Indicators of good-performance absorbents

https://doi.org/10.3389/fenrg.2021.785039

“Good-performance absorbents can greatly reduce the operating cost of the capture process and generally need to have the following properties (Liang et al., 2015): the cyclic capacity is high, the reaction kinetics is fast, the heat of absorption is relatively low, the resistance to oxidative and thermal degradation is high, and the corrosivity, volatility, viscosity, and cost are low. The high CO₂ cyclic capacity can reduce the solution’s circulation flow rate, thereby reducing the power of the pump and the energy consumption of the reboiler. The fast absorption kinetics reduces the size of the absorbers and strippers and also the maximal achievable rich loading, thereby reducing operating costs. The relatively low heat of absorption can help reduce the regeneration duty. The resistance to oxidative as well as thermal degradation is correlated with the quantity of solvent make-up as well as byproduct emissions to environment and volatility to the quantity of amine loss as well as emission. The low-viscosity solvents enhance mass and heat transfer, thus reducing the amount of packing and the size of the heat exchanger. Different amines have different molecular structures and absorption mechanisms, resulting in different absorption characteristics. There is a fast reaction rate, a low CO₂ cyclic capacity, and a high absorption heat for the primary and secondary amines (Rinker et al., 2000). On the contrary, tertiary amines and steric-hindered amines have a high CO₂ cyclic capacity, a slow absorption rate, and a low absorption heat (Dubois and Thomas, 2012). A mixed-amine system—mixed solvent of amines with different reaction mechanisms—combines the advantages of two alcohol amine solutions: a high CO₂ cyclic capacity, a low heat of absorption, and a fast absorption rate. Activators are usually added to steric-hindered amines or tertiary amines to increase the absorption rate. Monoethanolamine (MEA) and piperazine (PZ) are the most commonly used activators, and related mixed amine systems have been extensively studied (Aronu et al., 2011; Choi et al., 2009; Dash et al., 2011; Mandal et al., 2001; Puxty and Rowland, 2011; Sakwattanapong et al., 2009).”