Osmosis process

The success of a reverse osmosis process hinges direcdy on the pretreatment of the feed stream. If typical process streams, without pretreatment to remove partially some of the constituents Hsted, were contacted with membranes, membrane life and performance would be unacceptable. There is no single pretreatment for all types of foulants. Pretreatment methods range from pH control, adsorption (qv), to filtration (qv), depending on the chemistry of the particular foulant. Some of the pretreatment methods for each type of foulant are as foUow (43—45) ... 

Reverse osmosis processes for desalination were first appHed to brackish water, which has a lower I DS concentration than seawater. Brackish water has less than 10,000 mg/L IDS seawater contains greater than 30,000 mg/L IDS. This difference in IDS translates into a substantial difference in osmotic pressure and thus the RO operating pressure required to achieve separation. The need to process feed streams containing larger amounts of dissolved soHds led to the development of RO membranes capable of operating at pressures approaching 10.3 MFa (1500 psi). Desalination plants around the world process both brackish water and seawater (15). 

Given the first type of simulation, it is advantageous to be able to design a system of RO modules that can achieve the process objective at a minimal cost. A model has been iategrated iato a process simulation program to predict the stream matrix for a reverse osmosis process (132). In the area of waste minimization, the proper placement of RO modules is essential for achieving minimum waste at a minimum cost. Excellent details on how to create an optimal network of RO modules is available (96). 

Fig. 2. In the osmosis process, water flows through a membrane from a dilute solution to a more concentrated solution. In reverse osmosis, appHed...

S. Sourirajan, "Reverse Osmosis— Process Eundamentals" in The Encyclopedia of Environmental Science and Engineering Gordon and Breach Science Pubbshers, Inc., New York, 1976, p. 738. 

Operational temperatures of 4—27°C are maintained. In this process the flavor components are concentrated in the retentate. A reduced alcohol product is obtained by adding back water to give the desired flavor impact. Typical gas chromatographic results, comparing unprocessed 80° proof whiskey with reverse osmosis processed 54° proof whiskey and diluted 54° proof whiskey, indicate good congener retention in the alcohol-reduced (RO) processed whiskey (Table 7). 

The reverse osmosis process requires a pressure equal to or slightly greater than the... 

Reverse osmosis is applicable for the separation, concentration, and/or fractionation of inorganic or organic substances in aqueous or nonaqueous solutions in the liquid or the gaseous phase, and hence it opens a new and versatile field of separation technology in chemical process engineering. Many reverse osmosis processes are also popularly called "ultrafiltration", and many reverse osmosis membranes are also practically useful as ultrafilters. 

Emergence of Reverse Osmosis Processes and Reverse Osmosis Membranes... 

The above equations show that for a reverse osmosis system specified In terms of y, 9, and X, any one of the six quantities (performance parameters) C], C2, C3, C3, X or X or T, and A uniquely fixes all the other five quantities (112). Further, since the relationships represented by the set of eq 34 to 41 Involve 8 equations with 12 unknowns, namely, y, 9, X, Z, A, C-j, C2, C2, C3, C3, C3 and X or X or T, by fixing any four Independent quantities Included In the above unknowns, eq 34 to 41 can be solved simultaneously to obtain the remaining 8 quantities. The utility of this approach to system analysis for reverse osmosis process design and predicting the performance of reverse osmosis modules Is Illustrated In detail In the literature (6d,105,107,108,111,112,113). 

These facts shift cost estimation to much safer side, resulting into over-investment, which may reduce the advantage of reverse osmosis process over other processes. For the fiirther prosper of reverse osmosis, we definetely need more accurate and easier method to predict membrane life which may be determined by decrease in either flux through it or separation of solute. 

The economics of Reverse Osmosis Process will be highly favourable provided the desalination industry is taken up in a big way bringing down the capital investment. Water management and distribution particularly the water supply in the rural areas must be given top priority and should be under the direct control of central and federal government agencies and in this endeavour reverse osmosis has a potential... 

Reverse osmosis is a process in which freshwater is obtained from saltwater by forcing water from a region of low freshwater concentration to a region of high freshwater concentration. This is opposite of the natural process, and hence the name reverse osmosis. In a typical reverse osmosis process, a pressure of approximately 30 atmospheres is required to force freshwater to move from seawater across a semiperme-able membrane (Figure 11.5). 

Osmosis process in which a solvent flows from a diluted solution to a more concentrated solution across a semipermeable membrane... 

Resonance Structures any of two or more structures used to represent the overall structure and behavior of a compound even though the compound does not exist in any of the resonance forms Reverse Osmosis process in which pressure is used to force a solvent of a concentrated solution through a semipermeable membrane toward a diluted solution, often used to purify water... 

To ensure the successful design of a reverse osmosis process, several factors should be considered. These considerations encompass the feed solution, the membrane module, and the use of other processes in the pre- and post-treatment processes. A thorough knowledge of the feed stream and its components is essential to the prevention of membrane damage and product impurities. Once the feed stream is characterized and the process objective is defined, design can be initiated. 

Note that a solution more concentrated than the original one also results from the reverse osmosis process. This means that the method of reverse osmosis may also be used as a method for concentrating solutions. Fruit juices and radioactive wastes, for example, have been concentrated by this method. 

Fig. 4. Schematic of reverse osmosis process used ill desalination process. (Toyobo Co., Ltd., Osaka, Japan)...

Nomura, D., and I. Hayakawa1 Studies on Ctuicnillation of Change Juice by Reveise-osmosis Process, Jrnl. of Food Science Technology (Japan), 23, 404 (1976). 

So far only the energy requirement for a process in the form of work has been considered. Freezing, vapor compression, and reverse osmosis processes are examples of processes that require a work input. There are, however, other important processes, such as multiple-effect evaporation and flash evaporation, for which the energy input is in the form of heat. How does one relate the energy requirement of these processes to the minimum work of separation One method is to convert the heat requirement to a work equivalent by means of the Carnot cycle. If T is the absolute temperature of the heat source and T0 the heat-sink temperature, then one can use the familiar relation... 

P18.5 Sea water contains approximately 26,000 parts per million of dissolved NaCl, plus smaller amounts of other solutes, principally in the form of salts containing Mg2+, K+, Cl", Br, SO4-, and CO2-. In a water purification procedure, a reverse-osmosis process is used, in which half of the water is removed as pure water, leaving a concentrate that has twice the concentration of NaCl. Calculate the minimum work required to obtain a metric ton (103 kg) of pure water. Ignoring the impurities, the process is... 

Step 2 is a reverse osmosis process, after adjusting temperatures by heat exchanger. 

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