Filter medium polymer membranes

Filter-medium selection embraces many types of construction fabrics of woven fibers, felts, and nonwoven fibers, porous or sintered solids, polymer membranes, or particulate solids in the form of a permeable bed. Media of all types are available in a wide choice of materials. 

In cross-flow flltration, the wastewater flows under pressure at a fairly high velocity tangentially or across the filter medium. A thin layer of solids form on the surface of the medium, but the high liquid velocity keeps the layer from building up. At the same time, the liquid permeates the membrane producing a clear filtrate. Filter media may be ceramic, metal (e.g., sintered stainless steel or porous alumina), or a polymer membrane (cellulose acetate, polyamide, and polyacrylonitrile) with pores small enough to exclude most suspended particles. Examples of cross filtration are microfiltration with pore sizes ranging from 0.1 to 5 pm and ultrafiltration with pore sizes from 1 pm down to about 0,001 pm. 

Microfiltration (MF) is a membrane filtration in which the filter medium is a porous membrane with pore sizes in the range of 0.02-10 pm. It can be utilized to separate materials such as clay, bacteria, and colloid particles. The membrane structures have been produced from the cellulose ester, cellulose nitrate materials, and a variety of polymers. A pressure of about 1-5 atm is applied to the inlet side of suspension flow during the operation. The separation is based on a sieve mechanism. The driving force for filtration is the difference between applied pressure and back pressure (including osmotic pressure, if any). Typical configurations of the cross-flow microfiltration process are illustrated in Fig. 2. The cross-flow membrane modules are tubular (multichannel), plate-and-frame, spiral-wound, and hollow-fiber as shown in Fig. 3. The design data for commercial membrane modules are listed in Table 1. 

Filterability This test mimics the entrance of the polymer solution in the porous medium by passing the diluted solution through a filter with circular pores. It is an indicator of the solution injectivity. Method filtration at 2 bar on a 5 microns nucleopore membrane. 

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