Synthesis of β-picoline from 2-methylglutaronitrile over supported noble metal catalysts II. Influence of operation parameters Original Research Article

Activity, selectivity and stability of silica-supported Pd, Rh and Pt catalysts in the vapour phase hydrogenation of 2-methylglutaronitrile to β-picoline were strongly dependent on temperature, pressure, hydrogen partial pressure and space velocity. The activity and stability of the Pd catalysts increased with hydrogen pressure, while the selectivity for undesired by-products decreased above 600 K, due to the increased rate of the surface reactions of the intermediates. Rh catalysts showed substantially the same behaviour as Pd catalysts. Over platinum catalysts, an optimal operating temperature for the production of β-picoline was found by compromising between hydrogenolysis, intermolecular condensation and catalyst deactivation. Increasing temperature and space velocity, and decreasing total pressure and hydrogen partial pressure decreased hydrogenolysis, but favoured intermolecular condensations and, thus, the formation of coke precursors. The intermediates in the hydrogenation of 2-methylglutaronitrile reacted to β-picoline and by-products via a series of adsorption-reaction-desorption steps, with hydrogenolyzed by-products being thermodynamically favoured. A deactivating-front model was proposed to account for the observed loss of catalyst activity and selectivity.