Dynamic membrane filter

FIGURE 8.10 Schematic illustration of the Taylor vortices in the annulus of an axial rotating dynamic membrane filter. (From Figure 3 in Kroner, K.H. and Nissinen, V., J. Membr. Sci., 36, 85, 1988. With permission.)... 

FIGURE 8.30 Schematic diagram of rotating disk dynamic membrane filter. 

Figure 9-9 Schematic diagram of rotating disk dynamic membrane filter. From Ref. [1] with permission.

The following empirical relationship has been suggested to correlate the filtration flux to the shear rate for filtration with a rotating disk dynamic membrane filter ... 

Dynamic membranes are concentration—polarization layers formed in situ from the ultrafiltration of coUoidal material analogous to a precoat in conventional filter operations. Hydrous zirconia has been thoroughly investigated other materials include bentonite, poly(acryhc acid), and films deposited from the materials to be separated (18). 

FIGURE 1 Effect of (sequential) extrusion of MLV dispersions through polycarbonate membrane filters (Unipore) with pore sizes of 1.0, 0.6, 0.4, 0.2, and 0.1 ym on the mean liposome diameter. DXR-containing MLV (phosphatidylcholine/phosphatidylserine/ cholesterol 10 1 4) mean diameter of nonextruded dispersion about 2 ym pH 4. Mean particle size determined by dynamic Light scattering (Nanosizer, Coulter Electronics). (From Crommelin and Storm, 1987.)... 

The design of a cross-flow filter system employs an inertial filter principle that allows the permeate or filtrate to flow radially through the porous media at a relatively low face velocity compared to that of the mainstream slurry flow in the axial direction, as shown schematically in Figure 15.1.9 Particles entrained in the high-velocity axial flow field are prevented from entering the porous media by the ballistic effect of particle inertia. It has been suggested that submicron particles penetrate the filter medium and form a dynamic membrane or submicron layer, as shown in... 

Therefore, when operating in the filter cake mode, the axial velocity should be maintained at a level such that an adequate shear force exists along the filter media to prevent excessive caking of the catalyst that could cause a blockage in the down-comer circuit. For the separation of ultrafine catalyst particles from FT catalyst/wax slurry, the filter medium can easily become plugged using the dynamic membrane mode filtration. Also, small iron carbide particles (less than 3 nm) near the filter wall are easily taken into the pores of the medium due to their low mass and high surface area. Therefore, pure inertial filtration near the filter media surface is practically ineffective. 

Porous glass has been available for transpon studies for several decades, but its use as a membrane material commercially started only in the early 1980s. Its uses have been mostly in the biotechnology area. Porous silver membranes were available in the mid-1960s in the form of tubes and later in the shape of a disk. The use of silver membranes, however, has been limited. Porous stainless steel membranes have been used for years as high-quality filters or supports for dynamic membranes. 

This paper is an account of our attempts to apply these developments to a class which still poses formidable problems separation from each other of two substances, both dispersed in a liquid as aggregates of different but large size. Even though filters are now likely to be available of pore dimensions which should discriminate, the filter cake or dynamic membrane that builds up soon dominates, and the pore size of the filter becomes Irrelevant. One more than likely ends up concentrating both substances, rather than passing one with the liquid through the filter. 

Serra CA, Wiesner MR, Laine JM (1999), Rotating membrane disk filters design evaluation using computational fluid dynamics, Chem. Eng. J. 72 1-5. 

---