S. Kundu and B. CIPRIANO, W. R. Grace & Co., Columbia, Maryland; L. BOUGRAT, W. R. Grace & Co., Nashville, Tennessee; D. HOLDER, W. R. Grace & Co., Conway, Arkansas; and C. COOPER, W. R. Grace & Co., Houston, Texas
Transportation fuel demand is predicted to peak in the next 10 yr–20 yr. This is being driven by efforts to improve the fuel efficiency of vehicles as well as a decline in the demand for fuel in mature economies. Additionally, the broader energy transition away from fossil fuels has the potential to accelerate the decline in their demand.
This trend could challenge the future profitability of the fluid catalytic cracking unit (FCCU). However, given the catalyst product and feed flexibility of FCCUs, opportunities will be created that enable nimble refiners to capture and continue generating value from their assets. The reasons for this include the growing demand for petrochemicals, and the key role of oil in satisfying the increasing societal energy requirements for decades to come.
One of the most common petrochemical feedstocks, propylene, is generated in the FCCU. Propylene demand is projected to increase by 36% through 2030 (or 4% annualized). Throughout this same period, the share of propylene supply from the refinery is predicted to stay constant at just under 30%.1 An important advantage of refinery C3= is that it has a lower cost position vs. other propylene-producing technologies, and as fuels demand decreases, this cost competitiveness will provide an incentive and advantage for refiners to make more C3=.2,3 While society is pushing for a transition away from fossil fuels, it will take a significant overhaul of regulations and massive changes in the myriad ways society produces, stores, distributes and utilizes energy to reach net-zero emmisions.4,5 A sampling of the large-scale changes needed to reach net-zero emissions by 2050 includes:6
Given the very ambitious goals and timeline available to achieve net-zero emissions by 2050, it is likely that sustainable energy and fossil fuels will coexist for some time in the transport sector, as opposed to a scenario in which demand for transportation fuels abruptly declines. Within this context, how the FCCU is operated will be central to refiners’ strategies to produce fuels in a more sustainable manner given the FCCU’s feed and yield flexibility.
There is no doubt the future will challenge refiners, but this industry has successfully confronted many challenges before: low-sulfur fuel standards, International Maritime Organization (IMO) regulations, and the elimination of lead-based octane enhancers, to name a few. In all cases, refiners have adapted—this time will be no different.
The latest of these innovations from the authors’ company is a novel FCC catalysta that incorporates an advanced integral vanadium (V) trap into its bottoms upgrading catalystb and builds on the V tolerance of its high matrix activity bottoms upgrading technology. This article reports on the first trial of this technology, and the improvements observed to product yields and coke selectivity. The implications of reducing coke yield for producing fuels from the FCCU in a more sustainable manner will also be discussed in addition to the V chemistry in the FCCU and why it is so detrimental to FCC catalyst will be reviewed.
Zeolite destruction by vanadium and the role of rare earth (RE) traps. Metal contaminants such as nickel (Ni), vanadium (V) and iron (Fe) are naturally present in crude oil to various degrees. Furthermore, crude oil reservoirs are usually associated with brines that contain alkali metals and alkaline earth metals, including sodium (Na), calcium (Ca), magnesium (Mg) and, to a lesser extent, potassium (K) and barium (Ba). The deactivation mechanism by each contaminant and its effect on unit operation and product selectivity is distinct. V is particularly harmful to catalyst performance because it dealuminates the zeolite component and causes a loss in catalyst activity (FIG. 1).
In the FCCU regenerator, fully oxidized V oxide (+5) reacts with steam to form vanadic acid vapor,7 which then destroys the zeolite via acid hydrolysis of framework aluminum sites. Moreover, Na (and K) works synergistically with V to destroy zeolite crystallinity, where vanadic acid catalyzes the conversion of Na+ ions to form sodium hydroxide (NaOH), which then promotes the dissolution of zeolite crystals. Importantly, in this mechanism, vanadic acid is not consumed;8 it is a catalyst that is regenerated after each reaction cycle.
FIG. 2 shows the first-order rate constant for the destruction of zeolite crystallinity as a function of the Na content for varying levels of V. At any given V level, the rate of crystallinity loss increases with the sodium content. Moreover, the slopes of these lines increase as the V level increases, suggesting an interaction between Na and V. In addition to causing zeolite destruction and activity loss, V is also a dehydrogenation catalyst that increases hydrogen and coke yields. The dehydrogenation activity of V increases with the oxidation state of the metal; hence V+V is more active than V+IV. As a result, V is most detrimental when the FCCU is operated in full burn mode.
