Catalysts Contaminants

Contaminants that cannot be removed by conventional regeneration methods are considered as permanent poisons. They deactivate the catalyst either by an effect of porosity plugging or/and occupation of the active sites. It is therefore difficult to attribute a precise deactivation effect of a given poison for all catalysts, as it depends on the catalyst type(NiMo, CoMo, NiW, Pd, Pt), catalyst porosity, metals content, dispersion of active sites.

Some general ideas can however be given.

The most common poisons for hydrotreating catalysts are :

	Vanadium, contained in heavy petroleum fractions such as Vacuum Gas Oils, Atmospheric or Vacuum Resids. Poisoning effect can be noticed at concentrations above 5000ppm, on standard NiMo, CoMo catalysts. On specific resid hydroprocessing catalysts, the metal up take capacity is much higher, and in some case the catalyst can still be regenerated even with a V concentration of 20 wt% (see the article).
	Arsenic, contained in light to heavy oil fractions of specific crudes (Russian, African for example) strongly affects CoMo/NiMo as well as Palladium catalysts, by means of a direct adsorption on the active sites. This poison is badly affecting hydrotreating catalysts activity, at relatively low concentrations. For CoMo/NiMo catalysts Deactivation effect is already observed from concentration around 3000 ppm. Poisoning effect on Pd catalysts is more sever, but, in that specific case, regeneration can help restoring activity.
	Sodium, contained in insufficiently desalted crudes also affect catalysts activity by porosity plugging and potentially modification of active phase dispersion state. Na content should remain below 1500 ppm.
	Silicon, generally originating from antifoaming agents often affects hydrotreating catalysts treating coker naphthas. Some fresh catalysts contains Silicium as a constituent, that is important to distinguish from the silicon brought by the feed. It is generally admitted that the ex feed Silicium content should be below 3 wt%.
	Iron is not a real poison for hydrotreating catalysts, as it does not have a direct deactivation effect. However, iron may accelarate coking reactions.
	Low metals content catalysts (Palladium, Platinum) are sometimes sensitive to poisons at much lower concentration, and a particular attention must be paid when evaluating such a catalyst before regeneration. For instance, Hg, Cl, Si can have a strong de activation effect at concentrations in the range of 50 to 100 ppm.

Catalyst contaminants detection is one of the important items that Eurecat provide in the field of catalyst expertise services.