Cross-flow filtration
Filtration method where feed flows tangentially across the filter surface.
Cross-flow filtration, also known as tangential flow filtration, is a type of filtration used in chemical engineering, biochemical engineering, and protein purification. It differs from dead-end filtration in that the majority of the feed flow travels tangentially across the surface of the filter, rather than into it, which helps prevent filter blinding and allows for continuous operation.
- field
- Chemical engineering, biochemical engineering, protein purification
- known_for
- Tangential flow filtration, continuous filtration with reduced filter blinding
- type
- Unit operation
- driving_force
- Transmembrane pressure
- applications
- Reverse osmosis, nanofiltration, ultrafiltration, microfiltration, protein purification
Lore & Background
In cross-flow filtration, the feed is passed across the filter membrane at positive pressure relative to the permeate side. Material smaller than the membrane pore size passes through as permeate, while everything else is retained as retentate. The tangential motion of the fluid causes trapped particles on the filter surface to be rubbed off, allowing continuous operation at high solids loads without blinding. The main driving force is transmembrane pressure, which may decrease due to increased permeate viscosity, reducing efficiency; this can be prevented by diluting permeate or increasing flow rate.
Reader's Guide
Cross-flow filtration is significant because it enables continuous filtration of feeds with high proportions of small particle solids, where the permeate is most valuable, such as in extracting soluble antibiotics from fermentation liquors. Its advantages include higher overall liquid removal rates, the ability to keep the feed as a mobile slurry, and the possibility of fractionating particles by size. The technology is used widely in industry with polymeric or ceramic membranes, and its principles apply to reverse osmosis, nanofiltration, ultrafiltration, and microfiltration. In protein purification, it is called tangential flow filtration (TFF). Performance can be improved through techniques like backwashing, alternating tangential flow (ATF), clean-in-place (CIP), process flow disruption (PFD), and model-based fouling control. The flux or flow rate is given by the equation J = ΔP / (R_m + R_c), where ΔP is transmembrane pressure and R_m and R_c are membrane and cake resistances.
Did You Know?
- Cross-flow filtration is also known as tangential flow filtration.
- The principal advantage is that the filter cake is substantially washed away during filtration, increasing operational time.
- It can be a continuous process, unlike batch-wise dead-end filtration.
- In protein purification, the term tangential flow filtration (TFF) is used to describe cross-flow filtration with membranes.
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