An Overview Of Membrane Technology And Theory

Many simple filtration processes use a dead-end technique – the flow of liquid to be filtered is directed perpendicular to the filter surface, This is effective when the concentration of particles to be removed is low or the packing tendency of the filtered material does not produce a large pressure drop across the filter medium. Some common examples of dead-end filtration are home water filters, vacuum cleaners, and automobile oil filters. Typical industrial uses include the sterile filtration of water, beer, and wine.

In contrast, there are many process streams that have high concentrations of particles or macromolecules such as cells, proteins and precipitates that will rapidly compact on the filter surface when operated in a dead-end mode. Consequently, the filtration rate drops quickly to an unacceptable level. In these instances, a crossflow membrane system provides the means to maintain stable filtration rates. The key to the design of a crossflow system is selecting a membrane geometry that suits the physical characteristics of the process fluid. Crossflow membranes can be provided in tubular, flat sheet, spiral wound, and hollow fiber configurations, each of which provides certain advantages for specific process needs.

Virtually any membrane design can be applied on water-like liquids with low concentrations of suspended solids, but viscous streams and fluids with large amounts of solids can only be handled with membranes specifically designed for this purpose. In general, the more difficult a stream is to process, the higher the cost of a membrane system and the higher the operating costs. Thus, an optimization study is an important component of any potential crossflow installation.