Unsourced material may be challenged and removed. Partial crystallization can also be achieved by adding a dilute solvent to the mixture, and fundamentals of salt water desalination pdf and concentrating the mixture by evaporating the solvent, a process called solution crystallization. Fractional freezing is generally used to produce ultra-pure solids, or to concentrate heat-sensitive liquids. Barrels of beer were originally left outdoors to partially freeze, then the ice removed.
Such enrichment parallels enrichment by true distillation, where the evaporated and re-condensed portion is richer than the liquid portion left behind. The first material to freeze is not the water, but a dilute solution of alcohol in water. The liquid left behind is richer in alcohol, and as a consequence, further freezing would take place at progressively lower temperatures. Further stages of removing frozen material and waiting for more freezing will come to naught once the liquid uniformly cools to the temperature of whatever is cooling it. In practice, unless the removal of solid material carries away liquid, the degree of concentration will depend on the final temperature rather than on the number of cycles of removing solid material and chilling. When a pure solid is desired, two possible situations can occur. When the requirement is to concentrate a liquid phase, fractional freezing can be useful due to its simplicity.
In a process that naturally occurs with sea ice, frozen salt water, when partially melted, leaves behind ice that is of a much lower salt content. Likewise, the frozen water with the highest concentration of salt melts first. Either method decreases the salinity of the frozen water left over, and with multiple runs can be drinkable. The danger of freeze distillation of alcoholic beverages, is that unlike heat distillation, where the methanol and other impurities can be separated from the finished product, freeze distillation does not remove them. Thus the ratio of impurities may be increased compared to the total volume of the beverage. University of Vermont College of Medicine. This page was last edited on 23 October 2016, at 23:40.