Tangential-Flow Ultrafiltration

In tangential-flow ultrafiltration (also called cross-flow ultrafiltration), a fluid is pumped tangentially along the surface of a membrane. An applied pressure drives a portion of the fluid through the membrane (permeate) to the filtrate side. Particulates and macromolecules that are too large to pass through the membrane pores are retained on the upstream side (retentate).

The tangential flow of sample solution across the membrane surface helps slow the buildup of molecules and particles that can clog the pores or form a cake layer that reduces the permeate flow, i.e., “fouling” the membrane. This feature of tangential-flow ultrafiltration makes it an ideal process for fine-particle separations.

In ultrafiltration, a broad range of membranes with different size cutoff ranges can be employed to affect size separation, ranging from approximately 1 micrometer (μm) to 0.003 μm or approximately 1,000 kilodaltons (kDa) to 1 kDa on a molecular-weight scale. The membrane systems can be fabricated in a variety of mechanical configurations. Flatsheet membranes can be used in plate-and-frame or spiral-wound configurations. Hollow fibers of membrane material packed into a module are another common equipment design. Polymers are the most common porous materials used for ultrafiltration membranes, but some inorganic materials such as alumina are also used.

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