A jet mixer developed at the University of Utah creates fuel from algae – with less required energy than older conversion methods. The research team hopes that their discovery will turn biomass itself into a viable, cost-effective alternative fuel.

The creation of algal-based biofuel requires the extraction of lipids. The fatty acid molecules must be pulled from the microorganisms growing in ponds, lakes, and rivers.

Current extraction techniques, however, call for more power than the biofuel process actually creates.

The University of Utah’s new mixer extracts lipids in seconds.

The team's results were published in a new peer-reviewed journal, Chemical Engineering Science X .

"We have removed a significant development barrier to make algal biofuel production more efficient and smarter,” said Dr. Leonard Pease , a co-author of the paper. “Our method puts us much closer to creating biofuels energy parity than we were before."

In order to extract the oil-rich lipids from the algae, scientists have had to pull the water from the algae first – the most energy-intensive part of the process. The biomass residue is then mixed with a solvent, where the lipids are separated and then used to produce algae-based biofuel.

Dr. Pease says his team’s “confined impinging jet mixer” offers a more practical, energy-efficient, and economical process.

The researchers’ mixing extractor shoots jets of the solvent at jets of algae, creating a localized turbulence in which the lipids "jump" a short distance into the solvent stream. The solvent is then taken out and can be recycled to be used again in the process.

The high-speed lipid leap means less required energy – a “game-changing” development, Pease told Tech Briefs.

In the Q&A below, Pease explains how the mixer works – and how the technology may lead to a more mainstream use of algal biofuels.

Tech Briefs: What were some of the earliest methods for turning algae into fuel?

Dr. Leonard Pease: There are a handful of prior extraction methods, but perhaps the most common was the Bligh and Dyer method. In their method, the algae was dried in an oven, ground into a powder, mixed with strong solvents (methanol and chloroform), and then mixed at high speed to extract the oils or biocrude.

Tech Briefs: What is biocrude?

Dr. Pease: Biocrude is simply another term for the lipids or oils that were once inside the algae or other organisms. The term implies that these lipids are at the beginning of a process that will change them into useful oils.

Tech Briefs: How does your jet mixer improve upon early extraction methods?

Dr. Pease: In contrast, the impinging jet mixer uses the algae suspension as a liquid and performs extraction with weaker solvents (hexanes). In net, extraction with impinging jet mixers does not require the thermal energy of drying, the mechanical energy of grinding, or the strong solvents of the Bligh and Dyer method. Removing these elements significantly reduces the energy cost and makes the process more environmentally friendly. This is important because harvesting lipids from algae has historically been perhaps the most challenging and energy-intensive step.

Tech Briefs: Take me through the jet mixer. What does it look like? How does it work?

Dr. Pease: The impinging jet mixer is simply a means of mixing two liquid streams together at high speed. One stream carries the suspended algae cells, and the other stream adds the solvent (see the figure below). Within the mixing chamber, the two streams turbulently mix. The mixed fluid then comes out of a third outlet.

According to the theory within the mixing chamber, the turbulence creates thin layers of the solvent and water around the algae cells. The turbulence also shears the cells so that they stretch and release the lipids. Because the layers are so thin, the lipids can quickly jump across the water layers to the solvent layers. The combination of turbulent shearing and the short distances created by the turbulence is what makes this technique fast and efficient.

The jet mixer. In the image, algae (from left) and solvent streams (from right) impinge in a central chamber, exiting towards the bottom. (Image Credit: University of Utah)
Tech Briefs: What has been the holdup regarding the use of algae as biofuel?

Dr. Pease: From a technical point of view, for algae to be a mainstream competitive biofuel, it must achieve energy parity and cost parity with other transportation fuels. Energy parity means that the amount of energy used to prepare the fuel through its life cycle is equal to the amount of energy that can be used (e.g., to drive a vehicle). Cost parity means it costs the same amount to produce as it can be sold for.

When solar panels crossed energy and cost parity, solar panels went from demonstration projects to becoming available on houses across the globe. The same advances are needed for algal biofuels and other biofuels from single-cell organisms to advance from high-end demonstration projects to consumer commodities.

Tech Briefs: How do you envision biofuel being used in the future?

Dr. Pease: As we gradually transition to more renewable transportation fuels, I would like to see algae farms near conventional refineries. This will require innovations in algae production, lipid harvesting using impinging jet mixing extraction, conversion of lipids into biodiesel, and then mixing of the biodiesel into conventional diesel.

Tech Briefs: What’s most exciting to you about the possibilities of this jet mixer?

Dr. Pease: Though the applications of this jet mixer are vast, I am very excited about the potential of this impinging jet mixer for biocrude production and its potential to change the way we harvest the lipids. We see impinging jet mixing as a key element in a new system that achieves both energy and cost parity.

What do you think? How do you envision biofuel being used in the future? Share your comments and questions below.