Engineers at Iowa State University (ISU) have found a way to combine a genetically engineered strain of yeast and an electrocatalyst to efficiently convert sugar into a new type of nylon. According to the researchers, the process opens the door to the production of a broad range of compounds not available from petroleum-based feedstocks.

Previous attempts to combine biocatalysis and chemical catalysis to produce biorenewable chemicals have resulted in low conversion rates. That is typically because the biological processes leave residual impurities that harm the effectiveness of chemical catalysts.

According to the ISU researchers—Zengyi Shao and Jean-Philippe Tessonnier, both assistant professors of chemical and biological engineering—the ideal biorefinery pipelines, from biomass to the final products, are currently disrupted by a gap between biological conversion and chemical diversification. The pair developed a strategy to bridge this gap using a hybrid fermentation and electrocatalytic process.

Zengyi Shao and Jean-Philippe Tessonnier, ISU researchers who developed the bio-based nylon. Image credit: Christopher Gannon.Shao’s research group first created genetically engineered yeast—a “microbial factory,” she says—that ferments glucose into muconic acid. By applying metabolic engineering strategies, the group significantly improved the yield of the acid. Then, without any purification, Tessonnier’s group introduced a metal catalyst, lead, into the mixture and applied a small voltage to convert the acid. The resulting reaction added hydrogen to the mix to produce 3-hexenedioic acid.

After simple separation and polymerization, the engineers produced bio-based, unsaturated nylon-6,6, which has the advantage of an extra double bond in its backbone that can be used to tailor the polymer’s properties.

The engineers say the hybrid conversion technology offers several advantages: the reaction is performed at room temperature; it uses a cheap and abundant metal instead of precious elements such as palladium or platinum; and the other compounds involved in the reaction are produced from water.

“We gave it a try and it worked immediately,” Tessonnier says. “The process does not need additional chemical supplement, and it works amazingly at ambient temperature and pressure, which is very rare for this type of process.”

Moving forward, the engineers will work to scale up their technology by developing a continuous conversion process.