Advances in FCC catalyst performance
Upgraded manufacturing processes have produced an FCC catalyst with increased gasoline yield and high hydrothermal stability at high severity operation
Charles Keweshan and Daniel Neuman, BASF Corporation
Jeffrey Sexton, Mike Skurka and Scott Simon, Marathon Oil Company
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Refiners the world over are focused on optimising their operations and employing FCC solutions that help maximise margins. Lower refinery utilisation numbers due to current global pressures are challenging refiners’ earnings. Given these conditions and the pressures put on the FCC unit, flexibility in operation will be key for refiners looking to capture market opportunities and regain healthy margins. NaphthaMax III, part of BASF’s Distributed Matrix Structures (DMS) technology platform, has the commercially proven ability to provide high bottoms conversion with low delta coke, and higher yields of gasoline and light olefin products.
NaphthaMax III is the direct result of an R&D project aimed to optimise the manufacturing and performance of BASF’s DMS-based products. The project enabled a measurable improvement in quality and efficiency for this product line achieved through upgrades in commercial calcination and rare earth exchange operations.
The initial demonstration of this technology was undertaken at Marathon Petroleum’s Garyville, Louisiana, refinery in late 2008 after pilot plant testing in the circulating riser pilot plant at Marathon’s Catlettsburg, Kentucky, R&D facility. NaphthaMax III was selected after evaluating several catalyst systems from multiple suppliers. The commercial trial was back-to-back with NaphthaMax II, giving a perfect opportunity for a comparison with the leading gas oil maximum conversion product in the market. The pilot plant work conducted by Marathon demonstrated the coke selectivity and gasoline yields of the catalyst, and the commercial results validated the pilot plant findings. The testing results confirmed NaphthaMax III was the most coke-selective catalyst available for the processing objectives and feed quality of the Garyville unit. At constant conditions, regenerator temperature dropped by ~20ºF. The fall in regenerator temperature enabled unit circulation to wind up, resulting in higher conversion and greater gasoline and LPG yields. The projected economic benefit based on pilot plant testing was $0.68/bbl. The actual value determined from a post-audit performance review was $0.71/bbl, enabling the unit to meet its processing objectives.
DMS technology entered the FCC market with the introduction of NaphthaMax in 2000. The technology produced a catalyst with a pore architecture and optimised porosity suitable for the diffusion of heavy feed molecules. The catalyst’s selective zeolite-based cracking additionally provides deep bottoms conversion and high coke selectivity.
NaphthaMax was the first catalyst based on the DMS platform, as well as the first FCC catalyst developed to address the needs of short contact time process designs. The combination of higher catalyst activity along with typically higher reaction temperatures and shorter contact times, all contribute to increasing the importance of diffusion in the FCC catalyst. The structure imparted by the DMS matrix is designed to provide enhanced diffusion of the feed molecules to pre-cracking sites located on the external, exposed surface of dispersed zeolite crystals. The feed initially cracks on the zeolite surface itself, rather than on an active amorphous matrix material. This results in improved selectivities, with reduced coke formation, characteristic of zeolite cracking. The secondary diffusion pathway of the cracked products to the internal crystalline zeolite surface is also minimised, resulting in less over-cracking. The net result is high bottoms conversion with low delta coke, and higher yields of valued gasoline and light olefin products.
This structure of the DMS technology is illustrated in a SEM micrograph of the interior of a catalyst particle (see Figure 1). The well-developed pore structure is evident, and essentially the entire exposed pore surface is covered with zeolite crystallites. The external surfaces of these crystallites are exposed and accessible to hydrocarbon feed molecules, which diffuse readily through the open pore architecture.
BASF’s technology for FCC catalyst manufacture delivers FCC catalysts with attributes that provide refiners with high-yield, coke-selective FCC catalyst technology. The process involves crystallising Y zeolite in situ inside pre-formed microspheres. The key raw material in the process is kaolin clay (aluminium silicate). After mining, the kaolin clay undergoes a series of refining and conditioning steps in preparation for further manufacturing and tailoring for specific catalytic features (see Figure 2).
In the manufacture of the microspheres, the feed components (kaolin clay, active ingredients and binder) for microsphere formulation are combined into slurry and spray dried. The spray-dried particles (microspheres) are then transferred into rotary calciners, where they are treated at temperatures up to 1800°F (980°C) prior to zeolite crystallisation. This high-temperature calcination step gives catalyst produced by the in situ method the advantage of a stable, attrition-resistant matrix. The physical properties given to the microsphere at this stage of the process are relatively unchanged, as the catalyst is exposed to the lower-temperature environment of the FCC regenerator. Given the sensitivity of zeolite to high temperatures, this calcination step is a critical difference compared with manufacturing, where the zeolite is blended and spray dried with the other components prior to the calcination step.
The finished microspheres are then reacted with silicates and other nutrients along with zeolite precursors or seeds to promote the growth of zeolite crystals. The microspheres are treated with caustic to leach silica from the particle, thus forming a network of pore channels along which the zeolite crystals are grown in situ. This procedure results in complete dispersion of zeolite crystals along the pore walls of the alumina-rich matrix. Growth of the zeolite within the microsphere pore structures yields a high degree of interaction between the zeolite and matrix surfaces. Attrition resistance of the particle actually increases following the zeolite crystallisation step. The matrix zeolite bond stabilises the zeolite and makes it highly resistant to sintering or pore collapse, for hydrothermal stability. The crystallisation process conditions can be varied over a wide range of conditions to yield specific catalyst properties such as, in the case of DMS, providing maximum exposure of the active zeolite.
In a series of ion exchanges with ammonium and rare earth cations and drying and calcination steps, the crystallised products are subsequently converted into a low-sodium catalyst with high hydrothermal stability. Sodium cations have a negative impact on zeolite stability1 and sodium cations in the presence of steam form sodium hydroxide. Sodium hydroxide catalyses the hydrolysis of Si-OH bonds, leading to zeolite collapse.
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