Mar-2025

Co-processing of chemical recycling products in FCC units

To perform a techno-economic assessment it is important to determine the crackability and the yield structure effects of alternative feedstocks.

Rafael Orejas Contreras, Repsol
María Bescansa Leirós, Grace GmbH & Co. KG Spain
Nelson Olong and Stefan Brandt, Grace GmbH

Article Summary

Advanced chemical recycling is projected to increase over the coming years and decades to improve the circularity of plastics, reduce environmental pollution, and decrease the dependency on fossil crude. The use of unconventional feedstocks, such as waste-derived streams in refinery processes, continues to be evaluated from an economic, regulatory, and environmental perspective.

As Figure 1 shows, it is projected that the availability of plastic waste for chemical recycling will increase to about 7-20 million tons by 2030, with continued growth thereafter. Ideally, mixed plastic waste is converted by advanced chemical recycling processes to monomers as feedstocks for new plastic production to maximise carbon circularity. However, suitable conversion processes are not yet commercially available at scale. Pyrolysis technologies are finding increased application for advanced chemical recycling, producing a liquid product, plastics-derived pyrolysis oil (PDPO), which requires secondary conversion in existing refining or petrochemical assets for valorisation.

The fluid catalytic cracking (FCC) unit is one of the most flexible units in a crude oil refinery. The unique properties of the FCC unit allow significant adjustments to unit operation and, therefore, yield patterns within short periods of time. The daily catalyst addition allows for catalyst optimisation while the unit is operational.

Severe catalyst deactivation can be proactively mitigated by increased catalyst additions within the catalyst management strategy of the refinery. Longer term catalyst deactivation factors will require catalyst reformulation in collaboration with the FCC catalyst supplier. However, any significant feedstock change requires a thorough risk assessment regarding its consequences on unit operation, conversion, yield pattern, catalyst inventory and, if possible, downstream processing.

Risk assessment considerations
Determination of the physical and chemical attributes of respective feedstocks will provide a basic understanding of potential conversion and yield impacts and indicate contaminants that might affect catalyst management as well as downstream equipment. Physical attributes include density, viscosity, refractive index, boiling point distribution, and moisture content, influencing handling, transport, and processing. Chemical attributes involve elemental composition, molecular structure, and the presence of specific compounds, which determine reactivity, conversion efficiency, and compatibility with catalysts.

For example, Figure 2 depicts results from different plastics-derived feed samples received by Grace. The data proves the heterogeneity of the received samples in terms of contaminant and heteroatom contents and allows an initial assessment of impacts on FCC catalyst, operation, conversion, yield structure, and emissions.

Some of the feedstocks with very high Calcium (Ca) or Conradson carbon content will have an impact on catalyst deactivation and unit operation. Calcium is a known poison to the FCC catalyst, which deposits on the external surface of the catalyst particle, blocks feed molecule entry to the catalyst pore system and, therefore, affects the diffusion of feed or intermediate molecules to the active cracking sites (see Figure 3).

In addition, calcium is known to contribute to zeolite Y destruction by catalysing the dealumination processes, leading to the collapse or degradation of the zeolite framework. This results in a loss of surface area, pore volume, and catalytic activity, significantly impairing the catalyst’s performance. The presence of calcium not only reduces cracking efficiency but also increases the likelihood of deactivation and fouling, necessitating frequent regeneration or replacement of the catalyst. These effects make calcium a critical contaminant to monitor and manage in FCC feedstocks.

Based on the chemical determination of contaminants in alternative feed samples, a steady-state equilibrium catalyst (Ecat) metals calculator might be used to allow an understanding of potential catalyst deactivation effects.

To perform a techno-economic assessment, it is important to determine the crackability and yield structure effects of alternative feedstocks too. For this purpose, different scales of pilot plant equipment are available, such as fixed bed, fixed fluidised bed, and fully circulating riser pilot plants. An example of such an evaluation of catalytic testing results is described in the following discussion.

Project scope
Repsol is a leading multi-energy company that works to advance the energy transition using different technologies that contribute to reducing the carbon footprint. With its commitment to a sustainable world and the vision to be a global energy company that relies on innovation, efficiency, and respect to create sustainable value in the service of societal progress,² Repsol believes that the current energy transition should be urgently rethought and a new, fairer model set up so as to involve all of society and leave no one behind.³

In connection with the company’s vision for the energy transition, Repsol is considering the potential of processing lower carbon intensity feedstocks in FCC units. Such feedstocks can be of biogenic origin or waste-derived feedstocks.

Repsol and Grace collaborated on the assessment of yield structure effects of waste plastics-derived feedstocks. The refining company provided two plastics-derived pyrolysis oil samples (PDPO A and PDPO B) to support an initial techno-economic assessment (TEA) of processing such feed streams in an FCC unit (see Table 1).

Though unconventional feedstocks like bio- or waste-derived feed streams are co-processed in the refinery, the yield structure from such feed streams is of high interest in assessing the respective margin uplift. In most cases, pilot plant co-processing experiments in blends with fossil feed components are performed to assess the incremental yields from the alternative feed component.4 However, testing the alternative feedstock pure allows for similar information, if not limited by processing challenges in FCC pilot plant equipment.

Test programme
Waste plastics, when cracked, might yield more light olefins or aromatic compounds depending on the polymer type. To evaluate the crackability and resulting yield effects of cracking the plastics-derived pyrolysis oil samples, Grace’s proprietary single-receiver short-contact microactivity test unit (SR-SCT MAT)5 was selected. The SR-SCT MAT unit has proven its versatility in screening unconventional FCC feedstocks where impacts on testing equipment and process cannot be ruled out.

The respective samples of PDPO were compared to a typical vacuum gas oil (VGO) reference feed and converted in the SR-SCT MAT unit using a standard equilibrium catalyst sample from a VGO processing FCC unit.