(381r) Modeling Assisted Estimation of Adsorption Kinetics Using Gravimetric Method

Gravimetric techniques such as thermal-gravimetric-analysis (TGA) or dynamic vapor sorption (DVS) are widely used benchtop methods for measuring gas-phase adsorption isotherms. These methods are typically conducted using commercial TGA or DVS instruments. While these instruments can record the temporal variation of the adsorbed gas on the sorbent, this data does not accurately represent sorbent kinetics due to the reduced mass transfer near the sorbent sample caused by the diffusion boundary layer. The temporal data will also be impacted by the quantity of the sample in the chamber and the gas flow rate used in the test. In this presentation, we introduce a computational framework that utilizes computational fluid dynamics (CFD) and adsorption kinetics equations to simulate the mass transfer processes inside the experimental setup and extract the kinetic rate constants averaged over each sorbent particle. To illustrate the effectiveness of our approach, we focus on sorbents employed for CO₂ capture from ambient air. Additionally, we consider sorbents that follow Langmuir isotherm and first-order reaction kinetics, although our approach can be readily extrapolated to other sorbents. By simulating DVS experiments conducted on commercially available sorbent particles, we derive the rate constants. These rate constants are subsequently employed to simulate the breakthrough in a packed bed of sorbent particles. We highlight the disparity between the results obtained using the rate constants from our method and those obtained directly form the DVS data. Notably, our simulations, utilizing the corrected rate constants, exhibit good agreement with experimentally measured breakthrough data measured by flowing ambient air through a packed bed of the sorbent. We also utilize our model to establish a correlation between the DVS data and breakthrough testing with air flow, as expected in direct-air-capture contactors, which is further validated experimentally. Overall, our method provides a convenient approach for approximating kinetics rates of sorbents using benchtop equipment, which is typically employed for obtaining adsorption isotherms. By leveraging computer simulations, we can extract valuable information about the kinetics of sorbents, expanding the capabilities of existing benchtop instruments. This allows for a more comprehensive understanding of the sorption process and facilitates the development of efficient sorbents for various applications.