Terpenes may be the most unloved class of energy molecule of all time, if you compare R&D spending to potential. Even ARPA-E, the home of high-risk, high-reward government research into energy, hasn’t delved into terpenes since 2012’s OPEN invite, where Allylix picked up a single $467,6905 award to develop a “Renewable Platform for Production of Sesquiterpene Aviation Fuels & Fuel Additives from Renewable Feedstocks”. Then, Allylix was acquired by Evolva, which has focused its portfolio on stevia, resveratrol and nootkatone and put terpene fuel capabilities on the back burner.
Allylix was making super-dense fuels that could serve as high-energy additives, or ultimately serve the JP-10 market — think $25 per gallon missile fuel. One problem? The feedstock was sugar, which started the process with a cost albatross around its neck.
But what about isoprene? At the end of the day, two isoprene molecules make up a terpene and three make up a sesquiterpene. And there’s much to love about isoprene.
4 Reasons to love bio-isoprene
1. Love drop-in fuels? Isoprene is a hydrocarbon, C5H8.
2. Dislike the loss in vehicle range with ethanol and EVs? Isoprene checks in at 107,000 BTUs/gallon, roughly 40% ahead of ethanol, and about 6 percent short of gasoline.
3. A fan of high octane? Isoprene is a chart-buster, checking in with a RON of 132, compared to 109-120 for ethanol and 84-85 for standard gasoline at the refinery.
4. One more thing to prize in isoprenes is that they also serve a higher-value chemicals market — bio-isoprene is a perfectly good material for tires — so, a project to make isoprenes has a natural high-value, small-volume market but translates well to bigger markets that large production volumes can unlock.
The basic idea
If you follow the basic chemical math, you won’t make isoprene the way that organisms do, but it’s easier to get the idea:
5CO2 + 4H2O —> C5H8 + 4 O2
Plants give off free oxygen, that’s the O2 there — and C5H8, that’s our friend isoprene. To make it, they use three inputs which they obtain for nothing, and even in an industrial setting, CO2 is cheap, water is even cheaper, and sunlight is free.
Lots and lots of source micro-organisms
The word champ in terms of R&D interest has been Botryococcus braunii, a species of green micro-algae that lives in and uses seawater. Here’s some work on that.
We call him Brownie, for short. As Wikipedia notes:
In folklore, a brownie resembles the hob, similar to a hobgoblin. Brownies are said to inhabit houses and aid in tasks around the house. However, they do not like to be seen and will only work at night, traditionally in exchange for small gifts of food.
As JGI points out:
Approximately 40 percent of the B. braunii cells is made up of hydrocarbons, and the oil produced can be easily converted and used for vehicle and jet fuels with more than 90 percent efficiency. B. braunii has been studied for several decades not just for its potential as a source of biofuel but for its ability to sequester carbon.
But there are other candidate microorganisms — this research project looked at isoprene made by diatom strains (Thalassiosira weissflogii and Thalassiosira pseudonana), prymnesiophyte strains (Pleurochrysis carterae), dinoflagellate strains (Karenia brevis and Prorocentrum minimum), and cryptophyte strains (Rhodomonas salina).
Prefer macroalgae? Try this research project.
Do Brownies make isoprene? Here’s what the researchers at Alchetron have to say:
Up to 86% of the dry weight of Botryococcus brauniican be long-chain hydrocarbons. The vast majority of these hydrocarbons are botryocuccus oils: botryococcenes, alkadienes and alkatrienes…Botryococcenes are unbranched isoprenoid triterpenes having the formula CnH2n-10. The A race produces alkadienes and alkatrienes wherein n is an odd number 23 through 31. The B race produces botryococcenes wherein n is in the range 30 through 37…Botryococcenes are preferred over alkadienes and alkatrienes for hydrocracking as botryococcenes will likely be transformed into a fuel with a higher octane rating.
Brownie gets sequenced
So, here’s some of the best news that has come down the fuel pathway for some time:
The genome of the fuel-producing green microalga Botryococcus braunii has been sequenced by a team of Texas A&M AgriLife researchers. In addition to sequencing the genome, other genetic facts emerged that ultimately could help his team and others studying this green microalga further research toward producing algae and plants as a renewable fuel source.
The report, in Genome Announcements, came after almost seven years of research, according to Dr. Tim Devarenne, AgriLife Research biochemist and principal investigator in College Station. In addition to sequencing the genome, other genetic facts emerged that ultimately could help his team and others studying this green microalga further research toward producing algae and plants as a renewable fuel source.
So, that’s the claim and it’s almost true.
It’s actually what they call a “draft genome.”. Devarenne said that because only portions of the B. braunii genome in this report are “spelled out”.
“It’s not perfect, but it’s still very usable and valuable to the other researchers who are studying this alga,” he said. He added that sequencing B. braunii genome has been very challenging to assemble because of lots of repetitive sequences in it.
“Assembling the genome is not a trivial process at all,” Devarenne explained. “We send DNA to be sequenced by the Joint Genome Institute, which is part of the U.S. Department of Energy, and they sequence it in lots of very small fragments. These fragments of DNA may be anywhere from 150 to 300 base pairs long. So imagine if we have 166 million bases in our genome, and it is sent back to us in little fragments that have to be assembled back together to arrive at 166 million bases. We used the Texas A&M Supercomputer Center to help.”
As more gaps are filled in, he said, a more complete genome will emerge, and that will help researchers dive deeper into the biochemical processes in this alga.That information will then help them understand how and why the organism makes hydrocarbons in very high quantities, how that process is regulated and what the particular biosynthetic pathways are used to make the hydrocarbons.
Brownies: petroleum’s missing link?
How exactly was petroleum created in the first place? Our genome team here points out that “hydrocarbons from B. braunii have long been associated with petroleum deposits, indicating that over geologic time the alga has coincided with and contributed to the formation of petroleum deposits.”
“Essentially,” said Devarenne, “if we were to use the hydrocarbon oils from this alga to be a renewable fuel source, there would be no need to change any kind of infrastructure for making the fuel. It could be put right into the existing petroleum processing system and get the same fuels out of it.”
The silence
You’d think that the world would be all over a microbe that makes petroleum out of thin air and water. It ought to be the state animal of Texas, replacing the armadillo and the Texas Longhorn, which are animals of great repute but they don’t synthesize oil, do they?
The problem is, as always, an organism that makes the right concentrations of target material, but never fast enough. Back in the age of the dinosaurs, no one was on the clock, take a million years, no worries. But here we are in the 21 century and the operative word in this bioeconomy is speed. Hard to get three year payback.
So, someone has to get Brownie into the gym and work hard on productivity. And make all those lovely isoprenes.
A project to watch
Meanwhile, here’s one project in South America.
HHT was selected for the conceptual design of a pilot plant to demonstrate the photosynthesis of isoprene from algae in closed bioreactor systems. The conceptual design included the processing facility, laboratory, gas storage, utilities, offices and maintenance.
The Bottom Line
By Brownie or any other source, why aren’t we spending more time on isoprenes? Just sayin’.