Ethanol Solubility

Ethanol is a polar substance therefore it is miscible in water. It is a hydroxyl functional group which makes it a polar compound and helps it dissolves in polar water. Ethanol has a two carbon chain and a hydroxyl (OH) group. Water being of polar nature attracts the OH group. The carbon is repelled as it is non polar.

Now the matter of solubility depends on the strength of the two forces that are the forces of attraction of the hydroxyl group and the forces of repulsion of the carbon group. If the attraction force is stronger than the repelling force, the compound is considered to be more easily soluble. However, solubility of alcohols is complex. But in alcohols like ethanol the OH attraction is very strong. This makes ethanol fully miscible.

Water dissolves any amount of it. When ethanol is added to water, some of the ethanol particles move into the water and few particles of water move into the ethanol. This happens at the boundary between the two liquids. In this process water – water, and ethanol – ethanol combinations are broken so as to form ethanol – water attractions. This attraction creates a hydrogen bond between the molecules. The ethanol molecules move as freely in water as they move in the pure ethanol solution. In the same manner the water molecules move as freely in the ethanol solution as it moves in water. This happens because the attractions between the particles are very similar.

Ethanol is fully soluble in water. But one can separate ethanol from water with the help of the differential solubility of sulfur in ethanol and water. If we use distillation technique, the separation of water from ethanol requires more energy than can be produced by burning the resultant distilled ethanol. So it is not that feasible. On the other hand if we use the separation by sulfur technique then the energy released by burning the separated ethanol is much higher than that required in the process of separating it from water. In the separation technique, sulfur is added to the ethanol and water mixture. According to the temperature of the mixture, a small amount of sulfur would dissolve ethanol. Sulfur in any form is insoluble in water. But a form of sulfur is slightly soluble in ethanol. Thus, the sulfur ethanol mixture would settle down at the bottom.

The sulfur ethanol mixture can be then bled off. Now to separate ethanol from sulfur the given mixture is heated. Volatile ethanol is separated from the non volatile sulfur. Once this separation is completed, the left over sulfur can be added to another batch of ethanol and water mixture, and the same process can be carried out. The energy consumed in the separation process is less as only a small portion that was bled off from the original mixture is heated. Energy is not applied to the entire ethanol and water mixture. There is an alternative technique also, in which the ethanol, water and sulfur mixture is placed in a retort. In the retort, it is heated and pressurized to a level above the critical temperature and pressure of ethanol but below the critical temperature and pressure of water.

Again, the ethanol will dissolve in sulfur and will settle down at the bottom from where it can be piped out. The water will not dissolve the sulfur. By further heating the sulfur and ethanol mix, ethanol can be separated and the remaining sulfur can be reused to carry out the same process again. The second version is most suitable in case of industries.