Parallel PSA Process for Recovery of Krypton

Abstract

Innovative semiconductor processes using microwave-excited high-density plasma equipment have been proposed. The feature of these processes is the use of Kr for one of the process gases. Kr is very expensive because the atmosphere contains Kr at only 1.14 ppm by volume. Therefore, it is necessary to recover and reuse Kr from exhaust gas containing about 50% N₂ and about 50% Kr.
Isotherms and self-diffusivities for adsorption of N₂ and Kr were measured on commercial active carbons and zeolites. It was found that active carbons and Na-A zeolite exhibited thermodynamic and kinetic selectivity, respectively. Kr recovery equipment comprising an equilibrium based separation process (PSA I ) and kinetically controlled separation process (PSA II) has been developed. The equipment was able to produce Kr with 99.5% recovery and at a purity of 99.99%. Kr reuse can be achieved by additional use of a purifier.