Bench-Scale Demonstration of Molten Alkali Metal Borates for High-Temperature CO₂ Capture

Abstract

The molten alkali metal borates represent an opportunity for carbon dioxide capture and the on-going challenge of adapting to a carbonconstrained world with the immediacy of climate change. We demonstrate the performance of this new class of materials at the bench scale, highlighting the ability to operate isothermally at high temperatures through the use of steam as a sweep gas. Breakthrough curves for a wide set of conditions are presented and linked to the sorbents' underlying thermodynamic and kinetic properties. We demonstrate the ability to capture over 99.9% of incoming CO 2 even at low concentrations or to capture ∼90% CO 2 under high flow rates and utilize a greater portion of the sorbent capacity. The advantages of the molten alkali metal borates scale well, and their unique position as high-temperature liquid phase sorbents may enable new process designs for efficient low-cost CO 2 capture facilities.

Understanding Material Compatibility in CO2 Capture Systems Using Molten Alkali Metal Borates

“…Nitrogen is an inert gas in this process and extracts CO 2 by reducing the partial pressure of CO 2 . Rather than nitrogen, steam would be used in practice as the steam from the CO 2 /steam product could be condensed and high-purity CO 2 recovered . However, nitrogen is preferred as steam cannot be used reliably within the thermogravimetric analyzer due to challenges with condensation.…”

Sorbents for the Capture of CO2 and Other Acid Gases: A Review

“…This temperature difference may be driven by internal sources from the plant, usually steam, , from external sources such as electricity, , or from a separate high temperature source. , On the other hand, pressure swings involve a difference in partial pressure between the sorber and desorber. When the partial pressure is already high, as in reducing environments, this can simply involve letting the pressure down. , In low pressure settings, a vacuum can drive the same process but requires recompression of the gaseous product. , Another approach is to use a sweep gas that dilutes the product; in this case, a condensable gas, such as steam, is required to ultimately generate a high purity gas product. − …”

“…Molten salts are a recently discovered class of liquid phase sorbent that operate at elevated temperatures. A number of advantages of certain salts for CO 2 capture, including high capacities, fast kinetics, and excellent stability, have been demonstrated with molten alkali metal borates. ,, These materials may be tuned for entirely liquid phase reactions or for the phase change precipitation of reaction products, introducing opportunities to handle captured SO x and NO x impurities . As high temperature liquid phase materials, these sorbents are uniquely positioned, although a number of uncertainties and challenges remain around their corrosive nature and their practical operation at scale. , …”

Net-Negative Emissions through Molten Sorbents and Bioenergy with Carbon Capture and Storage

“…Molten sorbents are liquids under high temperatures at which CO 2 is exposed to the sorbent and separated from the flue gas stream, typically 600–700 °C. , Significant opportunities exist despite the fact that molten sorbents are at a lower technology readiness level than other sorbents. Advantages of molten sorbents include high capacities, fast kinetics, excellent stability, combined capture of multiple acid gases, and low energy penalties. , The work presented here follows the principles presented in our previous analyses, which proposed a conceptual design for a large 800 MW e coal fired power plant. The design places the capture system inside the boiler for high-temperature operation, captures multiple acid gases simultaneously, and uses steam as a sweep gas for sorbent regeneration.…”

“…Advantages of molten sorbents include high capacities, fast kinetics, excellent stability, combined capture of multiple acid gases, and low energy penalties. 24,25 The work presented here follows the principles presented in our previous analyses, 26 which proposed a conceptual design for a large 800 MW e coal fired power plant. The design places the capture system inside the boiler for high-temperature operation, captures multiple acid gases simultaneously, and uses steam as a sweep gas for sorbent regeneration.…”