Electrochemically-mediated amine regeneration for carbon dioxide separations

Abstract

This thesis describes a new strategy for carbon dioxide (CO₂) separations based on amine sorbents, which are electrochemically-mediated to facilitate the desorption and regeneration steps of the separation cycle. The absorption of CO₂ is accomplished in a similar manner to standard thermal scrubbing techniques. The desorption of the CO₂ from the loaded amines is achieved through the oxidation of a copper metal anode, which generates cupric ions that compete for the amine binding sites. For many amines, the complexation with cupric ions is more favorable than the complexation with CO₂. Reduction of the cupric ions from the amine sorbent onto a separate copper metal cathode regenerates the solution's ability to capture CO₂, completing the capture and release cycle. The electrochemically-mediated amine regeneration (EMAR) process has several advantages over standard thermal scrubbers. EMAR systems do not require reconfiguration of internal turbine systems for low-pressure steam extraction; this makes EMAR more attractive for the retrofit of existing plants. EMAR systems can also generate CO₂ at elevated pressures, reducing the need for downstream compression. A thorough evaluation of 13 metals and 14 amines for the EMAR cycle is presented. Based on cost, amine binding strength, and cation reduction potentials, copper was determined to be the best metal for this process. Polyamines, due to their ability to chelate the cupric ions, were identified as the best amines candidates. Ethylenediamine (EDA) and aminoethylethanolamine (AEEA) were investigated experimentally for their thermodynamic and kinetic properties. For EDA, experiments demonstrated that a system operated at open-circuit could achieve 70% efficiency with respect to a perfectly reversible process. Kinetic experiments and transport modeling are used to extrapolate the performance to a real system operating at closed circuit conditions. A proof-of-concept system was constructed and was capable of separated CO₂ at a rate of 800 sccm/m2 membrane area with an electrical requirement of 100 kJ/mole CO₂. Suggestions and specifications for future designs of next generation bench-scale systems are provided. A techno-economic analysis shows the potential of several configurations of industrial scale EMAR systems compared with thermal scrubbing technologies.