Jet Fuel from Trees (or Almost Anything Else)

Out of the dozens of press releases that hit my email inbox in the last week, one that caught my eye was for a gathering of a group called the Northwest Advanced Renewables Alliance (NARA) in Missoula, Montana this Thursday.  Their agenda is focused on "challenges to develop a residual woody biomass to jet fuel and valuable co-products industry in the Pacific Northwest."  Somewhat more snappily, their website calls this "from wood to wing."  With oil prices (UK Brent) persistently over $100 despite the weak global economy, the appeal of such an effort is not hard to understand.  Whether it's feasible at an acceptable price remains to be seen.

Making fuels from waste or non-food crops is an attractive idea, and aviation fuels look like an especially promising market for bio- and synthetic fuels, for several reasons.  Unlike the markets for motor fuels--gasoline and diesel--you wouldn't have to convince millions of customers of the efficacy of using a new fuel.  You'd only have to convince the fuel buyers and chief engineers of a handful of airlines and aircraft leasing companies, along with the even smaller universe of engine suppliers.  Certifying that your fuel meets all relevant specifications is a key step in that process, though in some respects that should also be easier than for gasoline and diesel engines. If you doubt that, just consider the current fuss over increasing the ethanol content of gasoline from 10 to 15%.  Of course, having your car engine fail on the interstate is a very different proposition than having both engines shut down at 40.000 ft--or during take-off.

Fortunately, turbine engines are very reliable and fairly flexible.  The best proof of the latter is that the turbine at the heart of a natural-gas-fired power plant is essentially just a bigger version of the ones hanging under the wings of a Boeing or Airbus aircraft, which burn a close cousin of kerosene, a simple distillate refined from a wide variety of crude oils. Turbines on ships burn a fuel similar to diesel. Many of the specifications that jet fuel must meet have more to do with the conditions under which aircraft operate than the specific sensitivities of jet engines.  One example of that is the temperature at which a jet fuel becomes difficult to flow, just before it freezes solid.  That's one reason that many oilseed-based biojet fuels require essentially oil-refinery levels of processing.  Stepping back from such details, however, I'm skeptical that crop-based biofuels are the long-term solution to the fuel-diversification needs of aviation, for many of the same reasons we see playing out with regard to corn ethanol during the current drought.

Supporters of various biojet efforts often focus on two main benefits of renewable jet fuel.  The first is the reduction of greenhouse gas emissions, since the principal alternative available to airlines or military aviation is further efficiency improvements, which face diminishing returns, or reduced operations.  The other benefit that I often see cited is potential cost savings versus petroleum, though I regard this as largely illusory, at least on the level of the fuel customer.  As I've described at length, the output of even a captive biojet facility is worth its price in the market--set by petroleum jet fuel--not its cost of production.  That argument should also hold true for airlines buying oil refineries.  However, to the extent that biojet could be scaled up enough to apply competitive pressure on the 6 million barrel per day global jet fuel market, or in  isolated regional markets, that would benefit both airlines and consumers. Production at that scale will require feedstocks that are readily available in large quantities.

Many companies and researchers are pursuing renewable jet fuel pathways that don't rely on food- or food-competitive crops.  The RenewableJetFuels.org website of the Carbon War Room provides a portal into some of these efforts, including fuels based on factory waste gases, algae, and various other approaches.  Some of these have progressed to demonstration-stage production and fleet certification, though as we've seen with cellulosic motor fuels, scaling up to truly commercial production represents a much higher hurdle that could shake out many of these contenders.  For that reason, it's encouraging to see the NARA effort, nor should they worry about being too late to the party.