The distillation technique most suited for separating glycerol from spent-lye in the soap industry is :
Distillation under reduced pressure
As we learnt ,
Distillation under reduced pressure -
This method is used to purify liquid having high boiling points and decomposes below their boiling point.
Glycerol is high boiling liquid with boiling point 290oC . It can be separated from spent lye by the method of distillation. In this method , liquid is made to boil at lower temperature than its normal temperature by lowering the pressure on its surface. As external pressure is reduced , then boiling point of the liquid lowers.