Determining average bed temperature of nonisothermal fixed-bed hydrotreater

Employing three catalysts in three parallel pilot-scale fixed-bed reactors, hydrotreating experiments were performed in both isothermal and ascending temperature modes to investigate kinetics and to determine a representative bed temperature. Assuming 1.5th-order for hydrodesulfurization (HDS) and 1st-order for both hydrodenitrogenation (HDN) and mild hydrocracking (MHC), kinetic parameters were obtained from the isothermal mode operation. With the activation energies from isothermal operations, equivalent isothermal temperatures (EITs) in the ascending mode operations were established for specific HDS, HDN and MHC. Employing 19 thermocouple readouts in the catalyst beds and applying an Arrhenius-type rate equation containing the same activation energy, the representative bed temperature was determined. The temperature so determined is called kinetic EIT. The kinetic EIT was found to be the best to represent the nonisothermal bed temperature. The kinetic EIT has been applied to monitoring the catalyst activity in commercial hydrotreating units.