Experimental data on the maximum supercooling ΔTmax, a measure of metastable zone width, for solutions saturated at a temperature T0, as a function of cooling rate R are analyzed, for some solute−solvent systems chosen as examples, using Nývlt’s semiempirical approach and a new approach based on the classical theory of three-dimensional nucleation combined with the formation of n-sized embryos from monomers according to the law of mass action. Instead of a linear relation between ln(ΔTmax) and lnR of the Nývlt’s approach, the new approach predicts a linear dependence of (T0/ΔTmax)2 on lnR with slope F1 and intercept F. The quantity F1/F is independent of saturation temperature T0, characteristic of a solute−solvent and is associated with the growth of the stable three-dimensional nuclei to visible entities. The value of F1 is determined by thermodynamic and solvation processes, while that of F is governed by thermodynamic and kinetic parameters as well as processes associated with solvation of solute ions...

Novel Approach to Analyze Metastable Zone Width Determined by the Polythermal Method: Physical Interpretation of Various Parameters

Nucleation kinetics of paracetamol–ethanol solutions from metastable zone widths

Nucleation kinetics of paracetamol-ethanol solutions from induction time experiments using Lasentec FBRM ®

Nucleation behavior of eszopiclone-butyl acetate solutions from metastable zone widths

Liquid–liquid equilibrium of aqueous two-phase systems containing poly(ethylene glycol) of different molecular weights and several ammonium salts at 298.15 K

In this paper, the crystal growth of sodium nitrate and potassium nitrate from aqueous solutions, in a perfectly stirred batch crystallizer, has been studied considering the effect of temperature, supersaturation degree, and the size of seed crystal growth rate. The mass transfer coefficients obtained correlated with Re, Sc and NL dimensionaless numbers. Supersaturation curve determination using a 0.5 mW He-Ne laser, connected to an automated data acquisition system, was the first stage of the study. The supersaturation and saturation curves were closely parallel with average DT value of 4.1 and 6.8 °C for KNO3 and NaNO3 respectively. For the growth kinetics order, unit values were found for both salts, with diffusion as a controlling stage.

Determination of Mass Transfer Coefficients for Crystal Growth of Nitrate Salts

A study was made on a isothermal process for the crystallization of potassium sulfate as an alternative to the cooling process. The process employs addition of 1-propanol to aqueous salt solutions to achieve the salting-out of the K 2 SO 4 . This work was carried out using an automated Mettler Toledo model RC1 reactor-crystallizer with 800 ml capacity, and controlled isothermally at 25°C to test the crystallization of K 2 SO 4 by addition of the alcohol, and from 50 to 10°C for the cooling crystallization. In both systems, the line of nucleation points was shown to be approximately parallel to the saturation curve, with an average width of 13°C or 3 % mass for crystallization by cooling, compared with 0.2 to 1 % by salting-out. In experiments on crystallization by cooling, the K 2 SO 4 crystals were 0.27 mm in mean size, showed 7 % agglomeration, and contained 8.5 % moisture. Crystals obtained by salting-out had a mean size of 0.79 mm, 28 % agglomeration, and 9-10 % moisture content. A crystal shape factor of approximately of 0.7 was obtained in both systems, apart from the agglomeration.

T. A. Graber

Papers

Determination of Mass Transfer Coefficients for Crystal Growth of Nitrate Salts

Crystallization of potassium sulfate by cooling and salting-out using 1-propanol in a calorimetric reactor