The Physics of Heat Transfer in Alcohol Distillation

Alcohol Distillation

Heat transfer in alcohol distillation is a primary factor limiting energy costs during separation processes, so its intensity determines energy requirements for alcohol distillation. Higher heat transfer equates to decreased energy requirements. Steam, electricity and chemical inputs serve as energy sources in this regard.

Immiscible liquids often form an azeotrope (where the boiling points of both components overlap in a band), which can be broken by simply applying external pressure, or exploiting differences in vapor pressure between pure components using techniques like dehydration.

Batch distillation uses a column to ensure optimal separation of vapor and liquid streams. A liquid of desired composition – for instance water or ethanol – is heated in the column before its vapors are cooled so only those components desired condense overhead. Finally, this vapor stream is collected, while liquid returns back down through a reflux ratio that controls how often liquid layers return up through its depths.

Distillation may seem complex, but its practical applications can often be easily grasped. For instance, many distillation systems contain marbles which prevent the vapor streams from interacting efficiently resulting in high heat transfer per pass (HETP) values that require tall columns. This could be reduced using packing that spreads the liquid evenly, such as trays or lattices to distribute it more evenly as it moves down.