Enthalpies of Absorption of Carbon Dioxide in Aqueous Sodium Glycinate Solutions at Temperatures of (313.15 and 323.15) K

The enthalpies of absorption (ΔrH) of carbon dioxide in aqueous sodium glycinate (SG) solutions of 0.10 in mass fraction were determined at temperatures of (313.15 and 323.15) K and a pressure of 12.00 MPa using an isothermal high-pressure flow calorimeter. Very exothermic absorption enthalpies are obtained at the two temperatures studied. ΔrH values expressed in kJ·mol−1 of SG decrease very quickly as CO2 loading increases until saturation is reached; from this point, a slowly decreasing value is obtained for the absorption enthalpy. CO2 loading is expressed as mol CO2/mol amine (α). The calorimetric data provide a means to determine the saturated loading point of CO2 in the solution; values of (0.90 and 0.86) mol CO2/mol SG were estimated for this magnitude at temperatures of (313.15 and 323.15) K, respectively. Enthalpies of solution of CO2 were also calculated. These enthalpies become more exothermic as α decreases until a limit value characteristic of each amine is observed for low CO2 loading. This value can be regarded as the enthalpy of solution at infinite dilution. Limit values of (−72.5 and −59.5) kJ·mol−1 are obtained for SG solutions of 0.10 in mass fraction at temperatures of (313.15 and 323.15) K, respectively. In spite of the complex zwitterionic mechanism involved in the reaction between glycinate and carbon dioxide, SG enthalpies of solution at infinite dilution and SG saturated loading points are of similar magnitude than those previously reported for other primary and secondary amines at the same or similar amine molal concentration and temperature.