Scaling-out selective hydrogenation reactions: From single capillary reactor to monolith

Selectivity and kinetic studies of the Pd-catalysed hydrogenation of 2-butyne-1,4-diol were performed in a single capillary channel, and monoliths consisting of 1256 capillaries and 5026 capillaries in (I) the pressure range 100–300 kPa (II) the temperature range 298–328 K using a 30% v/v 2-propanol/water solvent. All reactors were operated in downflow mode such that the reaction fluid was in Taylor flow. Transport calculations indicated that liquid–solid transport resistances were low (<5%) and energies of activation were found to be in the range 32–34 kJ mol−1. While the reaction was first order in hydrogen concentration, the order with respect to 2-butyne-1,4-diol changed over the concentration range investigated. A model based upon a Langmuir–Hinshelwood mechanism was applied and found to predict reasonably well the experimental reaction rates. High selectivity values towards the 2-butene-1,4-diol were found in both the single- and multiple-capillary reactors, even at 100% conversion of the alkyne.