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\u2019t delved into terpenes since 2012\u2019s OPEN invite, where Allylix picked up a single $467,6905 award to develop a \u201cRenewable Platform for Production of Sesquiterpene Aviation Fuels & Fuel Additives from Renewable Feedstocks\u201d. 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.<\/p>\n
Allylix was making super-dense fuels that could serve as high-energy additives, or ultimately serve the JP-10 market \u2014 think $25 per gallon missile fuel. One problem? The feedstock was sugar, which started the process with a cost albatross around its neck.<\/p>\n
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\u2019s much to love about isoprene.
\n4 Reasons to love bio-isoprene<\/p>\n
1. Love drop-in fuels? Isoprene is a hydrocarbon, C5H8.<\/p>\n
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.<\/p>\n
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.<\/p>\n
4. One more thing to prize in isoprenes is that they also serve a higher-value chemicals market \u2014 bio-isoprene is a perfectly good material for tires \u2014 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.<\/p>\n
The basic idea<\/p>\n
If you follow the basic chemical math, you won\u2019t make isoprene the way that organisms do, but it\u2019s easier to get the idea:<\/p>\n
5CO2 + 4H2O \u2014> C5H8 + 4 O2<\/p>\n
Plants give off free oxygen, that\u2019s the O2 there \u2014 and C5H8, that\u2019s 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.<\/p>\n
Lots and lots of source micro-organisms<\/p>\n
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\u2019s some work on that<\/a>.<\/p>\n We call him Brownie, for short. As Wikipedia notes:<\/p>\n 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.<\/p>\n As JGI points out:<\/p>\n 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.<\/p>\n But there are other candidate microorganisms \u2014 this research project<\/a> 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).<\/p>\n Prefer macroalgae? Try this research project<\/a>.<\/p>\n Do Brownies make isoprene? Here\u2019s what the researchers at Alchetron have to say:<\/p>\n 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\u2026Botryococcenes 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\u2026Botryococcenes are preferred over alkadienes and alkatrienes for hydrocracking as botryococcenes will likely be transformed into a fuel with a higher octane rating.<\/p>\n Brownie gets sequenced<\/p>\n So, here\u2019s some of the best news that has come down the fuel pathway for some time:<\/p>\n