(156e) Scale-up of CO2 Capture from Powdered Sorbent to Sorbent-Washcoated Monolith for Direct Air Capture

A large portion of CO₂ emissions in ~5.2 gigatons (Gt) is released in relatively small quantities from distributed sources emitted each year in the U.S. Therefore, for such emissions, point source CO₂ capture is not feasible and direct air capture (DAC) is an indispensable part of a diversified portfolio of technologies to mitigate U.S. greenhouse gas emissions. Successful DAC technologies require the separation of high purity CO₂ (e.g., >95%) with high selectivity toward CO₂, low energy requirements, minimum chemical and thermal degradations, reliability, long lifetime, etc.

Adsorption-based CO₂ separation for DAC requires low pressure drop and cost-effective supports that are coated with or contain sorbent particles. In this study, a DAC system was scaled up from sorbent in a powdered form to sorbent-washcoated monolith structure. A performance comparison between the two different forms was made between 20 and 35 °C. Adsorption kinetic model plays a key role in interconnecting the two different systems. A CO₂ adsorption kinetic expression for our CO₂ sorbent particles was determined in a continuously flowing reactor. The mass transfer of CO₂ in the porous sorbent bed can be modeled by solving the convection-diffusion equation within the porous sorbent. Intraparticle diffusion of CO₂ inside the sorbent is modeled with adsorption kinetics. CO₂ adsorption isotherm data is obtained for 100-400 ppm CO₂ in ambient air at temperatures up to 35 °C using chemisorption. The adsorption kinetic model is described by coupling air flow with external and intraparticle diffusion. The phase of sorbent particles washcoated onto monolith surfaces was characterized for the morphology and pore data to link to the washcoated phase.

Our CFD model is combined with external mass transfer, CO₂ adsorption kinetics, and pore diffusion. This combined model will predict the performance of volumetric CO₂ productivity in terms of monolithic geometry (i.e., cell size, cross-sectional area, and length), temperature, inlet wind speeds and directions. The model predictions based on this scale-up principle will provide the key design information on overall CO₂ capture efficiency, volumetric productivity, and throughput in terms of dimensions of monoliths including pitch sizes.