2025 AIChE Annual Meeting

(311d) Multi-Stage Column Design and Simulation of an Electrochemical Reduction Process from Carbon Dioxide to Ethanol

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Authors

Xiaodong Cui - Presenter

Yifei Wang, University of California, Los Angeles

Shruthi Munukutla, University of California, Los Angeles

Dominic Peters, University of California, Los Angeles

Swapnil Varhade, University of California, Los Angeles

James Kastin, University of California, Los Angeles

Carlos Morales-Guio, University of California, Los Angeles

Philippe Sautet, University of California, Los Angeles

Dante Simonetti, UCLA

Panagiotis Christofides, University of California, Los Angeles

Utilization and transformation of CO₂ feedstocks have gained significant attention in recent years [1]. Among the various clean energy technologies, electrochemical CO₂ reduction reaction (CO₂RR) represents a state-of-the-art approach. However, studies focusing on pathway for translating the CO₂RR method into practical industrial production of economically valuable products are still scarce. In this work, a multi-stage electrolyzer column is proposed to convert a CO₂-rich source into a value-added product (i.e. ethanol) via electrochemical reduction. To investigate intrinsic dynamic behavior, a 20-stage column is simulated using continuously stirred tank reactors (CSTRs) in series in Aspen Dynamics. This simulation framework incorporates ion-ion interactions, gas solubility, thermodynamic interaction properties, and vapor-liquid equilibrium using built-in active models. The column is comprised of three separate sections, which transform consecutively CO₂to CO, CO to acetaldehyde and acetaldehyde to ethanol, respectively. Data-driven models based on the coupling of CO₂ mass transport and electrochemical reduction kinetics, initially proposed in [2], are employed to capture the dynamic behavior of these electrochemical reactions. The user-defined mass transport governing equations are implemented to simulate the transient behavior of the electrolysis process between steady-states. To investigate temperature variations in each stage under practical conditions, electrical heating duties are specified for each stage (~360 W per stage). Four heat exchangers are applied to the column electrolyzer to lower the average temperature of the system to the 20-40 ^oC range. At high pressure (~30 bar), the solubility of each gas species remains high enough to facilitate the delivery of reactants (CO₂ and CO) to the catalyst surface to sustain electrochemical reactions. To simulate the practical column, two column diameters are used to maintain a high enough gas linear velocity and a practical pressure drop at each stage. Results demonstrate that with an inlet CO₂ feed of 0.030 kmol/hr, the conversion of CO₂ is approximately 90% and the ethanol production is 0.011 kmol/hr. The total usage of electric power is 7.6 kW, while the heat exchangers remove 1.7 kW. The established model provides a robust basis for subsequent economic column evaluation and machine learning-based model predictive control implementation.

References:

[1] Banerjee, A. and Morales-Guio, C.G., Integrated CO 2 capture and electrochemical conversion: coupled effects of transport, kinetics and thermodynamics in the direct reduction of captured-CO 2 adducts. EES Catalysis 2025,3, 205-234

[2] Morales-Guio, C., Jang, J., Ruscher, M., Winzely, M., Rodriguez, D., Reyes-Lopez, E., Srivastava, S., Christofides, P. and Sautet, P., 2024. Electrochemical CO₂ Reduction Mechanism on Copper: Relation between Mesoscopic Mass Transport and Intrinsic Kinetics. DOI: 10.21203/rs.3.rs-4189647/v1