Microfiltration hollow-fiber membrane

Blood cells are separated from blood (hematocrit 40%) by microfiltration, using hollow-fiber membranes with an inside diameter of 300 pm and a length of 20 cm. The average flow rate of blood is 5.5 cm s T Estimate the filtrate flux. 

Microfiltration and UF membranes are available in tubular, spiral wound, and hollow fiber membrane module configurations. Tubular and spiral MF and UF modules are similar to RO tubular and spiral wound membrane modules described in Chapters 4.3.2 and 4.3.3. However, while the thickest feed spacer in a spiral RO module is 34-mil, UF and MF modules nominally have up to a 45-mil spacer due to the relatively high concentration of suspended solids these membranes are called upon to treat (TriSep Corporation offers a special 65-mil spacer for dairy applications). 

Microfiltration and UF hollow fiber membranes are different than the hollow fine fibers discussed in Chapter 4.3.4. The MF and UF membranes are thicker and not quite as flexible, resembling fine-diameter straws rather than human hair. Diameter of fibers ranges... 

A radiation-induced grafting technique has been commercialized for the production of ion-exchange membranes as separators of batteries, hydrophilized hollow-fiber membranes for microfiltration of protein solutions, and ion-exchange nonwoven fabric for the removal of trace amounts of gases from ultraclean rooms [1,2]. 

Zhanga X, Fanga D, Lina B, Donga Y, Menga G, and Liu X. Asymmetric porous cordierite hollow fiber membrane for microfiltration. 7. AZZoy. Compd. 2009 487 631-638. 

Figure 3 Membrane modules for microfiltration and ultrafiltration, (a) Tubular membrane module. (From Zeman and Zydney, 1996.) (b) Cassette membrane assembly. (From Perry et al., 1997.) (c) Spiral wound membrane module. (From Purchase, 1996.) (d) Hollow fiber membrane module. (From Zeman and Zydney, 1996.)...

Sawada Y, Fujii R, Igami I et al. Removal of endotoxin from water by microfiltration through a microporous polyethylene hollow fiber membrane. Appl Environ Microbiol 1986 51 813-820. 

Wickramasinghe et al. (2004b) obtained about 4 log clearance of MVM by flocculation of a Chinese hamster ovary cell feed stream spiked with MVM. After addition of the flocculant, microfiltration was conducted using 0.2-p,m pore size hollow-fiber membranes (GE Healthcare, Fairfield, CT). In the absence of flocculant, only about 1 log clearance of MVM was obtained in the permeate, while for vims particles suspended in buffer no rejection was observed. In these studies, rejection of MVM is due to the cake layer and not the membrane. Consequently, careful control of the TMP and feed flow rate will be required to ensure similar cake properties. 

Three key elements determine the potential and applications of a hollow-fiber membrane (1) pore size and pore size distribution, (2) selective layer thickness, and (3) inherent properties (chemistry and physics) of the membrane material. Pore size and its distribution usually determine membrane applications, separation factor, or selectivity. The selective layer thickness determines the membrane flux or productivity. Material chemistry and physics govern the intrinsic permselectivity for gas separation and pervaporation, fouling characteristics for RO (reverse osmosis), UF (ultrafiltration), and MF (microfiltration) membranes, chemical resistance for membranes used in harsh environments, protein and drug separation, as well as biocompatibUity for biomedical membranes used in dialysis and biomedical and tissue engineering. 

The study of dual-layer asyimnetric hollow-fiber membranes formed by the phase-inversion process started in the late 1980s. In 1987, Yanagimoto invented dual-layer asymmetric flat-sheet and hollow-fiber membranes to improve the antifouling properties of membranes for ultrafiltration and microfiltration (Yanagimoto, 1987, 1988). Since then, Kuzumoto and Nitta (1989) simultaneously extruded inner and outer dopes containing the same polymer but different solvents and additives to improve water permeability. Ekiner et al. (1992) disclosed the procedures for the fabrication of dual-layer hollow fibers for gas separation. Li et al. (2002) developed a delamination-fiee dual-layer asymmetric... 

One specific advantage of this process is that the dense polymer layer firmly adheres to a porous support offering the ability to withstand high pressure. Hollow fiber membranes utilized in gas separation need to withstand continuous pressures up to and exceeding 1000 psi. For gas separation, it is desirable to have a continuous porous stmrture as the support without macrovoids, which can often be produced if the phase inversion variables (such as polymer solution concentration) are not optimized. For ultra- and microfiltration membranes, macrovoids often exist but do not critically restrain the... 

Poly(vinylidene fluoride) (PVDF) is one of the promising polymeric materials that has prominently emerged in membrane research and development (R D) due to its excellent chemical and physical properties such as highly hydrophobic nature, robust mechanical strength, good thermal stability, and superior chemical resistance. To date, PVDF hollow-fiber membranes have dominated the production of modem microfiltration (MF) ultrafiltration (UF) membrane bioreactor (MBR) membranes for municipal water and wastewater treatment and separation in food, beverage, dairy, and wine industries. In the last two decades, increasing effort has been made in the development of PVDF hollow fibers in other separation applications such as membrane contractors [6,7], membrane distillation (MD) [8-11], and pervaporation [12,13]. 

B.J. Cha and J.M. Yang. (2006). Effect of high-temperature spinning and PVP additive on the properties of PVDF hollow fiber membranes for microfiltration, Macromol. Res. 14 596-602. 

Whereas the liquid-solid filtration processes described so far can separate particles down to a size of around 10 xm, for smaller particles that need to be separated, a porous polymer membrane can be used. This process, known as microfiltration, retains particles down to a size of around 0.05. im. A pressure difference across the membrane of 0.5 to 4 bar is used. The two most common practical arrangements are spiral wound and hollow fiber. In the spiral wound arrangement, flat membrane sheets separated by spacers for the flow of feed and filtrate are wound into a spiral and inserted in a pressure vessel. Hollow... 

The hollow-fiber systems for gas separation or the tubular microfiltration systems have to be pyrolyzed before mounting in the membrane housing, because of the large shrinkage during pyrolysis. That is the most critical step in the fabrication of a separation system. 

Microfiltration - pLTRAFILTRATION] (Vol 24) -hollow-fiber technology [HOLLOW-FIBERMEMBRANES] (Vol 13) -pretreatment for membrane feed [REVERSE OSMOSIS] (Vol 21)... 

In contrast to hemodialysis that uses ultrafiltration membranes, plasma separation (also called plasmapheresis) requires microfiltration membranes with a pore size from 0.2 to 0.6 pm, in order to transmit all proteins and lipids, including LDL cholesterol (2000kDa) and retain completely platelets (2 pm diameter), red blood cells (8 pm diameter) and white blood cells. Thus, membrane plasmapheresis can yield high-quality platelet-free plasma and red cells can be either continuously returned to the donor or saved in another bag for blood transfusion. But it is important, in the case of plasma collection from donors, to minimize the membrane area, in order to reduce the cost of disposable hollow-fiber filters and to avoid the risk of hemolysis (free hemoglobin release) due to RBC damage by contact at the membrane if the pressure difference across the membrane is too high. 

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