QUESTIONS AND ANSWERS

I.FLUID CATALYTIC CRACKING:               www.wissensenschaftler-avh.in

B.CATALYST/ADDITIVES(Contd.)

Q-62:

It  is well known that oxygen enrichment necessitates increased catalyst additions. Are some catalysts more tolerant of oxygen enrichment than others? Has anyone developed a good test to determine which catalysts can better withstand the oxygen enrichment environment?

A-62:

The use of oxygen enrichment will accelerate the catalyst deactivation rate due to a number of related effects. Bulk regenerator temperatures will increase due to the smaller nitrogen dilution effect. Catalyst particle temperatures will probably increase by even more than what is indicated by the bulk bed temperature, due to accelerated burning kinetics, although there is not any good way to directly measure this.
Since hydrothermal catalyst deactivation is caused by the presence of steam at high temperatures, the effect of concentrating the steam partial pressure formed from hydrocarbon burning with lower nitrogen dilution will also be present. The higher temperature and higher localized oxygen concentration will also accentuate vanadium mobility and, therefore, vanadium destruction of the zeolite.

All of these things occurring simultaneously will increase the catalyst deactivation rate. Commercial experience from one unit has shown deactivation rate increases by 40% with the use of oxygen enrichment. This increases the importance of activity and hydrothermal stability in catalyst selection.

High levels of both zeolite and active, stable matrix are employed to withstand these effects, without needing to go to excessive catalyst addition rates. If the base case catalyst is high zeolite-to-matrix ratio, it will probably be prudent to consider lowering it, since there is a limit to how much zeolite you can add, and higher matrix catalysts will hold up to the severe environment with more stability.

Certainly, for the case with oxygen enrichment, a more severe steaming treatment will be required to simulate what the regenerator operation will do, with some combination of higher temperature, time, and/or steam partial pressure.It is always a good practice to make sure the deactivation severity used in testing matches reasonably well in terms of microactivity test activity, zeolite and matrix properties and surface area retentions, with the known base catalyst in the commercial unit.

       

QUESTIONS AND ANSWERS

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B.CATALYST/ADDITIVES(Contd.)

Q-61:

What conditions or contaminants will deactivate ZSM-5 additive? What is the half-life of ZSM-5 in clean feed operation?Will contaminants such as vanadium, sodium or other metals adversely affect the propylene selectivity of ZSM-5? What is the best way to monitor the effectiveness of the ZSM-5?

A=61:

The deactivation mechanism for FCC catalyst is primarily related to unit cell size reduction and, eventually, collapse or sintering of the zeolite crystal. The mechanism of ZSM-5 deactivation is quite different.

The deactivation mechanism is simply the dealumination of the ZSM-5 crystal, and activity is lost through the loss of active aluminum sites. The crystal structure does not collapse. The activity retention and half-life of the ZSM-5 additive in the circulating inventory is strongly affected by hydrothermal conditions within the regenerator with temperature being the dominant variable
.
ZSM-5 additive activity is less affected by contaminant metals than is FCC catalyst due to the fact that heavy feed molecules containing contaminant metals, such as vanadium, are less likely to crack on ZSM-5. ZSM-5 will therefore maintain its activity longer than will the FCC catalyst.

It is worth pointing out that a unit experiencing high equilibrium vanadium levels will likely experience a loss in conversion, which will reduce LPG yields. This loss may give the appearance of a ZSM-5 effect. The propylene selectivity will likely remain unaffected.

The activity retention difference between ZSM-5 and FCC catalyst will increase as the equilibrium metals level increases. Intercat has evaluated ZSM-5 additive half-lives for several units and found a typical half-life of about 18 days, with a minimum of 2 days and a maximum of 36 days.

ZSM-5 additive activity in an operating unit is strongly affected by the catalyst replacement rate. Units having a very high replacement rate present a higher average ZSM-5 activity than units with very low changeout rate. A paper presented at the 2000 American Chemical Society conference investigated the subject of LPG selectivity differences in detail. This study reviewed additives having different ZSM-5 crystal content, different levels of additive additions in the FCC, additives from different manufacturers, additives with different silica-to-alumina ratios, and additives steamed at different severities.

The results of the study can be plotted on one chart. These data demonstrate that if one additive were more selective than another, the propylene yield would fall on a different line, which did not occur. All additives tested at all concentrations fell on the same line. We also found that the propylene yield increases faster than butylene yield and that higher delta LPG yield leads to higher propylene yields.

Additive zeolite content, type, method of manufacture, and steaming severity have no effect on the selectivity of the final LPG product. The ratio of propylene to butylene in the final product depends only on how much LPG is made. The conclusion is that ZSM-5 additive selectivity is determined by the zeolite structure alone. Therefore, measuring activity differences is more important than looking for selectivity differences with a standard ZSM-5 additive. (Please note that these results apply only to standard ZSM-5 technology.)

While propylene selectivities are determined by the ZSM-5 crystal structure, the activity and stability of the various additives are determined by the crystal stabilization technology employed plus the interaction of the crystal with the matrix. An additive containing properly stabilized ZSM-5 crystal, combined with a strong matrix, will result in excellent activity retention with superior propylene yields when compared to other technologies.

Intercat and other suppliers have invested significantly in development of ZSM-5 additive technology, which is reflected in our broad product portfolio. Intercat possesses an extensive range of ZSM-5 additives maximizing propylene, butylene, and octanes. Additionally, Intercat produces ZSM-5 additives that minimize LPG increase for wet gas compressor-limited operations.

There are several selectivity-based ratios that can be used in monitoring ZSM-5 performance. These include: propane olefinicity, propylene yield vs. LPG, propylene vs. conversion, propylene vs. butylene, and propylene vs. gasoline. The most important of these ratios are the propane olefinicity and the propylene-to-LPG ratio.

                 

QUESTIONS AND ANSWERS

I.FLUID CATALYTIC CRACKING:                  www.wissenschaftler-avh.in

B.CATALYST/ADDITIVES(Contd.)


Q-60: Can you suggest a commercial additive in FCC capable of offering cost
           effctive opportunities for the refiner who runs heavy feeds or has problems
           in  maintaining catalyst activity and  selectivities due to metal contamination.
           The additive must be added separately to the FCC unit so that the amount
            of additive in the unit inventory can be adjusted to achieve the optimum
            level of additive and unit performance

A-60:

QUESTIONS AND ANSWERS

I.FLUID CATALYTIC CRACKING:                   www.wissenschaftler-avh.in

B.CATALYST/ADDITIVES(Contd.)


Q-59:How to interpret the Equilibrium Catalyst Data Sheets to asses the Operation of the FCC Unit and Trouble Shooting to formulate a catalyst management policy consistent with the goals of the Refiner?

A-59:

QUESTIONS AND ANSWERS

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.

QUESTIONS AND ANSWERS

I.FLUID CATALYTIC CRACKING:                             www. wissenschaftler-avh.in

B.CATALYST/ADDITIVES:(Contd.)

A-57:(Contd.)

1. 

QUESTIONS AND ANSWERS

I.FLUID CATALYTIC CRACKING:                             www.wissenschaftler-avh.in

B.CATALYST/ADDITIVES(Contd.)


A-57(Contd.)