March 2025
Catalysts
Design improved resid hydrotreating catalyst systems for higher RFCC profitability
This article summarizes the authors’ JV’s recent development of two new improved catalytic materials for the residue desulfurization (RDS) process, and provides a case study showing how these materials can be used in synergy with RFCC technology to improve refinery margins.
An effective strategy for managing the bottom-of-the-barrel can significantly enhance refining margins. Catalytic conversion technologies for resid can be used to maximize yields of higher-value products and increase refinery flexibility to process lower-cost opportunity crudes. The authors’ JVa has continuously developed new catalysts for hydrotreating and hydrocracking resid to help refiners get the most value from their refinery operations.
One common solution for resid upgrading is to hydrotreat atmospheric resid to produce feed for a downstream resid fluid catalytic cracking unit (RFCCU) to produce transportation fuels or petrochemicals.1 To overcome the high sulfur-content carbon residue (CCR), the presence of contaminant metals and low hydrogen content in many resids, pretreatment in a fixed-bed hydrotreater can enhance the crackability of resid and improve processability in an RFCCU. As part of the energy transition, new RFCCUs are being designed to increase petrochemical production, taking advantage of the flexibility and adaptability of a typical FCCU.2 This article summarizes the authors’ JV’s recent development of two new improved catalytic materials for the residue desulfurization (RDS) process, and provides a case study showing how these materials can be used in synergy with RFCC technology to improve refinery margins.
Synergy between resid hydrotreating and RFCC. To maximize the profitability of this process configuration, the RDS catalyst system must be tailored to produce high-quality RFCC feed throughout its run cycle. To accomplish this, the RDS catalyst system is typically designed with several catalyst layers (FIG. 1).
FIG. 1. Layers of catalyst used in a typical RDS system.
The grading and demetallation layers are primarily responsible for capturing large particulates and metal contaminants from the feed, protecting the downstream catalyst layers and enabling them to maintain high catalytic performance. The transition layer still has a high tolerance for feed metals, while delivering strong activity for sulfur removal and some conversion of carbon residue. The conversion and deep-conversion layers have the highest catalytic activity and primarily function to convert more difficult sulfur, nitrogen and carbon residue species to meet critical product specifications. Superior individual catalyst components, layered into a well-designed catalyst system, are an essential piece of getting the most value from resid hydrotreating. Through decades of research and development efforts and commercial operating experience at refineries worldwide, the authors’ JV has continuously developed new catalytic materials to expand the profitability of resid upgrading.
The product from the RDS unit is often used directly as feed for the RFCCU. Because of this, any improvement to the RDS catalyst system can determine the operations, product yields and economics of the downstream RFCCU—this plays a significant role in the overall refinery’s profitability.
Enhanced downstream catalyst protection from a new demetallation catalyst. Managing the contaminant metals [e.g., nickel (Ni), vanadium (V), iron] in resid feeds is critical to maintaining high catalytic activity throughout the life of the RDS unit, and for enabling manageable metals load to a downstream RFCCU. A new demetallation catalyst (800)b was designed with higher capacity for capturing metals from resid, enabling more protection of downstream hydrotreating and FCC catalysts. This enhanced protection can potentially be used to target higher-quality RDS products or to process economically advantaged feeds with higher metals content, both of which can lead to increased refinery profitability.
The metal-containing molecules in resid feeds tend to be large, and the rate of metals removal is often limited by the rate of their diffusion into the catalyst pellets.3 The pore structure of the new demetallation catalyst (800)b was designed to enable greater access of metal-containing molecules to the interior of the catalyst pellets, allowing for improved hydrodemetallation (HDM) reaction rates and higher metals uptake at the end of catalyst life. To demonstrate this, demetallation catalysts were used for single-catalyst tests to study their effectiveness in removing metals from heavy atmospheric resid feed. FIG. 2 compares the results from HDM performance testing of the authors’ JV’s new demetallation catalyst (800)b vs. the previous generation catalyst (187)c. These results show that the new catalyst (800)b maintains high HDM activity throughout its life, achieving higher total metals uptake at end-of-life.
FIG. 2. Catalyst life test results comparing HDM performance of the new demetallation catalystb with the previous generation catalystc.
