Better Choice of Tertiary Alkanolamines for Postcombustion CO₂ Capture: Structure with Linear Alkanol Chain Instead of Branched

To give better guidance of tertiary alkanolamine selection with proper structures for postcombustion CO₂ capture, effects of the alkanol chain structure and intramolecular hydrogen bond were investigated. First, water solubilities of 2.5 M aqueous solutions were experimentally investigated for 11 tertiary alkanolamines, and data of boiling point and vapor pressure for pure chemicals were collected also. The physical property results showed a biphasic phenomenon were observed in 2.5 M fresh 1-diethylamino-2-propanol (1DEA2P) solution and CO₂-loaded 4-diethylamino-2-butanol (4DEA-2B) solution, and 1-dimethylamino-2-propanol (1DMA2P) and 1DEA2P have a dramatically relative lower boiling point and a higher vapor pressure, indicating the existence of an intramolecular hydrogen bond, especially in amines with branched alkanol chains. In addition, the pH values for fresh and equilibrium CO₂-loaded amine solutions (2.5 M, 313 K), equilibrium CO₂ solubility (2.5 M, 313 K, and 15 kPa), first-order reaction rate constant (0.1–0.4 M and 313 K), and dissociation constant (293–333 K) were measured, and the results showed amines with linear alkanol chains can have relatively strong basicity, absorption capacity, and a reaction rate with CO₂ owing to weaker influences of the intramolecular hydrogen bond. Finally, the CO₂ capture performance was comprehensively compared by Δ_rG_m and Δ_rH_m screening methods as well as the fast solvent screening method with cyclic capacity, and the results further confirmed that amines with linear alkanol chains can present better CO₂ capture performance, like 3-dimethylamino-1-propanol (3DMA1P) and 3-diethylamino-1-propanol (3DEA1P). It also suggests that the selection or design of tertiary alkanolamines should with the linear alkanol chain instead of branched to have better CO₂ capture performance for industrial applications.