Effect pressure

Direct studies of the effect of pressure on surface charging are rare. The conductance of an anatase dispersion in HCI increased with pressure [179], This suggests a release of pre-adsorbed HCI from the surface at elevated pressure. On the other hand, the pressure effect was negligible in anatase dispersions in water or in NaCl. The experimental setup was designed to study desorption kinetics, and only the sign of the pressure effect could be determined. A similar method was used to study the pressure effect on proton adsorption on alumina dispersions in water [2928,3059], and in NaCl [2928], HNO,. and NaNO, [927] solutions, and the effect was negligible for a pressure of about 10 Pa. On the other hand, the same pressure had a substantial effect on uptake of heavy-metal cations [927] and of anions [2928,3059] on alumina. 

The effect of pressure on surface charging may be studied indirectly on the basis of the relationship 

In general, the pressure of a reaction system can increase for three reasons (1) evaporation of low boiling chemicals, (2) formation of gaseous by-products as a result of the desired reaction, and (3) production of gases as a consequence of undesired reactions or decompositions. For normal operations, it is imperative to know how deviations in operating conditions affect the gas production. Further, the effect of increased pressure on the reaction rate must be determined to avoid uncontrollable pressure increases in confined systems. 

In case of undesired reactions, an emergency may develop. The combination of heat generation and gas production may accelerate the decomposition rate disproportionally. 

Gas production and subsequent pressure-time histories can be investigated successfully only in pressure vessels such as the VSP. If the gaseous product dissolves partly in the reaction mixture (i.e., the vapor-liquid equilibrium is changed), careful investigations of the pressure effect within the possible variations of the operating conditions are necessary. Pressurized vessels are also useful to investigate any mass transfer improvement for gas-liquid or gas-dissolved (suspended) solid reactions. 

De Haven [127] gives an overview of the results of accelerating rate calorimeter (ARC) experiments. The ARC was described in Section 2.3.2.3. As mentioned in the previous description, care must be taken in scale-up of results from experiments with relatively high phi-factors. For direct simulation of plant operating conditions, a phi-factor of 1.0 to 1.05 is required. As stated in [127], a decrease in the phi-factor from 2.0 to 1.0 increases the adiabatic temperature rise by a factor of 2, but the maximum self-heat rate increases by a factor of 20. Later in Chapter 3 (Section 3.3.4.6), an example of scale-up of ARC results is given. 

The Reactive System Screening Tool (RSST) was described in Section 33.2.7. This apparatus is a relatively recent development. Therefore, only limited literature data are available regarding the application of results from this equipment for direct scale-up of reactor systems. The Vent Size Package (VSP) is discussed further in Section 3.3.2.6. 

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Randzio S L 1994 Calorimetric determination of pressure effects Solution Calorimetry, Experimental Thermodynamics vol IV, ed K N Marsh and PAG O Hare (Oxford Blackwell)... 

Creel M, Muschenborn H-J, Guttler F, Renn A and Wild U P 1993 Single molecule spectroscopy pressure effect on pentacene in p-terphenyl Chem. Phys. Lett. 212 71-7... 

Houle F A 1986 A reinvestigation of the etch products of silicon and XeF2 doping and pressure effected. Appl. Phys. 60 3018-27... 

At equilibrium, these concentration and pressure effects must be equal and opposite for Eq. (8.75) to apply. Equation (8.13) describes the concentration dependence of jui, and Eq. (8.12) describes the pressure effect. Assembling these results, we write... 

C. R. Bennet, R. S. Ring, and P. J. Petersen, Pressure Effects on Macromolecular—Water Interactions with Synthetic Membranes, ACS 181st National Meeting, Atlanta, Ga., Mar. 1981. 

The absolute pressure may have a significant effect on the vapor—Hquid equiHbrium. Generally, the lower the absolute pressure the more favorable the equiHbrium. This effect has been discussed for the styrene—ethylbenzene system (30). In a given column, increasing the pressure can increase the column capacity by increasing the capacity parameter (see eqs. 42 and 43). Selection of the economic pressure can be faciHtated by guidelines (89) that take into consideration the pressure effects on capacity and relative volatiHty. Low pressures are required for distillation involving heat-sensitive material. 

J. P. Knapp, Exploiting Pressure Effects in the Distillation of Homogeneous Ac otropic Mixtures, Ph.D. dissertation. University of Massachusetts, Amherst, 1991. 

