(136e) Electrochemically Modulated Mitigation of Acid Gas Emissions

Authors: 
Hatton, T. A., Massachusetts Institute of Technology
Significant changes in global climate patterns and increasing ocean acidities with their negative impacts on the health of our planet have been ascribed to the ever-increasing rise in atmospheric CO2levels, primarily attributed to anthropogenic sources such as the combustion of fossil fuels. The mitigation of these acid gas emissions is a daunting task, both because of the scale of the problem and because of the economic ramifications associated with the capture of the greenhouse gases and their subsequent utilization or subsurface storage. Effective means for the direct treatment of emissions with CO2concentrations of 5 to 15% from a wide range of sources, such as in the power industries, at industrial facilities and from on-board vehicle exhausts, are sorely needed. Of late, there has also been some interest in the capture of CO2directly from the atmosphere, at concentrations close to 0.04%, which offers its own challenges for implementation.

The traditional means for CO2capture and release generally rely on either chemical or physical absorption in solvents with subsequent heating of the solution to release the captured CO2and regenerate the solvent. The captured CO2can then be compressed for injection and sequestration in subsurface geological formations. These processes require significant energy integration which adds complexity and cost to the overall capture operation. An example is the use of amine solutions where the capture is done at about 40-60°C, while regeneration at temperatures in the 120 to 150°C range is generally required. Isothermal operations that obviate or significantly reduce the heat integration requirements in these processes could have significant advantages over the traditional methods. One such approach is to exploit electrochemical technologies for the capture and release of CO2, which can be operated isothermally, and can rely only on renewable energy resources, if desired.

We will describe two different approaches for CO2capture from a wide range of sources. The first relies on an indirect approach, based on the electrochemical release of a metal ion to an anode chamber to displace the bound CO2on an amine via a competitive complexation process; the CO2can be recovered in a flash tank. The amines are regenerated in the cathode compartment of the cell, where the metal ion is reduced and plates out on the electrode, leaving the amine free for cycling back to the absorber. In the second approach, an electroactive moiety complexes directlywith the CO2upon activation by electrochemical reduction and releases the CO2when it is re-oxidized on reversal of the applied cell voltage.

The general principles underlying these two electrochemically modulated acid gas separation processes will be outlined, with an emphasis on the thermodynamic and transport considerations required for their effective implementation in carbon capture, together with an initial economic evaluation of their performance.