In laboratories around Europe and the Americas, scientists are busy researching alternatives to fossil fuels. Besides the damaging emissions and escalating costs of petroleum products, recent geopolitical instability in the east of Europe has added to the pressure of seeking new energy sources. So, what kind of synthetic fuels are under development today?
Below, we explore what renewable and synthetic fuels are. Please read on to learn more, including their advantages, production methods and availability.
Synthetic fuels, such as synthetic diesel fuel or synthetic gasoline, come from renewable raw materials or electricity generated using three renewable energy sources: solar, wind or wave power. In the latter case, the resulting synthetic fuels are sometimes called e-fuel.
The production of renewable fuel, or e-fuel, first involves the electrolysis of water to produce hydrogen, with oxygen as a by-product. Then, the introduction of carbon yields either liquid fuel or methane (synthetic natural gas or SNG), the simplest organic compound.[1]
To produce one ton of bio-ethanol, four to five tons of straw are required. Worldwide, agricultural residues are available for reprocessing in enormous quantities, from rice straw across Asia to sugar cane in Latin America and harvest waste in the U.S..[2]
By producing sustainable liquid synthetic fuels, it should be possible to run combustion engines without adding to net carbon dioxide emissions, according to engineers at the Technical University of Kaiserslautern. The motor industry is increasingly expressing interest in synthetic fuels. In Germany, for example, Audi operates a power-to-gas e-fuel production plant.
Other synthetic fuel examples include synthetic oil for generator use. Direct methanol fuel cells (DMFC) are gaining commercial popularity, especially in vehicles for materials handling, such as forklift trucks, because topping them up with synthetic fuels is much quicker than recharging batteries. Also, refueling supplies occupy less warehouse floor space than charging stations.[3]
According to the European Commission, straw-based bioethanol synthetic fuels emit only one-tenth of the greenhouse gases released by burning conventional petrol. Not even synthetic diesel oil produced from rapeseed is that efficient; it emits around half of all gaseous carbon emissions.[4]
There is little doubt that the internal combustion engine will become obsolete. Nonetheless, scientists and companies are working on ways to extend its life. Biofuels – and now synthetic fuels as well – appear to be a clean alternative to ensure sustainable mobility and minimize pollution.
Liquid synthetic fuels have a higher energy density than gas and can use the existing network of filling stations.[4] In addition to the environmental benefits, the logistics are less complex than hydrogen fuel cell handling and storage.
To date, a significant disadvantage of synthetic fuels has been the cost. However, according to Reinhard Otten at Audi, developing an efficient power-to-gas operation of a reasonable scale could reduce the cost of synthetic fuels.[5]
However, synthetic fuels are environmentally friendly only when produced using renewable energies. While these green credentials are not the case everywhere, the future could see improvements. Furthermore, decisions made by the European Council following the events in Ukraine are set to usher in a series of moves toward prioritizing renewable energy.
To understand the difference between synthetic fuels and biofuels, let us consider an example of biofuel production: ethanol from wheat straw. In 2012, the Basel-based company Clariant AG built a pilot plant in Bavaria, Germany, to extract cellulose and sugars from straw.
Specifically developed enzymes break down these sugars and convert them into ethanol. The next step is to achieve stable production at industrial levels. Audi has extended its research to developing a biotechnological process in the USA with the company Joule. In this joint venture, laboratory experiments have seen microorganisms absorb carbon dioxide and water while secreting ethanol or alkanes, the basic building blocks of synthetic diesel oil.
As distinct this is from processes that convert plants or algae into biomass that must regrow, this new microorganism-based method is regenerative: the cells remain alive. The result is biofuel.
First-generation biofuels come from maize, rape seed or palm oil. In contrast, the latest biofuels come from biogas or biomass. Because their production removes as much gaseous carbon dioxide from the atmosphere as their eventual combustion releases, these second and third-generation biofuels are CO2-neutral.[6]
EU directives say the blending of fuels derived from feed, rapeseed and beet will end by 2030. Instead, the production of second-generation biofuels will ramp up to more than 12 million tons.
A similar product, oxygen methylene ether (OME), is more efficient than conventional diesel. This synthetic diesel is also cleaner, thanks to its relatively high level of oxygen. Significant to say is that it is possible to blend e-diesel with its fossil counterpart to facilitate a gradual introduction of synthetic fuels and vehicle adjustments, if necessary.[6]
Recently, a spokesperson for the University of Aachen said that there was an increase in efficiency of more than 10 percent in synthetic fuel production. Approximately 45 to 60 percent of the produced energy is a surplus, depending on the production method and product chemistry. In part, the resurgence of interest in synthetic fuels stems from claims by Porsche's head of R&D, Dr. Michael Steiner. He mentioned that e-fuels might enable the company to sell internal combustion engine cars alongside BEVs (Battery-powered electric vehicles) – even after 2030. Porsche and Siemens have been developing synthetic fuels at a plant in Chile in line with these corporate hopes. Synthetic fuels are currently a low-volume product for specialist applications. As a result, the eFuel Alliance envisages a gradual increase in the addition of synthetic fuel admixtures – rather than a direct swap with today's petroleum-based fossil fuels. The eFuel Alliance expects a 4 percent admixture by 2025, 12 percent by 2030 and 100 percent by 2050.[7]
In summary, synthetic gas and biofuel can significantly reduce the output of CO2 and other pollutants released into the environment. However, synthetic fuel for cars and synthetic aviation fuel for commercial flights are still a long way off. As a result, blending is likely to be necessary until production can cater to widespread demand.
Sources
[1] Synthetic kerosene or highly flammable gases, i.e., butane and methane, comprising only chained carbon and hydrogen atoms. https://en.wikipedia.org/wiki/Alkane
[2] https://www.sciencedirect.com/topics/earth-and-planetary-sciences/bioethanol
[3] https://fuelcellsworks.com/knowledge/technologies/dmfc/
[4] https://www.thyssenkrupp-industrial-solutions.com/power-to-x/en/green-sng
[5] https://www.audi.com/en/innovation/alternative-drive-systems/energy-revolution.html
[6] https://synhelion.com/news/synthetic-fuels-explained#:~:text=The%20main%20difference%20between%20fossil,natural%20processes%20using%20renewable%20resources.
[7] https://ed-info.de/synthetische_kraftstoffe_undbiokraftstoffe/#:~:text=Regenerative%20Kraftstoffe%20(Biokraftstoffe)%20werden%20im,Mais%2C%20Raps%20oder%20Palm%C3%B6l%20hergestellt