For the past few years a quick development of membrane technology has been observed. Currently, they are commonly used in the processes of liquid and gas separation in almost every branch of industry.

The engineer communities move away from conventional separation methods for the membranes, due to their high ecological factor, but also the tightening legal regulations regarding environmental protection and emission of pollutants.

What Are the Membranes?

A membrane is a barrier that stops only a part of the substance and passes the rest. Thus, it is a kind of filter, with a difference that it is more accurate than the filter we usually work with every day.

The membranes can be porous and non-porous. As far as the first type is concerned, the pores can have a size of even several dozen nanometres. Such size of membrane pores makes that the membranes can be qualified as high technology and nanotechnology. The pores that are so small allow the membranes to stop particles of size compared to the size of pores. When it comes to non-porous membranes, there is a different mechanism of separation (dissolution and diffusion), which allows the membrane to stop even the single ions.

The membranes are produced of many materials. The most popular ones are the polymer, ceramic and metal membranes.

It should be remembered that the most prolific producer of membranes is nature. The membranes found in nature include cell membranes in humans, animals and plants. It is by observing nature, people could come up with so sophisticated product as a membrane.

What Are the Membrane Techniques?

The membrane techniques are processes that utilise the membranes. Depending on the type of used membrane and on the conditions of conducting the process different models of membrane techniques can be distinguished. A part of them is already widely known in the industry, another part is beginning to gain approval in plants, and the rest of them is mainly known to the researchers.

The most popular membrane techniques in the industry include the membrane filtration techniques, the task of which is to purify the liquids from formed solid particles or dissolved compounds. These are: microfiltration, ultrafiltration, nanofiltration and reverse osmosis. The application of those techniques is illustrated on the drawing below:

The increased interest of the industry is now directed at pervaporation - a membrane process allowing to separate two or more liquids. The characteristic feature of this process is that the obtained product is more pure than the one acquired by the distillation process.

The developing membrane technique that is stepping in to the industry is the membrane separation of gases. Thanks to the membrane properties it is possible to separate the gas components of different mixtures.

A great advantage of the membrane techniques is the fact that in the processes they utilise only the physical phenomena. As a consequence the performance of that process does not require additional chemical substances, which sometimes can cause much more problems than the starting substance.

Where Can We Apply the Membranes?

The membranes can be applied in all places, where there is something to separate, purify or fractionate. The membranes are used in all kinds of industries - food industry, transportation, medicine, pharmacology, sewer treatment plants, light and heavy industry, mines, gas engineering, refineries and many others.