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Pressure concentration effects

The counterions form a diffuse cloud that shrouds each particle in order to maintain electrical neutrality of the system. When two particles are forced together their counterion clouds begin to overlap and increase the concentration of counterions in the gap between the particles. If both particles have the same charge, this gives rise to a repulsive potential due to the osmotic pressure of the counterions which is known as the electrical double layer (EDL) repulsion. If the particles are of opposite charge an EDL attraction will result. It is important to realize that EDL interactions are not simply determined by the Columbic interaction between the two charged spheres, but are due to the osmotic pressure (concentration) effects of the counterions in the gap between the particles. [Pg.126]

Saturation of the oil with hydrogen is maintained by agitation. The rate of reaction depends on agitation and catalyst concentration. Beyond a certain agitation rate, resistance to mass transfer is eliminated and the rate oecomes independent of pressure. The effect of catalyst concentration also reaches hmiting values. The effects of pressure and temperature on the rate are indicated by Fig. 23-34 and of catalyst concentration by Fig. 23-35. Reaction time is related to temperature, catalyst concentration, and IV in Table 23-13. [Pg.2113]

Gurgel and Grenier s results showed the bed conductivity to increase from 0.14 to 0.17 W/mK as the pressure was raised from 4 mbar (evaporating pressure) to 110 mbar (condensing pressure). The principle reason stated for this small variation is the reduction in the gas conductivity with decreasing pressure (Knudsen effect) in the macropores. The solid grain conductivity varied linearly from 0.61 to 0.65 W/mK as the methanol concentration varied from 0 to 31%. [Pg.335]

The expression for K involving the concentrations of the species involved is found to be independent of volume. This implies that any change of pressure is not going to change the final state of equilibrium. The same result can be obtained by taking into consideration the alternative expression involving the partial pressures. If the pressure on the system is increased to n times its original value then all the partial pressures will be increased in the same proportion. This obviously implies that the equilibrium is independent of the pressure. The effect of some other factors on this reaction may now be considered. One such factor can be the addition of substances. For example, on addition of more A2, the partial pressure of A2 in the reactor would increase momentarily from pAl to some value, p A/. It has already been seen that... [Pg.253]

In solution polymerization, monomers mix and react while dissolved in a suitable solvent or a liquid monomer under high pressure (as in the case of the manufacture of polypropylene). The solvent dilutes the monomers which helps control the polymerization rate through concentration effects. The solvent also acts as a heat sink and heat transfer agent which helps cool the locale in which polymerization occurs. A drawback to solution processes is that the solvent can sometimes be incorporated into the growing chain if it participates in a chain transfer reaction. Polymer engineers optimize the solvent to avoid this effect. An example of a polymer made via solution polymerization is poly(tetrafluoroethylene), which is better knoivn by its trade name Teflon . This commonly used commercial polymer utilizes water as the solvent during the polymerization process,... [Pg.55]

The catalyst activity depends not only on the chemical composition but also on the diffusion properties of the catalyst material and on the size and shape of the catalyst pellets because transport limitations through the gas boundary layer around the pellets and through the porous material reduce the overall reaction rate. The influence of gas film restrictions, which depends on the pellet size and gas velocity, is usually low in sulphuric acid converters. The effective diffusivity in the catalyst depends on the porosity, the pore size distribution, and the tortuosity of the pore system. It may be improved in the design of the carrier by e.g. increasing the porosity or the pore size, but usually such improvements will also lead to a reduction of mechanical strength. The effect of transport restrictions is normally expressed as an effectiveness factor q defined as the ratio between observed reaction rate for a catalyst pellet and the intrinsic reaction rate, i.e. the hypothetical reaction rate if bulk or surface conditions (temperature, pressure, concentrations) prevailed throughout the pellet [11], For particles with the same intrinsic reaction rate and the same pore system, the surface effectiveness factor only depends on an equivalent particle diameter given by... [Pg.319]

These are radical-radical reactions or reactions of methyl radicals with a product of a radical-radical reaction (owing to concentration effects) and are considered less important than reactions (3.72) and (3.86). However, reactions (3.72) and (3.86) are slow, and reaction (3.92) can become competitive to form the important methoxy radical, particularly at high pressures and in the lower-temperature region of flames (see Chapter 4). [Pg.115]

