Guarding against contaminants Analysing spent hydroprocessing catalyst underpins the development of guard bed catalysts to counter contaminants

摘要

Avery important parameter for the cycle length of a hydro-processing unit is the deactivation rate of the installed catalyst. The deactivation of a hydrotreating catalyst can be coke induced and contaminant induced. Coke deposition is to a large extent controlled, but also dictated, by the unit operating regime (temperature, hydrogen availability, residence time and partial pressure of hydrogen). This will normally cover most middle distillate units making ULSD or lighter products. However, in units processing heavier feedstocks like vacuum gas oil (VGQ), heavy coker gas oil (HCGO), deasphalted oil (DAO), or even heavier cuts, the refinery normally faces a dual type deactivation. The coking reactions here are even more significant because the feedstock is heavy and contains lots of aromatic coke precursors in the high boiling fraction. But heavy feedstocks will often also contain a significant amount of heavy metals and other contaminants. In particular, this includes nickel, vanadium, iron, silicon, arsenic, phosphorus, calcium and sodium. These contaminants are present in processed feedstocks at ppm or even ppb levels, but the effect is significant. Following a non-reversible pathway, heavy metals will be deposited on active catalyst following different mechanisms. The outcome is that activity is lost permanently and will thus not even be regained during catalyst regeneration.