How do you solve a problem like jet fuel?
Posted on Tuesday, May 6th, 2008

First published in Petroleum Review, May 2008.

Say what you like about Sir Richard Branson, but you cannot fault his willingness to suffer in the cause of a photo-opportunity. At the launch of a recent Virgin Atlantic test flight to demonstrate a jet fuel made from coconut and babassu oil, the Virgin boss took a swig of the new biofuel from a coconut shell to drive home his message that aviation could be “truly sustainable” and endured the consequences, burping biofuel, for the rest of the event.

©David Strahan

But then desperate times require desperate measures, and aviation is in a fix. First, the airline industry is rightly seen as the cuckoo in the nest of carbon reduction. Britain is now legally bound to cut CO2 emissions 60% to 65MtC by 2050, but under the government’s “best case” projection UK aviation alone will emit 15.7MtC in that year, almost a quarter of the economy’s entire carbon ration. According to the Tyndall Centre for Climate Change, if the additional “radiative forcing” impacts of aviation are taken into account, that figure could rise to over 100%. Either forecast is of course entirely unsustainable.

Second, aviation is uniquely exposed to peak oil. Whereas ground transport could in theory be completely electrified and run on renewable power, for jet engines there is no alternative to energy dense liquid fuels. And while soaring crude prices are already hammering airline finances at $110 per barrel, analysts Goldman Sachs now forecast potential spikes of $150-$200, a risk Sir Richard acknowledged during his biofuel launch: “In about four or five years’ time there’s going to be more demand for fuel than there is fuel on this planet. So fuel prices will go through the roof, and we’ve all got to come up with alternatives”.

If airlines are to have any chance of staying aloft in post-peak, carbon-constrained world, they must quickly find an alternative fuel with low emissions, but one which also matches the stiff technical standards of jet kerosene. Because planes have to lift their fuel into the sky, and carry every gallon for the entire journey, it has to be energy dense. Because they fly at altitude, it needs to remain fluid at minus 50C. Because they fly long distances, chemically identical supplies must be available all over the world. And because they have long lives, the new fuel must be compatible with the existing fleet. What’s needed, in other words, is an exact replica of fossil jet kerosene – a so-called ‘drop-in’ replacement – which also emits substantially less carbon. “Meeting all these conflicting demands is a very tall order” says Dr Mike Farmery, Global Fuel Technical and Quality Manager at Shell Aviation. “There are lots of exciting ideas, but it will be hard to achieve quickly”.

Until recently it was widely thought that using biofuels in aviation was a complete non-starter. The natural freezing point of vegetable oils is too high, so they would congeal at thirty thousand feet, and they contain too much oxygen, which adds weight to the fuel but not energy. But now those technical problems seem to have been cracked. The Finnish oil company Neste has devised a way to produce an oxygen-free biodiesel called NExBTL, which could in theory be applied to jet fuel. And Imperium Renewables, the company that supplied the biofuel for the Virgin Atlantic flight, has developed a method of reducing the freeze point – that was the purpose of the demonstration.

The problem with so-called first generation biofuels remains the amount of feedstock and land required. During Virgin’s test flight from London to Amsterdam, the Boeing 747 consumed 22 tonnes of fuel, of which only 1.1 tonnes (or 5%) was neat biofuel. Producing even that much, says Imperium’s Director of International Business Development, Brian Young, required the equivalent of 150,000 coconuts. So had the hour-long flight run entirely on biofuel, it would have consumed 3 million coconuts – an astronomical number that highlights the scale of the problem. However Virgin and its partners Boeing and GE stressed that the test flight was simply a ‘proof of concept’, and accepted that producing meaningful amounts of fuel would require “next generation” feedstocks.

One option, Sir Richard suggested, would be to produce fuel from the nuts of jatropha curcas, a hardy bush that grows in the tropics on relatively poor land with little water or fertilizer, and so need not compete with food production. However, the amount of land that would be required to replace the world’s jetfuel consumption would still be prodigious.

