Apr-2016

An alternative to rare earth elements in FCC catalysts - the use of Phinesse at Shell Sarnia

Rare earth (RE) elements have been utilised since the 1960s to stabilise Y-zeolites used in Fluidized Catalytic Cracking (FCC) catalysts. Of the RE elements, lanthanum is by far the most commonly used in RE containing catalysts.

Alexis Shackleford, Thomas Masak, Qi Fu, Gary M Smith and Bilge Yilmaz, BASF Corporation
Robert D Culp and Piotr Gawecki, Shell Global Solutions

Article Summary

Cerium is also used in addition to lanthanum to an extent, with no current commercial FCC catalyst using solely cerium. China, which in 2010 provided 99% of the world’s Rare Earth Oxide (REO) supply, dramatically reduced export quotas that same year resulting in lanthanum prices increasing from $8/kg to a high of $140/kg in 2011. (As of 2015, China provides 93-96% of the world’s REO and there are currently no export quotas.)² In response to this situation, BASF developed Phinesse™ FCC catalyst, which uses phosphorus modification for the stabilisation of Y-zeolite. Phosphorus acts as an extra-framework species to stabilise the Y-zeolite framework, allowing lower REO content with no performance debits. This technology has been commercially demonstrated at the Shell Sarnia FCC unit.

Phinesse is the first BASF catalyst that uses phosphorus-stabilisation on Y zeolite. Based upon BASF’s proven Distributed Matrix Structure (DMS) technology,³ Phinesse is designed for vacuum gas oil (VGO) feed applications and to give the same yield structure and activity as BASF’s NaphthaMax III®⁴ with 50% less RE.

The product was successfully scaled up and demonstrated in 2012-2013 at the Shell Sarnia refinery. This paper discusses the results of that effort.

Phinesse Concept and Development
Extensive work has been done to increase the hydrothermal stability of zeolites through the inclusion of rare earth ions. Rare earth ions (RE3+) are exchanged for Na+ in Y-zeolite to balance the negative charge in the catalyst framework (AlO2--SiO2). RE3+ cations help retain acid sites under severe hydrothermal conditions of FCC operation to improve both the activity and the hydrothermal stability of the catalyst. Rare earth ions also promote hydrogen transfer so refiners can use RE3+ loading to manipulate catalyst activity and selectivity. The resultant effect is higher gasoline yield at the expense of lower octane, lower LPG olefins yield, and higher delta coke when RE-exchanged catalyst is used.⁵

Consideration of alternative elements that would function as rare earth elements in stabilising the zeolite Y framework has been a research topic of great interest for some time. When looking for an RE alternative, BASF research went back to the basics starting with the periodic table of elements. Elements were first excluded if they were more expensive than RE, radioactive, toxic, gases, gave undesirable reactions at FCC conditions or would melt at FCC conditions. Out of the short list of remaining elements, BASF tested many options arriving at phosphorus giving the best results. Phosphorus modification serves a dual function of stabilisation and catalytic activity enhancement. Phosphorus is known to stabilise catalytic activity in zeolites and is commercially applied to FCC additives (e.g. ZSM-5) and Methanol-to-Olefins catalysts (e.g. ZSM-5). The phosphorus treated samples retain their acidity and activity much better than the untreated zeolite during the steaming treatment. The mechanism through which phosphorus increases the stability of the zeolite structure has been widely studied in academic literature. It was demonstrated that during steaming, more aluminum atoms remain attached to the framework due to Al-O-P chemical bond formation.^6,7

BASF developed a novel way to apply phosphorus to BASF’s proven DMS based materials.^{8 ,9} Phosphorus not only increases catalyst activity but also increases hydrogen transfer giving the comparable yield performance as REO. Through a detailed pyridine FT-IR characterisation study comparing Phinesse with NaphthaMax III, the results showed that phosphorus stabilises the zeolite framework Al acid sites in both supercages and small cages, decreases the number of non-framework Al acid sites and introduces new P-OH acid sites (Figure 1).