An effective V-trap integrated in the FCC catalyst system can dramatically reduce the ability of V to destroy the active components of FCC catalyst and, therefore, maintain high cracking activity. Additionally, V-traps minimize the dehydrogenation activity of V, facilitating lower hydrogen yields and improved coke selectivity in FCCUs.
The authors’ company pioneered the use of integral rare earth-based V-trapping technology in several of its catalyst product familiesc,d,e that are proven commercially over decades. While attempts using MgO and CaO-based V-traps may show promise under laboratory testing conditions, silica and sulfur within the FCCU regenerator conditions can poison these traps to form stable compounds, such as Mg2SiO4 (forsterite) and CaSO4 (anhydrite), rendering them ineffective. The incorporation of the company’s integral V-trapc,d,e has been proven to enhance activity retention and coke selectivity in units with high V.10 The authors’ company’s resid feed catalysts that contain integral rare earth-based V-traps are effective even in units with low vanadium mobility.
The catalysta is the company’s latest advancement in V-trapping technology: a high-matrix activity FCC catalyst with an advanced RE-based V-trap. This novel V-trapping technology builds on bottoms cracking and metals trapping capabilities of the company’s bottoms upgrading technologyb, which cracks deep into the bottom of the barrel, enhancing total distillate and liquid yield.
The success of the bottoms upgrading technologyb is due to the matrix effectively cracking all feed types—from heavy resids to shale oil-derived feeds—via the three-step bottoms cracking mechanism discovered by Zhao.11 To accomplish this, the bottoms upgrading technologyb contains an optimal balance of mesoporosity in the range of 100 Å–600 Å and macroporosity in the > 1,000 Å range. Moreover, the proprietary matrix in the bottoms upgrading technologyb can withstand high levels of contaminant iron and calcium.12
With the incorporation of the advanced RE-based V-trap, the catalysta maintains bottoms upgrading and Fe tolerance yet demonstrates improved V tolerance, as indicated by higher zeolite activity retention and improved coke selectivity. Not only does this allow refiners to widen their operating window and increase feed flexibility, but it also increases the yield of liquid products at constant carbon emissions, enabling the FCCU to produce fuels more sustainably. In the next section, the novel FCC catalysta is compared to the bottoms upgrading catalystb in terms of metals tolerance and overall yield performance.
Comparison. To show the differences in zeolite surface retention between the two catalysts discussed above, a sample of each was subjected to cyclic propylene steaming (CPS) deactivation in the laboratory. The V level was varied while maintaining a constant Ni level at 2,500 mg/kg. FIG. 3 clearly demonstrates that with increasing V, the catalysta shows significantly higher zeolite surface area and UCS retention compared to the bottoms cracking catalystb and validates the improved V- trapping present in the new catalysta. Importantly, at low V levels the unit cell size (UCS) of both catalysts are the same. This result emphasizes that the RE-based V-trap in the novel FCC catalysta is located in the matrix and not exchanged into the zeolite where it can affect hydrogen transfer activity. Therefore, there is no conflict between RE-based V-trapping technologies and achieving a low hydrogen transfer. It is worth noting that the novel FCC catalystsa can be formulated over a wide range of properties, including low RE/Z grades that are the best fit for resid FCCUs targeting high yields of light olefins.
A Davison Circulating Riser™ (DCR) pilot plant study was conducted to compare the performance of the catalysta against the bottoms upgrading catalystb and a catalyst with a balance of bottoms upgrading and coke selectivity characteristicsf. All the catalysts were impregnated with 3,000 mg/kg and 2,000 mg/kg vanadium and nickel, respectively, and deactivated using standard CPS deactivation. At a given conversion, compared to a bottoms upgrading catalystb, the new catalysta provides the same bottoms yield but offers a significant drop in coke yield and an increase in gasoline yield (and total liquid product), as demonstrated in FIG. 4. When compared against the balanced catalystf, the catalysta showed improved bottoms upgrading and slightly improved coke selectivity. The improved coke to bottoms performance confirms that the advanced V-trapping technology of the new catalysta outperforms the metals tolerance of traditional catalyst systems. In the following sections, the improved coke selectivity that will allow refiners to realize a more profitable yield slate and produce fuels in a more sustainable manner is discussed.
