Cyclic water gas shift reactor (CWGS) for carbon monoxide removal from hydrogen feed gas for PEM fuel cells

Abstract

Reduction of the carbon monoxide content in a hydrogen-rich reformate feed gas for fuel cell applications down to a level of 10-50ppm normally involves high and low temperature water gas shift reactors followed by selective oxidation of residual carbon monoxide. In this contribution it is shown that the carbon monoxide content can be reduced in one single reactor, namely by a cyclic water gas shift reaction process (CWGS) which is based on an iron redox cycle. During the reduction phase of the cycle, the raw gas mixture of H 2 and CO reduces a Cr203-Fe 3 O 4 -CeO 2 -ZrO 2 sample, while during the oxidation phase steam re-oxidizes the iron and simultaneously hydrogen is being produced. The activity of Cr 2 O 3 -Fe 3 O 4 -CeO 2 -ZrO 2 was investigated during the reduction by H 2 and CO, and the re-oxidation by H 2 O and CO 2 . The Cr203-Fe304-Ce02-Zr02 showed high activity and stability during 100 repeated reduction/oxidation cycles. Some carbon monoxide in the hydrogen product stream was observed during the re-oxidation phase which was formed by steam gasification of carbon deposited on the iron surface. The carbon formation can be suppressed by controlled oxygen conversion in the Cr203-Fe304-Ce02-Zr02. The investigated cyclic process generated hydrogen with a CO content less than 10 ppm.