Solid–Liquid Phase Boundaries in the System: Glycine–NaOH–NaHCO3–H2O

Abstract

In this work, the solid–liquid equilibrium (SLE) of the systems glycine (Gly)–H2O, Gly–NaOH–H2O, Gly–NaHCO3–H2O, and Gly–NaOH–NaHCO3–H2O was determined using a freezing point depression (FPD) setup. A total of 131 new data points are listed in the concentration range 0 < b (sodium glycinate (SG)) < 25 mol SG/kg water. The system Gly–NaOH–H2O with five different mole ratios (nNaOH:nGly) 1:1, 1:2, 1:5, 2:1, and 5:1 and the CO2-loaded system Gly–NaOH–NaHCO3–H2O were analyzed in a loading range of 0.1–1 mol CO2 per mol SG. Eutectic points and hydrate formations were identified in the systems Gly–H2O, Gly–NaOH–H2O, and Gly–NaOH–NaHCO3–H2O. The solubility of SG increased linearly with higher concentrations for systems with an excess of NaOH. The solubility of SG decreased significantly with an excess addition of NaOH and glycine. The same trend was observed in the CO2-loaded system. The new data create a better understanding of phase equilibria in this system. This understanding is useful for the thermodynamic modeling of the system, which can potentially be used for CO2 capture. The data give a clear representation of the degree of safe operation in terms of managing a plant without solid formation.