(628d) Adsorption Kinetic Model for Direct Air Capture

A large portion of CO₂ 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 is an indispensable part of a diversified portfolio of technologies to mitigate U.S. greenhouse gas emissions. Successful direct air capture (DAC) technologies are required to separate high purity CO₂ (e.g., >95%) with high selectivity toward CO₂, low regeneration energy requirements, minimum chemical and thermal degradation, reliability, long lifetime, etc.

Adsorption kinetic model plays a key role in designing DAC systems. In this study, an adsorption kinetic model for our CO₂ sorbent has been studied for DAC potential by integrating CO₂ adsorption kinetics with a flow model. 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 400 ppm CO₂ in ambient air at temperatures up to 40 °C and relative humidity using chemisorption. The model will couple the adsorption kinetics with external and intraparticle diffusion.

After the model result is validated with lab-scale experimental data, the model is used to investigate the direct effects of system parameters on the overall CO₂ capture efficiency and flow throughput for the design of a DAC system. Currently, the sorbent is to be washcoated onto monolith to be installed inside the DAC system. This model predictions will provide the key design information on overall CO₂ capture efficiency, volumetric productivity, and throughput in terms of dimensions of monoliths including pitch sizes.