I.FLUID CATALYTIC CRACKING: www.wissenschaftler-avh.in
B.CATALYST/ADDITIVES(Contd.):
Q-58: What are the Strategies for Addressing Catalyst Iron Poisoning in FCCU ?
A-58:
Having the right pore structure that allows feed molecules to transport inside the catalyst for cracking is critical in any catalyst that delivers high activity and bottom cracking selectivity, particularly for catalysts slated for resid applications. For the FCCU operator the key question is how to maintain the pore structure in the face of iron contamination ,and prevent pore closing that results in catalyst performance deterioration. Based on the data collected,the following strategy is recommended.
1.Establish that any catalyst performance deterioration observed is indeed due to rising iron levels on the equilibrium catalyst.
Sometimes iron may rise after a feed change accompanying loss of activity and bottoms cracking. Before concluding the increased iron levels have poisoned the catalyst, the refiner should establish that the performance deterioration is not due to a change in feed crackability and increase of other metals(e.g., Na, V, Ni)deleterious to catalyst performance. SEM, EPMA and optical microscopy analysis of the equilibrium catalyst can be used to look for the surface composition and texture characteristic of iron poisoned catalyst.
2. Try to reduce the iron coming into the unit.
Measures that can be employed to reduce iron coming with the feed is to stop using high iron feeds and/or to buy low iron feed to blend with the high iron one.It has been suggested that acids in the feed(e.g., naphthenic acids) can corrode hardware increasing the iron content of the feed. Reducing the acid content, or purchasing low acid content feeds can reduce hardware corrosion, and thus decrease the amount of iron in the feed.
3 .Reduce the Na and Ca content of the feed.
Na and Ca as fluxing agents severely aggravating the catalyst poisoning effect of iron. It is therefore critical that either low Na and Ca feeds are used ,or that the amounts of these metals in the feed are reduced by desalting or other suitable process.
4. Use an appropriately designed iron resistant Al-Sol catalyst.
When the unit does not have the flexibility to implement other solutions, or other
solutions fail, Al-Sol catalysts have been proven to provide excellent resistance to iron contamination, and maintain activity and bottoms cracking even at iron levels on equilibrium catalyst which are the highest in the industry.
