Hollow-fiber membranes

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Hollow fiber membranes are capillary fibers with diameters ranging from 0.2-3.00 mm and wall thicknesses around 20-500µ. This type of membrane is considered to be the most economical as while assembled in a module, these modules have high surface-to-volume ratio (high surface area of membrane in small volume of the module). In hollow fiber membranes, filtration occurs through the porous wall and similarly to flat sheet membranes, the pore size of the wall defines which component will be transferred through the membrane and which ones will be retained.

Raw Materials Properties Comparison

  • PSU/PES have tight pore sizes while PVDF have a large spread
  • PSU/PES have wide pH resistance but limited chlorine resistance on the contrary PVDF has limited pH resistance but wide chlorine resistance
  • PSU/PES have low mechanical strength while PVDF has excellent ductility
  • PSU/PES can be made into a tight UF pore size while PVDF has a wide pore sizes

 

Depending on application and the morphology of membrane cross section, hollow fiber membranes can be used in two different modes: inside-out and outside-in. The former mode means that the feed solution is supplied inside the hollow fiber and the permeate is collected on the outside. While the latter mode implies that feed stream is sent on the outside of the fibers and the filtrate (permeate) is collected inside the fiber.

Fabrication of hollow fibers is a challenging process which requires careful optimization of multiple process parameters and precise manufacturing equipment. One of key elements in hollow fiber spinning process are spinnerets, where coagulation of polymer solution starts upon its contact with bore solution supplied through the central needle to form a hollow part of the fiber.