Stemming From Biocatalytic Roots
It all started when a project director from the U.S. Defense Advanced Research Projects Agency approached Richard Gross and challenged his jointly owned company, SyntheZyme, to develop a bioplastic that could be degraded back to a liquid fuel. Consequently, the professor of chemical and biological science of Polytechnic Institute at New York University successfully developed a method for producing a biodegradable bioplastic using yeast that feed on plant-based lipids such as those from palm oil.
Specifically, Gross employs a biocatalytic fermentation route that uses a genetically modified strain of Candida tropicalis that, when fed on plant-based fatty acids, is capable of producing large quantities of monomers called omega-hydroxyfatty acids. When the omega-hydroxyfatty acid monomers are strung together in long repeating units, they form a polymeric bioplastic material that could be used as a viable substitute for petroleum-based polyethylene. His findings were published in the Journal of the American Chemical Society.
“I wanted to be able to break the plastic back down to molecules that look a lot like biodiesel,” Gross tells Biorefining. “I knew I had to redesign the fatty acid so that it has another functional group on the other side of the molecule so I could make polymers from it.”
With help from two DARPA funding cycles totaling approximately $4 million, Gross was able to focus much of his work on identifying an ideal yeast strain. “Engineering the organism involved removing 16 enzymes; essentially moving 16 gene fragments from the yeast to finally get to the yeast that can make a monomer,” Gross says. “We got really good yields and have demonstrated the potential to develop a low-cost process from a carbon source like palm oil.”
According to Gross, the biocatalytic fermentation pathway is capable of producing approximately 112 grams-per-liter of omega-hydroxyfatty acid from plant-based fatty acid. “That’s about two grams per liter per hour,” Gross says, adding that production run rates are being improved to increase the desired yield of omega-hydroxyfatty acids. “The fermentation takes about 55 hours, but we’re looking to bring that down to 40 hours or so and improve the productivity a bit,” he says. “They’re close to commercially acceptable numbers.”
Traditionally, omega-hydroxyfatty acids are produced via a difficult and expensive petrochemical pathway that leads to a high-cost product. “People have been using these to make fairly long chain hydroxyl acids that can be cyclized to make the musk in fragrances,” he says.
Gross says samples of its omega-hydroxyfatty acid were sent to some of the prominent specialty chemical manufacturers in the market. So far, the interest is overwhelming. “They’ve assessed our product and they like what they’re seeing,” Gross says, adding that he envisions SyntheZyme deploying a pilot plant within the next three or four years capable of producing 30 million tons annually of omega-hydroxyfatty acid materal. “We’re discussing possible collaborations to bring our product to market.”
As it turns out, the challenge initiated by DARPA was originally intended to serve a dual purpose: to produce a bioplastic, and biodiesel for military engines after it’s depolymerized to omega-hydroxfatty acid monomer units. With the successful production of polymerizing omega-hydroxyfatty acids to form bioplastic now complete, research is underway to convert the bioplastic into biodiesel, according to Gross.
In addition to producing bioplastics based on its biocatalytic fermentation technology, SyntheZyme is also capable of producing a suite of bioproducts for applications in fragrances, vinyl monomers, biosurfactants and biopesticides. The company is backed by 16 granted and pending patents.