Silica Gel Supported Solid Amine Sorbents for CO₂ Capture

Point source CO₂ capture (PSCC) is crucial for decarbonizing various industrial sectors, while direct air capture (DAC) holds promise for removing CO₂ directly from the air. Sorbents play a critical role in both technologies, with their performances, efficiency, cost, etc., largely depending on which type is used (physical or chemical). Solid amine sorbents (SAS) employed in the chemical adsorption of CO₂ are suitable for both PSCC and DAC. SAS offer significant advantages over liquid amines such as monoethanolamine (MEA), due to their ability to perform cyclic adsorption–desorption with much lower energy requirement. The environmental concern associated with MEA can be mitigated by SAS. Support materials have a significantly important role in stabilizing amine and enhancing stability and kinetics; varieties of support materials have been screened at a laboratory scale. One promising support material is a silica gel (SG), which is commercially available and attractive for designing cost-effective sorbents for large-scale CO₂ capture. Various impregnation methods such as physical adsorption and covalent functionalization have been employed to functionalize silica surfaces with amines. This review provided a comprehensive critical analysis of SG-based SAS for CO₂ capture. We discussed and evaluated them in terms of their adsorption capacity, adsorption, and desorption conditions, and the kinetics involved in these processes. Finally, we proposed a few recommendations for further development of low-cost, lower carbon footprint SAS for large-scale deployment of CO₂ capture technology.