Role of FCC process and catalysts in the energy transition
In the evolving circular economy, proper leveraging of FCC technology and operations can deliver value for refiners in the decades going forward.
Maria Nieves Alvarez
Meryt Catalysts & Innovation
Viewed : 263
Refinery fluid catalytic cracking (FCC) as a secondary chemical conversion process breaks down hydrocarbon fractions present in crude oil feedstocks into simpler fractions that can be commercially utilised, including olefinic gases, gasoline, and various other important petroleum-based products.
Cracking catalysts have made a huge contribution towards FCC flexibility. They are, in fact, the heart of the process. After all, it is the catalyst that reacts with the feedstock. The history of FCC catalyst development described in Figure 1 eventually led to sustained catalyst activity and product differentiation. Figure 1 shows the evolution of advanced FCC processing designed to obtain more specific products from higher activity fluidised bed catalysts.
FCC process and catalyst innovations have enabled a continuous adaptation of the technology to meet the needs of refining for more than 80 years. While the FCC unit was initially designed to meet the rapid increase in gasoline demand that began in the 1940s, the last 30 years have seen the advent of significant new drivers expanding and reshaping the process (see Figure 2).
Over the past few decades, economic and population growth have stirred a significant increase in oil demand, with a current consumption of 100 Mb/d and additional demand growth of 1 Mb/d per year expected for the next decade.1 This is mostly due to the expanding automotive and aviation transportation sectors.
No less important is the high products and energy consumption leading to expansion of the chemical sector. In parallel, efficiency improvements, important advances in clean energy generation, and environmental concerns accompanied by stricter policies are expected to result in far slower growth in the use of oil-derived fuels in the second half of the decade and a likely demand decrease after 2030.
In contrast, petrochemicals demand is not expected to stop growing in the foreseeable future. In the next two decades, oil-based feedstock demand for petrochemicals is expected to increase to 34% of the total oil market in 2040, in contrast to the current 15%. These petrochemicals include light olefins in the C₂−C₄ range and aromatics (mostly benzene, toluene and xylenes [BTXs]).
Currently, these petrochemicals are primarily produced via steam cracking and as FCC byproducts. Industry’s concern over minimising operating costs of petroleum refining processes has made FCC the best alternative for cracking petroleum fractions, predicating increased demand for FCC catalysts, with an emphasis on increasing yields.
A wide variety of relevant proprietary processes have been proposed, such as DCC (RIPP/SINOPEC), CPP (RIPP Kellog), MIP_GCP (RIPP), PetroFCC (UOP), and HPFCC (Grace Davison). These processes are conducted at an elevated reaction temperature with an increased catalyst/feed recycle ratio on the catalyst based on modified zeolite ZSM-5. The yield of propylene can reach 20% or more. In the proprietary MAXOFIN (KBR) process, gasoline is recycled into a separate riser reactor, thereby making it possible to change the yields of cracking products flexibly.
Although the cracking of light feedstocks proceeds under more severe conditions, it is characterised by a higher yield of propylene as compared with the cracking of a vacuum distillate. Thus, the yield of propylene in the cracking of paraffin base light gasoline can reach 50%.
Using catalysts and processes that improve FCC feedstocks has a substantial, positive impact on FCC unit conversion. Hydroprocessing of cracker feeds, vacuum gas oil (VGO) or mild hydrocracking/hydrocracking of VGO and residues has a dramatic effect on FCC unit performance, basically because hydroprocessing increases the ratio H/C in streams fed to the FCC.
The resulting product makes a good feed for FCCs, reducing catalyst make-up, obtaining a better-quality product with less sulphur, and increasing yields of valued products while diminishing SOx and NOx emissions.
In contrast to noncatalytic processes, the use of FCC allows for better control over product selectivity. Many FCC systems for processing VGO and/or oil residues to produce light olefins have been developed and commercialised. As summarised and reviewed by Bogle and Corma, most of these technologies rely on high-severity operations using single or dual riser reactors with optional naphtha recycling. Injection of recycled naphtha is preferred at the end of the riser or in a second riser to minimise dry gas and coke yields.
Together with USY, ZSM-5 is the second most widely used zeolite in catalytic cracking applications. Initially added in smaller amounts as a gasoline booster, the use of ZSM-5 also increases propylene production by 1-5 wt% over conventional FCC processes that yield 4-6 wt% of propylene. Oil-to-chemicals technologies are expected to increase this number up to 20 wt%.
A key aspect of improving light olefin yield (in addition to higher temperatures) is the modification of the parent zeolite to minimise hydrogen transfer reactions (and consequently aromatisation and coke formation).
Phosphorus stabilisation has been shown to result not only in lower hydrogen transfer ability but also in improved attrition resistance and hydrothermal stability., In addition to P, incorporation of Fe₂O₃ and/or B₂O₃ leads to higher isobutene and LPG yields and lower coke production.
In the coming decades, the energy and chemicals markets will face a very important reshaping. Chemicals represent one of the fastest-growing crude-oil-demand sectors. The use of oil in the petrochemicals sector is likely to become a key source of oil demand after the 2020s. At the same time, environmental regulations predicate the use of biofeedstocks and waste (such as plastic waste) to deliver products for the petrochemical value chain (such as olefins and polymers). For this task, FCC units become a major propylene source with minimal energy intensity.
One of the consequences of this petrochemical shift in the way refineries operate in the future can be seen in the process and catalyst development challenges and the research opportunities therein. Against this backdrop, the refinery of the future, with CO₂ neutrality as a major objective, will achieve its objectives through breakthroughs in some of the following intertwined areas:
• Maximisation of chemicals production with integrated carbon capture
• CO₂ capture and transformation to products such as e-fuels, olefins, and other products for the chemical industry
• Reduce emissions along with the use of renewable energy in the process
• Process intensification by miniaturisation of physical footprint where applicable and overall maximum reduction in the number of unit operations, thereby significantly reducing energy and capital intensity
• Integration of new intelligent process control systems for implementing rapidly corrective and preventive actions (in line with market demands)
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