Filtration flat-sheet

The basic hydrodynamic equations are the Navier-Stokes equations [51]. These equations are listed in their general form in Appendix C. The combination of these equations, for example, with Darcy s law, the fluid flow in crossflow filtration in tubular or capillary membranes can be described [52]. In most cases of enzyme or microbial membrane reactors where enzymes are immobilized within the membrane matrix or in a thin layer at the matrix/shell interface or the live cells are inoculated into the shell, a cake layer is not formed on the membrane surface. The concentration-polarization layer can exist but this layer does not alter the value of the convective velocity. Several studies have modeled the convective-flow profiles in a hollow-fiber and/or flat-sheet membranes [11, 35, 44, 53-56]. Bruining [44] gives a general description of flows and pressures for enzyme membrane reactor. Three main modes... 

Ultrafiltration experiments were carried using the same setup, except the flat-sheet membrane module had a filtration area 38 mm long, 29 mm wide, and 1.6 mm high, with a surface area of 11 cm2. The permeate side had 11 grooved channels that supported the membrane, leaving an effective filtration area of 6.4 cm2. However, the total membrane area including the supports was used in calculating the fluxes. The feed consisted of cellulase enzyme solution (5.0 g/L of supplied cellulase, unless noted otherwise). 

Microfiltration units can be configured as plate and frame flat sheet equipment, hollow fiber bundles, or spiral wound modules. The membranes are typically made of synthetic polymers such as Polyethersulfone (PES), Polyamide, Polypropylene, or cellulosic mats. Alternate materials include ceramics, stainless steel, and carbon. Each of these come with its own set of advantages and disadvantages. For instance, ceramic membranes are often recommended for the filtration of larger particles such as cells because of the wider lumen of the channels. However, it has been shown that spiral wound units can also be used for this purpose, provided appropriate spacers are used. 

Crossflow filtration membranes can be produced in flat sheet, hollow fiber, tubular formats when using polymeric materials, and in monolith and tubular configurations when using inorganic membrane materials. Table 14.2 summarizes the various module configurations. 

Cassette Cassette products are widely used in the biopharmaceutical industry and specifically dominate the protein concentration purification market due to their compactness, which provides excellent product recovery capabUity. Cassette modules contain presealed flat sheet membranes separated by feed and filtrate spacers. This is an improved design compared to earher plate and frame configurations, making installation and replacement much easier and more reliable for the end user (shown in Figure 14.5). 

The HEPA filter is normally constructed of borosili-cate microfibers, formed into a flat sheet by a process similar to papermaking (Fig. 2). This sheet is pleated to increase the overall filtration surface area, in order to minimize the static pressure drop across the filter... 

Membrane filters include flat sheet, spiral wound, and hollow fiber (Fig. 23). In addition, there are also rotating discs, annual gap, and vibrating disc systems for membrane cross-flow filtration. 

Microfiltration membranes are similar to UF membranes but have larger pores. Microfiltration membranes are used to separate particles in the range of 0.02-10 pm from liquid or gas streams. Commercial MF membranes are made from a wide variety of materials including polymers, metals, and ceramics. A wide variety of membrane module designs are available including tubular, spiral wound, pleated sheet, hollow fiber, and flat sheet designs. Some modules are best suited for crossflow filtration, and others are designed for dead-end filtration. In dead-end filtration, the feed liquid flows normal to the surface of the membrane, and retained particles build up with time as a cake layer on the membrane surface or within the pores of the membrane. 

A concentration boundary layer theory clearly is needed to relate C to C, so that membrane properties such as L, a, and P can be correlated with R, at various operating conditions. Slso, since ir in Equations 1 and 5 is an independently determined function of C, a boundary ayer theory could correlate the observed filtrate velocity, J (averaged along the fiber length), with average applied pressure AP. For sufficiently high axial flow velocities, C == C, and a major theoretical barrier to data analysis is removeS. Some early work in reverse osmosis ( ) was done with flat-sheet membranes and large feed stream velocities. 

Shape Bead, flat sheet or hollow fiber membrane, amorphous aggregate Crystal Ease of filtration, Control of diffusion path length and flow properties Simple preparation... 

Clarification, or harvest, is typically the first step in downstream processing. During clarification, the cells, cell debris, and other particulates are removed from the cell culture broth, which contains the product. Clarification can be accomplished by depth filtration or by centrifugation followed by some form of filtration. Tangential flow filtration (ITT), sometimes also referred to as cross-flow filtration (CFF) is also used for clarification. Tangential flow filters are designed either in a flat sheet mode or hollow fiber mode. 

Fig. 11.5. Effect of glucane from Botrytis cinerea on flat-sheet filtration (Dubourdieu, 1982) 1. Dry white wine made from healthy grapes. II. The same wine +200 mg/1 of glncane...

The wine should be properly clarified prior to flat-sheet filtration at the time of bottling to ensure a satisfactory flow rate. This preliminary clarification may involve spontaneous settling, fining, centrifugation (Section 11.11) or filtration through a diatomaceous earth precoat (Section 11.6). 

Flat-sheet filtration is subject to the law of gradual clogging of pores under well-defined conditions. A test (Serrano, 1981) to check a wine s aptitude for clarification by flat-sheet filtration may be carried out using the apparatus shown in Fignre 11.12. 

If these criteria are not satisfied, this means that the wine has not been sufficiently clarified in advance to ensure that flat-sheet filtration will be efficient and cost-effective. 

These criteria are necessary to ensure that flat-sheet filtration will provide proper clarification and a satisfactory elimination of microorganisms, combined with an adequate flow rate (Table 11.7). 

---