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 (Na 2 CO 3 (s)) and solid sodium bicarbonate (NaHCO 3 (s)) in different ratios and also trona (Na 2 CO 3 ·NaHCO 3 ·2H 2 O(s)) were allowed to recrystallize and equilibrate with the mixed solvents at the given temperatures. The solubility of CO 3 2- was generally found to decrease with increasing ethylene glycol content irrespective of the occurring solid phase, while HCO 3 - solubility displayed a minimum at (80 to 90) mass % (salt-free solvent) ethylene glycol and then increased sharply. For pure carbonate phases, CO 3 2- solubility displayed little temperature dependence. In equilibrium with mixed carbonate−bicarbonate phases, the CO 3 2- solubility usually decreased with temperature, most likely because it was linked to the HCO 3 - concentration via the solid's solubility product. The solubility of HCO 3 - increased significantly with temperature for all sodium bicarbonate containing solid phases. For the temperature range from (30 to 90) °C and an ethylene glycol concentration range of (50 to 100) mass % (of salt-free solvent), the CO 3 2- solubility varied between (0.058 and 1.023) mol/kg solution, and the HCO 3 - 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. They were identified in the recrystallization experiments as sodium carbonate anhydrate (Na 2 CO 3 (s)), sodium carbonate monohydrate (Na 2 CO 3 ·H 2 O(s)), trona (Na 2 CO 3 ·NaHCO 3 ·2H 2 O(s)), wegscheiderite (Na 2 CO 3 ·3NaHCO 3 (s)), and sodium bicarbonate (NaHCO 3 (s)). No solvate phases with ethylene glycol were observed.