HDO pathway products
~550 Nm /m (3,300 SCFB)
Octadecane
Octadecane
HDO
+16H
Docosane
O
Rapeseed oil
O
O
9c – Oleic acid
CO + H
H O + CO Reverse water-gas shift
O
CO + 3H
H O + CH Methanation
O
13c – Erucic acid
O
9c12c – Linoleic acid
+7H
Decarboxylation pathway products
Heptadecane
Decarboxylation
Heptadecane
~240 Nm /m3 (1,440 SCFB)
Henicosane
Figure 4 Fundamental HEFA chemistry
that a hydrocracking component will be required in a HEFA- SPK process for SAF production. Furthermore, the product paraffin content is inadequate to meet the cold flow prop - erties required for jet fuel needs. Hence, a hydroisomerisa- tion, or dewaxing, step will also be required. Fortunately, existing hydroprocessing technologies can incorporate both, which will be discussed subsequently. Co-processing renewables with fossil fuel feeds For fossil fuel refiners, a straightforward entry into SAF production is to utilise existing hydroprocessing units, appropriately modified, to co-process some percent - age of renewable feedstocks with petroleum feedstocks. Co-processing in hydrocracking and distillate hydrotreating units is an option that has been actively employed in refin - ing scenarios for well over a decade.7 Based on the chemistry, there are a variety of new chal- lenges compared to petroleum-based hydroprocessing units. These units must have specialised guard catalysts and operating adjustments to assure the integrity of a cata- lyst load cycle and mitigate effects from contaminants such as alkali and alkali earth metals (Na, K, Ca, Mg) and high acid content, as well as the strong phosphorus poisoning
effect from the presence of phospholipids. The unit may require some level of revamp to address the variability of feed acidity, higher product paraffin content, and the need for adequate hydrogen and temperature control to handle the higher oxygen and olefin content and concurrent reac - tion exotherms. The increase in off-gases will drive the need for higher gas recycle rates and hydrogen addition rates to address the higher purge rates needed to adequately keep CO lev- els moderated and hydrogen-treat gas purity. CO is not removed by amine scrubbing, as is CO2, and it is a catalyst activity inhibitor. The combination of water and CO 2 pro- duced can create carbonic acid downstream and needs to be properly addressed. Concurrently, renewable feeds with high levels of free fatty acids pose corrosion issues in the feed systems analo- gous to high TAN fossil feeds. Several hydroprocessing unit types are amenable to some level of revamp to co-process, including kerosene hydrotreaters, diesel hydrotreaters, VGO (vacuum gas oil) hydrotreaters, and hydrocrackers. The first three, likely with liquid recycle, will have some flexibility toward SAF selectivity but will produce notable amounts of RD. 9,10
Typical contaminants and levels and the range of levels specified by technology providers
Raw feed
FFA, %
P, ppm 5-250 15-30
Metals, ppm
CI, ppm
Polyethylene, ppm
Vegetable oils
<3 <6
100-300
<5
– –
Palm oill
20-60
<15
UCOs
1-10 2-35 5-20
<20
<50
20-100 50-500
0-200
Animal fats
50-1,000
200-2,000
0-1,000
Technology provider specs
2-3
5-10
5-50
50
FFA is free fatty acid content; metals include Ca, Mg, Fe, Na, K, B, Si, Zn, Al
Table 2
69
PTQ Q1 2025
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