Although planes can take us to places far and wide, climate change has made people reconsider the carbon footprint of flying. The flight industry is looking towards sustainable aviation fuels (SAFs) or e-fuels as a potentially greener alternative to traditional fuels.
For The Big Questions, IFLScience’s podcast, we spoke to Sophie Zienkiewicz and Alasdair Lumsden, co-founders of Carbon Neutral Fuels, to find out if e-fuels could revolutionize the future of the fuel industry and help offset climate change.
What is carbon-neutral fuel?
Sophie Zienkiewicz (SZ): Carbon-neutral fuel is hopefully part of the solution to climate change. We sequester carbon dioxide from the atmosphere, combine that with clean hydrogen, and create a carbon-neutral fuel in the sense that, when it’s burnt, the carbon dioxide (CO2) is released and then recaptured as feedstock. This could be used as a sustainable alternative for the huge amount of fuel used in aviation.
Are the terms carbon-neutral fuels and e-fuels interchangeable?
Alasdair Lumsden (AL): Absolutely. The term e-fuels came about because they are often made using electricity. We can collect CO2 to make e-fuels, but that requires energy, which is where the “e” part comes from. It has to be low-carbon electricity though, because otherwise you’re still burning fossil fuels.
With traditional fossil fuels, nature has done the energy collection for you. Plants get their energy from sunlight, and then over hundreds of millions of years, those plants have decayed into the ground and become oil and coal, for example.
Around 30 percent of carbon dioxide emissions are absorbed into the oceans...where it could be collected.
Humans have come along and dug it up as an effectively free energy supply. Unfortunately, this is having the unintended consequence of filling our atmosphere up with excess CO2, which is contributing to climate change.
How are e-fuels made?
AL: The first step is capturing the carbon. When we started our company, we were looking at a technological pathway for sucking CO2 out of the oceans, where it’s quite concentrated.
The reason for that is around 30 percent of carbon dioxide emissions are absorbed into the oceans and it stays at the surface level, where it could be collected. Liquids take up a lot less volume, around 1,000 times difference between a gas and a liquid, and so again, so it would be more efficient.
However, that technology isn’t yet established so instead we looked at direct air capture. This uses adsorbents that react with the CO2 in the air and then another technique is used to release a clean stream of CO2 from the adsorbent.
You also need hydrogen – people might remember doing electrolysis in chemistry class maybe doing electrolysis, where you stick an anode and a cathode in a beaker, apply some electricity and you get hydrogen at the cathode. We collect hydrogen in that way; you can buy pretty beefy electrolyzers, that can apply anywhere from one megawatt up to hundreds of megawatts.
Once you get the CO2 and the hydrogen, you need to combine them somehow. CO2 is very stable as a molecule, so it first must be converted to carbon monoxide. That can be combined with hydrogen to make syngas, which is very commonly used in the chemical industry. The syngas is then put through a Fischer Tropsch reactor.
The reactor typically has an iron or cobalt catalyst, and it starts growing long-chain hydrocarbons. Depending on the configuration of the reactor, the conditions, the pressure, the temperature, and the catalysts, you can determine what distribution of hydrocarbons you get. The technology we’re looking at will predominantly produce things in the kerosene range.
It’s a steady-state operation; once everything is built, it will be capturing the CO2 and feeding that real-time into the rest of the system, with the hydrocarbons coming out.
The process also makes methane as a waste product and not all of the CO2 or hydrogen reacts, so a method is needed for recycling those products back in, and we’re quite early on in our journey to do this.
Can we build upon existing methods or frameworks when looking to make e-fuels?
AL: What’s quite interesting is that a lot of the technology has already been invented. For example, Fischer Tropsch’s chemistry was invented close to 100 years ago and they originally used it to convert coal to liquid fuels. However, it wasn’t widely used because of the abundance of liquid fuels, so [the chemistry has] been used in some countries that didn’t have easy access to liquid fuels – South Africa and Germany have used it, for example.
