A Gas Separation Membrane Highly Selective to CO
in the Exhaust of Internal Combustion Engines
Southwest Research Institute has developed a passive, flow-through, membrane which separates carbon dioxide (CO2) from other exhaust gas species. Stoichiometric exhaust gas for 0% ethanol fuels contain approximately 14% CO2 by concentration. The membrane consists of a ceramic substrate impregnated with lithium zirconate (Li2ZrO3). In the presence of temperatures of 400-600 °C the CO2 reacts with lithium zirconate to form lithium carbonate (Li2CO3). The new compound moves from the inner surface of the membrane via partial pressure gradient to the outer wall of the membrane and desorbs into a low concentration CO2 environment, e.g. atmospheric air with 400 ppm CO2. SwRI has tested the membrane under engine-like conditions, comparable to 2000 rpm 10 bar BMEP operation, on a standalone burner rig (ECTO-lab burner). On the SwRI ECTO-lab burner rig temperature, flow-rate and exhaust gas products can be independently varied. Results confirmed that the 150 mm membrane section could selectively reduce the CO2 concentration by 5% from the inlet to the outlet of the membrane. Tests were also performed under rich exhaust conditions with increased carbon monoxide (CO) concentrations and determined that the membrane preferentially separates CO vs CO2. The membrane design and fabrication are discussed in the paper along with potential applications for the technology, namely as a method to alter exhaust-gas recirculation composition for improved performance.