Microporous polypropylene

For the separation of D,L-leucine, Ding et al. [62] used poly(vinyl alcohol) gel-coated microporous polypropylene hollow fibers (Fig. 5-11). An octanol phase containing the chiral selector (A-n-dodecyl-L-hydroxyproline) is flowing countercur-rently with an aqueous phase. The gel in the pores of the membrane permits diffusion of the leucine molecules, but prevents convection of the aqueous and octanol phase. At a proper selection of the flow ratios it is possible to achieve almost complete resolution of the D,L-leucine (Fig. 5-12). 

These gas transfer membranes or membrane contactors employ microporous polypropylene hollow fiber membranes arranged in a modular design. Oxygenated water flows on the shell side of the hollow fibers, and a strip gas (such as nitrogen) or a vacuum is applied to the inside (lumenside), with the hollow fibers acting as a support medium for intimate contact between the water and gas phases. 

Fignre 27.3 shows a typical spectroelectrochemical cell for in sitn XRD on battery electrode materials. The interior of the cell has a construction similar to a coin cell. It consists of a thin Al203-coated LiCo02 cathode on an aluminum foil current collector, a lithium foil anode, a microporous polypropylene separator, and a nonaqueous electrolyte (IMLiPFg in a 1 1 ethylene carbonate/dimethylcarbonate solvent). The cell had Mylar windows, an aluminum housing, and was hermetically sealed in a glove box. 

As the separator, microporous polypropylene film (PORP by NPO UFIM, Russia) with the thickness of 25 pm was used. 

In lithium-based cells, the essential function of battery separator is to prevent electronic contact, while enabling ionic transport between the positive and negative electrodes. It should be usable on highspeed winding machines and possess good shutdown properties. The most commonly used separators for primary lithium batteries are microporous polypropylene membranes. Microporous polyethylene and laminates of polypropylene and polyethylene are widely used in lithium-ion batteries. These materials are chemically and electrochemically stable in secondary lithium batteries. 

Lithium CFj. The Li/CF rbattery consists of a lithium anode, polycarbon monofluoride cathode, and microporous polypropylene separator saturated with organic electrolyte. These batteries are used as power sources for watches, portable calculators, memory applications, and so on. 

Lithium SO2. The lithium SO2 systems are mainly used in military and some industrial and space applications. This system is particularly known for its capability to handle high current and high power requirements, for its excellent low-temperature performance, and for its long shelf life. They are typically fabricated in cylindrical structure by spirally winding rectangular strips of lithium foil, a microporous polypropylene separator, the cathode electrode, and a second separator layer. 

The most common material used is cellophane, which is a cellulose film, which acts as a membrane and is capable of resisting zinc penetration. The cycle life of cells utilizing this material is severely limited due to the hydrolysis of the cellophane in alkaline solution. Various methods have been tried to stabilize cellulose materials, such as chemical treatment and radiation grafting to other polymers, but none have, as of now proved economically feasible. The most successful zinc migration barrier material yet developed for the nickel—zinc battery is Celgard microporous polypropylene film. It is inherently hydrophobic so it is typically treated with a wetting agent for aqueous applications. 

Moeder M, Martin C, Koeller G (2004) Degradation of hydroxylated compounds using laccase and horseradish peroxidase immobilized on microporous polypropylene hollow fiber membranes. J Memb Sci 245(1) 183-190... 

Recently developed blood oxygenators are disposable, used only once, and can be presterilized and coated with anticoagulant (e.g., heparin) when they are constructed. Normally, membranes with high gas permeabilities, such as silicone rubber membranes, are used. In the case of microporous membranes, which are also used widely, the membrane materials themselves are not gas permeable, but gas-liquid interfaces are formed in the pores of the membrane. The blood does not leak from the pores for at least several hours, due to its surface tension. Composite membranes consisting of microporous polypropylene and silicone rubber have also been developed. 

Membranes can be classified as porous and nonporous based on the structure or as flat sheet and hollow fiber based on the geometry. Membranes used in pervaporation and gas permeation are typically hydrophobic, nonporous silicone (polydimethylsiloxane or PDMS) membranes. Organic compounds in water dissolve into the membrane and get extracted, while the aqueous matrix passes unextracted. The use of mircoporous membrane (made of polypropylene, cellulose, or Teflon) in pervaporation has also been reported, but this membrane allows the passage of large quantities of water. Usually, water has to be removed before it enters the analytical instrument, except when it is used as a chemical ionization reagent gas in MS [50], It has been reported that permeation is faster across a composite membrane, which has a thin (e.g., 1 pm) siloxane film deposited on a layer of microporous polypropylene [61],... 

In the membrane introduction ion trap MS (MIMS) technique, a membrane composed of a microporous polypropylene hollow support fiber coated with an ultrathin ca 0.5 p,m) polydimethylsiloxane layer serves as the interface between the sample and the vacuum chamber of the mass spectrometer. The simultaneous diffusion of volatile and semivolatUe compounds through the ultrathin polydimethylsiloxane MIMS membrane is one of the method s strengths, in that all the analytical information is obtained in a relatively short time (in the order of seconds to minutes). Lead and nickel / -diketonates could be detected by the MIMS technique. ... 

Liqui-Cel Extra-Flow (Figure 19.12) is one of the well studied hollow fiber modules for concentration-driven mass transfer. This module consists of several microporous polypropylene fibers, which are woven into a fabric and wrapped around a central tube feeder that supplies the shell side fluid. The woven fabric allows more uniform fiber spacing, which in turn leads to higher mass transfer coefficients than those obtained with individual fibers. The fiber lumen diameter and wall thickness are 240 and 30 pm, respectively [93,130]. The smallest Liqui-Cel modules are 2.5 in. in diameter and contain 1.4 m of contact area, while the largest are 10 in. in diameter and offer 130 m of contact area by virtue of 225,000 fibers. The large modules can handle liquid flow rates of several 1000 L/min. 

Jian-Mei, L., et al. Microporous polypropylene and polyethylene hollow fiber membranes. Part 3. Experimental studies on membrane distillation for desalination. Desalination, 115, 153, 2003. 

Barbe, A.M., Hogan, P.A., and Johnson, R.A. Surface morphology changes during initial usage of hydrophobic, microporous polypropylene membranes, J. Membr. Sci., 172, 149, 2000. 

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