Membrane elements

The membrane material varies from alumina, zirconia, glass, titania, cordierite, mulUte, carbon to such metals as stainless steel, palladium and silver. The resulting pore diameter ranges from 10pm down to4 nm and the membrane thickness varies from 3 to 10 pm. The membrane porosity depends on the pore size and is 40-55%. 

A generalization of this concept of a monolithic multi-channel honeycomb structure is described in a patent by Hoover and Roberts [1978]. An integral support of porous ceramic material has a multiplicity of parallel passageways (or open channels). These passageways are substantially uniformly spaced. On the surface of these channels are coated with a permselective membrane layer. The feed stream flows inside the channels. The membrane, being the first layer in direct contact with the process stream, is selective to one or more species in the stream. In the normal cases of properly weued membrane pores, the permeate under a driving force will uansport through the membrane, any 

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Fig. 12. A spinal-wound leveise osmosis membrane element (a) schematic depiction (b) cross section of a spinal-wound thin-film composite RO Filmtec...

Fig. 13. A hoUow-fibet reverse osmosis membrane element. Courtesy of DuPont Permasep. In this twin design, the feedwater is fed under pressure into a central distributor tube where half the water is forced out tadiaUy through the first, ie, left-hand, fiber bundle and thus desalted. The remaining portion of the feedwater flows through the interconnector to an annular feed tube of the second, ie, right-hand, fiber bundle. As in the first bundle, the pressurized feedwater is forced out tadiaUy and desalted. The product water flows through the hoUow fibers, coUects at each end of the element, and exits there. The concentrated brine from both bundles flows through the concentric tube in the center of the second bundle and exits the element on the right.

Cassettes Cassette is a term used to describe two different cross-flow membrane devices. The less-common design is a usually large stack of membrane separated by a spacer, with flow moving in parallel across the membrane sheets. This variant is sometimes referred to as a flat spiral, since there is some similarity in the way feed and permeate are handled. The more common cassette has long been popular in the pharmaceutical and biotechnical field. It too is a stack of flat-sheet membranes, but the membrane is usually connected so that the feed flows across the membrane elements in series to achieve higher conversion per pass. Their popularity stems from easy direct sc e-up from laboratoiy to plant-scale equipment. Their hmitation is that fluid management is inherently veiy hmited and inefficient. Both types of cassette are veiy compact and capable of automated manufacture. 

Membrane systems consist of membrane elements or modules. For potable water treatment, NF and RO membrane modules are commonly fabricated in a spiral configuration. An important consideration of spiral elements is the design of the feed spacer, which promotes turbulence to reduce fouling. MF and UF membranes often use a hollow fiber geometry. This geometry does not require extensive pretreatment because the fibers can be periodically backwashed. Flow in these hollow fiber systems can be either from the inner lumen of the membrane fiber to the outside (inside-out flow) or from the outside to the inside of the fibers (outside-in flow). Tubular NF membranes are now just entering the marketplace. 

MDMA is not likely to be involved in the ability of these eompounds to cause serotonin terminal degeneration. The preponderanee of the evidence supports the hypothesis that the assoeiation of [ H]MDA with synaptosomes is primarily wi membrane elements. 

Spiral-wound reverse osmosis membrane element, 26 75 Spiramycin... 

A single-pass experimental study used a 2.5 inch by 40 inch commercial membrane element. The recovery and reject results are calculated from ... 

The design work to produce a commercial competitive product showed that lowering the temperature of brine to less than 50°C, which was necessary in the demonstration plant, added additional equipment and installation costs to the skids. A series of experiments were carried out on a new improved membrane element, developed for higher brine temperature. In this way we could feed dechlorinated brine to the skid without addition of a cooler. The results of these experiments are shown in Table 11.1. 

Rejection of sodium sulphate was exceptional at the lower temperatures but permeate recovery was low. The testing at 81°C fulfilled Kvaerner s need to reduce overall skid costs and provide good rejection with an acceptable recovery rate. The use of high temperature membranes has provided the means to optimise the number of membrane elements, reduce the equipment costs and ensure that the SRS skid is an economically attractive package. 

