Recovery of Krypton and Xenon

Krypton and xenon, which have a concentration of 1.138 ppm and 0.086 ppm in the atmospheric air, are mainly recovered as secondary products from air separation. The worldwide demand increases annually. In 2001, the global annual Xe-produc-tion amounted to about 6800 m, the Kr-production to about 67 000 m. Owing to its low concentration in the air the xenon price is high with typical 4000-8000 per m and is strongly fluctuating. The price for krypton, which occurs about 13 times more frequently in the air than xenon, is lower by about this factor. Typically the noble gases Kr and Xe are recovered in two steps  

In the first step, a pre-enrichment of about 4000 ppm of Kr and 400 ppm of Xe in liquid oxygen is achieved in the sump of an additional column (4), (Fig. 3.1). This column is integrated into the air separation unit 

In a second step, the products are extracted from this pre-concentrate in a unit, operating independently from the air separator. The production rate of this preenriched liquid is low. 

Due to this low production rate, the pre-product is often stored in a tank, which is periodically transported to a central fine-purification plant. In order to keep 

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