Filters crossflow

Crossflow units — Flat sheet membranes - Rotating filter elements... 

Crossflow Filters - These are usually membrane-type filters used for ultrafiltration. In the field of biotechnology these types of filters are used in ultrafiltration devices used in concentrating solutions, and performing buffer exchanges. 

The first two categories, clarifying and crossflow filters, have been very well developed and optimized for use in biotechnology and standard wastewater treatment applications. Equipment is easily available for these applications, whether as small 0.2 micron sterilizing filter used to terminally sterilize 100 ml of product solution, or a small 500 ml crossflow filter used to concentrate a small amount of antibody solution. Many vendors of this equipment to wastewater treatment applications have their origins in the CPI (Chemical Process Industries), and have incorporated many of the scale-up and optimization properties developed in much larger units used in large scale chemical production. As a result, these two filtration unit operations are one of the most optimized and efficient used in wastewater treatment. 

Tangential crossflow filtration Process where the feed stream sweeps the membrane surface and the particulate debris is expelled, thus extending filter life. The filtrate flows through the membrane. Most commonly used in the separation of high-and-low-molecular weight matter such as in ultrapure reverse osmosis, ultrafiltration, and submicron microfiltration processes. 

Cross-flow filters behave in a way similar to that normally observed in crossflow filtration under ambient conditions increased shear-rates and reduced fluid-viscosity result in an increased filtrate number. Cross-microfiltration has been applied to the separation of precipitated salts as solids, giving particle-separation efficiencies typically exceeding 99.9%. Goemans et al. [30] studied sodium nitrate separation from supercritical water. Under the conditions of the study, sodium nitrate was present as the molten salt and was capable of crossing the filter. Separation efficiencies were obtained that varied with temperature, since the solubility decreases as the temperature increases, ranging between 40% and 85%, for 400 °C and 470°C, respectively. These workers explained the separation mechanism as a consequence of a distinct permeability of the filtering medium towards the supercritical solution, as opposed to the molten salt, based on their clearly distinct viscosities. 

The fermentation of S. paucimobilis SC 16113 culture was carried out in a 750-liter fermentor. From each fermentation batch, about 60 kg of wet cell paste was collected. Cells harvested from the fermentor were used to conduct the biotransformation in 1-, 10-, and 210-liter preparative batches under aerobic or anaerobic conditions. The cells were suspended in 80 mM potassium phosphate buffer (pH 6.0) to 20% (w/v, wet cells) concentration. Compound (6) (1-2 g/ liter) and glucose (25 g/liter) were added to the fermentor and the reduction reaction was carried out at 37°C. In some batches, at the end of the fermentation cycle, the cells were concentrated sevenfold by ceramic crossflow microfiltration using a 0.2-pm filter, diafiltered using 10 mM potassium phosphate buffer (pH 7.0), and used directly in the bioreduction process. In all batches of biotransformation, the reaction yield of >85% and the e.e. of >98% were obtained (Table 4). The isolation of compound (7) from the 210-liter preparative batch was carried out to obtain 100 g of product (7). The isolated (7) gave 83% chemical purity and an e.e. of 99.5%. 

Whole-broth clarification Rotary vacuum drum filtration Centrifugation Crossflow MF, UF Maintains high throughput Does not require filter aids... 

A study was carried out into the potential recovery of plasticiser and solvent from waste PVC plastisols using a ceramic multi-bore crossflow tube filter. The procedure employed to perform the test sequence involved clean water flux measurement, media acclimatisation, optimisation trial, concentration run, cleaning trial and final water flux measurement. Permeate samples were analysed using gas chromatography and compared with standards of diisononylphthalate(DINP)/white spirit mixtures. The ceramic membrane successfully recovered a clear mixture of DINP and white spirit. 

Gillot, J., G. Brinkman and D. Garcera, 1984, New ceramic filter media for crossflow microfiltration and ultrafiltration, presented at Filtra 84 Conf., Paris, France. 

A special case arises when the "skin" (membrane) layer of a normal composite membrane element is immobilized with a catalyst and not intended for separating reaction species. Consider the example of an enzyme, invertase, for the reaction of sucrose inversion. Enzyme is immobilized within a two<layer alumina membrane element by filtering an invertase solution from the porous support side. After enzyme immobilization, the sucrose solution is pumped to the skin or the support side of the membrane element in a crossflow fashion. By the action of an applied pressure difference across the element, the sucrose solution is forced to flow through the composite porous structure. Nakajima et al. [1988] found that the permeate direction of the sucrose solution has pronounced effects on the reaction rate and the degree of conversion. Higher reaction rates and conversions occur when the sucrose solution is supplied from the skin side. The effect on the reaction rate is consistently shown in Figure 11.6 for two different membrane elements membrane A is immobilized by filtering the enzyme solution from the support layer side while membrane B from the skin layer side. 

Ceramic membrane systems are achieving widespread appheation in the place of centrifuges. These systems do not require filter aid media or a separate follow-on clarification step. HoUow-fiber crossflow modules are preferred for the separation of mammalian cells, which require particularly gentle handling. They can also be used as disposable filters for perfusion and... 

Microfilters use membranes with pores in the 0.1-1 pm range. They can filter out particles of dust, activated carbon, and ion exchange resin fines, and most microorganisms. Microfilters require low differential pressures (5-20 psi) and are available both as normal flow ( dead end ) and crossflow configurations. In pharmaceutical water purification systems, they are often used as disposable cartridge filters after activated carbon filters, softeners, and ion exchange beds. 

OperationaUy, there are several ways to start up the system (1) ibuprofen and lysine can be mixed in a separate tank/transfer vessel and then added or (2) the contents of the system at the end of one run can be saved for the next. It was decided to charge a slurry of diastereomers to be separated to the dissolver at the beginning. The slurry in the dissolver was continuously filtered via a ceramic crossflow filter of 0.2 p,m pore size. The supersaturated permeate was transferred to the crystallizer. Simultaneously, the slurry in the crystallizer could be filtered via another ceramic filter, and the clear saturated (with respect to S-ibu-S-lys) permeate filtrate could be sent to the dissolver. Both permeates would be kept at the same rate to maintain the volumes in both the dissolver and crystallizer. However, fluidized bed operation was clearly more convenient. Table 7-3 summarizes the results of two kilogram-scale experiments. As shown in the table, the final optical purity of S-ibu-S-lys is greater than 98%, starting with 50% S-ibu-S-lys and 50% R-ibu-S-lys in the dissolver. 

Figure 5. Gelman pleated crossflow filter cartridge. Cartridge components (A) a porous pleated support screen to provide mechanical support under applied pressure (B) the pleated microporous filtration element (C) the pleated spacer which creates the thin flow channel and promotes turbulent flow (D) the impermeable film which creates the flow channel (E) a porous support tube to provide an exit for permeate (F) open-end cap which provides for exit of product flow (G) closed-end cap completely which seals one end of module (H) outer seal ring which creates the seal between the impermeable film in the module and the interior of the housing. The back pressure support tube is not pictured. The ends of the cartridge are potted and sealed. A space between the ends of Film D and the end seals is provided to allow the entrance and exit of the flow-channel fluid.

Figure 17. Plugging test results a, pilot microscreen effluents b, filtrates from polishing by crossflow filtration through Ll-pm Acropor filter in axial filter (1.5 psi, 1000 rpm) and in pleated cartridge (loop).

Mechanisms of filtration (a) cake filter (i) clarifying filter (c) crossflow filter. 

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