Fuel Cell Carbon Monoxide Purification

The DOE Fuel Cells for Buildings program is developing PEM fuel cell system components for building cogeneration applications. This fuel cell system uses natural gas as a raw material to produce reformate, which is the feed gas to the fuel cell. Such reformate contains about 2,000 ppm of carbon monoxide. It must be purified to prevent poisoning the fuel cell components, and degrading its performance.

The overall goal of the present program is to develop a catalytic technology for reacting carbon monoxide (CO) with hydrogen, to produce water-soluble products that can be scrubbed from the reformate by water, and discarded or recycled. The technology must operate at near-ambient conditions of temperature and pressure. The objective is to reduce reformate CO concentrations from about 2,000 ppm CO to about 20 ppm CO.

The pilot plant system has been operated for over 1000 hours with two catalytic reactors and a water scrubber. The objective was to demonstrate that the system could operate continuously on a 24/7 basis, for weeks at a time, with low CO concentrations in the effluent gas. The feed gas to the pilot plant was a mixture of hydrogen with 2,000 ppm CO. The operating conditions were about 115oC and less than 2 atmospheres pressure.

During the operating period, the effluent CO from the pilot plant was shown to be reduced to concentrations as low as 10 ppm. In addition, carbon balances were performed around the unit, showing that all the inlet carbon in the carbon monoxide could be accounted for by the measured products. Rigorous Quality Assurance and Quality Control (QA/QC) protocols require such carbon balances, to assure confidence in the validity of the measurements and the successful identification of all important byproducts. Also, tests were performed by saturating the inlet gas with water vapor, to verify that no deleterious catalyst effects would be observed. The unit continued to be able to produce exit carbon monoxide concentrations of about 10 ppm, and 100% accountability was maintained in carbon balances.