Decarbonisation Technology May 2025 Issue

SAF production via the HEFA route: chemistry and catalysis The crucial role of the catalyst system in producing sustainable aviation fuel from waste and residue oils and fats via the HEFA route

Jaap Bergwerff Ketjen

G lobal mandates and incentives are driving efforts to increase the production of sustainable aviation fuel (SAF). Although alternative methods, such as alcohol-to-jet processes and the production of e-fuels, are being developed, hydrotreated esters and fatty acids (HEFA) are expected to remain the primary feedstock for commercial-scale SAF production in the coming years ( S&P Global, 2025 ). Operators of HEFA units are increasingly inclined to switch production from renewable diesel to SAF. Several approaches can be employed to convert oils and fat streams into products that meet the specifications for the SAF component, which can be blended with conventional kerosene. These approaches are illustrated in the schematic process schemes in Figure 1 . One approach involves mixing the renewable feedstock with a conventional kerosene fraction

to be co-processed in an existing kerosene hydrotreater, producing aviation fuel with a certain renewable content that meets JET A-1 specifications. This approach requires (i) hydroprocessing of the kerosene fraction to remove nitrogen and sulphur compounds, (ii) hydrodeoxygenation (HDO) of the triglycerides, and (iii) dewaxing to reduce the freezing point of the final product, all within a single reactor under the same operating conditions. This constraint typically limits the amount of renewable feedstock that can be co-processed to no more than a few per cent. Alternatively, standalone processes can be used to convert oils and fats into a SAF stream that can be blended with conventional kerosene. In any case, HDO and subsequent hydroisomerisation (HI) of the n-paraffins generated are required. Two types of processes can be distinguished to produce 100%

Co-processing

100% HVO - Single stage

100% HVO - Two stage

Waste oils & fats in fossil kero

Waste oils & fats

HDO

HYDRO ISOMERISATION

HDO

HDS/HDN

HYDRO ISOMERISATION

On-spec kerosene with % SAF

Renewable diesel & SAF

On purpose SAF

Figure 1 Schematic representation of different processes for the production of SAF via the HEFA route