PTQ Q1 2026 Issue

Strong metal poisons As (3 ppb), Sn (?), Pb (50 ppb), Hg (3 ppb) Mass transfer inhibitors Si (1 ppm), P (0.5 ppm), Fe (20 ppb), Ni (0.1 ppm), V (50 ppb) Halogens - corrosion risk Converted to acids under hydrogenating conditions Alkali metals and alkaline earth metals Na (125 ppb), Ca (500 ppb), K (500 ppb) Other elements of possible concern (darker colour=found in WPO samples in literature)

K V CrMnFe CoNi CuZnGaGeAsSe Br Kr Al Si P S Cl Ar B C N O F Ne He Rb Sr Y Zr NbMoTc Ru RhPd AgCd In Sn Sb Te I Xe Cs Ba La Hf Ta W Re Os Ir Pt AuHg Tl Pb Bi Po At Rn Fr Ra Ac Rf Db Sg Bh Hs H Li Be Na Mg Ca Sc Ti

Figure 4 (left) Periodic table of inorganic impurities Table 1 (right) Published limits for steam cracker feedstock⁶

the second catalyst is applied in a separate fixed bed reac - tor for catalytic upgrading of the oil vapours. From the boil - ing point distribution curves in Figure 2 , it can be observed that application of the catalyst in the pyrolysis reactor sig- nificantly decreases the boiling point of the produced oil, making that a larger fraction of the oil is in the naphtha fraction and hence, suitable as a feed for steam crackers. As we look at the molecular distribution of the oil, as pre - sented in Figure 3 , we can see what has happened and the role of the catalysts. By comparing the product com- position of non-catalytic pyrolysis (left) to the pyrolysis product with the presence of a catalyst in the pyrolysis reactor (middle), it can be seen that the catalytic pyrolysis has resulted in the cracking of larger C15 + molecules into olefins. Subsequently, the product slate after the upgrading step demonstrates that, in the fixed bed reactor, these ole - fins are isomerised, creating an oil that is highly paraffinic and has very good properties to be used as a steam cracker feed (right). Hydrothermal liquefaction and gasification are alter - native primary conversion routes, particularly for mixed or contaminated plastic streams. These processes oper- ate under higher pressure and temperature. Currently, most are non-catalytical, while some catalytic processes under development require robust catalysts to withstand harsh conditions and manage a wide range of feedstock impurities. Upgrading: hydroprocessing and catalytic aromatisation Plastics that are mechanically recycled need to meet defined standards for composition, type, and level of contamination, thus limiting their provenance. The chemical recycling path- ways are complementary to mechanical pathways and can cast a much wider net of feedstock materials. It results in a wider range of compositions and contaminants that vary with source, method of collection, and intended use, which change over time. The oils produced from primary conversion are typically unstable and contain a variety of contaminants, includ - ing chlorine, nitrogen, metals, and oxygenates that must be removed before integration into petrochemical assets. Hydroprocessing (hydrotreating and hydrocracking) meth- ods, similar to those applied for upgrading fossil-derived

feeds, are very suitable for upgrading oils from primary conversion and are now being adapted for waste plastic oils (WPOs). Catalysts that stabilise reactive molecules (di-olefins), trap inorganic impurities (phosphorus, silicon) and ena- ble precise control over boiling point distributions. Guard bed catalysts are essential for protecting downstream units from catalyst poisons, while hydrocracking catalysts facilitate the production of feedstocks suitable for steam crackers. Catalytic aromatisation technologies are being developed to convert pyrolysis products into aromatic compounds (benzene, toluene, xylene), which are critical building blocks for the chemical industry. Different processes are being explored where the catalyst is employed during pyrolysis or in a separate fixed bed or fluidised bed reactor. Valorisation: integration with petrochemical assets The final stage, valorisation, involves feeding upgraded products into conventional petrochemical units. FCC units, for example, can co-process WPOs with traditional feeds to produce monomers (especially propylene), fuels, and spe- cialty chemicals. However, the presence of contaminants such as iron and sodium in WPOs can deactivate conven- tional FCC catalysts. Catalysts are designed with tailored porosity and composition to maintain activity and selectiv- ity even in the presence of high impurity loads. This inno- vation enables refiners to incorporate recycled feedstocks without compromising performance or product quality. Valorisation of WPO via steam cracking is expected to be one of the leading chemical recycling pathways in the coming decade. 4 However, there are substantial safety and operational risks when using WPO instead of con- ventional fossil-based feedstocks. This is due to the vast number of contaminants. WPO can only meet the specifi - cations set for industrial steam cracker feedstocks if they are upgraded, with hydrogen-based technologies being the most effective, in combination with an effective pre - treatment. Moreover, steam crackers are reliant on stable and predictable feedstock quality and quantity, which rep - resents a challenge as plastic waste is largely influenced by consumer behaviour, seasonal changes, and local sort - ing efficiencies.

PTQ Q1 2026