Phase Equilibrium of NaNO3/KNO3 in Glycerol + H2O Mixed Solvent System at 288.15 K and 298.15 K

Abstract

Materials. All the chemicals (purity > 99.5 %), including sodium nitrate, potassium nitrate, and glycerol were purchased from Sinopharm Chemical Reagent Co. Ltd., and used without further purification. The salt was dried to constant weight for 48 h at 110 °C and stored in desiccators prior to use. Double-distilled water was used throughout this work. Apparatus and Procedure. All samples were prepared by mass with electronic balance (AL204, Mettler Toledo, accuracy of ±1 • 10 −4 g). The experimental apparatus and process are the same as those reported in our former work. 9-11 The mixed solvent (glycerol and water) was firstly placed in a 10 ml syringe (the mass fraction of glycerol in the mixed solvent varied from 0.0 to 1.0). Excessive amounts of NaNO 3 and KNO 3 were then added into the mixed solvent. Next, the samples were stirred for 48 h and settled for a further 24 h to ensure that equilibrium was established. The temperature was controlled within an accuracy of ±0.1 K. After equilibrium was achieved, the solutions were withdrawn and analysed. The unsaturated solutions were prepared by adding salt to the mixtures of glycerol-water at a certain ratio. Refractive index and density of both saturated and unsaturated solutions were determined using RXA 170 refractometer (Anton Paar) and DMA 4500 vibrating tube densimeter (Anton Paar) with a precision of 4 • 10 −5 and ±1 • 10 −5 g cm-3 , respectively. Both the instruments were calibrated prior to initiation of each series of measurements, using air and double-distilled water as reference substances. The content of the salts and glycerol was analysed using density-refractive index method, 9 because refractive index and Phase Equilibrium of NaNO 3 /KNO 3 in Glycerol + H 2 O Mixed Solvent System at 288.15 K and 298.15 K Solubility, density, and refractive index were determined for the ternary systems of NaNO 3 /KNO 3 + glycerol + H 2 O at 288.15 K and 298.15 K. The solubility of the salts was calculated by the method of combining density and refractive index. In all cases the solubility of the salts decreased with the increase in glycerol content. A reverse trend for the refractive indices was observed. However, NaNO 3 density tended to decrease and KNO 3 density tended to increase with the addition of glycerol in the solution. Moreover, the experimental data were correlated using a four-parameter and seven-parameter empirical equation for the saturated and unsaturated solutions, respectively. Therefore, research of such kind of system has potential theoretical and practical application for the purification process and thermodynamic chemistry.