Alfa Laval - membrane filtration
           It’s all about size
            Membrane filtration enables you to bring down
            overall production costs, and boost product quality 
            – both at the same time.
            Alfa Laval’s experience within membrane filtration
            dates back almost as far as the technology itself,
            and we wish to share our experience with you.
            Membrane filtration complement our range of
            separation technologies and allows us to provide you
            with the most efficient solution.
            2 Alfa Laval – membrane filtration 
                     What is membrane filtration?
                     Physical separation
                     Membrane filtration is a physical sep-
                     aration process in which the driving
                     force is the difference in pressure
                     between the two sides of a special
                     membrane. This process is character-
                     ized by the ability to separate mol-
                     ecules of different sizes and
                     characteristics.
                     Almost all industrial membrane filtration
                     is carried out as cross-flow filtration,
                     where the liquid being filtered flows
                     parallel to the membrane at high vel-
                     ocity and under pressure.
                     Physical barrier
                     In its most basic terms, membrane
                     filtration involves passing a single feed
                     stream through a membrane system           Passing through                             Small-scale
                     that separates it into two individual      The pores of such membrane material         To put the size of these pores into
                     streams, known as the permeate and         are so small that they are measured in      perspective – it has been said that if
                     the retentate. The membrane that                         -10                           one square foot of membrane material
                                                                Angstrom (10     m), and pressure is
                     separates them is a physical barrier       required to force the liquid through        were the size of the entire Pacific
                     with highly specialized characteristics    them. In fact, the pores in the             Ocean, one single reverse osmosis
                     – a barrier that only certain selected     membranes used for nanofiltration and       pore in that material would be roughly
                     components in the feed stream can          reverse osmosis are so small that they      the size of a US dime.
                     pass through.                              cannot be seen even with a scanning
                                                                electron microscope.                        Types of membrane filtration
                                                                                                            There are four commonly accepted
                                                                                                            categories of membranes. These are
                                                                                                            defined on the basis of the size of
                                                                                                            material they are required to separate
                                                                                                            from the feed liquid. The membrane
                                                                                                            types are known as reverse osmosis,
                                                                                                            nanofiltration, ultrafiltration and
                                                                                                            microfiltration, in order of increasing
                                                                                                            pore size.
                     4 Alfa Laval – membrane filtration