(11d) Carbon Dioxide Capture By an Electrochemically-Mediated Amine Regeneration

With the increasing evidence of global warming and its correlation to carbon dioxide (CO₂) emission, developing cost-effective, large-scale and efficient CO₂ capture technologies is critical. Thermal amine scrubbing is the most developed of these technologies, but is expensive to retrofit it into existing power plants. Recently, we demonstrated an electrochemically-mediated amine regeneration (EMAR) as a low-energy, efficient, and potentially scalable method of capturing CO₂ from flue gas [1, 2]. In an EMAR, the CO₂ rich stream is exposed to electrochemically generated copper ions (i.e., Cu = Cu²⁺ + 2e^−) to destabilize the reaction product of amines and CO₂ and release CO₂. Once the gas is flashed off, the lean loading stream is regenerated via the electrochemical plating of copper from the copper-amine complex (Cu²⁺ + 2e^− = Cu). Therefore, electrochemical modulation of the concentration ratios of cupric ion and amine could afford a rather efficient, energy-saving and absorption-based CO₂ separation process.

The EMAR approach offers several advantages compared to other thermal driven amine-based processes of capturing CO₂. Unlike the thermal processes, EMAR can be operated at low temperatures, thereby minimizing thermal amine degradation. It also offers the possibility to desorb CO₂ at moderate pressures, leading to minimizing the downstream compression costs for CO₂ storage. The modular nature of EMAR, as an electrochemical cell, makes it easier to scale up and to operate with fluctuating loadings.

We studied the kinetics and thermodynamics of the EMAR process. In a rotating disk electrode and using the Tafel expression of the kinetics, we investigated several combinations of metals (the complexing agent), amines and background electrolytes. Among them, an EMAR system based on copper (i.e., Cu/Cu²⁺), ethylenediamine, and sodium sulfate electrolyte was promising. In order to describe the thermodynamics of the system, twelve aqueous speciation reactions are solved simultaneously together with the extended Debye-Hückel activity coefficient model. These kinetics and thermodynamics data can give useful insight into designing an optimized system.

Since EMAR is a relatively new approach for capturing CO₂, there are still many opportunities to further improve the performance of the process. The initially developed EMAR used two identical copper plates as the electrodes. Recently, we studied the importance of the electrode by investigating different carbon-based electrodes (i.e., carbon paper, carbon cloth, carbon felt, and carbon foil). The results showed that the EMAR performance could be improved by using commonly-used and inexpensive carbon felts, mainly due to a lower charge transfer resistance, a higher surface area, and a faster nucleation rates.

The presentation will describe the EMAR process in detail and with updated performance results obtained in the lab-scale setup. The presentation will also highlight the challenges of the EMAR process as well as the various steps being undertaken in order to improve the efficiency of the process.

References

[1] M.C. Stern, F. Simeon, H. Herzog, T.A Hatton, Post-combustion carbon dioxide capture using electrochemically mediated amine regeneration, Energy Environ. Sci. 6, 2013, 2505-2517.

[2] M.C. Stern, T.A Hatton, Bench-scale demonstration of CO2 capture with electrochemically-mediated amine regeneration, RSC Adv. 4, 2014, 5906-5914.