Distillation is a commonly used method for purifying liquids and separating mixtures of liquids into their individual components. Some examples of its uses include the distillation of crude fermentation broths into alcoholic spirits such as gin and vodka, and the fractionation of crude oil into gasoline and heating oil. In the organic lab, distillation is used for purifying solvents and liquid reaction products.
How does it work?
At any temperature, some molecules of a liquid possess enough kinetic energy to escape into the evaporation phase and some of the molecules in the condensation. An equilibrium is set up, with molecules going back and forth between liquid and vapor. At higher temperatures, more molecules possess enough kinetic energy to escape, which results in a greater number of molecules being present in the vapor phase. Imagine for example heating cyclohexane, a liquid hydrocarbon, and measuring its vapor pressure at different temperatures. As the temperature of cyclohexane is increased the vapor pressure also increases. This is true for all liquids. At some point, as the temperature is increased, the liquid begins to boil. This happens when the vapor pressure of the liquid equals the applied pressure (for an apparatus that is open to the atmosphere the applied pressure equals atmospheric pressure (1 atm = 760 mm Hg)). The definition of the boiling point of a liquid in an open container then is the temperature at which its vapor pressure equals atmospheric pressure.
How does it work?
The substance can be poured from one container to the other. This should be done in such a manner that the insoluble material does not leave the first container. In most cases, a choice will have to be made. Either a small portion of the liquid will need to be sacrificed or a small amount of sediment will need to be permitted in the liquid. It can be extremely difficult, if not impossible, to manually decant all of a liquid. Decantation is sometimes mistakenly used interchangeably with the word “filtration.” These two processes both accomplish similar goals. They are, however, not the same. Decantation is done because in many cases the insoluble matter is undesired. In the case of wine, decantation leaves only the liquid, so a person does not have to be concerned with sediment when her glass is agitated. In a case such as wastewater treatment, it removes solids that cannot be broken down or treated along with the liquid waste. The process of decantation is fairly simple, although some skill and practice may be required if it is done manually. There usually must be a minimum of two containers. One should have the substance that needs to be decanted. The other will be used to collect the liquid.
Decantation
Decantation is a process used to separate a mixture. It usually involves removing the liquid portion of a substance while leaving behind the sediment. This process is used in a variety of instances. Red wine is a common example of a substance that is decanted. Wastewater may also be processed using this method. Insoluble matter is something that does not dissolve in a liquid. Instead, it tends to float and will generally settle if the substance is left at rest. The purpose of decantation is to separate the liquid from this type of matter.
Filtration
Filtration is a process that removes particles from suspension in water. Removal takes place by a number of mechanisms that include straining, flocculation, sedimentation and surface capture. “Is a process by which suspended solid particles are separated from a liquid by passing the liquid through a porous, medium (e.g., a sand bed) capable of entrapping the suspended particles.”
How does it work?
The process of filtration involves the flow of water through a granular bed, of sand or another suitable media, at a low speed. The media retains most solid matter while permitting the water to pass. The process of filtration is usually repeated to ensure adequate removal of unwanted particles in the water. This type of slow filtration over a granular bed is generally known as slow sand filtration. It is the oldest method of filtration but still widely used in municipal water treatment plants today. More modern filtration systems use carbon as the main constituent material of the filter. This carbon is compressed into a solid block form, as opposed to the more loosely structured, granular, sand filters. Such filters often include other media substances, in addition to the compressed, solid carbon. This type of water filter is known as a multimedia filter. These filters clean water through physical processes. They perform the same function as slow sand filters, blocking the passage of unwanted materials with molecular structures that are larger than water. Through the process of adsorption, the atomic charge of the carbon and other media encourages unwanted particles to abandon their bond with the water and chemically attach to the media. The water then passes through the filter, cleansed of undesirable materials. The addition of extra media to the standard filter constitution of sand or carbon allows for more particles to chemically bond to the media, resulting in greater filter performance and efficiency. Water is generally directed through several stages carbon and multimedia filters to ensure the removal of all unwanted materials. The first filtration stage will remove the most concentrated chemicals, like chlorine, while subsequent stages will remove smaller and more evasive chemicals, like pesticides.