Hydrogen pressure-composition-temperature

One of the most useful features of metal-hydrogen systems are their pressure-composition-temperature data, P-C-T. Such relationships for palladium-hydrogen are shown in Figure 1. For compositions and temperatures within the envelope, two solid phases coexist, as required by the phase rule. The lower hydrogen-content a-phase represents solution of hydrogen into the metal, and the higher hydrogen-content jS-phase is the hydride. Both a and (3 are... 

Figure 1. Pressure-composition-temperature relationships for palladium-hydrogen (43)...

Pressure-composition-temperature and thermodynamic relationships of of the titanium-molybdenum-hydrogen (deuterium) system are reported. 0-TiMo exhibits Sieverts Law behavior only in the very dilute region, with deviations toward decreased solubility thereafter. Data indicate that the presence of Mo in the 0-Ti lattice inhibits hydrogen solubility. This trend may stem from two factors for Mo contents >50 atom %, an electronic factor dominates whereas at lower Mo contents, behavior is controlled by the decrease in lattice parameter with increasing Mo content. Evidence suggests that Mo atoms block adjacent interstitial sites for hydrogen occupation. Thermodynamic data for deuterium absorption indicate that for temperatures below 297°C an inverse isotope effect is exhibited, in that the deuteride is more stable than the hydride. There is evidence for similar behavior in the tritide. 

Pressure-composition-temperature (P-C-T) relationships were reported for hydrogen and deuterium in a-titanium. Both systems obey Sieverts Law in the dilute region (10) i.e., the square root of equilibrium pressure is linearly proportional to the solute content. McQuillan (3) extended the hydrogen P-C-T data into the 7-phase. For a maximum equilibrium hydrogen pressure of 500... 

LIB] Libowitz, G. G., A pressure-composition-temperature study of the Zr-H system at high hydrogen contents, J. Nucl. Mater., 5, (1962), 228. Cited on page 131. 

C, 0.356—1.069 m H2/L (2000—6000 fU/bbl) of Hquid feed, and a space velocity (wt feed per wt catalyst) of 1—5 h. Operation of reformers at low pressure, high temperature, and low hydrogen recycle rates favors the kinetics and the thermodynamics for aromatics production and reduces operating costs. However, all three of these factors, which tend to increase coking, increase the deactivation rate of the catalyst therefore, operating conditions are a compromise. More detailed treatment of the catalysis and chemistry of catalytic reforming is available (33—35). Typical reformate compositions are shown in Table 6. 

Figure 1. Ideal pressure-composition isotherms showing the hydrogen solid-solution phase, a, and the hydride phase, j3. The plateau marks the region of coexistence of the a and fl phases. As the temperature is increased the plateau narrows and eventually disappears at some consolule temperature...

Tn the synthesis of methane from carbon monoxide and hydrogen, it is desired to operate the reactor or reactors in such a way as to avoid carbon deposition on catalyst surfaces and to produce high quality product gas. Since gas compositions entering the reactor may vary considerably because of the use of diluents and recycle gas in a technical operation, it is desirable to estimate the effects of initial gas composition on the subsequent operation. Pressure and temperature are additional variables. 

This recommended practice summarizes the results of experimental tests and actual data acquired from operating plants to establish practical operating limits for carbon and low alloy steels in hydrogen service at elevated temperatures and pressures. The effects on the resistance of steels to hydrogen at elevated temperature and pressure that result from high stress, heat treating, chemical composition, and cladding are discussed. 

Detonation pressure and temperature of hydrogen-air mixtures starting from 101.3 kPa (1 atm) and 298 K (25°C). Chapman-Jouguet calculations using the Gordon-McBride code. (After Gordon, S. and McBride, B.J., Computer Program for Calculation of Complex Chemical Equilibrium Compositions and Applications, NASA Reference Publication, Cleveland, Ohio, 1994.)... 

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