A liquid contains a number of dissolved or dispersed components of different molecular or particle sizes. By using membranes with pores of different sizes, it is possible to separate exactly the components you wish into separate liquid streams. Membrane filtration is a technology that separates a liquid into two streams using a semi-permeable membrane.
A difference in pressure forces the components that are smaller than the membrane pores through the membrane as "permeate". The remaining components are retained as "retentate". A substantial flow moving parallel to the membrane prevents the membrane surface from blocking during the process. This is known as cross-flow filtration.
Cross-flow filtration as opposed to dead-end filtration makes it possible to run the filtration process continuously without filter blockage and with constant filter characteristics. Dead-end filtration can be compared to the use of a coffee filter.
In cross-flow filtration most of the feed flow travels tangentially across the surface of the filter, rather than into the filter.
Crossflow filtration provides a number of advantages: