Influence of Partial Pressure

Dessau worked at very low partial pressures (1-10 Torr) in order to limit olefin reequilibration. At low space times, still under conditions of complete methanol conversion to hydrocarbons. 

---

Fig. 23 a Naphtha pyrolysis. Influence of partial pressure of hydrocarbons on ethylene yield (the results are obtained with a given feedstock and constant residence tune and seventy). 

The influence of partial pressures of propane and oxygen was studied at 550°C have been correlated using the well known Mars and van Krevelen [9] mechanism... 

Figure 4.5.11 shows the influence of partial pressure on the effectiveness factor and on the effective rate. Consequently, an increase and subsequent decrease of the gas phase concentration leads to the interesting phenomena of a hysteresis loop of jjex and rA eff. 

Extensive testing of alloys has shown that many alloys establish parabolic time dependence after a minimum time of 1000 hours in air at temperatures above 900°C. If the surface corrosion product (scale) is removed or cracked so that the underlying metal is exposed to the gas, the rate of oxidation can be much faster. The influence of partial pressure on oxidation above 900°C is specific to each alloy, as illustrated for some common alloys in Fig. 15.17. Most alloys do not show a strong influence of the concentration upon the total penetration. Alloys such as Alloy HR-120, and Alloy 214 even exhibit slower oxidation rates as the concentration increases. These alloys are rich... 

Y HIDA et ak, Influence of Partial Pressure of Oxygen in the Atmosphere on the Formation of Acicular Calcium Ferrite, Transactions of the Iron and Steel Institute of Japan, 24( 1984), B331. 

Fig. 13. Influence of partial pressure of water vapor p /p on the rate of growth of dehydration patches.

For many years, researchers did not worry about the influence of gas pressures in gas-solid reactions, admitting implicitly that speed was necessarily proportional to the number of shocks of gas molecules on surface per unit of time and thus proportional to the pressure. It was only in the sixties that Besson, Barret, and their collaborators undertook systematic studies of the influence of partial pressures of the reactants on reactions of oxidation and sulfurization of metals. 

For coalescence of grains and for reactions between sohds that do not comprise any gas as principal component, the study of the influence of partial pressures of gas is very recent and is very profitable to describe mechanisms. 

On the whole, the studies on the influence of partial pressures of gases had several significant advantages. They were helpful in determining the mechanisms in the same way that the influence of the concentrations of the reactant and product have been, in homogenous kinetics. Thus, to interpret the results, it has been necessary to introduce the steps of adsorption and desorption of ses on the one hand and the construction of the modeling of steps to be used at various interfaces on the other. In continuation to this work, we will see the importance of the influence of gas pressures on reaction models. 

We studied [PIJ 94] the reduction in porosity and the coalescence of grains of ceria and the influences of partial pressures of gas and concentrations of some foreign cations on the speed. 

Expressions that are apparently very different are identified. We get a speed without influence of partial pressures, such as ... 

Some influences, of catalytic type, are occassionally attributed to steam, even though this is not a main component of the reaction. For reactions between a gas and a solid, it has been reported that the influences of partial pressure are extremely varied, ranging from no the reactant gases having no influence to homographic influences of the pressure or its square root with expressions such as ... 

To sum up, studies of the influence of partial pressures of gases are cracial for understanding the mechanisms of a reaction, such as the influence of the concentrations of reactants and products in homogeneous kinetics. 

This generic law is complicated by both the influence of partial pressures of various gases and the temperature. We note in particular that in this veiy generic case, Arrhenius law is not followed for rates at constant partial pressures. 

This expression also shows the complex influence of partial pressures from both gases and that temperature does not follow Arrhenius law. As before, simpler expressions can be established with some approximations. The second column in Table 13.2 shows such solutions. 

D) An agent whose rate of rise of partial pressure in the lung is influenced minimally by uptake into the blood. 

Let us now look at the situation in which we deal with real gases, that is, with a situation in which intermolecular forces between the molecules cannot be neglected (as will be even more the case for liquids and solids, see below). These forces influence the (partial) pressure of the gas molecules, but not the amount of the gaseous compound(s). This real pressure is called fugacity. 

Although water vapor exerts an Inhibiting effect on the rate (A), its concentration here was so low, because of the low H2/CO ratios used and the occurrence of the water-gas-shift reaction, that its Influence can be Ignored. Equation (2) can be re-written in terms of partial pressure of H2 by applying Henry s law,... 

Fig. 10. Influence of component concentrations and of pH on average volumetric rate of absorption

partial pressure and catalyst concentration, (b) Effects of sulfite and sulfate concentration, (d) Effects of pH and partial pressure. 

In sub-configuration (A) hydrogen will permeate through the hydrogen selective membrane tube under the influence of a pressure difference over the membrane and it will be carried away with an inert sweep gas (steam). The partial pressure of hydrogen in the reaction mixture will decrease cmd the equilibrium will shift to the product side. 

Therefore, even small traces of technological admixtures in the solid oxygen-ionic electrolytes (for example, iron, vanadium, and titanium), which usually accumulate on the grain boundaries, can substantially influence the limits of the practical applicabiUty of electrolytes by temperature and by the level of partial pressure. 

The influence of reactant pressures upon selectivity can be easily explained by the above mechanism the changes of selectivity essentially concern the complementary formations of unsaturated alcohol and hydrocarbons which i the re uk of competitive 1,2 and 1,4 additions of hydrogen. An increase of the partial pressure of prenal on the initially saturated surface, is likely to induce a change of the adsorption configuration of the molecule in favor of a 1,2 di-o adsorption and consequently of a selective hydrogenation of the C=0 bond. 

Various ways have been searched to equalize the condensibility factor. One approach is to compare the adsorption of vapors at equal ratios of partial pressure to saturation pressure.14 Pearce et al.15 sought to equalize the influence of condensibility by conducting the adsorption of each vapor at a temperature corresponding to its boiling point. 

A second fundamentally important area of research, in which the influence of temperature was poorly understood, and in which an influence of hydrostatic pressure was unknown, was the physiological and biochemical action of narcotics and other drugs. Quantitative interpretations were attempted through various hypotheses, based for example on correlations between potency of action and solubility of the drug in olive oil, and distribution of the drug between water and olive oil at different temperatures.Other theories were based on partial agreement of quantitative effects with adsorption isotherms or on specific properties of the drug. - ... 

The question of to what extent brain edema itself or increased intracranial pressure induced by edema and tumor are responsible for the depression in blood flow, is difficult to answer. The results indicate that the extent of local edema seems to be directly responsible for the reduction in regional blood flow. The influence of intracranial pressure may be partially neglected since the dura was open during the intraoperative rCBF measurements. Since the mean arterial blood pressure remained normal in these patients, the regional cerebrovascular resistance increased with increasing water content. It may be concluded that... 

Therefore an increase in equUibrium ceU voltage with the logarithm of the partial pressures is expected thermodynamicaUy. However, the performance increase of fuel cells with pressure is normaUy much more pronounced because the kinetics of the reactions are strongly influenced by partial pressure increases (the reaction rate of the electrochemical reactions increases with higher concentrations). 

The pressure increases because a non-condensable gas is produced in the process, for example following decomposition or synthesis reactions. The partial pressure of the liquid in the mixture then is comparatively low. For design calculations the solubility of the gas in the liquid phase has to be taken into account. Pure gassy systems are very rare in the process industry since the influence of vapour pressure increases with rising temperatures. 

Palmeira EM, Gardoni MG. The influence of partial clogging and pressure on the behaviom of geotextiles in drainage systems. Geosynthetics International 2000 7 403-431. 

Although CO2 apparently has no direct effect on the rate, it does indirectly influence the partial pressures of H2, CO, and H2O via the WGS reaction and this needs to be taken into account when modeling the system. The negative effect of H2O on the FT rate is in keeping with the speculations in the section Kinetics of the FT Reaction regarding surface oxidation of the catalyst. The rate equation deduced from the studies at Sasol turned out to be identical to that derived earlier by Anderson (14). It is interesting to point out that although different approaches were used in the mechanistic derivation of the rate equation, the end results were the same (14,65). This shows that kinetics cannot always be used to prove a particular mechanism. 

---