Liquid–Liquid–Solid Equilibria in the Ternary System Water–Phosphoric Acid–Cyclohexane at 25 and 35 °C: Stability Domain of Hemihydrate and Anhydrous Phosphoric Acid

Abstract

The water−phosphoric acid−cyclohexane ternary system was studied at 25 and 35 °C under atmospheric pressure, and the binodal curve was determined by the cloud-point method. In addition, the isoplethic section between 2H 3 PO 4 •H 2 O−cyclohexane was investigated using a Tammann diagram based on the thermal analysis of different samples with the determination of hemihydrate melting temperature. The concentration of phosphoric acid and cyclohexane was assayed by volumetric titration and gas chromatography, respectively; the amount of water was calculated by the material balance equation. The miscibility between phosphoric acid and cyclohexane was found to be very low with the appearance of a three-phase stability domain liquid−liquid−solid by the presence of phosphoric acid crystals: hemihydrate (2H 3 PO 4 •H 2 O) and anhydrous phosphoric acid (H 3 PO 4 ).

Enhancement of Orthophosphoric Acid Extraction by the Synergic Effect of Tributyl Phosphate and Methyl Isobutyl Ketone in the Quaternary System H2O–H3PO4–TBP–MIBK at 298.2 K

“…The first step consists of delimiting the demixing region for the ternary systems and the isoplethic sections for the TBP/MIBK mass-percent ratios (30/70, 50/50, and 80/20). Therefore, the composition of binodal curves was determined using the cloud point method, ,− and the specific procedure is described as follows: a binary mixture of water + phosphoric acid or solvent + phosphoric acid was first placed in a 250 mL double-walled beaker powered by a VWR 1197P thermostat under magnetic stirring. Water or solvent was then added dropwise using a microburet of 5 mL (±0 01 mL) under stirring until the cloud point appeared.…”

“…The purity of the raw materials was given by the supplier, while the composition of P 2 O 5 was verified by volumetric titration using NaOH, and water used throughout the process was deionized with a conductometric value of 5 μS at 290.2 K. Pure phosphoric acid was prepared using phosphorus pentoxide (P 2 O 5 ) and deionized water, while the composition was verified by volumetric titration using sodium hydroxide (NaOH). The experimental setup and the reliability of the equipment were described previously, − and all measurements were done using an analytical balance with a ± 0.0001 g precision.…”