We´ve already written a good deal about the new sustainable aviation biofuels, including how their increasing use is a huge plus not only for the environment, but also for the economy of Spain, which is in a strong global position to lead its production and exports. But this time we´re going to delve a bit deeper into how it´s manufactured.
According to Spain´s State Agency for Air Security, there currently exist eight techological processes for manufacturing SAFs, depending on the raw materials used:
Thermochemical
Here the focus is on converting “lignocellulosic” material – basically dry plant matter – into synthetic paraffinic kerosene. This can come from wood, agricultural or forestry waste (that is, from the cultivation of forests). It also includes certain forms of municipal solid waste (paper, cardboard, etc.) generated by households and businesses.
The conversion into synthetic paraffinic kerosene is gasified at very high temperatures. This yields so-called syngas (or synthesis gas), composed of carbon monoxide and hydrogen, which is then transformed into liquid hydrocarbon thanks to the Fischer-Tropsch process, developed in Germany in 1925 and used in many of the models of obtaining SAF.
This process yields an SAF known as FT-SPK, as well as FT-SPK/A, which incorporates aromatic components.
Oleochemical and Lipíd
The best known of these processes is also the one that best allows for production on a large scale. It´s based on fats (lipids) not suitable for food consumption: used cooking oil, animal fats, and vegetable oils, and yields a synthetic paraffinic kerosene called HEFA-SPK synthetic paraffinic kerosene.
The lipid part is extracted from these fats and combined with a light alcohol such as methanol in a process called transesterification. If the fats come from used oil, for example, they´re first subjected to a pretreatment and filtration process that eliminates unneeded waste.
And by the way, a byproduct of this oleochemical process is glycerin, a sugar alcohol with many uses, including in soaps and detergents; medicines; products for skin, hair, and other personal care; and some foods (as a sweetener, solvent, and preservative).
Biochemical
Here the raw material is sugar or starch, with the fermentation of glucose producing pyruvic acid and then carbon dioxide to end up being ethanol – in short, creating hydrocarbons from sugars.
But not all biochemical pathways explored are certified. Today there are two types of SAF approved by the venerable and highly respected international standards organisation ASTM, one of the entities that certify these biofuels: HFS-SIP, which uses modified yeasts, and ATJ-SPK, which obtains hydrocarbons from dehydration, oligomerisation and hydroprocessing of alcohols derived from sugars.
Power to Liquid
This one involves not a biofuel but an “electrofuel”, as it´s totally synthetic, using raw materials such as electricity, CO2 , and water.
Furthermore, the electricity used in this manufacturing is from renewable energy sources – usually sun and wind – making it a clean and environmentally friendly process. That´s why these electrofuels are also known as synthetic sustainable fuels.
There are different methods to obtain it, such as the aforementioned Fischer-Tropsch process or by synthesising methanol. And the end product is a fuel that´s both highly sustainable and very efficient.
Why SAFs (and Their Manufacture) Are Sustainable
The raw materials they´re made from are of renewable origin, such as used oils and fats (or grown specifically and controlled for this purpose), plant waste, clean energies.
They do not require deforestation, nor large amounts of water.
Those which are biologically/organically derived nonetheless do not compete with food cultivation.
Additional Advantages in Terms of Sustainability
No adaptation of current aircraft engines is needed. Existing models can use SAFs as is, so there´s no need to make a large investment or manufacture new aircraft (which of course also benefits the environment). Similarly, airport instrastructure can also handle the arrival of SAFs without requiring any changes or adaptations.
So on balance, SAFs save our planet some 80 percent in terms of emissions, compared to traditional fuels. That is, it not only emits less CO2 and other harmful greenhouse gases while the plane flies, but also as this fuel is manufactured- and this can eventually rise to 100 percent. A resounding win for the environment!