Membranes schematic

Figl Structural features of the mesoporous alumina membranes Schematic cross section (before removal of A1 backing) and schematic top view, together with an atomic force microscope AFM (Voltage) image for a membrane produced by anodisation at 40 V. 

Fig. 4 Structure of a heterogeneous membrane (schematic). Colloidal ion-exchanger particles (1-10 pm in diameter) are embedded in an inert binder. (From Ref.. )...

Figure 5.8 Hindered transport through porous membranes. Schematic diagram of model for hindered transport of a spherical particle in a cylindrical pore.

Membrane Technology, Fig. 2 Oxygen-permeation flux through a ceramic membrane (schematically). Gas flow 1 is of high oxygen pressure (air), gas flow 2 is vacuum or methane... 

Figure 4.18 In-vivo electron transfer in photosynthetic membranes. Schematic representation of the reaction centre in the chromatophore membrane. The immediate reactants arc cytochrome c molecules (C2) BB is the dimer of bacteriochlorophyll, 1 is bacteriopheophytin, and Q is a quinone. Firom Ref. [48,b].

Micellar structure has been a subject of much discussion [104]. Early proposals for spherical [159] and lamellar [160] micelles may both have merit. A schematic of a spherical micelle and a unilamellar vesicle is shown in Fig. Xni-11. In addition to the most common spherical micelles, scattering and microscopy experiments have shown the existence of rodlike [161, 162], disklike [163], threadlike [132] and even quadmple-helix [164] structures. Lattice models (see Fig. XIII-12) by Leermakers and Scheutjens have confirmed and characterized the properties of spherical and membrane like micelles [165]. Similar analyses exist for micelles formed by diblock copolymers in a selective solvent [166]. Other shapes proposed include ellipsoidal [167] and a sphere-to-cylinder transition [168]. Fluorescence depolarization and NMR studies both point to a rather fluid micellar core consistent with the disorder implied by Fig. Xm-12. 

The concept of the reversed fuel cell, as shown schematically, consists of two parts. One is the already discussed direct oxidation fuel cell. The other consists of an electrochemical cell consisting of a membrane electrode assembly where the anode comprises Pt/C (or related) catalysts and the cathode, various metal catalysts on carbon. The membrane used is the new proton-conducting PEM-type membrane we developed, which minimizes crossover. 

Schematic diagram of an enzyme-based potentiometric biosensor for urea in which urease is trapped between two membranes.

Fig. 12. Schematic of hoUow-fiber membrane cartridge employed for blood dialysis. Courtesy of Cordis-Dow.

Several human receptors for the neurohypophyseal hormones have been cloned and the sequences elucidated. The human V2 receptor for antidiuretic hormone presumably contains 371 amino acids and seven transmembrane segments and activates cycHc AMP (76). The oxytocin receptor is a classic G-protein-coupled type of receptor with a proposed membrane topography also involving seven transmembrane components (84). A schematic representation of the oxytocin receptor stmcture within the membrane is shown in Eigure 4 (85). 

A schematic diagram of the polymer precipitation process is shown in Figure 8. The hot polymer solution is cast onto a water-cooled chill roU, which cools the solution, causing the polymer to precipitate. The precipitated film is passed through an extraction tank containing methanol, ethanol or 2-propanol to remove the solvent. Finally, the membrane is dried, sent to a laser inspection station, trimmed, and roUed up. The process shown in Figure 8... 

Fig. 10. Schematic of casting machine used to make microporous membranes by watervapor imbibition. A casting solution is deposited as a thin film on a moving stainless steel belt. The film passes through a series of humid and dry chambers, where the solvent evaporates from the solution, and water vapor is absorbed from the air. This precipitates the polymer, forming a microporous membrane that is taken up on a collection roU (25).

Fig. 11. Schematic of Loeb-Sourirajan membrane casting machine used to prepare reverse osmosis or ultrafiltration membranes. A knife and trough is used to coat the casting solution onto a moving fabric or polyester web which enters the water-filled gel tank. After the membrane has formed, it is washed...

