By Jim Lane
ARPA-E has been working hard on feedstock diversity — so much so that we kid them about changing their name to ARPA-Agriculture — yes, from time to time they work on fuels, but not so much on energy density.
Too bad — because a moonshot-oriented mission aimed at transforming energy density sets up really well for revolutionizing the way we do lots of things. Like moonshots. And other ways we use transport fuels, all of us back here on the good Earth.
Density matters, that’s how we see it. Super-dense fuels are superfuels and they have a real place in our economy — not to mention our advanced bioeconomy. They have functional advantages that matter.
There are fuels that have twice the density of kerosene (which is the highest density-fuel widely available, and used for jet fuel). Superfuels are not more widely available because they are wildly expensive to make from petroleum. As in, $5,000 per gallon. Yep, that’s the price the US pays for some of this stuff. $40 an ounce. More than the wholesale price of Chanel No. 5, just in case you were wondering.
So, today, we’re going to chat about a molecule so difficult to pronounce that you get a prize for saying it three times real fast:
I think the Sherman Brothers originally wrote about it in an early draft of lyrics for Mary Poppins.
even though the sound of it it something quite insane
if you buy it cheap enough, man, how it flies a plane
But Disney went in a different direction with Mary Poppins, and so it’s left the The Digest to chat up this unloved nitroamine propellant with the exotic chemical formula C6H6N12O12. Since it’s completely unpronounceable, it’s known as HNW or CL-20, the CL in this case standing for China Lake Naval Weapons Research Lab.
The density is impressive. 2.04 grams per cc compared to 0.8 g/cc for kerosene, which is used primarily for jet fuel. The military’s current incumbent for high-energy explosive and propellant — the fuel of choice for Trident missiles and the Peacekeeper ICBM is HMX, also known as octogen. And that checks in at 1.91 g/cc.
As previously advertised above, HMX is pricey. Last we heard, it was running $100 per kilo, and CL-20 itself, produced in small quantities by Thiokol mostly, is running something like $1300 per kilo.
What can you use a fuel like CL-20 for?
Besides, missile propellant, consider the opportunities in space. Right now, a limiting factor for satellite launches and anything else in the commercial side of space is the cost per pound of payload.
To illustrate: the Space Launch System due very soon will require 5.5 million pounds of spacecraft to put 154,000 pounds in orbit. 89 percent of the weight is in the propellant. So, consider the opportunities.
Why does density matter? Just for rockets and stuff?
The story of propulsion and the modern economy is one of increasing energy density. Wind propulsion and the use of draft animals was replaced by steam, steam to coal, coal to petroleum, petroleum to nuclear. Progress that tamed the roads, then the seas and finally the skies and stars — it’s been all baed on generating more energy density, generating more thrust, storing more power.
For that reason, electric vehicles and to some extent hydrogen are a major anomaly in what otherwise has been a progression that paralleled and in part caused the Industrial Revolution. Batteries don’t provide more energy per cubic foot, they provide less, and on a per pound basis they are not even yet in the ballpark of consideration.
So, it’s worth considering whether renewables should be looking to provide more density instead of less — which would lead to more range and convenience, and more energy-efficient vehicle designs.
The energy density, carbon-intensity landscape
Here’s an illustration, not drawn precisely to scale, which gives you a sense of the choices we make as a society when it comes to density and carbon intensity. There are other considerations — cost and availability are very important factors not illustrated in this chart, but they matter.
But these are real issues. If it were just a matter of carbon, we’d use sails to move trucks. If all we wanted was energy density and sustainability didn’t matter, we’d all have nuclear packs propelling us around, or we’d remove the catalytic converters in our engines.
Superfuels offer a unique potential to maximize energy density and reduce carbon. Interesting then, the work going on in high energy density fuels, known in the trade as HEDFs.
Work on high energy-density fuels
Gevo and LANL are looking to develop a low-cost, catalytic technology that would be bolted-on to Gevo’s existing isobutanol-to-hydrocarbons process to produce high energy density fuels. With the successful scale-up of this technology, it is believed that Gevo’s HEDFs could be produced at a lower cost than the petroleum-based equivalent, even at current oil prices.
Simultaneous to that announcement, a sister announcement said it will be partnering with the National Renewable Energy Laboratory, Argonne National Laboratory and Oak Ridge National Laboratory on a project to fine-tune the composition of the catalyst used in Gevo’s proprietary ETO process, in order to improve performance and accelerate scale-up efforts. ChemCatBio, a consortium within the US Department of Energy, awarded funding to the national labs in support of the project.
JP-10 is an interesting fuel, used because of cost considerations only in missiles, where range and not cost is the primary consideration — JP-10 adds a functional advantage.
More on that effort here in Sierra Hotel: Los Alamos, Gevo to develop ultra long-range missile, aviation fuels.
And we looked at the entire JP-10 landscape here, in Making superfuels affordable, via biofuels: the JP-10 story
A cautionary note
Paul Bryan the former Chevron Biofuels VP and noted industry consultant, who served as DOE Biomass Program manager a few years back and also sits on the Digest’s Due Diligence Wolfpack, had some cautionary notes for The Digest and the pursuit of high energy density fuels:
One point about the chemistry of fuels vs. explosives. Energy density is important for both, of course, but with explosives, of equal importance is that they carry their own oxidizing agent right on board the molecule — typically nitrogen is the best, oxygen second best, often the two are combined as “nitrates,” and occasionally you’ll find some more exotic elements, too. Fuels, on the other hand, at least for jet aircraft, use the oxygen in the air, and the fuel itself mostly has only the elements that GET oxidized, like carbon and hydrogen. Rocket fuels are sometimes more like explosives, especially solid rocket fuels, or they use a more exotic oxidizer (liquid oxygen, hydrogen peroxide, etc.) to get that extra oomph.
But for true explosives, you need to have the oxidizer present on a molecular level, because you can’t deliver oxygen from the air to it fast enough for the reaction to proceed at a rate considered to be an “explosion.” FAE (fuel-air explosives) are an exception, but those require an organic vapor to be dispersed in a large volume of air before the mixture is ignited — very much like the explosions that happen in the cylinders of internal combustion engines.
For gunpowder, the oxidizer is salt peter, aka potassium nitrate. For dynamite, it’s the nitrogen and oxygen in the nitroglycerin molecule. For TNT, it’s the nitrogen and oxygen in the tri-NITRO-toluene molecule, and so on.
So, there’s energy density to consider, but oxidation for fuels is important too. We don’t want planes and cars to, ahem, explode.
The Bottom Line
Are superfuels a moon-shot? Yes.
But then again, a trip to the Moon is by definition is a moon-shot, and we’re going there, the Moon that is, unless we go to Mars first. Why not have better fuels to take with us — and, especially, fuels that you perhaps could make on the surface of Mars? From some of that CO2, water and sunlight sitting around — and a gas station a hundred million miles away.
It’s the kind of high-risk, high-reward target that ARPA-E generally looks at. So, why not density?