In this talk, we present our computational studies elucidating the anomaly that carbamate formation can be kinetically more favorable than bicarbonate formation at high stripping temperatures (&gt; 400 K) from the reaction between CO2 and 2-amino-2-methyl-1-propanol (AMP) in aqueous solution, while the latter becomes predominant during CO2 capture at low absorber temperatures (&lt; 330 K). This finding provides explanation for the intriguing observation of oxazolidinone formation as the major product of AMP degradation, which is known to occur via carbamate as also seen from thermal degradation of aqueous monoethanolamine (MEA) in CO2 capture processes. From ab initio molecular dynamics simulations coupled with metadynamics sampling, the free-energy barrier for carbamate formation is predicted to substantially decrease with increasing temperature from 313 K to 413 K in 25 wt% AMP solution, whereas that for bicarbonate formation increases. Likewise, the predicted free-energy barrier for carbamate formation in aqueous MEA also decreases with temperature, but significantly less compared to the AMP case. Our further analysis demonstrates that the increase of temperature results in enhancing the disruption of hydrogen-bond network around the basic nitrogen atom of AMP (or MEA), allowing more facile CO2 access to form carbamate. Our work provides new insight into the strong temperature dependence of CO2 capture mechanism and kinetics in aqueous solutions of amines, arising from changes in the hydrogen bond structure and dynamics around amines.

On the origin of peculiar facile carbamate formation at high stripping temperatures from CO2 capture in aqueous 2-amino-2-methyl-1-propanol

ACS Spring Meeting 2021

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