BASIC OF ULTRA FILTRATION
Ultrafiltration membranes can be made from both organic (polymer) and inorganic materials. There are several polymers and other materials used for the manufacture of UF membrane. The choice of a given polymer as a membrane material is based on very specific properties such as molecular weight, chain flexibility, chain interaction, etc. Some of these materials are polysulfone, polyethersulfone, sulfonated polysulfone, polyvinylidene fluoride, polyacrylonitrile, cellulosics, polyimide, polyetherimide, aliphatic polyamides, and polyetherketone. Inorganic materials have also been used such as alumina and zirconia [Mulder, 1996]. The structure of UF membrane can be symmetric or asymmetric. The thickness of symmetric membran (porous or nonporous) is range from 10 to 200 µm. The resistance to mass transfer is determined by the total membrane thickness. A decrease in membrane thickness results in an increased permeation rate. Ultrafiltration membranes have an asymmetric structure, which consist of very dense toplayer or skin with thickness of 0.1 to 0.5 µm supported by a porous sublayer with a thickness of about 50 to 150 µm. These membranes combine the high selectivity of a dense membrane with the high permeation rate of a very thin membrane. The resistance to mass transfer is determined largely or completely by thin toplayer.
ULTRAFILTRATION SYSTEM DESIGN
Ultrafiltration (UF) is a low-pressure operation at transmembrane pressures of, typically, 0.5 to 5 bars. This is not only allows nonpositive displacement pumps to be used, but also the membrane installation can be constructed from synthetic components, which has cost advantage. UF membranes can be fabricated essentially in one of two forms: tubular or flat sheet. Membranes of these designs are normally produced on a porous substrate material. The single operational unit into which membranes are engineered for use is referred to as a module. This operational unit consists of the membranes, pressure support structures, feed inlet, concentrate outlet ports, and permeate draw-off points. Two major types of UF modules can be found in the market, hollow fibers (capillary), and spiral wound. Other modules are plate and frame, tubular, rotary modules, vibrating modules, and Dean vortices.