Naphtha hydrotreater catalyst deactivation by lead

[Milutin]

Dear all,

Our naphtha hydrotreater feed is straight run naphtha from ADU unit, it prepare naphtha for platformer unit. Lead content is all time below detection, below 10ppb.

There is an idea to process slop oil which contain lead on ADU by blending small quantities of slop oil together with crude oil to keep naphtha lead content up to 10ppb. 10ppb is quantity of maximum lead content in naphtha feed set by process licensor.

I am aware if we introduce lead that catalyst poisoning will be permanent or in other words, catalyst regeneration wouldn't recover activity lost by lead poisoning.

Is it a way how to calculate catalyst life and cycle length if we introduce lead to naphtha feed?

I suppose that mechanism of catalyst poisoning is similar to poisoning with mercury, so if anybody can provide some literature about I welcome.

Regards,

Milutin

 

[epoisses]

Hi milutin,

I guess 10 ppb means "there should be no lead in the feed" as lead is a permanent poison as you wrote. As a rule of thumb, 1 wt% lead on the catalyst leads to 50% activity loss (source Albemarle catalysts). Of course there is never a clear point at which you can consider your catalyst dead, but talking in terms of orders of magnitude, 10 wt% would definitely be too high while 0.1 wt% would still give a decent activity. So your calculation basis would be 0.1 to 1 wt%.

However the naphta hydrotreater catalyst is NOT a perfect filter. You MAY see lead breakthrough to the PLATFORMER before serious deactivation occurs. If your plan leads to frequent replacement of platformer catalyst, the economics may change considerably.

 

[Milutin]

Hi epoisses,

Thank you for your answer. I am guessing what will happen in period of time when we process naphtha contaminated with lead. Catalyst activity will start to decrease, to keep same level of desulfurisation it will be necessary to increase reactor inlet temperature, which can produce more coke on catalyst, this will additionally accelerate catalyst deactivation.

Taking in account cost of HDS and platformer catalyst and more frequent downtime for catalyst regeneration/catalyst replacment this can be costly option.

Regards,

Milutin