Because of the whole “green” transition, electrolyzers are also now becoming widely available, as well as carbon capture. All it’s taking, hopefully, is for us to come along and integrate those technologies together to have a complete system for doing this.
How are governments and other organizations involved in bringing e-fuels to fruition?
AL: One key thing that is enabling e-fuels is that governments worldwide, including in the EU and the UK, are looking at introducing mandates to require people to uplift sustainable fuels because traditionally, these sustainable fuels cost a lot more than the free fossil fuels we’re getting.
To process fossil fuels, you just need a distillation column to separate out the different weights of fuels, whereas e-fuels are made from scratch, and that’s very expensive to do. With mandates, it can compel airlines to use some e-fuel, which could enable further development and hopefully bring the price down over time.
SZ: Because creating e-fuels is such a new process, there isn’t a huge amount of precedent that’s been set in the UK in terms of how to go about building a facility either. There’s been engagement with the government; the Jet Zero Council, for instance, is championing the work focusing on developing and growing the market. Aviation is an international industry, and the UK government would like to lead the charge in terms of sustainability.
The implications for the aircraft have to be considered.
We’re also conscious about research and universities and how the detailed elements of the science behind the process come into play.
Let’s say we’re a little bit further down the line and e-fuel is being produced, could you go to an airline and say, “Let’s put this in your planes”?
SZ: That is possible, yes. [The premise] exists, to a certain extent, today. Some already use blended fuel, where the majority of the fuel will be traditional kerosene, but biofuels and other sustainable alternatives are blended in. Hopefully, over time, the amount that is blended will increase in percentage terms.
It would be great if, one day, 100 percent of fuel was SAF, but the implications for the aircraft have to be considered.
Traditional kerosene contains impurities, such as sulfur and other “nasties”, but they serve a lot of valuable functions in the actual engine of a plane – they act as lubricants, and you need them to be there in terms of the safety requirements because it’s what the plane has always been used to.
As such, getting to 100 percent SAF may have implications that we aren’t necessarily aware of at the moment. There’s a lot of testing going on to get to that point but currently, it’s not quite there.
Are there other types of SAF, besides the e-fuels you’re working on?
AL: SAF encompasses many different types of fuel. For example, there are biofuels, made from crops, and HEFA fuel, which is made from waste oil products like cooking oil. More recently, household bin bag waste is being looked at as a potential carbon feedstock to make sustainable fuels – I think this is a little bit sketchy because that is carbon that was going to landfill to stay there and we’re talking about turning that into fuel, effectively throwing it into the air as carbon dioxide.
The majority of SAF that’s going into planes today is biofuels, although we are starting to see other sustainable fuels entering the market.
Also, in the European Union and the UK, around 10 percent of the petrol in a car is made from biofuel sources. Aviation is looking to move up to 10 percent between now and 2030. Synthetic fuels, like e-fuels, are a more expensive way of doing it than biofuels, so the mandate for them is going to be point 0.1 percent by 2030.
However, e-fuels are the cleanest way to [reach the target] because you don’t need a lot of land, you don’t need fertilizer, and it doesn’t compete with food crops so you’re not driving up food prices. There are a lot of benefits to power-to-liquid fuels, but it involves the newest and the most immature technology.
How big of a production plant would you need to reliably produce e-fuel?
SZ: We would like to keep it as small as possible because, much like the nuclear industry, there’s a lot of time, money, and effort that goes into producing massive installations. Once they’re up and running, they’re fantastic, but the time and the cost to the environment to get to that stage is quite extreme.
It can be looked at in a modular way instead – think about scaling and growth in terms of the number of units versus the scale of units. Size-wise, installations would be quite small. We’re looking at shipping container module sizes, plus the surrounding land needed. It’s not going to be massive by any stretch of the imagination, and I think that’s where the real opportunity for growth and having a big impact on climate change can come into play.
