A specific type of alcohol-to-jet (ATJ) fuel recently became the latest kerosene alternative to be approved for use in commercial aviation – a milestone that its only producer hopes will light the touchpaper for the explosion in airline demand needed to economically scale up production.

On 1 April, certificating body ASTM International revised its D7566 jet fuel standard to include the alcohol-to-jet synthetic paraffinic kerosene (ATJ-SPK) pathway for fuel manufactured using isobutanol as a feedstock. At the moment, only Colorado-based Gevo produces this type of ATJ fuel.

Similar fuels using ethanol as a feedstock, such as those produced by Byogy Renewables and LanzaTech, remain uncertified for use in commercial aviation. However, the ASTM specification “outlines a pathway for inclusion of any C2-C5 alcohol feedstocks as additional data is generated by such producers”, says the Commercial Aviation Alternative Fuels Initiative (CAAFI).

ATJ-SPK approval has been more than six years coming, and follows the certification of four other alternative jet fuel pathways. These include fuels produced from plant oils and animal fats (hydroprocessed esters and fatty acids, or HEFA); fuels derived from plant sugars converted into farnesane (synthesised iso-paraffins, or SIP) and two types of fuel developed using Fischer-Tropsch technology (FT-SPK and FT-SKA).

Unlike HEFA and FT fuels, which have been certified for use up to a 50% blend with kerosene, ATJ-SPK can only be blended up to 30% for the time being. SIP fuels are certified to a 10% maximum blend.

“We originally put in for 50%, but this would have required more work. We can go back and do that later,” says Gevo chief executive Patrick Gruber. “We haven’t focused on it yet. As we’re such a tiny drop of nothingness, 30% is more than adequate for now.”

The recent approval by ASTM gives the green light for Alaska Airlines to operate the first commercial flight using ATJ fuel, and gives Gevo cause to hope it can to drum up enough demand from other carriers to enable it to build more facilities and ramp up production.

“Airlines are interested, there’s no question. Now that we’ve got ASTM approval we’re having dialogues with lots of people,” says Gruber. “ASTM approval was the trigger – now [airlines] are willing to put the effort in… nothing happens without demand from airlines. They’ve got to put their money where their mouth is.”

Last July Alaska Airlines signed a strategic alliance agreement to purchase Gevo’s fuel and operate an alcohol-to-jet-fuelled commercial flight. The airline says it will still “be scheduling a test flight”, but has not provided any details on when. Gruber expects it to happen “relatively soon”.

Lufthansa was also an early mover, agreeing in 2014 to help co-ordinate an evaluation of Gevo’s fuel as part of a European Union-funded project.

Gruber believes the feedstocks used to create Gevo’s fuel – primarily corn starch and sugarcane, although “in future we will see wood and agricultural waste used” – can be much more readily grown than the feedstocks used to produce HEFA fuels, meaning the opportunities to scale up production are greater.

“What’s good is that there is an abundant supply of carbohydrates around the world,” he says, noting that carbohydrate crops can be grown at a fifth of the cost and at twice the volume of their vegetable oil-producing counterparts. “Our [fuel] is a different game – we’re going for something that works across the world and can be scaled up.

“Our technology is the most cost-effective technology to be approved. It is 98% efficient to convert chemical isobutanol to jet fuel, so the economics make this the most cost-effective route.”

However, for alternative fuels to truly take off, airlines may have to accept that reducing their impact on the climate will come at a higher price than continuing to solely burn fossil fuels – particularly while oil prices remain at their current low levels.

“Today, with the oil price down, we would be at a premium. But [when oil gets to the] $75 [per barrel] range then it starts to be cost-competitive,” says Gruber.

The type of airlines that accept they will have to pay a premium will be the first movers that demonstrate a real commitment to reducing their emissions. But not all carriers fall into this category, as Gruber points out: “There are two camps of people: one that says ‘I will do something’, like Alaska and United Airlines, and another that says, ‘just tax me’.”

When it comes to scaling up production – always the key issue with renewable aviation fuels – there are two steps for Gevo to take. The first is to add the capability to produce jet fuel at its existing plant in Luverne, Minnesota, at an initial volume of 10 million US gal (38 million litres) a year. The next step would be to build multiple plants with licensees, with the capacity to produce up to 50 million gal a year.

The type of feedstock used for each plant would vary, depending on its geographical location. For instance, in Minnesota it would be corn starch, whereas in South America or Australia it would more likely be sugarcane. In the longer run, cellulosic sugars – sugars derived from non-food biomass – could be used, although Gruber says this “is not ready for primetime yet”. Gevo was awarded a $5 million grant by the US Department of Agriculture in 2011 to develop cellulosic jet fuel from woody biomass and forest product residues.

Adding to the Luverne plant would take about two years because “we have so much installed there already” says Gruber, while other plants developed alongside partners would take an additional two years as they would be starting from scratch. Gevo already operates a biorefinery in Silsbee, Texas, in collaboration with South Hampton Resources.

Gruber says the company “should be able to do something relatively soon” on the partnership front now that ASTM approval has been secured, describing it as a “chicken and egg” process. “We have to get the supply contracts and we’ve got to get people from all sides working together,” he says.

Gevo has also been working with the US Department of Defense for several years to develop and test its fuel. The company signed an initial contract to supply more than 16,000gal of fuel to the US Army, as part of its energy security strategy to certify 100% of its air platforms on alternative/renewable fuels by 2016.

In 2013, the Sikorsky US-60 Black Hawk helicopter became the first US Army aircraft to fly on a 50/50 blend of Gevo’s isobutanol ATJ fuel. The following year, the US Navy tested a 50/50 ATJ blend in supersonic afterburner operations – a test needed to clear the Boeing F/A-18 Hornet for ATJ operations throughout its entire flight envelope.

“The DoD has been our biggest sponsor during development and we would never have been able to get this far without them,” says Gruber, adding that the Lockheed Martin F-35 “is the only airframe in the [US] military that hasn’t flown” on Gevo’s fuel.

With the US DoD firmly on board and with certification now secured, it is up to commercial airlines to create the demand needed to ensure that companies such as Gevo can scale up production of alcohol-to-jet fuels to commercially viable levels.

Gruber emphasises: “If the aviation industry really wants to reduce its greenhouse gas emissions, it must have renewable carbon as a feedstock.”

Source: FlightGlobal.com