Pressure irreversible

We report in Fig. 5 the spectra resulting from adsorption of NH3 on activated cloverite deposited on silicon. When NH3 is introduced in small quantities, it appears that the bands characteristic of hydroxyls are not perturbed. Spectra in the 5(NH) range show a band at 1614 crn i attributed to coordinated species. The band at 1460 cm T is then very small showing that few NH3 molecules are protonated. All these species disappear by evacuation at 423 K, whereas the spectrum of the activated cloverite is recovered. When NH3 is introduced under a 250 Pa equilibrium pressure, irreversible transformations occur ... 

Bonding with heat and pressure (irreversible bond)... 

Increasing the pressure of irreversible vapor-phase reactions increases the rate of reaction and hence decreases reactor volume both by decreasing the residence time required for a given reactor conversion and increasing the vapor density. In general, pressure has little effect on the rate of liquid-phase reactions. 

Single reactions. For single reactions, a good initial setting is 95 percent conversion for irreversible reactions and 95 percent of the equilibrium conversion for reversible reactions. Figure 2.9 summarizes the influence of feed mole ratio, inert concentration, temperature, and pressure on equilibrium conversion. ... 

It suffices to carry out one such experiment, such as the expansion or compression of a gas, to establish that there are states inaccessible by adiabatic reversible paths, indeed even by any adiabatic irreversible path. For example, if one takes one mole of N2 gas in a volume of 24 litres at a pressure of 1.00 atm (i.e. at 25 °C), there is no combination of adiabatic reversible paths that can bring the system to a final state with the same volume and a different temperature. A higher temperature (on the ideal-gas scale Oj ) can be reached by an adiabatic irreversible path, e.g. by doing electrical work on the system, but a state with the same volume and a lower temperature Oj is inaccessible by any adiabatic path. 

Figure A2.1.5. Irreversible changes. Two gases at different pressures separated by a diathemiic wall, a piston that can be released by removing a stop (pin).

In an irreversible process the temperature and pressure of the system (and other properties such as the chemical potentials to be defined later) are not necessarily definable at some intemiediate time between the equilibrium initial state and the equilibrium final state they may vary greatly from one point to another. One can usually define T and p for each small volume element. (These volume elements must not be too small e.g. for gases, it is impossible to define T, p, S, etc for volume elements smaller than the cube of the mean free... 

The assumption (frequently unstated) underlying equations (A2.1.19) and equation (A2.1.20) for the measurement of irreversible work and heat is this in the surroundings, which will be called subsystem p, internal equilibrium (unifomi T, p and //f diroughout the subsystem i.e. no temperature, pressure or concentration gradients) is maintained tliroughout the period of time in which the irreversible changes are... 

Essentially this requirement means that, during die irreversible process, innnediately inside die boundary, i.e. on the system side, the pressure and/or the temperature are only infinitesimally different from that outside, although substantial pressure or temperature gradients may be found outside the vicinity of the boundary. Thus an infinitesimal change in p or T would instantly reverse the direction of the energy flow, i.e. the... 

In reality most solids in contact under macroscopic loads undergo irreversible plastic defonnation. This is caused by the fact that at high nonnal forces the stresses in the bulk of the solid below the contact points exceed the yield stress. Under these conditions the contact area expands until the integrated pressure across the contact area is equal to the nonnal force. Since the pressure is equal to the yield strength of the material cr, the plastic contact area is given by... 

For an irreversible reaction Pj - 0 at the center of the pellet when the size of the pellet becomes very large. Thus p — YT p at the center of large pellets. Clearly, from (11.45), the pressure rises towards this value on moving into the pellet when n > 1 and falls to it when n < 1. Thus we can define the following bounds for the pressure... 

Extensive intercalation of polar molecules takes place in this substance in an irreversible manner, and marked hysteresis results (Fig. 4.28). The driving force is thought to be the interaction between the polar molecules and the exchange cations present in the montmorillonitic sheets, since non-polar molecules give rise to a simple Type B hysteresis loop with no low-pressure hysteresis. 

Butyrolactone reacts rapidly and reversibly with ammonia or an amine forming 4-hydroxybutyramides (175), which dissociate to the starting materials when heated. At high temperatures and pressures the hydroxybutyramides slowly and irreversibly dehydrate to pyrroHdinones (176). A copper-exchanged Y-2eohte (177) or magnesium siUcate (178) is said to accelerate this dehydration. 

Transformations in the Solid State. From a practical standpoint, the most important soHd-state transformation of PB involves the irreversible conversion of its metastable form II developed during melt crystallization into the stable form I. This transformation is affected by the polymer molecular weight and tacticity as well as by temperature, pressure, mechanical stress, and the presence of impurities and additives (38,39). At room temperature, half-times of the transformation range between 4 and 45 h with an average half-time of 22—25 h (39). The process can be significantly accelerated by annealing articles made of PB at temperatures below 90°C, by ultrasonic or y-ray irradiation, and by utilizing various additives. Conversion of... 

A flow diagram for the system is shown in Figure 5. Feed gas is dried, and ammonia and sulfur compounds are removed to prevent the irreversible buildup of insoluble salts in the system. Water and soHds formed by trace ammonia and sulfur compounds are removed in the solvent maintenance section (96). The pretreated carbon monoxide feed gas enters the absorber where it is selectively absorbed by a countercurrent flow of solvent to form a carbon monoxide complex with the active copper salt. The carbon monoxide-rich solution flows from the bottom of the absorber to a flash vessel where physically absorbed gas species such as hydrogen, nitrogen, and methane are removed. The solution is then sent to the stripper where the carbon monoxide is released from the complex by heating and pressure reduction to about 0.15 MPa (1.5 atm). The solvent is stripped of residual carbon monoxide, heat-exchanged with the stripper feed, and pumped to the top of the absorber to complete the cycle. 

At temperatures above 50°C, irreversible hydrolysis to formate and ammonia becomes important. If the heat of reaction is not removed, the increased temperature accelerates the decomposition and can create high pressure in a closed vessel. 

Irreversible Processes. Irreversible processes are among the most expensive continuous processes. These are used only in special situations, such as when the separation factors of more efficient processes (that is, processes that are theoretically more efficient from an energy point of view) are found to be uneconomicaHy small. Except for pressure diffusion, the diffusion methods discussed herein are essentially irreversible processes. Thus,... 

To avoid decarburization and Assuring of the carbon and low-alloy steels, which is cumulative with time and, for all practical purposes irreversible, the limitations of the Nelson Curves should be followed religiously, as a minimum. Suitable low-alloy plate materials include ASTM-A204-A, B, and C and A387-A, B, C, D, and E, and similarly alloyed materials for pipe, tubes, and castings, depending upon stream temperatures and hydrogen partial pressures, as indicated by the Nelson Curves. 

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