Membrane separations began in the 1960s as an alternative means to distillation for the desalination of salt (i.e. sea) and brackish waters. This was called reverse osmosis because it works by applying a transmembrane pressure greater than the natural osmotic pressure between the two solutions (seawater, say, and desalted water). The various processes in which […]
Membranes are made in a variety of ways, according to how they are to be used, with basic formats as flat sheets, tubes of very different diameters and solid blocks, on the surfaces of which the membrane is later deposited. The various manufacturing processes can be broadly summarized as: ● sintering of fine graded particles […]
As the term is applied nowadays, membranes can be porous or non-porous, polymeric or inorganic. They can be used for a range of separations including solids from liquids, liquids from liquids, and gases from gases, but in particular it is the filtration of micrometre and sub-micrometre size particles from liquids and gases where membranes have […]
In terms of filtration and separation technology, membranes have become one of the most important components. It is almost impossible to separate membrane media from the processes and equipment in which membranes are used, so this is only the briefest of introductions to membranes, with more detailed coverage in Sections 3 and 4. In separation […]
A completely different constructed cartridge has a perforated cylindrical core around which is wound a continuous filament or yarn. With a plastic filament or metal wire, the core may be threaded and the first layer of the filament is wound into the threads, giving the required degree of spacing of consecutive turns. The cartridge may […]
Similar to the edge filter in appearance, in that it has an array of disc-shaped components held on a central core, the stacked disc filter differs because the discs are actually hollow, with filter media over the faces of the disc. It employs individual discs, porous on both sides – that are stacked over a […]
Edge filters involve the use of cartridge elements where the element is composed of a stack of discs or washers of paper, felt, plastic or metal, clamped together in compression. Liquid flow takes place from the outer edge inwards between the discs, which may be in intimate contact in the case of non-rigid disc materials, […]
The majority of the specific filter media discussed so far in this Section have been porous materials, usually continuous in original format, with an intrinsic porosity consequent upon their method of original manufacture. Somewhat like the assembled bar types of media described in Section 2D, there is a very useful group of filter elements that […]
A quite different use for metal in making filtration media comes in the structures that are built up from individual bars, rods or wires that may have been processed to change their shape. The filter elements made from these media are thus assembled rather than produced in sheets or rolls. As a result they are […]
Expanded metal is made from a metal sheet by a repetitive process that involves first cutting it to form a series of short slits, and then stretching the sheet to open up these slits into the characteristic diamond apertures (Figure 2.17). This may be followed by calendering (pressing between rolls) so as to flatten the […]
