Filtration conventional

The process of filtration separates the particles from a suspension, by forcing a fluid through a filtering medium, or by applying positive pressure to the upstream side or a vacuum to the downstream side. The particles retained on the filtering medium as a deposit are termed cake, while the fluid that has passed through 

Biochemical Engineering A Textbook for Engineers, Chemists and Biologists, Second Edition. 

Shigeo Katoh, Jun-ichi Horiuchi, and Fumitake Yoshida. 

The two main types of conventional filter used for cell separation are platefilters (filter press) and rotary drum filters-. 

The rate of filtration - that is, the rate of permeation of a liquid through a filtering medium - depends on the area of the filtering medium, the viscosity of the liquid, the pressure difference across the filter, and the resistances of the filtering medium and the cake. 

As liquid flow through a filter is considered to be laminar, the rate of filtration d Vf/dt (m3 s ) is proportional to the filter area A (m2) and the pressure difference across the filtering medium Ap (Pa), and is inversely proportional to the liquid viscosity /i (Pa s) and the sum of the resistances of the filtering medium RM (m ) and the cake Rc (m ). Thus, the filtration flux JF (ms-1) is given by  

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Mechanical Squeezing of Cakes. Mechanical squeesing of the cake in the so-called variable chamber filters has been used relatively recendy to lower moisture content of the final cake. This is appHcable only to cakes that are compressible. Many filters are available in which some form of mechanical expression of the cake is used either to foUow a conventional filtration process or to replace it. 

It does not matter, from the fundamental point of view, how the pressure drop is generated in the filter. In the case of the centrifugal filters there is an additional phenomenon of the mass forces acting on the Hquid within the cake. The conventional filtration theory must be amended to include this effect (2). 

Conventional filtration theory has been challenged a two-phase theory has been appHed to filtration and used to explain the deviations from paraboHc behavior in the initial stages of the filtration process (10). This new theory incorporates the medium as an integral part of the process and shows that the interaction of the cake particles with the medium controls filterabiHty. It defines a cake-septum permeabiHty which then appears in the slope of the conventional plots instead of the cake resistance. This theory, which merely represents a new way of interpreting test data rather than a new method of siting or scaling filters, is not yet accepted by the engineering community. 

Some horizontal belt vacuum filter designs incorporate a final compression stage for maximum mechanical dewatering. This is achieved by another compression belt which presses down on the cake formed in the preceding conventional filtration stage. 

In reverse osmosis membranes, the pores are so smaH, in the range 0.5— 2 nm in diameter, that they ate within the range of the thermal motion of the polymer chains. The most widely accepted theory of reverse osmosis transport considers the membrane to have no permanent pores at aH. Reverse osmosis membranes are used to separate dissolved microsolutes, such as salt, from water. The principal appHcation of reverse osmosis is the production of drinking water from brackish groundwater or seawater. Figure 25 shows the range of appHcabHity of reverse osmosis, ultrafiltration, microfiltration, and conventional filtration. 

Fig. 25. Reverse osmosis, ultrafiltration, microfiltration, and conventional filtration are related processes differing principally in the average pore diameter of the membrane filter. Reverse osmosis membranes are so dense that discrete pores do not exist transport occurs via statistically distributed free volume areas. The relative size of different solutes removed by each class of membrane is illustrated in this schematic.

Many compounds can cause problems in pollutant-control equipment. Particulate matter, liquids, or solids in the waste stream can plug the adsorber beds, heat-recovery beds in regenerative thermal incinerator systems and biofilters. Conventional filtration systems are used to remove particulate matter before or after the process. 

Fig. 16.2. Reverse osmosis, ultrafiltration, microfiltration and conventional filtration with distinct pore size.

It is not possible at present to provide an equation, or set of equations, that allows the prediction from fu st principles of the membrane permeation rate and solute rejection for a given real separation. Research attempting such prediction for model systems is underway, but the physical properties of real systems, both the membrane and the solute, are too complex for such analysis. An analogous situation exists for conventional filtration processes. The general... 

The solid-liquid separation of shinies containing particles below 10 pm is difficult by conventional filtration techniques. A conventional approach would be to use a slurry thickener in which the formation of a filter cake is restricted and the product is discharged continuously as concentrated slurry. Such filters use filter cloths as the filtration medium and are limited to concentrating particles above 5 xm in size. Dead end membrane microfiltration, in which the particle-containing fluid is pumped directly through a polymeric membrane, is used for the industrial clarification and sterilisation of liquids. Such process allows the removal of particles down to 0.1 xm or less, but is only suitable for feeds containing very low concentrations of particles as otherwise the membrane becomes too rapidly clogged.2,4,8... 

The advantages of cross-flow filtration over conventional filtration are ... 

Conventional filtration cannot be applied to the separation in purification of metal nanoparticles. If the metal nanoparticles are protected by polymer, however, the membrane filter, which can cut off the pol5mer with certain molecular weight, can be used to separate the polymer protected metal nanoparticles. Free metal nanoparticles which are not protected by polymer can pass through the membrane. Ion filter like cellulose can be used to separate ionic species from the reaction mixtures. 

Meindersma and Kuczynski (1996) compared conventional filtration with a filter aid and membrane technology for the separation of enzymes. In cases in which the enzyme is sufficiently cheap for once-through use filtration is the process of choice, whereas for... 

Pharmaceutical Removal of suspended matter is a frequent application for MF. Processes may be either clarification, in which the main product is a clarified liquid, or solids recovery. Separating cells or their fragments from broth is the most common application. Clarification of the broth in preparation for product recovery is the usual objective, but the primary goal may be recovery of cells. Cross-flow microfiltration competes w l with centrifugation, conventional filtration by rotary vacuum filter or filter press and decantation. MF delivers a cleaner permeate, an uncontaminated, concentrated cell product... 

Membrane processes. Conventional filtration processes can separate particles down to a size of around 10 xm. If smaller particles need to be separated, a porous polymer membrane can be used. Microfiltration retains particles down to a size of around 0.05 xm. A pressure difference across the membrane of up to 4 bar is used. The two most commonly used arrangements are spiral wound and hollow fiber, as discussed in Chapter 8. 

The solids-liquid separation of slurries containing particles below 10 xm is difficult by conventional filtration techniques. A conventional approach would be to use a slurry thickener in which the formation of a filter cake is restricted and the product is discharged continuously as a concentrated slurry. Such filters use filter cloths as the filtration medium... 

All of the membrane processes listed in Table 8.1 are operated with such a cross-flow of the process feed. The advantages of cross-flow filtration over conventional filtration are ... 

This technology removes dissolved metals from liquid wastes at a lower cost then other treatment options, such as precipitation followed by clarification and conventional filtration, ion exchange, reverse osmosis, and electrolysis. An advantage of the DuPont/Oberlin microfiltration technology is that it produces a dry, stabilized cake that can be landfiUed when used in conjunction with a filter aid/cake stabilizing agent. 

The settling of the acid sludge in the presence of propane is said to be sufficiently complete to allow neutralization with a small amount of fine-meshed clay, which is introduced into the acid oil-propane solution and passes with the oil through the propane recovery unit. The clay is removed from the oil by conventional filtration to produce a finished bright stock with a good color (48). 

MF can be categorized between conventional filtration and UF. The process is used to filter very small particles (usually <10 pm in size) from a suspension, by using a membrane with very fine pores. Examples of MF include the separation... 

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