A low pressure cryogenic trap for cleaning of feed stream in dilution refrigerator

Cryogenic traps are frequently used for removing impurities from gases and conventionally use the cryo-adsorption technique with activated carbon adsorbents. Such purification instruments are often operating at high pressure to aid the adsorption process to its maximum extent. In a system which operates at low pressure and low gas flow rates the residual concentration of the adsorptive gas is determined only by its vapor pressure in relation to the total pressure. In a dilution refrigerator the process gas circulates at sub-atmospheric pressure and it becomes a challenge to remove impurities by cryogenic trap at substantially low pressures. In this paper we describe a simple one column liquid nitrogen cooled cryogenic trap for entrapment of O₂ and N₂ from the circulating process gas. Two different types of adsorbents, LiLSX and activated carbon were investigated using volumetric adsorption approach and break-through studies.