Date of Award

12-2025

Document Type

Thesis

Degree Name

Master of Science (MS)

Department

Mechanical and Civil Engineering

First Advisor

Darshan G. Pahinkar

Second Advisor

Hamidreza Najafi

Third Advisor

Xianqi Li

Fourth Advisor

Troy V. Nguyen

Abstract

Temperature swing adsorption-based (TSA) carbon dioxide (CO2) separation processes, which involve an alternating flow of gases and liquids in adsorbent-coated microchannels, have been shown to yield superior and environmentally friendly performance than the existing processes. This technique begins by sending the impure gas mixture through hydrophobic silicalite adsorbent-coated microchannels, which results in the adsorption of CO2. Subsequently, hot water heat transfer fluid (HTF) flows through the same channels, displaces the purified gas stream, heats the adsorbent, desorbs the CO2, and removes that desorbed CO2 from the channel. This stage is followed by cooling and purging of the liquid in preparation for the next cycle. In this novel TSA cycle, the second or regeneration stage involves a complex and poorly studied set of transport phenomena involving multiphase interaction between hot liquid water HTF, solid adsorbent layer, adsorbed CO2, dissolved CO2, and gaseous CO2. The successful development and deployment of this shared-channel adsorption-driven separation (SCAD) process hinges on a complete understanding of these phenomena. The computational models in this work study the interplay between viscous forces on the liquid HTF and desorbing CO2, and capillary forces on the liquid HTF to track the interface location within the adsorbent layer, which would result in the accurate timescale prediction for the removal of CO2. The gPROMS ProcessBuilder modeling platform is used for solving complex differential equations with an expansive bank of thermophysical property data. Species balance and energy balance, coupled with the momentum balance and adsorption isotherm equations, are implemented to monitor the local and temporal pressure, velocity and concentration variations. The computational models reveal a straw-like movement of liquid water through the porous adsorbent layer, which shows water entering the porous layer guided by capillary forces and then promptly pushed out of the layer with the increase in gaseous pressure attributed to desorption. When the substantial mass of the CO2 is rejected to the channel, then the liquid water begins to move inside the adsorbent layer, which is aided by the capillary effect and absorption of CO2 into water to achieve mechanical equilibrium. These effects are quantified further and incorporated into a comprehensive adsorbent-coated channel model, where the coupled transport phenomena within the adsorbent layer and the channel are also simulated to quantify the amount of CO2 desorbed in such a process as a function of contact angles and temperature. This multiphase and multiphysics analysis is expected to bring new insights into the research field of gas separation systems, especially CO2 removal systems.

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