S. KUMARI, H. MISHRA, S. KUKADE and P. KUMAR, Hindustan Petroleum Green R&D Centre, Hindustan Petroleum Corp. Ltd., Bengaluru, India
Fluid catalytic cracking (FCC) is a vital refining process used to convert heavy hydrocarbon fractions into more valuable, lighter products such as cracked naphtha, distillate and olefins. It relies on a catalyst—typically composed of zeolites—to break down large hydrocarbon molecules into smaller valuable hydrocarbons. The process occurs in a fluidized bed reactor where hot catalyst particles mix with the feedstock, undergoing cracking reactions that produce a range of hydrocarbon products.
One of the most common feedstocks for FCC is vacuum gasoil (VGO), a heavy distillate obtained from crude oil vacuum distillation. VGO contains long-chain hydrocarbons that are cracked into smaller valuable hydrocarbon products such as cracked naphtha, liquefied petroleum gas (LPG) distillate and olefins through catalytic cracking. The catalyst, after being deactivated by coke deposition, is regenerated in a regenerator where the coke is burnt off, restoring the catalyst activity for reuse in the process.
As refiners explore alternative feedstocks to reduce reliance on fossil fuels and address environmental concerns, feedstocks like plastic pyrolysis oil (PPO) are being considered for processing in an FCC unit (FCCU). PPO is obtained via thermal pyrolysis of plastic waste such as low-density polyethylene (LDPE), high-density polyethylene (HDPE), polypropylene (PP), polytetrafluoroethylene (PTFE), etc., producing a mixture of hydrocarbons that resemble petroleum-based feedstocks. Integrating PPO into FCC operation offers environmental benefits, such as diverting plastic waste from landfills, reducing crude oil consumption, lowering emissions and improving sustainability. FIG. 1 illustrates the strategy for maximizing the value of PPO within a refinery, demonstrating its integration through coprocessing in an FCCU for enhanced circularity.
Operational challenges. Unlike VGO, which is relatively stable and well-characterized, PPO contains a variety of contaminants, including chloride, nitrogen, sulfur, olefins, diolefins, oxygenates and metals, which can negatively impact catalyst performance and operational stability.
One major concern is the presence of oxygenates and olefinic components in plastic pyrolysis oil, which may lead to excessive coke formation during processing in an FCCU. High coke yield can reduce catalyst efficiency and necessitate frequent regeneration cycles, increasing operational costs. Additionally, contaminants such as chlorine, nitrogen and sulfur can cause corrosion in the main fractionator and gas concentration section of the FCCU, leading to maintenance issues and possible equipment degradation.
High chloride and nitrogen content of PPO causes ammonium chloride corrosion in the top trays of the main fractionator, whereas high sulfur content causes ammonium sulfide corrosion in the main fractionator overhead condenser. Ammonium chloride salt deposition can be avoided by operating the main fractionator column’s top temperature above that of the ammonium chloride sublimation temperature, whereas ammonium sulfide corrosion can be reduced in the overhead section by using wash water and corrosion inhibitors. The composition of PPO also tends to vary depending on the source and type of plastic waste used in pyrolysis, making process optimization challenging.
Ultimately, while FCC is a highly efficient process for converting VGO into valuable products, adapting it for alternative feedstocks like PPO requires overcoming technical and operational challenges. Advances in catalyst technology, feedstock treatment and process optimization will play a crucial role in enabling the successful integration of plastic waste-derived feedstocks into the existing refining infrastructure.
Coprocessing of PPO in an FCCU. The co-processing of plastic pyrolysis oil included the selection of oil suitable for the authors’ company’s FCCUs, studying the impact of PPO on FCC product yields, the tuning of FCC process parameters to mitigate corrosion issues in the main fractionator and gas concentration section, and injection in the FCCU’s riser. Various qualities of PPO are evaluated to identify suitable PPO with minimal chlorine, sulfur, nitrogen, oxygenates and diene content, ensuring reduced negative effects on FCC product yields. This selection process helps mitigate operational challenges such as corrosion and gum formation. Catalytic cracking experiments using the optimized PPO were conducted at the authors’ R&D center to assess its performance and feasibility in FCC applications.
Catalytic cracking experiments. The catalytic cracking experiments for coprocessing of plastic pyrolysis with FCC feed were carried out in a fixed-fluid-bed, micro-reactor unit. Product gas was analyzed using a micro-gas chromatography and the liquid product was analyzed in low-temperature simulated distillation equipment. The liquid product cuts considered were cracked naphtha [C5 to 221°C (430°F)], light cycle oil (LCO) [221°C–343°C (430°F–649°F)] and resid [≥ 343°C (≥ 650°F)]. Conversion was obtained by the sum of the yields of dry gas, LPG, cracked naphtha and coke. Mumbai refinery resid FCCU catfeed along with 0.5 and 5% of PPO was used as feedstock. Properties of catfeed and PPO are given in TABLE 1. Mumbai refinery resid FCC equilibrium catalyst (Ecat) was used for catalytic cracking experiments, and the properties of Ecat are given in TABLE 2. Catalytic cracking experiments were carried out at 540°C (1,004°F), and a cat/oil ratio of 7. In lab experiments, it was observed that the coprocessing of PPO increases LPG, dry gas and coke and reduces cracked naphtha, LCO and resid yields. The product yields obtained in lab experiments with 0.5% and 5% PPO processing are given in FIG. 2.
