Regeneration of CuO-ZnO-Al2O3/γ-Al2O3 catalyst in the direct synthesis of dimethyl ether

Abstract

This paper deals with the regeneration of a CuO-ZnO-Al2O3/γ-Al2O3 catalyst used in the direct synthesis of dimethyl ether. When coke combustion (subsequent to aging treatment) is performed in a thermobalance, two coke fractions with different combustion kinetics are identified. One coke fraction, deposited on the metallic sites and whose combustion is activated by these sites, has a kinetic constant of combustion 7–26 times higher than that corresponding to the coke located at the Al2O3 support. Uninterrupted operation is feasible in reaction–regeneration cycles in a fixed bed reactor as long as the reaction and regeneration steps are carried out at 325°C, which are limiting conditions in order to avoid irreversible deactivation by sintering of the metallic function. The regeneration with O2 diluted with He (5% of O2) allows the complete combustion of coke. Under conditions of partial coke combustion it is observed that the removal of the fraction deposited on the metal makes it possible to recover the initial activity of the catalyst, which subsequently undergoes fast deactivation.