Continuous innovation for residue FCC catalyst technology
Although Tight Oil has captured the attention of the world and changed the landscape of North American refining, resid type feeds continue to play a key role in the global FCC market with around 66% of the catalyst supplied on an annual basis being specifically targeted for this segment.
Alexis Shackleford and Bilge Yilmaz
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This is true across all regions even in North America where the Tight Oil boom is occurring; the North American FCC catalyst market in 2014 is 42% resid on a volume basis. From an operational stand point resid feeds provide unique challenges to refiners as they contain higher aromatic, conradson carbon residue (CCR), and metals content compared to VGO feeds. BASF’s research and development efforts have been aligned with these market needs and a progression of innovative FCC catalyst products are in the developmental phase or have been commercialised aimed specifically at the resid market.
FCC resid catalysts are engineered to improve operation and meet these unique challenges. Due to large aromatic compounds such as asphaltenes in resid feeds, Figure 1, optimised catalyst pore structure is critical to convert the heavier material to more valuable products. Contaminant metals found in higher levels in resid feedstocks including nickel (Ni), vanadium (V) and iron (Fe), catalyse a variety of unwanted secondary reactions in the FCCU. Resid catalysts are designed to have high tolerance to these metals and reduce the impact of the unwanted side reactions. BASF research and development efforts have yielded a strong portfolio of resid FCC catalysts based on innovative technology and manufacturing platforms.
This article will describe recent development of BASF’s resid catalysts, and introduce the latest in resid catalyst innovation: Boron Based Technology (BBT).
A Flexible Portfolio of Products
BASF currently offers a number of flexible catalyst solutions for resid feed processing, Figure 2.
The product lines are based off BASF award winning Distributed Matrix Structure (DMS) platform and Proximal Stable Matrix and Zeolite (Prox-SMZ) platform, both of which have optimised porosity to allow the diffusion of heavy molecules into the catalyst for maximum bottoms upgrading. The DMS platform has the highest zeolite content for maximum conversion to gasoline and lighter products such as propylene and butylenes. DMS matrix is designed to provide enhanced diffusion of feed molecules to pre-cracking sites which are located on the external, exposed surface of highly dispersed zeolite crystals. The feed pre-cracks on the zeolite itself, rather than on active amorphous matrix material resulting in less coke and gas. This allows high bottoms conversion with low coke, and higher yields of gasoline and light olefins. The Prox-SMZ technology is designed for distillate maximisation. The technology is built on two main features: the presence of an ultra-stable and coke selective matrix and the close proximity of an ultra low sodium zeolite, which are created in one single synthesis step. Unlike conventional low zeolite to matrix surface area ratios (Z/M ratios), accentuated matrix cracking with poor coke and gas selectivities does not occur.
Traces of nickel and vanadium have detrimental effects on performance. Nickel, and to a lesser extent vanadium catalyse dehydrogenation reactions leading to coke and hydrogen production. Vanadium is mobile under regenerator conditions and also leads to the destruction of zeolite. By examining equilibrium catalyst (Ecat) 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, as depicted in Figure 4. Based on the understanding of how metals deposit, BASF uses a specialty alumina in the catalyst particle to trap the nickel. For vanadium, which is mobile and distributes evenly, BASF uses a separate particle vanadium trap.
DMS Platform: Fortress
BASF’s Fortress™ catalyst is based on the latest FCC catalyst manufacturing innovation, Multi-Stage Reaction Catalyst (MSRC) platform introduced in 2010 . The approach of the novel MSRC platform is to combine two or more existing FCC catalyst functionalities within a single catalyst particle.
In state of the art resid FCC catalysts like Flex-Tec®, a specialty alumina is integrated in the catalyst formulation to trap the nickel and form nickel aluminate which is less deleterious for dehydrogenation reactions in the FCC riser. Since nickel mainly deposits and accumulates on the outer surface of the catalyst, as depicted in figure 4, it would be advantageous to concentrate the nickel trapping alumina at the outer layer to make it more effective. With all current catalyst technologies, the specialty 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 essentially wasted. By using the MSRC concept, the spatial distribution of this specialty alumina within the particle is adjusted to maximise its efficacy in nickel trapping and lead to improved catalyst performance.
With the MSRC approach, the inner stage of the catalyst has the DMS structure to allow enhanced diffusion of heavy molecules, maximising yields. The outer-stage is also based on DMS technology, but is enriched with specialty alumina to trap the nickel directly where it enters and deposits on the catalyst as depicted in Figure 5. The improved spatial distribution of the trapping alumina offers more efficient material utilisation and better performance.
The first commercial trial was a short contact time resid unit located in the United States. The unit operated in deep partial burn and low reactor severity, with primary constraints of wet gas compressor and air blower limit. With the improved metals tolerance of Fortress, the unit could alleviate the wet gas compressor limit, and improve the coke selectivity to allow more operating flexibility. The unit successfully transitioned from Flex-Tec to Fortress. The hydrogen selectivity improved by 12% at equivalent metals and coke selectivity improved 17%. With the reduction in hydrogen and coke, liquefied petroleum gas (LPG) plus gasoline increased 0.7 wt%.
Prox-SMZ Platform: Stamina
BASF’s Stamina™ catalyst is the second catalyst, and first resid catalyst based on the Prox-SMZ platform. Prox-SMZ was first introduced in 2008 with HDXtra™, a catalyst designed for distillate maximisation with VGO feed. In an effort to extend the Prox-SMZ family to resid feed applications, the novel resid distillate maximisation catalyst Stamina was introduced in 2009. With maximum distillate catalysts, the amount of zeolite is moderated, and matrix increased to suppress over cracking to gasoline and lighter products while maintaining good bottoms conversion. The advantage of Prox-SMZ catalyst is a significantly better bottoms upgrading of distillate to bottoms at constant coke versus competitive matrix material. BASF’s unique manufacturing process of in-situ forms the matrix and zeolite in a single step, bringing them in intimate contact with one another. While other catalyst technologies can incorporate zeolite and matrix materials into the same catalyst particle, they do not have the capability to bring them together in such proximity. The binder used in these processes creates a barrier and will act as a separator between the matrix and zeolite. It is this unique synergy between the zeolite and matrix that leads to rapid transfer of reactants and feed molecules from zeolitic acid sites to matrix acid sites. BASF then combined the matrix and zeolite with improved porosity to handle heavier resid feeds and incorporate metals passivation technologies to develop Stamina. Testing shows Stamina exhibited a 6% improvement in distillate selectivity at constant conversion over Flex-Tec, while the coke yield stayed constant. A bottoms reduction of 2% and an increase in gasoline by ~1% was also observed.
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