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ERTC 2025

Chemical recycling at scale for high-quality drop-in naphtha production

Milica Folić topsoe

The move toward a circular plastic economy requires the chemical recycling of mixed plastic waste so it can be turned into high- quality drop-in naphtha for steam crack- ers and new plastic products. Variability in waste composition and liquefaction meth- ods makes upgrading essential to ensure not only the drop-in naphtha quality for steam crackers, but also to absorb all the fluctuations in feedstock quality. One solution from Topsoe, PureStep™, has been developed through pilot tests of more than 60 various plastic pyrolysis oils, and delivers on-spec naphtha and heavier steam cracker feedstocks by combining advanced analysis, hydroprocessing expertise, and targeted contaminant removal. Already in commercial operation, it offers flexible solu- tions for diverse pyrolysis oils, helping turn plastic waste into valuable inputs for a more sustainable plastics value chain ( Figure 1 ). Chemical vs mechanical recycling of plastics Plastics can be recycled through two main routes: chemical and mechanical. Mechanical recycling is most effective when the waste stream is clean, sorted, and made up of a single polymer type, such as PET bottles. It can yield high-quality products with relatively low energy use, but repeated processing gradually reduces material per- formance, often resulting in ‘downcycling’ from food packaging to lower-value prod- ucts such as textiles or garden items. Chemical recycling is better suited for mixed or contaminated waste, including typical household packaging. By breaking down polymers and stripping away impu- rities, it produces feedstocks capable of making new plastics with virgin-level qual- ity, including those for food and pharma- ceutical applications. Processes such as pyrolysis and hydro- thermal liquefaction (HTL) thermochemi- cally convert solid plastic waste into plastic pyrolysis oils (PPOs), a liquid comparable in some ways to fossil feedstocks. However, PPOs contain significant levels of contami- nants (metals, halogens, and heteroatoms) that prevent direct use in steam crackers or fluid catalytic cracking (FCC) units without heavy dilution. Scaling chemical recycling and reducing dependence on virgin fossil carbon requires upgrading PPOs. Topsoe’s PureStep hydro- processing technology addresses this by removing contaminants and fine-tun- ing product properties, turning raw PPOs into high-quality steam cracker feedstock ( Figures 2 and 3 ). This bridges the qual- ity gap between pyrolysis oils and steam cracker feedstock, enabling higher recy- cling rates and supporting a robust circular plastics economy. PPOs are a growing feedstock opportunity PPOs are emerging as valuable feedstocks for refining and petrochemicals. Topsoe

Stabilisation section

Guard reactor

Main hydrotreating reactor

Conversion reactor

New plastic

FBP

Waste collection

Steam cracker

Metals

S Cl

Reactions:

Diene removal Styrene removal Light olen removal

P removal and metal removal (Si, As, Fe, etc.) Olen saturation

Halogen removal (Cl, Br, F) Sulphur removal Nitrogen removal Aromatic saturation Removal of halogens, nitrogen, sulphur, aromatics.

Hydrocracking Isomerisation

Conversion to liquid

PureStep™

Reduction of BP range, Improvement of cold ow properties.

Stabilise to avoid polymerisation reactions.

Pick up of metals and phosphorous.

