Non-Aqueous Solvents Unlikely to Present Any Cost Benefit for Post-Combustion CO2 Capture

Abstract

A water-lean solvent for post-combustion CO2 capture was techno-economically assessed and compared with its parent water-based solvent. At a first glance, the use of nonaqueous solvents, appears to offer lower energy requirements and reduced solvent degradation. However, it is necessary to look at the full picture to avoid rushing to develop a concept that may not deliver all that it promises. A nonaqueous solvent technology requires less regeneration energy compared with using standard aqueous amine solvents, especially if combined with a flash vessel instead of a regeneration column, and has a lower amine degradation rate compared with the aqueous solvent. However, using a nonaqueous formulation offers important technical challenges in terms of operability (increased solvent viscosity) and health, safety and environmental risks (higher amine emissions). The economic evaluation shows a hypothetical reduction of 15% in unit total cost based on savings in energy consumption and solvent refill. However, implementing measures to mitigate viscosity changes and amine emissions nullifies these gains. Therefore, no economic improvement over the benchmark is likely from using the nonaqueous version of a solvent. It is expected that the same risks apply for other nonaqueous technologies, so it is very unlikely that a magic bullet will be found to make nonaqueous solvents an attractive option for CO2 capture.