Gases like Helium, Neon, Argon, Krypton, Xenon and Radon are referred to the group of inert gases. The last three of them (Krypton, Xenon, Radon) are not to be named nominally inert gases as beginning since 1961 many stable chemical compounds of those gases with fluorine, chlorine and even with a classic oxidizer as is oxygen have been generated. That’s why the group of “inert substances” was transferred from a zero subgroup to the eighth one of the Mendeleev periodic table, it was suggested to name these gases “noble”. Nevertheless the term “inert gases” got implanted in scientific and technical literature and till now it is being widely used.

The volume content of Argon in atmospheric air is 0.93%. Argon is produced through separation of air in quantities estimated at millions normal cubic meters per year (nm3/year). Many natural gas fields contain Helium in merchantable concentration, and Helium is produced commercially at prime gas and gas concentrate processing. Therefore Helium and Argon are not considered as “rare” inert gases.

The rareness gas is Radon the content in air of which is insignificant (at the average 6×10-18 % by volume), though there are some areas where the content of Radon surpasses an average value hundred times. Radon is not produced as an industrial gas; especially because it is radioactive at half-decay period of slightly more than three days. Radon is produced in laboratory environment by blowout of some gas through radium salts water solution for scientific researches and medical purposes.

The remainder gases (Neon, Krypton and Xenon) are produced from atmospheric air by several stages. The volume content of Neon in air is 18×10-4 %, of Krypton - 1.14×10-4 %   and Xenon - 0.086×10-4 %. The first stage of production is linked with processing immense air quantities at high efficiency air separation plants (ASP) operating at Kapitza low pressure cycle with expansion turbines. 


Pure Neon production is realized by three stages:

  1. Air processing at the ASP. If compare in some way the ASP and a living organism the main condensers that execute simultaneously nitrogen overcondensation and liquid oxygen evaporation, will be “lungs” of the air separation plants. At the same time all low-boiling relative to nitrogen impurities (helium, hydrogen, neon) are accumulated in the side of the nitrogen tract. To provide operating capacity of the main condensers some part of nitrogen with enumerated impurities is forced to be removed. After that the removed flow is processed in the fractional distillation tubes to eliminate a part of nitrogen with following production of a prime neon-helium concentrate.

  2. At the second stage the said concentrate undergoes additional processing in the separate plants where the following processes take place: catalytic burning of hydrogen, high temperature adsorptive purification of reaction products (water and carbon dioxide gas), additional low temperature nitrogen dephlegmation as well as low temperature purification of the flow the result of which is a purified neon-helium mixture (60÷75 % neon and 25÷40 % helium) also containing impurities of nitrogen, hydrogen, oxygen, and some very small impurities.

  3. At the third stage the purified neon-helium mixture is processed at special low temperature plants where an initial adsorption purification of the mixture from cited above impurities takes place; after that during rectification process neon (at purity up to 99.9998 %)  and not very pure helium ( with impurities of neon up to 10÷15 %) are produced.

Annual production volume of pure neon is 350÷400 thousand nm3.


Xenon and Krypton are produced by three stages:

  1. Air processing at the ASP. Thanks to their physical properties heavy inert gases (Krypton, Xenon and Radon) are concentrated in the ASP in the liquid oxygen flows.  Also in these flows hydrocarbons are concentrated and accumulated (methane, ethane, propane, butane, acetylene etc.); it may result in creation of dangerously explosive situation when the ASP is operating. That’s why special systems of safe hydrocarbons concentration (they don't allow their precipitation on the surface of apparatuses and pipe lines in solid form) are used. A little part of liquid oxygen with maximum concentration of hydrocarbons is withdrawn from the ASP through a special withdrawing pipeline – sui generis “a rectum” of the plant, and "is splashed" on a very hot surface of a remote evaporator of liquid oxygen. It is in this flow that the main part of Krypton, Xenon and Radon going to the ASP together with in-process air, is concentrated. If there is a system of prime Krypton concentration the flow is named a PKC (a prime Krypton concentrate at Kr+Xe 0.1÷0.5 % content by volume). If there is no such a system the flow is named the flow of "dirty" oxygen that takes out explosive impurities. It is to notice that in the flows above cited besides enumerated components there is a whole "bunch" of different offensive compounds (CF4, C2F6, SF6, CO2, CO, NO, NO2, N2O, CCl4 and other components of technogeneous origin); in the sequel it is necessary to apply special purification methods as well a certification to produce high purity Krypton and Xenon.

