DEACTIVATION AND REGENERATION OF PD-AG MEMBRANES FOR DEHYDROGENATION REACTIONS

Experiments on commercially available palladium-silver (Pd-Ag) tubular membranes were carried out to: (1) verify the validity of both Sievert's and Fick's laws for H-2 permeation through the membrane; (2) quantify the deactivating effects of methylcyclohexane (MCH), toluene (TOL), sulphur (S), and chlorine (Cl) on membrane permeability; and (3) develop regeneration procedures to restore the original H-2 permeation rates. The results showed that the H-2 permeability data were represented by Sievert's and Fick's laws. Initial exposure of the fresh membrane to MCH or TOL caused inhibition of H-2 permeation but after air oxidation, the membrane permeability was restored and constant for 32 h at 633 K in the presence of MCH. The H-2 permeation rates through the membrane were 14% lower in the presence of MCH or TOL. S and Cl poisoned the membrane strongly but redox procedures for S and a water vapour treatment for Cl were sufficient to restore the original H-2 permeation rates. The application of a catalytic membrane reactor (CMR) with a sulphided, monometallic, commercial catalyst is illustrated for MCH dehydrogenation where twice the equilibrium value of TOL was obtained.