Hydrogenation of 2-pentyne over Pd/Al2O3 catalysts: Effect of operating variables and solvent selection

Hydrogenation of 2-pentyne over 1 wt.% Pd/Al2O3 was studied in a 2.65 L baffled stirred vessel. The effects of stirring speed, hydrogen pressure, concentration of substrate, catalyst loading, solvent selection and catalyst preparation method upon the rate and selectivity were investigated. It was shown that increasing the stirring speed from 445 to I 100 rpm and crushing the particles from > 150 to 4575 mu m led to increases in the reaction rate, confirming the existence of mass transfer resistances. Catalyst preparation method (Type A: crushing followed by impregnation or Type B: impregnation followed by crushing) had a strong effect on reaction behaviour, with Type B particles showing a much higher metal dispersion and consequently faster reaction rate than Type A. Solvent selection was found to have a very strong effect upon reaction rate and selectivity and in heptane the reaction rate was faster than isopropanol. In a 50/50 mixture of heptane and isopropanol the rate of alkyne hydrogenation was intermediate to that observed in the solvents individually while selectivities were up to 5 times greater. The most favourable conditions in terms of selectivity were 2 bar of hydrogen, a stirring speed of 445 rpm and a solvent mixture of 1:1 heptane/isopropanol, where the highest cis/trans pentene ratio was 25.39, and the highest pentene/pentane ratio was 49.41. (C) 2009 Elsevier B.V. All rights reserved.