COMPARING MONOMETALLIC AND BIMETALLIC NOBLE-METAL CATALYSTS IN A CATALYTIC MEMBRANE REACTOR FOR METHYLCYCLOHEXANE DEHYDROGENATION

A catalytic membrane reactor (CMR) containing a catalyst bed and a tub ular palladium-silver (Pd-Ag) membrane to separate the coproduced Ha, was used to obtain higher than equilibrium conversions in the dehydrog enation of methylcyclohexane (MCH). A monometallic, Pt/Al2O3 (MM30S), and a bimetallic, Pt-Re/Al2O3 (BM30), noble-metal catalysts and two me mbranes with 0.1 and 0.2 mm wall thickness were employed. Experiments in the CMR at 573-673 K, 1-2 MPa, and liquid hourly space velocities ( LHSVs) up to 12 volume feed/(h . reactor volume) showed that catalyst MM30S was outstanding in performance giving significant improvement in toluene (TOL) and Ha yields over the equilibrium values at commercial ly relevant conditions. Catalyst BM30 deactivated exceeding equilibriu m yields to extents considerably lower than those with catalyst MM30S. However, the ratios of Ha permeation to generation rates, a, were alm ost equal for the two catalysts under comparable conditions. The exten t by which the equilibrium conversions were exceeded, decreased as the LHSV increased due to permeation limited operation. Reactor axial tem perature profiles showed the existence of two cold spots in the CMR. A n attempt is made to correlate the extent of MCH conversion to TOL in the CMR with the operating variables.