Role of steam, hydrogen and pretreatment in chrysotile gas–solid carbonation: Opportunities for pre-combustion CO2 capture

Enhancing gas–solid carbonation of serpentines could prefigure the emergence of new dry processes that may compete with aqueous carbonation. The hypothesis of pre-combustion CO2 capture to decarbonize shifted syngas in integrated gasification combined cycle plants was examined in this work from a chemistry standpoint. A systematic gas–solid carbonation study of chrysotile was carried out in a basket reactor using model (H2O/H2/CO2) shifted syngas where CO2 uptakes were measured after 1 h carbonations between 100 °C and 220 °C at 3.2 MPa total pressures. Partial dehydroxylation and steam mediation substantially enhanced meta-chrysotile carbonation achieving uptakes as high as 0.7 CO2 moles per Mg mole at 130 °C. Also, combined X-ray powder diffraction, X-ray photoelectron spectra and CO2 uptake studies indicated that the presence of H2 did not prevent carbonation of meta-chrysotile nor derailed Mg availability towards hydrides or metallic Mg. Chrysotile pre-dehydroxylation in the conditions of gasification was also emulated using catalytic steam reforming of a model-tar compound. However, post-carbonation of spent chrysotile, before and after coke burn-off, achieved at best ca. 0.02 CO2 uptakes suggesting that using the same magnesium silicate batch in gasification then in carbonation may be impractical.

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► Partial dehydroxylation and steam mediation enhanced meta-chrysotile carbonation (uptakes >0.7 CO2 moles per Mg mole at 130 °C).
► H2 did not prevent carbonation of meta-chrysotile nor derailed Mg availability towards hydrides or metallic Mg.
► Chrysotile gasification pre-dehydroxylation emulated using catalytic steam reforming of a model-tar compound prior to CO2 capture.