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 ΔrGm and ΔrHm 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.
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