Jul-2011

Multi-stage reaction catalysts

BASF’s Multi-Stage Reaction Catalyst (MSRC) platform takes advantage of staged reactions with different catalytic attributes in much the same way that staged hydrotreating catalyst loading permits different reaction zones in a fixed-bed reactor vessel.

Joesph McLean, Bram Hoffer, Gary Smith, David Stockwell and Alexis Shackleford
BASF

Article Summary

The concept of staged reactions is not new to the refining industry, but its application to a circulating system such as FCC is an advancement in catalyst technology.

The manufacturing platform can utilise any of the existing catalyst technologies including BASF’s Distributed Matrix Structures (DMS)1,2 and Proximal Stable Matrix and Zeolite (Prox-SMZ)3,4 to create the stages. The location of the various stages can be specifically engineered to achieve maximum performance. There are multiple possibilities for combining different catalyst technologies in the inner and outer stages, depending on specific objectives such as the processing of heavier feedstocks or to maximise specific product yields.

This manufacturing process is based on in situ technology and involves several key sequential manufacturing steps. One of the key success factors in the development of MSRC technology is the binding process, unique to the in situ manufacturing process, where Y zeolite grows across the boundary between catalyst stages, acting as a binder and giving the catalyst particle high attrition resistance.

The first product utilising MSRC manufacturing is Fortress. Fortress is designed for resid feed applications, where contaminant metals passivation is critical. MSRC 
manufacturing technology was scaled up and demonstrated in 2010 with Fortress, and two refinery trials were initiated. 

Halo, the second catalyst offering from BASF under the MSRC manufacturing platform will be ready for commercial trials in the third quarter of 2011. Halo is engineered to provide attrition resistance comparable to Petromax with yields, coke and bottoms selectivity equivalent to NaphthaMax III. As with Fortress, a two-stage system is used, but in this case it delivers an outer stage with highly active zeolite. The staged approach allows for a reduction in the level of Y zeolite in the particle, as well as a reduction in the diffusion path length. The inner stage is composed of activity modifying material, which also serves as an anchor for the outer stage. Due to the reduced level of zeolite in the catalyst particle, there is an additional benefit in the form of a reduction of RE level with no performance deficit. 

Fortress
Fortress is designed for resid feed applications, where contaminant feed metal passivation is crucial. Feed metals, in particular nickel, catalyse dehydrogenation reactions, producing the undesirable products of hydrogen and coke. In resid FCC catalysts such as Flex-Tec, a speciality alumina is integrated in the catalyst formulation to trap the nickel and form nickel aluminate, which is less deleterious to dehydrogenation reactions in the FCC riser. By examining spent FCC catalysts from refineries with electron microscopy, it was generally observed that, while vanadium is distributed homogenously through the particles, nickel mainly deposits and accumulates on the outer surface of the catalyst (see Figure 1).

It would thus be an advantage to concentrate the nickel-trapping alumina at the outer layer of the catalyst to make it more effective. With current catalyst technology, the speciality alumina is uniformly distributed through the catalyst microsphere. This makes a large portion of it, located in the interior of the particle, unavailable to react with the nickel and is, in essence, wasted.

In the MSRC approach, the inner stage of the catalyst has the DMS structure to allow enhanced diffusion of heavy molecules and selective pre-cracking on the exposed zeolite surface, maximising gasoline yields.1 The outer stage is also based on DMS technology, but is enriched with speciality alumina to trap the nickel directly where it enters and deposits on the catalyst (see Figure 2). The technology is analogous to that employed with Flex-Tec2 and Stamina4, but the improved spatial distribution of the trapping alumina offers more efficient material utilisation and better performance potential.

The manufacturing process for this two-stage reaction catalyst is based on in situ manufacturing technology and involves multiple consecutive steps (see Figure 3). First, a precursor microsphere with a reduced particle size is formed. This microsphere is then added to a second slurry, which has a Flex-Tec-like formulation, including elevated concentrations of the nickel-passivating speciality alumina, and spray-dried again to yield a two-stage microsphere with the required final FCC particle size.

The FCC catalyst is then manufactured by growing zeolite from the kaolin nutrients in the multistage microsphere. The zeolite grows in both stages and across the interface, and acts as a binder to hold the stages together, preventing selective attrition of the outer stage. Zeolite growth and catalyst activity are in line with current DMS products, as are all physical properties.

Development of Fortress
The basis for the development of the Fortress catalyst was the observation that nickel accumulates mainly in the outer 5–10 µm of the equilibrium FCC catalyst5 (see Figure 1). Geometric calculations show that the weight ratios of the two stages for a ~8 µm outer-stage thickness and a normal FCC particle size distribution are about 1:1. The addition of a solid inner-stage particle to the recipe makes the production of MSRC more complex than for existing FCC catalysts. Scanning electron microscopy of the early samples demonstrates the multi-stage configuration of the particles (see Figure 4).

By modifying the microsphere formulation, the density of inner- and outer-stage components was optimised to allow maximum diffusion rates without impacting the staged configuration. After demonstration of manufacture on a pilot scale and encouraging test data, the project was transferred to a commercial manufacturing scale. The plant production trials required the capabilities of multiple manufacturing plants to make first the inner-stage microspheres, followed by the construction of the outer-stage material, and finally zeolite crystallisation and finishing to make the catalyst (see Figure 2).