Operational scheme for PPO processing in an FCCU. Since PPO is not a typical feedstock for the FCCU in a refinery, a dedicated PPO skid was installed near the FCCU to facilitate its injection into the riser. The skid includes a storage tank, an inlet hose for receiving PPO from a tanker, an outlet hose, a pump and a flowmeter. PPO along with lift steam was injected into the riser, with no heating provisions provided for the storage tank and feeding line. The process flow scheme of the PPO skid is illustrated in FIG. 3.
Demonstration of PPO coprocessing in an FCCU. A trial of coprocessing of PPO was carried out in a Mumbai, India refinery resid FCCU (RFCCU). This FCCU has a feed capacity of 1.27 MMtpy. 0.5% of the PPO was processed with FCC catfeed. No gum formation or atomization issue were observed while injecting PPO. On the basis of the chloride and nitrogen content of PPO, ammonium chloride sublimation temperature was estimated [~104°C (~219°F)] and, accordingly, the main fractionator’s top temperature was kept higher than the sublimation temperature to avoid ammonium chloride corrosion in the top trays of the main fractionator. Due to the low sulfur and nitrogen content of the PPO used for the trial, no ammonium sulfide corrosion was anticipated. The main fractionator’s top temperature and respective ammonium sublimation temperature before and during the PPO trial are shown in FIG. 4.
The coprocessing of PPO increased conversion, dry gas, LPG and cracked naphtha and reduced LCO, resid and coke yields. Product yields obtained during the trial are shown in FIG. 5.
Impact of coprocessing of PPO on corrosion parameters. Processing PPO is suspected to cause corrosion in the main fractionator’s top trays and overhead condenser due to high chloride and sulfur content. However, corrosion parameters such as ammonium chloride sublimation temperature, overhead condenser boot water pH, chloride and iron content were within the desired limits due to low chloride, low sulfur and low nitrogen content of the PPO selected for processing in the FCCU. The main fractionator’s boot water corrosion parameters monitored before and during the PPO trial are shown in FIG. 6.
Achieving circularity on processing PPO in an FCCU. PPO was processed in an FCCU, where it was transformed into fuels and propylene (propylene present in LPG fraction). If propylene is recovered from the LPG fraction, recovered propylene can be again converted to plastics such polypropylene, polyacrylonitrile, etc., which closes the plastic loop and enhances circularity and sustainability. This process not only reduces dependence on virgin fossil resources but also helps mitigate the accumulation of plastic waste. By integrating PPO into refining operations, industries can contribute to a more resource-efficient and environmentally responsible economy.
Takeaway. PPO processing in an FCCU was successfully completed without negatively impacting FCC product yields, and no major operational issues were faced while PPO processing in an FCCU in terms of unit corrosion and gum formation. The coprocessing of PPO increased conversion, dry gas, LPG and cracked naphtha and reduced LCO, resid and coke yields. HP
Sanju Kumari has been working in the energy industry for 7 yrs. She works as a Manager – R&D at the Hindustan Petroleum Green R&D Centre in Bengaluru. She earned an M.Tech degree in chemical engineering at the Indian Institute of Technology in Kharagpur. Her research pertains to FCC catalyst/additives development and evaluation, process simulation and technical services related to the FCC domain.
Hemant Mishra has been working in the energy industry for 7 yrs. He works as a Manager – R&D at the Hindustan Petroleum Green R&D Centre in Bengaluru. He earned an M.Tech degree in chemical engineering at the Indian Institute of Technology in Kanpur. His research is focused on projects related to fluidized bed internals design and computational fluid dynamics (CFD), process simulation and technical services in the FCC domain.
Somanath Kukade is a Chief Manager-FCC at the Hindustan Petroleum Green R&D Centre in Bengaluru. He has 20 yrs of research experience and holds a BS degree from the National Institute of Technology, Karnataka, and an M.Tech degree from the Indian Institute of Technology, Kharagpur, both in chemical engineering. He has 28 granted patents for FCC processes and catalyst/additives. His areas of management include gas-solid fluidization, cold flow hydrodynamics, CFD, FCC process simulation, FCC catalyst evaluation/pilot plant studies, FCC process design and process development, technical services/troubleshooting for FCCUs and the scale-up of catalysts and additives.
Pramod Kumar is a General Manager in the Corporate R&D Center of Hindustan Petroleum Corp. Ltd. in Bangalore, India. He has more than 24 yrs of experience in process design, research, engineering and technical services in FCC, delayed coking, biomass conversion processes, methane pyrolysis and catalyst scale-up. He holds an M.Tech degree in chemical engineering from IIT-Kanpur. He is responsible for the commercialization of FCC feed nozzles, the catalytic visbreaking process, and FCC catalysts and additives. He has been awarded more than 30 patents in the FCC, crude-to-chemical, catalyst, etc., segments.