Solid-Liquid Phase Equilibria For The Reforming Process To Produce Calcium Hypophosphite

Calcium hypophosphite is a common used hypophosphite which has been extensively ultilized as an anti-corrosive agent, flame retardant, fertilizer, assistant for Ni electroless plating and animal nutrition supplements. To get high purity and edible calcium hypophosphite, we can prouct it using the replacement reaction of sodium hypophosphite and calcium chloride.The design, optimization and control of this production method need the support of the related phase equilibria data. But we have not found the phase equilibria data of this quaternary system and even the related ternary systems phase equilibria study are also very short. According to this situation, the solid-liquid phase equilibria of Ca2+,Na+//Cl-,H2PO2--H2O quaternary system at 298.15K and optimum technology were studied in this work. The specific results are following:(1) The solubility of calcium phosphate is from 15.66 g/100 H2O to 16.42 g/100 H2O between 0 ℃ and 90 ℃ which is in little change with the temperature.(2) Phase equilibrium study:In this work, the solid-liquid phase equilibria of Ca(H2PO2)2-CaCl2-H2O, Ca(H2PO2)2-NaH2PO2-H2O, NaCl-NaH2PO2-H2O ternary systems and Na+,Ca2+//Cl-,H2PO2--H2O quaternary system at 298.15 K were studied experimentally via the classical isothermal solubility equilibrium method and the phase equilibria data and phase diagrams for these three ternary systems and one quaternary system were obtained. The existing forms of the solid phase were CaCl2·6H2O, Ca(H2PO2)2, NaCl, NaH2PO2·H2O and one incompatible double-salt (NaCa(H2PO2)3). For the high solubility of NaH2PO2·H2O and CaCl2·6H2O, they occupy large solid field, and Ca(H2PO2)2 has low solubility, it occupies a large solid field.(3) According to Na+,Ca2+//Cl-,H2PO2--H2O quaternary system study, the phase diagram was plotted and it contents three invariant points,seven univariant curves.The existence of NaCl-Ca(H2PO2)2 univariant curve shows that calcium hypophosphite can produce using the replacement reaction of sodium hypophosphiteand calcium chloride. While the existence of NaCl-NaCa(H2PO2)3 and Ca(H2PO2)2-NaCa(H2PO2)3 univariant curves will influence the yield and purity for sodium hypophosphite reforming to Produce calcium hypophosphite.(4) Process optimization:Through the experiments of balance time under different temperature, ingredients ratio and water addition, the process optimization to improve the production rate of calcium phosphate is obtained:At 40 ℃ to reaction, the reaction time is 300 minutes, the ratio of calcium chloride and sodium hypophosphite is 1.2:1, when adding 157.20 g CaCl2 and 250 g NaH2PO2-H2O, the water addition is 270.30 g.