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.

Use of heavy fraction of bio-oil as fuel for hydrogen production in iron-based chemical looping process

“…In CLH process, the reaction scheme of iron oxide reacting with the fuel in FR is more complicated than the oxidation reactions occurred in SR and AR [26,27]. The reduction of Fe 2 O 3 generally occurs with the formation of different iron oxides at lower valent state or metallic Fe depending on the employed operating conditions and the properties of oxygen carrier.…”

Phase distribution and stepwise kinetics of iron oxides reduction during chemical looping hydrogen generation in a packed bed reactor

“…Bohn et al [32] proposed Fe 2 O 3 /FeO as the proper redox couple for stable H 2 production in a packed bed reactor because reduction reactivity was lost when Fe 2 O 3 was reduced to Fe. Then, Kierzkowska et al [33] suggested that the addition of 40 wt.…”

Experimental investigation of chemical-looping hydrogen generation using Al 2 O 3 or TiO 2 -supported iron oxides in a batch fluidized bed

“…Bohn et al [39] simulated CLHG in a packed bed and obtained hydrogen suitable for use in fuel cells (<25 ppm vol CO). It was suggested that the further reduction of FeO to Fe in the reduction phase was not recommended, because the reactivity of the iron oxide went bad after ten cycles.…”