Chapter 6 - Regeneration

Abstract

This chapter explores regeneration, that is considered to be the process for removal of the coke deposited on catalyst surface. This also requires the recovery of surface area and porosity. To be suitable for regeneration, the content of contaminant metals in spent catalyst should not exceed 5 wt.%. Otherwise, at least 80% recovery of the original activity to make regeneration attractive may not be achieved. Such a level of catalyst activity recovery can be readily achieved for the spent catalysts after hydroprocessing atmospherics distillates and lighter feeds. It is difficult to reach this level of the activity recovery when both coke and metals, which were deposited from the feed, are present on the catalyst surface. The most widely used method for activity recovery involves the coke removal via oxidative regeneration using diluted air and/or air and steam mixture. Potentially, other oxidative agents can also be used. The oxidative regeneration technique has been used on a commercial scale for several decades. Attempts are also made to use steam and CO2 as oxidative agents. The most established regeneration method involves the oxidative removal (by burn-off) of carbonaceous deposits, generally referred to as coke, which deposited on the catalyst surface during the operation. To ensure safety, the diluted air has been used as the oxidation medium during the early stages of regeneration. The last stages of the regeneration process, i.e., after the most reactive components of coke are removed, may be completed using air. Under properly controlled regenerating conditions, almost complete removal of carbon deposited on catalyst can be achieved. The oxidative regeneration using air is also possible provided that the regenerator temperature is carefully monitored. In this case, either the redesign of the regenerator or installation of a cooling system may be necessary. However, the additional cost of these changes must be compensated for by improved efficiency of regeneration.