Normal osmosis

Reverse osmosis, (a) When the external pressure (P) is less than the osmotic pressure (71-) (P < it), normal osmosis occurs, (b) When the external pressure exceeds the osmotic pressure, water flows in the opposite direction, producing reverse osmosis. Reverse osmosis can be used to obtain fresh water from seawater. 

Reverse osmosis and normal osmosis (dialysis) are directly related processes. In simple terms, if a selective membrane (i.e., a membrane freely permeable to water, but much less permeable to salt) separates a salt solution from pure water, water will pass through the membrane from the pure water side of the membrane into the side less concentrated in water (salt side) as shown in Figure 2.8. This process is called normal osmosis. If a hydrostatic pressure is applied to the salt side of the membrane, the flow of water can be retarded and, when the applied pressure is sufficient, the flow ceases. The hydrostatic pressure required to stop... 

Applying sufficient back pressure to force the normal osmosis process to go in reverse. 

FIGURE 11.10 Osmosis (a, b) and reverse osmosis (c). (a) In normal osmosis, water molecules pass through the semipermeable membrane from the less-concentrated into the moreconcentrated solution, in this case from pure water into the brine (salt water), (b) At a certain height of the brine solution in this apparatus, the pressure of the column of water is equal to the osmotic pressure and the flow stops, (c) In reverse osmosis, the application of external pressure greater than the osmotic pressure forces water molecules from the salty side to the pure water side. 

The osmosis described by this equation is called normal osmosis and it is observed in dilute solutions and inert (noncharged) membranes. The osmosis of electrolytes solutions through charged ionic membranes is called anomalous osmosis because in this case the solute diffusion enhances (positive anomalous osmosis) or decreases (negative anomalous osmosis) the solvent transfer. The solvent transfer through a membrane under an electric current across the system is called electro-osmosis [3]. 

Poly(vinyl chloride)(PVC)/artificial amphiphiles composite membranes were prepared in which the weight fraction of amphiphile was 15wt%. The composite membrane was obtained by evaporating solvent from a tetrahydrofuran (THF) solution of PVC and artificial amphiphile at 313 K. The diffusive permeability coefficient, P was evaluated in a normal osmosis experiment using KCl 10wt% solution and deionized water partitioned by the composite membrane. 

The water transport properties were measured in normal osmosis experiment. Deionized water and aqueous solution of KCl of 10wt% were placed in each of the two chambers of... 

The process of reverse osmosis has been applied to the problem of purifying water. In particular, the method has been used to desalinate ocean water (that is, remove salts from seawater to make drinkable or industrially usable water). In normal osmosis, the solvent flows from a dilute solution through a membrane to a more concentrated solution. By applying a pressure equal to the osmotic pressure to the more concentrated solution, the process of osmosis can be stopped. By applying an even greater pressure, the osmotic process can be reversed. Then, solvent flows from... 

Let us now turn to a more detailed examination of these processes Both nanofiltration (NF) and reverse osmosis (RO) draw on principles of osmosis for their implementation. The principal features of this phenomenon and its manifestation in reverse-osmosis operations are illustrated in Figure 8.8a. Consider a selective membrane, i.e., one that is freely permeable to water but much less so to salt, separating a salt solution from water, as shown in Part 1. In such an arrangement, water will flow from the pure-water side into the side less concentrated in water, i.e., the saltwater side. This process is referred to as normal osmosis. If, now, a hydrostatic pressure is applied to the salt side, the flow of water will be retarded, and if that pressure is sufficiently high, the flow will ultimately cease completely. At this point we will have reached what is termed osmotic equilibrium (Part 2), and the hydrostatic pressure associated with this state is referred to as the osmotic pressure. A further increase in applied pressure will act to reverse the flow from the... 

When the external pressure P is less than the osmotic pressure, n(P< w), normal osmosis occurs,... 

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). 

