Nickel vapor pressure, high temperature

Finally, selective hydrogenation of the olefinic bond in mesityl oxide is conducted over a fixed-bed catalyst in either the Hquid or vapor phase. In the hquid phase the reaction takes place at 150°C and 0.69 MPa, in the vapor phase the reaction can be conducted at atmospheric pressure and temperatures of 150—170°C. The reaction is highly exothermic and yields 8.37 kJ/mol (65). To prevent temperature mnaways and obtain high selectivity, the conversion per pass is limited in the Hquid phase, and in the vapor phase inert gases often are used to dilute the reactants. The catalysts employed in both vapor- and Hquid-phase processes include nickel (66—76), palladium (77—79), copper (80,81), and rhodium hydride complexes (82). Complete conversion of mesityl oxide can be obtained at selectivities of 95—98%. 

Catalytic dehydrogenation takes place in the liquid phase at 150°C and atmospheric pressure, in the presence of Raney nickel. An inert high-boiling solvent is used to raise the reaction temperature and to keep the mixture in the liquid state. The catalyst remains in suspension by means of agitation, which is either mechanical or achieved by the circulation of fluids by a thermosyphon effect The heat required for the reaction and the heat of vaporization of the products are provided by external heating and the introduction of the feed in the vapor state. 

The phase diagram for carbon (Figure 2.2) is not clearly defined due to the possible doubtful measurements at the high pressures and temperatures involved. The triple point for graphite (Figure 2.3), where solid, liquid and gas are in equilibrium, is about 4180 K at 10.13 MPa. Carbon vaporizes about 4500 K and 1 kb (100 MPa) or, at 200 K, a pressure of 1000 kb (100 GPa) would be required. Although diamonds can be made at 10 kb (1 GPa) and 1000 K, conversion would be extremely slow and production can be effectively speeded up with catalysts such as nickel, at 100 kb (10 GPa) and 2000 K. Strictly SI does not use multiples and submultiples so N/m x 10 preferred to MN/m. But this is unwieldy and I have used multiples etc and Pa instead of N m to come into line with composite nomenclature. 

While other materials have been used as feed to uranium-enrichment processes, the most widely used volatile compound of uranium is the hexafluoride. At room temperature, UFe is a colorless solid with a density of 5.1 g/cm. It sublimes at atmospheric pressure, and at room temperature has a vapor pressure of 100 torr. The main disadvantage of working with UFe is its high chemical reactivity. It reacts vigorously with water, but is not very reactive with dry air. UF5 reacts with most metals however, nickel, copper, and aluminum are resistant. This holds only for pure UFg the presence of even small amounts of HF increases the rate of attack on even the resistant metals. 

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