Reverse osmosis hyperfiltration

Reverse osmosis (hyperfiltration) Pressure gradient <1 nm Dissolved salts, small organics... 

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). 

Membrane processes of the reverse osmosis (hyperfiltration) or electrodialysis types are used, but usually for smaller scale facilities (Fig. 5.4). Reverse osmosis units use high pressures of brackish water or seawater charging on one side of a semipermeable membrane, sufficient to exceed the osmotic... 

Nanofiltration spans the gap in particle size between reverse osmosis (hyperfiltration) and ultrafiltration. It can separate high molecular weight compounds (100-1(X)0) from solvents, and can also separate monovalent from multivalent ions. The driving force is a pressure difference of about 0.3-3 MPa (even greater than ultrafiltration). The nanofiltration process can reject selected (typically polyvalent) salts and may be used for selective removal of hardness ions in a process known as membrane softening [10]. 

Membrane separation Pressure Electrical field Concentration gradient Heterogeneous Homogeneous Ultrafiltration (s — 1) Reverse osmosis (hyperfiltration) (s-1) Dialysis (s -1) Electrodialysis (s — 1) Electrophoresis (s — 1) Permeation (1 — 1, g - g) Gas diffusion (g - g)... 

Membranes are being used increasingly for the removal of dissolved and colloidal contaminants in wastewater streams. Reverse osmosis (hyperfiltration) is well known for its ability to concentrate ionic species while ultrafiltration has found broad utility for the removal of dispersed colloidal oil, non-settlable suspended solids, and larger organic chemical molecules. One of the major problems these processes have faced is the fouling or blinding of the membranes after limited use. Various approaches have been developed in an effort to minimize this deterrent. Cross-flow filtration, where the contaminants are constantly flushed or washed from the membrane surface by the feedwater stream, is one of these approaches. The unit goes farther. Rather than a thin... 

Ranoval of the compound by reverse osmosis (hyperfiltration) from wastewater is successful depending on the type of membrane used. Membranes such as cellulose acetate lead to 40-60% separation of 2-propanol, whereas cross-linked polyethyleneimine and aromatic polyamine membranes yield 80-90% separation of 2-propanol. 

Preliminary concentration of the whey to 21-25% dry matter by reverse osmosis (hyperfiltration), followed by concentration to 50-55% dry matter via falling-film evaporators and spray drying. 

Wastewater can be treated by several physical processes. In some cases, simple density separation and sedimentation can be used to remove water-immiscible liquids and solids. Filtration is frequently required, and flotation by gas bubbles generated on particle surfaces may be useful. Wastewater solutes can be concentrated by evaporation, distillation, and membrane processes, including reverse osmosis, hyperfiltration, and ultrafiltration. Organic constituents can be removed by solvent extraction, air stripping, or steam stripping. 

The types of membrane separation technologies include reverse osmosis, hyperfiltration, ultrafiltration, and electrodialysis. At present, reverse osmosis is the only membrane separation technology that has been used as a mobile system and thus is the only such technology discussed in this section. 

Membrane Sep r tion. The separation of components ofhquid milk products can be accompHshed with semipermeable membranes by either ultrafiltration (qv) or hyperfiltration, also called reverse osmosis (qv) (30). With ultrafiltration (UF) the membrane selectively prevents the passage of large molecules such as protein. In reverse osmosis (RO) different small, low molecular weight molecules are separated. Both procedures require that pressure be maintained and that the energy needed is a cost item. The materials from which the membranes are made are similar for both processes and include cellulose acetate, poly(vinyl chloride), poly(vinyHdene diduoride), nylon, and polyamide (see AFembrane technology). Membranes are commonly used for the concentration of whey and milk for cheesemaking (31). For example, membranes with 100 and 200 p.m are used to obtain a 4 1 reduction of skimmed milk. 

Ultrafiltration separations range from ca 1 to 100 nm. Above ca 50 nm, the process is often known as microfiltration. Transport through ultrafiltration and microfiltration membranes is described by pore-flow models. Below ca 2 nm, interactions between the membrane material and the solute and solvent become significant. That process, called reverse osmosis or hyperfiltration, is best described by solution—diffusion mechanisms. 

