Distillation

     Distillation is a process in which a liquid is vaporized to a gas, recondensed to a liquid, and collected in a receiver. The liquid which has not vaporized is called the residue, and the liquid which is collected in the receiver is called the distillate. Distillation is used to purify liquids and to separate one liquid from another. It is based on a chemicals volatility, or the relative ease of which the molecules leave the surface of a liquid. Every chemical has a unique volatility, usually a more volatile chemical has a lower boiling point. The successful application of distillation techniques depends on several factors. These include the difference in boiling points of chemicals present, the size of the sample being distilled vs. the size and type of distillation apparatus, the occurrence of azeotrope formation, and the care you exercise.
     You may think that boiling a liquid will release the lower boiling compound first. In reality a mixture of the chemicals being distilled will vaporize. There will be more of the lower boiling chemical, but, depending on how close each chemicals boiling point are to one another, and the ratio of their volumes, the exact compositions will vary. In general, the earlier portion of a distillation will be higher in the lower boiling component. As the volume of that material becomes less and less, more and more higher boiling component will be distilled over. When the boiling points of the chemicals are very close, it is difficult to separate them. Sometimes two or more chemicals will form an azeotrope, or a constant boiling mixture that can not be separated which has its own unique boiling point different from its components. A common azeotrope is ethyl alcohol and water, distillation can only get around 95% alcohol and 5% water at best.
     Since not all chemicals distill the same way, there are several distillation techniques that are used. These include simple distillation, fractional distillation, steam distillation, and vacuum distillation. Some important things to remember for all distillations: Do not fill a distilling flask more two-thirds of the way, and never distill a flask to dryness because explosive peroxides tend to form and are concentrated enough to blow a flask to pieces. Also, you may want to use a boiling stone to prevent bumping, that is a sudden gushing of liquid that rushes upwards and may splash out of the flask in simple distillations and hinder fractional distillations. A boiling stone is a small piece of marble gravel.

Simple Distillation

     A simple distillation is for purifying liquids of one component (separating a liquid from solid contaminants), multiple liquids where the differences in boiling points is very large (a low boiling liquid from a high boiling liquid), or where time is at a minimum. Simple distillations are not effective in removing multiple solvents from one another with a high degree of success.
     Assemble the glassware as pictured in figure 1. The picture shows standard taper glassware which is superior to ordinary glassware. Ordinary glassware can be substituted for standard taper equipment. There should be a clamp on the distilling flask neck, the right angle adapter neck, the middle of the condenser, and the receiving flask neck. You may need a separate stand for the condenser/receiver clamps.
     Before connecting the distilling flask, add 1 or 2 boiling stones and, of course, the materials to be distilled. Adjust the depth of the thermometer so that the bulb is slightly below the sidearm leading into the condenser, this is to measure the temperature of the vapor, not the liquid in the distilling flask. If you are using ordinary equipment, use a short length of glass tubing bent at a 45° angle with rubber or cork stoppers large enough to fit into the distilling flask and the ordinary. The stopper in the distilling flask should be a 2-hole, a thermometer fits into the other hole. The condenser should be angled downward and the thermometer bulb should be just below the bottom of the stopper. The glassware on the end of the condenser (drip adapter) that leads into the receiver is not really necessary, it is just convenient. The vacuum adapter doubles as a drip adapter for standard taper glassware. A drip adapter can be purchased or a length of angled glass tubing can be stoppered from the condenser to the receiver. Sometimes hot distillate will escape if no drip adapter is used, omit at your own risk. The receiver can be a beaker, graduated cylinder, flask, etc.
     Make sure all connections are tight and firm, the clamps tend to pull apart the connections as they are assembled. The water inlet of the condenser is always the lower nipple (closer to the receiver), the outlet is at the top (closer to the distilling flask). The outlet should be pointing up so the water is forced to completely fill the jacket. Double check that everything is clamped securely and that coolant water is circulating through the condenser. Do not have the water pressure so high that the hose pops off.
     Begin heating the distilling flask until boiling begins. Adjust the heat level so that amount of distillate is a steady 2 or 3 drops per second. Discard the first several drops as they may have contaminants. Continue distilling until only a small residue remains, not to dryness, if distilling pure liquids. When distilling mixtures, the more volatile component will be collected in greater concentration at first. As the distillation proceeds a greater percentage of the less volatile component will be collected. It may help to change the receiver several times to collect different fractions. These separate fractions may then be redistilled to collect even purer fractions of each component. Fractional distillations handle this task far more efficiently.