Phosphoric acid phase diagrams

Fig. 5. Vapoi—liquid phase diagram of the H2O—P20 system at 101 kPa (1 atm), where 3 is ortho, 2 pyro, and 1 meta phosphoric acid. The soHd line...

Orthophosphate salts are generally prepared by the partial or total neutralization of orthophosphoric acid. Phase equiUbrium diagrams are particularly usehil in identifying conditions for the preparation of particular phosphate salts. The solution properties of orthophosphate salts of monovalent cations are distincdy different from those of the polyvalent cations, the latter exhibiting incongment solubiUty in most cases. The commercial phosphates include alkah metal, alkaline-earth, heavy metal, mixed metal, and ammonium salts of phosphoric acid. Sodium phosphates are the most important, followed by calcium, ammonium, and potassium salts. 

Mg(H2P04)2.4H2O as was the case in the reaction between MgO and simple phosphoric acid solutions. Inspection of the diagrams of Belopolsky, Shpunt Shulgina (1950) shows that newberyite is the stable phase at lower concentrations of phosphate. Presiunably, in the present case, aluminium locks up some phosphate and so reduces the phosphate available for the magnesium phosphate phase. 

Fig. 11.12. Schematic diagram of a column-switching HPLC system. V-l, V-2, and V-3 switching valves. The position of °—c means position 1, and ° ° is position 2. P-1 and P-2 pumping system at 0.2 mL min-1 flow rate. Detector electrochemical detector with diamond electrodes. Column-1 and Column-2 Inertsil ODS-3. Loop 500 pL. A Mobile phase of 60% methanol-water containing 0.5% phosphoric acid.

As a typical example from industrial practice we consider the simulation of a process with the reaction of methylphosphinic acid and butanol to methylphosphinic acid butyl ester and water, which was modeled by Gordana Hofmann-Jovic at InfraServ Knapsack [C28]. Because of the lack of experimental data for the binary systems with phosphorous compounds, COSMO-RS was used for the prediction of the binary activity coefficients. Then the results were fitted by an NRTL equation and the entire process was modeled by a commercial process simulator. The resulting phase diagrams were in close agreement with experimental measurements obtained later (Fig. 8.2). 

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