Electrochemically driven carbon dioxide separation

Abstract

This project explored the viability of a Ni(OH) 2 based hydroxide exchange membrane carbon capture (HEMCC) device for direct air capture. It is built off an H 2 fuel cell based HEMCC previously developed in the Yushan Yan group at University of Delaware. Taking the same membrane-based, electrochemically driven pH gradient concept, similar flux performance was able to be seen in the Ni(OH) 2 system as the H 2 system when using comparable current densities. The project produced two types of membrane electrode assemblies (MEA). The first was a traditional MEA with two electrodes and a membrane, the second was a flow-through membrane MEA. Consistent performance was achieved with the traditional MEA with an energy cost of 1.1 MWh∙ton -1 and flux of 82 kg∙m -2 ∙yr -1 . This was the most stable of the two designs. This project investigated strategies to improve performance with a flow-through membrane design. Two designs were made, one with a cast phase inversion membrane, and one with powdered membrane layer. The template phase inversion membrane achieved low pressure drop but had performance limitations due to a skin layer of membrane limiting CO 2 gas transport. The powdered membrane layer had better performance but higher pressure drop. Finally, using the powdered membrane, commercial battery materials were able to be used in order to achieve higher flux. This showed that the flow through membrane design does have the capability to overcome flux inefficiencies in the traditional MEA. Moreover, the process design of the system is proposed and given in this project. The process mass and energy balances were calculated for a reference plant of 1000 t/yr CO 2 capture, which contains several subsystems, e.g. air processing subsystem, electrical subsystem, and CO 2 purification and compression subsystem is designed and evaluated. Based on our calculation, When the power consumption for stack is 1 MWh t -1 CO 2 , Additional 382 kWh t -1 CO 2 will be consumed by other subsystem of the plant, i.e. The total power consumption of 1.38 MWh t -1 CO 2 , lower than the final milestone of 1.5 MWh t -1 CO 2 in this project.