Phase Equilibria for the Glycine–Methanol–NH4Cl–H2O System

An investigation of the phase equilibria of the glycine–methanol–NH4Cl–H2O system was carried out with the objective of optimizing the monochloroacetic acid (MCA) process for the production of glycine. Phase equilibrium of the glycine–NH4Cl–H2O system at temperatures over the range of 283.2–353.2 K was determined for concentrations ranging up to the multiple saturation points. The solubilities of both glycine and NH4Cl were found to increase with increasing temperature, as well as with increasing concentration of other solutes. The Bromley–Zemaitis model for ions and the Pitzer formulation for glycine neutral species implemented in the OLI platform were used in the regression of the experimental solubilities. The average absolute deviations between the regressed solubility values and the experimental data were found to be 1.4% for glycine and 0.93% for NH4Cl. Three binary interaction parameters of the Pitzer formulation were newly obtained and coupled with the Bromley–Zemaitis parameters documented in OLI’s databank to predict the multiple saturation points of the system. Additionally, the solubility of glycine in methanol–H2O mixtures was also measured from 283.2 to 323.2 K, and a sharp decline was observed as a function of the content of methanol. Such thermodynamic information is definitely useful for improving the existing industrial process, as well as providing fundamentals for the development of new glycine production processes.