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

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.