Electrochemical CO2 Reduction to Ethanol: Comparison of Cell Designs, Process Modeling, Downstream Processes, and Techno-Economic Assessments

Abstract

The electrochemical carbon dioxide reduction reaction (CO2RR) is of increasing importance for the development of a closed carbon cycle. Ethanol is an attractive target product due to its high energy density and large market size. Therefore, publications describing the CO2RR to ethanol are first compared. Both flow cells and zero-gap cells show the most promising results. However, this work has shown that accumulation of liquid organic products in the catholyte of a flow cell would lead to a significant increase in the overpotential. The resulting low concentration of products in the catholyte (<3.5 mol %), which should not be exceeded, leads to high separation costs. Consequently, a downstream process is developed based on the product stream of the most promising CO2RR in a zero-gap cell. Afterward, a techno-economic assessment (TEA) of the entire process from CO₂ capture to CO2RR to product purification was performed. The electricity for the CO2RR is still the main cost driver, followed by the CO₂ recovery, whose costs are caused by the low single-pass CO₂ conversion. Strategies for improving the entire process are outlined, and an Excel calculation tool for adapting the TEA is provided.