Effect of alkanol chain length of primary alkanolamines and alkyl chain length of secondary and tertiary alkanolamines on their CO2 capture activities

The effect of the alkanol chain length in primary alkanolamines and the alkyl chain length in secondary and tertiary alkanolamines on CO2 absorption and desorption kinetics, equilibrium CO2 loading, heat duty, cyclic capacity, and pKa were studied. A selection strategy developed in our earlier work was used to identify potential solvents which could be used in a blend. Based on the strategy, alkanolamines that had a combination of high absorption parameter and high desorption parameter should be selected. The results of this study showed that, for absorption parameters, longer alkanol chain lengths of primary alkanolamines and longer alkyl chain lengths of secondary and tertiary alkanolamines led to higher equilibrium CO2 loading and pKa. However, the influence of mass transfer limitations on these positive effects resulted in a maximum trend for initial rate of CO2 absorption for secondary and tertiary alkanolamines. On the other hand, for the desorption parameters, the increase in the chain lengths also caused the generation of larger amounts of bicarbonate ions which resulted in higher CO2 desorption rates and cyclic capacity, but lower heat duty. However, the longer chain alkanolamines also had high viscosities which adversely modified their performance by also introducing mass transfer limitations. Based on chain length alone, BMEA came out as the best overall alkanolamine component which could be used in a blend.