Role of FCC catalyst in refinery profitability
By switching to a rare earth-free FCC catalyst, a refiner raised its output of premium grade gasoline and increased its operating margin
IVAN CHAVDAROV, DICHO STRATIEV, IVELINA SHISHKOVA and ROSEN DINKOV, Lukoil Neftohim Burgas JSC
VLADIMIR JEGOROV, Grace Catalysts Technologies
PETKO PETKOV, University ‘Prof Dr Assen Zlatarov’ Burgas
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The FCC unit is the main contributor (51-52%) to the refinery gasoline pool of the Lukoil Neftohim Burgas refinery in Bulgaria, with the next largest contributor being the reformer (about 27%). The gasoline sensitivity (research octane number minus motor octane number [RON – MON]) from the FCC unit and reformer is about 12 and 11 numbers, respectively, resulting in an overall MON shortage in the refinery gasoline pool. Considering MTBE has a MON of 94-97, alkylate a MON of 93 (both of which are produced from C4 olefins) and FCC gasoline a MON of about 82, increasing the production of C4 olefins at the expense of gasoline in the FCC unit will increase the MON of the overall gasoline pool.
A catalyst selection was performed with the objective of increasing MON. Grace proposed the REsolution catalyst, which was trialled in the FCC unit and subsequently led to an increase in gasoline MON by 0.5 numbers. This allowed the refinery to increase the production of automotive gasoline by 1.3%, and to increase the share of premium automotive gasoline from 68% to 73%. This resulted in an annual six-figure improvement in refinery economics.
The Reid vapour pressure (RVP) of gasoline from the FCC unit correlates to the content of C4 hydrocarbons in the gasoline, with lower RVP values obtained by producing more C4 at the expense of gasoline. Optimising the FCC gasoline RVP during the winter season (RVP was reduced from 60 to 50 kPa) and increasing the C4 olefins yield (leading to a higher MON in alkylate production) resulted in an additional improvement in refinery economics by a five-figure number (US $/y).
Lukoil Neftohim Burgas’s FCC unit
Commercial investigations were carried out on the FCC unit, which consists of a feed hydrotreater section, the FCC reactor and regenerator, as well as the main fractionator and vapour recovery sections. The FCC reactor is equipped with the modern UOP VSS riser termination device and the UOP Optimix feed injection system. Typical feed for the FCC unit is hydrotreated vacuum gas oil distilled from Urals crude, of which the physical and chemical properties are shown in Table 1.
Optimisation of FCC catalyst technology
In response to rapidly inflating rare earth metal prices in 2011, Grace developed the REpLaCeR series of rare earth-free FCC catalysts. The REsolution catalyst belongs to this series and is based on the rare earth-free Z-21 zeolite. Within each family of REsolution catalysts, the ability to independently adjust the activity and selectivities of zeolite and matrix, as well as the ratio of zeolite/matrix activity, enables maximum formulation flexibility. For low metal applications, REsolution catalysts are proven to match, and even improve on, the performance of traditional rare earth based catalysts. To date, there have been more than 15 successful applications of the REsolution catalyst in the EMEA region.
Based on laboratory, pilot plant and commercial data using Catalyst X from Supplier 1, Lukoil Neftohim Burgas switched to the Grace REsolution catalyst in 2011, with the objective of increasing the FCC gasoline MON. As Table 2 shows, the REsolution catalyst differs significantly from the previous catalyst, primarily in terms of rare earth content, which is 16 times lower than in the catalyst from Supplier 1. Even though REsolution is a rare earth-free catalyst, the e-cat still contains a small amount of rare earth, as the inventory was not 100% changed out. Typical FCC unit operating conditions from periods using Catalyst X and the Grace catalyst are shown in Table 3.
Table 4 shows the yield structure for FCC products obtained using Catalyst X and the REsolution catalyst. The slightly higher conversion obtained with Catalyst X is due to the higher catalyst to oil ratio resulting from the higher outlet temperature and lower feed temperature used in this period. The catalyst consumption rate was the same for both catalysts, at 0.350 kg catalyst addition per ton of feedstock. Generally, both catalysts displayed very similar product selectivities.
Table 5 shows the FCC product properties from Lukoil Neftohim Burgas. Compared to Catalyst X, the REsolution catalyst provided FCC gasoline with an increased MON of 0.5 numbers. This can be explained with the increased aromatics in gasoline. It is well known that increased hydrogen transfer activity results in the increased conversion of olefins and naphthenes to paraffins and aromatics. Conventional understanding of typical FCC catalysts would explain that a lower rare earth content and smaller unit cell size (as found in the REsolution catalyst) should result in decreased hydrogen transfer activity. However, the data shown in Table 5 demonstrate that the REsolution catalyst displayed higher hydrogen transfer activity, resulting in a lower olefin content of FCC gasoline, as well as the C4 and C3 fractions. This is due to the Z-21 technology utilised in this catalyst.
Figure 1 shows how the proportion of different grades of automotive gasoline within the gasoline pool changed when switching from Catalyst X to the REsolution catalyst. The REsolution catalyst increased the proportion of premium gasoline A-95 from 68% to 73% at the expense of the regular grade.
Figure 2 highlights the structure of the gasoline pool using Catalyst X and the REsolution catalyst. Catalyst X produced FCC gasoline with a RON of 94 and a MON of 81.7, resulting in a gasoline pool with a RON of 95 and a MON of 84.2, which complies with the requirements of standard EN228:2012 for RON but not MON. Switching to the REsolution catalyst increased the MON of FCC gasoline from 81.7 to 82.2, resulting in a final MON of 84.5 for the gasoline pool with the RON unchanged. Since FCC gasoline accounts for the majority of the gasoline pool (over 50 vol%), the FCC catalyst clearly has a significant impact on the octane number of the total gasoline pool.
Based on operational data from the FCC unit, the economic efficiency of using both catalysts from different suppliers was determined by applying a refinery model, which uses software for linear programming by Honeywell (RPMS). The results from RPMS demonstrate that replacing Catalyst X with the Grace catalyst results in an increased profit of 4% for the overall oil refining operations of Lukoil Neftohim Burgas. This demonstrates the important role that the FCC catalyst plays in refining operations profitability.
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