The structure–activity relationships of reaction heat in secondary amine aqueous solutions for CO2 capture

Developing amine solutions with low energy consumption is of great significance for CO2 capture technology. Currently most of studies focused on reducing sensible heat and heat of vaporization by anhydrous absorbents and phase-change absorbents based on amines. It should be noted that CO2 reaction heat of amines is also an important section for energy consumption. In this work, CO2 reaction heat of 7 secondary amines was investigated aiming to reveal structure–activity relationship between CO2 reaction heat and the length of the carbon chain, methyl side chain and hydroxyl group in secondary amines. The CO2 reaction heat of 7 secondary amines was directly measured by microcalorimeter with high precision. Results showed that increasing the length of carbon chain, introducing hydroxyl group and removing methyl side chain in secondary amines could increase CO2 reaction heat. The lengthening of carbon chain and the addition of the hydroxyl group led to an increase in the electronegativity in N atom of the secondary amines, thereby increasing the reactivity and reaction heat of the secondary amine. The steric hindrance caused by methyl side chain reduced the reactivity and reaction heat of secondary amine. This study could help to screen and develop energy-saving secondary amine absorbents for CO2 capture.