AL: The scale will depend on how much fuel you want to produce. The UK uses about 15 billion liters of aviation fuel every year and they’re targeting 10 percent of it to be sustainable by 2030, so that’s 1.5 billion liters. We are aiming to create a small demonstration plant that can produce just under 1 million liters.
Have any planes successfully used SAF fuel made from the power-to-liquid process?
AL: There have been test flights. There are planes taking off with traditional biofuel-based SAF today, and certain airports have a very small percentage in their fuel tanks in the airports – any planes that land at that particular airport will be uplifted with some SAF.
However, with power-to-liquids, it’s been mostly test flights. There are companies in the US, and there’s one other competitor in the UK that was working with the RAF; they flew an RAF test flight on their power-to-liquid to fuel, so there is precedent.
When you burn e-fuels in an aircraft, you’re still producing CO2 – how does the process become carbon-neutral?
AL: We are effectively recycling the CO2 by taking it back up; there is no net increase in CO2 emissions and you’re displacing fossil fuels where traditionally that CO2 was stored underground, put in a plane, and released, bringing overall CO2 levels up.
E-fuels are a fantastic bridge technology to rapidly decarbonize aviation.
There are still some challenges with e-fuels – the engine may still produce nitrous oxides. When you have heat in an engine, it can bring some nitrogen and oxygen together, and NOx is not necessarily what you want at ground level.
Electric cars are great because you’re getting rid of the NOx, you’re getting rid of the CO2 and you’re getting rid of all the unburned things, but the challenge with aviation is that it doesn’t have a lot of options to decarbonize really quickly between now and 2030.
There are no electric planes or hydrogen planes in service today with passengers on board. They are developing them, but the big problem is energy density, and batteries are orders of magnitude less energy-dense than liquid fuel. There are some electric plane companies and hydrogen plane companies that are making a lot of progress. It looks like we may get those sooner than you think, but those are going to be for short-haul flights with smaller passenger numbers, so it’s going to be quite some time until you see all the planes in the sky going down that route.
E-fuels are a fantastic bridge technology to rapidly decarbonize aviation. A plane might have a 30-year lifespan and lots of CO2 has been used to make the plane and in refining the metals and manufacturing it. If you have to replace that plane with a new electric one, it also contributes CO2 emissions in its manufacture, so it makes sense to run planes to the end of their useful life and if you can stick in a carbon-neutral fuel, then that’s great.
It seems like SAFs will require less change – do you think that the more the technology evolves, the easier it will be to transition away from fossil fuels and into power-to-liquid fuels?
AL: Yes. And you can make any kind of fuel. For example, there is a lot of talk about how we can quickly move away from methane. Natural gas in peoples’ homes for heating and cooking and heat pumps are great, but they are very expensive, and often you need a big overhaul.
In theory, carbon-neutral methane could be fed into the gas distribution network. There are many other places you could deploy this technology as a bridge to buy us time whilst we transition to alternatives.
SZ: There’s also blue sky thinking – what can you do once you’ve got those facilities established? This process is carbon-neutral, but what about achieving carbon-negative? How can we take this technology one step further and what would that look like in 10, 15, 20 years’ time?
It would also be cool if these facilities were located near abandoned oil wells and pumped extra CO2 back down into the ground, making fuel but also sequestering CO2. There are loads of opportunities and ideas that we haven’t even thought of yet. Once we’ve got this technology established, then we can leapfrog to anywhere.
What are the biggest challenges facing the aviation e-fuels industry?
SZ: The one that we are encountering is having a provable market – that means investors want to invest. Concerns around it being, thus far, unproven technology, are understandable, despite the fact that the individual components are proven.
Putting everything together and having the funds to set up a facility is expensive, and it takes a very brave, conscious investor to say, “Yes, we think this is a good idea”. Funding is tricky. but I think mandates really help because they give validity, and it gives confidence to people that we don’t otherwise have currently.
AL: The Department for Transport is doing a lot of work looking at how to decarbonize aviation and they set aside £165 million ($204.3 million) to fund sustainable aviation fuel projects. That includes biofuels and the bin bag waste project. That funding being available has also demonstrated to private investors that the government takes this seriously, they believe in the technology.
