Acrylonitrile Vapor Phase Hydrogenation Of Alumina Supported Palladium, Nickel Catalyst And Kinetic Study

The present paper presents the application of the catalytic hydrogenation technique in the field of fine chemical in brief, Introduces both application and preparation of supported Pd catalyst. The fixed-bed reactor for gas phase hydrogengation of acrylonitrile to propionitrile at normal atmospheric pressure was established. The effect of both prepared conditions of Pd/Al2O3 and the alkali oxides(CaO,Na2O ,K2O)-modified Pd/Al2O3 on gas phase hydrogenation of acrylonitrile to propionitrile were studied. Then the kinetic reaction of gas phase hydrogengation of acrylonitrile to propionitrile in fixed-bed was performed. The following were conclusions : Palladium has a unique character among precious metals as a hydrogenation catalyst. Palladium supported on alumina has a high selectivity for the hydrogenation of acrylonitrle to propionitrile ,and no other products are detected besides propionitrile .Experiments demonstrated that the conversion of acrylonitrile decrease as a function of time on steam because of the deactivation of Pd/Al2O3. The optimum prepared conditions of Pd/Al2O3 are as follows: pH=4 of PdCl2 impregnant ,calcined at 473 K ,palladium content below 0.3%. It was also observed that the stability of catalyst reduced by 36% formaldehyde was better than that reduced by hydrogenation at different temperature. The activity and the stability of Pd/ Al2O3 superior to that of Ni/ Al2O3. Nickle content below 10%,calcined and reduced with hydrogen at 723K are the optimum prepared condition for Ni/ Al2O3. The stability of palladium can been enhanced after the catalysts are modified with alkali oxides. On the contrary ,nickle catalysts modified with alkali oxides show a faster deactivation . The Pd/Al2O3-CaO catalyst contained CaO 30% show the best catalytic performancecompared with Pd/Al2O3-Na2O contained Na2O 30% and Pd/Al2O3-K2O contained K2O 30%. Experiments also show that the catalysts prepared with impregnation method show better catalytic behavior than prepared with sol-gel method. The cause that the addition of alkali oxide increase the stability of Pd/Al2O3 is attributed to three aspects: the first alkali oxide can decrease Pd crystallite size and enhance Pd dispersion.the second the addition of alkali oxide is know to decrease the acidity of the alumina surface. The third, alkali oxide can change the electronic effect between the palladium and the alumina. kinetic experiments on gas phase acrylonitrile hydrogenation over CaO modified palladium catalyst were conducted in fixed-bed reactor at the reaction temperature below 170℃. The hydrogenation rate can be expressed in the following equation:...