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Distillation
From theEthanolSource.com
Contents |
Overview
Distillation is the method by which a substance dissolved in a solvent is isolated. In ethanol distillation, ethanol is dissolved in water and must be separated. Distillation is a common method used by chemists to isolate a substance. Vacuum and thermal distillation are two forms of distillation that exploit the phase change differential of water and ethanol. Differential miscibility exploits the solubility in other substances, and is another potential and less costly way to produce anhydrous ethanol.
Fractional Distillation
Temperatue Differential
In a fractionating column, ethanol is separated from water. Since ethanol boils at a lower temperature than water, it stays in vapor form longer than water. Vapors are piped into the column. As water condenses before ethanol, ethanol has the tendency to move to the top of the column, where it condenses and is extracted. Ethanol that condenses before it reaches the top of the column falls downward, is reheated by the steam, and continues it path towards the collecting condensor. At atmospheric pressure an azeotrope stops water and ethanol from separating completely. Thus the maximum proof of alcohol that can be produced by a fractionating column is approximating 96% percent.
Pressure Differential
By exploting Boyle's Law and lowering the pressure of the fermentation vessel, ethanol can boil at much lower temperatures. This is an excellent way to reduce energy costs. However, the fractionating column and the vessel must be able to contain lower pressures. At lower pressures the azeotrope ethanol forms with water also disappears. The ability to produce pure anhydrous ethanol without a molecular sieve should be investigated.
Differential Miscibility
Another method to lower cost and produce anhydrous ethanol is to exploit the differential miscibility of water and ethanol. Miscibility describes the solubility of a substance in a solvent. By exploiting a solvent that dissolves ethanol but doesn't dissolve water, ethanol can be extracted. Castor oil is an excellent example. Ethanol is completely miscible in castor oil but water is not. In the fermenting vessel, a layer of castor oil poured on top of the yeast/water layer provides a method of reducing distillation energy and setting a foundation for continuous processing.
