Impact of Vaporization On Catalyst Deactivation: Part II - High Pressure ULSD Production

Grass roots units for ULSD production are typically designed for a high operating pressure (1100+ psig). Refiners use these high-pressure units for processing feed blends that contains more refractory sulfur molecules than those processed in low-pressure units. Cracked materials like Light Cycle Oil and Coker Distillates are typically the main feed blending components to high-pressure ULSD hydrotreating units. These feed streams contain high levels of refractory sulfur molecules, organic nitrogen, coke precursors, and metal contaminants that are poisonous to the catalyst activity.

Observations of commercial operations show that catalyst deactivation in high-pressure ULSD units typically occurs from both metals poisoning and coke formation. As with low-pressure ULSD units, high vapor to liquid ratios (above ~ 80 wt% vaporization) result in reduced hydrogen partial pressure and increased coke formation tendencies in the end-of-cycle operating environment for high-pressure ULSD units. The effects of metals poisoning and excessive vaporization due to chemical properties of its feed components and physical phenomena in the reactor at high operating temperature of a specific commercial high-pressure (~ 1300 psig) ULSD unit causing the acceleration of catalyst deactivation at end-of-cycle are discussed.