Electrochemically Enhanced Amine Regeneration Process for Next Generation Carbon Dioxide Capture
- Tseng, Yen-Wen
- Advisor(s): Simonetti, Dante
Resulting of fossil fuel usage, CO2 concentration in the atmosphere has increased drastically throughout the past century. This increase in CO2 concentration has led to global warming and more frequent extreme weather events that threaten the habitability of the planet. Therefore, it is essential to decrease the CO2 concentration in the atmosphere to mitigate global warming. Post-combustion capture using amine absorbent is one of the most widely used methods, given its feasibility in retrofitting existing fossil fuel-consuming facilities. However, several challenges, including high energy requirements and low cyclic capacity, limit the commercialization of the post-combustion capture technology. In this work, an electrochemically enhanced amine regeneration process is developed to tackle these challenges. The electrochemically enhanced amine regeneration system utilizes the hydrolysis reaction, generating proton and hydroxide to complete an acid- and base-swing regeneration cycle. The electrochemical amine regeneration cell was constructed by stacking multiple ion exchange membranes, acrylic spacers, and rubber gaskets. Several studies were conducted to test, build and optimize the electrochemical amine regeneration system. Amine absorption and desorption baseline were established in different amine-based absorbents to understand the CO2 absorption and desorption profile. Proton-induced CO2 desorption from the absorbent was studied by HCl addition to the CO2-loaded amines. This study validated that complete CO2 desorption can be achieved under ambient temperature. The regeneration of amine by the combination of acid-swing and base-swing was validated by HCl and NaOH addition. The electrochemical cell was then used to perform the acid swing. Different cell structures, exchange membranes, and ionic solutions usage were tested. The acid swing of amine and complete CO2 desorption can be achieved using a four-compartment cell. The base swing of acidified amine was performed by anion exchange. It is validated that electrochemical acid-swing and anion exchange base-swing can successfully regenerate amine. The reabsorption capacity of regenerated amine is the same regardless of the regeneration method used. The optimization study of the electrochemical amine regeneration system focuses on improving energy efficiency and reducing process complexity. Proton requirements for complete CO2 desorption and CO2 loading capacity of various amine absorbents were characterized. It is found that Piperazine has the lowest proton to CO2 ratio, which will result in less energy requirement for electrochemical amine regeneration. A five-compartment electrochemical cell is designed to replace the need for anion exchange resin for base swing. It is validated that the five-compartment cell can complete acid-swing and base-swing to achieve amine regeneration in a continuous operation mode. This cell design reduces the complexity of the process, increases energy efficiency, and facilitates the system's scale-up. In conclusion, an electrochemical amine regeneration system has been developed. Compared to the state-of-art method, it can achieve >80% cyclic capacity with low energy consumption. With further optimization studies, the energy consumption can be further reduced, and this system can potentially serve as the method for the next generation of CO2 capture.