The relationship between oxidative degradation and ammonia emission of carbon capture amines based on their chemical structures

Abstract

Abstract This work investigates the effect of chemical structural positioning of different functional groups in 29 amines covering primary, secondary and tertiary alkanolamines as well as multi-alkylamines and cyclic amines on both amine degradation and ammonia (NH3) emissions during post-combustion amine-based carbon dioxide capture. The results helped to elucidate possible relationships between degradation and emissions as related to the chemical structure of the amine. The results showed that longer alkyl chain lengths in multi-alkylamines caused a more drastic decrease in both degradation and NH3 emissions followed by secondary alkanolamines. The decrease in those activities for primary and tertiary alkanolamines as well as cyclic amines was low and more so for NH3 emissions. In contrast, the increase in hydroxyl groups in secondary alkanolamines caused a drastic increase in degradation and NH3 emissions. On the other hand, having more hydroxyl groups in sterically hindered primary and tertiary alkanolamines caused a more drastic decrease in degradation and a smaller decrease in NH3 emissions due to the steric hindrance within their structure. An increase in the number of amino groups in an amine caused an increase in both degradation and NH3 emission rates because these provided the reactive sites for the formation of free radicals. This effect was not as large in alkyl-cyclic amines as in multi-alkylamines due to the ability of the former to resist oxidative degradation. Furthermore, branched alkyl groups between amino and hydroxyl groups more drastically increased both the degradation and NH3 emission activities than branched alkyl groups located at the nitrogen atom.