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Fractional distillation

Fractional distillation is the separation of a mixture into its component parts, or fractions, such as in separating chemical compounds by their boiling point by heating them to a temperature at which several fractions of the compound will evaporate. It is a special type of distillation. Generally the component parts boil at less than 25&nbsp;Â°C from each other under a pressure of one atmosphere (atm). If the difference in boiling points is greater than 25&nbsp;Â°C, a simple distillation is used.

Laboratory setup




As an example, consider the distillation of a mixture of water and ethanol. Ethanol boils at 78.4&nbsp;Â°C while water boils at 100&nbsp;Â°C. So, by gently heating the mixture, the most volatile component will concentrate to a greater degree in the vapor leaving the liquid. Some mixtures form azeotropes, where the mixture boils at a lower temperature than either component. In this example, a mixture of 96% ethanol and 4% water boils at 78.2 Â°C, being more volatile than pure ethanol. For this reason, ethanol cannot be completely purified by direct fractional distillation of ethanol-water mixtures.

The apparatus is assembled as in the diagram. (The diagram represents a batch apparatus, as opposed to a continuous apparatus.) The mixture is put into the round bottomed flask along with a few anti-bumping granules (or a Teflon coated magnetic stirrer bar if using magnetic stirring), 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, known as trays, inside the column, and runs back down into the liquid below, refluxing distillate. The column is heated from the bottom. The efficiency in terms of the amount of heating and time required to get fractionation can be improved by insulating the outside of the column in an insulator such as wool, aluminium foil or preferably a vacuum jacket. The hottest tray is at the bottom and the coolest is at the top. At steady state conditions, the vapor and liquid on each tray are at equilibrium. Only the most volatile of the vapors stays ingaseous form all the way to the top. The vapor at the top of the column, then passes into the condenser, which cools it down until it liquefies. The separation is more pure with the addition of more trays (to a practical limitation of heat, flow, etc.) The condensate that was initially very close to the azeotrope composition becomes gradually richer in water. 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.

Typically the example above now only reflects the theoretical way fractionation works. Normal laboratory fractionation columns will be simple glass tubes (often vacuum jacketed, and sometimes internally silvered) filled with a packing, often small glass helices of 4 to 7&nbsp;mm diameter. Such a column can be calibrated by the distillation of a known mixture system to quantify the column in terms of number of theoretical plates. To improve fractionation the apparatus is set up to return condensate to the column by the use of some sort of reflux splitter (reflux wire, gago, Magnetic swinging bucket, etc.) - a typical careful fractionation would employ a reflux ratio of around 10:1 (10 parts returned condensate to 1 part condensate take off).


From Yahoo Answers


Answers:How about asking a complete question?

Question:i need a diagram and a flow chart showing the process of fractional distillation of air ASAP please.. google isn't being much help :) Thanks

Answers:This is really quite simple for you to construct as once liquefied, the gases simply boil off in order of their boiling points. You don't say what level you want to do this at eg as normal or are you trying to separate individual rare gases like Kr as well. The necessary detail can be found by searching on the individual gases. The basic stages for your diagram are : 1] Air is filtered to remove dust 2] Water vapour condenses, and is removed using absorbent filters 3]carbon dioxide freezes at 79 C, and is removed 4] It is then cooled in stages until it reaches 200 C. At this temperature it is a liquid. 5] The liquid nitrogen and oxygen are then separated by fractional distillation. 6] nitrogen boils off first at 196 C 7] oxygen then boils off at 183 C


Answers:True.. Distillation means separting mixture. Fractional distillation is just a kind of distillation where the mixture components have boiling point very close to each other.. usually a fractionating column is used.. Hope that helps,

Question:Please could someone describe this process to me and find a diagram. Any help much appreciated as I really am stuck

Answers:Click on the link..

From Youtube

Distillation :Check us out at www.tutorvista.com Distillation is a method of separating mixtures based on differences in their volatilities in a boiling liquid mixture. Distillation is a unit operation, or a physical separation process, and not a chemical reaction. Commercially, distillation has a number of applications. It is used to separate crude oil into more fractions for specific uses such as transport, power generation and heating. Water is distilled to remove impurities, such as salt from seawater. Air is distilled to separate its components notably oxygen, nitrogen, and argon for industrial use. Distillation of fermented solutions has been used since ancient times to produce distilled beverages with a higher alcohol content. The premises where distillation is carried out, especially distillation of alcohol, are known as a distillery. Laboratory display of distillation: 1: A heating device 2: Still pot 3: Still head 4: Thermometer/Boiling point temperature 5: Condenser 6: Cooling water in 7: Cooling water out 8: Distillate/receiving flask 9: Vacuum/gas inlet 10: Still receiver 11: Heat control 12: Stirrer speed control 13: Stirrer/heat plate 14: Heating (Oil/sand) bath 15: Stirring means eg(shown), anti-bumping granules or mechanical stirrer 16: Cooling bath.

Fractional distillation :Crude oil is a mixture of many different hydrocarbons. Hydrocarbons are separated using a process called fractional distillation.