July 2025
Catalysts
Efficient separation technologies for sustainable refining and petrochemical industries
As global demand for energy continues to surge, the refining sector is confronted with the dual challenge of meeting escalating demand while simultaneously reducing carbon emissions. This article proposes a comprehensive strategy to retrofit or upgrade existing complex refineries utilizing fluidized catalytic cracking (FCC) and resid FCC (RFCC) units.
Increased emissions and energy losses are realities when driving FCC units (FCCUs) to produce propylene for petrochemical production. Refiners are actively developing new solutions to decarbonize this process and the finished products (e.g., transportation fuels, commodity chemicals) as part of this energy transition. As a result, refiners are now exploring the co-feeding of alternative feedstocks, including renewable and recyclable oils, as a means of lowering the carbon footprint of their final products. Given its inherent flexibility, the FCC process has the potential to lower the carbon intensity in this effort. However, these new feeds still present challenges, such as additional contaminants, instability and miscibility issues, along with elevated acidity that can lead to a variety of operational challenges in an FCCU.1 On the path carbon neutrality, it is expected that global demand for crude oil-based gasoline and diesel will significantly decline, forcing most refineries to shift to producing more petrochemicals, including liquid renewables, to remain profitable while maintaining their focus on decarbonization.2
To make more petrochemical feedstocks while also becoming more decarbonized, the operational limits for the FCCU must be expanded. This will intensify the potential for hazardous waste and emissions from various sources, such as fired heaters, boilers, catalytic cracking units and waste oil generation. Measured emissions will require refiners to take a holistic approach to the entire refinery operational plan. Specifically, refiners must design a tailored carbon neutrality framework that incorporates carbon reduction, catalyst fines mitigation and offsetting strategies to reduce waste. This strategy requires a clear path to decarbonization for refiners aiming to achieve net-zero emissions. This article will discuss several challenges along the path to decarbonization, including shifting away from transportation fuels due to increased propylene demands by means of the FCC process.1,2
Improving efficiency to optimize yields. Upgrading the FCCU can significantly enhance the integration of petrochemical processes within refineries. The unit primarily converts heavy petroleum feedstocks into lighter, more valuable products like gasoline and diesel. However, by implementing specific upgrades, refineries can optimize the FCCU to produce higher yields of petrochemical feedstocks, thus improving overall operational efficiency and profitability. Implementing advanced process control systems can optimize the FCCU’s performance in real time. These systems can adjust parameters dynamically based on feedstock variations, desired product specifications and product economics, minimizing waste to support the refinery’s net-zero goals. Benefits can also be found by upgrading heat exchangers and integrating heat recovery systems—not only to recover heat energy losses, but also to improve FCCU energy efficiency. By capturing and reusing heat generated during the cracking process, refineries can reduce overall energy consumption and enhance the economic viability of producing petrochemical products.3
Another option in support of decarbonization and increasing profits from the production of propylene is through catalyst selection. Choosing advanced catalysts that are more selective toward lighter olefins, such as propylene and ethylene, can enable refiners to significantly increase their output of petrochemical precursors while still concentrating on reducing emissions. Maximizing catalyst accessibility, which is a measure of how easily heavy oil molecules can navigate the catalyst pore structure to find active cracking sites, will result in improved primary products such as improved liquefied petroleum gas (LPG) olefinicity, increased gasoline selectivity and an increased light cycle oil (LCO)/slurry ratio. Reducing the rare earth on zeolite (REO/Z) will result in decreased hydrogen (H2) transfer, and increases in gasoline octanes and LPG olefinicity—however, simply reducing the REO/Z without extensive knowledge of FCCU operations and the catalyst system is unwise. When designing the optimum REO/Z, refiners should have a thorough understanding of the FCCU’s regenerator severity and the underlying catalyst systems incorporated. A well-designed active matrix can reduce undesired products like slurry and improve the primary products mentioned earlier.
ZSM-5 is a shape-selective zeolite that is known to crack gasoline olefins into desired petrochemical products such as propylene, butylene and—at times—ethylene. Mobil invented the ZSM-5 zeolite in the 1960s. The co-author’s companya has incorporated ZSM-5 into FCC catalysts since 19844 and has since improved the use of ZSM-5, along with other shape-selective zeolites and FCC catalyst synergies. In the 1990s, the co-author’s company developed a catalyst familyb to maximize propylene. The company’s butylene catalystc, which incorporates a ZT-100 shape-selective zeolite, was introduced in 2005. These shape-selective zeolites are now a common component for maximizing petrochemical precursor feedstocks in the refining industry. However, focusing solely on catalyst is not enough: the FCC riser itself must also be considered.
