Catalysis 2026 Issue

legacy crude mix with an equal amount of anything offered without looking into contaminants and their impact on prod- uct yields. Phosphor and metal content of co-processed biofeeds should be monitored to avoid accelerated catalyst deac- tivation; the FFA and chlorine content needs to be tracked to reduce corrosion risk; and polyethylene should be limited to avoid equipment plugging. Special attention is required when co-processing feeds without pretreatment, not so much because the contaminant level is higher than pre- treated feeds, but because contaminant content tends to fluctuate more in untreated feeds. Storage is also a risk area: vegetable oils and animal fats should be stored as cool as possible to minimise thermal degradation, but warm enough to avoid solidification. In addition, contact with water, especially oxygen, during stor- age should be avoided. Somewhat less critical but nevertheless not to be neglected is the fatty acid structure of the co-processed biofeed. A higher content of C 18 + acid chains will increase the cloud point of the product, and hydrogen consumption will be affected by the content of unsaturates in the triglyc- eride structure. A Ranoo Pathak, Technical Service Specialist, Topsoe, RAPK@topsoe.com Co-processing renewables into traditional fossil units brings operational challenges. This can sometimes result in unpre- dictable cycle performance, mainly driven by variable feed quality, different reaction chemistry versus fossil feed, and insufficiently adapted monitoring. Controlling this requires a focused approach to feed management, a tailored catalyst system, an operating strategy, and better monitoring. The renewable feed quality can vary from batch to batch. To ensure the unit receives as stable a feed quality as pos- sible, clear limits on the co-processing share are required based on available hydrogen, reactor temperatures, and the target cycle length. In addition, strict limits on feed speci - fications for water, oxygen content, TAN, contaminants (Na, K, Ca, Mg, Fe, Si, P, Cl), solids, and polymers/gums are essential. Off-spec feeds (for example, higher contaminant levels) must either be rejected or processed at reduced co- processing rates. In parallel, renewable feeds should be stored under nitro - gen blanketing to limit oxidation and gum formation, which can lead to equipment fouling. Where possible, tanks with capability should be used to smooth out batch-to-batch quality swings. Having a clear derating strategy (i.e., allow- able renewables) share as a function of feed quality param - eters helps avoid sudden cycle deterioration. Much of the unpredictability in the performance cycle is linked to faster catalyst deactivation and pressure drop build-up due to high reactivity of the renewable feeds, as well as high levels of contaminants and other impurities. Robust front-end protection is therefore critical. High- efficiency filtration upstream from the reactor helps minimise solids entering the unit. Within the reactor, achieving the tar- geted cycle length and stable operation requires a compre- hensive catalyst system consisting of specialised renewable

grading catalysts with improved water tolerance and opti- mised hydrogenation activity, followed by HDS/HDN and, where relevant, selective dewaxing catalysts. Operating strategy must be revisited for renewables. Co-processing renewables increases hydrogen consump- tion and exotherm. Therefore, sufficient hydrogen partial pressure must be maintained to avoid local hydrogen starva- tion and coke formation. Reactor inlet temperature and bed ΔT should be closely controlled; where available, inter-bed quench should be used to limit hot spots. Change in the co- processing share should be made gradually, rather than in step changes. Finally, robust monitoring and process controls are key enablers. Regular tracking of feed composition (including renewable share and contaminants), reactor pressure drop and ΔT, hydrogen consumption, hydrogen partial pressure, recycle gas composition, and product quality enables early detection of abnormal trends. Process controls maintain the unit to operate within a safe envelope by adjusting the renewable co-processing ratio and severity against con- straints such as temperature limits, ΔP trend, hydrogen par - tial pressure, and gas-to-oil ratio. In practice, stabilising cycle performance when co‑pro - cessing renewables can be achieved by regulating feed quality, a tailored catalyst system, an appropriate operating strategy, and continuous monitoring. Q What is needed to scale up chemical recycling of waste- plastic pyrolysis oils to the 10-30% range? A Ignacio Fabian Costa, Licensing Manager, IFCO@ topsoe.com and Dmitry Kuzmichev, Technical Service Specialist, DKU@topsoe.com, Topsoe Scaling chemical recycling of waste-plastic pyrolysis oils (PPO) to the 10-30% range requires overcoming both tech - nological and economic barriers across the entire value chain. While upgrading technologies such as Topsoe’s PureStep have reached full commercial maturity, the main constraints now lie upstream in the continuous, economical production of high-quality pyrolysis oil and in broader market conditions surrounding steam cracking and plastic recycling. One of the biggest bottlenecks today is achieving con- tinuous, industrial-scale, and energy-efficient pyrolysis oil production. Many existing pyrolysis technologies scale by adding more identical trains rather than increasing throughput per unit. This leads to higher Capex without true economies of scale, which limits cost competitiveness and restricts the total volume of PPO available for upgrad- ing. There are many promising technologies evolving, and hopefully, in the upcoming years, this will gradually become less of a constraint. A second, often underestimated challenge is logistics and siting. To supply a world-scale pyrolysis plant, large volumes of waste plastic have to be collected and transported to one location. The alternative approach, many smaller, local pyrolysis units, reduces waste transport distances but then requires transporting PPO to centralised upgrading and steam cracking hubs. Either way, there is a trade-off between transporting low-density, heterogeneous solid waste and

Catalysis 2026