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Combining mesoporosity with metals tolerance for residue upgrading in FCC

This article highlights the performance of Grace resid FCC catalysts with a range of zeolite-to-matrix (Z/M) ratios, optimised mesoporosity and metals tolerance.

Colin Baillie and Daniel McQueen
Grace Catalysts Technologies
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Article Summary
Case studies will be discussed highlighting the high performance of Grace resid catalysts, as well as some of the critical drawbacks associated with low Z/M catalysts from alternative suppliers, particularly in terms of poor coke and hydrogen selectivity.

Grace Catalyst technology forresid processing
Mesoporosity is an important feature of FCC catalysts with respect to the conversion of large feed molecules that are present in resid feedstocks. Figure 1 shows the relationship between diffusion levels within an FCC catalyst with the pore-to-molecule size ratio. It can be seen that an optimum diffusion level is obtained at a pore-to-molecule size ratio between 10-20. At larger ratios there is a trade-off between diffusion and probability of active sites. Considering that heavy feed molecules found in resid feedstocks are in the size range of 10-30 Å, using a multiplication factor of 10-20 means that pore diameters in the mesopore range of 100-600 Å are required for free diffusion to occur. As also shown in Figure 1, Grace resid catalysts can undergo a proprietary pore restructuring process, which provides a boost in exactly this range of mesopores, enabling cracking deep into the bottom of the barrel.

However, many FCC units processing resid feedstocks are constrained by air-blower and wet-gas capacity, as well as limits in regenerator temperature. Therefore, FCC catalysts also need to include metals-tolerance functionality to limit coke and hydrogen formation, and allow refiners to operate within their constraints. Grace’s resid FCC catalysts incorporate highly functionalised, novel matrix materials and undergo proprietary processing operations in order to endow the catalyst with the activity, stability, metals tolerance, acid catalytic sites and pore structure required for cracking heavy feeds with high levels of contaminant metals. These matrices can incorporate highly effective integral metals traps to passivate contaminant metals such as nickel or vanadium, and minimise catalyst deactivation and coke formation. Additional modifications of the catalyst properties, such as the physical restructuring of mesopores described above, allow deeper bottoms cracking and improved coke selectivity. Hydrothermally stable and metals-tolerant zeolites provide the catalysts with the activity, stability and, ultimately, the product selectivity needed.

Case study at Refinery X: one of the world’s most challenging resid feedstocks
Refinery X is in the Middle East and has a resid FCC unit that processes one of the most challenging feedstocks in the world. They started up on a catalyst from Competitor B, but switched to a Grace resid catalyst from the NEKTORTM series in 2009. At the time a benchmarking exercise was performed using the extensive Ecat database available to Grace. The data was used to compare Ecat properties from Refinery X (using catalysts from both Competitor B and Grace) with the industry averages. Figures 2 and 3 plot Ecat Coke and Gas Factors against nickel equivalents from 84 FCC units in EMEA, and shows that Grace catalysts significantly outperform catalysts from Competitors A and B. The Coke and Gas Factors obtained at Refinery X using Grace catalyst are ca. 20% and 25% lower, respectively, than obtained at Refinery X using catalyst from Competitor B. This is despite the fact that nickel equivalents were nearly 2,000 ppm higher.

The RFCC unit at Refinery X processes an extremely challenging feedstock whilst being constrained by limits in regenerator temperature in particular. Table 1 shows average feedstock properties, operating conditions, Ecat properties and product yields for periods using catalysts from Competitor B and Grace. It can be clearly seen that feedstock properties deteriorated, with specific gravity, sulphur content, concarbon, nickel content and vanadium content increasing considerably. Operating conditions were comparable. The table also shows the excellent performance obtained with the Grace catalyst. Conversion increased by more than 1 wt.%, translating to a significant increase in propylene yield, which is a key unit objective. In addition, bottoms yield was reduced by nearly 1 wt%. The excellent coke and gas selectivity of the NEKTORTM catalyst are the fundamental factors that allow the unit to achieve its objectives in terms of product yields and bottoms conversion whilst operating within the unit constraints.

The performance of the NEKTORTM catalyst at Refinery X has been exceptional. As part of the recent catalyst-selection process in the tender for future catalyst supply, Refinery X performed a sophisticated analysis to evaluate the impact of using catalysts from the main suppliers on FCCU profitability. Results from catalyst testing at an independent catalyst evaluation laboratory were used by a second independent company that performs advanced process modeling. The outcome clearly indicated that the NEKTORTM catalyst was the most suitable catalyst for the operation at Refinery X, resulting in a significant increase in FCCU profitability compared to competitor catalysts. Subsequently Refinery X rewarded Grace with a three-year contract.

Case study at Refinery Y: improved yield structure using NEKTOR
Refinery Y is in Western Europe with an FCC unit processing resid feedstock. Conradson carbon residue was over 2 wt%, with Ecat nickel levels up to 3,000 ppm, and Ecat vanadium levels up to 7,000 ppm. The refinery switched from a low Z/M catalyst from Competitor B to a Grace NEKTORTM catalyst with optimised mesoporosity in October 2010. The main unit objectives for the new catalyst were lower fuel gas (H2 + C1-C2s), maximisation of C3s, increased gasoline yield, improved bottoms conversion and improved coke selectivity. In addition, they desired an improvement in catalyst attrition properties.

Figure 4 shows ACE® Ecat data comparing the Grace catalyst with Competitor B. At constant nickel equivalents, the Grace catalyst clearly shows lower Gas Factors and Hydrogen Factors. Figure 5 shows that MAT activity was maintained (even increased), with the Grace catalyst despite the vanadium levels being twice as high as the previous period. In addition, Davison Index (DI) measurements, which are a measure of catalyst attrition, show considerable improvements moving to Grace.

Figure 6 shows key FCC unit yields from Refinery Y. In line with unit objectives there was a lower fuel gas, higher yield of C3’s, increased gasoline yield, improved bottoms conversion and improved coke selectivity. The catalyst switch was considered a complete success, and the refinery calculated an improvement in FCC unit profitability in the region of US$ 2-3 million per year.

Case study at Refinery Z: improved yield structure using NEKTOR-ULCC™
Refinery Z is in Western Europe and has an FCC unit that processes up to 20% residue. This results in a Conradson carbon residue of approximately 2 wt%, with Ecat nickel plus vanadium levels of up to 6,000 ppm. They moved from a low Z/M catalyst from Competitor A to a low Z/M catalyst from Competitor B in March 2010, and in a recent publication Competitor B claimed a successful switch purporting to result in an improved yield structure. In reality, the refinery subsequently switched to Grace in October of the same year. Due to hydrogen and coke limitations a NEKTOR-ULCCTM catalyst with optimised mesoporosity was recommended.
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