Membrane spacer

There are a number of critical variables in the design of successful electric membrane equipment. Among these are the properties and cost of the membranes, the design and cost of the spacers, the size, cost, and construction of the alternating membrane-spacer-assembly—called the membrane stack—and the current density at which the unit is operated. 

The short history of electro dialysis to date provides several notable examples of field operation where substantial polarization-induced precipitation was encountered after apparently successful laboratory tests. For these reasons it is our firm conclusion that the only conclusive test of the mechanical and electromechanical adequacy of membrane-spacer combinations is operation on natural saline waters under field conditions over periods of several months and without recourse to recirculation. By such field tests the suitability of Nepton CR-61 and Nepton AR-111A on 4-ounce dynel has now been demonstrated. 

Table 3.5 Typical membrane area and number of membrane envelopes for 40-in.-long industrial spiral-wound modules. The thickness of the membrane spacers used for different applications causes the variation in membrane area...

The typical spiral-wound membrane, as shown in Figure 4.20, consists of four layers wrapped around a central collection pipe membrane, spacer (providing a permeate channel), membrane, and a new spacer (providing a feed channel). The feed-side spacer acts as a turbulence promotor, whereas on the permeate side the flow is directed toward the central pipe. The spiral-wound membrane will typically be a polymeric composite material, and is much used also for liquid separation. The packing density of this type of module will depend on the channel height, but is usually within the range of 300-1000 m /m [1]. Several modules may be assembled in one pressure vessel. 

Since oxygen is one of the products of electrolysis, if the electrolytic cell is undivided, reoxidation of U " ion takes place which hampers the production of uranyl with higher concentration. Cation-selective membrane spacers are effective in improving the production of uranyl nitrate solution. 

Many more membranes, spacer frames, and another end frame... 

Neutralization dialysis is proposed to be suitable for water purification because weak acids (such as acetic acid, carbonate, bicarbonate ions), and weak bases (like amines, ammonia) easily permeate through the membranes.188 190 Soluble silicate compounds in water can be removed by this method. Also, desalination of protein solutions containing sodium chloride has been reported by using a spiral module, in which a cation exchange membrane, spacer and anion exchange membrane were wound alternately.191... 

Integral membrane-spacer-gaskets were being developed by the SACSIR in... 

Gaskets and Membrane Spacers. In considering tolerances of components, reference must be made to the gaskets and spacer material used in the FSG plant. 

Cation-exchange membrane Spacer Anion-exchange membrane... 

Anion-Selective Membrane Coated Titanium Anode Anion-Selective Membrane Spacer... 

The typical spiral-wound manbrane, as shown in Figure 7.21, consists of four layers wrapped around a central collection pipe membrane, spacer (providing a permeate channel), membrane, and a new spacer (providing feed channel). The feed-side spacer acts as a turbulence promoter, whereas on the permeate... 

A recent development of the secondary flow-enhanced membrane processes is the helical membrane module, which is characterized by a DNA helical-like spacer enveloped by polyester filter cloth with a pore size around 22 pm [31-33]. Figure 10.12 shows the schematics of the helical membrane spacers with different twisted helical angles. The main parameters of the helical membrane include the angles of twist of the spacer or membrane and the ratio of the membrane width to the length. 

There are several common elements in the design of any electrodialysis stack end blocks, end frames with electrodes, membranes, spacers between membranes, and manifolds for inlet and outlet of fluids. The electrodes used in an electrodialysis stack must withstand the electrochemical reactions and the solutions that circulate within the electrode chambers, as well as to the electrolytes, which are carried there due to electrodialysis and form as a result of electrolysis. Residue must not be formed inside the electrode chambers, while the chamber itself must be thin enough to not create too much resistance to the electric current... 

Spacers A mesh-like material used in flat-sheet modules (e.g. plate, spirals, pleated sheet) to separate successive layers of membranes. Spacers control the feed channel dimensions in these modules. Serve as turbulence promoters in spiral-wound membrane elements. 

Field studies were done with commercial-scale spiral wound modules. Membrane, spacers and adhesives were wound around the central permeate pipe to form the module. Modules were both vacuum and high pressure tested to insure integrity. 

MANY MORE MEMBRANES, SPACER FRAMES, AND ANOTHER END FRAME... 

The assembly formed by a cation exchange membrane, an anion exchange membrane, spacers and gaskets, is called a cell pair or cell. An electrodialyzer can consist of up to 300 cells. The difference of potential appUed is usually set between 0.75 and 1.5 V/cell (depending on the membranes used and the concentration of the solutions). It is obvious, then, that an electrodialyzer works with high values of the difference of potential between the anode and cathode (Fig. 2). 

Cross-flow Input Membrane Spacer Membrane Cross-flow output... 

Today, microelectrodes can be prepared and used as electrical, magnetic, or acoustic probes or sensors. In a future process the membranes, spacers or modules could be equipped with a pattern of microelectrodes for different types of measurements and the collected data would be used for optimizing the process conditions within the membrane process. It could also be possible that, in an industrial process, there would for instance be one test module equipped in this way that could be placed somewhere in the process design. 

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