Distillation — Separating Substances by Boiling Point

Distillation is one of humanity's oldest chemistry techniques. It separates two liquids with different boiling points through a heat → vaporize → condense cycle.

Heat a fermented mash containing water (boiling point 100°C) and ethanol (78°C), and ethanol vaporizes before water. Collect that vapor and cool it back into liquid — you get a higher-proof spirit. That's how soju starts.

Basic Mechanism

1. Heat the liquid mixture — the lower-boiling component vaporizes first
2. Channel the vapor through a tube — the higher-boiling component stays behind as liquid
3. Pass vapor through a cold tube (condenser) — it returns to liquid
4. Collect the condensed liquid — concentrated in the lower-boiling component

Simple vs Fractional Distillation

The larger the boiling-point difference, the easier the separation.

• Simple distillation — when boiling points differ by 25°C+. One heat-condense cycle is enough. Seawater → drinking water, makgeolli → soju

• Fractional distillation — when boiling points are close. Vapor undergoes dozens to hundreds of evaporation-condensation cycles inside a fractionating column. Crude oil → gasoline / kerosene / diesel

Vacuum Distillation — Lowering the Boiling Point

Lower pressure means lower boiling point (same reason water boils faster on a mountain).

Heat-sensitive substances (volatile aromas in perfume, vitamins) decompose at 100°C, so vacuum pumps reduce pressure to distill at 40-60°C. Essential in petroleum refining, pharmaceuticals, and high-end perfume extraction.

Distillation in Daily Life

• Soju, whiskey — distilling fermented liquid raises alcohol content (details)

• Perfume, essential oils — steam distillation extracts aroma compounds from flowers and herbs

• Distilled water — pure water with minerals and bacteria removed. Used in medicine, labs

• Petroleum refining — fractional distillation separates crude into gasoline (40-205°C), kerosene (150-275°C), diesel (200-350°C)

• "Angel's share" in whiskey — ethanol that evaporates from oak barrels each year ("taken by angels")

• Some home water purifiers — distillation removes 100% of minerals

Limitations

• Azeotrope — some mixtures have a fixed boiling point at certain ratios and can't be separated further. Ethanol+water azeotropes at 95.6% — 100% anhydrous ethanol requires a different method

• Energy-intensive — boiling requires significant heat. Industrial setups require heat-recovery systems

• Non-volatile components stay behind — substances like salt don't boil, so distillation can't separate them out (which is exactly why it works for desalinating seawater)

History

• ~3500 BCE — Distillation traces in Mesopotamian perfume

• 9th century — Arab chemist Jabir ibn Hayyan systematized the alembic still. "al-kuhl" → origin of "alcohol"

• 12th century — Spread to Europe. Wine-distilled "brandy" appears

• Goryeo Dynasty (Korea) — Mongol invasions brought distillation to the peninsula → soju