Interfdci l Composite Membra.nes, A method of making asymmetric membranes involving interfacial polymerization was developed in the 1960s. This technique was used to produce reverse osmosis membranes with dramatically improved salt rejections and water fluxes compared to those prepared by the Loeb-Sourirajan process (28). In the interfacial polymerization method, an aqueous solution of a reactive prepolymer, such as polyamine, is first deposited in the pores of a microporous support membrane, typically a polysulfone ultrafUtration membrane. The amine-loaded support is then immersed in a water-immiscible solvent solution containing a reactant, for example, a diacid chloride in hexane. The amine and acid chloride then react at the interface of the two solutions to form a densely cross-linked, extremely thin membrane layer. This preparation method is shown schematically in Figure 15. The first membrane made was based on polyethylenimine cross-linked with toluene-2,4-diisocyanate (28). The process was later refined at FilmTec Corporation (29,30) and at UOP (31) in the United States, and at Nitto (32) in Japan. 

Fig. 25. Reverse osmosis, ultrafiltration, microfiltration, and conventional filtration are related processes differing principally in the average pore diameter of the membrane filter. Reverse osmosis membranes are so dense that discrete pores do not exist transport occurs via statistically distributed free volume areas. The relative size of different solutes removed by each class of membrane is illustrated in this schematic.

Depth filters are usually preferred for the most common type of microfiltration system, illustrated schematically in Figure 28. In this process design, called "dead-end" or "in-line" filtration, the entire fluid flow is forced through the membrane under pressure. As particulates accumulate on the membrane surface or in its interior, the pressure required to maintain the required flow increases until, at some point, the membrane must be replaced. The useful life of the membrane is proportional to the particulate loading of the feed solution. In-line microfiltration of solutions as a final polishing step prior to use is a typical apphcation (66,67). 

Fig. 28. Schematic representation of dead-end and cross-flow filtration with microfiltration membranes. The equipment used in dead-end filtration is simple, but retained particles plug the membranes rapidly. The equipment required for cross-flow filtration is more complex, but the membrane lifetime is...

Fig. 35. Schematic diagram of a plate-and-frame electro dialysis stack. Alternating cation- and anion-permeable membranes are arranged in a stack of up to...

Fig. 44. Schematic examples of facUitated transport of gases and metal ions. The gas-transport example shows the transport of oxygen across a membrane using hemoglobin (HEM) as the carrier agent. The ion-transport example shows the transport of copper ions across the membrane using a Uquid...

Fig. 45. Schematic of transdermal patch in which the rate of deUvery of dmg to the body is controlled by a polymer membrane. Such patches are used to...

Fig. 2. Schematic of the G-proteia coupled receptor (GPCR). The seven a-heUcal hydrophobic regions spanning the membrane are joined by extraceUular and iatraceUular loops. The amino terminal is located extraceUulady and the carboxy terminal iatraceUulady.

Fig. 18. Schematic representation of cycling of low density Hpoprotein (LDL) receptors from the plasma membrane to the cell interior.

Measurable Process Parameters. The RO process is relatively simple ia design. It consists of a feed water source, feed pretreatment, high pressure pump, RO membrane modules, and ia some cases, post-treatment steps. A schematic of the RO process is shown ia Figure 2a. 

Fig. 11. Schematic of membrane-based hybrid process for ultrapure water production.

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

Since membrane fording could quickly render the system inefficient, very careful and thorough feedwater pretreatment similar to that described in the section on RO, is required. Some pretreatment needs, and operational problems of scaling are diminished in the electro dialysis reversal (EDR) process, in which the electric current flow direction is periodically (eg, 3—4 times/h) reversed, with simultaneous switching of the water-flow connections. This also reverses the salt concentration buildup at the membrane and electrode surfaces, and prevents concentrations that cause the precipitation of salts and scale deposition. A schematic and photograph of a typical ED plant ate shown in Eigure 16. 

Redox flow batteries, under development since the early 1970s, are stUl of interest primarily for utility load leveling applications (77). Such a battery is shown schematically in Figure 5. Unlike other batteries, the active materials are not contained within the battery itself but are stored in separate tanks. The reactants each flow into a half-ceU separated one from the other by a selective membrane. An oxidation and reduction electrochemical reaction occurs in each half-ceU to generate current. Examples of this technology include the iron—chromium, Fe—Cr, battery (79) and the vanadium redox cell (80). 

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