    Xenon and Xenon are well sorbed in the systems of air and oxygen purification but in rectification blocks they have a propensity for spreading in the apparatuses. To group them together in correct flows additional technological efforts should be made. The specialists of the " Chromium " Ltd together with the research workers of the Bauman MSTU carried out the complex calculated and experimental investigations of Xenon and Krypton distribution and their keeping in all components of purification and concentration of modern ASPs, as a result several technical decisions to enhance the extraction ratio of these components (10÷30 %) were elaborated and protected by patents. During investigations we based on published results and great experience of the public corporation "Kriogenmash" (town of Balashikha) that was recognized as a leading enterprise in the USSR (now Russia) to develop and manufacture practically all large ASPs operating on the CIS's territory. It is necessary to notice that the ASP explosion safety systems developed and realized in "Kriogenmash" including technological systems, apparatuses execution and normative support are the most reliable in the world.

  2. At the second stage the PKC goes from the blocks equipped with systems of prime Krypton concentration to processing at the plants of crude Krypton (PCK), and the Krypton-Xenon mixture (KXM) is generated. The PKC is compressed in the compressor up to 0.5 MPa; then, the hydrocarbons are burnt from the PKC by catalytic oxidation method, the oxidation products (CO2 and H2O) are removed by adsorption. After that the purified PKC is separated into oxygen and Kr-Xe mixture in the rectification column, the Kr+Xe concentration is increased from 0.1÷0.2 % up to ~98 % by volume. At the same time all radon going to the ASP together with in-process air is practically in the KXM. The standard KXM produced that corresponds to GOST 10218-77, is a "cocktail" consisting not only of Krypton and Xenon but O2, N2, Ar, H2, CH4, C2H6, C3H8, H2O, CF4, C2F6, SF6, CO2, CO, NO, NO2, N2O, CCl4 and other traces.

    Up to 90-ies of the last century there were two serial modifications of crude Krypton plants - УСК-1М and УСК-0,45 manufactured according to an oxygen compressor scheme. At the end of 90-ies the "Chromium" Ltd elaborated a new industrial-scale safe and high efficient plant "Chrom-3" to process the PKC and produce the KXM. This plant has no oxygen compressed in the compressor, thanks to this fact the capital expenditure is significantly lowered because it is not necessary to place equipment in separate premises. All processes including catalytic oxidation take place under pressure lower than 0.07 MPa. The coefficient of Krypton and Xenon extraction is enhanced. The plant is equipped with original systems of internal compression of the liquid oxygen flow without mechanical devices as well as waste flows cold utilization. The main engineering solutions on which is based the operation of the plant are protected by patents of the Russian Federation.  In total all these facts allow decreasing cost price of the PKC processing more than twice as compared to the plants of УСК-1М and УСК-0.45 type, also the explosion safety at operation is increased. At present 7 plants have been manufactured, 6 of them are fully operational and produce more than 20% of annual world volume of the Krypton-Xenon mixture generation.

    Up to 1999 the blocks of air separation without components of prime Krypton concentration didn't produce the mixtures containing heavy inert gases. In 1998 the "Chromium" Ltd. elaborated a new adsorption technology for generation of Xenon-Nitrogen mixtures, it gives the possibility to extract up to 70% Xenon going to the ASP with in-process air. The technology has been protected by the patents of the Russian Federation, Ukraine, Kazakhstan and Rumania. Based on this technology a production run of the adsorption plants named Х-0,06 (the following modification is X-0,1)  has been elaborated. 15 plants are fully operational and produce about 4% annual world volume of Xenon as a mixture component.

  3. The third stage is processing the multicomponent mixtures containing heavy inert gases (Krypton-Xenon, Xenon-Nitrogen and others mixtures) to produce ultra high purity Xenon and Krypton. For this purpose the “Chromium” Ltd. elaborated a universal technology and created a unique plant that might process a large range of mixtures commercially and produce ultra high purity Xenon and Krypton (above 99.99999% by the main component volume). The technology is protected by the patents of the Russian Federation, Ukraine and China; now the patents are being patented in Europe, USA and Japan. Also are elaborated and registered in the public register the methods of measuring impurities in Krypton and Xenon regarding to fifteen elements at the level 1÷10 ppb that is 1,000 times lower than GOST requirements acting in the Russian Federation. Concerning particularly “heavy” impurities the methods of measuring at level of 10-12÷10-15 of volume fractions were elaborated and implemented.

Annual production volume of Xenon and Krypton is:

Krypton – 115,000÷125,000 nm3 per year;

Xenon – 9,500÷10,500 nm3 per year.


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