Solid-Liquid Phase Equilibria For The Conversion Process Of Magnesium Hypophosphite Production

Magnesium hypophosphite Mg(H2PO2)2 is an important hypophosphite,and used as an drugs for the treatment of rheumatoid arthritis,Plastic stabilizer,flameresistant material,fertilizer additive and the amendment of the soil.Studies have also shown that it can be used for treating obesityin humans.Magnesium hypophosphite can be synthesized via neutralization reaction of hypophosphorous acid(H3P02)and magnesium hydroxide Mg(OH)2,or double decomposition reactions of sodium hypophosphite(NaH2PO2)and soluble Magnesium salts,such as Magnesium chloride,nitrate,sulfuric.Solid-liquid phase equilibria(SLE)data and phase diagrams are essential for process development,design and control.However,SLE data forMg2+-Na+//Cl--(H2PO2)--H2O system and subsystems are not found in the opening literatures.The results were as follows.(1)For binary Mg(H2PO2)2-H2O system,The solubility along with liquid densities from freezing point to boiling point of binary system Mg(H2PO2)2-H2O.Two type solid salts of hexahydrate Mg(H2PO2)2·6H2O and anhydrous Mg(H2PO2)2 was found at lower and high temperature respectively.The alter point of Mg(H2PO2)2·6H2O to Mg(H2PO2)2was estimated to be within 322.15 K to 330.15 K by DSC and TG testing.The largest solubility of 33.35%at 325.15 K was determined,which means the solubility of Mg(H2PO2)2·6H2Oincrease with temperature,and Mg(H2PO2)2 decrease with temperature.The freezing and boiling points of Mg(H2PO2)2 saturated solution under ambient pressure of 101.3 kPa was determined to be270.65 K and 375.65 K.(2)The solubilities wet-solids and densities data of ternary system NaCl-NaH2PO2-H2O,Mg(H2PO2)2-NaH2PO2-H2O and Mg(H2PO2)2-MgCl2-H2Oat 298.15 K.The type solid salts is NaCl?NaH2PO2·H2O;MgCl2·6H2O?Mg(H2PO2)2·6H2O?Mg2(H2PO2)2Cl2·6H2O;NaH2PO2·H2O,Mg(H2PO2)2·6H2O,NaMg(H2PO2)3.The two double salt of Mg2(H2PO2)2Cl2·6H2O,NaMg(H2PO2)3 is different composition complex salt.For the high solubility of NaH2PO2-H2O and MgCl2·6H2O,they occupy large solid field,and Mg(H2PO2)2 has low solubility,it occupies a large solid field.(3)For Na+,Mg2+//Cl-,H2PO2--H2O quaternary system study,the phase diagram was plotted and it contents four quaternary invariant,six ternary points,and six single solid phase region.The Mg(H2PO2)2 and NaCl is stability of salt and NaH2PO2·H2O and MgCl2·6H20 is unstable salt.The existence of NaCl-Mg(H2PO2)2 univariant curve shows that magnesium hypophosphite can produce using the replacement reaction of sodium hypophosphite and magnesium chloride.While the existence of NaCl-NaMg(H2PO2)3 and Mg(H2PO2)2-NaMg(H2PO2)3 univariant curves will influence the yield and purity for sodium hypophosphite reforming to produce magnesium hypophosphite.(4)Through interactive quaternary system of Na+,Mg2+//Cl-,H2PO2--H2O phase diagram's univariant curve NaCl-Mg(H2PO2)2 shows that magnesium hypophosphite can produce using the replacement reaction of sodium hypophosphite and magnesium chloride.Product Magnesium phosphate's the maximum conversion rate is 82.67%by sodium hypophosphite.