Waste Not, Want Not

New glycerin use efforts are expected to keep pace with increased supply
By Bryan Sims | February 09, 2011

As the biodiesel industry ramps up production to help fulfill the 800-billion-gallon biomass-based diesel mandate under RFS2, efficient and cost-effective routes are underway for glycerol utilization, other than the traditional pharmaceutical and industrial routes currently being applied. Keerthi Venkataramanan, a graduate student at the University of Alabama-Huntsville’s biotechnology doctoral program, may have unlocked a novel glycerin application route for producers to tap into.

In his research, Venkataramanan used a strain of bacteria commonly found in soil, called Clostridium pasteurianum, which feeds on glycerol as its sole carbon source whereby it can biologically produce a range of useful byproducts such as butanol, 1,3 propanediol and ethanol, in addition to trace amounts of acetic and butyric acid. Venkataramanan admits he’s not the first to study glycerol conversion processes like this. Since other firms, including DuPont, have developed a proven process that produces 1,3 propanediol from glycerol using a genetically engineered strain of E. coli, Venkataramanan decided to focus on butanol extraction instead.

“In our bacteria strain on glycerol, we can produce about 30 to 40 percent butanol and another 25 to 30 percent into chemical intermediates,” Venkataramanan tells Biodiesel Magazine. “These studies are all batch fermentations so the yield varies comparatively between each batch. The maximum we’ve got is 40 percent and the average was around 22 percent; in other words, 22 grams of butanol per 100 grams of glycerol.”

Unlike other commonly used bacteria strains, such as Citrobacter, that are highly pathogenic in nature, Clostridium bacteria is an anaerobe that is nonpathogenic, according to Venkataramanan, adding that he’s finding more productive strains that can be bioengineered.

“The bacteria make butanol to a greater extent, but at the same time there are challenges,” he says, “because butanol is toxic to the cells and any of its cell growth at higher concentrations. We’re focusing on overcoming those challenges in terms of increasing butanol yield.”

In addition to producing butanol and other biochemicals using the Clostridium bacteria, Venkataramanan adds that he’s also successfully extracted butanol from the methyl ester itself. “Blending butanol in biodiesel would actually increase the calorific—or fuel value—of biodiesel,” he says. “[A biodiesel producer] wouldn’t have to go outside the biodiesel plant to carry out the synthesis. You can integrate it into biodiesel plants so that you can blend butanol with biodiesel again.”

Venkataramanan points out another advantage of using the Clostridium bacteria. “When you scale up an anaerobic process, it’s economically favorable comparable to aerobic processes by a margin of 40 percent,” he says. “Many biodiesel companies will be restarting or contemplating restarting and that means, eventually, there will be more glycerin out there. If there’s going to be more glycerol out there and they have problems of disposing of it, you need to come up with a viable solution like a biological conversion.”

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