PhD Julie Zimmerman explained biofuel from algae is sustainable and renewable. (Photo: yale.edu)

Progress made toward a cheaper way to make biodiesel from algae

UNITED STATES
Thursday, June 21, 2012, 00:30 (GMT + 9)

Scientists described an advance toward a long-sought economical process that could turn algae into a revolutionary new and sustainable source of biodiesel and other "green" fuels. Their report on the use of an environmentally friendly process for extracting oil from algae came at a session of 16th annual Green Chemistry & Engineering Conference, held this week by the Green Chemistry Institute, part of the American Chemical Society (ACS).

"Algae has great promise as a next-generation biofuel, a fuel that is sustainable and renewable," explained Julie Zimmerman, PhD, who leads the research team. "It has more oil per pound than corn and soybeans, does not divert crops from the food supply and can potentially be grown in sewage water and seawater without impacting the freshwater supply."

Lindsay Soh, a graduate student in Zimmerman's lab, described their efforts toward a simple process that would extract the fatty molecules called lipids used to make biodiesel from algae and transform them into usable fuel in one fell swoop. This could make biodiesel production from algae cheaper, faster and greener than current methods, which require separate steps — each with its own vessel and chemicals — to perform those operations.

This "one-pot" reaction uses so-called supercritical carbon dioxide, which uses elevated pressures and temperatures so that it fills its container like a gas but is as dense as a liquid.

Zimmerman pointed out that the process is nontoxic, which makes carbon dioxide an attractive alternative to some of the harsher, potentially toxic chemicals used in other algae-to-biofuel technology, she noted.

"But this really is the first time that scientists have realized that a green system like supercritical CO2 might have applications in producing biofuel from algae."

Soh explained that similar approaches have been proposed for using supercritical methanol and ethanol, but the use of supercritical carbon dioxide requires lower temperatures, making it easier to work with and less energy-intensive. Another advantage, Zimmerman noted, is that the supercritical carbon dioxide, which acts as a solvent for oil, can be tuned to extract only specific components from algae oils, saving time and resources.

Zimmerman and Soh have already shown in previous research that supercritical carbon dioxide can extract lipids from algae. Soh now is moving ahead with the next step, which involves converting the lipids to biodiesel, with the ultimate goal of performing the entire extraction and conversion in a single production chamber.

"Supercritical carbon dioxide is a pricey technology because it requires a good deal of energy and initial capital. If we can combine this into one step, it will reduce the costs and bring us closer to commercialization," Soh explained.

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