new-generation catalysts are reserved for more demand- ing zones. CarboDump, UltiCat, and EBoost are marks of Eurecat. Q How can unpredictable cycle performance be controlled when co-processing renewables? A Rich Smith, Advisor, Becht, rsmith@becht.com Factors to consider when creating predictable, and ideally longer, reactor cycle lengths focus on reactor operations and catalyst considerations, as well as the immediate impact of co-processing renewables. As discussed elsewhere, these impacts include increased hydrogen consumption and associated first-bed temperature rise. Reactor average temperatures required to meet product specifications may also increase. Before addressing factors that influence reactor catalyst run length, it is important to recognise that other parts of the plant may be affected during the cycle. Co-processing renewables can introduce or shift damage mechanisms and change which equipment is most susceptible. Two exam- ples include the movement of the water dewpoint further upstream toward the reactor in the effluent cooling system due to increased water production, and an increased poten- tial for carbonate stress corrosion cracking (SCC) resulting from CO₂ generated by decarboxylation reactions. Manage renewable feedstock qualities Consistent and effective renewable feed pretreatment is critical to maximising catalyst utilisation. Of particular impor- tance are maintaining stable and low levels of alkali and alka- line earth metals, other metals, filtrable solids, chlorides, and acid number. Consider catalyst impact: hydrotreating base metals and dewaxing Ni-Mo–based catalysts are generally preferred when co-pro- cessing renewable feedstocks with fossil-origin feeds. This preference is typically attributed to the higher sensitivity of Co-Mo active sites, relative to Ni-Mo, to temporary deacti- vation from CO produced during decarbonylation reactions associated with renewable feed hydrotreating. Catalyst run length must also be considered when produc- ing distillate products for markets with stringent cold-flow property specifications (e.g., cloud point, pour point, and cold filter plugging point). If a distillate dewaxing catalyst is used in the same reactor as the hydrotreating catalyst to address impacts from normal paraffins produced during renewable feed hydrotreating, the resulting displacement of hydrotreat- ing catalyst volume should be considered. In addition, the potential impacts on light ends and naphtha production, particularly at end of run, should be accounted for. Manage hydrogen partial pressure Increased propane and CO/CO₂ formation will reduce hydro - gen partial pressure if not properly managed. In units with recycle loops and amine absorbers, care must be taken to manage increased rich amine loading from combined H₂S and CO₂. In systems without amine absorbers, higher
hydrogen bleed rates may be required to control CO₂ and propane build-up in the recycle gas. Avoid unmanageable reactor pressure drop build-up Renewable feeds typically contain higher levels of phos - phorous, heavy metals, and calcium than fossil-origin feeds, making proper grading and optimisation of demetallation catalyst essential. Changes in feed acid number, combined with susceptible metallurgy in elevated-temperature feed sections, may also increase corrosion rates, contributing to reactor pressure drop build-up from corrosion products. A Dhairya Soni, Technical Service, Renewables Lead, Crystaphase, Dhairya.soni@crystaphase.com Cycle length in co-processing units can become unpredict- able when the fouling drivers for that specific service are not clearly understood. Contaminants drive fouling not only in the hydrotreater but also in upstream equipment such as feed preheat exchangers, which can accelerate pressure drop rise. Co-processing adds complexity because renewable and fossil feedstocks can each introduce unique foulants. Fossil feeds with high total acid number (TAN) can generate corro- sion products that build up as solids in the reactor. Renewable feeds can contain higher levels of phosphorus, metals, and free fatty acids (FFA), each of which can contribute to foulant formation through different mechanisms. In both feed types, higher unsaturation can increase the tendency for carbon- based polymerisation deposits. Getting cycle performance under control starts with more frequent, more accurate combined-feed analytical testing so operators can quantify what is being delivered in the feed and connect it to ∆P trends. From there, lowering contami - nant levels – by purchasing a pretreated renewable feed or pretreating on-site – can significantly reduce foulant genera - tion and extend run length. Even once contaminants in the feed have been reduced, a strategically designed filtration system in the hydrotreater is often necessary, as fouling can still be prevalent and pressure drop can still be the cycle-limiting constraint. Incorporating catalytic activity into a filtration system using materials such as ActiPhase technology encourages fouling in the filtration section rather than deeper in the reactor, thereby helping to slow pressure drop growth. ActiPhase is a mark of Crystaphase. A Joris Mertens, Principal Consultant, KBC (A Yokogawa Company), joris.mertens@kbc.global Co-processing comes with a risk of catalyst deactivation, corrosion and cold flow property degradation, as we dis - cussed in PTQ Q1 2026. The main takeaway was that a cost/ benefit analysis should be made when increasing the levels of co-processing bio-feeds in conventional hydrotreaters. However, once a co-processing baseline has been estab- lished, there is still a risk of premature shutdown, and con- trolling cycle performance when co-processing vegetable oils and animal fats is primarily an issue of controlling the quality of the biofeeds. Biofeeds should be checked prior to feeding to a hydrotreater, just as a refinery will not replace a
6
Catalysis 2026
www.digitalrefining.com
Powered by FlippingBook