Solid-liquid equilibria in the ternary NaBr-Na2CO3-H2O system at (298.15, 323.15 and 368.15) K and its application

Abstract

To comprehensively utilize the waste residue produced in pure terephthalic acid (PTA) production, the ternary NaBr-Na2CO3-H2O system at (298.15, 323.15 and 368.15) K were investigated by using the isothermal dissolution equilibrium method, and the corresponding equilibrium phase diagrams were plotted. There are six invariant points, nine univariant curves, nine single salt crystallization regions and six cocrystallization zones in total in the diagrams. Pitzer and HW models were combined with experimental data to fit out the ion interaction parameters θBr-CO3 and ψNa-Br-CO3 at different temperatures. There is an excellent agreement between the calculated and experimental solubilities. The purity of sodium bromide in the waste residue was increased to 97.67% using the ternary NaBr-Na2CO3-H2O system at 368.15 K, and then a small amount of sulfuric acid was added. With the ternary NaBr-Na2SO4-H2O system at 308.15 K, the purity of the obtained NaBr production could reach 99.48%, which met the superior product requirement of HGT 3809–2006. Meanwhile, Na2CO3 obtained in this separation process can be reused in PTA production with a recovery of 99.46%.