Experimental procedure for kinetic studies on egg-shell catalystsThe case of liquid-phase hydrogenation of 1,3-butadiene and n-butenes on commercial Pd catalysts

Abstract

A study of the liquid-phase hydrogenation of 1,3-butadiene on commercial Pd/Al2O3 catalysts of the “egg-shell” type has been performed. Experimental conditions (40◦C, 4 atm and high conversion of the di-olefin) were selected in accordance to industrial operating conditions employed for selective hydrogenation of 1,3-butadiene. Three experimental schemes were tested: a slurry reactor, a rotating-basket reactor, and a recirculation system with an external fixed-bed reactor. Significant drawbacks shown by the two former devices were mainly derived from the very high activity and the egg-shell structure of the catalysts. Instead, the recirculation system was found to be an excellent alternative. Although Pd is present only within a very thin external layer (around 50–250mm), strong diffusion effects impairing selectivity were observed. Plausible kinetic expressions corresponding to nine series–parallel overall reactions are derived from a mechanistic model. To deal with this network of fast reactions, a rather complex set of computational and predictive tools were employed. A worked out example from several replicates demonstrates the capability of both, experimental and data analysis procedures, for inferring kinetic parameters of the proposed model.