SZ: Other challenges are around electricity supply. Electricity in the UK is expensive and it is a massive component of the process. However, there are alternative options out there.
Once small nuclear reactors are up and established, there is going to be a whole host of low-carbon electricity out there that people like us can capitalize on. There are also a lot of opportunities in Scotland and similar places, where there’s an excess supply of electricity that could be tapped into.
Are there concerns over the safety of e-fuels and production facilities?
S: There are a few elements to safety. As we’ve mentioned before, the discreet components of the process are proven, and they already have existing rules and regulations that surround them – I’m very confident that each of those components is safe.
However, when you put it all together, what does that look like and how do you regulate it? In the UK, we are a heavily regulated industry. My background is in nuclear energy, so I’m acutely aware of all kinds of regulations that need to be followed.
The good thing is that, because climate change is such a pressing problem, we are being a lot more logical and a lot more sensible about how we address safety concerns. We are looking at it with a bigger picture and going, “This is a massive safety problem in terms of the security of the world. Let’s talk about how we enable those processes that are going to help it.” We haven’t got to that stage yet, but I’m pretty confident that the right process will be in place.
AL: It’s worth mentioning that the chemical engineering discipline that we’re going to be employing has standard processes and practices for designing chemical plants. We’re going through what’s called a front-end loading process, where you try and do as much of the front-end design of the plant prior to engaging with an engineering company that will build it. Part of that front-end loading process includes things like HAZOPs – hazard and operability studies.
For example, solid oxide electrolyzers, which we are hoping to use, operate at very high temperatures. You might not necessarily want to put those next to your hydrogen storage tanks, so this whole process will look at the layout of the plant and make sure that it’s designed to be as safe as possible.
Could e-fuels affect contrails?
AL: Contrails contribute quite a lot to the warming effect of planes, and that’s because of water vapor. The reason contrails form is, quite often, that ice crystals form around soot and dust particles. Therefore, impurities in the fuel can contribute to making contrails. Sustainable fuels have a lot fewer impurities – we don’t have the studies with evidence yet, but in theory, power-to-liquid fuels should reduce contrails.
How far away do you think this technology is from becoming mainstream?
Within 5 to 10 years, you’ll start to see noticeable amounts of power-to-liquid SAF coming out.
AL: I think by 2030 we’ll start to see very small amounts in planes. The UK government has said that by that time, 0.1 percent of the fuel in a tank must be e-fuel. KPMG put out a report that said to meet our net zero ambitions by 2050, power-to-liquid fuels will need to be at least 40 percent of a plane's tank or 40 percent of the total global supply will need to be power-to-liquid fuels.
It’s going to depend a lot on the country and how electric and hydrogen planes go, but I am pretty confident that within 5 to 10 years, you’ll start to see noticeable amounts of power-to-liquid SAF coming out. Whether or when we will get to 100 percent, I am not sure, and how much of it will be biofuels versus power-to-liquid fuels remains to be seen.
The airline industry is very price-sensitive. They want ticket prices to be as low as possible and fuel makes up a very large percentage of the ticket price, especially for long-distance flights. Power-to-liquid fuels are one of the more expensive SAFs, so if fossil fuels are squeezed out, fuel may be 75 percent biofuels and 25 percent power-to-liquid.
However, the KPMG report also found that biofuels can’t be scaled to the size required for this industry and therefore power-to-liquid, which doesn’t suffer the same constraints, might take over in the future. So, it might be 75 percent, 25 percent, in favor of power-to-liquids.
SZ: Having said that, there is a planned flight that is being run by Virgin Atlantic in November this year. It’s a one-off and it’s been a huge undertaking, but they are planning on flying from Heathrow to somewhere in America purely on a 100 percent blend SAF. It won’t be mainstream for a very long time, but there are things happening in 2023, so that’s pretty exciting.