Influences of Diamine Molecular Structures on the Phase-Change CO2 Capture From Flue Gas

The amino groups and its substituents of organic amine absorbents have an important influence on the CO₂ absorption and desorption performance. In this study, four diamines with the same primary amino group and another different amino groups were selected as absorbents, including 1,3-propanediamine (1,3-PDA), 3-methylaminopropylamine (MAPA), 3-dimethylaminopropylamine (DMAPA), and 3-diethylaminopropylamine (DEAPA). The phase-change absorption system uses a mixture of polyether and H₂O as the solvent. The CO₂ absorption performance of flue gas was studied with the analysis on absorption and desorption rate, cycle capacity, and desorption ratio. The effect of diamine molecular structures on phase-change CO₂ capture was investigated by nuclear magnetic carbon spectroscopy. The results show that DEAPA exhibits highest absorption capacity of 1.21 mol CO₂/mol amine and recycling capacity of 1.09 mol CO₂/mol amine. The absorption rate of primary and secondary diamines in the phase-change system is significantly higher than that of primary and tertiary diamines. The diamine system with tertiary amino groups has significantly faster desorption rate, higher desorption ratio, and cycle capacity than the primary and secondary diamine systems. The intramolecular tertiary amino group is more conducive to promoting the absorption of CO₂ than the intermolecular tertiary amino group, which can increase the absorption rate of CO₂ by the primary amino group and enhance the CO₂ desorption.