减压蒸馏Vacuum distillation

根据克劳修斯-克拉佩龙方程，蒸气压与温度呈指数关系，压力降低沸点随之降低。经验上，压力每降低一半，沸点约降低 15 °C；从常压降至约 2.7 kPa（20 mmHg）时，许多有机物的沸点可降低约 100–120 °C。可用压力-温度列线图估算不同压力下的沸点。

By the Clausius–Clapeyron relation vapour pressure depends exponentially on temperature, so lowering the pressure lowers the boiling point. As a rule of thumb each halving of pressure lowers the boiling point by about 15 °C, and going from atmospheric to about 2.7 kPa (20 mmHg) lowers many organic boiling points by about 100–120 °C. Pressure–temperature nomographs estimate boiling points at other pressures.

装置由克氏蒸馏头（或带毛细管的蒸馏瓶）、冷凝管、多头接液管（“猪形”接收器，可不中断真空更换馏分）、安全瓶、冷阱和真空泵（水泵或油泵）组成，并配压力计。减压时不能用沸石，需用毛细管引入气泡或磁力搅拌防止暴沸。玻璃仪器须无裂纹，必要时加防护罩；结束时先撤热源、冷却后再缓慢放气，最后关泵。

The apparatus has a Claisen head or a flask with a capillary bleed, condenser, multi-way 'cow' receiver for changing fractions without breaking vacuum, safety trap, cold trap and a water aspirator or oil pump, with a manometer. Boiling chips do not work under vacuum, so a capillary air bleed or magnetic stirring prevents bumping. Glassware must be free of cracks and shielded if necessary; at the end remove the heat, cool, release the vacuum slowly and only then switch off the pump.

实验室用于纯化高沸点液体（如苯胺、DMSO、乙二醇）和热敏性化合物；工业上用于炼油厂减压塔分离润滑油馏分、精制植物油和香料，以及分子蒸馏（短程蒸馏）提纯维生素 E、鱼油等。

In the laboratory it purifies high-boiling liquids such as aniline, DMSO and ethylene glycol and heat-sensitive compounds; in industry it is used in refinery vacuum columns for lubricating-oil fractions, refining vegetable oils and fragrances, and in molecular (short-path) distillation of vitamin E and fish oil.