For the liquid-phase mass-transfer coefficient /cl, the effects of total system pressure can be ignored for all practical purposes. Thus, when using Kq and /cl for the design of gas absorbers or strippers, the primary pressure effects to consider will be those which affect the equilibrium curves and the values of m. If the pressure changes affect the hydrodynamics, then Icq, and a can all change significantly. 

Fair s method may also be modified to design forced-recirculation reboilers with horizontal tubes. In this case the hydrostatic-head-pressure effect through the tubes is zero but must be considered in the two-phase return Tines to the column. 

The ambiguity of the total pressure effect can be seen by a comparison of the gas-phase- and liquid-phase-controlled cases when the gas phase controls, the liquid-phase resistance is negligible and Kg( = K npf is independent of the total pressure. For this case the coefficient K g< is inversely proportional to the total system pressure as shown in Eq. (14-66). On the other hand, when the liquid phase controls, the correct equation is... 

Nonisothermal hquid-phase processes may be driven by changes in feed temperature or heat addition or withdrawal through a column wall. For these, heats of adsorption and pressure effects are generally of less concern. For this case a suitable energy balance is... 

Reactive Chemicals Reviews The process chemistry is reviewed for evidence of exotherms, shock sensitivity, and other insta-bihty, with emphasis on possible exothermic reactions. It is especially important to consider pressure effects— Pressure blows up people, not temperature The pumose of this review is to prevent unexpected and uncontrolled chemical reactions. Reviewers should be knowledgeable people in the field of reactive chemicals and include people from loss prevention, manufacturing, and research. 

Explosion venting is always accompanied by flame propagation plus pressure consequences in the surrounding areas. Tne flame length will be larger with a lesser static activation pressure and smaller vent area. Depending on the volume of the protected equipment, it can reach up to 50 m. The pressure effect in the vicinity of the vent area is... 

Gas can be condensed by (a) mechanically refrigerating it, (b) compressing and expanding it, using turboexpanders, or, (c) pressure effects such as by Joule-Thomson cooling and overcoming the vapor pressure. The liquefaction of methane can involve all three of these effects. These effects can be separately evaluated to show the effectiveness of each in producing liquid. 

The process illustrates the use of mechanical refrigeration in its high-efficiency temperature range the maximum use of compression energy because of its high efficiency and the use of turboexpansion at a low temperature—its Carnot efficiency is best at low temperatures, especially because it permits large use of the efficient pressure effect. 

For pressure effects, the Bunsen coefficient is used and is calculated from the equation as follows ... 

Liquids have relatively low compressibility compared with gases and, thus, the mobile phase velocity is sensibly constant throughout the column. As a consequence, elution volumes measured at the column exit can be used to obtain retention volume data and, unless extreme accuracy is required for special applications, there is no need for the retention volume to be corrected for pressure effects. 

Refers to the elapsed time after an adhesive is applied until pressure effects curing. Intermediate-stage reaction step for various thermosetting resins. During this stage the material swells when in contact with certain liquids and... 

Severity Death tolls and damage from pressure effects vary widely in cases presented. 

On December 9, 1970, a liquefied propane pipeline ruptured near Port Hudson. About 24 minutes later, the resulting vapor cloud was ignited. The pressure effects were very severe. The blast was equivalent to that of 50,000 kg of detonating TNT. 

Changes in pressure typically have a greater impact on retention than on selectivity. Most studies of CSPs have indicated little effect of pressure on stereoselectivity [28, 31]. However, Bargmann-Leyder et al. reported pressure-related changes in selectivity for an amylose-based CSP, though the magnitude of the pressure effect was not the same for all the compounds studied [58]. Pressures in the range of 15-20 MPa are common for chiral SFC. 

A corresponding pressure effect on the flow stress was observed on hydrostatic extrusion of conical specimens of the same alloy through a die of 5 mm dia at 220°C. The basic alloy was extruded at P = 12 kbar up to the area ratio equal to 4.1 while the alloy hydrogenated to a = 0.20 extruded to the area ratio of 7.6 even at a lower pressure, P = 11 kbax . Similar pressure/hydrogen effects on the flow stress were also observed on hydrostatic extrusion of ZrH,c, VH,c and Nb,c alloys with x = 0 and 0.1-0.2 wt.%. 

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