hollowfiber

Hollow fiber, or hollowfiber, refers to a type of porous membrane formed into thin-walled, capillary-sized tubes with a central lumen. The membranes are typically closed at the distal end and open at the base, allowing feed solution to flow either through the lumen (inside-out configuration) or around the exterior of the fibers (outside-in, in module flow). The porous wall provides selective passage of solvent and small solutes while rejecting larger species.

Materials and fabrication: Common materials include cellulose derivatives (cellulose acetate, cellulose triacetate) and synthetic polymers such as polyethersulfone (PES), polysulfone (PSU), polyvinylidene fluoride (PVDF), and polyacrylonitrile (PAN). Hollow fibers are manufactured by spinning and phase inversion, often in dry-wet processes, to create an asymmetric wall with a dense inner layer and a more porous outer region. Post-treatment may adjust hydrophilicity and fouling resistance.

Applications: Hollow-fiber membranes are used in ultrafiltration and microfiltration processes for water treatment, wastewater treatment, and groundwater pretreatment, removing colloids, bacteria, and macromolecules. They are also used in hemodialysis as dialyzer membranes, where blood flows through the lumens and a dialysate flows around the fibers. Some hollow-fiber membranes are employed in gas separation and other specialized separations.

Advantages and limitations: The hollow-fiber format yields very high surface-area-to-volume ratios, enabling compact modules and high permeate flux. They are scalable and modular but are prone to fouling, compaction under pressure, and limited chemical resistance depending on material; cleaning and sanitization are required to extend life.