Reverse Osmosis and Ultrafiltration. Reverse osmosis (qv) (or hyperfiltration) and ultrafilttation (qv) ate pressure driven membrane processes that have become well estabUshed ia pollution control (89—94). There is no sharp distinction between the two both processes remove solutes from solution. Whereas ultrafiltration usually implies the separation of macromolecules from relatively low molecular-weight solvent, reverse osmosis normally refers to the separation of the solute and solvent molecules within the same order of magnitude in molecular weight (95) (see also Membrane technology). 

Hyperfiltration (Reverse Osmosis) is a form of membrane distillation or desalination (desalting) operating with membrane pore sizes of perhaps 1 to 10 Angstrom units. The various individual RO component technologies have improved tremendously over the last 20 to 25 years, and resistance to fouling and permeate output rates have benefited. Nevertheless, all RO plants remain susceptible to the risk of fouling, and adequate pretreatment and operation is essential to minimize this problem. 

Separation and concentration by means of hyperfiltration (reverse osmosis). 

Spiegler, K. S. and Kedem, O. Desalination 1 (1966) 311. Thermodynamics of hyperfiltration (reverse osmosis) criteria for efficient membranes. 

Belfort, G. In Synthetic Membrane Processes, Belfort, G. (ed.) (Academic Press, Orlando, 1984). Desalting experience by hyperfiltration (reverse osmosis) in the United States. 

Twenty years ago two researchers laboring diligently at the University of California at Los Angeles developed the first modified asymmetric membranes which seemed to have commercial potential for what was to become the exciting field that today is known as hyperfiltration or reverse osmosis. Since that time, these dedicated scientists have given freely of themselves and their talents not only to further contribute technically, but also to help guide, teach, and train others to grow in this frontier area. 

Intrinsic Membrane Compaction and Aqueous Solute Studies of Hyperfiltration (Reverse-Osmosis) Membranes Using Interferometry ... 

Mahlab, D., Ben-Yosef N. and Belfort G, "Concentration Polarization Profile for Dissolved Species in Unstirred Batch Hyperfiltration (Reverse Osmosis) - II Transient Case." Desalination, 24, 297-303 (1978)... 

As we discussed in Section 3.2, samples of solution and solvent separated by a semipermeable membrane will be at equilibrium only when the solution is at a greater pressure than the solvent. This is the osmotic pressure. If the solution is under less pressure than the equilibrium osmotic pressure, solvent will flow from the pure phase into the solution. If, on the other hand, the solution is under a pressure greater than the equilibrium osmotic pressure, the pure solvent will flow in the reverse direction, from the solution to the solvent phase. In the last case, the semipermeable membrane functions like a filter that separates solvent from solute molecules. In fact, the process is referred to in the literature by the terms hyperfiltration and ultrafiltration, as well as reverse osmosis (Sourirajan 1970) however, the last term is enjoying common use these days. 

GILL, W.N., DERZANSKY, L.J. and DOSHI, M.R., Convective diffusion in laminar and turbulent hyperfiltration (reverse osmosis) systems , in reference 9 4, 261-360 (1971)... 

By convention, the term reverse osmosis is used to describe the separation of an aqueous salt solution by pressure-driven flow through a semipermeable membrane. Recently, the same type of process has been applied to the separation of organic mixtures. For example, Mobil Oil has installed a large plant to separate methyl ethyl ketone (MEK) from MEK-oil mixtures created in the production of lubricating oil [14] as described in Chapter 5. Separation of this type of mixture is probably best called hyperfiltration. 

Microporous membranes can be used in a manner similar to reverse osmosis to selectively allow small solute molecules and/or solvents to pass through the membrane and to prevent large dissolved molecules and suspended solids from passing through. Microfiltration refers to the retention of molecules typically in the size range from 0.05 to 10 pm. Ultrafiltration refers to the range from 1 to 100 nm. To retain even smaller molecules, reverse osmosis, sometimes called hyperfiltration, can be used down to less than 2 nm. 

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