(45f) Mg(OH)2-Based Sorbents for Combined CO2 Capture and Storage in Gasification Systems
- Conference: AIChE Annual Meeting
- Year: 2013
- Proceeding: 2013 AIChE Annual Meeting
- Group: Topical Conference: Advanced Fossil Energy Utilization
Monday, November 4, 2013 - 10:07am-10:25am
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.