The molten alkali metal borates represent an opportunity for carbon dioxide capture and the on-going challenge of adapting to a carbon-constrained 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 CO2 even at low concentrations or to capture similar to 90% CO2 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 CO2 capture facilities.