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Diagram of cross-flow filtration
In chemical engineering, biochemical engineering and protein purification, crossflow filtration
(also known as tangential flow filtration) is a type of filtration (a particular unit operation).
Crossflow filtration is different from dead-end filtration in which the feed is passed through a
membrane or bed, the solids being trapped in the filter and the filtrate being released at the other end.
Cross-flow filtration gets its name because the majority of the feed flow travels tangentially across the
surface of the filter, rather than into the filter. The principle advantage of this is that the filter cake
(which can blind the filter) is substantially washed away during the filtration process, increasing the
length of time that a filter unit can be operational. It can be a continuous process, unlike batch-wise
This type of filtration is typically selected for feeds containing a high proportion of small particle size
solids (where the permeate is of most value) because solid material can quickly block (blind) the filter
surface with dead-end filtration. Industrial examples of this include the extraction of soluble antibiotics
from fermentation liquors.
Ceramic membrane for industrial cross-flow filtration
In crossflow filtration, the feed is passed across the filter membrane (tangentially) at positive pressure
relative to the permeate side. A proportion of the material which is smaller than the membrane pore size
passes through the membrane as permeate or filtrate; everything else is retained on the feed side of the
membrane as retentate.
With crossflow f