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Purification of streams of liquids is mostly one of the larger issues in every industrial plant. Restrictive law forces the users and consumers of water to use them in rational way. The purification of the technological water is usually required at the beginning of the technological process and at the end of it - before the water is discharged or turned back to the cycle.

The membrane techniques can provide a solution to those problems. It is commonly believed that by using the membrane techniques every stream of liquids can be separated to clean solvent and highly concentrated suspended or diluted substances. There are many solutions available on the market that are used for separation of liquids with membrane techniques. The choice is based on the input product that we have to work with, and the end product that we want to obtain. PolymemTech offers the technical solutions involving different membrane techniques.

These include:

  • microfiltration– a technique that stops particles visible to the naked eye, that is all sorts of suspensions; it is mostly used in food industry, e.g. for clarification of liquids such as wine or juice
  • ultrafiltration – a technique that separates particles of fats and proteins used in e.g. chicken egg processing industry
  • nanofiltration – a technique that stops individual multivalent ions (ions of magnesium, calcium, iron); it is used to remove iron from water, softening of water or in agriculture to remove pesticides from the water
  • reverse osmosis– an absolute filter – separation of all particles, the effect of which is the clean solvent e.g. water.
  • pervaporation – a technique that successfully replaces the distillation process and allows to obtain better results; it is used to separate two different liquids, e.g. water and alcohol (bio-fuels production)

Microfiltration belongs to a group of pressure membrane techniques. It means that the driving force of the process is pressure difference on both sides of the membrane. The task of that technique is to stop the particles visible to the naked eye, which is to create a turbid suspensions, and also to stop the bacteria. It is generally accepted that microfiltration works as a sieve, which stops particles and micro-organisms larger than 0.2 micrometre. Among the pressure membrane techniques, the pressures used in this technique are the lowest, between 1 and 5 bar.
Microfiltration is used in many branches of industry for initial water purification. It commonly sets a first step in larger technological sequences of water purification. It can also be the single and last element in the water purification system, as long as the water quality requirements are not that high. Microfiltration is also widely used in food industry. There are many possible applications of it, such as: clarification of wine and juice (removal of their turbidity) or cold pasteurisation of products, e.g. milk. The microfiltration membranes are also used in processes of oil dehydration or water deoiling.

Ultrafiltration is next pressure membrane technique. The ultrafiltration membranes can even stop the particles of fats and proteins. Moreover, they stop almost all viruses that liquid contain. It is generally accepted that ultrafiltration stops particles of size larger than 0.01 micrometre. Due to higher accuracy of separation compared to microfiltration the pressure used in this technique is higher and is around 4-10 bar.
Ultrafiltration is now more frequently used in processes of initial water purification superseding on that field the microfiltration technique. In the food industry the ultrafiltration method is used to dehydrate the protein products, e.g. chicken egg white or milk. The ultrafiltration method is also used in dairy process to produce all kinds of cheese from concentration of milk fermented products.

Nanofiltration is next pressure technique using in liquid processing. Nanofiltration thanks to the membranes of very small size of pores and additional surface charge of the membrane is able to stop individual multivalent ions (e.g. ions of magnesium, calcium, iron). That membrane technique uses the pressure of up to 50 bar.
The most common application of nanofiltration are the processes of iron removal from water and water softening. In agriculture industry it is used to remove pesticides from the water. Moreover, nanofiltration is used in the chemical industry to purify solutions of different chemical compounds, e.g. different types of acids or bases.

Reverse osmosis, sometimes called an absolute filter, is also pressure membrane technique. This process utilises the dense, non-porous membranes. The task of reverse osmosis is to stop all the particles, except the particles of a solvent. Reverse osmosis uses the pressure between 10 and 150 bar.
Reverse osmosis is applied in processes of sea water desalination, but also it is the final stage of obtain the demineralised water. Presently, most of the industrial plants that use very clean water, takes it from the reverse osmosis stations.

Pervaporation is relatively new membrane technique. It uses the difference of partial pressures of vapours of two separating liquid ingredients. That technique successfully replaces the distillation process and allows to obtain better results. The purity of the product obtained with that technique is greater than the one obtained by distillation process. Pervaporation demonstrates an ability to purify the liquid mixtures above the azeotropic point.
Pervaporation as a method of separating the liquid mixtures may be applied to separate the alcohol from water (to both removing the water from alcohol and vice versa). Pervaporation can also be applied to produce bio-fuels.
In the field of pervaporation, PolymemTech has applied for a patent, the subject of which is purification and dehydration of glycol used for defrosting of aircrafts.

PolymemTech is currently working, as part of its research operation, on the liquid separation membranes that have new functionality. Those functionalities are applied to the membranes by incorporating into the membrane structure nanoparticles of different compounds, which indicate such properties as bactericidality and bacteriostaticity, reduction of fouling or filtration parameters variability depending on the liquid temperature or its pH reaction.

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