Fractional distillation occurs when a crude substance is heated to a gaseous state and then recollected in different stages from the top of the apparatus. In contrast, simple distillation involves heating a liquid to a gaseous state and then allowing the gas to condense as it flows through a secondary tube. Fractional distillation of crude oil creates many important commercial products that are used daily around the country.
Laboratory fractional distillation columns differ significantly from the large tanks built by heavy industry. Still, in either case, the overall distilling process is much the same. In the lab, a liquid is placed in the distilling flask and direct heat is applied. The gases that escape rise into the fractionating column, where they will condense and vaporise several times before reaching the top of the column. When they reach the top, the gas flows through the condensing tube, where it condenses into a liquid.
The big commercial beneficiary of fractional distillation process is the petroleum industry. Instead of using scientific apparatus, large refineries are built to break down the raw material. Once the crude oil is heated, various liquids will be released as gases. A sample of crude oil will release petroleum gases at 25 degrees Celsius, gasoline at 45C to 75C, all the way up to fuel oil, which boils off at 350C. As each gas is released, it is collected and condensed into a liquid.
Besides the significant employment of fractional distillation to produce numerous petroleum products, this distilling process can also be used to isolate nitrogen and other atmospheric gases. The source is the air we breathe, so the fractional distillation will also produce moderate amounts of oxygen, along with some argon, krypton and xenon. The air is dried before it is fed through the distiller, to remove the water vapour and carbon dioxide. To separate the nitrogen from the rest of the gases, fractional distillation is run at a very cold temperature (-321 degrees F). Once the nitrogen is isolated, it can be used as a processing agent in chemical plants, an ingredient in fertilisers or as an aid to manufacturing electronic components.
Other Industrial Uses
Fractional distillation can also be used at petrochemical and chemical plants, as well as natural gas processing facilities. Producing these products on such a large scale requires the designing and development of rather large distilling tanks, whose height may reach to 200 feet. Still, the principle is basically the same as that used in the lab apparatus, where different gases are removed at the appropriate temperature and then condensed.