How Algae Could Create Better, More Efficient Gasoline Than Corn

CREDIT: Sapphire Energy


CREDIT: Sapphire Energy

Looks like algae can be added to bacteria and fungus on the list of organisms that could turn biofuels from an energy policy misfire into a viable green power source.

A new study out of the University of Virginia, and published in the peer-reviewed journal Bioresource Technology, investigated the biofuel production process at a New Mexico demonstration plant owned by Sapphire Energy. They grow the algae in large outdoor ponds, then turn it into fuel using a high-heat and high-pressure process called hydrothermal liquefaction. They use salt water to avoid cutting into fresh water supplies, and have worked to keep their input needs as low as possible. It’s still at the pilot-project phase, but Sapphire Energy did recently pay off a $54.5 million loan from the Energy Department.

The study looked at Sapphire Energy’s current pilot-scale results, but they also projected them forward to see what full-scale production would look like. They found two things worthy of note.

At full-scale production, the life cycle greenhouse gas (GHG) emissions for algae biofuels are far lower than traditional corn-based biofuels and petroleum fuels. Corn-based biofuels dump a lot of GHGs into the atmosphere through the agricultural process, undoing most of the advantage inherent to not being a fossil fuel.

Cellulosic biofuels also manage to avoid that problem, but they currently come with a very low energy return on investment ratio (EROI). That’s the amount of energy you have to put into the process of making the fuel versus the final amount of energy you get from the fuel. It’s not the only consideration in a fuel’s viability, but it’s an important economic factor. Cellulosic biofuels have an EROI of around one, meaning just as much energy goes in as comes out, while traditional gasoline and diesel are between four and five. Algae biofuel lands between two and three, making it an improvement.

The EROI ratio and GHG emissions of (a) algae-derived diesel and (b) algae-derived gasoline produced using hydrothermal liquefaction.

The EROI ratio and GHG emissions of (a) algae-derived diesel and (b) algae-derived gasoline produced using hydrothermal liquefaction.

CREDIT: X. Liu et al. / Bioresource Technology 148 (2013)

A few other things worth mentioning: One, like cellulosic biofuels, which use crop waste, switchgrass, wood chips, and the like, algae-based biofuels’ feedstocks don’t compete with food supplies. That avoids the worst second-order effect of traditional corn-based biofuel.

Two, algae biofuels’ EROI may go higher, while petroleum fuels’ may go lower. The latter used to be at a stratospheric 100 or above, but that dropped precipitously as humanity tapped out the planet’s easy-to-reach oil reserves. Now we’re going after unconventional oils in shale, tar sands, the Arctic, and the like, which require far larger expenditures of energy and technological prowess to reach. Meanwhile, the study’s projections for full-scale algae biofuel production only covered the next five years. So it’s EROI will likely keep going up as technology and processes keep improving. It may not be long before the two ratios equal out, further solidifying algae biofuels preferability to traditional gasoline and diesel. (It’s also worth mentioning that the EROI for wind and solar already far outstrips both biofuels and petroleum fuels.)

Three, one thing the study’s analysis of life cycle GHG emissions didn’t account for is land use. That matters for biofuels, because natural forests and grasslands store more carbon dioxide than cropland. So beyond running the equipment and generating the power needed for production, making traditional biofuels adds carbon to the atmosphere just by converting land. But this also highlights another advantage of algae biofuels: the algae can be grown on marginal land that’s already not doing anything much to take carbon out of the atmosphere. Sapphire Energy’s set up, for instance, is out in the middle of the New Mexico desert. So adding in the land use factor is unlikely to change algae biofuels’ advantage in terms of GHG emissions.

Finally, the biocrude produced from algae is similar enough to traditional crude that it can be dropped into the refining process with few tweaks. So it could be scaled up into a major American fuel source with little change to our current infrastructure. It’s also cleaner, meaning refineries would be saved the effort and costs they currently spend getting thing silk sulfur and heavy metals out of oil.

Obviously, these results are preliminary. Sapphire Energy’s production is still at the pilot project level, and lots of research and analysis still needs to be done on algae biofuels’ viability. But the initial signs are good.

HT: CleanTechnica