Solid phases and their solubilities in the system Na₂CO₃ + NaHCO₃ + ethylene glycol + water from (50 to 90) °C

Solubilities in the system sodium carbonate + sodium bicarbonate were measured over a range of temperatures from (50 to 90) °C in mixed aqueous solvents containing (50 to 100) mass % (salt-free solvent) ethylene glycol. Mixtures of solid sodium carbonate anhydrate (Na₂CO₃(s)) and solid sodium bicarbonate (NaHCO₃(s)) in different ratios and also trona (Na₂CO₃·NaHCO₃·2H₂O(s) ) were allowed to recrystallize and equilibrate with the mixed solvents at the given temperatures. The solubility of CO₃^2- was generally found to decrease with increasing ethylene glycol content irrespective of the occurring solid phase, while HCO₃^- solubility displayed a minimum at (80 to 90) mass % (salt-free solvent) ethylene glycol and then increased sharply. For pure carbonate phases, CO₃^2- solubility displayed little temperature dependence. In equilibrium with mixed carbonate-bicarbonate phases, the CO₃^2- solubility usually decreased with temperature, most likely because it was linked to the HCO₃^- concentration via the solid's solubility product. The solubility of HCO₃^- increased significantly with temperature for all sodium bicarbonate containing solid phases. For the temperature range from (30 to 90)°C and an ethylene and glycol concentration range of (50 to 100) mass % (of salt-free solvent), the CO₃^2- solubility varied between (0.058 and 1.023) mol/kg solution, and the HCO₃^- solubility concentration ranged between 0.000 (i.e. the lower detection limit of the analytical method) and 1.153 mol/kg solution. The occurring solid phases were the same as those formed in the aqueous system. The were identified in the recrystallization experiments as sodium carbonate anhydrate (Na₂CO₃(s)), sodium carbonate monohydrate (Na₂CO₃·H₂O(s)), trona (Na₂CO₃ ·NaHCO₃·2H₂O(s)), wegscheiderite (Na₂CO₃·3NaHCO₃(s)), and sodium bicarbonate (NaHCO₃(s)). No solvate phases with ethylene glycol were observed.