Aviation currently consumes around 5 million barrels of jetfuel per day, or 238 million tonnes per year. On current jatropha yields – 1.7 tonnes of oil per hectare – replacing that would take almost 1.4 million square kilometres, well over twice the size of France. To put this in context, D1 Oils, the British company pioneering biofuel from jatropha in countries such as India, Zambia and Indonesia, plans to plant 10,000 square kilometres over the next four years.

If vegetable oil looks likely to remain in short supply, another approach would be to make jet fuel from plant material using the Fischer Tropsch chemical process developed in Germany in the 1920s. Originally designed to produce synthetic diesel from coal, Fischer Tropsch can also make fuel from a wide range of organic matter. The feedstock is heated without oxygen to create a synthetic gas which is then passed through a catalytic reaction to produce high quality liquid fuels – including synthetic jet fuel which is indistinguishable from conventional kerosene. Depending on its source, in principle the fuel could also be very low carbon and not compete with food production, but unfortunately all the feedstocks have significant drawbacks.

Fischer Tropsch jet fuel is already produced from coal by Sasol in South Africa, where planes refueling in Johannesburg fill up with a half-and-half blend of kerosene and coal-to-liquids (CTL) fuel. The problem with CTL is that lifecycle emissions are roughly double those of kerosene, making aviation even more damaging to the climate.

The Fischer Tropsch process can also take natural gas as a feedstock, and gas-to-liquids (GTL) jet fuel was trialed by Airbus and Shell earlier this year. Well-to-wing emissions are lower than CTL, but surprisingly no better than conventional kerosene, because the Fischer Tropsch process itself consumes so much energy. According to Airbus’s rival Boeing, GTL jet fuel emits 1.5 times as much CO2 as kerosene.

The only realistic hope of producing Fischer Tropsch jet fuel with substantially lower emissions is to use some form of plant material as the feedstock – so-called biomass-to-liquids, or BTL – as championed by the German company Choren, which plans to start full-scale production by 2012. The company’s website boldly proclaims a vision of “potentially infinite production of renewable energy”, but a closer look at the numbers suggests the real outlook is rather less grandiose.

In a presentation at the World Future Energy Summit in Abu Dhabi in January, Choren CEO Tom Blades said the company’s BTL fuel could achieve greenhouse gas reductions of up to 91%, and insisted it would not compete with food production. One reason for both these advantages is that a large proportion of the feedstock will come from waste construction timber and existing forestry – to start with, at least. However Mr Blades acknowledged that to expand BTL production in future would require increasing amounts of specially grown energy crops such as willow or miscanthus. Within ten years more than half of Choren’s feedstock will come from energy crops, and this again raises the issue of land.

Mr Blades cited the EU’s Biomass Action Plan, which suggests that Europe has the potential to produce around 100 million tonnes of energy crops annually by 2030, and that total available biomass, including waste and forestry, could amount to 315 million tonnes. Since Choren’s BTL process takes 5 tonnes of dry biomass to produce a tonne of fuel, this would produce just over 60 million tonnes of fuel per year. That sounds a lot until you remember that in 2006 the EU consumed more than 700 million tonnes of crude. “We’re not replacing oil”, Mr Blades admitted, “just making it last a little bit longer”.

In the context of global aviation, the numbers are even more daunting. To produce the world’s current jet fuel from BTL would require – assuming the average European crop yields suggested by Mr Blades of 10 tonnes of biomass per hectare – nearly 1.2 million square kilometres. That’s well over three times the size of Germany, and makes no allowance for the predicted rapid growth in aviation. On the same assumptions, replacing all current transport fuel requires more than 10m km2 – bigger than China – demolishing any claim that second generation biofuels would not compete with food production.

The one remaining alternative on the horizon that might produce low-carbon jet fuel without competing with agriculture is algae, which can be grown in ponds of seawater built on non-productive land. Given the right conditions some species multiply quickly and contain oil, which can then be extracted and refined. It is widely agreed that such a system could deliver much higher yields than first generation oil crops such as palm or jatropha – meaning less space would be needed – although quite how much higher is still controversial.

The technology itself is nothing new. Dr Ami Ben-Amotz, a senior scientist at Israel’s National Institute of Oceanography, has been farming algae commercially for over 20 years, producing beta-carotene food supplements for the Japanese market. In 2004 he founded a new company, Seambiotic, to produce algae for biofuel on the site of a coal fired power station on the coast at Ashkelon.

