Characterization of mass transfer in adsorbents for use in oxygen separation from air.

Abstract

Production of high-purity oxygen from air by pressure-swing adsorption (PSA) is of interest for a variety of applications. One recognized area for which this technology could be particularly useful is the development of a source of medical oxygen for ill or injured astronauts. Currently, medical oxygen in space is provided in the form of compressed oxygen tanks, which are heavy, offer a limited supply of oxygen, and can cause the oxygen concentration limit in the atmosphere of the International Space Station to be exceeded. Oxygen separation by PSA offers potential solutions to each of these problems, but current PSA technologies are still too large and energy-inefficient to be employed in space. Of fundamental importance to the development of next-generation PSA technologies that can meet the demands of space-related applications is the characterization of the adsorption rates of atmospheric gases on new adsorbents.

Frequency response (FR) techniques are among the most effective techniques for studying adsorption rates, as they are able to distinguish between different transport mechanisms that can govern the rate of adsorption. This work comprises FR studies of adsorption rates in gas/adsorbent systems that are vital to the development of rapid PSA technologies designed to produce high-purity oxygen from air. First, a novel apparatus is presented, which is capable of performing three different types of FR experiments. Then, the new apparatus is used to characterize adsorption rates of CO2 on 13X zeolite; pure O2, N2, and Ar on carbon molecular sieve (CMS); binary mixtures of O2 and Ar on CMS; and O2 and N2 on LiX zeolite. In these systems, the governing transport mechanisms are identified and useful rate parameters are measured.

The insights gained through this work should prove useful to the advancement of PSA-based oxygen purification technologies and should also contribute significantly to the broader aim of advancing the present understanding of gas transport in adsorbents.