How do you solve a problem like jet fuel?

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”.