(709g) Electrochemical Strategies for Reduction of Greenhouse Gas Emissions

Stern, M. C., Massachusetts Institute of Technology
Hatton, T. A., Massachusetts Institute of Technology
Herzog, H., Massachusetts Institute of Technology

Anthropogenic carbon dioxide (CO2) in the Earth’s atmosphere has been cited as a primary cause of global climate change and threatens global public health and welfare. Carbon Capture and Sequestration (CCS) is an effective and important part of CO2 emission abatement strategies, with the major CCS efforts to date focusing on the removal of directly from large-scale carbon emitters and storing it in secure geologic reservoirs. Thermal-swing operations using aqueous base scrubbing followed by stripping at elevated temperature have been the chemical sorption processes most investigated over the past two decades for CO2 capture. Considerable quantities of steam and heat are required to release the CO2 after capture at low temperatures, and substantial parasitic energy losses result from the need to use excess steam and heat in order to meet the kinetic requirements of the process.

Electrochemically-mediated amine regeneration is a new post-combustion capture technology with the potential to exploit the excellent removal efficiencies of thermal amine scrubbers while reducing parasitic energy losses and capital costs. The improvements result from the use of an electrochemical stripping cycle, in lieu of the traditional thermal swing, to facilitate CO2 desorption and amine regeneration; metal cations generated at an anode react with the amines, displacing the CO2, which is then flashed off, and the amines are regenerated by subsequent reduction of the metal cations in a cathode cell. The advantages of such a process include higher CO2 desorption pressures, smaller absorbers, and lower energy demands. Several example chemistries using different polyamines and copper are presented. Experimental results indicate an open-circuit efficiency of 54% (15 kJ/mole CO2) is achievable at the tested conditions and models predict that 69% efficiency is possible at higher temperatures and pressures. A bench scale system produced 1.6 mL/min CO2 while operating at 0.4 volts and 42% Faradaic efficiency; this corresponds to a work of less than 100 kJ/mole.