Influence of CO₂ on the Solubility of Potassium Glycinate in Glycine–KOH–H₂O, Glycine–KHCO₃–H₂O, and Glycine–KOH–KHCO₃–H₂O

Abstract

In this study, solid–liquid equilibria (SLE) were measured in the systems glycine (Gly)–KOH–H2O, Gly–KHCO3–H2O, and Gly–KOH–KHCO3–H2O using the method of freezing point depression (FPD). A total of 211 new data points are presented in the concentration range 0 < b (potassium glycinate (PG)) < 28 mol of PG/kg of water. The PG solubility was measured for the systems Gly–KOH–H2O and Gly–KHCO3–H2O with mole ratios of 1:1, 1:2, 1:5, 2:1, 5:1 (n KOH:n Gly) and 1:1, 3:1 (n KHCO3 :n Gly). Eutectic points were identified in these systems. The SLE of CO2 loaded systems Gly–KHCO3–H2O and Gly–KOH–KHCO3–H2O were studied in order to identify the limits for safe operation of a carbon capture plant. Results revealed that PG (n KHCO3 :n Gly, 1:1) was less soluble in a 0.5 mol of CO2/mol of PG loaded solution than in a 0.1 mol of CO2/mol of PG solution. The understanding of the solubility of aqueous PG solutions with and without the influence of CO2 is critical in order to avoid precipitation issues related to solvent mixing, solvent handling, and during operation of a carbon capture plant. The data are important for the development of thermodynamic models.