(649e) Electrified Low-Temperature Process for CO2 Capture and Conversion

Industrial amine-based CO₂ absorption technologies are used for direct capture from the air, while suffering from low working CO₂ absorption capacities and requiring large amounts of energy (>5.4 GJ per ton of CO₂) to recover only a small fraction (~50%) of the CO₂ trapped from the amine-based solution. The poor energy efficiency and the high operating cost are the major hinderance of the implementation of such units. A Mixed-Salt Process (MSP) that uses a liquid mixture of ammonia, potassium carbonate and water to capture CO₂ (NH₃-K₂CO₃-CO₂-H₂O) has been shown to have high efficiency for CO₂ capture (> 90%), very high CO₂ loading (>10 wt%), a high-pressure CO₂ product (>10 bar), low NH₃ emission, and low reboiler duty (2.0 to 2.3 GJ per ton of CO₂) in a large pilot-scale integrated system [1]. Although the MSP process represents a step-change in solvent-based capture technologies, the energy used in the reboiler is still over 10 times larger than the thermodynamic minimum for CO₂ capture from a power plant exhaust (~200 MJ/ton CO₂). Additional energy inefficiencies in this process arise from large changes in temperature and pressure between the absorber unit (20-40^oC and 1 bar) and the regenerator unit (>120 ^oC and 20 bar) which result in large exergy destruction across the whole process.

A change in paradigm is hence required. Electrochemical cells are uniquely positioned to overcome the problems of industrial amine-based CO₂ absorption technologies mentioned above. In this talk, we present our approach to the minimization of exergy destruction in an electrochemical cell operating at constant temperature and pressure. We present the complete development of an experimental setup that allows the quantification of mass, heat and charge transfer contributions to the release of CO₂ from the MSP electrolyte as well as the direct reduction of amine-CO₂ complexes to fuels and chemicals on the surface of transition metal electrodes. We present detailed experimental procedures to differentiate direct proton-electron coupled electrochemical transformations at electrode/electrolyte interfaces from pH-swing-type mechanisms where the release of CO₂ is the results of changes in local pH environments near electrode interfaces. We also present electrode corrosion challenges that arise in the testing of transition metal electrodes in the MSP electrolytes and offer alternatives on how to reduce these corrosion rates by modifying operating conditions in electrochemical cells.

[1] DOE/NETL Capture Program R&D: Compendium of Carbon Capture Technology, May 2020, https://netl.doe.gov/sites/default/files/2020-07/Carbon-Capture-Technolo...