Modifying the FCCU’s riser section allows for better catalyst distribution and contact time with the feedstock. A design that promotes turbulent flow can enhance catalyst effectiveness by improving the distribution of catalysts within the unit. Modern maximum propylene riser termination devices can either increase residence time or increase the catalyst-to-oil (C/O) ratio to increase reaction severity. The implementation of a secondary or dedicated riser to crack recycled light naphtha or light hydrocarbons in general can play a fundamental role in maximizing light olefins yield, especially in the range of ethylene and propylene under severe reaction conditions. Additionally, upgrading to advanced feed injection systems ensures uniform dispersion, optimum atomization, reduced hydrocarbon partial pressure and optimal contact between feed and catalyst.
Simple adjustments can be accomplished without the addition of expensive upgrades or catalyst trials. Adjusting operating conditions—such as cracking temperature, pressure and feedstock composition—can help in maximizing desired olefins production. Increasing the severity of the cracking process can lead to higher yields of lighter products but requires careful balancing to avoid excessive coke formation and catalyst deactivation. Maximizing riser outlet temperature (ROT) is one of the first independent process variables to consider due to the relative ease and flexibility to change it. Most FCCUs will operate in the region of 520°C–530°C (968°F–986°F) for maximum gasoline output. Increasing the ROT will increase LPG olefin production. For maximum LPG olefins, high-severity FCCUs can operate at > 540°C (1,004°F). More extreme process conditions can be applied when the FCCU is upgraded to high-severity or maximum propylene, where it can operate at > 560°C (1,040°F) with reduced hydrocarbon partial pressure (> 7 wt% dispersion seam) and a C/O ratio > 15 wt/wt in some cases.3
Investment in these new FCC technologies is an excellent prospect for olefins optimization. An advancement like the high-severity FCCU (HS-FCCU) is actually a downer (not a riser), with contact times < 1 sec and at even more elevated C/O ratios. These improvements to the well-known FCC process can achieve a considerably higher level of light olefins production, in particular propylene, to bridge the gap between the refining and petrochemical industries.
By focusing on these upgrading strategies, refineries will not only boost their FCCU’s efficiency but will also enhance their capability to produce a broader range of valuable petrochemical products, aligning with market demands and economic trends. Investing in existing equipment is well within the framework of reaching net-zero goals. The cost of upgrades to the FCCU or new catalyst trials to enhance process conditions and optimize the unit’s severity is offset by better yields. On average, these yields can provide > $15 MM/yr of additional revenue while supporting refinery decarbonization.
Slurry oil yields and properties. As might be expected, slurry oil quality is a function of such variables as the properties of the FCCU’s feed, severity of the operation, type of catalyst and operating conditions in the FCCU, among others. The marketability of slurry is penalized on its density, clarity and contaminate contents. Slurry oil yields ranging from 1 vol%–2 vol% for easy-to-crack feeds to as much as 24 vol% on RFCCU feeds or maximum diesel applications have been observed. Upgrading slurry oil is problematic due to its low API gravity and high content of asphaltenes in resid operations. The properties of typical slurry oils can be found in TABLE 1.
Resid [> 565.5°C (> 1,050°F)], in general, and asphaltenes, in particular, are large hydrocarbons with a high carbon-to-H2 ratio. Resid molecules have a molecular size > 25 Å, and asphaltenes have a molecular size of > 100 Å. These compounds are especially rich in metals and contain nickel (Ni) and vanadium (V), which promote coke generation when deposited on FCC catalysts. When cracking residual feedstocks, the zeolite pores (< 14 Å, 7.4 Å through the super cages) are not large enough to crack these large asphaltene structures small enough to enter the pores of the catalyst and therefore pass along to the slurry. A well-designed resid FCC catalyst will contain an active matrix with mesopores (100 Å–500 Å) to increase the cracking of these large hydrocarbon compounds. The level of conversion of asphaltenes in an RFCCU is then a function of the accessibility and the selectivity of the active matrix in the catalyst.3,5
Catalyst particles in the slurry, besides containing Ni and V, can also bring in sodium and other feed metals that are deposited onto the catalysts. Slurry oil may also contain other solid FCC particles, such as sulfur oxide (SOx) reduction, a carbon monoxide (CO) promoter, fuel sulfur reduction, metals traps and bottoms cracking additives. The elements in these additives (magnesium, platinum, palladium, cerium, calcium, etc.) can change the quality of the slurry/sludge.
