EXTRACTION OF OXYGEN FROM CO2 USING GLOW-DISCHARGE AND PERMEATION TECHNIQUES

A promising method to extract oxygen from CO2, which constitutes more than 95% of the Mars atmosphere, is by using glow-discharge dissociati on of CO2 combined with the permeation of the generated oxygen through a Ag membrane. Quadrupole mass spectrometry was utilized to measure t he oxygen flux through a 0.35-mm-thick, 2.01 cm(2) area membrane separ ating a two-chamber system. On the upstream side of the membrane, a de glow discharge was established with 350 V and 5 mA current. It was fo und that as much as 75% of the CO2 was dissociated to form CO and O (p art of which recombined to form O-2) The atomic and molecular oxygen g enerated were adsorbed on the membrane surface, subsequently dissolved into the Ag, and diffused through the membrane thickness to the downs tream surface where it desorbed as molecular oxygen. The resulting oxy gen flux was studied as a function of upstream CO2 pressure, discharge current, discharge probe to membrane distance, and membrane temperatu re. It was found that the atomic oxygen generated a much higher concen tration gradient across the membrane than did the molecular oxygen whi ch resulted in a correspondingly higher oxygen flux through the membra ne. The total oxygen flux through the membrane with a CO2 glow-dischar ge pressure of 5 Torr and a membrane temperature of 450 degrees C was found to be greater than 10(14) cm(-2) s(-1). This method can be used to continuously and efficiently supply oxygen for astronauts in a futu re manned mission to Mars. (C) 1996 American Vacuum Society.