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Mar-2013

New catalyst increases FCC distillate yield

A FCC trial with a new residue maximum distillate catalyst provided an improved yield structure at a similar fresh catalyst addition rate and rare earth level

CARL KEELEY, JEREMY MAYOL, STEFANO RIVA and VASILEIOS KOMVOKIS
BASF Corporation, Refining Catalysts
STEPHEN CHALLIS, Chalcat Consulting
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Article Summary
The FCC unit at a refinery in western Europe is a Shell design adapted to process some residue. The base catalyst was a VGO processing catalyst with a high Z/M ratio and 2.3 wt% rare earth level. 

In 2009, the FCC unit’s operating objective changed from maximum conversion to maximum distillate production. Aligned with this change in operating objective, the unit began to process 15-20 wt% of residue comprising of vacuum residue and wash oil from the vacuum distillation unit. Wash oil from the vacuum distillation unit (VDU) is the material from the heaviest pumparound between the bottom and the heavy distillate. This pumparound is set to limit coking in the flash zone of the VDU tower. Part of this material was drawn as a product and sent to the FCC unit. This resulted in Conradson carbon residue (CCR) of up to 2 wt% and a moderate contaminant metal level, with nickel and vanadium up to 6000 ppmw on equilibrium catalyst (e-cat). 

A trial with another supplier’s maximum distillate catalyst (with a low Z/M ratio) was abandoned as it was judged that, at a higher coke yield, the total gain in LCO from both a reduced gasoline yield and improved bottoms upgrading was below expectation. Since the driver for a catalyst change was still valid, BASF was invited to help improve the unit’s performance. This resulted in the selection of BASF’s Stamina catalyst for selectively maximising distillate with a residue feed. 

This article presents the details of a Stamina catalyst trial conducted at the refinery in 2010. Operating data and results for a 65% change-over to Stamina catalyst are discussed; these were the basis of the refinery’s decision to engage in a long-term supply contract.

Catalyst selection
BASF provides technical service to understand unit operation and all the constraints. The company has a large range of tools that are selectively used, based on specific needs, to ensure a flawless catalyst change and optimised unit operations with the new catalyst. The tools selected in this case were:
• Cold Eyes Review: to develop a detailed understanding of the unit’s objectives, constraints and operation
• Operating Data Analysis: to review the base operation, and to help monitor and optimise unit performance during the trial
• Real-time Circulating Catalyst Activity Estimator: to manage catalyst additions during the trial.

Stamina catalyst was selected to best fit the objectives, constraints and operation of the unit, and to deliver the highest value. This FCC unit was one of the first to trial Stamina catalyst. Since then, the catalyst has been used in many units.

Stamina is based on BASF’s Proximal Stable Matrix & Zeolite (Prox-SMZ) platform (see Figure 1).1,2  This platform is built on two main features, one being the presence of an ultra-stable and coke-selective matrix and the other being the close proximity of an ultra-low sodium zeolite and the matrix, which are formed in a single manufacturing step. Stamina shows superior zeolite and matrix surface area retention compared to other technologies,2 which reflects the advantages of the novel Prox-SMZ matrix and the ultra-low sodium zeolite technology. It is the synergy between the zeolite and matrix that leads to rapid transfer of reactants from the matrix acid sites to the zeolitic acid sites. This enhanced transfer helps to stabilise coke precursors produced by the matrix cracking, leading to higher LCO production without producing excessive amounts of dry gas and coke.

BASF has made strides in developing catalyst technologies with the lowest sodium levels, as it is well known that sodium cations have a negative impact on zeolite stability.3 Sodium cations in the unit feed stream and at operating conditions are converted to sodium hydroxide, which catalyses the hydrolysis of the zeolite silica-hydroxide (---Si-OH) bonds, leading to zeolite collapse.

Thus, BASF FCC catalysts suffer less sodium acid site neutralisation and zeolite deactivation, and have inherent vanadium resistance. Furthermore, because of the low sodium content of these catalysts, hydrogen transfer reactions are minimised, which improves the LCO quality — particularly the cetane — at a similar rare earth oxide/zeolite level. Note that the added sodium was similar, but the resulting total sodium on e-cat was much lower due to the lower sodium on the fresh catalyst (see Figure 4c), and BASF FCC catalysts also use a separate particle vanadium trapping technology.

To meet the refinery’s objective of distillate maximisation, the Stamina catalyst was customised. The rare earth content was similar to that of another supplier’s catalysts (see Figure 2a). To improve bottoms upgrading, the matrix surface area was significantly increased (see Figure 2b) and the zeolite surface area was similar; thus, the total surface area increased (see Figure 2c).
 
Catalyst performance
Comparing operating conditions during the Stamina catalyst trial with another supplier’s distillate catalyst trial:
•  Feed CCR, density and unit feed rate were similar (see Figure 3)
•  Vanadium and nickel were similar (see Figures 4a and b)
•  The added sodium was similar, but the resulting total sodium on e-cat was much lower due to the lower sodium on the fresh catalyst (see Figure 4c)
•  The fresh Stamina catalyst had similar iron on catalyst content. However, the added feed iron was significantly higher during the Stamina trial, resulting in a higher e-cat iron measurement (see Figure 4d). Despite the relatively high level of iron in the unit feed, flushing e-cat was not required, as there were no signs of catalyst surface sintering, dry gas selectivity deterioration and/or activity loss. Note that BASF FCC catalysts are highly engineered particles with a designed pore structure and high overall porosity, and therefore are resistant to iron pore-plugging deactivation
•  The Stamina catalyst at a similar fresh catalyst addition rate provided a significantly improved yield structure towards maximising LCO
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