High purity hydrogen from biogas via steam iron process: Preventing reactor clogging by interspersed coke combustions

Abstract

Production of high purity hydrogen from biogas by combined dry reforming of methane and steam iron process (SIP), outlines a serious drawback with the possible formation of coke deposits along reduction steps of the iron oxide. Steam used along reoxidations, which regenerates the iron oxide and force the release of high purity hydrogen, could also be responsible of the gasification of such coke deposits and the consequent contamination of hydrogen with carbonaceous species such as CO or CO2. Oxidations at low enough temperature can inhibit coke gasification, but paradoxically, increasing amounts of coke upon repeated cycles will provoke reactor clogging sooner or later. To circumvent this issue, a strategy consisting of interspersing coke combustion stages with diluted oxygen within the regular cycles of reduction with biogas and reoxidation with steam releasing hydrogen, has been analyzed with three solids based on iron oxide. It has been verified that including coke combustion stages within the regular scheme of redox cycles, not only counteracts both bed clogging and catalyst deactivation by coking, but also breaks down the trend to lose (by sintering) active material for the redox process, thus allowing the extension of the useful life of the solid.