What is the purpose of a vacuum tower?

• A. Reduce boiling point so you don't have to get as hot to boil
• B. Increase boiling point to speed up boil
• C. Remove non-volatile residues
• D. Store separated fractions

Answer: (A)

Vacuum distillation lowers the boiling points of liquids by reducing the pressure around them. In a vacuum tower, the liquid is boiled at a pressure below atmospheric, so heavy fractions that would need very high temperatures to boil can vaporize at much lower temperatures. This lets you separate components without exposing them to heat that could cause degradation or unwanted reactions, and it also saves energy because you’re not driving the process at as high a temperature. So the main function is to reduce the boiling point so you don’t have to heat things as much to boil. The other ideas—raising the boiling point, removing non-volatile residues, or storing separated fractions—don’t describe what a vacuum tower does: it’s about enabling boiling at lower temperatures to achieve efficient separation.