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Filtration is the physical-chemical process used for the physical separation of solids and fluids (liquids or gases), through the use of a medium called a filter. The requirements that must be met to carry out the filtration are the following:
- the existence of the so-called « food », which is the suspension of particles in a fluid, which can be liquid or gaseous.
- The filter , which is a porous surface that, depending on the thickness of its pores, will prevent the passage of particles of a predetermined size, greater than the caliber of said pores.
- Filtered material , or simply filtrate, which is the part of the separation that passes through the filter. Filtration is often imperfect, so it is common for some particles to escape into the filtrate.
- Force , which is necessary for the food to pass through the filter. It can be gravity, which drags a fluid down; pressure, which pushes the mixture through the filter; or a suction force that forces the fluid through the filter.
Sieving is often considered a type of filtering, since both work on the same type of principle. In fact, a sieve is a filter with larger pores.
Filtration Types
- Filtration in general . It is the basic type of filtration that uses gravity to move food through the filter. An example of this type of filtration would be the traditional preparation of coffee.
- Vacuum filtration . It is a type of filtration that uses a Büchner flask and a hose that generates a vacuum to suck the food through the filter. Usually this vacuum filtration setup is also aided by gravity. Another type of vacuum filtration uses a pump to create a pressure difference between the two sides of the filter.
- Cold filtration . This filtration allows the collection of dissolved particles. In this method, quenching crystallizes the solid so that it can be collected on the filter. In the laboratory, chilling the solution in an ice bath before filtration often works.
- Hot filtration . Contrary to what happens in cold filtration, in this case the aim is also to minimize the formation of crystals. Heating the feed, filter and funnel helps prevent the growth of crystals that could clog the filter or the formation of unwanted crystals in the filtrate.
Filtration Alternatives
Filtration is not the only method used to separate mixtures, as it can also be done by decantation and centrifugation .
In settling, a mixture is separated based on its properties, such as density and miscibility. An advantage of settling is that no material is lost to the filter media. But decanting doesn’t work for all mixes.
Centrifugation uses centrifugal force to separate the components of the mixture based on size, density, and viscosity. After centrifugation, the solids form a firm cake. Decanting the liquid results in less loss of liquid or solid after centrifugation.
Sources
Helmenstine, A. (2020). What Is Filtration? Definition and Processes. Retrieved 5 April 2021, from https://sciencenotes.org/what-is-filtration-definition-and-processes/
