定义Definition
分馏是在蒸馏烧瓶与冷凝管之间加装分馏柱，使上升的蒸气与下流的冷凝液在柱内多次进行热交换和传质，相当于多次简单蒸馏，从而分离沸点相近的液体混合物。工业上称为精馏。
Fractional distillation places a fractionating column between flask and condenser, where rising vapour and descending condensate repeatedly exchange heat and matter, the equivalent of many successive simple distillations, so that liquids with close boiling points can be separated. In industry it is called rectification.
原理Principle
分馏柱内的填料或塔板提供了很大的气液接触面积，蒸气每部分冷凝再汽化一次，易挥发组分就进一步富集。分馏效率用理论塔板数表示，维格罗柱约 2–4 块，填充柱可达 10 块以上，旋转带分馏柱可达上百块。回流比（返回柱内的液体与馏出液之比）越大，分离越好，但耗时越长。
Packing or plates in the column provide a large vapour–liquid contact area, and each partial condensation and re-evaporation further enriches the volatile component. Efficiency is expressed in theoretical plates: about 2–4 for a Vigreux column, over 10 for a packed column, and hundreds for a spinning-band column. A higher reflux ratio (liquid returned to the column versus distillate taken) gives better separation but takes longer.
工业应用Industrial use
石油炼制中常压塔把原油分馏为液化气、石脑油、煤油、柴油和重油等馏分；空气深冷分离通过精馏得到高纯氧、氮和氩；乙醇、苯、甲苯等化工产品都用精馏提纯。精馏是化工过程中能耗最大的单元操作之一。
In refining, the atmospheric column fractionates crude into LPG, naphtha, kerosene, diesel and heavy oil; cryogenic air separation rectifies air into pure oxygen, nitrogen and argon; and ethanol, benzene, toluene and other chemicals are purified by rectification. It is among the most energy-intensive unit operations in chemical engineering.
操作要点Practical points
加热要缓慢均匀，使柱内建立稳定的温度梯度；柱外可用石棉绳或铝箔保温；馏出速度一般控制在每秒 1–2 滴；按沸点范围更换接收瓶收集不同馏分。
Heat slowly and evenly so a steady temperature gradient forms in the column; insulate it with wrapping or foil; take distillate at about one or two drops per second; and change receivers to collect fractions by boiling range.
年表Timeline
- 1813
塞利耶-布卢芒塔尔发明连续蒸馏塔
Cellier-Blumenthal invents a continuous distillation column
- 1895
林德空气液化精馏
Linde's air liquefaction and rectification
- 1913
现代炼油厂常压分馏塔出现
Modern refinery atmospheric columns appear