As with any catalyst, the deactivation rate is a function of processing similarity; and consequently, if the unit is targeting lower octane values, regeneration requirement can become less frequent. It is really up to the refiner to make the decision as to whether or not to let the cycle extend out longer because of the lower production of the coke or to regenerate more proactively on an annual basis to ensure that the yield losses are maintained at a minimum.

Changing catalyst suppliers is not an uncommon practice. It is done successfully in many different locations. Typically, cost and yield improvements are the most influential factors. However, there are some other key considerations before making the change.

To meet Tier 3 10 ppm sulfur in the gasoline pool, FCC naphtha will need to be treated to 10 to 35 ppm. The target FCC naphtha sulfur level is based on the sum of all the other sulfur species in the pool, as well as the percent of FCC naphtha in the pool, as indicated in the plot.

Historically, disulfide oils would be blended back into the gasoline pool; but in the days of Tier 2 gasoline, this option is no longer available. The question of how to dispose of disulfide oils is one that comes up frequently within the company. Options that are often discussed are whether or not disulfide oils can be reprocessed in the cat cracker, the crude unit, or the coker.

I think the first consideration is: Do you have access to a reliable supplier? Your alky plan needs a supplier, either onsite or a third party, who meets your requirements in terms of on-time delivery and quality. Refineries do not want to have a slowdown or shutdown due to delivery issues of acid to the alky plant.

We have seen considerable interest in pressure, temperature, level, and flow instrumentation to monitor auxiliary seal flush systems as specified in API Standard 682, as well as the special flush piping plans for hydrofluoric acid services as specified by the process licensor.

In sulfuric acid alkylation plants, alkaline water is used to neutralize acidic components that are present in the hydrocarbon effluent. To achieve the neutralization, the alkaline water pH is typically maintained between 11 and 12, and the temperature controlled between 120°F and 160°F.

The HF alkylation reaction is a two-step process. The first step of the reaction goes rather quickly, and anything that slows a reaction down will allow a stable organic fluoride to form. So, the factors that increase organic fluoride formation are temperature at I/O ratio and usually acid strength.  

Again, I am focusing mostly on sulfuric acid units because that is where I have experience. Carbonyl sulfide (COS) is a noncombustible gas that will follow propane and propylene. So, if you are running all of your FCC olefins, then you will get it into the reactor and into the refrigeration section.

We have found that if we can bring the unit down in a controlled fashion – specifically, if we can clean up the acid by circulating isobutane for a few hours and clear the acid of any reactants, then we can let it sit there for 24 to 36 hours, maybe even 48 hours, without any kind of issue.