Module Designs

The design of a membrane module for use with an MPM presented some considerable challenges. The basic constraints imposed by the MPM on the design of the module were as follows  

The maximum dimensions of the module are dictated by the dimensions of the microscope stage, which is 115 mm by 115 mm. 

The working depth, defined as the distance between the tip of the objective and the point of imaging must not exceed approximately 1 mm. 

Depending on the type of materials to be used for membrane separation, the module may have different configurations. The footprint of the membrane separation unit may be an important issue where it is going to be placed, and packing density of the module (m /m ) will then have to be considered. Some modules may be suitable for large-volume applications, some for smaller. In most cases investment cost and lifetime of the membrane will decide which one should be chosen. If specific process conditions are necessary for optimum performance of the membrane (pressure, temperature, filtering, and drying of gas), required utilities must be included in cost estimation. 

The basic equations for flux and selectivity are given in Section 4.2. Inserting the relevant flux equation for /, into Equation 4.22 below, the required membrane permeation area, A , may be calculated  

In a real case there are several additional variables to be taken into account possibility of concentration polarization, pressure drop, heat transfer, and Joule-Thomson effect across the membrane. The J-T effect may be significant when there is a large AP across the membrane and with nonideal gases permeating. Fugacities should then be used in the calculations. These effects are discussed by several authors [105,106]. 

The standard module configurations are presented below. With the development of new membrane materials for various applications (as discussed in Section 4.3), new configurations for optimum gas separation may be expected on the market in the future. 

FIGURE 4.18 Effect of stage cut 6, and flow pattern on permeate purity. Operating conditions (air) are as follows Xf o, = 0.21, a — 10, Ph/Pi = 5, Poj = 500 Barrer. Line (1) is counter-current flow, line (2) is cross-flow, line (3) is cocurrent flow, and line (4) is complete mixing. (From Walawender W.P., Stem S.A., Sep. Sci., 7, 553, 1972. With permission.) 

Suspended material Molecular Wei t (nominal average) Equivalent Pore Size (pm) 

Parallel flow in sections Flow in series between sections 

Hollow-fibre membrane modules are similar to the capillary type described above, but with fibres of outside diameters ranging from 80 to 500 pm. It is usual to pack a hollow-fibre module with many hundreds or thousands of these fibres, thus membrane area per unit volume is extremely hi. It should be apparent that filtration using hollow-fibre modules is only realistic with process fluids prefiltered to prevent fibre blockage fins limits the technology and it is applied mainly in UF. Also used in uhrafiltration is a spiral-wound membrane module which is often compared to a Swiss roD. The membrane and a spacer are wound round a former, with an appropriate permeate spacer flow is introduced and removed from the ends. This module design is not appropriate for solid-liquid separation, even when filtering colloids, because of the possibility of flow channel blockage and so it will not be discussed any finther. 

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Modified starch Modified starches Modifiers Modularity Modulation contrast Modulation doped FETs Module designs Mogadon... 

Fig. 24. (a) Typical tubular ultrafiltration module design. In the past, modules in the form of 2—3 cm diameter tubes were common more recendy, 0.5—1.0... 

A third factor is the ease with which various membrane materials can be fabricated into a particular module design. Almost ah membranes can be formed into plate-and-frame, spiral, and tubular modules, but many membrane materials caimot be fabricated into hollow-fine fibers or capihary fibers. Finahy, the suitabiHty of the module design for high pressure operation and the relative magnitude of pressure drops on the feed and permeate sides of the membrane can sometimes be important considerations. 

The key determinants of future cost competitiveness of a-Si H PV technology are a-Si H deposition rates, module production yields, stabilized module efficiencies, production volume, and module design. Reported a-Si H deposition rates vary by more than a factor of 10, but most researchers report that the high quaUty films necessary for high stabilized efficiencies require low deposition rates often due to high hydrogen dhution of the Si (and Ge) source gases (see Semiconductors, amorphous). 

Ot-HehcalBundles. The a-helix is the most extensively studied protein stmctural motif. Because a-hehces form internal hydrogen bonds between the C=0 of residue i and the N—H of residue i + 4 (see Fig. 2), the individual helix is stabili2ed and can exist in isolation. Individual heUces can be manipulated as independent stmctural modules designed to associate in some predetermined manner. Often, a minimalist approach to the design of a-hehces has been taken. In this approach the goal is to obtain the desired stmctural motif using the simplest possible constmction. 

Other The cassette (Fig. 22-54), a modification of a plate-and-frarne device that is favored because of the ease of scale-iip from lab-oratoiw to small plants is widely i ised in pharrnace i itical microfiltration and iiltrafiltration. An entirely different module also called a ca.s.sette is used in the IVIF of vv ater. There are a host of other clever module designs in use, and new ones appear frequently. 

