专业英语 Lesson 6.doc

Lesson 6 Fractional DistillationFractional distillation is the separation of a mixture of compounds by their boiling point, by heating to high enough temperatures. Fractional Distillation in a LaboratoryApparatus round bottom flask conical flask Liebig condenser anti-bumping granules thermometer rubber bungs (unless quick fit apparatus is used) MethodAs an example, consider the distillation of a mixture of ethanol and water. Ethanol boils at 78.5C whilst water boils at 100C. So by gently heating the mixture, the ethanol will boil off first. Some mixtures form azeotropes, where the mixture boils at a lower temperature than either component. In the ethanol example, a mixture of 95% ethanol and 5% water boils at 78.2C, so the ethanol cannot be completely purified by distillation. The apparatus is assembled as in the diagram. The mixture is put into the round bottomed flask along with a few anti bumping granules, and the fractionating column is fitted into the top. As the mixture boils, vapor rises up the column. The vapor condenses on the glass platforms inside the column, and runs back down into the liquid below, refluxing distillate. Only the most volatile of the vapors stays in gaseous form all the way to the top. The vapor at the top of the column will be almost pure ethanol. This then passes into the condenser, which cools it down until it liquefies. The process continues until all the ethanol boils out of the mixture. This point can be recognized by the sharp rise in temperature shown on the thermometer, from the boiling point of ethanol to the boiling point of water. Industrial uses of Fractional DistillationOil refinery The most important industrial application of fractional distillation is the distillation of crude oil. The process is similar in principle to the laboratory method described above except for scale, continuous feed and operation, and the fact that crude oil has many different compounds mixed together. The fractionating column has outlets at regular intervals up the column which allow the different fractions to run out at different temperatures, with the highly volatile gases coming out the topmost outlet graduating to the less volatile road tar, (bitumen) coming out at the bottom. Words & Phrasesazeotrope共沸混合物,恒沸物bitumen沥青liquefy(使)溶解, (使)液化thermometer温度计, 体温计volatile挥发物anti-bumping granules防暴沸小粒boiling point沸点conical flask锥形烧瓶fractional distillation分馏liebig condenser李比希冷凝器oil refinery炼油厂road tar筑路焦油round bottom flask圆底烧瓶 第6课 分馏分馏是根据混合物里面的化合物的沸点，将其加热到足够高的温度从而达到分离的一种方法。 在实验室中的分馏技术实验装置： 圆底烧瓶锥形瓶李比希冷凝器抗爆沸圆板颗粒温度计橡胶塞 (除非快速适应使用)试验方法： 例如，乙醇和水的混合物蒸馏。酒精在78.5C时沸腾，而水的沸点是100。因此，通过轻轻加热混合物，酒精会首先沸腾。一些混合物形成共沸物，在较低的温度下的那个混合物会比另一成分的化合物先沸腾。在乙醇的例子中，由95乙醇和5的水组成的混合物煮沸到78.2C。所以不能完全将乙醇蒸馏提纯。 该实验装置配备如图所示。将混合物装入线圆底烧瓶并放入一些防碰撞颗粒，并且将分馏柱安装在顶部。当混合物沸腾时，蒸汽上升到分馏柱。蒸汽在冷凝管中凝结，向下流动回流冷却蒸馏物聚成液体。只有大部分挥发性的蒸汽处于气体状态一直到达顶部。在分流柱顶部的蒸汽几乎是纯乙醇。然后传递到冷凝管，使它冷却下来，直到它液化。这个过程持续到将所有的乙醇从混合物中蒸发出来。这一点能够通过温度计中温度的急剧上升而识别出从乙醇的沸点到水的沸点。 工业分