Design of hydrothermally-stable dawsonite-based sorbents in technical form for CO2 capture†
Among prospective sorbents for CO2 capture, systems based on the formation of dawsonite (XAlCO3(OH)2, X = Na, K) have received limited attention, despite displaying attractive reversible uptakes under hydrothermal conditions. Here, we combine a detailed understanding of the nanoscale structural transformations, originating the higher total and net capacity of potassium dawsonite-based systems with respect to those based on sodium dawsonite or hydrotalcite, with the mesoscale challenges faced in translating this promising performance to industrially-relevant, mm-sized shaped forms such as extrudates. In comparison with the extrusion of bulk precursors, the impregnation of alumina bodies uniquely enables the attainment of shaped sorbents of non-negligible porosity and of variable potassium loading and distribution. Examination of internal cross-sections of the sorbents by scanning electron microscopy coupled with energy dispersive X-ray analysis and focused ion beam cutting clearly discerns the critical relation between these parameters and the loss of mechanical integrity due to internal stresses caused by the growth of needle-like dawsonite crystals upon carbonation. The latter can be avoided through the strategic application of common pore formers and binders, resulting in stable performance over multiple cycles without compromising the net capacity, while favourably reducing kinetic limitations observed over densely-packed extrudates. These results unambiguously demonstrate the importance of adopting a multiscale approach for the development of improved CO2 capture technologies.