Membranes and Membrane Processes
- PDF / 15,618,417 Bytes
- 6 Pages / 604.8 x 806.4 pts Page_size
- 66 Downloads / 270 Views
BULLETIN/MARCH 1999
conditions; a low fouling rate; long and reliable Operation; and cost-effective production. The possibility of meeting these requirements is directly associated with the nature of the material used for the membrane synthesis and the production routes. In general, it is quite difficult for a Single material to satisfy all the constraints just listed; polymeric, inorganic, or even biological materials are e m ployed, depending on the particular demands of the end application. Because of the distinct advantages that polymer m e m b r a n e s offer compared with inorganic membranes—including production cost-efficiency and Perfor m a n c e — commercial separations are dominated by polymeric materials. However, intensive research efforts are being made in the development and improvement of inorganic membranes for use in separations that are poorly, if at all, attainable by conventiona 1 poly mer membranes. In general, inorganic membranes can be advantageous for high-temperature separations, owing to their relatively high thermal stability. They can also be used in environments that require high chemical stability and biocompatibility and hence preclude the employment of routinely used polymeric materials. These exceptional properties of inorganic membranes have challenged a number of research laboratories around the world to formulate novel synthesis routes that will lead to end products tailored to specific appli cations and without the typical weaknesses of ceramic and other inorganic materials, such as poor reproductivity and intrinsic brittleness. In addition to already commercialized membranes and membrane separations, new materials and processes are conti nually emerging. New glassy polymers, carbon molecular sieves, and nanostructured zeolites are used for the Separation of gas mixtures, especially oxygen/nitrogen
and methane/carbon dioxide. Permselective graft polymers are rapidly evolving into key materials for biomedical applica tions such as the encapsulation of living cells, exhibiting enhanced biocompatibil ity and diffusivity with limited protein adsorption. Novel membranes have been developed for reverse-osmosis Operation with improved thermal and chemical stability, higher throughput, and higher salt rejection. The unique Performance of membrane materials in a variety of industrial applications has also inspired the design of so-called hybrid processes, a combination of membrane and more conventional processes, which may give rise to the development of modern, technically advanced, and cost-effective pro duction strategies. Examples are the combination of pressure-swing adsorp tion with microporous membranes for gas Separation and the electrocatalytic regeneration of ion-exchange resins.1'2 Various market studies have been performed that take into account the current commercial usage of membranes as well as the prospects offered by focused re search activities. lt is estimated that sales of state-of-the-art membrane products will continue to grow at an annual rate of —10%, amo
Data Loading...
