KINETICS, MASS-TRANSFER, AND PALLADIUM CATALYST DEACTIVATION IN THE HYDROGENATION STEP OF THE HYDROGEN-PEROXIDE SYNTHESIS VIA ANTHRAQUINONE

Hydrogenation of 2-ethYl-5,6,7,8-tetrahydroanthraquinone is a key step in the industrial production of hydrogen peroxide via anthraquinone with the process named all-TETRA. This reaction on palladium-supported catalysts is very fast; consequently, the chemical regime can hardly be achieved and kinetics is always masked by mass-transfer limitations. Nevertheless, it is possible to demonstrate that the reaction occurs with a zero- and first-order kinetics with respect to hydrogen and to the organic reagent, respectively. These reaction orders can be explained on the basis of reasonable reaction mechanisms described and discussed in this paper. Kinetics has been studied by performing runs in two different laboratory reactors: a semibatch and a continuous stirred tank reactor. In particular, the continuous reactor has been used for studying catalyst deactivation. Two types of catalyst poisoning have been recognized, a reversible one, related to the presence of water, and a permanent, not yet explained one. A kinetic expression is given also for deactivation. The kinetic parameters obtained from the experimental runs have been verified by simulating the behavior of an industrial reactor also considering catalyst deactivation.