Sealing of the membrane

HF/cm2. From a capacitance calibration curve similar to Figure 6b and Equation 6, a value of 15.4 nF was obtained for Ct when Cm was zero. Membrane resistances in the absence of ionophores ranged from 300 Mi2 to 20 G 2 as determined from X2. These values varied considerably because they are probably measures more of the quality of the seal of the membrane to the aperture than of a real property of the membrane. 

A concept for a methanol (or ethanol) fuel processor based upon steam reforming and membrane separation was presented by Gepert et td. [400]. As shown in Figure 5.33, the alcohol/water mixture was evaporated and converted by steam reforming in a fixed-bed catalyst, into which palladium capillary membranes were inserted. The retenate then entered the combustion zone, which was positioned concentrically around the reformer bed at the reactor wall. Air was fed into the combustion zone and residual hydrogen, carbon monoxide and unconverted methanol combusted therein. The sealing of the membranes at the reactor top was an issue solved by air-cooled elastomers. 

A methanol fuel processor based on steam reforming in a fixed catalyst bed and membrane separation was described by LedjefF-Hey et al. [401]. The system consisted of an evaporator, a steam reformer, which was supplied with heat by a catalytic burner, and a membrane separation module, which carried membranes of a very high thickness of 7.5 mm. At 5-bar system pressure and S/C ratio of 2.0, a hydrogen flow equivalent to 1.1-kW thermal power was generated by the system, which had an overall efficiency of 54%. Between 40 and 62% of the hydrogen produced by the reformer could be separated by the membrane module. Leakages in the sealing of the membrane module led to carbon monoxide spill-over to the permeate, but this was limited to carbon monoxide concentrations well below 100 ppm. 

To avoid collecting deposits, the tip of the electrode is coated with silicone oil using a cotton wad before the first use. This oil is also supplied by the manufacturer. During all manipulations with the electrode surface extreme caution is required to insure that the seal of the membrane cemented into the electrode body is not damaged ... 

Resonant Sound Absorbers. Two other types of sound-absorbing treatments, resonant panel absorbers and resonant cavity absorbers (Helmholtz resonators), are used in special appHcations, usually to absorb low frequency sounds in a narrow range of frequencies. Resonant panel absorbers consist of thin plywood or other membrane-like materials installed over a sealed airspace. These absorbers are tuned to specific frequencies, which are a function of the mass of the membrane and the depth of the airspace behind it. Resonant cavity absorbers consist of a volume of air with a restricted aperture to the sound field. They are tuned to specific frequencies, which are a function of the volume of the cavity and the size and geometry of the aperture. 

Spiral Wound. A spiral-wound cartridge has two flat membrane sheets (skin side out) separated by a flexible, porous permeate drainage material. The membrane sandwich is adhesively sealed on three sides. The fourth side of one or more sandwiches is separately sealed to a porous or perforated permeate withdrawal tube. An open-mesh spacer is placed on top of the membrane, and both the mesh and the membrane are wrapped spirally around the tube (Fig. 16). 

Spiral-wound modules consist of several flat membranes separated by turbulence-promoting mesh separators and formed into a Swiss roll (Figure 16.18). The edges of the membranes are sealed to each other and to a central perforated tube. This produces a cylindrical module which can be installed within a pressure tube. The process feed enters at one end of the pressure tube and encounters a number of narrow, parallel feed channels formed between adjacent sheets of membrane. Permeate spirals roward the perforated central tube for collection. A standard size spiral-wound module has a diameter of about 0.1m, a length of about 0.9 m and contains about 5 m2 of membrane area. Up to six such modules may be installed in series in a single pressure tube. These modules make better use of space than tubular or flat sheet types, but they are rather prone to fouling and difficult to clean. 

The above test provides a basis for evaluating a seal material s capability at the desired operating temperature. However, in realistic stack conditions, a seal material is under a shear stress. A double tube arrangement can be used to study the seal behavior. A disc can be sealed on both sides, and both tube enclosures can be pressurized to the same level. Such condition will eliminate the flexing of the membrane causing the seal to delaminate at a fairly low pressure when tested above Tg. In fact, a repeat test of the above seal with a double-tube arrangement showed that the seal could withstand 20 psi pressure before a small leak developed. 

The polycarbonate membranes are stretch-oriented during fabrication in order to improve their mechanical properties. If the membrane is subsequently heated above its glass-transition temperature ( 150°C), the polymer chains relax to their unstretched conformation and the membrane shrinks. This shrinking of the membrane around the Au nanowires in the pores causes the junction between the nanowire and the pore wall to be sealed. This is illustrated in Fig. 5, which shows voltammograms for tri-methylaminomethylferrocene (TMAFc+) before (Fig. 5A) and after (Fig. 

We have used voltammetric measurements in the absence of the electroactive species to quantitatively evaluate this heat-sealing procedure. The magnitude of the double layer charging current can be obtained from these voltammograms [25,68-70], which allows for a determination of the fractional electrode area (Table 1). This experimental fractional electrode area can then be compared to the fractional pore area calculated from the known pore diameter and density of the membrane (Table 1). In order to use this method, the double layer capacitance of the metal must be known. The double layer capacitance of Au was determined from measurements of charging currents at Au macro-disk electrodes of known area (Fig. 6, curve A). A value of 21 pF cm was obtained. 

Research effort at Albany International Research Co. has developed unit processes necessary for pilot scale production of several species of reverse osmosis hollow fiber composite membranes. These processes include spin-dope preparation, a proprietary apparatus for dry-jet wet-spinning of microporous polysul-fone hollow fibers, coating of these fibers with a variety of permselective materials, bundle winding using multifilament yarns and module assembly. Modules of the membrane identified as Quantro II are in field trial against brackish and seawater feeds. Brackish water rejections of 94+% at a flux of 5-7 gfd at 400 psi have been measured. Seawater rejections of 99+% at 1-2 gfd at 1000 psi have been measured. Membrane use requires sealing of some portion of the fiber bundle for installation in a pressure shell. Much effort has been devoted to identification of potting materials which exhibit satisfactory adhesion to the fiber while... 

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