The distillation technique most suited for separating glycerol from spent-lye in the soap industry is:

The distillation technique most suited for separating glycerol from spent-lye in the soap industry is distillation under reduced pressure. At atmospheric pressure, the boiling point of glycerol is 290oC. At this temperature, it decomposes before it distills. Hence, the distillation is carried out under reduced pressure by applying vacuum which decreases the boiling temperature of glycerol and prevents its decomposition.