(45f) Mg(OH)2-Based Sorbents for Combined CO2 Capture and Storage in Gasification Systems

Mg-bearing sorbents, specifically solid or aqueous Mg(OH)₂, derived from silicate minerals or industrial wastes, can directly capture and store CO₂ while eliminating an energy intensive sorbent regeneration step. By integrating in-situ mineral carbonation into various energy conversion systems, greater sustainability can be achieved in the use of carboneous fuels. In the water-gas shift reaction, used industrially to tailor synthesis gas composition for downstream applications, gas-solid or slurry phase Mg(OH)₂ carbonation will enhance H₂ production as the CO₂ is converted to MgCO₃ and the equilibrium is shifted. Steam, already a reactant in the water-gas shift, functions as both a H₂ source and carbonation promoter. This work investigates the pathways of enhanced Mg(OH)₂ carbonation at elevated temperatures and CO₂ pressures (up to 400 ºC and 15 atm) in the presence of steam as well as in the slurry phase. The extent of carbonation increases dramatically with increasing H₂O loading. Fundamental mechanisms for water enhanced carbonation are suggested, and the reaction conditions responsible for hydrated and anhydrous carbonate product phases are evaluated. The results suggested that a hydrated environment facilitates the formation of intermediate hydrated magnesium carbonate species, which subsequently decompose to MgCO₃. The carbonation reaction is integrated with the water gas shift reaction in a gas-solid, flow-through reactor and semi-batch slurry reactor to investigate the effect of in-situ carbonation on water-gas shift reaction characteristics, namely enhanced H₂ yield. Optimal reactor arrangements are proposed. Comprehensive solid analyses via TGA, XRD, UV-Raman, and SEM allow for qualitative and quantitative compositional characterizations of reacted solids and micro GC provides online gas phase analysis.