REFINING INDIA 2025

refining india 2025

Co-processed SAF via the kerosene hydrotreater is low-cost and readily available

Raju Chopra and Ignacio Costa TOPSOE

volumes. The catalyst system must manage both deoxygenation and dewaxing to ensure jet fuel meets freeze point requirements. Meeting freezing point specifications with dewaxing catalysts Biogenic feedstocks, when hydroprocessed, tend to produce straight-chain paraffins (n-paraffins), which can raise the freezing point of the jet fuel product. This poses a challenge when meeting strict SAF speci- fications, such as Jet A or Jet A-1. To meet the cold flow properties requirements of Jet A and Jet A-1 fuels, deep dewaxing of these biogenic paraffins is essential. To address this, highly selected, high- performance dewaxing catalysts such as Topsoe’s TK-930 D-wax™ are deployed. These catalysts use selective isomerisation to reshape the molecular structure, lowering the freezing point without sacrificing bio- genic carbon retention or yield. The n-par- affins are isomerised to iso-paraffins, which have much better cold flow properties with- out losing any biogenic carbons to the gas and naphtha ( Figure 1 ). This catalyst has been designed to operate even at reactor pressure as low as 25 barg. At this level, a highly selective dewaxing catalyst and HDO selective grading serve as a drop-in replace- ment for existing kerosene hydrotreaters. Figure 2 demonstrates how to maximise SAF yield in a kerosene hydrotreater with the right catalyst loading, using selective hydrodeoxygenation (HDO) and isomerisa- tion catalyst.

As the aviation sector accelerates its decar- bonisation efforts, sustainable aviation fuel (SAF) is seen as the most promising tool to cut lifecycle emissions. One of the quick- est and readily available ways to scale SAF output is by using co-processing – a method that integrates renewable feedstocks directly into conventional refinery units. It is also cost-effective and easily implementa- ble because co-processing leverages cur- rent refining, transport, and storage assets, minimising capital expenses. Among the ways refineries can introduce co-processing, the kerosene hydrotreater stands out as the most immediate and effi- cient route. However, what are the technical enablers of co-processing SAF in kerosene hydrotreaters, and why is this approach par- ticularly suitable in terms of readiness, effi- ciency, and compliance? Co-processing: rapid route to renewable jet fuel Co-processing blends renewable feed- stocks, such as used cooking oil, vegeta- ble oil or animal fats, with fossil-based feed in existing refinery units. The result is a drop-in, partially renewable fuel that com- plies with American Society for Testing and Materials (ASTM) specifications for jet fuel. Unlike standalone renewable fuel units, co-processing requires only limited invest- ment. It takes advantage of existing assets and can be implemented quickly with rela- tively simple changes. Topsoe, for exam- ple, has supported more than 90 successful co-processing projects globally to produce various renewable fuels, demonstrating that this pathway is not experimental – it is proven, refined, and reliable.

Number of carbon atoms: 14 Boiling point: 254˚C Melting point: 6˚C

Hydrocracking

Number of carbon atoms: 18

Boiling point: 317˚C Melting point: 28˚C

-25

-50

Normal alkanes 3-methyl isomers 2-methyl isomers

Hydroisomerisation

-75

-100

Number of carbon atoms: 18 Boiling point: 313˚C Melting point: -6˚C

Carbon atoms in molecule

Figure 1 Hydroisomerisation as a more efficient pathway for lowering the freezing point