FIG. 3 shows that the new catalyst (800)b also maintains strong hydrodesulfurization (HDS) performance late into the run cycle. This is an important consideration for demetallation catalysts, as the heat released by the exothermic reactions in this first bed provides the temperature increase needed for downstream catalyst layers to function at their highest potential late in the run. Early in the run, the demetallation catalyst has only a minor impact on the overall system HDS activity, and the initially mild HDS performance of the new catalyst (800)b is compensated by the more active catalyst lower in the RDS bed.
FIG. 3. Catalyst life test results comparing HDS performance of the new demetallation catalystb with the previous generation catalystc.
Obtaining higher hydrotreating activity with a new catalyst conversion layer. Another key function of the RDS catalyst system is to convert sulfur and nitrogen to meet environmental specifications while improving the crackability of resid by reducing its carbon residue and nitrogen content, as well as increasing its API gravity and hydrogen content. The authors’ JV has continuously advanced its high-activity conversion and deep-conversion catalyst technologies to enable customers to take advantage of market conditions in the face of tightening fuel specifications. The authors’ JV’s new catalyst (199)d has been recently commercialized as a conversion catalyst layer with improved activity for sulfur, nitrogen and carbon residue conversion, while also achieving higher tolerance for Ni and V deposition from the feed.
To study how the catalytic activity of this single catalyst layer compares to other conversion catalyst layers throughout its lifecycle, the new catalyst (199)d was tested using an accelerated aging test protocol. By reoptimizing the active metals formulation and alumina support to maximize the availability of catalytic sites, the new catalyst (199)d sustained higher reaction rates for the removal of sulfur, carbon residue and nitrogen than the previous generation catalyst (181)e (FIG. 4). Through a rigorous development and testing process, the new catalyst (199)d achieved advantages in HDS, microcarbon reduction (HDMCR) and hydrodenitrogenation (HDN) activity throughout its entire lifecycle, as well as enabled a higher tolerance for feed metals.
FIG. 4. A comparison of the new conversion catalyst (199)d start-of-run (SOR) activity for the removal of sulfur, carbon residue and nitrogen vs. the previous catalyst generation (181)e.
Using catalyst 800b and catalyst 199d to design a high-performance RDS catalyst system. These two new catalyst grades can be used to optimize the layering of the entire RDS catalyst system, making it possible to increase unit throughput, target longer run length, improve the quality of RFCC feed or process economically advantaged resid feeds. To demonstrate this, side-by-side system tests were conducted to demonstrate the benefit of switching to catalyst 800b and catalyst 199d vs. the previous generation catalysts (187c and 181e). FIG. 5 compares the layering of the Base Case system with the new system. The Base Case is a representative RDS catalyst system design, using the previous generation demetallation catalyst 187c and conversion catalyst 181e, along with layers of transition, conversion and deep-conversion catalysts. To show how the new catalysts (800b and 199d) can be applied to improve RFCC feed quality, the new system was designed for higher catalytic activity.
FIG. 5. Catalyst layering for RDS full system life tests.
The higher performance of catalyst 800b makes it possible to achieve the same level of metals removal from the feed with a smaller volume of demetallation catalyst. The new system was layered with 10 vol% less demetallation catalyst than the Base Case. This made it possible to increase the amount of conversion catalysts in the new system by 10 vol% to maximize system activity for removing sulfur, carbon residue and nitrogen.
Life tests were conducted on both catalyst systems using atmospheric resid feeds and representative operating conditions for RDS units. FIGS. 6 and 7 show that the new system configuration has a 5°F–10°F performance advantage in HDS and HDMCR activity compared to the Base Case for the duration of the RDS catalyst lifecycle. This enhanced catalytic activity is attributed to the increased volume of high-activity conversion catalyst and the replacement of catalyst 181e with catalyst 199d. The HDM performance and metals uptake are similar for both testing systems, showcasing that catalyst 800b makes it possible to use a lower volume of demetallation catalyst while maintaining the same level of protection for downstream catalysts. The enhanced catalytic activity of the new RDS catalyst system, while maintaining equivalent RDS product metals content, can provide significant economic benefits to RFCC applications.
FIG. 6. Normalized HDS performance comparison of RDS full catalyst systems.
FIG. 7. Normalized MCR conversion performance comparison of RDS full catalyst systems.
