Question

Theoretically, fractional distillation gives better separation than simpledistillation

.� Use mole ratios for early and late fractions from both simple and fractionaldistillations determined by GC analysis to calculate the volume and mole %composition of each. Present a single model of those calculations.

� Compare these mole % composition results to explain whether your experimentaldata supports this theory.

Data: Mole Ratio cyclohexane:touluene

Orginal mix: 1:1.05

early fractional simple : 1: 0.37

Late fractional simple : 1: 25

Early Fraction fractional: 1: 0.204

Late fraction fractional: 1: 194

Answer 1

The higher surface area given by a fractional distillation gives the vapors a better opportunity to decide whether to stay as a gas, or condensate back down.

Simple distillation is a procedure by which two liquids with different boiling points can be separated. Simple distillation (the procedure outlined below) can be used effectively to separate liquids that have at least fifty degrees difference in their boiling points. As the liquid being distilled is heated, the vapors that form will be richest in the component of the mixture that boils at the lowest temperature. Purified compounds will boil, and thus turn into vapors, over a relatively small temperature range (2 or 3°C); by carefully watching the temperature in the distillation flask, it is possible to affect a reasonably good separation. As distillation progresses, the concentration of the lowest boiling component will steadily decrease. Eventually the temperature within the apparatus will begin to change; a pure compound is no longer being distilled. The temperature will continue to increase until the boiling point of the next-lowest-boiling compound is approached. When the temperature again stabilizes, another pure fraction of the distillate can be collected. This fraction of distillate will be primarily the compound that boils at the second lowest temperature. This process can be repeated until all the fractions of the original mixture have been separated.

When heating a mixture of two or more liquids, even with quite different boiling points, some of the heavier liquid will vaporise and contaminate the recovered lighter liquid.
When performing a Simple distillation, you'll find that a second and even a third 'Run' of the recovered liquid each time will be necessary to improve the separation and purity of the distillate.
With Fractional Distillation, the exchange between vaporising, rising vapours and condensing, falling liquids (reflux), performs the extra separation process in a single and continuous operation.
The rising vapour in contact with the liquid on each tray will give up its heavy ends to the liquid on the tray as it rises, and the falling liquid will give up its lighter components to the rising vapour as it bubbles through the liquid flowing across the tray. This interchange continues to take place on each tray in the column, (there is usually a large number of trays). Each tray is, in essence, behaving as a simple distillation process giving multiple separations in one operation. This results in a high purity product from each product offtake