As refiners introduce more resid into the FCCU, slurry oil yields will increase, and the quality of the slurry oil will decrease. In addition, a larger proportion of asphaltenes and heteroatoms will enter the FCCU. This is relevant because the level of asphaltenes in the slurry oil becomes a factor in deciding which technology is best for removing particulate solids. Mechanical filtration becomes problematic in these scenarios due to the occlusion from asphaltenes and waxes present in heavier resid feedstocks used to produce high levels of propylene in petrochemical development. This leaves most complex refineries looking for a more effective source of clarification, in addition to a reliable fines removal system.5,6
Slurry oil particulate removal technologies. Holding tanks have been used to allow solids to settle out of the slurry oil. The resultant decanted oil solids’ content will be a function of the design of the sedimentation tank, the physical characteristics of the slurry, the temperature of the storage tank and if settling aids are used. It should be noted that another product is being generated along with decanted/clarified oil: sludge. In most cases, this sludge is recycled back to the riser. Slurry oil holding tank sludge has been classified as a hazardous waste; therefore, special treatments and, consequently, extra expenses are required for its disposal. Depending on the tank size and rate of slurry oil production, cleaning can cost millions of dollars. In the absence of countermeasures, increasing resid feed to the FCCU will tend to increase the rates of both slurry oil production and sludge formation.3
Mechanical filtration, first put into slurry oil service around 1990, operates at temperatures up to 315°C (599°F) and employs tubular porous metal elements. The solids collect on the inside of the elements, while the filtrate passes through to the outside. Some filters use porous sintered woven wire mesh metal filters and operate at 232°C–343°C (450°F–649°F). Others employ a 2-micron to 5-micron woven wire filter element, using LCO as a backwash at 176°C (349°F), and claim 85%–95% solids removal from the feed slurry.7
Electrostatic separation of FCC catalyst fines from slurry oil has been in commercial operation for > 30 yr. Electrostatic separation uses a charge, causing the catalyst particles to become trapped in beds of glass beads while maintaining flow without significant pressure drop. In this way, electrostatic separators have been able to remove > 97% of the catalysts present in slurry oils. As the concentration of vacuum tower bottoms in FCC feeds grows, modern techniques used for the selection of catalyst removal from slurry oil will increasingly favor electrostatic separation because it is inherently less likely to foul or coke due to increasing asphaltene levels in the slurry. Particle size distribution ranges for a variety of slurry oils are shown in TABLE 2.
Note that for these slurry oils, > 90% of the particles range in size from 0 microns–25 microns. In comparison, this means that very large holding tanks and long holding times are required to meet higher-value product specifications in decanting processes, and smaller particles can pass through mechanical processes.8
The bottom line. Achieving net-zero emissions will come at a cost, but optimizing processes and utilizing advanced technologies will provide offsetting dividends to a refiner’s bottom line. Some of the value generated from an electrostatic separator in removing FCC catalyst fines from slurry oil can be illustrated using the following example. An 80,000-bpd gasoil FCCU has a slurry oil yield of 4 vol% (3,200 bpd). The catalyst content of the slurry oil is 4,000 ppm. All cases are compared against the base case in which the refinery uses a holding tank to reduce its solids. The slurry holding tank is assumed to require cleaning once a year at 2,000-ppmw slurry solids at a cost of $1.5 MM. Increased catalyst loads will incur higher frequencies of cleaning for the slurry holding tank, resulting in higher total costs. A portion of the FCC feed is used to backwash the electrostatic separator, after which it and the associated catalyst are fed back to the FCCU, thus reducing fresh FCC catalyst costs. FCC catalyst costs are assumed to range from $3,000/metric t–$7,000/metric t. It is estimated that the average product upgrade values for this clarified slurry oil can be between $8/bbl and $12/bbl.
Benefits from not having to purchase chemical settling aids were not considered, even though such costs are estimated to be in the order of $0.12/bbl–$0.40/bbl treated.7 Heating costs to maintain the holding tank at temperature are not considered but can be substantial. The reduction of environmental waste and the decrease in catalyst loss support the refinery’s net-zero goals while providing increased profits in the process. The operation and reliability are supported by the ability of the electrostatic separator to maintain operation without blocking or plugging, so no downtime is realized.