Another factor that differentiates the solubility of gases from solids and liquids is the effect of pressure. The effect of pressure on gas solubility was studied extensively by a contemporary and close associate of John Dalton named William Henry (1775-1836). Henry s Law states that the solubility of a gas is directly proportional to the partial pressure of that gas over the solution. Stated mathematically, Henry s Law is c = kP, where c is the concentration of the dissolved gas in moles per liter, k is Henry s law constant for the solution, and P is the partial pressure of the gas above the solution. Henry s Law is demonstrated every time a carbonated beverage is opened. During the carbonation process, carbon dioxide is dis-... [Pg.131]

Diazoxide is similar chemically to the thiazide diuretics but has no diuretic activity. It is bound extensively to serum albumin and to vascular tissue. Diazoxide is partially metabolized its metabolic pathways are not well characterized. The remainder is excreted unchanged. Its half-life is approximately 24 hours, but the relationship between blood concentration and hypotensive action is not well established. The blood pressure-lowering effect after a rapid injection is established within 5 minutes and lasts for 4-12 hours. [Pg.237]

The vitrification of liquids and polymers can be effected not only by the decrease of temperature but also by the increase of pressure [4]. Shishkin and Novak [5] obser ved the dependence of free hydroxyl concentration upon pressure. This effect can be described by Eq. (6) or (8) in the same way as the course of vitrification upon decreasing temperature. [Pg.493]

The balance over the ith species (equation IV. 5) consists of contributions from diffusion, convection, and loss or production of the species in ng gas-phase reactions. The diffusion flux combines ordinary (concentration) and thermal diffusions according to the multicomponent diffusion equation (IV. 6) for an isobaric, ideal gas. Variations in the pressure induced by fluid mechanical forces are negligible in most CVD reactors therefore, pressure diffusion effects need not be considered. Forced diffusion of ions in an electrical field is important in plasma-enhanced CVD, as discussed by Hess and Graves (Chapter 8). [Pg.249]

Influence of the Acidic Lipid. To a rapid inspection (see Figure 2), the presence of the acidic DPPA (in mixed DPPA-DPL films spread onto the electrolyte solution) produced AV — tt curves which are similar to those in the absence of the acidic lipid. Two features are striking. First, in the AV — ir curves, the AV difference between CaCl2 (filled symbols) and NaCl (empty symbols) is nearly the same whether the concentration of acidic lipid was 10 or 50% differential concentration effects, however, show some specificities in the low film pressure regions (see Figure 2) and in the AV — area curves at given film pressure values (2,3,4). Secondly, inasmuch as the appearance of the negative fixed... [Pg.63]

The effect of increasing the concentration of salt in the feed solution on membrane performance is illustrated in Figure 5.2(b). Increasing the salt concentration effectively increases the osmotic pressure term in Equation (5.1) consequently, at a constant feed pressure, the water flux falls with increasing salt concentration at a feed pressure of 1000 psi. The water flux approaches zero when the salt concentration is about 10 wt%, at which point the osmotic pressure equals the applied hydrostatic pressure. The salt rejection also extrapolates to zero rejection at this point but increases rapidly with decreasing salt concentration. Salt rejections of more than 99 % are reached at salt concentrations below 6 %, corresponding to a net applied pressure of about 400 psi. [Pg.194]

Abstract The fluxes of water and solutes across membranes are expressed as functions of differences of the hydraulic and osmotic pressures at both sides. Such difference equations are deduced from more fundamental differential equations. The distributions of concentration and pressure in a series array of membranes are derived. The order in which the individual membranes are placed exerts a strong influence upon the effects of the applied differences of hydraulic and osmotic pressures. The effect of the interchange of two membranes in a series array of an arbitrary number of membranes can be summarized in four simple rules. The special case of reversal of the flow is also discussed. [Pg.213]


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See also in sourсe #XX -- [ Pg.141 , Pg.142 ]




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Pressure concentration

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