• Catalyst : A shift from NiMo to CoMo catalysts will be required to limit CO inhibition, and the isomerisation potential should be considered to limit cold flow property degradation. • Hardware adjustments : More limited adjustments to hardware can be considered, such as quench changes, col- umn improvements, enhanced water separation, and better drainage systems. Increasing co-processing will inevitably come at a cost in terms of catalyst, cycle length, feed, and capital expen- diture. The key is to balance these costs against the ben- efits using the following techno-economic approach that includes: • Risk identification, as mentioned earlier. • Process simulation, design verification, and collaboration with the catalyst supplier to identify and quantify mitigation measures. • Economic evaluation that balances the increased product value against operational and capital costs. A Milica Folić, Product Line Director, Topsoe, MFOL@ topsoe.com Raising the renewable feed co-processing ratio for sus- tainable aviation fuel (SAF) from the ASTM D1655 limit of 5% to 10% or higher demands a holistic strategy, balanc- ing catalyst performance and process safety to maintain Optimising unit performance at elevated co-processing levels means fine-tuning temperature, hydrogen-to-oil ratio, and space velocity for controlled reactions and desired yields reliability and product quality in existing refinery units. Co-processing renewable feedstocks introduces opera- tional changes, including high hydrogen demand for oxy- gen removal and olefin saturation, increased exotherms, increased water formation, and corrosion risk. These feedstocks also contain high levels of contami- nants, such as metals and phosphorus, which can accelerate catalyst deactivation. Therefore, specialised hydrodeoxy- genation catalysts with optimal activity become essential to efficiently remove oxygen and contaminants. Additionally, a deep dewaxing is required to convert n-paraffins into i-paraffins, ensuring the final product meets jet fuel speci - fications (for example, freezing point) while keeping the renewable molecules in the jet product. Topsoe’s selective dewaxing catalyst TK-930 D-wax has demonstrated opti- mal results for this purpose. Increasing the co-processing share to 10 vol% or more would require improved feedstock quality, consistent con- taminant monitoring, and a tailored catalyst management strategy. In some cases, additional reactor volume or cata- lyst beds may be necessary to maintain throughput and
product quality over a reasonable cycle length. On the pro- cess side, limitations intensify at higher blends: more water and heat increase the risks of exotherms, corrosion, and process instability. Robust water management, including improved separa- tion, treatment, and possible wash water injection, is critical. Existing metallurgy may need upgrades to resist corrosion from increased water and organic acids. Hydrogen supply, distribution, gas-liquid separation, and compressor capac- ity must be reviewed and potentially upgraded to handle higher demands and flows. Optimising unit performance at elevated co-processing levels means fine-tuning tempera - ture, hydrogen-to-oil ratio, and space velocity for controlled reactions and desired yields. With ASTM D1655 currently capping co-processing at 5%, any increase requires regulatory compliance and con- tinuous, accurate tracking of sustainability attributes and biogenic content for credits. Each refinery faces unique challenges, so partnering with a trusted catalyst and technology provider through feasibility studies, process design, and catalyst selection ensures a safe, efficient transition to higher SAF co-processing when regulations permit. This integrated approach positions refiners to meet future mandates and capitalise on the growing SAF market. Q Under what circumstances do you see transmix pro - cessing facilities delivering value? A Rainer Rakoczy, Technology Advisor Fuels, Clariant International Ltd , rainer.rakoczy@clariant.com There is always interest in upgrading transmix fractions to generate value beyond skimming through distillation by midstream companies operating pipelines or termi- nals. There are various options for generating high-value hydrocarbons through flexible hydroprocessing solutions that deliver value within or beyond the fuel market. With skid-mounted modular concepts improving constantly, even very small streams can be handled with attractive economics. The biggest obstacle for many interested com- panies is the transformation from a skimming or distilla- tion operation to a conversion operation, particularly from the perspective of the local authorities’ permit process. Clariant receives numerous inquiries in this field and offers case studies. Q How can higher volumes of straight-run VGO be con- verted to Euro VI quality distillates? A Rainer Rakoczy, Technology Advisor Fuels, Clariant International Ltd, rainer.rakoczy@clariant.com With the reduction in demand for gasoline and other light products, VGO conversion to optimise distillates yields that fulfil Euro VI requirements can be quite challeng - ing, focusing solely on FCC unit operation. Having VGO pretreating available, there are options to apply Hydex catalysts to optimise the VGO pretreater’s product slate to gain value from kerosene fractions and ultra-low sul- phur diesel.
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PTQ Q1 2026
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