Distillation tower

Ethanol boils at 78 °C, water at 100 °C. Boil the mix at the bottom, cool it at the top, and twelve trays sort the two by temperature.

• Reboiler: steam boils the liquid at the bottom. The vapor rises through every tray.
• Sieve trays: vapor bubbles up through a pool on each tray. Water in the bubbles condenses; ethanol in the pool boils off. Each tray is a little richer in ethanol, and a little cooler, than the one below.
• Downcomers: liquid spills over each weir and falls to the tray below, so liquid flows down while vapor flows up.
• Condenser: cooling water turns the top vapor back to liquid. Part returns as reflux; the rest is the product.
• More reflux means purer product but less of it. Ethanol and water form an azeotrope at 89 mol% (≈96% by volume), so no column can pass it.