CO2 capture materials for sorption enhanced steam reforming

The Ca-looping cycle is a chemical process that alternates capture and release of CO2 using a Ca-based sorbent which can be applied to hydrogen production by steam reforming.
Adding sorbent particles to the reformer achieves nearly pure hydrogen with higher yields via the ‘sorption enhancement’ effect. The major disadvantage is deactivation of the sorbent following multiple cycles and suggested solutions have been incorporation of inert material and
regeneration by hydration. This work investigates Ca-based sorbents with a focus on their use for steam reforming of liquid feedstock.

Thermodynamic analysis was used to understand the equilibrium of the steam reforming of three different feedstocks with and without CaO as the sorbent. Addition of sorbent significantly increased the H2 yield and the H2 molar fraction for all three feedstocks.

Inert material was incorporated into CaO and CaO derived from Ca-D-gluconate. The resulting sorbents were investigated using thermogravimetric analysis (TGA) and a bench scale reactor in combination with X-ray diffraction (XRD) and N2 adsorption. Incorporation resulted
in a reduction in pores in the 50-100 nm size range and caused self-reactivation behaviour over multiple cycles. The capture capacity and morphology of the sorbent was altered by the CaO precursor but XRD spectra were not.

In situ XRD coupled with Rietveld refinement yielded new insights into the mechanism of Ca-based carbonation and sorbent stability. Agreement between in situ XRD and TGA data was found for carbonation of CaO and Ca(OH)2, and the mechanism of CO2 capture in partially hydrated CaO was investigated. Ca(OH)2 formed CaCO3 without the CaO intermediate, and anisotropic diffraction peak broadening was observed in the partially hydrated sorbent.

Steam reforming of ethanol and glycerol with and without a Ca-based sorbent was investigated using a novel reactor featuring a nichrome resistance wire with a heating
element/catalyst double function. Wire morphology had significant impact on feedstock conversion and the activity of the wire could be increased using a redox pretreatment which caused the formation of chromium oxides on the wire surface. The addition of sorbent by coating resulted in CO2 capture but not sorption enhancement. The coating also hindered water gas shift and eroded with time on stream.