Nov-2024

Sustainable aviation fuel production via the HEFA route: Insights and innovations (ERTC 2024)

Global mandates and incentives drive efforts to increase sustainable aviation fuel (SAF) production.

Jaap Bergwerff
Ketjen

Article Summary

While alternative pathways are under development, hydrotreated esters and fatty acids (HEFA) will remain the primary feedstock for commercial-scale SAF production in the coming years. Operators of HEFA units are increasingly drawn to shifting production from renewable diesel to SAF. Neste, a leader in SAF production, has employed ReNewFineTM catalyst solutions to achieve remarkable results.

By 2026, Neste aims to scale its production capacity for SAF from its NEXBTLTM process to more than two million metric tons per year, a significant contribution to global SAF production. This journey has provided invaluable experience that is now available to the industry.

The challenge of producing SAF from waste fat and oil streams is illustrated in Table 1, which shows the typical properties of a hydrogenated triglyceride stream produced in the hydrodeoxygenation (HDO) reactor vs the specifications for SAF as blending component and the final aviation fuel. It is obvious that a significant shift in boiling point and freezing point needs to be established in the hydroisomerisation reactor to produce in-spec SAF.

In a dedicated production campaign to produce SAF, Neste operated a NEXBTL hydroisomerisation reactor at high severity. Figure 1 shows that a liquid product with a cloud point of on average -46°C was achieved during a one-year period, a good indication that severe isomerisation is being achieved. During this year, no significant deactivation of the catalyst system was observed, as can be derived from the stable weighted average bed temperature (WABT) during this period.

The use of residue and waste streams as a feed meant that nitrogen compounds were present at significant concentrations in the feedstock, causing a potential problem for the activity and stability of the hydroisomerisation catalyst. Hence, the observed stability also shows that the ReNewFine HDO catalyst system upstream was working effectively in preventing any N-slip to the hydroisomerisation stage. Total liquid product yields during this campaign were well above 90% on a litre product per litre HEFA feed basis. The relevant properties of the total liquid product and the SAF and renewable diesel fractions obtained from it are presented in Table 2. Fractionation resulted in 74 wt% SAF, comfortably meeting all product specifications, while the remaining fraction was high-quality renewable diesel.

When producing SAF, the challenge is to maximise the yield of SAF vs renewable diesel, while at the same time minimising the yield loss to renewable naphtha or lighter products via unselective cracking.

Severe isomerisation requires running at a higher temperature, which makes it even more difficult to prevent the formation of light products. The high yields obtained during this production campaign are a testament to the high isomerisation selectivity of the ReNewFine catalyst system. Furthermore, this selectivity effectively prevented any operational issues that may be caused by uncontrolled cracking, such as a severe exotherm or excessive product vaporisation.

This short article originally appeared in the 2024 ERTC Newspaper, which you can VIEW HERE