(406a) Lithium Silicates for High Temperature CO2 Capture.

Hydrogen is produced from natural gas (or biomass) by the two-step steam-reforming and the water-gas shift reactions. This is an ideal opportunity for process intensification via sorption-enhanced reaction, in which CO₂ is chemically fixed to a suitable sorbent, thus driving the equilibrium produce more hydrogen at lower temperatures. Lithium-based CO₂ sorbents, notably lithium orthosilicates (Li₄SiO_4, or LOS), have been evaluated as candidates for this purpose. A novel surfactant-assisted approach to preparing a nanostructured LOS has been developed by adding a polyether amine surfactant to the sol-gel preparations. The novel synthetic approach generates a product-like precursor phase with nanoscale domains of lithium metasilicate and lithium carbonate stabilized by a carbonaceous component that originates from the degradation of citrate and surfactant species. Preferred LOS compositions sorb 26 wt% CO₂ within 1 minute from a 50 vol% CO₂/N₂ stream and show no observed loss in a 33 wt% working capacity in over 30 one-hour isothermal steam cycles. Physically meaningful rate constants and diffusivities are provided by a piece-wise adaptation of the Ishida and Wen core-shell model, confirming faster reaction and diffusion kinetics for these high-performing CO₂ sorbents. An overall working hypothesis of key results helps to explain robustness in sorption cycling and suggests the advantages of a product-focused sorbent design.