Study On The Synthesis Mechanism Of Sodium Phosphite

All that including both sodium phosphite and sodium hypophosphite,as new products of phosphates,are widely applied for chemical industries and materials as various reductors.What the reason exists is that the reducibility of phosphite is weaker and more stable than sodium hypophosphite,to some extent,it is with better stability and safety when replacing sodium hypophosphite as redactor.Research on the production of sodium hypophosphite is seldom carried out in the domestic and overseas now,which is mainly recovered from sodium hypophosphite in industrial waste in the method of metathesis reaction,but products recovered is with low yield,poor quality,complicated operation and no environmental protection.The sodium hydroxide and sodium carbonate,as raw materials,respectively make a neutralization reaction with phosphorous acid to become sodium phosphite in order to obtain high quality sodium phosphite with production process,crystallization thermodynamics and crystallization kinetics studied to acquire the optimized production process and crystallization kinetics equation of disodium hydrogen phosphate,which provides theoretical guidance for industrial production in this paper.There were two transitions in the neutralization titration process between phosphorous acid and sodium hydroxide or sodium carbonate by the potentiometric titration,and the reaction product was mainly in the form of disodium hydrogen phosphite at pH 6 to 8.Effect on the neutralization reaction temperature and time,phosphorous acid concentration and molar ratio to reaction product by single factor test was discussed to obtain the optimum conditions below:?1?phosphorous acid was neutralized with sodium hydroxide to disodium hydrogen phosphite,with 1:2 as molar ratio?H3PO3:NaOH?,concentration of phosphorous acid of below 8.54 mol/L,and no effect on reaction temperature and reaction time to reaction product.?2?sodium carbonate was reacted with phosphoric acid to disodium hydrogen phosphite,with 1:1 as the molar ratio?H₃PO₃:Na₂CO₃?and no effect on reaction temperature,reaction time and phosphorous acid concentration to reaction product.The products prepared under the optimized conditions were characterized by XRD,and the product was identified as disodium hydrogen phosphite.The crystallization thermodynamics of disodium hydrogen phosphate was investigated by static method to determine the solubility and super solubility in the aqueous solution in temperature of 25°C to 80°C.The results showed that the solubility and super solubility of disodium hydrogenphosphite at 25?to 80?was increasing with the increase of temperature.It was consistent with the classical nucleation theory that the simplified empirical equation of Apelblat was obtained by fitting to obtain the distribution of metastable zone of disodium hydrogen phosphite at20?to 80?found the metastable zone becoming narrower with the increase of temperature as well as the stirring rate and the metastable zone becoming widened with the increase of the cooling rate.Crystallization thermodynamics analysis showed that the crystallization operation of bisulfite was carried out under the conditions of stirring rate of 200 rpm and cooling rate of 15?/h.The crystallization kinetics of disodium hydrogen phosphite was studied by intermittent dynamic method to prove that phosphorous acid and sodium hydroxide were easy to form uniform and small disodium hydrogen phosphite whose crystal growth was not relevant to particle size at the particle size of above 15?m.The volume fraction of particle size of the product was measured to gain the nucleation rate of corresponding time interval by laser particle size analyzer based on relationship between grain number balance and mass balance by moment transformation method to be crystal growth rate equation of the reaction with retrogression.a small amount of coarse seeds were added at the position of the central partial in the metastable zone bias over super solubility curve could acquire larger crystal of sodium hydrogen phosphite crystals with the evaporation temperature of roughly 150?and 200 rpm stirring speed crystallization,which was consistent with the conclusion of crystallization thermodynamics.