Another point not considered is the increase in FCCU production, which is realized by not using heavy cycle oil or LCO as backflush oil required by mechanical filters. In this case, the electrostatic separator uses raw FCC feed for backflush, thereby increasing the middle distillate production and the bottom line of the refinery.6
Profitable markets and new applications of slurry oils are detailed in TABLE 3.
Takeaways. Petrochemicals are the traditional extension of the refinery value chain, as there are synergies in the production of both fuels and commodity chemicals in an integrated facility. Petrochemicals typically achieve significantly higher prices over transport fuels and thus increase FCCU profitability. By using heavier resid cracking units alongside high-severity complex reactors with specialized catalysts, refiners can maximize propylene product profitably. These integrated sites are highly competitive compared to those of standalone-fuel refiners, with the flexibility to switch yields between fuels and chemicals. This suggests that refiners’ shift toward petrochemicals must be methodical and well planned to capture significant value and to position a site in their individual decarbonization plan. Such an investment is unlikely to be available to all, as any petrochemical investment must be significant to be competitive against new facilities under development. It is during the initial development that the framework to decarbonization must be considered.2
New technologies exist to reduce operational costs by minimizing the need for expensive chemical additives or labor-intensive processes. To reach net-zero emissions while maintaining profitability, the reduction of waste and energy consumption must be compared to traditional separation methods to allow the dramatic reduction in carbon emissions, leading to reduced operational costs. Carbon offsetting can be achieved by divesting carbon-intensive assets and investing in separation technology to reduce the emissions from the cracking process.
Achieving net-zero emissions is often viewed as cost prohibitive or process burdening, but the selection of the right technology helps maintain a healthy bottom line. Electrostatic separation is a strategic investment for refineries aiming to optimize productivity, reduce costs and improve sustainability, while also reducing their environmental footprint by efficiently limiting harmful emissions and waste.
NOTES
a Ketjen Corp.
b Ketjen’s AFX™ catalysts
c Ketjen’s Action™ catalysts
LITERATURE CITED
1 Vincent, G., S. Riva, F. Barrios, F. Dubois and S. Golczynski, “Tackle operational challenges with FCC coprocessing applications,” Hydrocarbon Processing, May 2024.
2 Rana, D. and J. Melancon, “Decarbonization pathway for net-zero by 2050: Carbon neutrality roadmap strategy for an integrated refinery and petrochemical facility,” Hydrocarbon Processing, January 2025.
3 Ketjen, “FCC process course: FCC catalysts,” Houston, Texas, March 2024.
4 Yanik, S., R. Campagna, E. Demmel and A. Humphries, “A novel approach to octane enhancement via FCC catalysts,” NPRA (now AFPM), March 1985.
5 Motaghi, M., K. Shree and S. Krishnamurthy, “Anode grade coke from traditional crudes,” PTQ, 2Q 2010.
6 Paraskos, J. and V. Scalco, “Optimize value from FCC bottoms,” Hydrocarbon Processing, April 2013.
7 Minyard, W. F. and T. S. Woodson, “Upgrade FCC slurry oil with chemical settling aids,” World Refining, November/December 2009.
8 Platts, “Methodology and Specifications Guide, Petroleum Product and Gas Liquids: U.S., Caribbean and Latin America,” January 2012.
The Authors
Since 1997, Victor Scalco has been an integral part of process design and developmental downstream solutions for hydrocarbon recovery. Working in support of key players in the industry, his current position allows for new development of filtration and separation systems. He is principally involved in the technical development and training with engineering, procurement and construction (EPC) and FCC/RFCC licensors worldwide. His experience includes program development for commercial applications, scoping studies and commissioning. Scalco holds an MA degree from San Diego State University (U.S.) and has worked for more than 20 yr in the design and implementation of hydrocarbon filtration systems.
Clifford Avery has > 39 yr of experience in the FCC/hydrocarbon processing industry and is the subject matter expert for FCC processes for Ketjen in Houston, Texas. In this role, he leads the global FCC effort in training, troubleshooting and performing unit health checks for Ketjen’s FCC customers and sales teams. Previously, he held positions in business, technical services (FCC) and sales (hydroprocessing and FCC). He has experience working with FCCUs globally, especially in the North American and Asia-Pacific regions. Avery earned a BS degree in chemical engineering from California State University, Long Beach.
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