Anomalous Facile Carbamate Formation at High Stripping Temperatures from Carbon Dioxide Reaction with 2-Amino-2-methyl-1-propanol in Aqueous Solution

Based on first-principles simulations, we present that carbamate formation can be kinetically more favorable than bicarbonate formation at high stripping temperatures (>400 K) from the reaction between CO2 and 2-amino-2-methyl-1-propanol (AMP) in aqueous solution, while the latter tends to be predominant during CO2 capture at low absorber temperatures (<330 K). This finding offers 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 from 11.7 to 5.5 kcal/mol with increasing temperature from 313 to 413 K in 25 wt % AMP solution whereas that for bicarbonate formation increases from 9.6 to 12.4 kcal/mol. Likewise, the predicted free-energy barrier for carbamate formation in aqueous MEA also decreases with temperature but is significantly less compared to the AMP case. Further analysis demonstrates that the increase of temperature results in enhancing the disruption of the 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 on the strong temperature dependence of the CO2 capture mechanism and kinetics in aqueous solutions of amines, arising from changes in the hydrogen bond structure and dynamics around amines.