The newly developed Phinesse catalyst was scaled-up to manufacturing in 2011 and 2012. A catalyst sample obtained from commercial manufacturing was tested versus NaphthaMax III, BASF’s state of the art maximum conversion VGO FCC catalyst. The samples were hydrothermally deactivated at 1450 °F for 24 hours before testing. The catalytic evaluation was performed in an Advance Cracking Evaluation (ACE®) unit at 1020°F with a gasoil feed with 0.79 weight % concarbon and 22 API.

During catalytic evaluation, Phinesse exhibited slightly higher activity despite having 50% less REO while no selectivity penalty was observed, as shown in Table 2.
 
Commercial Performance of Phinesse
The first commercial trial of Phinesse was at Shell’s Sarnia Refinery in Ontario, Canada. This is a VGO unit, with a significant portion of the feed from Canadian conventional and synthetic crudes. The unit objectives were to maximise profits with liquefied petroleum gas (LPG) olefins, gasoline and light cycle oil (LCO) being highly valued.

At the time, the unit used BASF’s NaphthaMax catalyst. BASF proposed Phinesse FCC catalyst with similar physicochemical properties as NaphthaMax but with half the REO. Catalyst properties for both NaphthaMax and Phinesse are shown in Table 3. In support of the trial, BASF tested three catalysts: NaphthaMax, the proposed Phinesse, and an equivalent NaphthaMax III catalyst at 2wt% REO. As Phinesse is based on NaphthaMax III manufacturing, it was expected to have improved coke selectivity over the incumbent NaphthaMax catalyst. The NaphthaMax III catalyst was included in the testing to differentiate between differences due to the RE replacement technology and due to the NaphthaMax III technology. The three catalysts were deactivated using cyclic steaming to match the unit’s equilibrium catalyst (Ecat) properties and then ACE tested. Figure 2 shows the results of this test. The delta yields at 75% conversion are shown off the base Sarnia NaphthaMax catalyst. Phinesse shows similar performance to NaphthaMax III, with half the REO, with both catalysts giving approximately 1wt% lower coke yield resulting in 1.5wt% higher gasoline yield compared to NaphthaMax.

Based on the positive testing results, Phinesse entered the FCC unit in November 2012. The Ecat REO immediately started to decrease from 2 wt%, as shown in Figure 3. The unit was 75% turned over after three months, and essentially 100% turned over at 6 months. The metals showed an initial increase due to a feed change, and then proceeded to moderate.

Phinesse shows high activity stability. The catalyst held activity as well as the previous catalyst NaphthaMax at comparable metals and catalyst addition rates, even through the high metals excursion period (Figures 5 and 6). Even though Phinesse has half the RE, the stability is equivalent to the higher RE catalyst showing that the phosphorus modification effectively stabilises the zeolite.

In addition to providing stabilisation of the zeolite, the phosphorus modification also provides selectivity shifts equivalent to that of RE modification. Phinesse gives the same gasoline selectivity with half the RE of NaphthaMax, as shown in Figure 7. This is a key proponent of the catalyst chemistry as units wishing to avoid the high cost of RE can switch to a lower RE catalyst and increase activity with high addition rates to off-set the lower stability. However, the lower gasoline selectivity with lower RE catalyst (due to the lower H-transfer) cannot be offset. Phinesse gives equivalent activity, stability and gasoline selectivity as NaphthaMax. Phinesse also gives higher LPG and LPG olefinicity than NaphthaMax. This is due to the improved coke selectivity of Phinesse resulting in higher cat to oil and higher LPG selectivity, Figure 8. With high olefin pricing, this was a desirable outcome.

Phinesse also gave excellent LCO selectivity and bottoms upgrading (Figures 9 and 10). All unit operating data is confirmed with standard Ecat ACE testing throughout the trial showing that Phinesse gives equal performance for gasoline, LCO and bottoms selectivity along with improved coke selectivity.