Carbamate Formation and Amine Protonation Constants in 2-Amino-1-Butanol–CO2–H2O System and Their Temperature Dependences

Abstract

The apparent protonation constant of an amino butanol (AB) and its carbamate formation constant in the CO2–H2O–AB system were determined at T = 298.15–328.15 K, and at various ionic strengths up to 0.2 mol·L−1 by potentiometric titration. The Debye–Hückel equation was used to extrapolate the protonation constants to zero ionic strength. The variation of the thermodynamic equilibrium constant for carbamate formation with temperature was modeled according to the relationship of log10 K1 = 280.91/T − 0.1105, while the temperature dependency of the amine protonation constant was correlated by log10 K2 = 1926.53/T + 2.9482. Van’t Hoff type plots of the pK values showed linear relationships indicating that the standard enthalpy changes of reaction are constant over this range of temperatures. Hence, our current findings are crucial for designing efficient unit operations involving separation of CO2 from natural or flue gases.