Membrane filtration is based on the use of a physical interface (barrier) called a membrane. Its porosity, which is very precisely calibrated, provides selective permeability for certain solutes below a given size. If a pressure differential is applied, the solvent passes through the membrane, whose pore size means that specific solutes are retained. By maintaining circulation parallel to the filtration surface, it is possible to control material build-up, limit membrane fouling, and optimize flow rate.
Two output flows are produced: a concentrated fraction (the retentate), enriched by the elements retained by the membrane; and a more diluted fraction (the permeate), which contains only the substances able to pass through the membrane. The filtration flow rate results from the balance between the transmembrane pressure and the tangential velocity.
These are typically classified in descending order, according to membrane pore size: microfiltration, ultrafiltration, nanofiltration, and reverse osmosis.
Tangential flow microfiltration
This process, also called cross-flow filtration, uses membranes with micropores (between 0.1 and 10 µm). Depending on the application, they are made of ceramic, organic polymer, or stainless steel with a titanium dioxide coating. They serve to clarify liquids and extract micro-organisms. Generally, fluid velocity is high and pressure is low.
Tangential flow ultrafiltration
Pore size is generally between 0.01 and 0.1 µm. This process concentrates macromolecules and lets single solutes through. They serve to extract and concentrate proteins and polymers. As with microfiltration, organic or mineral membranes are used, depending on the application.
Tangential flow nanofiltration
Pore size is close to nanometric, allowing the selective retention of molecules between 1 and 100 nm in size. Transmembrane pressure (in the region of 10-25 bar) is the main factor in permeability. Nanofiltration separates monovalent from divalent ions, and monomers from dimers (glucose/saccharose, glucose/lactose, etc.)
Reverse osmosis (RO)
Requiring dense membranes, this allows the extraction of pure water from a solution containing salts (or other dissolved substances). The osmotic pressure limits flow, and increases with the concentration of solutes in the retentate. Transmembrane pressure is high (30-60 bar). This is the standard process for producing demineralized water.
Membrane filtration is used in many purification and concentration processes. It is the ideal pretreatment before more-selective separation operations such as chromatography and ion exchange.
The main applications are…
Whey concentration and demineralization: for this application, nanofiltration is combined with other technologies in Eurodia-patented processes (up to 90% demineralization).
Concentration of food ingredients such as proteins, sugar, etc. In this case, reverse osmosis achieves a very high quality of filtration.
Purification of sweetened juices (obtaining high-purity glucose, etc.) using nanofiltration.
Clarification of sweetened juices, fermentation musts, and plant extracts; pasteurization; milk and blood fractionation; production of water and non-pyrogenic liquids… for which tangential flow MF and UF are widely used.
Generic advantages of membrane filtration
Advantages of Eurodia membrane filtration
Combinable with our other processes to solve each industrial challenge with a turnkey, custom process solution that guarantees eco-efficiency: quality, production cost, effluent reduction and/or valorization.
Exclusive membrane know-how and dedicated technology R&D, combined with constant industry monitoring of materials development and membrane manufacture, mean we can always offer the most suitable membrane-filtration solutions.