Seambiotic algae ponds at Ashkelon, Israel

It is an undeniably neat arrangement. Cooling water from the power station is diverted to flow through the ponds before returning to the sea. Flue gas from the station’s chimney supplies CO2 to feed the algae. And energy for pumping and harvesting is available at minimal cost. Seambiotic is delighted with the results and will complete a larger, 5 hectare (50,000 square metre) pond on the same site by the end of the year. Dr Ben-Amotz says that breweries and refineries could provide similar opportunities.

There is huge excitement about algae, not only because it has the potential to moderate CO2 emissions but also because of the amount of fuel it might produce. Shell, which is building a pilot facility in Hawaii, claims algae could be 15 times more productive than traditional biofuel crops. Boeing maintains algae could produce 10,000 to 20,000 gallons per acre per year and that the world’s jet fuel could therefore be produced in an area the size of Belgium. However such claims leave the scientists who have done most research into algae production askance.

The fundamental problem, explains Al Darzins, who coordinates algae research at the US National Renewable Energy Laboratory, is that although algae grow very quickly, most of their biomass is usually carbohydrate. In order to achieve a higher proportion of oil, the algae must be stressed in some way – starved of nutrients such as nitrogen for example – which in turn limits their growth rate. As a result, Darzins thinks 5,000 gallons per acre is a reasonable target.

Dr Ben-Amotz is even more doubtful. To grow algae cheaply means using open ponds, which are open to invasion by local algae species that do not produce oil, or by predatory micro-organisms. There are also the day-to-day problems of keeping temperature and salinity constant, so theoretical levels of productivity are hard to maintain at large scale and over the long term. “If people say it’s possible let them show me”, says Ben-Amotz, “but usually they only show me a bucketful”.

With over twenty years’ production experience, Ben-Amotz is convinced that the maximum practical yield is 25 grams of biomass per square metre per day, of which 40% might be oil. That equates to 4,300 gallons per acre per year, meaning that to replace current jet fuel consumption would take 70 thousand square kilometres, or two times Belgium. Massively better than BTL, but still enormous.

Nevertheless the interest in algal jet fuel is intense. America’s Defense Advanced Research Projects Agency (DARPA) recently tendered research contracts with the aim of finding ways to produce JP-8 military jet fuel for less than $3 per gallon. And given the limits on other potential sources of low carbon fuel, the stakes are high: nothing less than the survival of aviation as we know it.

The biggest shortage may be not so much space as time. At the Virgin launch, Sir Richard suggested that algae might produce enough fuel for the entire airline industry, and that such technological breakthroughs represented the only chance of mitigating peak oil, which he said could arrive within six years. But when asked if fuels like jatropha or algae could be ready by then, he did not sound so confident: “we have to try our best to make them available as fast as we possibly can”.

4 Comments on “How do you solve a problem like jet fuel?”

auntiegrav Says:
May 6th, 2008 at 9:21 pm

First step: Prove that anyone actually, truly, NEEDS to fly anywhere.
Airlines down the tubes? No great loss except to those who have built empires on fooling people into believing they “absolutely, positively HAVE to be there overnight.”
No, they don’t.
Poor planning and egotistical systems that simply suck resources out of the ground and spew them into the stratosphere are no replacement for cooperating with the environment which spawned us and taking the time to do things locally and with care.
I spent the best parts of my life working on aircraft. I love them. But as with most of the things we fall in love with, they are simply infatuations, and it’s time to grow up.