Modeling the impact on RFCC profitability. At the same RDS operating conditions, the product from the new RDS catalyst system containing catalyst 800b and catalyst 199d produced higher-quality feed for RFCC processing. TABLE 1 provides a summary of important FCC feed property shifts with the new RDS catalyst system compared to the Base Case system near the middle and end of the RDS run cycle.
Established models for RFCC operation were used to calculate the expected impact of improved RDS product quality on optimal RFCC operating conditions. The improved FCC feed quality was predicted to provide the following operational shifts in the FCCU, resulting in improved yields of higher-value products (TABLE 2).
The increased feed API (increased crackability), reduced CCR and reduced metals content were predicted to reduce delta coke, reduce the regenerator temperature, and increase cat-to-oil and catalyst circulation rate. The better feed crackability, increased catalyst circulation rate, reduced basic nitrogen content and increased Ecat activity (due to reduced V content) were predicted to increase conversion in the FCCU, thereby producing more LPG and gasoline, and less LCO and slurry. Using standard pricing, the average economic uplift was predicted to be +$0.34/bbl (mid-cycle) and +$0.40/bbl (end-cycle) due to the improved feed quality using catalysts 800b and 199d in the RDS process. This uplift would translate to > $6 MM/yr for a typical 50,000-bpd FCCU.
In addition to providing FCC yield and operability improvements, the latest generation RDS catalysts (800b and 199d) would also provide additional FCC operating flexibility, which could further extend FCC uplift improvement potential. Some potential debottlenecking opportunities include:
- Reduced flue gas sulfur oxides (SOx) and nitrogen oxides (NOx), which could allow reductions in required SOx or NOx additive usage, or reductions in caustic usage.
- If maximum air rate is a unit constraint, the cleaner FCC feedstock could provide the flexibility to increase feed rate while still maintaining similar/higher conversion levels compared to the Base Case.
- If maximum regenerator temperature or maximum wet gas compressor rates are constraints, the cleaner FCC feedstock could provide the flexibility to increase the feed rate, run at higher severity, increase recycles, etc.
- Cleaner and improved FCC feed quality provides flexibility to refiners to pursue other unit optimization options such as increasing the resid percentage in the combined FCC feed, or processing lower cost imported feedstock to further boost FCCU profitability.
Takeaway. Catalytic conversion of the bottom-of-the-barrel presents an opportunity to upgrade lower-value process streams to higher-value products. This article has presented a case study of how the latest developments in resid hydrotreating catalysts can further improve the synergy between RDS and RFCC operations. RDS system testing results have shown one example of how the new demetallation catalyst 800b and new HDS conversion catalyst 199d can be used to design a more active RDS catalyst system, leading to improved product quality. By using a demetallation catalyst with higher capacity for metals removal, it is possible to decrease the volume of demetallation catalyst in the full system and achieve the same run length. This enables an increased volume of catalysts with higher activity for the removal of sulfur, carbon residue and nitrogen, leading to an easier-to-crack feed for the RFCCU.
The improved RDS product quality can be leveraged to increase the yield of high-value products from downstream RFCC processing, with significant economic benefits. RFCC modeling has provided an example of how the enhanced crackability of the RDS product stream can lead to higher yields of valuable gasoline and LPG, while reducing slurry yield. The higher-activity RDS catalyst system can be used to further optimize the operations of the RDS-RFCC complex by increasing RDS throughput, targeting a longer run length, processing economically advantaged feedstocks or increasing RFCCU operating severity.
NOTES
a ART Hydroprocessing™
b ART Hydroprocessing™’s ICR 800 catalyst
c ART Hydroprocessing™’s ICR 187 catalyst
d ART Hydroprocessing™’s ICR 199 catalyst
e ART Hydroprocessing™’s ICR 181 catalyst
LITERATURE CITED
1 Brossard, D. N., “Chevron Lummus Global RDS/VRDS hydrotreating—Transportation fuels from the bottom-of-the-barrel,” Handbook of Petroleum Refining Processes, 3rd Ed., 1986.
2 International Energy Agency (IEA), “The future of petrochemicals,” October 2018, online: https://www.iea.org/reports/the-future-of-petrochemicals
3 Tamm, P. W., H. F. Harnsberger and A. G. Bridge, “Effects of feed metals on catalyst aging in hydroprocessing residuum,” Industrial & Engineering Chemistry Process Design and Development, April 1981.
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