Direct conversion of wet algae to biodiesel

By Bryan Sims
Posted Sept. 1, 2010

Researchers at the University of Michigan have published the feasibility of a two-step hydrolysis-solvolysis process to produce biodiesel directly from wet algal biomass, eliminating the need for costly biomass drying, organic solvent extraction and catalysts. The paper on the process was published in the ACS journal Energy & Fuels.

In the first step, wet algal biomass contained 80 percent moisture and was reacted with subcritical water to hydrolyze intracellular lipids, conglomerate cells into an easily filterable solid that retained the lipids and produced a sterile, nutrient-rich aqueous phase. In the second step, the wet, fatty acid-rich solids underwent supercritical transesterification with ethanol to produce fatty acid ethyl esters (FAEEs). The team used Chlorella vulgaris algae, which contained 53.3 percent lipid content.

According to Phillip Savage, lead researcher on the project, the team gathered the wet algae grown from the lab and centrifuged it to transform the algal biomass into a paste-like substance. "At large scale that probably wouldn't be applicable for an economical process," he noted. "We got something that was probably around 10 to 20 percent solids to the balance of water."

The research yielded promising results, Savage added, but the project is anticipated to be refined and optimized in order for to demonstrate greater economic and environmental feasibility of the process on a larger scale.

"More remains to be understood regarding how whole cells, hydrothermally processed algal biomass and intracellular constituents influence supercritical transesterification and potentially contribute to nonester components in the final fuel product," the paper reported. "Additional research and process optimization are likely to improve yields and reduce process inputs (e.g. ethanol), thereby minimizing the overall environmental impact of algal biodiesel production. To be economically viable, biodiesel yields must be above 95 percent and preferably higher than current norms achieved with alkali-catalyzed processes."
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