Biofuels for aviation are still facing multiple challenges, the greatest being finding ways to make production economical, according to a report jointly released in September by the French Académie des Technologies and Académie de l’Air et de l’Espace. The experts admit the environmental benefit, although proven in principle, is difficult to quantify. Using vegetable oil as a basis for hydro-treated esters and fatty acids (HEFA) is seen as the only path immediately accessible.
A biofuel is intrinsically more expensive than a fossil fuel, as it has to pay for renewal costs–the growing of the plant. A biofuel for aviation is also more expensive than its road transportation counterpart, the report notes–in particular, technical requirements are more stringent, such as the need to eliminate oxygen.
Also, if biojet fuel is produced along with biodiesel, it will be 30 percent more expensive, French energy research center IFP-EN estimates. The final price will be at least twice that of conventional kerosene. The price of vegetable oil is closely linked to that of crude oil, Olivier Appert, executive officer of the Académie des Technologies, noted.
Recurring costs are not the only issue. Should biofuels cover all of air transport’s needs, hundreds of billion dollars would have to be invested in biofuel production facilities, the report goes on. In fact, they will cover just a few percent of the needs in the mid-term. The European Union, for instance, has set itself a goal of having 3.5 percent of total aviation fuel consumption being biofuel by 2020. However, as this represents two million metric tons, the experts suggest this will not be achieved.
Another factor is the competition between various uses of a limited resource. The experts mention the production of heat, electricity and fuel. The fuel itself can be sold to other sectors, the obvious one being road transport. Jet fuel accounts for six percent of petroleum-based products globally. Therefore, the air transport industry fears it could be neglected and the experts recommend that governments heed air transport needs in the production of biofuel.
The main point of using biofuels is to cut greenhouse gas (GHG) emissions. Measuring precisely how much is cut, however, has proved difficult and a standard still has to be found. “It is a bit early to evaluate the gain from field to wing,” Bruno Jarry, one of the authors and a specialist in biotechnology, said. Depending on the path, GHG emission savings are in the 60-90 percent range, according to IFP-EN expert Alain Quignard.
The HEFA path is only in the 60-percent class but is seen as “mature, industrially proven…and having a strong synergy with developing vegetable oil resources.” Therefore, the report says no other path will be ready by 2020. It is certified for a 50-percent blend in an aircraft’s fuel tank.
The biomass-to-liquid path uses the Fischer-Tropsch process, also certified and historically well known in aviation, but it suffers from the cost of collecting the raw material–essentially waste from forestry activities. It nevertheless retains a strong potential for high-volume production and GHG reduction.
From a technical standpoint, the use of biojet fuels has been described for a few years as a no-brainer. During flight-tests with various percentages of biofuel in the blend, no engine has ever been reported to perform differently and no maintenance problem has ever emerged. However, “we don’t have enough experience to rule out the possibility of a long-term problem,” warned Paul Kuentzmann, honorary advisor at French aerospace research center Onera. Since 2014, an Air France A320 has been flying every week from Toulouse to Paris with 10 percent of Farnesane–a sugar cane-based fuel developed by Total-Amyris–in its tanks, which should provide useful feedback.
Betting on Isobutene
Start-up company Global Bioenergies and sugar giant Cristal Union are joining efforts to start operations in 2018 at the factory they are to build in France. From carbohydrates, it will produce an annual 50,000 metric tons of biofuel–10 to 20 percent possibly being earmarked for aviation–made via isobutene.
The latter substance is a basis for a very pure biofuel, according to Bernard Chaud, Global Bioenergies’ v-p for industrial strategy. The process means that a mix of low-purity sugars from various origins can still be used to obtain a single molecule. Therefore, the resulting biofuel easily meets the drop-in requirement–it contains no oxygen, has a low viscosity and withstands cold temperatures, Chaud said. An industrial pilot is running near Reims, eastern France, and a demonstration plant is being built in Leuna, Germany.