Testing and experience in FCC catalyst selection
Resolving differences between test results and unit experience in FCC catalyst selection
CAREL POUWELS, Albemarle Catalysts Company
KEN BRUNO, Albemarle Corporation
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For refiners, the choice of an FCC catalyst is a challenging task. Is the incumbent catalyst the best option for the FCC unit and delivering the highest margin? Or should the catalyst be optimised through a reformulation? Or is there perhaps a different and better technology? About half of the industry relies on the R&D department or a third party laboratory to carry out a catalyst testing programme as their main tool to determine the best catalyst. This is valid for both VGO (gas oil) applications as well as for FCC units processing resid feedstock (see
We have reported about this market segmentation on earlier occasions.1 A more detailed analysis of the FCC market then revealed that there is a remarkable difference between catalyst technologies used by those refiners that test and those that select their catalyst in different ways.
In the market analysis that was carried out, Albemarle found that refiners that test predominantly use catalysts which are high in zeolite content and contain relatively low levels of alumina matrices as active ingredients. In this article we will further refer to these catalysts as ‘high Z/M catalysts’. Refiners that do not test mostly use catalysts which are relatively moderate to low in zeolite and moderate to high in alumina matrices and will be referred to as ‘low Z/M catalysts’. This observation was made for all feed types, but is particularly evident for resid applications (see Figure 2).
This disconnect between laboratory testing and reality in the FCC unit is caused by insufficient simulation of catalyst deactivation as well as the testing methodology. These deficiencies penalise low Z/M catalysts with excessively high coke yields while at the same time giving insufficient credit to better bottoms conversion. When the test results are plugged into FCC models without any correction, these high coke yields from the test lead to unrealistically high regenerator temperatures. Consequently, low Z/M catalysts are considered high risk and are almost never selected. Figure 3 illustrates the large coke penalty for laboratory deactivated catalysts (D-cat) compared to the FCC unit. When equilibrium catalysts (E-cat) are used, the shortcoming of the testing method becomes apparent and clearly shows the difference with reality defined by the FCC unit.
For decades Albemarle has been supplying the broadest range of catalysts from very high Z/M to very low Z/M and has experienced dozens of cases where refiners have switched between such different types of catalysts. These cases confirm that low Z/M catalysts do not show excessively high coke selectivity or strongly increasing regenerator temperatures. More details of 19 side-by-side cases have been reported.
Recently, several testing refiners took a novel approach to their catalyst selection. These refiners previously chose their supplier by thorough catalyst testing and selecting the catalyst that had the best laboratory results. But this time, analysis of test results either was modified, or the refiner decided to trial a catalyst that was not the winner of the testing programme, and/or the refiner decided on other grounds. Examples include:
• Resid FCC unit 1 in the Asia-Pacific region trialled a low Z/M catalyst that reduced bottoms and increased LCO, contrary to test results evaluated at constant coke
• Resid FCC unit 2 in the Asia-Pacific region trialled a low Z/M catalyst that increased gasoline and LPG olefins, contrary to test results evaluated at constant coke
• VGO FCC unit 1 selected the winning maximum propylene catalyst based on testing. Unit yields were not in line with the test results and the refiner trialled a second catalyst which was far superior and exceeded expectations based on the test
• Major refiners 1 and 2 apply a correction to lab coke yields for all catalysts (compressing the coke differences)
• Major refiner 3 applies a correction to lab coke based on excessive lab H2 yields
• Major refiner 4 applies a correction to lab coke based on the matrix content of the catalysts
• Multiple refiners that start with low levels of a catalyst of interest and increase its percentage step-wise.
These refiners are happy with the new technology they are applying. It opened the door to more technology options and increased their FCC margins.
Albemarle recognises the importance of catalyst testing. Catalyst testing is an essential tool to develop new catalysts with innovative ingredients or a novel assembly technology and which brings the performance that refiners are seeking. Catalyst testing is obviously very important for those refiners that choose to select their catalyst by testing. At Albemarle we realise that catalyst testing has its benefits. The results we get in testing are not identical to the changes obtained in the unit. All test data need to be corrected and translated. When a new catalyst technology has been used, a post evaluation is required for further refinement of the correction and translation model.
Refineries that regularly switch catalysts are interesting subjects for learning purposes. This is particularly the case when these switches include different suppliers and thus different catalyst technologies. One of those cases concerns a refiner that is continuously seeking the optimum catalyst for its operations and switches regularly. Due to the relatively small inventory and high catalyst consumption of this resid application, the change-out time is short. Catalyst evaluations can thus be done in a short time frame and the incumbent catalyst supplier can respond quickly for further fine tuning if required.
This FCC unit processes a mix of different feeds, including a substantial amount of residue. The feed has a specific gravity of 0.91 and Conradson carbon residue above 2 wt%. Metals on equilibrium catalyst vary over time, but are typically of the order 3000 ppm nickel and 6000 ppm vanadium.
The refiner operates this FCC unit to maximise LCO and LPG olefins. The main limitations are air blower, wet gas compressor and regenerator temperature.
The commercial case which we discuss concerns three different catalysts from three different manufacturing technologies (see Table 1):
• Cat #1: moderate Z/M catalyst with moderate RE2O3
• Cat #2: high Z/M catalyst with high RE2O3
• Cat #3: low Z/M catalyst with low RE2O3.
In the study, yields of all three catalysts are compared against each other. As in almost all FCC units, conditions are never exactly the same. In order to make a sound comparison, one needs to normalise the cases. This means that products need to be corrected to the same cut-points, feed quality, and process conditions through a FCC process simulation model. At identical conditions, all three catalysts can then be compared.
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