Dehydrogenation of propane in a palladium membrane reactor

Abstract

The dehydrogenation of propane in a palladium membrane reactor was studied. The study was divided into 3 main parts: kinetic study of 0.3 wt%Pt-0.3 wt%Sn-0.6 wt%K/y-Al2 O3 catalyst, permeation study of hydrogen through a palladium membrane and study on the membrane reactor. The Pt-Sn-K/y-AI2 O3 was selected because of its high resistance in catalyst deactivation. Reaction rate constants for the Pt-Sn-K/y-Al2 O 3 catalyst were determined by fitting the experimental results with power-law kinetics at the reaction temperature ranging between 723 and 873 K. The reaction rate constant based on the active site for the Pt-Sn-K/y-Al2O3 catalyst at 773 K was 1.40x10-28 mol/(site•s•Pa). In addition, the frequency factor and the activation energy were 5.68x10-23 mol/(site-s-Pa) and 60.5 kJ/(mol-K), respectively. The permeation study of pure hydrogen through a Pd-Ag membrane with 5 mm diameter and 0.1 mm thickness was carried at 573, 673 and 773 K. The permeation was assumed to follow Sievert’s law. The obtained permeation coefficient at 773 K was 9.42x10-9 mol/(m2•s•Pa0.5) and the activation energy was 9.7 kJ/(mol•K). In the membrane reactor study, hydrogen was continuously removed from the reaction zone along the membrane length; thereby equilibrium composition and the reaction were continuously moved forward. In this work both mathematical modeling and experimental work were carried out. It was found that simulation results agree well with experimental values with error about 3 - 8 %. Membrane reactor performance was superior to a conventional packed bed reactor when operated at high sweep gas flow rate and W/F. This is particularly pronounced with a membrane with very thin Pd layer thickness. In the range of study, it was found that the radial dispersion effect was not significant. Finally, it was concluded that to obtain the same conversion, the membrane react or can be operated at a lower temperature, resulting in energy saving.