Jet fuel alternative produced by bacteria

The complex molecules requires to propel rockets at launch could be generated by bacteria and food waste
02 August 2022

Interview with 

Pablo Cruz-Morales, DTU-Biosustain


picture of a rocket launching


Fuel prices may be astronomically high at the moment, but this week, we are focusing on fuel which can take us astronomically high: jet fuel. Similar to the petrol we fill our cars with, jet fuel is often sourced from non-sustainable sources giving it a hefty carbon footprint. But researchers at Novo Nordic Foundation Center for Biosustainability in Denmark have found a method to generate power-packing propellant from plants. Julia Ravey spoke to Pablo Cruz-Morales, who told her about a synthetic molecule called “syntyn”, developed as an alternative rocket fuel in the 1960s, which inspired this work…

Pablo - Syntyn is a synthetic fuel as a replacement for rocket fuels, which are typically kerosenes. It was developed by Soviet scientists in the Soviet Union and used successfully in the upper phases of the Soyuz rockets. The process involved the presence of certain chemicals that are explosive and toxic, and the process wasn't very efficient. But it's known that syntyn is a good fuel, it provides higher energy and higher impulses for the rockets than kerosene.

Julia - To get a jet off the ground. I'm guessing you need a fuel that packs a lot of energy, but you are also constrained by the size of the fuel tank. And then there's a problem with if you build a bigger tank, you're carrying more weight. So how can we chemically pack a bigger punch when it comes to the components of jet fuel?

Pablo - The difference between gasolines and jet fuels, for example, is the content of carbon chains that are a circular molecule. So you can have eight member, six member carbon cycles, etc. The shortest is three carbons. And for making these rings so small, you need to bend the carbon-carbon bonds and that requires more energy. When you burn it, you release more energy

Julia - In terms of the volume of fuel, if the components in it are bent into these circular carbon structures, you're essentially getting a similar volume of say, like other fuel, like petrol, where you don't have these things in, but because they have these bent structures in them, they when - burnt - release a lot more energy?

Pablo - That's the idea. In simple words it's called energy density. Higher energy density means that you can have more energy stored in a smaller volume of the fuel.

Julia - The process of making syntyn, which was one of these types of molecules, sounded like it was quite nasty. So is there a way that we can make these higher energy-structured molecules in a more sustainable way?

Pablo - Yes, the idea is to use biology. There are some organisms in the planet that are able to make extraordinary chemistry. So we're looking for potential molecules that look similar to syntin, and then we can take the genes that direct the synthesis of these molecules, put them into a bacteria that we can put in a flask, and then we will produce this. Instead of nasty chemicals, we just add sugars and then we will produce these molecules.

Julia - So you just feed the bacteria sugar and because they have the right enzymes in them, is that right? The right enzymes in them, they then produce these really quite complex structured molecules, which are good for the type of fuel?

Pablo - Yes, that is correct.

Julia - And you said in your process that you fed these bacteria sugar, but could we use say waste products as the substrate for the bacteria in making this fuel and that would then make the process even better for the planet?

Pablo - Yes. At this point in our research, we are feeding sugars because this is a proof of concept level. But if we were to make a sustainable fuel at large scale, the ideal scenario would be to feed substrates that are derived from example from lignocellulosic biomass, from agricultural waste, or maybe plastics that have been broken down using some chemical process, for example, that you can convert into something that the bacteria can eat and then make into this biofuels. A biofuel that is made with lignocellulosic biomass or plastic waste benefits from being sustainable because it's not taking carbon from petroleum, which is a non-renewable resource. Instead of that, if we take lignocellulosic biomass, the carbon is trapped by the plants, and then we convert it into these products. Then if we borrow the products, they will go back the plant. So it's circular

Julia - Is this process scalable?

Pablo - It is possible. And the team in California 's working on it, but it is an important challenge. I will add to that now that we know that we can make the chemistry, it makes sense to put an effort to increase a tighter yield because before we didn't know that it was even possible.


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