Fractional distillation is a technique used to separate close boiling materials and to produce high purity distillates...
In fractional distillation, not all of the vaporized material is collected. Some vaporized material is allowed to flow back down the fractional distillation column (reflux) so that it can be distilled again and again. This repeated distillation due to refluxing further separates the close boiling materials and produces higher purities then by simple distillation...
Purification is further aided by the fractional distillation column. Inside the distillation column, packing or a spinning band is used to maximize the contact between the ascending vapor and the descending reflux. More vapor liquid contact equates to a better fractionation.