FCC catalysts for resid processing
The diversifying feedstock scenario for FCCU operations has resulted in significant growth in the resid feed sector
Simon Reitmaier, Daniel McQueen and Colin Baillie, Grace Davison Refining Technologies
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The thousands of e-cat samples tested each year at the Grace Davison laboratories provide valuable insight into FCCU operations, including the type of feedstock refiners are currently processing. Extensive analysis of this database reveals a general trend towards increasing e-cat contaminant metals levels. Figure 1 shows this trend for resid processing applications (defined as Ni+V >3000 ppm) over the past five years. Nickel (Ni), and to a lesser extent vanadium (V), acts as a dehydrogenation catalyst, which results in an increase in unwanted hydrogen and coke product. Vanadium is also mobile under FCC regenerator conditions and reduces catalyst activity by destroying the zeolite framework.
The trend displayed by Figure 1 clearly indicates that FCCU operators are shifting towards processing heavier feedstocks. In response, a portfolio of catalyst families have been developed specifically for the resid feed sector.
Approach to catalyst design
The Grace Davison EnhanceR technology platform for improving the cracking of heavy feeds involves four technologies: EPR (pore restructuring), EMR (metals resistance), EAM (acidity modification) and ESS (structure stabilisation). Instead of making separate modifications to the catalyst’s zeolite and matrix components, as in previous approaches to catalyst design, EnhanceR enables the processing of input materials, intermediate products and end product FCC catalysts. By this means, the four EnhanceR technologies can be deployed synergistically, avoiding the antagonistic consequences frequently encountered when using the separate matrix/zeolite approach. The four technologies are described as follows:
• EPR technology causes physical restructuring of mesopores, impacting pore connectivity and pore size distribution. EPR brings deeper bottoms cracking and improved coke selectivity
• EMR technology provides improved contact of metal-passivating catalyst sites with metal-containing heavy feed molecules. EMR enables the chemical passivation of metal contaminants, protecting the zeolite and matrix functions, while retaining excellent catalyst physical properties
• EAM technology involves the alteration of surface chemistry profiles, and the modification of the number, type, strength and distribution of acid sites. EAM enables the customisation of catalytic activity and selectivity to better match specific processing requirements
• ESS technology results in higher compositional and topographic integrity at both the micro and macro scales. ESS brings improved resistance to hydrothermal deactivation.
The initial application of the EnhanceR approach to catalyst design resulted in a first generation of catalyst families, including Nektor and Nomus. In resid processing applications, refiners using Nektor are taken advantage of the superior coke selectivity and metals tolerance of the catalyst to relieve air blower constraints, increase the volume of feed processed and improve bottoms cracking via increased cat-to-oil and/or decreased regenerator temperature. The high intrinsic bottoms cracking of Nomus allows for deeper cracking into the bottoms and is the catalyst of choice for FCCUs that are circulation limited but have spare air capacity.
Case study 1: higher conversion of heavy feeds at Refinery A
The benefits of Nomus for resid feed applications are highlighted by the experiences of Refinery A, which is located in the Middle East. This refinery operates a proprietary UOP high-efficiency FCCU in full-burn mode. The typical e-cat microactivity is 70 wt%, while average Ni and V levels are 2500 and 1300 ppm, respectively. The refinery is constrained by regenerator temperature, as well as an LPG limit in the bottom of the debutaniser. Its target were maximum bottoms upgrading and gasoline yield, as well as maximum feed rate and residue content within the limitations of the cat-to-oil ratio and the air blower. In order to meet these targets, the refinery switched to Nomus-220P catalyst.
On moving to Nomus, e-cat analysis revealed much higher activity (+4%) at the same specific catalyst addition rate. In addition, a lower SAK number was observed, which led to a measurable improvement in catalyst strippability, providing relief on the regenerator temperature limit and allowing for the processing of heavier feed. Table 1 shows SR-SCT-MAT selectivity shifts using refinery e-cats and feed. It can be seen that, at constant coke, Nomus resulted in higher conversion, lower gas, increased gasoline and lower bottoms yield.
Table 2 shows FCCU data from the transition period to Nomus. The resulting higher activity and stability provided a 20% reduction in specific catalyst addition rate, as well as the use of a more aromatic and heavier feed (as indicated by a reduced UOP-K factor). In addition, a significant increase in conversion through improved bottoms conversion to gasoline was observed. These improvements were achieved with minimum coke penalty. Nomus allowed all of the targets to be achieved at Refinery A, and the trial was considered a complete success.
Case study 2: improved metals tolerance and resid process ability at Refinery B
The following experience of Refinery B, located in Northern Europe, highlights the benefits of Nektor for resid feed applications. This refinery operates a proprietary Kellogg side-by-side FCCU and processes a heavy feedstock with some of the highest contaminant metal levels observed in Europe. To process resid feeds more profitably, the refinery switched from a Kristal catalyst to Nektor. Unit operation is severely constrained by catalyst circulation, making optimum coke selectivity of the catalyst a key parameter. The FCCU’s objectives were to reduce dry gas yield, maintain LPG yield, increase gasoline yield and decrease bottoms yield.
The main effects of the catalyst change on the standard yields are shown in Table 3. It clearly demonstrates that the change resulted in improved yields and selectivities. For example, the LPG yield was maintained and the gasoline yield increased substantially. This was accompanied by a reduction in dry gas and DCO yields. Furthermore, an increase in conversion of 0.55 wt% was observed. It is also noteworthy that these yields were obtained during a period in which e-cat Ni+V levels increased sharply. From the time that Nektor entered the unit until 85–100% change-out was achieved, the Ni+V levels increased from about 4800 to 11 000 ppm, giving a clear indication of the metals tolerance of Nektor.
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