Figure 1 Circular plastic economy with Topsoe’s PureStep technology

Figure 2 Technology ‘building blocks’ of PureStep

Detailed studies using scanning elec- tron microscopy reveal that conventional fossil catalysts tend to trap contaminants near the surface, leaving much of the cata- lyst unused. Topsoe’s advanced guard cata- lyst, developed specifically for PPOs, allows silicon and phosphorus to be absorbed throughout the entire catalyst structure, which increases overall capacity. This specialised catalyst also provides moderate hydrotreating activity, which is useful for removing nitrogen and chlorine and helps to limit coke formation that can deactivate the catalyst. Flexible options for upgrading PPOs PureStep technology provides adaptable methods for converting plastic pyrolysis oils into feedstock suitable for steam crack- ers. The process uses a combination of optional stabilisation, guard beds with cus- tom catalysts, hydrotreating, and optional hydrocracking, selected according to the feedstock’s properties and the desired product. Usually, at least two process steps are chosen to address the reactivity, contam- inants, and boiling range of PPOs. This approach supports a high proportion of recycled content in cracker feed and helps maintain the reliable operation of existing facilities. Expanding recycling with hydroprocessing Chemical recycling through pyrolysis is expected to play a significant part in the circular economy by supplying recycled feedstocks to current steam cracker units. Hydroprocessing is vital for expanding this value chain, as it can work with existing refinery equipment, allows for upgrades, and improves economics by enabling much greater volumes of PPOs to be used. Scaling up pyrolysis and reducing costs remain challenges, but progress is being made through collaboration across the industry and increased investment. As technologies develop and production vol- umes increase, hydroprocessing is posi- tioned to become a dependable method for circular plastic manufacturing.

began working with them in 2014, lever- aging decades of hydroprocessing experi- ence to meet rising demand for sustainable alternatives. While PPOs share traits with fossil and non-fossil feedstocks, they differ in key ways. They have a hydrogen content simi- lar to that of straight-run diesel, but contain more nitrogen and less sulphur. Compared to tyre-derived oil, PPOs are less aromatic and contain fewer impurities, which lowers hydrogen consumption during processing, delivering an economic and environmental advantage. Their manageable impurity lev- els and strong processing potential make PPOs an ideal candidate for customised upgrading solutions that align with circular economy goals and lower carbon intensity. Understanding feedstock variability PPOs contain many of the same contami- nants found in fossil-derived feedstocks, such as silicon, phosphorus, nitrogen, sul- phur, oxygen, and halogens, but in distinct molecular forms and concentrations. This difference stems from their origin: plastics carry additives and residual substances, such as stabilisers, flame retardants, adhe- sives, and other post-consumer waste components. As a result, traditional hydroprocessing methods require modification and fine-tun- ing to handle PPOs effectively. Developing catalysts specifically designed to address certain contaminants is critical. In some cases, PPOs also tend to polymerise, mak- ing early stabilisation (prior to hydrotreat- ing) necessary. Analytical testing can identify when this step is required. Optimising PPO processing demands a detailed understanding of its variability. This means collecting and evaluating sam- ples from a wide range of liquefaction tech- nologies and suppliers, and performing analysis at a molecular level to pinpoint spe- cific contaminant species, rather than rely- ing solely on bulk composition data. Producing naphtha from PPOs Compared with conventional naphtha feedstocks for steam crackers, PPOs pre- sent significant challenges. More than

Figure 3 Raw PPO and PureStep hydro- processed PPO

half of a typical PPO’s volume boils above 200°C – well beyond standard naphtha specifications – with heavy fractions often accounting for about 60% of the total. To meet boiling point limits, PureStep can incorporate hydrocracking to shift the dis- tillation profile downward. Contaminant distribution adds another layer of complexity. Fractionation studies have shown that silicon and chlorine are dispersed across the entire boiling range, from light naphtha to vacuum gas oil (VGO), rather than being confined to heavier cuts. Because even individual distillation frac- tions can hold 30-60% of the total silicon content and varying chlorine levels, sim- ple separation by fractionation is ineffec- tive. PureStep addresses this by combining deep contaminant removal with boiling point adjustment, enabling the entire PPO range to be converted into compliant steam cracker feedstock. This integrated approach ensures maximum utilisation of the feed and consistent product quality. Catalyst development for pyrolysis oils Fossil-based catalysts are sometimes applied to circular feedstocks such as plas- tic pyrolysis oils; however, custom-designed catalysts achieve much higher efficiency. Silicon and phosphorus contaminants found in PPOs have different sources compared to those in fossil or bio-based oils, which means tailored approaches are necessary.

Contact: mfol@topsoe.com