Plate Modules

Stainless steel is used as a construction material for support plates for the membranes and for spacers. Chemically stable elastomeres, like EPDM or per-fluorinated polymers are used as gasket material, more widely used is expanded graphite, due to its excellent chemical and thermal resistance. Preferentially the 

Membrane Support Plate Feed Plate Support Plate Membrane Spacer 

Usually all membranes in a module are arranged for parallel flow of the feed. The feed channel, between membrane and supporting plate, has a height between 0.5 to 1 mm, linear flow velocities of the liquid feed are of the order of a few centimeters per minute. Serial flow would be desirable in order to allow for higher linear flow velocities and higher Reynolds numbers, but then feed-side pressure losses will become too high. When used with a vaporous feed the feed channels need to be widened and linear velocities over the membrane should be of the order of 1 m per minute. 

Alternative designs are very similar to plate heat exchangers, in which the supported membrane replaces the heat-exchanger plates. These modules may be open or closed to the outside on the permeate side, with internal ducts for feed and retentate and, when closed, for permeate removal. It has been proposed to integrate plate heat exchangers as preheaters and permeate condenser into such modules. 

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The other example, called the nickel/ zinc battery [(-Zn)/KOH/NiOOH(+)], has attracted more attention in two different versions from the "application" and "cell design" viewpoints one is the small cylindrical consumer cell [30], the other one is the flat-plate module for electrotraction [31], A very interesting review with an extended collection of references was pub-... 

In the case of purification of water the permeate is the cleaned water and the removed components are collected in the concentrate [111-113]. Various modules can be used, such as plate-modules, tubes, and capillary modules. For water purification and recycling processes the following aspects have to be considered ... 

The treatment of ADUF by reverse osmosis [13] was found to be useful in concentrating activity in small volume while making a larger volume of the decontaminated effluent for direct disposal after required dilution. Porous cellulose acetate membranes were used in plate module configurations. The concentration of ammonium nitrate in the permeate stream is not very different from that of the contaminated retentate. With the addition of flocculating aids, the decontamination factors in the range of 1000 with VRFs in the range of 100 were achieved. 

The viscosity of the mixture was adjusted by the addition of approximately 50 % of toluene. The pilot plant consist of oxo-reactor and the membrane unit, which was directly connected to the reactor. Standard plate modules from Dow (Type DDS 30-4.5) were used. The conditions of the membrane separation were overflow 200 1/h, separation temperature 40 °C, transmembrane pressure 1 MPa. The unit was continuously operated over a period of 12 weeks. No decrease of activity of the catalyst was observed. In order to obtain a dialdehyde selectivity > 90 %, the Rh concentration must be increased to 100 ppm. Most of the loss of ligand was due to traces of oxygen, which could not excluded totally on pilot scale. 

Membrane processes are used to filter liquids. Instead of conventional filter materials (e.g. filter cloth, filter candles,) microporous membranes are employed with molecular size pores. First the industry had to learn how to manufacture membranes with controlled pore sizes. To optimise the filtration capacities specific filter structures had to be designed in which the liquid followed well defined flow patterns on one side of the membrane. Many different systems were developed for the varied applications, all having their advantages and also disadvantages, i.e. plate modules, tubular modules, spiral wound membranes, etc. Research and development in this field is far from being exhausted. Today membrane systems are available which are sufficiently resistant to chemical, mechanical and thermal stress. They are produced from plastic... 

Fig. 11 Plate module. (View this art in color at www. dekker.com.)...

Contradicting results were foimd concerning the Hquid flow rate. Urkiaga et al. [129] used plate modules with PEBA membranes and showed an increase in the removal efficiency with increasing flow rate due to a minimiza-... 

A further generality of the MDPE is that knowledge of the actual shape and geometry of the membrane within the MCS is not necessary. The equation is not restricted, and can be applied to any chosen shape (plate module, hollow fiber, spiral wound, and so on). 

Fig. 3.16 Plate modules, different sizes (Sulzer Chemtech GmbH).

There has been a development on spiral-wound modules for dehydration applications, too. So far this did not lead to apphcations in industrial plants. Chemical-stabihty problems of the components and too high pressure losses in the permeate-side spacer could not be solved satisfactorily, and the costs of the modules and for the installation in a plant were not reaUy lower than those for plate modules. 

Hollow fibers or capillary modules have not yet found an industrial application in pervaporation or vapor-permeation processes. A few data have been reported where organic capillary structures with an outside diameter of 0.5 to 1 mm have been coated with silicon and used in organophilic separation. With the flow on the shell side permeate pressure losses inside the bore of the fiber control the process. For specific organophilic applications, these pressure losses may be tolerable. For hydrophilic processes, however, the useful length of a module would be of the order of 20 to 30 cm only, even at an inner diameter of the capillary of 1 mm. Such a module, including housing and connection in any industrial application, is more costly than a plate module. So far no potting material is available that combines the necessary chemical and mechanical stability at the operation temperature and pressure of a dehydration plant. 

Each PZT stack (Noliac, Denmark) had an overall size of 5mm x 5mm x ISnun and was composed of 8 active plates (modules) and 2 inactive endplates. Each individual active plate (5mm x 5mm x 2mm) was a multilayer actuator with an inter-digital electrode (IDE) configuration that included 30 PZT layers each 67 pm thick. The 5mm x 2mm surfaces of the active plates were coated with silver that served as an external electrode. These silver-coated plates were interconnected with a bus wire in a zigzag pattern. The rated voltage and capacitance of PZT stack were 200 V and 0.76 pF, respectively,... 

Several models exist, depending on membrane layout. Plate modules, derived from filter-presses, used to be the first used. (Figure 11.6). The fiuid to be treated circulates between the membranes of two adjacent plates. This assures the mechanical support of the membrane and the draining of the permeate. The systems currently in use are equipped with spiral or tubular modules. Membrane surface is often maximized to compensate for the low delivery rate of these systems. Several modules must be installed in parallel to have a satisfactory delivery rate. 

Submerged rotating plate modules (comparable to a rotating disk reactor)... 

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