Vacuum Sorption Pumping at Cryogenic Temperatures of Argon and Oxygen on Molecular Sieves

摘要

Cryosorption pumping is a method of excavating enclosed volumes by adsorbing gas on a deep bed of solid sorbent (typically a zeolite) at cryogenic temperatures. Modeling the dynamic behavior of these systems for air pumping requires information on two major constituents of air, oxygen and argon, which had not been previously studied, as well as data on a nonadsorbing specie, helium. Deep beds of Davison 4A molecular sieves were subjected to a metered flow of pure gas and the pressure history of the experiment was monitored, using computer data acquisition techniques. Particle size variations is the major variable in determining the mechanism of the process. The data acquired in the current study compare favorably with previous experiments. Previously developed models for the dynamic sorption behavior of deep beds under vacuum for two extreme conditions, micropore and micropore control were tested in this study. The sorption behavior of argon clearly fit into the category of macropore controlled sorption, indicating that these species are adsorbed primarily on the surface of the zeolite crystals, much like the theoretical and experimental results for N sub 2 cryosorption on the same sieves of Crabb. On the other hand oxygen sorption is most likely micropore controlled, and may be molded by the method of Praznick. 11 refs., 7 figs., 1 tab. (ERA citation 13:047454)