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.