Ultrasound Makes Better Biofuel

Friday, May 31, 2013 @ 06:05 PM gHale

High-frequency sound waves could better break down plant materials in order to cook up a better batch of biofuel.

By “pretreating” a wide variety of feedstocks (including switch grass, corn stover, and soft wood) with ultrasound consistently enhances the chemical reactions necessary to convert the biomass into high-value fuels and chemicals, said David Grewell, Iowa State University associate professor of agricultural and biosystems engineering, and his colleagues Melissa Montalbo-Lomboy and Priyanka Chand.

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In one example of ultrasound’s positive impact on biofuel production, the Iowa State researchers found they could increase the efficiency of removing lignin from biomass in solution. Lignin is the chemical compound that binds cellulose and hemicellulose together in plant cell walls.

Commonly, enzymes or chemicals work to remove Lignin from biomass and allow the freed sugars to dissolve for further processing into biofuel. Grewell found pretreating instead with ultrasound makes lignin removal so efficient that sugar dissolution occurs in minutes rather than the hours needed with traditional mixing systems.

Grewell’s team also found hydrolysis of corn starch could greatly accelerate using ultrasonics. In a conventional ethanol plant, ground corn ends up steamed with jet cookers at boiling point temperatures. This breaks down the corn, leaving a starch mash that then cools and gets treated with enzymes in a process known as hydrolysis to release glucose for fermentation.

The Iowa State team replaced the initial steaming with ultrasound, sonically smashing the corn into tiny particles in the same way physicians use ultrasound to shatter kidney stones. The smaller corn fragments provided more surface area for enzymatic action, and therefore, resulted in fermentation yields comparable to jet cooking.

The potential cost savings for this method, Grewell said, are very encouraging.

“Economic models have shown that once implemented, this technology could have a payback period of less than one year,” he said.

Grewell and his colleagues report a third application for ultrasound in biofuel production, showing they can accelerate transesterification, the main chemical reaction for converting oil to biodiesel.

In one case, the researchers found that subjecting soybean oil to ultrasound transformed it into biodiesel in less than a minute, rather than the 45 minutes it normally takes.

Similarly, Grewell’s team found yeast populated with sugar and starved with glycerin, a co-product of biodiesel production, could produce high yields of oil that could end up extracted and simultaneously converted to biodiesel with ultrasonics in less than a minute.

This is a dramatically faster and less complicated method than traditional techniques requiring multiple steps and relatively long cycle times.

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