ERTC 2024
Sustainable aviation fuel production via the HEFA route: Insights and innovations
JAAP BERGWERFF KETJEN
Global mandates and incentives drive efforts to increase sustainable aviation fuel (SAF) production. While alternative pathways are under development, hydrotreated esters and fatty acids (HEFA) will remain the primary feedstock for commercial-scale SAF pro- duction in the coming years. Operators of HEFA units are increasingly drawn to shift- ing production from renewable diesel to SAF. Neste, a leader in SAF production, has employed ReNewFine TM catalyst solutions to achieve remarkable results. By 2026, Neste aims to scale its produc- tion capacity for SAF from its NEXBTL TM 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 proper- ties 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 reac- tor to produce in-spec SAF. In a dedicated production campaign to produce SAF, Neste operated a NEXBTL hydroisomerisation reactor at high sever- ity. 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 sig- nificant 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 concentra- tions in the feedstock, causing a poten- tial problem for the activity and stability
Property
Typical HDO product
ASTM D7566 A2
Aviation jet fuel JET A-1
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 specifica- tions, while the remaining fraction was high- quality renewable diesel. When producing SAF, the challenge is to maximise the yield of SAF vs renewable die- sel, 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 dur- ing 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 exo- therm or excessive product vaporisation. DID you Know? When producing SAF, the challenge is to maximise the yield of SAF vs renewable diesel, while minimising the yield loss to renewable naphtha or lighter products via unselective cracking
(mixture of linear paraffins) (requirements for SAF component)
(final spec)
Density (kg/m 3 ) Freezing point (°C)
770-790
730-772 Max. -40
775-840 Max. -47
20-30
Flash point (°C)
>50
Min. 38
Min. 38
Distillation 10 vol% (°C) Distillation FBP (°C)
275-290 310-325
Max. 205 Max. 300
Max. 205 Max. 300
Table 1 Typical properties of a hydrogenated HEFA feed and specifications for SAF product
-20
Stable WABT during production campaign
-25
dWABT = 10˚C
-30
-35
-40
-45
-50
Average product cloudpoint: -46˚C
-55
0
2
4
6
8
10
12
Time on stream (months)
Figure 1 Liquid product cloud point and WABT during a year-long SAF production campaign
Total liquid product
SAF fraction, 74 wt% yield
Renewable diesel
fraction, 26 wt% yield
Density (kg/m 3 ) Cloud point (°C) Freezing point (°C)
775 -46
771 P
787 -30
-52 P 40 P
Flash point (°C)
Table 2 Average properties of total liquid product ex hydroisomerisation and the SAF and renewable diesel fractions obtained during a dedicated SAF production campaign
N-slip to the hydroisomerisation stage. Total liquid product yields during this cam- paign were well above 90% on a litre prod- uct per litre HEFA feed basis. The relevant
of the hydroisomerisation catalyst. Hence, the observed stability also shows that the ReNewFine HDO catalyst system upstream was working effectively in preventing any
Contact : jaap.bergwerff@ketjen.com
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