Factors controlling sintering of a Co-Mo/Al2O3 hydrotreating catalyst during oxidative regeneration

Catalyst deactivation resulting from sintering and phase transformation is a serious problem in oxidative regeneration of hydrotreating catalysts. The key to the control of these undesirable changes, occurring during generation, is to understand the factors which enhance them. In the present work, the effect of parameters such as temperature, gas flow rate, and oxygen concentration on the sintering of an industrial gas-oil hydrotreating catalyst during regeneration was investigated. Chemical changes and phase transformations, occurring in the catalyst during regeneration, were also examined. The results revealed that, during the decoking process, extensive surface area loss occurred due to sintering at high (>5%) oxygen concentrations and high flow rates of the regeneration gas. Increasing the initial combustion temperature above 440 degrees C led to considerable sintering of the catalyst. Pore size distribution data of catalysts, decoked at different temperatures, showed a progressive pore enlargement with increasing temperature. At temperatures above 700 degrees C, a substantial loss of molybdenum from the catalyst, together with phase transformations in the alumina support, occurred.