Palladium overall pressure

Membrane-based separation processes to capture either H2 or CO2 from the gasifier are new and less studied methods of CO2 separation and capture. Membranes separate the desired gas component without requiring phase changes or chemical or physical sorption. The cost of membrane separation is generally dictated by the overall pressure drop. Membranes made of various types of materials such as polymers, metals, and rubber composites have been investigated. Palladium and molecular sieves are currently under study. ° ... 

The same group has looked into the conversion of NO on palladium particles. The authors in that case started with a simple model involving only one type of reactive site, and used as many experimental parameters as possible [86], That proved sufficient to obtain qualitative agreement with the set of experiments on Pd/MgO discussed above [72], and with the conclusion that the rate-limiting step is NO decomposition at low temperatures and CO adsorption at high temperatures. Both the temperature and pressure dependences of the C02 production rate and the major features of the transient signals were correctly reproduced. In a more detailed simulation that included the contribution of different facets to the kinetics on Pd particles of different sizes, it was shown that the effects of CO and NO desorption are fundamental to the overall behavior... 

The gas-phase process, successfully commercialized independently by Bayer and USI,417 involves passing a mixture of ethylene, acetic acid and oxygen over a supported palladium catalyst contained in a multitubular reactor at 150 °C and about 5-10 atm pressure. The overall yield in vinyl acetate is about 92%, and the major by-product is C02. The catalyst consists of a palladium salt (e.g. Na2PdCl4) deposited on silica (or alumina) in the presence of a cocatalyst (e.g. HAuC14), reduced and impregnated with potassium acetate before use.384,418 The lifetime of the catalyst is about 2... 

Overall, the most reliable catalyst for these hydrogenolyses proved to be palladium black which gave the most rapid reactions at atmospheric pressure and in all cases apart from the C-4 phenyl derivative 140, gave the best 45 4R ratio. 

Currently ranked 41st in American volume of production, vinyl acetate is made by the vapor phase reaction of ethylene with acetic acid at 170-200°C. Pressures of 5-8 atm and a palladium catalyst supported on carbon are required to give conversions of 10-15% on ethylene and 15-30% on acetic acid. Equation 19.28 is an overall representation of the stoichiometry of the complex process. 

Alper et al.97,98 immobilized palladium-modified PAMAM-like dendron complexes onto silica for carbonylation of iodobenzene in MeOH to generate methyl benzoate under low pressures of CO at 100°C. Product yields were high overall and the catalyst could be recycled 4 5 times without significant loss of activity. This type of PAMAM-type dendron-Pd complex was also used for the oxidation of terminal alkenes to generate methyl ketones under mild conditions 99 oxidative selectivity toward the terminal versus internal double bonds was also determined. 

---