How do copper caps enhance reflux?

As a liquid mixture is heated in an industrial distillation column, the vapor generated is more concentrated in the lower-boiling (more volatile) material, while the liquid is more concentrated in the higher-boiling material. By harnessing this principle, distillation columns can separate components of mixtures.

Stacks of metal trays, oriented horizontally across the column’s interior, are designed to hold up liquid while the rising vapor flows upward. The trays have openings to allow vapor to flow upward through the column, as well as conduits (downcomers) to allow condensed liquid to flow downward (Figure).

The tray is designed to promote intimate contact between the upward-moving vapor and downward-moving liquid. Each tray effects a portion of the separation before the vapor and liquid move to the next tray in the column until the desired concentrations (purities) are reached. Common types of trays include bubble-cap trays.