Oil refining, water purification and alcoholic beverage production are a few important uses of distillation in industry. Distillation is a physical process, known since ancient times, that extracts desirable pure substances from an original source through heating and other means. By itself, it does not involve chemical reactions; it separates substances but doesn't alter them. Distillation is important to many business operations, both large and small.
Distillation is a physical process widely used for petroleum refining and purifying water, and for making biofuels and alcoholic beverages.
In chemistry, a mixture is a combination of two or more pure substances such as salt and water. In nature, you frequently find desired substances mixed with others that may be useful and others that aren’t. To get the substances you want, you must remove the ones you don’t. Distillation offers ways of separating naturally-occurring mixtures into valuable pure substances.
Most forms of distillation have three basic steps: heating, evaporation and condensation. Carefully heating the source mixture raises the temperature until one or more of the component substances boils. As it boils, the desired substance turns to vapor, then passes through pipes to a cooling chamber. There, it condenses from vapor back to a liquid where it collects in a separate container. By repeating the process through multiple steps, distillation can reduce a complex original mixture down to any number of different pure substances, as long as they were present in the original.
Many forms of distillation have come into use over hundreds of years of chemical research. Each offers efficiency advantages or a specialized mode of operation tailored to particular substances. The following examples represent a few distillation methods.
A simple distillation apparatus separates different liquids by their boiling point temperatures. This method works only if the boiling points of each substance are distinctly different; otherwise, it would take some other process to separate them.
When the boiling points of two liquids are close, fractional distillation does a better job of separating them than simple distillation. The apparatus is similar but the vapors pass into a fractional distillation column; it contains a material with a large surface area that makes condensation more efficient.
For most liquids, reducing pressure also lowers the boiling point. Vacuum distillation occurs at near-zero pressure; liquids boil at lower-than-normal temperatures. This improves the efficiency of the distillation process; less heat can mean energy savings. For liquids that break down with heat, vacuum distillation avoids high temperatures and allows more effective processing of these substances.
Freeze-drying is a technique closely related to vacuum distillation. A substance is dissolved in water or some other solvent, then frozen. A vacuum turns the ice to vapor without heating or melting, leaving a solid dry substance behind. Uses include food processing and packaging microbes and other biological materials.
It doesn’t take much equipment to perform simple distillation; you can easily do it on a tabletop or home kitchen. It works just as well in large, sprawling oil refineries or warehouse-sized craft liquor companies. With compact modern electronic controls, a smaller setup can have much of the sophistication of a large one. The main differences between big and small operations are their cost and the volume of their production.
The production of gasoline, diesel and other fuels and chemicals is a very important industrial application of distillation, amounting to many billions of dollars’ worth of processing annually. The process feeds crude oil, a combination of many substances, into one end of a refinery. Each distillation step removes lighter substances such as kerosene, gasoline and lubricating oil, leaving heavier materials such as tar.
In addition to being a key step in making gasoline and diesel from crude oil, distillation is also essential for the production of biofuels. In this case, heat liberates methanol from corn and other organic materials. Unlike petroleum refining, which starts with a liquid, the sources for biofuels are organic solids, which also contain water, sugars and other substances. Distillation is one step in the process; other steps chemically generate the desired fuel liquids, and distilling extracts and purifies them.
In the manufacturing of medicine, the purity of chemical substances is crucially important. At the same time, drug makers want products that are consistent in quality, and which can be manufactured in industrial quantities economically. Distillation is one process that gives pharmaceutical companies tight control over purity and consistency, and can produce large amounts of the desired substances.
Some organic compounds such as lubricating oil and solvents are discarded long before their useful lifetime is over. The main problem is not chemical breakdown but contamination with dirt, water and other unwanted substances. Distillation boils off the oil or solvent, which is purified and reclaimed when it condenses and cools. The contaminants are left behind and can be disposed of.
Vacuum distillation is useful for extracting fragrances from plants and other biological materials. These substances are fragile and can break down at high temperatures; vacuum distillation is well-suited to obtaining them from natural sources. Scented oils find their way into soap, air fresheners and other household and personal care products.
Distillation is behind much of the success of the newly-burgeoning cannabis industry and the wide range of products that have become available. Various distillation processes extract tetrahydrocannabinol (THC) and cannabidiol (CBD) in pure form from the plant; these substances are then sold as-is or added to teas, candies and other consumables.
Ultra-cold liquids such as nitrogen, oxygen and argon can be distilled from the air, which contains all of these gases at room temperature. Because each of these elements boils at a different temperature, distillation can separate them from the original mixture. Unlike other forms of distillation, the air is compressed and cooled instead of heated.
Some parts of the world don’t have easy access to clean water; they might have to rely on processing salty seawater so people can drink it. A large distillation plant can provide thousands of gallons of water for drinking, food preparation and general human consumption. Though distilled drinking water costs money, it provides better health and a higher standard of living in desert regions.
Ethanol, or ethyl alcohol, is a main ingredient in vodka, bourbon and other alcoholic beverages; other substances present add color and flavor to the drink. A traditional brewing process combines water and yeast with potatoes, grains or berries. At a later stage in the process, distillation increases the concentration of alcohol, giving the drink greater potency as well as changing the flavor.