Rhodium 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%. 

The major process units include an air compressor to provide feed air to the process, and an ammonia vaporizer and superheater for pretreatment of the feed ammonia. A reactor vessel with a fixed platinum/rhodium catalyst bed quickly oxidizes the ammonia at reaction temperatures approaching 950°C. The reaction yield is 95%. A heat exchanger train immediately following the reactor is used to recover reaction heat. Reaction heat is recovered for both gas expansion (to provide shaft power for the air compressors) and for production of medium-pressure steam (at 380°C and 4000 kPa). The high-level energy available in the process is shared approximately equally between gas expansion and steam production. About 40% of all steam production is delegated to in- house process requirements, leaving about 3200 kg/hour available for export. 

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