Production of Very Pure Hydrogen with Simultaneous Capture of Carbon Dioxide using the Redox Reactions of Iron Oxides in Packed Beds

Abstract

A chemical looping process, which uses a packed bed of the various oxides of iron, has been formulated to produce separate, pure streams of H 2 and CO 2 from syngas. The process has the following stages: (1) Reduction of Fe 2 O 3 to Fe 0.947 O in the syngas from gasifying coal or biomass. This stage generates pure CO 2, once the water has been condensed. (2) Subsequent oxidation of Fe 0.947 O to Fe 3 O 4 using steam, to simultaneously produce H 2 . (3) Further oxidation of Fe 3 O 4 to Fe 2 O 3 using air to return the oxide to step 1. Step 1 was studied here using a mixture of CO + CO 2 + N 2 as the feed to a packed bed of iron oxide particles, while measuring the concentrations of CO and CO 2 in the off-gas; step 2 was investigated by passing steam in N 2 through the packed bed and measuring the quantity of H 2 produced. The third step simply involved passing air through the bed. Reduction to Fe, rather than Fe 0.947 O, in step 1 gave low levels of H 2 in step 2 after 10 cycles of reduction and oxidation and led to the deposition of carbon at lower temperature. Step 3, i.e. reoxidizing the particles in air to Fe 2 O 3, led to no deterioration of the hydrogen yield in step 2 and benefited the process by (i) increasing the heat produced in each redox cycle and (ii) preventing the slip of CO from the bed in step 1. The proposed process is exothermic overall and very usefully generates separate streams of very pure H 2 and CO 2 without complicated separation units.