esearchers Greg O’Neil of Western Washington University and Chris Reddy of Woods Hole Oceanographic Institution (WHOI), have exploited an unusual and untapped class of chemical compounds in the microalgae Isochrysis to synthesize both biodiesel and jet fuel, in parallel. The new study was published in the journal Energy & Fuels.
“It’s far from a cost-competitive product at this stage,” says O’Neil, the study’s lead author, “but it’s an interesting new strategy for making renewable fuel from algae.”
For their study, O’Neil, Reddy, and colleagues targeted Isochrysis for two reasons: First, because growers have already demonstrated they can produce it in large batches to make fish food. Second, because it is among only a handful of algal species around the globe that produce fats called alkenones. These compounds are composed of long chains with 37 to 39 carbon atoms, which the researchers believe hold potential as a fuel source.
Alkenones are well known to oceanographers because they have a unique ability to change their structure in response to water temperature, providing oceanographers with a biomarker to extrapolate past sea surface temperatures. But biofuel prospectors were largely unaware of alkenones. “They didn’t know that Isochrysis makes these unusual compounds because they’re not oceanographers,” says Reddy, a marine chemist at WHOI.
Reddy and O’Neil began their collaboration first by making biodiesel from the FAMEs in Isochrysis. Then they had to devise a method to separate the FAMEs and alkenones in order to achieve a free-flowing fuel. The method added steps to the overall biodiesel process, but it supplied a superior quality biodiesel, as well as “an alkenone-rich…fraction as a potential secondary product stream,” the authors write.
“The alkenones themselves, with long chains of 37 to 39 carbons, are much too big to be used for jet fuel,” says O’Neil. But the researchers used a chemical reaction called olefin metathesis (which earned its developers the Nobel Prize in 2005). The process cleaved carbon-carbon double bonds in the alkenones, breaking the long chains into pieces with only 8 to 13 carbons. “Those are small enough to use for jet fuel,” O’Neil says.
The scientists believe that by producing two fuels – biodiesel and jet fuel – from a single algae, their findings hold some promise for future commercialization. They stress that this is a first step with many steps to come, but they are encouraged by the initial result.