FCC Catalyst Selection Considerations | RefinerLink
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FCC Catalyst Selection Considerations

By Miles Hoyer

Mar 16, 2015
 

Insightful tips for your next FCC catalyst selection endeavor.

 
 

It is that time of the year where you’re invited to sit down with FCC catalyst vendors to review the post year audit, discuss their latest catalyst technologies, trend the cost of rare earth and ultimately an opportunity to determine the most fitting catalyst profile for your refinery.  

 

Over the decades, FCC catalyst technology has evolved immensely and expanded overall process capabilities. In today’s world, while distillate is king, how can the conventional gas making machine maximize distillate make while limiting residual bottoms to generate the most cash in our tight margin business?

 

FCC catalysts are composites containing zeolite dispersed in an amorphous matrix. The zeolite component comprises 10-50 wt % of the catalyst and provides activity, stability, and selectivity. The matrix comprises 50-90% of the catalyst and provides desirable physical properties, as well as some catalytic activity.

 

Over the years, the amount of active catalytic components-both the zeolite and active matrix-within the FCC catalyst has changed to allow optimal unit performance and achieve the various refinery product objectives.

 

A few things to consider before chatting with your FCC vendors:

 

BOTTOMS CRACKING

 

The increased cracking activity of the matrix can upgrade the bottoms material in the feed to valuable products because the large-pore matrix permits relatively easy access of very large feed molecules.

Heavy molecules crack according to three basic mechanisms:

 

Cracking on the external zeolite surface  - Cracking on the external zeolite surface results in minimal bottoms upgrading because the external surface represents only about 3% of the total zeolite surface.

 

Thermal cracking - Thermal cracking is nonselective and tends to degrade heavy hydrocarbons to gas and coke.

 

Matrix cracking - Matrix cracking permits the most efficient upgrading of bottoms material into higher-valued gasoline and light cycle oil products.

 

For example, a highly active matrix may not be advantageous with heavy resid feedstocks. This is because the poor coke selectivity of a high-activity matrix can adversely affect operation and result in a net increase in bottoms yield.

 

OCTANE

 

The degree of octane enhancement achievable with zeolite catalyst depends on the sodium content and the amount of rare earth exchange. When choosing catalyst, a question that is often asked by vendor is how important gasoline octane is on the overall list of objectives?

 

Certain zeolite catalysts dramatically increases FCC conversion and gasoline yield at the expense of octane number, while others can improve research octane number by increasing gasoline olefinicity and improve motor octane number (MON) by increasing gasoline component branching and aromaticity. 

 

COKE SELECTIVITY

 

In addition to their octane-enhancing characteristics, another important feature is good coke selectivity, i.e., they produce lower delta coke.

 

Delta coke is an important variable affecting the FCC reactor-regenerator system. It is simply the difference between coke on spent catalyst and coke on regenerated catalyst, and it is related to the catalyst type, feed type, and process conditions. Delta coke is defined as coke yield divided by the catalyst-to-oil ratio (C/O), in lb/lb.

 

The coke yield (wt % of feed), on the other hand, is determined by the unit heat balance, in which the reactor heat requirements are met by the combustion of coke in the regenerator.

 

At a constant reactor temperature, a coke-selective catalyst reduces the regenerator temperature. Coke-selective catalysts also allow more flexibility in running the FCC, compared to the use of a conventional catalyst-particularly when the regenerator air compressor or temperature are near their maximum.

 

For example, the reactor temperature can be increased for higher octane, the catalyst circulation or activity can be increased for higher conversion, or heavier feeds can be processed.

 

ZSM-5 ADDITIVE

 

A novel zeolite, ZSM-5, was introduced in the 1980’s as an octane-enhancing additive to other FCC catalysts.

 

ZSM-5 selectively cracks low-octane straight chain paraffin and olefin components at the higher end of the gasoline boiling range to mainly C3 and C4 olefins. Some olefins may be isomerized to more branched, higher octane components.

 

ZSM-5 does not affect aromatics or naphthenes. It is normally used in small quantities, typically 1-5% of the conventional FCC catalyst.

 

Since its introduction, the use of ZSM-5 zeolite in fluid catalytic cracking has been growing. ZSM-5 may be more advantageous than other octane-increasing options such as increasing reactor temperature. ZSM-5 also provides a quicker octane boost than a time-consuming switch to a new FCC octane catalyst.

 

RESID CRACKING

 

Increasing amounts of residual feedstocks are being processed in FCCs. Research has been devoted to developing FCC catalysts and additives to cope with and mitigate the high levels of coke precursors and metals in resid feeds, while maintaining good conversion and selectivity to valuable liquid products.

 

Coke-selective and metals-resistant catalysts, metals passivators, and SOx emission-reducing catalysts are now available to refiners. And catalyst manufacturers are seeking further improvements in resid catalysts.

 

There is no optimum catalyst for all resid processing applications. The important items to consider in choosing a resid FCC catalyst are the objectives and the specific operating constraints of the unit.


FCC feed CCR content is an indication of its coking potential because much of the CCR produces rapid coke deposition on the catalyst, depending on the e of feed, catalysts and condition.

 

A slide valve or plug valve-controlled FCC operates at essentially constant coke make with no additional catalyst-cooling capacity. As the feed CCR increases, the regenerator temperature increases, the C/O ratio decreases, and conversion declines.

 

A unit constrained by the air blower or regenerator temperature may require a catalyst with very low coke selectivity. An active matrix under these circumstances may have the net effect of lowering conversion and bottoms cracking because of a lower C/O ratio in a heat-balanced unit, because matrix activity has poor coke selectivity.

 

ADDITIVES

 

FCC catalytic additives are important tools refiners use to meet particular yield, product property, or environmental requirements.

 

In addition to small-pore ZSM-5 additives for octane enhancement, other additives include:

  • Passivation agents routinely used to counteract nickel and vanadium
  • SOx-reduction additives used to reduce SOx emissions from the FCC regenerator
  • High-density fines used as fluidization aids.

 

FCC CATALYST COST

 

U.S. refiners may be unwilling to pay more than about $3,000/ton because of tight operating budgets, even if they gain extra benefits. FCC catalyst is generally the second greatest refinery operating expense, after crude oil purchases.

 

A big factor in FCC catalyst cost is the price of rare earth oxides which is function of global supply and demand. China used to produce 95% of global rare earth and more recently other non-China sources started up softening market price.

 

Current U.S. catalyst consumption is estimated to only be half of manufacturing capacity. During the time of high crude oil prices and heavier feed processing, catalyst consumption increased and manufacturers expanded facilities. With recent lower crude prices, catalyst market growth has slowed, creating a highly competitive catalyst market.

 

With intense competition, it is not surprising that FCC catalyst profit margins are reportedly no more than 3-4% of sales.

 

 

So now that you’re armed with more insight on catalyst decision factors, let’s see how you use this information to do good for your refinery.

 
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