Dynamic membranes applications

Dialysis operates by the diffusion of selected solutes across a nonporous membrane from high to low concentration. An early industrial application of dialysis was caustic soda recovery from rayon manufacturing. It had been a viable process because inexpensive but alkali-resistant cellulose membranes were available that were capable of removing polymeric impurities from the caustic. Gradually however, dialysis is being replaced by dynamic membrane technology for caustic soda recovery because of the latter s much higher productivity. 

Biomaterials, Synthesis, Fabrication, and Applications Bioreactors Distillation electrochemical Engineering Fluid Dynamics Membrane Structure Membranes, Synthetic (Chemistry) Molecular Hydrodynamics Nano-structured Materials, Chemistry of Pharmaceuticals, Controlled Release of Solvent Extraction Wastewater Treatment and Water Reclamation... 

Some of those developments at Oak Ridge were believed to spin off in some form at Union Carbide and some aspects of the efforts led to the commercialization of dyiuunically formed membranes primarily for ultrafiltration and hypeiTiltration (reverse osmosis) applications. In these dynamic membranes, a mixture of zirconium hydroxide and polyacrylic acid deposited on a porous support which provides the necessary mechanical strength. The support is mostly made of porous carbon although porous ceramic and stainless steel are also used. These non-sintered membranes, in great contrast to most of the membranes discussed in this book, are formed in situ and require periodic regeneration with new zirconium hydroxide and polyacrylic acid. 

There is another type of membrane that is conceptually different from the membranes prepared according to the above methods. It is called dynamic membranes. They are formed, during application, on microporous carriers or supports by deposition of the colloidal particles or solute components that are present in the feed solution. This in-situ formation characteristic makes it possible to tailor them for specific applications in ultrafiltration and reverse osmosis (hyperfiltration). 

While the formed-in-place or dynamic hydrous zirconium oxide membranes on porous stainless steel supports have been studied mostly for biotechnology applications, they have also demonstrated promises for processing the effluents of the textile industry [Neytzell-de-Wilde et al, 1989]. One such application is the treatment of wool scouring effluent. With a TMP of 47 bars and a crossflow velocity of 2 m/s at 60-70°C, the permeate quality was considered acceptable for re-use in the scouring operation. The resulting permeate flux was 30-40 L/hr-m. Another potential application is the removal of dyes. At 45 C, the dynamic membranes achieved a color removal rate of 95% or better and an average permeate flux of 33 L/hr-m under a TMP of 50 bars and a crossflow velocity of 1.5 m/s. 

Dynamic membranes originated in the research at the Oak Ridge National Laboratory in the 196O s. Development has produced commercial ultrafiltration and hyperfiltration membranes for industrial separation applications. Research continues in several laboratories to improve the selectivity and productivity of the membranes and to tailor them for specific applications. The development of dynamic membranes and current research is reviewed briefly. Research on polyelectrolyte blend membranes is described in detail as a representative method for tailoring dynamic membranes. 

The properties of dynamic membranes can be influenced at each step in the formation by altering the materials and procedures. Hence, dynamic membranes are expecially suited for tailoring to optimize a membrane s performance in a specific application, and a variety of experimental and commercial membranes have been formed. 

In many cases it is possible to remove the membrane by chemical means, recondition the porous support, and reform either the same type or a different type of dynamic membrane at the application site. This feature gives each module a long operating life. 

Successful applications of dynamic membranes in a number of industrial separation processes, membrane stability at high temperature and over a broad pH range, and membrane reformation capability on durable substrates have attracted a significant research and development effort. Much of the research has been directed toward... 

This paper reviews some recent developments in dynamic membrane research, describes properties and applications of commercial membranes, and reports properties of dynamic polyblend membranes. Formation of Dynamic Membranes... 

The poineering research and subsequent development of useful dynamic membranes was accomplished by Johnson and co-workers at the Oak Ridge National Laboratory. This very extensive research has been reported in a series of reports and in numerous publications and patents. Papers of special interest are the detailed report of the initial process for forming dynamic membranes with attractive hyperfiltration properties by Marcinkowsky, et al. (1 ), an early review of the research properties by Johnson ( ), and a subsequent review of hyperfiltration models and the development of hyperflltra-tion membranes by Dresner and Johnson ( ). These reviews cite the major references related to the formation, theory, properties, and applications of dynamic membranes. 

Two useful membranes developed by the group at the Oak Ridge National Laboratory have dominated the application of dynamic membranes the hydrous zirconium oxide ultrafilter and the hydrous zirconium oxide-poly(acrylic acid) hyperfilter. The technology of formation and utilization of zirconium oxide-poly(acrylic acid) dynamic membranes has been described in detail by Thomas ( ). The effects of molecular weight of the poly(acrylic acid), pore diameter of the porous support, formation cross-flow velocity, formation pressure, and pH of poly(acrylic acid) solution during initial deposition of the polyacid on the hyperfiltration performance are described and discussed. 

The continued development of such membranes and their integration into other structures will take us closer to this goal and in the meantime dynamic membranes are finding numerous applications in improving existing technologies. 

A number of commercially available rotating disk dynamic membrane systems have been tested for different applications. The DMF module (Pall Corp., New York) consists of several disks mounted on the same shaft, such that each can rotate between two annular membranes with maximum rotation speed of 3450 rpm, corresponding to an azimuthal velocity of 20 m/s at the disk tip. Pali s lab-scale system has been tested for protein separation [64] and filtration of recombinant yeast cells [65]. The studies of the application of the rotating disk dynamic membrane indicated that high-shear-enhanced filtration is much less sensitive to the solid concentration. 

Fluoroelastomers are presently widely used in the industry as 0-rings, V-rings, gaskets and other types of static and dynamic seals, as diaphragms, valve seals, hoses, coated clothes, shaft seals quick connector o-rings, dynamic sealing applications, membranes, [185], expansion joints, etc. [186]. They are also used in cars as O-rings for fuel, shaft seals and other components of fuel and transmission systems [35,58,62-65]. 

The overall scope of this book is the implementation and application of available theoretical and computational methods toward understanding the structure, dynamics, and function of biological molecules, namely proteins, nucleic acids, carbohydrates, and membranes. The large number of computational tools already available in computational chemistry preclude covering all topics, as Schleyer et al. are doing in The Encyclopedia of Computational Chemistry [23]. Instead, we have attempted to create a book that covers currently available theoretical methods applicable to biomolecular research along with the appropriate computational applications. We have designed it to focus on the area of biomolecular computations with emphasis on the special requirements associated with the treatment of macromolecules. 

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