FCC co-processing of biogenic and recyclable feedstocks: Part I

Refinery sustainability drivers predicate a focus on renewable and recyclable feedstocks and the challenges and solutions for co-processing them in FCC units.

Jon Strohm, Darrell Rainer, Oscar Oyola-Rivera and Clifford Avery

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Article Summary

To adapt to the world’s energy and material transition, refiners and chemical manufacturers are challenged to rethink their processes to accommodate the use of renewable and recyclable (R&R) feedstocks. Depending on the installed assets, available feedstocks, and local incentives and regulations, different R&R feedstocks may be selected, and different routes towards valorisation may be taken. A number of these strategies are illustrated in Figure 1, where the crucial role of catalytic processes such as FCC and hydroprocessing is apparent.

We can follow the industry trends by reviewing the publicly available International Sustainability and Carbon Certification (ISCC) requests. Ketjen categorises the R&R feedstocks to the FCC under the three headings described in Figure 1. These categories are based on their source, hydrocarbon types, general characteristics, and the overall process and catalytic challenges for the FCC unit.

Fats, oils, and greases (FOG) are triglyceride based, with plant and animal oils as the source. Of the FOGs, used cooking oil (UCO) is the most difficult to process due to the decomposition and added metals from cooking/frying. Crude or unprocessed vegetable oils may have elevated metals if not refined (bleached, degummed). FOGs are a high molecular weight (MW) paraffinic/olefinic oil. The second classification is waste plastic oil (WPO). The WPO, with a boiling point in the naphtha/diesel range and the K-factor dependent on the source, is produced by liquefaction/pyrolysis of some type of polymer. This product will exhibit a boiling point in the diesel range, from paraffinic to aromatic, depending on the source.

Plastic contaminants
The source of plastic is particularly important, determining the aromaticity, contaminant metals levels, and oxygen content (if present). The most common plastics (polypropylene [PP], and polyethylene [PE], polystyrene [PS]) are low in metals and oxygen. Waste electrical and electronic equipment (WEEE) along with tyres is the most difficult to co-process and can contain elevated metals and other contaminants. Finally, bio-oil (cellulosic or bio-waste applications) represents the third group and exhibits elevated metals, contaminants, aromatic content, oxygen, and water content.

Many refiners have either conducted or are considering trials for processing plant, animal-based oils, or recycled oils in their units, and some of these have chosen to declare their use through the ISCC. The focus of this review is specifically on the ISCC certification as an indicator of industry trends.

ISCC certification is a voluntary programme applicable to the bio-economy and circular economy, including food, feed, chemicals, plastics, packaging, textiles, and renewable feedstock derived from a process using renewable energy sources. A wide variety of biomass, waste and residues, non-biological renewables, and recycled carbon materials can be certified under ISCC.

Certification and co-processing
Co-processing can cover anything from converting the source material to oils, fuels or chemicals, polymers, or final products. A survey of these certifications can provide a good indication of the industry trends in making R&R products. Since 2010, there have been more than 52,000 certificate requests. Of these requests, more than 26,000 (roughly half) specify FOG as the feed. In 2023 alone, there were more than 3300 requests for processing FOGs (see Figure 2), with only 255 for processing waste plastic (WP). This number is far lower than for the FOGs, but the increase on a year-by-year basis has been significant since the first WP applications appeared in 2018. There are far fewer bio-oil certificates. Certificates are generally valid for one year, and the numbers include recertification cases. Co-processing trends are clear (Figure 2, line). The first co-processing certificate was in 2018, and the number of certificates has increased significantly since 2020.
Co-processing applications are for a variety of process units, including hydrotreating, steam cracking, FCC, distillation, coker, and many other routes. The number of co- processing certificates has increased from four in 2019 to 118 in 2023. Approximately 40 of the applications were to process FOG, with 11 for WP and eight for bio-oils. While the number of plans to co-process WPO and bio-oils has been considerably lower than that of FOG, there has been an increase over the last couple of years.
WP is reaching our waterways and landfills. Globally, there is a need to establish more thorough, efficient ways to recover and recycle the 250+ MM tons/year of highly cost-effective product. Various companies are pursuing more sustainable, systematic approaches to gathering, collecting, cleaning, and sorting plastics, establishing them as the recyclable resource they were designed to be. Eleven companies received WP co-processing ISCC status, and many others recycled WP in 2023.