A real-world example. The company’s customer’s FCCU operation was being challenged by processing a mixed vacuum gasoil (VGO) and resid feed with increasingly higher feed metals, particularly Fe and V. The high metals content in the feed led to more than 10,000 mg/kg V+Na and more than 4,000 mg/kg added Fe on Equilibrium catalyst (Ecat). One of the key unit constraints at the time was the main air blower capacity. The incumbent catalyst at this customer’s facility was the balanced catalystf technology. Over time, the unit suffered from classic symptoms of Fe poisoning, including the formation of Fe nodules on the catalyst surface and loss of diffusivity. Additionally, high Na and V levels on Ecat led to poor zeolite stability and loss of cracking activity. As a result, unit conversion, total liquid yield and bottoms cracking all began to suffer.
The authors’ company collaborated with the customer on a catalyst reformulation that would meet the following objectives:
The refiner met this objective by implementing a catalyst reformulation to the new catalysta. FIG. 5 shows that, compared to the balanced catalystf, the catalysta displayed higher ZSA retention across a wide range of Ecat V (and Na) levels, confirming the effective V-passivation. Moreover, as indicated by inverse gas chromatography (IGC) data in FIG. 5,13 the catalysta maintained higher diffusivity than the balanced catalystf during periods of high feed Fe.
Unit operations varied between periods of the two catalysts’ use, and while the refinery observed the expected performance trends, the variability complicated the evaluation of the trial. Therefore, testing in the company’s DCR pilot plant and FCC-SIM modeling were utilized to help account for process variability and quantify the commercial trial benefits, as is common practice in the industry.
The DCR study was conducted comparing the balanced catalystb against the catalysta Ecats using both feed and operating conditions matching those of the FCCU during the commercial trial (the Ecat samples selected for the testing had similar metals levels). TABLE 1 shows the DCR interpolated yield pattern at constant conversion. The DCR data indicates that the catalysta met all trial objectives.
The results of the FCC-SIM modeling evaluation shown in TABLE 2 are aligned with the findings from the DCR study: the improved tolerance to V materialized as higher activity and improved coke and gas selectivity, as indicated by the lower regenerator temperature and dry gas yield. Further, the catalysta had the added—and significant—benefit of a volume swell increase. Using the FCC-SIM deltas and a generic U.S. Gulf Coast price set that favors diesel over gasoline, the increase in profitability for the catalysta relative to the balanced catalystf was estimated at $0.63/bbl.
Implications for producing fuels in a more sustainable manner. By design, the FCCU requires the production and combustion of coke to generate the heat required to vaporize the feedstock and drive the endothermic cracking reactions taking place in the riser. The combustion of this coke in the FCCU accounts for approximately 15%–20% of the CO2 emissions from the refinery.14,15 The coke produced in the FCCU stems from several contributors: hydrogen redistribution reactions in the catalytic cracking; cracking of heavy feed components; poor feed vaporization; dehydrogenation reactions catalyzed by contaminant metals in the feed; and unstripped hydrocarbons entrained in the catalyst leaving the reactor.
The coke yield directly contributes to Scope 1 or direct CO2 emissions from the FCCU. Factors that increase the coke yield (e.g., operating at a higher reaction temperature) will increase emissions from the FCCU. Reducing FCCU severity (lowering riser temperature), reducing C/O (increasing feed temperature, reducing catalyst cooler duty, etc.), or reducing slurry or LCO recycle rates will all reduce CO2 emissions from the FCCU, accomplishing the objective of reduced Scope 1 CO2 emissions. However, these moves will typically lead to reduced conversion and increased slurry yield from the FCCU. While it may be desirable to operate the FCCU at lower direct emissions by decreasing coke yield, this is generally not economically feasible.
Increasingly, jurisdictions are implementing CO2 taxation or increasing the magnitude of their CO2 tax. Countries in Asia-Pacific that have not had a carbon tax are now implementing or increasing them (e.g., Singapore),16 and the carbon tax in Europe has recently reached values of some €100/metric t (tonnes).17 Against this backdrop, one of the challenges in the near future for the FCCU will be to lower the carbon intensity of fuel production, meaning reducing the metric t of CO2 equivalent per metric t of fuel product, while maintaining a profitable yield slate. Catalyst technologies that exhibit improved coke selectivity such as the catalysta will help refiners achieve this.
