Experimental and computational study of the thermal degradation of primary amines used in CO₂ capture

CO2 loaded amine polymerizes during solvent regeneration at temperatures above 100 C-degrees, resulting in the deterioration of solvent performance. Herein, five primary amines were heated to 120, 135 and 150 C-degrees with CO2 loading of 0.4C/N to study thermal degradation. It was found that 2-amine-1-butanol showed the greatest amine loss of 38.5 % after heating to 135 C for 672 hrs while 2-amino-2-methyl-1-propanol was most stable with amine loss of 17.4 % under the same conditions. The degradation products were identified and the reaction pathway was studied through density functional theory (DFT) calculation. Furthermore, the transition state for ring closure and opening reactions was analyzed. The ring closure reaction to form oxazolidinones had a higher energy barrier, showing that it was the limiting step. This is further supported by the good agreement with experimental results. The structure-activity relationship showed the strong steric hindrance effect and the methyl group at beta-carbon improved the amine stability.