lows of the rare gas cycle are unlikely to be reproduced as they have in the past 10 - 15 years, there is no doubt that rare gases will continue to challenge suppliers and users alike over the coming years.