Importantly, a catalyst that produces improved conversion at constant coke affords refiners flexibility to maintain coke yield—and therefore FCCU CO2 equivalent emissions. This also improves conversion, lowers reaction temperatures and emissions while maintaining liquid product yields, or optimizes to somewhere in between, taking advantage of some increase in profitability while limiting Scope 1 emissions. Exploring a new operational range, such as processing a heavier feed, may also become possible. To illustrate the benefit that may be delivered by improved coke selective catalyst technologies, the authors’ company predicted the reduction in carbon emissions and savings in carbon taxes using DCR comparisons between the new catalysta and the bottoms upgrading catalystb and the catalysta and the balanced catalystf technologies. These catalysts were compared at constant liquid product yield (LPG + gasoline + LCO). These estimates were conducted for a 78,000-bpd FCCU and a carbon taxation value of $80/metric t of CO2. As can be seen in TABLES 3 and 4, the savings in CO2 emissions and carbon taxation can be substantial even at neutral product value.
Takeaways. As the demand for transportation fuels slows and the energy transition away from fossil fuels gathers steam, pressure on refiners will increase to remain profitable while producing fuels in a more sustainable manner. Given the flexibility of the FCCU to process different feeds and change product yields, it will play an important role in refiners’ plans to produce fuels profitably and sustainably. The first trial of the new catalysta demonstrates that advanced catalytic solutions are available to minimize CO2 emissions while delivering significant economic value to the refinery. HP
NOTES
a PARAGON™
b MIDAS®
c IMPACT®
d NEKTOR™
e FUSION™
f GENESIS®
LITERATURE CITED
SHANKHA KUNDU is Principal Scientist for W. R. Grace & Co.’s refining technologies R&D group, located in Maryland, U.S. Dr. Kundu a PhD in Industrial chemistry from the University of Bochum and has a postdoctoral research experience at Brookhaven National Lab in the U.S. Dr. Kundu joined Grace in 2013 and has since led several new FCC catalyst product developments. Additionally, she has been a valuable technical partner to the marketing and sales teams to introduce new products and to support the catalyst selection process for customers globally to meet their market needs. She is a co-author on several papers and patents related to catalysis and has presented at various catalysis conferences globally.
BANI H. CIPRIANO is the FCC Segment Marketing Manager, Light Olefins, at W.R. Grace & Co. Dr. Cipriano manages the portfolio of max propylene catalysts and ZSM-5 additives for Grace. As the refining industry shifts its focus from fuels to petrochemical production, Dr. Cipriano’s priority is to commercialize technologies that will enable customers to maximize yields of petrochemical feedstocks from the FCC. He earned his BS degree and PhD in chemical engineering from the University of Maryland, College Park.
LUIS BOUGRAT is a Technical Sales Manager for W. R. Grace & Co., covering FCC accounts in the Americas. Since joining Grace in 2016, he has been responsible for account management and technical services responsibilities across Canada, the U.S. and Latin America. Prior to joining Grace, Bougrat worked with UOP Honeywell for more than 8 yr in various roles and responsibilities around the world, including R&D, field operating services, service account management and technical services.
DREY HOLDER is a Senior Technical Service Manager and has been providing FCC technical support and training to refiners across North America for W. R. Grace & Co. for five years. Prior to working with Grace, he spent 12 yr at a large U.S. Gulf Coast refinery working in multiple roles that included Process Engineer, Operations Supervisor, Logistics Planner, Economics Analyst, Economics Supervisor and FCC Engineering Supervisor. He earned a degree in chemical engineering from Louisiana Tech University and has 20 yr of refining and chemical industry experience.
CLINT COOPER is a Principal Technologist for Grace’s FCC business. In addition to serving on the Global Customer Technology team, Cooper utilizes his experience in FCC kinetic modeling to support broader technical service for Grace customers. He joined Grace in 2019 with the acquisition of Rive Technology, where he had worked for 5 yr as a Technical Services Manager to commercialize the novel FCC zeolite technology. Cooper began his career as an FCC Design Specialist for Stone & Webster and Lummus Technology. He holds a BS degree in chemical engineering from The University of Texas at Austin.