Measurement And Research Of Solid-liquid Equilibrium In Sodium Diacetate Crystallization Process

As a kind of green food additive, sodium diacetate(SDA) is widely used in foodindustry, for its high efficiency，nontoxicity and safety. Systematic studies should beperformed to resolve the problems occurred in our country industry manufacture ofSDA,such as unstable procudt quality in crystallization process.This study isregarding to crystallization process property of SDA to get solid-liquid law.Meanwhile, the solid-liquid experiment values are correlated by the modifiedJouyban-Acree model, the results of those provide the basic data and theory forcrystallization process property of SDA. The main research contents and conclusionsare as follows:The effect of different conditions on the crystallization process property of SDAwere studied in the first part. The influences of temperature, solvent composition andNaAc content on the solubility of SDA in water were investigated, the solubility ofSDA in different mass fraction methanol, ethanol, n-propyl alcohol, NaAc and watermixture solvents as the same as NaAc in different mass fraction ethanol solution weredetermined by dynamic method. In addition, the metastable zone of SDA in water andethanol solution (w=0.7996) were obtained. The following results were obtained:SDA was soluble in water, while slightly soluble in methanol, ethanol, n-propylalcohol; And, the order of the solubility of SDA in pure solvent was methanol,ethanol, n-propyl alcohol, the solubility of SDA in binary mixture solvent could bearranged as methanol, ethanol and n-propyl alcohol in water mixture solutions andwith the increase of methanol, ethanol, n-propyl alcohol, the solubility decreasedobviously, especially in methanol solution, ethanol solution secondly; Also, thesolubility of SDA decreased with the increase of NaAc in solvent mixtures, especiallythe mass fraction of NaAc was0.0832; What’s more, ethanol solution (w=0.8000) hadplayed an active role for the separation of SDA and sodium acetate in the range of300K~315K; Futhermore, the metastable zone of SDA in water gradually narrowedwith the increase of temperature, while in ethanol solution (w=0.7996) was littleinfluenced by temperature changes and narrower. Therefore, ethanol solution(w=0.7996) could be used as mixed solvent for crystallization and separation of SDA,and the supersaturated concentration should be controlled in the metastable zone.The solid-liquid equilibrium model and correlation with experiment data in thiswork were studied in the second part. On the basis of Apelblat equation and Jouyban-Acree equation, a hybrid model was set up, which can simultaneouslycorrelate the solubility of a solute with both temperature and initial mole fraction ofbinary solvent mixtures. Meanwhile, the solid-liquid experiment values werecorrelated by the modified Jouyban-Acree model, and the results were as follows: Theexperiment data showed good agreement with calculation values and the meanpercentage deviation (MPD) was1.9435, the points of individual percentage deviation(IPD)<3accounted for98.94%. As a consequence, the modified Jouyban-Acreemodel could be used to correlate binary mixture solvent, and the equation obtainedfrom the modified Jouyban-Acree model could be used as a basic equation ofcrystallization process of sodium diacetate.