Membrane Technology for Carbon Dioxide Separation in Life Support Systems

Future manned space missions and space stations require almost completely closed ECLSS-loops. One important problem is the separation and concentration of CO₂ from cabin air and the subsequent recovery of oxygen. A complete CO₂-processing system has been developed at Dornier consisting of a CO₂-separation and concentration unit (Solid Amine Water Desorption system - SAWD), a catalytic CO₂-methanation reactor (Sabatier) and a process water electrolyzer for final oxygen and hydrogen recovery [1]. The current work intends to develop an appropriate membrane-based process as an alternative to the SAWD-process, in order to reduce energy consumption, volume and weight and to provide continuous operation.

An extended screening of commercially available solution-diffusion membranes has been performed with the result that the polymers cannot meet the requirements for the advantageous replacement of the SAWD-system [2] [3].

A much better performance has been found by using novel carrier mediated transport membranes (facilitated transport). Significant improvements in permeability and selectivity were realized by using the flowing liquid membrane technology.

Another development route consists of using fixed carrier transport membranes (amine bases) and special selective polymer coated substrates.