(304c) Coupling Accelerated Mineral Carbonation and Direct Air Capture Processes

Global warming and climate change concern sparked significant interest in gigaton scale direct air capture (DAC) of carbon dioxide. Alkali hydroxide solutions such as sodium hydroxide solution are the benchmark solvents for CO₂ reactive absorption from thin air¹. However, recycling sodium hydroxide from aqueous sodium carbonate solution, which is the product of CO₂ absorption, is critical for the success of the process. Technologies based on lime-soda ash were previously proposed, which however requires regeneration of lime by high-temperature calcination². Also, the generated pure CO₂ from calcination needs to be sequestered through additional chemical production or geological storage processes. Instead, coupling of accelerated mineral carbonation and sodium hydroxide-based DAC process would remove the need for lime and energy-intensive calcination. Mineral carbonation works by converting Ca-rich aluminosilicate minerals or industry-derived residues into calcium carbonate in an aqueous solution. For successful coupling with DAC, we proposed to accelerate the slow carbonation of silicates in alkaline media (pH>12). So far, researchers mainly preferred acidic media for enhancement of its rate and alkaline pH received little attention. Based on our new observations in the silicate dissolution-carbonation mechanism, the solution chemistry of carbonate-bearing solutions may be tailored to achieve high carbonation efficiency. Using coal fly ash as an example, we present the ash carbonation kinetics and its dependence on solution chemistry and mineral phase heterogeneity. We will discuss the challenges with other feedstocks and present far-from-equilibrium thermodynamics as a new tool for rapid feedstock screening and process design.

References:

1. Lackner, K. S. et al. The urgency of the development of CO₂ capture from ambient air. Proc. Natl. Acad. Sci. U. S. A. 109, 13156–13162 (2012).
2. Sanz-Pérez, E. S., Murdock, C. R., Didas, S. A. & Jones, C. W. Direct Capture of CO2 from Ambient Air. Chem. Rev. 116, 11840–11876 (2016).