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

Abstract

The processes that produce CO 2 and other acid gases (SO x , NO x , and H 2 S) generate value for society. However, these gases are environmental pollutants, and their emission into the atmosphere undermines the value they create. In the face of climate change, CO 2 emissions require attention on an unprecedented scale. Abatement technologies focused on carbon capture, storage, and utilization (CCUS) enable the continued use of processes and resources that produce CO 2 (and other acid gases) while minimizing their effect on the environment. This review explores the role sorbents play in emission abatement and the acid gas "economy". We identify 15 sorbent categories, evaluating their performance at both the material and the system levels. We conclude with anticipated research opportunities and future trends in acid gas separation.

Capture and electrochemical conversion of CO2 in molten alkali metal borate–carbonate blends

“…12,17 Such behavior of the molten borates in a cyclical absorption–desorption process was ascribed to the “instantaneous” formation of carbonate salts and their subsequent dissociation resulting in carbonate ions being present in the borate without the diffusional transport restrictions imposed by solid product layers characteristic of solid adsorbents. 11–19…”

“…Our group has advanced molten alkali metal borates such as lithium borate (Li 3 BO 3 ) and mixed lithium, sodium borates as reversible CO 2 sorbents due to their large and temperature-reversible sequestration capacity for CO 2 and acid gases, which generally exceeds the capacity of other molten salts. 11–19 Thermoreversible reactions of the alkali metal borate glasses with CO 2 are well-documented. 11–20 The chemisorption of CO 2 by alkali metal (M) borate M 3 BO 3 results in the reversible formation of carbonate (M 2 CO 3 ), metal oxide (M 2 O)–boron oxide (B 2 O 3 ) binary compounds, and metaborate (MBO 2 ) as follows.4M 3 BO 3(l) + 3CO 2(g) ↔ 3M 2 CO 3(l) + M 6 B 4 O 9(l) 4M 3 BO 3(l) + 5CO 2(g) ↔ 5M 2 CO 3(l) + M 2 B 4 O 7(l) M 3 BO 3(l) + CO 2(g) ↔ M 2 CO 3(l) + MBO 2(l) 2M 3 BO 3(l) + 3CO 2(g) ↔ 3M 2 CO 3(l) + B 2 O 3(l) (M = Li, Na, K, etc .…”

“…11–19 Thermoreversible reactions of the alkali metal borate glasses with CO 2 are well-documented. 11–20 The chemisorption of CO 2 by alkali metal (M) borate M 3 BO 3 results in the reversible formation of carbonate (M 2 CO 3 ), metal oxide (M 2 O)–boron oxide (B 2 O 3 ) binary compounds, and metaborate (MBO 2 ) as follows.4M 3 BO 3(l) + 3CO 2(g) ↔ 3M 2 CO 3(l) + M 6 B 4 O 9(l) 4M 3 BO 3(l) + 5CO 2(g) ↔ 5M 2 CO 3(l) + M 2 B 4 O 7(l) M 3 BO 3(l) + CO 2(g) ↔ M 2 CO 3(l) + MBO 2(l) 2M 3 BO 3(l) + 3CO 2(g) ↔ 3M 2 CO 3(l) + B 2 O 3(l) (M = Li, Na, K, etc . ).…”

A State‐of‐the‐Art Update on Integrated CO2 Capture and Electrochemical Conversion Systems

“…Besides the well‐established processes based on amine and alkaline media, different sorbents have been investigated as agents for CO 2 capture [72] . Among these, two types are prominent, whose directed design leads to a wide range of application‐directed materials: ionic liquids (IL), a type of liquid sorbent, previously mentioned as an alternative for the amine scrubbing, and covalent organic frameworks (COFs), a solid sorbent [73] .…”

“…Besides the well-established processes based on amine and alkaline media, different sorbents have been investigated as agents for CO 2 capture. [72] Among these, two types are prominent, whose directed design leads to a wide range of application-directed materials: ionic liquids (IL), a type of liquid sorbent, previously mentioned as an alternative for the amine scrubbing, and covalent organic frameworks (COFs), a solid sorbent. [73] Changing the combination of cations and anions of ILs or the organic precursors of the COFs, their characteristics can be tuned, for example for an increased selectivity towards CO 2 , which is important for the capture from sources with a low concentration of CO 2 or a mixture of gases.…”