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Fractional freezing is a process used in process engineering and chemistry to separate substances with different melting points. It can be done by partial melting of a solid, for example in zone refining of silicon or metals, or by partial crystallization of a liquid, as in freeze distillation, also called normal freezing or progressive freezing. Partial crystallization can also be achieved by adding a dilute solvent to the mixture, and cooling 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. ==Freeze distillation== Freeze distillation is a misnomer, since it is not distillation but rather a process of enriching a solution by partially freezing it and removing frozen material that is poorer in the dissolved material than is the liquid portion left behind. Such enrichment parallels enrichment by true distillation, where the evaporated and re-condensed portion is richer than the liquid portion left behind. The detailed situation is the subject of thermodynamics, a subdivision of physics of importance to chemistry. Without resorting to mathematics, the following can be said for a mixture of water and alcohol: * Freezing in this scenario begins at a temperature significantly below 0 °C. * 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. The frozen material, while always poorer in alcohol than the (increasingly rich) liquid, becomes progressively richer in alcohol. * 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. * If progressively colder temperatures are available, * * the frozen material will contain progressively larger concentrations of alcohol, and * * the fraction of the original alcohol removed with the solid material will increase. * 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. * Thermodynamics gives fair assurance, even without more information about alcohol and water than that they freely dissolve in each other, that * * even if temperatures ''somewhat below'' the freezing point of ethyl alcohol are achieved, there will still be alcohol and water mixed as a liquid, and * * at some still lower temperature, the remaining alcohol-and-water solution will freeze without an alcohol-poor solid being separable. The best-known freeze-distilled beverages are applejack and ice beer. Ice wine is the result of a similar process, but in this case, the freezing happens ''before'' the fermentation, and thus it is sugar, not alcohol, that gets concentrated. For an in depth discussion of the physics and chemistry, see eutectic point. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Fractional freezing」の詳細全文を読む スポンサード リンク
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