The Effect of Total Pressure on

An important factor to be taken into account in any overall assessment is the effect of total pressure on the separation factor a. We can explore this 

It is clearly seen from the latter that the vapor-pressure ratio and hence the separation factor both increase with a decrease in boiling point or total pressure. This result has sometimes been cast into a sweeping rule-of-thumb that low-pressure distillation leads to improved separation. Many nonideal systems follow this rule, but there are also numerous exceptions, particularly in the azeotropic category. Nevertheless, low-pressure distillation is a worthwhile alternative to explore, provided some low-pressure equilibrium data are available to confirm the expected results. 

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To many, it seems counter intuitive that increasing the total pressure increases the vapor pressure, but such is the case. However, the change is small, and the effect of total pressure on vapor pressure can generally be ignored, unless large pressure changes are involved. 

Pressure variation. In Figure 17 are shown the effects of total pressure on the relative pressures (i.e., the ratio of the partial pressure to the total pressure) of silane, hydrogen, and disilane (Fig. 17a) and on the deposition rate (Fig. 17b). The RF frequency is 50 MHz, and the plasma power is 5 W. The relative pressure of hydrogen slowly increases, and the relative pressure of silane slowly decreases, both in model as well as in experiment. This is caused by an increase in silane depletion at higher total pressures, which results from a higher power dissipation... 

In like manner one can treat cases where the rate controlling step is adsorption or desorption of some species. Hougen (14) has considered the effect of total pressure on initial reaction rates for several cases where these processes are rate limiting. 

In the high temperature zone [29], the effect of total pressure on the maximum rate corresponded to an order of about 3.6 the order with respect to acetone alone is 1.0, and with respect to oxygen 2.2. 

If the effect of total pressure on the liquid fugacity is negligible in the neighborhood of the vapor pressure of pure component /, then... 

The effect of total pressure on the deposition rate present in Fig.4 is similar to that of flow rate. An increase in the pressure leads to an increase in the deposition rate. Further increase in the pressure does not affect the rate which reaches a plane. Among different studies on the variation of deposition rate with pressure, the results varied both qualitatively and quantitatively as described in introduction. Besmann explained the pressure dependence by involving two different deposition mechanisms. One mechanism was the direct decomposition of MTS to SiC via Rea.(2) as follows. CH SiCI, SiC+3HCI (2)... 

The overall reversible reaction is A(g) - -B(g) C(g) -l-D(g), and a stoichiometric feed of reactants A and B enters a packed catalytic tabular reactor. Each component adsorbs on a single active site on the catalytic surface. Sketch the effect of total pressure on the initial rate of reaction when adsorption of reactant A is the slowest step in the overall mechanism and the stable reactive intermediate does not occupy surface sites. 

NiMnCo alloy RF magnetic sputtering Preparation of Ti02 films on NiMnCo aUoy and investigation of the effect of total pressure on the structure of TiOy, fdms [569]... 

S. S. Hla, G. J. Duffy, L. D. Morpeth, A. Cousins, D. G. Roberts, J. H. Edwards, Investigation of the effect of total pressure on performance of the catalytic water-gas shift reaction using simulated coal-derived syngases, Catal. Commun. 11 (2009) 272-275. 

The effect of total pressure on the carbonylation of methanol was also studied. In the range of 7.5-12.5 bar the pressure had a positive effect on the carbonylation reaction, increasing both the rate of acetic acid and of methyl acetate formation Figure 8). At higher pressures (above 12.5 bar), the increase in rate of ester formation became slower while the rate of acetic acid started to decrease. A total pressure of 11-12.5 bar looks to be the optimal for the carbonylation of methanol over the H[Rh(CO)2l2]/CDB catalyst, it is not needed to run the reaction at higher pressure. The selectivity towards acetic acid reached the best values even at lower pressure, at around 10 bar. 

If an inert gas such as air is also present in the vapor space, it will have very little effect on the vapor pressure. In general, the effect of total pressure on vapor pressure can be considered as negligible for pressures of a few atmospheres or less. 

The present study primarily provides information needed in the design and evaluation of silica gel adsorbers for the removal of small quantities of methane from hydrogen gas. Comparisons are made of (1) isotherms of methane and nitrogen on silica gel, (2) several isotherms of methane from 75 to 88.5 K at the same relative pressure, and (3) the effect of total pressure on the adsorption of methane from hydrogen and on the adsorption of nitrogen from hydrogen at 76 K. 

In some of the American text-books definitions of the activity and activity coefficient are tised which are not quite identical with those adopted in the present chapter. The difference depends on the effect of total pressure on the free energy of a liquid phase and is usuaUy trivial unless the solution under discussion is at a pressure greatly in excess of one atmosphere. 

In a system of more than one substance, vapor pressure can refer to the partial pressure of a substance in a gas mixture equilibrated with a solid or liquid of that substance. The effect of total pressure on vapor pressure will be discussed in Sec. 12.8.1. This book refers to the saturation vapor pressure of a liquid when it is necessary to indicate that it is the pure liquid and pure gas phases that are in equilibrium at the same pressure. 

To a good approximation, by assuming an ideal gas mixture and neglecting the effect of total pressure on fugacity, we can apply Eq. 12.8.20 to a liquid-gas system in which the total pressure is not constant, but instead is the sum of pa and pb- Under these conditions, we obtain the following expression for the rate at which the total pressure changes with the liquid composition at constant T ... 

Here is the vapor pressure of pure liquid solute at the same temperature and total pressure as the solution. If the pressure is too low for pure B to exist as a liquid at this temperature, we can with little error replace with the saturation vapor pressure of liquid B at the same temperature, because the effect of total pressure on the vapor pressure of a liquid is usually negligible (Sec. 12.8.1). If the temperature is above the critical temperature of pure B, we can estimate a hypothetical vapor pressure by extrapolating the liquid-vapor coexistence curve beyond the critical point. 

Illustration 6.13 The Effect of Total Pressure on a. Part 2 Breaking an Azeotrope... 

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