https://newswise.com/doescience/?article_id=684986
2017-11-09 17:05:52
New Routes to Renewables: Sandia Speeds Transformation of Biofuel Waste
Into Wealth
LIVERMORE, Calif. — A Sandia National Laboratories-led team has
demonstrated faster, more efficient ways to turn discarded plant matter
into chemicals worth billions. The team’s findings could help transform
the economics of making fuels and other products from domestically grown
renewable sources.
Lignin, the tough material left over from biofuel production, contains
compounds that can be converted into products like nylon, plastics and
drugs. It is one of the main components of plant cell walls, and gives
plants structural integrity as well as protection from microbial attacks.
Products made from converted lignin could subsidize biofuel production,
making the cost of biofuels more competitive with petroleum.
Unfortunately, lignin’s toughness also makes it difficult to extract its
valuable compounds. Scientists have wrestled for decades with
deconstructing it. As a result, lignin often sits unused in giant piles.
Sandia bioengineer Seema Singh and her team have demonstrated two new
routes to lignin conversion that combine the advantages of earlier
methods while minimizing their drawbacks. The team’s recent findings are
described in the journal Scientific Reports.
To break the bonds between compounds that make up lignin, scientists
have either employed chemicals or tiny organisms such as bacteria or
fungi. The gentler biological methods do enable the production of
specific targeted compounds. But to fully break down lignin using this
approach can take weeks or even months.
Conversely, harsh chemicals can deconstruct lignin in hours or even
minutes. But this method requires expensive catalysts and is sometimes
toxic, and therefore unsustainable. Worse, chemical methods lead to a
mixture of compounds that each appear in extremely small quantities.
“You get a little bit of whole lot of various chemicals when you break
down lignin this way,” explained Singh. “The quantities yielded are not
terribly useful.”
Her team has demonstrated two new techniques that incorporate the speed
of a chemical method and the precision of a biological one. In both
cases, Singh’s team ultimately produced high-value chemicals that
currently are derived only from petroleum: muconic acid and pyrogallol.
Muconic acid can easily be turned into nylon, plastics, resins or
lubricants, and pyrogallol has anti-cancer applications. Together, Singh
reports, these chemicals have a combined market value of $255.7 billion.
“Muconic acid is what we call a platform chemical. From there, creating
new products is really just a matter of imagination,” she said.
The team’s first new conversion method is a multi-stage process that
begins by pre-treating lignin with a weak solution of hydrogen peroxide
and water. Intermediary molecules vanillin and syringate result from the
treatment.
A strain of E. coli specially modified by Sandia microbiologist Weihua
Wu then consumes these middle-stage compounds, several additional
compounds emerge in the mix, and ultimately the process results in the
two final chemicals.
However, Singh was not satisfied with the amount of muconic acid yielded
from this process. So, she and her team challenged themselves to find a
way to maximize their muconic acid yield, and tested a second conversion
method.
The second method skips the process of having to break down the lignin
altogether. Instead, the team genetically engineered a tobacco plant. As
it grows, the plant produces high amounts of intermediate compound
protocatechuate, known as PCA. Then, the only steps remaining were to
extract that compound and use the engineered E. coli to make the muconic
acid.
“We basically skipped three-quarters of the steps we were doing
previously by engineering the plant to grow intermediate chemicals,”
Singh said. “PCA can be easily extracted from the modified tobacco and
converted into muconic acid with little effort.”
This plant engineering route is not only more efficient, but it also
successfully solves the team’s self-imposed challenge of maximizing
muconic acid yield by as much as 34 percent over previous conversion
methods.
Sandia funded the majority of the work on this project through its
Laboratory Directed Research and Development program. The tobacco plant
engineering work was done by Singh’s collaborators from the feedstock
division at the Joint BioEnergy Institute in Emeryville, Calif.,
including Dominique Loque and Aymerick Eudes.
Singh directs the biomass pretreatment program at the institute, which
is staffed by scientists from a consortium of laboratories including
Lawrence Berkeley National Laboratory. She believes future research into
increasing lignin’s economic value will be heavily influenced by her
team’s demonstrations.
The biggest challenge in this field will be further maximizing the yield
of valuable chemicals and the rate at which they can be yielded.
“Everyone understands that hybrid approaches are key to lignin
valorization,” Singh said.
Industrial adoption of this technology will depend on the ability to
quickly produce large amounts of high-value product. “If you can only
make milligram amounts in a month from a bug, that just won’t cut it,”
Singh said. “You want the organisms to make kilogram amounts in less
than an hour, ideally.”
Sandia National Laboratories is a multimission laboratory operated by
National Technology and Engineering Solutions of Sandia LLC, a wholly
owned subsidiary of Honeywell International Inc., for the U.S.
Department of Energy’s National Nuclear Security Administration. Sandia
Labs has major research and development responsibilities in nuclear
deterrence, global security, defense, energy technologies and economic
competitiveness, with main facilities in Albuquerque, New Mexico, and
Livermore, California.