Using multi-pressure distillation, the ethanol and water mixtures are progressively closer to the azeotropic ratio of 95.5/4.5%. The further purification of ethanol up to 99.80% is done by dehydration using pressure swing system which includes molecular sieve 3A as adsorbents.
The very precise pore size of molecular sieves enables them to select and remove molecules of particular size from a bulk mixture containing molecules with large sizes and low polarity. Molecular sieve has a porous structure containing uniform cavities of a specific size. The selection of molecular sieves depends mainly on the size of the molecules to be removed from the mixture of other molecules. The water (H2O) molecular having size 3Å is easily getting adsorbed in the cavities present in the molecular sieves, whereas the ethanol(C2H5OH) molecule being larger in size than the water molecule cannot enter the cavities present in the molecular sieves.