An alternative method of purifying water is by reverse osmosis. Under normal conditions, if an aqueous solution is separated by a semi-permeable membrane from pure water, osmosis will lead to water entering the solution to dilute it. If, however, sufficient pressure is applied to the solution, i.e. a pressure in excess of its osmotic pressure, then water will flow through the membrane from the solution the process of reverse osmosis is taking place. This principle has been... 

The pre-boiler, FW supply should normally be of demineralized quality, such as may be provided by ion exchange, reverse osmosis (RO), or similar process. Extremely efficient mechanical deaeration also is required because the path length from the FW tank to the boiler is usually quite short, and thus the contact time is generally inadequate for the sole use of chemical oxygen scavengers (even catalyzed scavengers). 

Osmotic pressure plays an important role in biological chemistry because the cells of the human body are encased in semipermeable membranes and bathed in body fluids. Under normal physiological conditions, the body fluid outside the cells has the same total solute molarity as the fluid inside the cells, and there is no net osmosis across cell membranes. Solutions with the same solute molarity are called isotonic solutions. 

Applications of reverse osmosis are normally restricted to below 50°C. Reverse osmosis is now widely applied to the desalination of water to produce potable water. Other applications include ... 

Introduction of a water-soluble ionic substance into the vascular system results in an increase in the number of particles in the bloodstream as the contrast substance dissolves. The body possesses several internal regulation systems and, when perturbed by an injection, attempts to restore the concentrations of substances in the blood to their normal or preinjection levels. To re-equilibrate the system, water from the cells of surrounding body tissue moves into the blood plasma through capillary membranes. This transfer of water is an example of osmosis, the diffusion of a solvent (water) through a semipermeable membrane (the blood vessels) into a more concentrated solution (the blood) to equalize the concentrations on both sides of the membrane. To accommodate the increase in... 

In our case, sprouting in an effectively aerated water medium was selected as the sprouting method of choice. In our system the sprouts are moving and circulating vigorously with the water flow. Effective aeration is necessary seeds submerged in water without aeration do not sprout and eventually die. Normal tap water or reverse osmosis purified water (RO-water) can be used. 

During the migration of cations and anions towards their respective electrodes, each ion tends to carry solvated water along with it. As cations are usually more solvated than anions, a net flow of water towards the cathode occurs during the separation process. This effect, known as electro-osmosis, results in a movement of neutral species which would normally be expected to remain at the point of application of the sample. If required, a correction can be applied to the distances migrated by ionic species by measuring them... 

A—Separation of materials in solution is normally not simple. Reverse osmosis would also work. 

If an asymmetric membrane is reversed, and the reverse osmosis experiments are carried out, the degree of salt rejection will be quite different from the results obtained for the normal experiments. In this case, the salt rejection is given by ... 

In modern high-pressure systems, blowdown water is normally of better quality than the water supply. This is because plant intake water is treated using clarification, filtration, lime/lime soda softening, ion exchange, evaporation, and in a few cases reverse osmosis to produce makeup for the boiler feedwater. The high-quality blowdown water is often reused within the plant for cooling water makeup or it is recycled through the water treatment and used as boiler feedwater. 

Therefore, an effective water system is required. Nowadays, several techniques can be used to obtain water of high pharmaceutical quality. These include ionexchange treatment, reverse osmosis, distillation, electrodialysis, and ultrafiltration. However, there is no single optimum system for producing high-purity water, and selection of the final system is dependent on factors such as the quality of raw water, intent of its use, flow rate, and costs. In the pharmaceutical industry, the different water classes normally encountered are well water, potable water, purified water, and specially purified grades of water, such as water for injection (e.g., MilliQ water). 

Consider that a potential difference is applied across a glass capillary tube filled with an electrolytic solution (Fig. 6.134). What would one expect Of course, one would expect a current to flow through the capillary according to Ohm s law. In practice, however, a remarkable and unexpected phenomenon is observed. In addition to the current, the solution itself begins to flow—the phenomenon of electro-osmosis. Liquid flow is generally associated with the application of a pressure gradient, but in this case it appears that a potential difference is doing the job normally achieved by a pressure difference. 

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