High-productivity membrane

A state-of-the-art RO seawater system processes 50 million gallons per day with 50% feedwater recovery as potable water product using a 940-psi ( 65 bar) feed pressure [12]. These high pressures and flows are now routinely accommodated economically with compact vessels and high productivity membranes. An optimized thermal distillation plant with the same feedwater requires 1014 Btu/gal [78.5 (kwh)/m3] of water produced [8], while the state-of-the-art seawater RO system has an energy cost of only 2.2 (kwh)/m3 [8,12]. Using the current paradigm... 

MF and UF membrane processes are increasingly being used in the water and wastewater treatment. The outcome of rapid developments in membrane industry is low-cost high-productivity membranes making membrane processes economically feasible. Numerous studies and site experience have lead to better understanding of process parameters, allowing process optimization making membrane processes more technically feasible. 

High-Productivity (Low-Energy) Membrane Elements High-productivity membrane... 

Denser membrane leaf packing makes membranes also more susceptible to fouling, and their use requires high-quality source water and more elaborate pretreatment. To address this issue, the newest high-productivity membrane elements actually use wider spacers to compensate for the increased fouling potential and pressure. 

The pressure to be used for reverse osmosis depends on the salinity of the feedwater, the type of membrane, and the desired product purity. It ranges from about 1.5 MPa for low feed concentrations or high flux membranes, through 2.5—4 MPa for brackish waters, and to 6—8.4 MPa for seawater desalination. In desalination of brackish or sea water, typical product water fluxes through spiral-wound membranes are about 600—800 kg/m /d at a recovery ratio RR of 15% and an average salt rejection of 99.5%, where... 

For a profitable electrochemical process some general factors for success might be Hsted as high product yield and selectivity current efficiency >50%, electrolysis energy <8 kWh/kg product electrode, and membrane ia divided cells, lifetime >1000 hours simple recycle of electrolyte having >10% concentration of product simple isolation of end product and the product should be a key material and/or the company should be comfortable with the electroorganic method. 

Rules of Thumb With a few notable exceptions such as H2 through Pd membranes, membrane separations are not favored when a component is required at high purity. Often, membranes serve these needs by providing a moderate purity product which may be inexpensively upgraded by a subsequent process. Increasing the purity of N2 by the introduction of H2 or CH4 to react with unwanted O2 is a good example. Unless permeates are recycled, high product purity is accompanied by lower product recovery. 

Tubular membranes of 8 long were prepared from blend composition consisting of CA and PMMA and performance data for one month operation was collected. These datas show high product water flux (18-20 gfd.) with low flux decline slope. However, it was observed that these membranes initially showed fountains" which disappeared in about 30 minutes time. This was attributed to the peculiar membrane rheology and orientation of PMMA molecule with respect to CA molecule. This needed further study for confirmation. 

Commercial applications have been identified primarily in the electronics industry where requirements for dimensional stability, mechanical properties, and high temperature resistance make these systems attractive in advanced circuit board technology. Other commercial applications include high temperature membranes and filters where these materials offer performance improvements over glass, Kevlar, and graphite composites. Industrial development of these types of materials will most likely be dependent on monomer cost and advances in various product properties requirements. 

Widdas s quantitative model of the simple carrier was able to explain a number of earlier observations and to make predictions about what would be observed in more complex experiments on membrane transport. Thus it was a highly productive scientific insight. One of the earlier, apparently anomalous, results that the theory explained was the dramatic fall of membrane permeability found for solutes which were rapidly transported as solute concentration was increased. For example, in the human red blood cell, Wilbrandt and colleagues had previously measured a permeability constant for glucose which was 1000 times higher in dilute solutions of glucose than it was in a concentrated solution. This phenomenon, subsequently called saturation kinetics, is formally equivalent to the fall, as substrate concentration increases, in the proportion of substrate converted to product by a limited amount of an enzyme. 

The production of table salt from seawater, by the use of ED to concentrate sodium chloride up to 200 kg/m3 prior to evaporation and salt crystallization, has achieved a certain commercial importance, especially in Japan and Kuwait, even if it seems to be highly subsidized (Strathmann, 1992). The key to the success of this technology has been the low-cost, highly conductive membranes with a preferred permeability of monovalent ions. This allowed chloride ions to be cumulated in the concentrated stream, while Ca2+ and Mg2+ ions and sulfates were quite totally rejected in the diluting stream. 

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