Acid Gas Capture at High Temperatures Using Molten Alkali Metal Borates

Abstract

Materials designed for CO 2 capture provide both an opportunity and a challenge in that industrial emissions typically contain an assortment of acid gasses, which may include SO x and NO x alongside CO 2 . Growing pressure to reduce emissions of all acid gasses, CO 2 included, presents an opportunity for simultaneous capture and a challenge in handling the resultant products. Molten alkali metal borates embody a new class of hightemperature liquid-phase materials for carbon dioxide capture and we propose here that they can also be used to address the more general challenge of acid gas capture. We examine the melt capture performance at industrially relevant concentrations and mixtures, identifying the various reaction mechanisms and products, and propose designs for separating these products efficiently at high temperatures, so that they outperform the stateof-the-art CO 2 capture technologies in handling this opportunity challenge. We also discuss the conditions to avoid and the challenges that lie ahead for these materials in the context of emission reduction and environmental protection.

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

“…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. , …”

“…With growing concern for the environment, there has been an emerging interest in removing all acid gases at the same time. A number of sorbents have been proposed for the simultaneous capture of multiple acid gases, avoiding the need for sequential contacting units. ,, Strategies for handling multiple acid gases are necessary even with sequential units, however. Since complete removal is rarely feasible, downstream units will be exposed to, and usually interact with, other acid gases in either case.…”

“…97,124,125 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. 304 As high temperature liquid phase materials, these sorbents are uniquely positioned, although a number of uncertainties and challenges remain around their corrosive nature 305 and their practical operation at scale. 136,306 7.9.…”

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

“…As with the conventional process, lime is used to form gypsum. The aqueous sorbent, which may be returned to the high-temperature absorber/desorber cycle, is recovered …”

“…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.…”