Module design is veiy important for this case, as the high Ot may result in high permeate partial pressure. An example is the separation of HgOTrom air. 

Module design for this case is of lesser importance. 

Modules Eveiy module design used in other membrane operations has been tried in peivaporation. One unique requirement is for low hydraulic resistance on the permeate side, since permeate pressure is veiy low (O.I-I Pa). The rule for near-vacuum operation is the bigger the channel, the better the transport. Another unique need is for neat input. The heat of evaporation comes from the liquid, and intermediate heating is usually necessary. Of course economy is always a factor. Plate-and-frame construc tion was the first to be used in large installations, and it continues to be quite important. Some smaller plants use spiral-wound modules, and some membranes can be made as capiUaiy bundles. The capillaiy device with the feed on... 

Table 16.2. Module designs most commonly used in major separation processes...

The choice of the most suitable membrane module type for a particular membrane separation must balance several factors. The principal module design parameters that enter into the decision are summarised in Table 16.3. 

A system designed with these principles has been in use for more than a decade [6, 7]. The system, which has been continually refined and expanded during the 15 years since it was first used, involves a series of component modules designed to work together and that can be rapidly and flexibly customized. 

Modules Design-time units of development work Design decisions hidden in work units (packages) refinements used for submodule decompositions justifications, including rationale for choices made and choices rejected... 

Chondroitin 6-sulfate, 4 706 Chondroitin sulfates, 20 456 Chopped strand mat (CSM), 26 751 Chopper pumps, 21 78 Chop-stx number, for boron hydrides, 4 183 Chorinated trisodium phosphate, 4 52 Christmas tree module design, 15 835 Chromacity diagrams, 7 313-315 Chromaphores, 19 379 Chromate coatings, 9 827 Chromate conversion coatings, 16 218 Chromated copper arsenate, 3 276 ... 

Tapered module design, 15 835 Tapholes, blast furnace, 14 505-507, 509 Taphonomy, 5 752 Tapioca/cassava starch, 4 724t Tapping mode, in atomic force microscopy, 77 63 Tapping-mode AFM, 24 84 Tapping mode atomic force microscopy (TMAFM), 14 465, 16 501 Taq polymerase, 72 513 Taquidil... 

Table 17). IUCLID consists of several modules, both user modules and modules designed for the IUCLID system administrator. In all there are five components covering acquisition and information, a queiy module, a profile editor, administration and data exchange. 

A flow-modulated design of the TCD has become popular. In this design, a single filament is used and the column effluent is alternated with the pure helium through the flow channel where the filament is located. This eliminates the need to use two matched filaments. 

The catalytic esterification of ethanol and acetic acid to ethyl acetate and water has been taken as a representative example to emphasize the potential advantages of the application of membrane technology compared with conventional distillation [48], see Fig. 13.6. From the McCabe-Thiele diagram for the separation of ethanol-water mixtures it follows that pervaporation can reach high water selectivities at the azeotropic point in contrast to the distillation process. Considering the economic evaluation of membrane-assisted esterifications compared with the conventional distillation technique, a decrease of 75% in energy input and 50% lower investment and operation costs can be calculated. The characteristics of the membrane and the module design mainly determine the investment costs of membrane processes, whereas the operational costs are influenced by the hfetime of the membranes. 

Table 1.2 gives some of the reasons for the LGC setting up its automation team. The primary motivation was economic. LGC was often subject to constraints on staffing in parallel with large increases in analytical commitments. The introduction of cost-effective analyses, using mechanical or automatic instruments, reduces staff involvement and allows well qualified people to be released for the development of new analytical requirements. The analysis of beer samples by multi-channel continuous flow analyser [S, 6, 7] and the introduction of a mechanical solvent extraction and identification system to analyse and measure levels of quinizarin in gas oil, both for duty purposes, were prime examples [8], Both systems involved commercially available components and/or instruments integrated with modules designed and built in-house. 

The labor intensive replacement of membranes in plate and frame systems has been facilitated in the "leaf-module" design of Dorr Oliver (Figure 16). Here a number of plates are assembled in a disposable cartridge where the process stream flows over the plates and the permeate is ducted to a common header. 

Figure 16. Dorr Oliver leaf-module design (6)...

Fig. 19.4 Aspects of optimisation of the pervaporation process, apart from the membrane material 1 module design for optimum upstream and downstream conditions 2 condensation temperature(s) or aroma capture strategy 3 vacuum applied and type of vacuum pump. All aspects of the optimisation are interdependent in pervaporation and therefore need to be tackled as a whole, rather than individimlly...

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