Geoffrey Warrren Says:
May 6th, 2008 at 11:20 pm

This is the most detailed overview of Peak Oil from an aviation perspective I have read and while it is sobering to grasp the enormity of the challenge faced by aviation in a carbon-constrained world, it is also encouraging to see the progress already being made. In the light of the recent escalation of global food prices, it is vital that the solutions found to mitigate Peak Oil do not seriously undermine efforts to feed the world’s poor. If nothing else, this article highlights the bind we are in with our addiction to fossil fuels and documents the problem of scaleability very well. This is why alternative fuels like hydrogen and quite probably ethanol too are never going to be replacements for liquid fuels derived from crude oil. Hydrogen simply lacks the energy density except in liquid form but that requires very expensive cryogenics to keep the temperature not far above absolute zero. World scale ethanol production from crops requires huge amounts of land we simply don’t have. Even enhancing global liquid fuel use with 10% ethanol extender will prove difficult without compromising food production. The aviation industry is to be commended for facing up to the fuel challenge posed by Peak Oil well ahead of the political establishment and I will be following developments of synthesing fuel from jatropha, algae and timber waste with interest.

John Says:
May 25th, 2008 at 8:00 pm

There is in my opinion third option;

Releasing climate active agents during flight could make the airplanes CO2 negative at a large rate.

It is not the case that I believe this would be a good solution, it just is less worse.

We have to be able deal with scenarios worse than what the IPCC projects — this means, no matter how you flip it, doping the atmosphere with sun screen. Either water, or other cooling agents like the ones we get from large volcano eruptions. This mechanism is after all proven not to induce irrevocable catastrophe — while if the Tundra melts, or the Amazonas burns, then we are in hell.

There is no other realistic immediate delivery at the moment than airliners — they would spread the agents evenly, and the tech is there and a whole lot simpler than rocket tech.

Further, the costs could be shared between governments(through the quota system, and tax breaks), consumers (that could pay a premium to fly with planes on climate cooling duty), and the aviation industry out of self interest.

A small fact: the current IPCC models factor methane emissions from melting tundra. But they do not factor the emissions from the melting lakes in north russia. Measurements indicate that the methane release from the lakes is equal in size to that from ground. Mind that this is factors working into a feedback loop, and the halflife of methane that escapes to the atmosphere.

It is insane to accept a solution to a problem on this scale with no guarantee of success nor any fast enough mechanism to mitigate failure of either estimates or the implementations of the (too weak?) measures.

admin Says:
May 30th, 2008 at 8:07 am

This is guest post from Pushker Kharecha, climate researcher at NASA’s Goddard Institute for Space Studies in New York:

John’s suggestion boils down to the idea of geoengineering, i.e. planetary-scale technological ‘quick-fixes’ to help cool the global climate. The most common geoengineering proposal is injection of sulfate aerosols into the lower stratosphere, meant to mimic the effects of large volcanic eruptions (which have a temporary but significant cooling effect on global climate). John’s argument is essentially that (1) geoengineering is absolutely necessary at this point, and (2) airplanes could provide an effective means of dispersal of the cooling agents.

Geoengineering via sulfate injection has actually been proposed by some prominent scientists, e.g. Nobel laureate Paul Crutzen. It’s still a very controversial issue, and I won’t discuss the detailed pros and cons here. Suffice it to say that it’s based purely on theory, and although there could be significant benefits from the cooling effect, there would almost certainly be major negative impacts as well. Perhaps most important of these is the continuing acidification of the ocean, which among other things could cause mass extinction of marine organisms. Ultimately, although geoengineering might mitigate the warming effect of increasing atmospheric CO2, it does nothing to address the root cause, i.e. fossil fuel and land use emissions. These are just the basic facts….

As for my opinion of John’s argument, while part (2) might well have some merit, I don’t entirely agree with part (1), i.e. the premise. There are apparently some climate scientists who would agree with it, but I prefer to take a more optimistic approach. I think it’s entirely plausible that society will start curtailing CO2 emissions in time to avoid the need for drastic geoengineering measures — in fact, Jim Hansen, myself, and our colleagues have outlined such measures in detail in several recent papers (,

So, the main thing missing is the will, since the means are already there — although they are obviously not being applied to the necessary scale. The global public already seems to recognize not only the seriousness and urgency of the global warming problem, but it also seems to be willing to take action to resolve it (based on public opinion polls from around the world). So, it seems to me that the onus is really on elected leaders and leaders of industry to obey the public will! The change has to start here in the US and in other developed countries — mainly because they are responsible for the vast majority of the problem to date, but also because their actions would likely have a ripple effect among developing countries.

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