A few other players in the nuclear membranes activity also developed inorganic membranes for the filtration of liquids. This was the case with Norton-USA who with the know-how of Euroceral developed MF membranes made of an 0-AI2O3 tubular support with an a-Al203 layer. The inner tube diameter was 3 mm and the outer diameter 5 mm. In 1988-1989, Norton also produced the multichannel membrane elements. These membranes produced by Norton are now sold by Millipore under the trademark Ceraflo . 

In the second half of the 1980s, an increasing number of companies entered the field of inorganic membranes, the most significant ones being ceramic companies such as NGK of Japan which also developed a multichannel membrane element (19 channels, 3 mm diameter), Nippon Cement and Toto also from Japan and very recently Coming who also developed a multichannel membrane structure. 

Manufacturer Trade Name Membrane Material Support Material Membrane Pore Diameter Geometry of Membrane Element Tube or Channel Inside Diameter (mm)... 

Table 3.3. Mechanical Property Data of Various Inorganic Membrane Elements...

A membrane module may contain many membrane elements as shown in Figure 3.16, where 19 monolithic membrane elements each with 19 channels... 

Figure 3.14. Photograph of alumina membrane elements (Alcoa 1987).

Figure 3.15. Schematic of permeate flow path through a porous multichannel monolithic membrane element (Hsieh 1988, Hsieh, Bhave and Fleming 1988).

This same effect was since demonstrated in spiral-wound NS-300 membrane elements placed on test toward brackish water at Roswell Test Facility operated by the Office of Water Research and Technology, U.S. Department of the Interior. 

Table 6 lists several of the salient properties of this new composite membrane. When salt rejection was evaluated at different pressures in simulated seawater trials, potable water (containing less than 500 ppm dissolved salts) was generated at as low as 600 psi, with very good flux (12 gfd) at that pressure. In spiral-wound membrane element trials on actual 33,000 ppm seawater, potable water was obtained even at 500 psi, albeit at low flux. These results surpass by far the capabilities of any of the "NS" series of membranes. 

In a related case, FT-30 membrane elements were placed on chlorinated seawater feed at OWRT s Wrightsville Beach Test Facility. Flux and salt rejection were stable for 2000 hours at 0.5 to 1.0 ppm chlorine exposure. Chlorine attack did become noticeable after 2000 hours, and salt rejection had dropped to 97 percent at 2500 hours while flux increased significantly. Long term laboratory trials at different chlorine levels led to the conclusion that the membrane will withstand 0.2 ppm chlorine in sodium chloride solutions at pH 7 for more than a year of continuous exposure. 

Dl. Dallner, G., Studies on the structural and enzymic organization of the membranous elements of liver microsomes. Ada Pathol. Microbiol. Scand., Suppl. 166, 1-94 (1963). 

Mercury Elemental mercury Respiratory tract Soft tissues, especially kidney, CNS CNS tremor, behavioral (erethism) gingivostomatitis peripheral neuropathy acrodynia pneumonitis (high-dose) Inhibits enzymes alters membranes Elemental Hg converted to Hg2+. Urine (major) feces (minor)... 

The following table summarizes the important physical characteristics of the various membrane element device configurations available today ... 

In order for membranes to be used in a commercial separation system they must be packaged in a manner that supports the membrane and facilitates handling of the two product gas streams. These packages are generally referred to as elements or bundles. The most common types of membrane elements in use today include the spiral-wound, hollow fiber, tubular, and plate and frame configurations. The systems currently being marketed for gas separation are of the spiral-wound type, such as the SEPAREX and Delsep processes, and the hollow-fiber type such as the Prism separator and the Cynara Company process. 

The membrane system consists of membrane elements connected in series and contained within pressure tubes as shown in Figure 3. A rubber U-cup attached to the element serves to seal the element with the inner diameter of the pressure tube, thereby forcing the feed gas to flow through the element. The pressure tubes usually contain six elements each and are mounted in racks on a skid. Commercial size elements are typically 8 inches in diameter by 40 inches long and contain from 150 to 275 square feet of membrane area. 

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