Plastics recycling codes
Plastics have several classifications of recycling codes, facilitating the collection and disposal of products. The most popular classification, plastic recycling code 1, or polyethylene terephthalate (PET), is mechanically recycled or co-processed to provide containers for drinkable products (water, sodas). PET contains elevated oxygen and is hydrogen deficient. Some mixed plastic waste (MPW) streams contain levels of PET. The oxygen and low hydrogen represent an added concern for PET and MPW. A hydrotreating guard bed or thermochemical conversion technology to remove the elevated contaminants is desired before sending it to the FCC unit. For chemical recyclers, high-density polyethylene (recycling code 2), low-density PE (code 4), PP (code 5), and PS (code 6) have desirable properties for units like the FCC. These plastics are high in iso-paraffinic and iso-olefinic (codes 2, 4, and 5) or mono-aromatic (code 6) hydrocarbons and can be cracked to transportation fuels or processed back as plastic monomers. For the FCC, PVC (code 3) will require additional processing due to the high chloride content and hydrogen deficiency.

The most difficult WPOs to co-process are WEEE and end-of-use tyres. Computers and other electronics may have flame retardant and other atypical metals. Due to these elevated metals (see Figure 3), WEEE will need additional processing before sending to refining units like the FCC. There are more than one billion cars on the road globally. These vehicles need to replace tyres regularly.

Isolating contaminants (WPO)
There is an increasing focus on mechanically and chemically (pyrolysis/liquefaction) recycling these tyres.1 Tyres contain plastics that are high in nitrogen (polyurethane, nylon 6), sulphur (vulcanised rubber), and oxygen (polyurethane, polymethyl methacrylate, nylon 6). The FCC will require hydroprocessing or other types of contaminate removal before co-processing at high levels.

Ketjen has received a wide range of WPOs produced from various feedstocks and liquefaction/pyrolysis processes. In one such collaboration, neat WPOs from various liquefaction/pyrolysis processes were received from a company producing WPO. By isolating PP, PE, PS, WEEE, and tyres, the hydrocarbon types, metal levels, and other properties can be identified (see Figure 3). Assays of the received WPO samples were completed while also successfully evaluating FCC cracking performance, product yields, and properties to provide FCC unit yield projections and models for refiners.

Biogenic feed options
Over the last two decades, Ketjen has evaluated various biogenic feed options for both hydroprocessing and FCC applications. Like WPO, biogenic feed options can be diverse in composition, properties, and challenges for FCC co-processing. The biogenic sourced feedstock options include FOG and bio-oils (Figure 1). FOGs are mainly triglycerides from edible and non-edible plant-derived oils (palm oil, soybean oil, rapeseed/canola oil, distillers’ corn oil, jatropha oil, and pongamia oil), tallow, extracted lipids from algae, and UCO.

The paraffinic nature of triglycerides in FOG makes the co-feed highly crackable in the FCC unit. FOGs are soluble in conventional fossil feeds, do not contain free water, and have relatively low oxygen content (~11 wt%) that can be readily removed through hydroprocessing or catalytic cracking. They are produced at an industrial scale, exceeding 1 Mb/d in 2023. Regional availability and direct competition for use can lead to high pricing and greater price fluctuation. Competing conversion pathways for this feedstock include bio-/renewable diesel, SAF-HEFA, and food products.2

In the US, increased biodiesel, renewable diesel production, and sustainable aviation fuel (SAF) have inflated the price of soybean oil (SBO), as reflected by SBO price increases of more than 100% over the last few years. The use of crude FOGs that have not undergone pretreatment processes can help reduce feedstock costs to the refiner, but it will create additional FCC operational and catalytic issues. While UCO and inedible animal fats/greases do not directly compete for food use and are generally lower cost, they contain higher levels of metal contaminates and free fatty acids.

Although there is considerable fluidity in regulatory policies, financial incentives, and economics surrounding UCO and tallow, the increased incentives and mandates for use of waste oils have created strong competition for UCO supply, resulting in spot pricing comparable to virgin SBO. Evolving regulations and incentives, particularly in the EU and US, will place a higher value on renewable diesel and SAF derived from UCO (as a waste feedstock that does not compete with food or land usage). As a result, it is forecasted that demand for UCO could exceed the supply, further driving pricing for UCO over the price of SBO and canola oil in the next several years.

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