Fossil naphtha + gases Renewable propane

Fossil kerosene Renewable feed

Hydrotreating reactor

Splitter

Biogenic carbon Fossil carbon

HDO/HDS catalyst

2.7%

Dewaxing catalyst

Jet A or A - 1 SAF

2.5%

Figure 2 Co-processing renewable feedstocks in a kerosene hydrotreater

Fine-tuning operating conditions for optimal output

involves a few technical adjustments, and it may not be feasible for every kerosene hydrotreating unit. Renewable feedstocks contain high lev- els of oxygen, which must be removed during hydroprocessing. This increases hydrogen demand – sometimes by more than 30 times the consumption per volume of feedstock compared to fossil kerosene. Compressor upgrades or process adjust- ments may be needed to ensure supply. The kerosene hydrotreating unit should be eval- uated to ensure it can meet the tempera- ture requirements of the dewaxing catalyst. If the existing reactor heater cannot provide the necessary heat duty, an additional heat source may be required to achieve the new operating temperature. Corrosion control is an important ele- ment, as acidic components and chlorides in renewable feed can trigger corrosion. Material compatibility checks and, in some cases, repositioning of wash water injection points may be required to manage the for- mation of ammonium chloride salts. Also, triglyceride-based feedstocks produce more water as oxygen is removed. Units must account for this by increasing water handling capacity, particularly at the sepa- ration stage. Co-processing demands tailored catalyst configurations and, in some cases, higher

offer different trade-offs. Diesel hydrotreat- ers could be an option for producing SAF; however, the renewable carbon is dispersed across the diesel product range rather than being concentrated in jet fuel, making the SAF yield lower per input volume and, there- fore, less cost-competitive. With hydrocrackers, one advantage is flexibility. They can handle a broad range of feedstocks and are typically equipped with hydrocracking and/or dewaxing catalyst. They can also produce multiple renewable fuel types, including SAF. However, they are also key hydroprocessing units in the refin- ery, targeting a series of objectives, which can be detrimental to SAF yields, making this solution also less cost-competitive. It has been found that the majority of biogenic content (approximately 80-85%) is landed in diesel product. The kerosene hydrotreater, even with operating conditions that may not be opti- mal for advanced catalyst systems (for example, dewaxing catalyst), provides a narrow, efficient path for SAF producers who aim to scale rapidly and meet immedi- ate SAF mandates with minimal delay.

Operating conditions for co-processing SAF vary depending on feedstock type, target product, and unit design. Key parameters include: • Hydrogen-to-oil ratio : Must be increased to account for the high hydrogen consump- tion of the renewables feedstocks. • Temperature and pressure : Need to be optimised to balance reaction rates, cata- lyst activity and selectivity. • Liquid hourly space velocity (LHSV) : Influences contact time and conversion effi- ciency; must align with catalyst capacity and feed characteristics. Conclusion Co-processing is a fast track to SAF pro- duction that can function as a short-term solution to comply with the upcoming SAF mandates in the next few years. Among vari- ous options, co-processing renewable feed- stocks in kerosene hydrotreaters is a great choice for SAF production with respect to lower operating cost, lower capital invest- ment, higher recovery of biogenic carbon in the SAF product, short implementation time, and low payback period. This method can save up to two years of construction time compared to building new facilities.

Why the kerosene hydrotreater is the fastest route for SAF

Co-processing to produce SAF can be implemented across various hydroprocess- ing units in a refinery, including kerosene hydrotreaters, diesel hydrotreaters, and hydrocrackers. Among these, the kerosene hydrotreater and hydrocracker stand out as the most effective units for SAF production, offering flexibility and compatibility with current refinery operations. The kerosene hydrotreater, for instance, targets the jet fuel fraction specifically. This means more of the biogenic carbon from renewable feedstock ends up in the final SAF product. This is especially relevant in some regions, where carbon-14 analysis is used to verify renewable content. Another benefit is simplicity. Co- processing in this unit can reach up to 5% of renewable feedstock by volume, and it will require changes to the catalyst system of the unit and an increase in the hydro- gen supply. However, the low capital costs enable refiners to launch SAF production quickly and with a short payback period. Kerosene hydrotreaters vs alternative units While diesel hydrotreaters and hydrocrack- ers are also viable for SAF production, they

Modifications for co-processing in the kerosene hydrotreater

Although straightforward, co-process- ing SAF in the kerosene hydrotreater still

Contact: RACH@topsoe.com