According to Kaige Wang, a CSET researcher, and Robert C. Brown, CSET director and professor of mechanical engineering at Iowa State University, the research could help microalgae biorefineries move one step closer to economic and environmental feasibility.

“In general, catalytic pyrolysis is attractive for upgrading microalgae because it converts all of the components of this high nitrogen feedstock into fuels, chemicals, and nitrogen fertilizer,” the researchers said in a paper about the findings. Additionally, energy-intensive lipid extraction is eliminated in the process. The efficiency of such a system would greatly enhance the economy of a microalgae biorefinery.

Fast pyrolysis is used to heat the algae in the absence of oxygen at around 500 degrees C. To improve the process, the researchers mixed the algae with a catalyst prior to the pyrolysis.

With this approach, most of the nitrogen was reportedly converted to ammonia or retained in the char co-product, which suggests feasibility for recycling nitrogen as a nutrient for microalgae cultivation. Results also demonstrated that catalytic pyrolysis of microalgae produces better aromatic hydrocarbon yields and better aromatic distributions than catalytic pyrolysis of red oak. The maximum carbon yield of aromatics from microalgae was 24 percent, while that from lignocellulosic biomass was 16.7 percent.

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