Influence of Phenol on the Crystallization Kinetics and Quality of Ice and Sodium Sulfate Decahydrate during Eutectic Freeze Crystallization
2017
Becheleni, Emily M. A. | Rodriguez-Pascual, Marcos | Lewis, Alison E. | Rocha, Sônia D. F.
The presence of impurities in solution during crystallization can influence the crystallization kinetics of the desired product. Consequently, this affects the product quality parameters such as the crystal size distribution (CSD), purity, and morphology. This paper focuses on the application of eutectic freeze crystallization (EFC) to the purification of petrochemical brine rich in sulfate salts. The effect of phenol on the CSD, nucleation and growth rates, purity, and morphology of ice and sodium sulfate decahydrate crystals was evaluated using a batch EFC setup. Nucleation and growth rates were obtained from in situ image acquisition and analyses. In the presence of 0.2 wt % phenol, larger crystals were obtained for both ice and sodium sulfate decahydrate due to increased growth rates and reduced nucleation rates. The crystal habit of both ice and salt was not modified by the phenol impurity. Ice crystals presented elongated disk shapes and dendritic habit, and crystal sizes up to 1000 μm were obtained. Salt particles exhibited prismatic shape and monoclinic class as expected for Na₂SO₄·10H₂O. Ice purity of about 97% was obtained before washing in the presence of phenol. Three washing cycles increased the ice purity to 100% implying that impurities were physically adhered on the ice surfaces and not incorporated into the crystal lattice, which deserves additional studies to verify this proposal. X-ray diffraction (XRD) analyses of salt crystals confirmed that Na₂SO₄·10H₂O with the structure of thenardite was crystallized. Any other phase was detected.
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