HYDRODESULFURIZATION OF THIOPHENE ON HIGHLY DEACTIVATED COAL-LIQUID HYDROTREATMENT CATALYST - EFFECT OF DEPOSITED IRON SULFIDE

The hydrodesulfurization of thiophene was studied over highly deactiva ted NiMo on alumina catalysts, iron sulfide, and a combination of the two. Iron sulfide is one of the metals deposited along the periphery o f the catalyst particle during deactivation. For the supported NiMo ca talysts, the Arrhenius plots bend downward as temperature increases; i .e., the apparent activation energy decreases. This is as expected. Ho wever, at even higher temperatures, the plot for the highly deactivate d NiMo catalyst bends upward again; i.e., the apparent activation ener gy increases. A two-step series reaction mechanism can be used to expl ain the results over the highly deactivated catalyst. Step 2 controls the reaction rate on NiMo catalysts, while on iron sulfide alone step 1 controls the rate. A model is presented describing diffusion and rea ction within a catalyst pellet having a nonuniform activity distributi on. The model predicts the Arrhenius plots obtained over deactivated c atalysts, in particular, the increase in activation energy observed at high temperatures.