Sodium salts solubility in ternary glycerol+water+alcohol mixtures present in purification process of crude glycerol from the biodiesel industry

Abstract

In this work sodium salts solubility data were obtained for relevant systems involved in crude glycerol purification processes. Several binary and ternary mixtures of glycerol + water and glycerol + water + alcohol were saturated with sodium chloride (NaCl), sodium sulfate (Na2SO4) and sodium phosphate (Na3PO4) under different conditions and their respective solubility values were determined. The studied variables were the glycerol:water mass ratio (2:1, 4:1, 9:1), temperature (T = 293, 303 and 313 K) and type and alcohol concentration added to the mixture as anti-solvent at p = 0.1 MPa; ethanol, methanol and isopropyl alcohol were added as anti-solvents from 0 to 70 wt% for NaCl, and up to 40 wt% for Na2SO4 and Na3PO4 (in salt-free base glycerol + water + alcohol mixtures). Solubility, measured as the total content of anhydrous inorganic salt dissolved in the mixtures, was determined gravimetrically and using UV spectroscopy. The obtained results show the best anti-solvent effect by isopropyl alcohol followed by ethanol, with major efficiencies observed at higher alcohol concentrations. The water content in the mixture increased sodium salts solubility. Na3PO4 exhibit the lowest solubility values in the studied systems. Temperature effect was almost negligible in the studied range.