Postcombustion Capture of CO2 by Diamines Containing One Primary and One Tertiary Amino Group: Reaction Rate and Mechanism

Developing ideal amine solvents with a high CO 2 absorption capacity and a fast absorption rate is an attractive avenue to advance the amine scrubbing technology. In this regard, diamines bearing one primary and one tertiary amino group (1°/3° diamines) are proposed to be promising solvents for CO 2 absorption, which can exhibit the fast CO 2 absorption rate of primary amines while maintaining the diamines’ intrinsic high absorption capacity. Here, we present a detailed kinetic study of four 1°/3° diamines for CO 2 absorption and investigate the relationship between the structure of various 1°/3° diamines and their CO 2 absorption rate. Results showed that increasing alkyl spacer between two amino groups within 1°/3° diamines promoted the CO 2 absorption rate, while a large decrease in their reactivity with CO 2 was observed when the tertiary amino group existed in the cyclic structure. Among these studied 1°/3° diamines, 3-(dimethylamino)-1-propylamine (DMAPA) displayed the highest absorption rate under relevant conditions and also exhibited higher overall mass transfer coefficients than those of monoethanolamine over the entire range of CO 2 loadings, and the main reaction routes for CO 2 absorption into DMAPA solution via formation of the protonated DMAPA-carbamate were proposed.