Filtered
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Wikipedia-Article "Filtered"
- This article is about the separation process. For the mathematical concept see filtration (abstract algebra).
In chemistry and alchemy, filtration is the process of using a filter to mechanically separate a mixture.
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Methods of Filtration
There are many different methods of filtration, but all aim to attain the separation of two or more substances. This is achieved by some form of interaction between the substance or objects to be removed and the filter. In addition the substance that is to pass through the filter must be a fluid, i.e. a liquid or gas.
The simplest method of filtration is to pass a solution of a solid and fluid through a porous interface so that the solid is trapped, while the fluid passes through. This principle relies upon the size difference between the particles making up the fluid, and the particles making up the solid.
By extending this principle, it is possible to separate any two things with a significant or reliable size difference. For example an experiment to prove the existence of microscopic organisms involves the comparison of water passed through unglazed porcelain and unfiltered water. When left in sealed containers the filtrated water takes longer to go foul, showing that very small items (such as bacteria) can be removed from fluids by filtration.
Nuances of Filtration
It is also possible for other molecules to be removed from fluids using this method of filtration, as long as there is a size difference. However the smaller the channels through which the fluid that is being filtered must pass, the greater the physical interaction between the fluid and the filter. Thus the pressure required to achieve a flow through the filter rises very quickly.
A further disadvantage with the physical barrier method of filtration is that the substance being filtered from the fluid will clog the channels through the filter over time. Thus the filter becomes less and less efficient over time (for example, a vacuum cleaner bag). Thus methods have been developed to prevent this from happening. Most such methods involve replacing the filter. However, if the filter is needed for a continuous process, this is highly problematic, and complex scraping and in-situ cleaning mechanisms have to be used.
For separation where there is a very small size difference, chemical filters may be used. These will use a filter that has properties so that undesirable items are attracted and retained by the filter, and the fluid from which it is to be separated is not. Filters of this kind most often take the form of electrostatic attractions. These form of filters again have the problem of either becoming clogged, or the active sites on the filter all become used by the undesirable. However, most chemical filters are designed so that the filter can be flushed with a chemical that will remove the undesirables and allow the filter to be re-used.
Filtration is a more efficient method for the separation of mixtures than decantation, but is much more time consuming. If very small amounts of solution are involved, most of the solution may be soaked up by the filter medium.