Dialysis Piezodialysis

Diffusion dialysis Donnan dialysis Piezodialysis Neutralization dialysis Pervaporation Facilitated transport... 

Three other processes using ion exchange membranes (Donnan dialysis, diffusion dialysis and piezodialysis) are covered in Chapter 13. 

Now the major application of dialysis is the artificial kidney and, as described in Chapter 12, more than 100 million of these devices are used annually. Apart from this one important application, dialysis has essentially been abandoned as a separation technique, because it relies on diffusion, which is inherently unselec-tive and slow, to achieve a separation. Thus, most potential dialysis separations are better handled by ultrafiltration or electrodialysis, in both of which an outside force and more selective membranes provide better, faster separations. The only three exceptions—Donnan dialysis, diffusion dialysis and piezodialysis—are described in the following sections. 

Donnan dialysis successfully involves mosaic membranes which are an important part of piezodialysis. Their basic advantage is the close juxtapoation of anion- and cation-exchange resins in the same membrane. It is a pity that research on piezodialysis, a desalination process with great promise and hopes, has been abandoned. However, one may expect work on it will be reassumed as soon as some difficulties originated from the deficiency of mosaic membranes, as well as some engineering problems, are overcome. 

Ion exchange membranes have been used in various industrial fields, and have great potential for use in new fields due to their adaptable polymer membrane. As mentioned in the Introduction, membranes are characterized mainly by ion conductivity, hydrophilicity and the existence of carriers, which originate from the ion exchange groups of the membrane. Table 6.1 shows reported examples of applications of ion exchange membranes and the membrane species used in various fields. Various driving forces are usable for separation electrochemical potential, chemical potential, hydraulic pressure such as piezodialysis and pervaporation, temperature difference (thermo-osmosis), etc. Of these, the main applications of the membrane are to electrodialysis, diffusion dialysis, as a separator for electrolysis and a solid polymer electrolyte such as in fuel cells. 

Reverse Osmosis n Dialysis Electrodialysis Piezodialysis Gas Permeation Pervaporation... 

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