Membrane based CO2 removal from breathing atmospheres

Closed-loop inhabited spacecraft, including a space suit, require removal of carbon dioxide from the breathing atmosphere. A membrane device that separates CO₂ from breathing air can effectively control CO ₂ levels in the breathing loop by venting the carbon dioxide directly to the vacuum of space. Such a membrane device requires no regeneration and, therefore, imposes no limitations on mission length. Systematic studies have expanded our knowledge of the parameters most critical to the successful development of a membrane carbon dioxide removal system. The membrane type disclosed in this paper is an immobilized liquid membrane (ILM) in which the liquid is engineered to facilitate the transport of carbon dioxide while inhibiting the progress of oxygen. Selectivity superior to that achieved in previously published studies has been demonstrated and has approached values desired for an Extravehicular Mobility Unit (EMU) system. Useful membranes for an EMU application must demonstrate selectivity on the order of 3000, which corresponds to oxygen losses only a few percent of metabolic oxygen consumption, and carbon dioxide permeance on the order of 6×10^-4 scc/sec-cm²-cmHg, which corresponds to membrane area of 5.6 m ². This paper describes a variety of immobilized liquid membranes that were tested and will detail the result of CO₂ permeance and CO₂/O₂ selectivity measurements.