(94g) Does the LDF Approximation Work for Amine Based Adsorbents?

The linear driving force (LDF) approximation is a popular method for estimating mass transfer rates in adsorption processes. For traditional physisorption-based adsorbents, LDF offers a good balance between computational efficiency and accuracy, making it appropriate for process modeling. Direct air capture (DAC) is an emerging technology that utilizes chemisorption via amine-based adsorbents to remove CO2 from air. Unlike traditional adsorption processes, the applicability of LDF to amine-based chemisorbents in DAC is less understood. While some studies suggest LDF's suitability for these adsorbents [1], others propose alternative models that better account for reaction kinetics [2-4].

This presentation investigates the usefulness of LDF for amine-based adsorbents used in Climeworks' solid sorbent DAC technology. Two common methods for estimating the LDF constant - uptake and breakthrough experiments - were employed to collect data for fitting the constant. Since DAC processes encounter varying relative humidity conditions, the experiments were conducted under both dry and wet conditions to assess the impact of moisture on the fitted LDF constant. The presentation will discuss the experimental results and evaluate the practicality of the LDF approximation for modeling DAC processes.

References:

[1] Liu, Hongjun, et al. "Minimal Kinetic Model of Direct Air Capture of CO2 by Supported Amine Sorbents in Dry and Humid Conditions." Industrial & Engineering Chemistry Research (2024).

[2] Vallace, Anthony, et al. "Kinetic model describing self-limiting CO2 diffusion in supported amine adsorbents." Chemical Engineering Journal 472 (2023): 144838.

[3] Elfving, Jere, and Tuomo Sainio. "Kinetic approach to modelling CO2 adsorption from humid air using amine-functionalized resin: Equilibrium isotherms and column dynamics." Chemical Engineering Science 246 (2021): 116885.

⁴Serna-Guerrero, Rodrigo, and Abdelhamid Sayari. "Modeling adsorption of CO2 on amine-functionalized mesoporous silica. 2: Kinetics and breakthrough curves." Chemical Engineering Journal 161.1-2 (2010): 182-190.