Model development and analysis of PSA process for $CO_2$ capture using adsorbents characterized by S-shaped isotherms

Abstract

Adsorbents with S-shaped isotherms have received much attention on effective carbon capture as having high working capacity around their transition points. Despite their potential for reduced energy in gas separations, little research has analyzed pressure swing adsorption (PSA) fashion using these adsorbents at a process scale. The main obstacle of such analysis is the numerical complexity caused by S-shaped isotherms combined with the ideal adsorbed solution theory (IAST) for multi-component adsorption, which aggravates the inherent complexity of a dynamic PSA process model. Herein, this work develops a dynamic model of a PSA process as systems of nonlinear partial differential equations (PDEs) that adopts S-shaped isotherms, overcoming the aforementioned numerical issues. A continuous analytical expression for an S-shaped isotherm with 1-D discretization is applied to simulate the model. The simulation results of each step in the PSA process using flexible metal-organic frameworks (MOFs) are analyzed, and how S-shaped isotherm affects the bed profile is discussed. Lastly, sensitivity analysis on performance indicators of the PSA process is conducted to propose an insight into the proper operation of PSA using adsorbents with S-shaped isotherms.