Analysis of the performance of single capillary and multiple capillary (monolith) reactors for the multiphase Pd-catalyzed hydrogenation of 2-butyne-1,4-diol

The Pd-catalysed hydrogenation of 2-butyne-1,4-diol has been studied in the monolith CDC and in a single channel capillary reactor in (I) the pressure range 100-300 kPa, (II) the temperature range 298-328 K using a 30% v/v 2-propanol/water solvent. The monolith reactor was operated in downflow mode such that the reaction fluid was either single phase or in Taylor Flow. The latter was also employed in the single-capillary reactor. The kinetics were found to be a function of the hydrodynamic conditions. This was not found to be due to transport problems but to a function of the surface concentration of reacting species. Reaction rates varied from a positive order (0.13) to zero order to negative orders (-0.34 to -0.38) in 2-butyne-1,4-diol concentration. A model based upon a Langmuir-Hinshelwood mechanism was applied and found to predict reasonably well reaction rates and product distribution. High selectivity values towards the 2-butene-1,4-diol were found in both the single- and multiple-capillary reactor even at 100% conversion of the alkyne. (C) 2004 Elsevier Ltd. All rights reserved.