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16 August 2023
By Monica Tarantino
Novel enzyme could boost sustainable
production of aviation fuel
A biocatalyst discovered by Brazilian researchers
has the potential to increase renewable biofuel output by removing
obstacles in technology and production processes, as well as enhancing
the manufacturing of bioplastics and biopolymers. Credit: researcher’s
archive
In recent decades, scientists have sought solutions to improve the
sustainable production of biofuels from renewable sources. The latest
advance in this field was announced at the end of May by Brazilian
researchers and could boost the production of sustainable biofuels for
aviation and maritime shipping.
"After three and a half years of research, we identified an enzyme that
can replace the traditional catalysts used in thermochemical routes
for the production of aviation biokerosene," said Letícia Zanphorlin,
principal investigator for the project and head of the Brazilian
Biorenewables National Laboratory (LNBR) at the Brazilian National
Center for Research in Energy and Materials (CNPEM).
The enzyme discovered by the CNPEM group is OleTPRN,
a polyunsaturated alkene-producing decarboxylase belonging to the
cytochrome P450 superfamily.
This metalloenzyme derived from the bacterium Rothia nasimurium
promises to be the key to development of novel biotechnological routes
in the production of renewable hydrocarbons for aviation from
different feedstocks, such as oleaginous biomass from soy, macaw palm
(Acrocomia aculeata) or corn, among others, and lignocellulosic
biomass from sugarcane bagasse or straw and in the paper industry.
"Compared with conventional or chemical
catalysts, the novel enzyme decarboxylates fatty
acids [breaking the carbon-carbon
bond and removing the carboxyl group] with high
yields and is selective for different sizes and types of carbon
chain. It promotes deoxygenation, which is one of the trickiest
processes to master in producing SAF [sustainable aviation fuel],"
Zanphorlin explained.
Oxygen can damage aircraft parts and engines, she added, which helps
understand why biofuels already mass-produced in Brazil, such as
ethanol and biodiesel, are not used in aviation and explains the
demand for novel biocatalysts. In general, conventional catalysts used
in aviation fuel production involve metals such as cobalt, platinum,
nickel or palladium.
"To produce the deoxygenation reaction, these metallic catalysts must
be applied under severe conditions, particularly high temperature and
pressure, and can be environmentally harmful, producing technological
waste and leading to financial losses," she said.
An article on the research is published in Proceedings
of the National Academy of Sciences (PNAS).
According to the researchers, enzymes act as biological catalysts,
accelerating chemical
reactions in the living organisms present in nature. In the study
in question, the enzyme converted fatty acids in a single step into
alkenes (olefins), a type of hydrocarbon and an important chemical
intermediary.
Fatty acids are essential components of lipids, a class of organic
compound that includes all kinds of fat and oil. Lipids are found in
plants, animals and microorganisms.
The discovery and elucidation of the molecular mechanisms involved in
the enzyme's action were the fruit of a multidisciplinary approach.
The scientists searched public databases for enzymes with specific
properties and functions, using bioinformatics tools and genomic data
for microorganisms.
Candidate enzymes were analyzed at the atomic
level using synchrotron light, a type of high-flux high-brightness
electromagnetic radiation encompassing a large proportion of the
spectrum, from infrared through ultraviolet to X-rays. Synchrotron
light is produced when a beam of charged particles accelerated almost
to the speed of light is deflected by a magnetic field. When applied
to protein crystals, it causes electron diffraction and permits
elucidation of their three-dimensional structure.
"We evaluated the position of every amino acid in the enzyme's atomic
structure, and mapped its intermolecular interactions with fatty
acids," Zanphorlin said, noting that this showed them all the possible
applications of the discovery.
In parallel with this laboratory investigation, other teams at CNPEM
worked on patent filings and on technical, economic and environmental
analysis of the biological routes, the results of which will be
published soon.
"A patent on the enzyme was applied for in 2021. One of CNPEM's key
advantages is that we can develop a technological solution, implement
a pilot project, ramp it up to an industrial scale, and perform the
technical, economic and environmental assessments needed to detect any
potential improvements in the innovation as it's being developed,"
Zanphorlin said.
There are exciting possibilities for the production of aviation
biofuels using the enzyme. "Brazil currently produces some 150 million
metric tons of lignocellulosic waste from sugarcane in dry mass terms.
This could be increased without adverse environmental impacts," she
said.
To implement the technology, biofuel production facilities would need
to be adapted, but the distribution infrastructure used by fossil
fuels could be shared by renewables acting as "drop-in"
fuels—substitutes for petroleum-derived hydrocarbons that would not
require adaptation of engines, fuel systems or distribution networks.
The researchers are optimistic about applications in several
industrial sectors. "The versatility of this enzyme makes it adaptable
for use in different sectors. Alkenes are produced by enzyme reaction
and are the basis for some two-thirds of the products made by the
chemical industry today, especially polymers and plastics. They're
also essential to the food, cosmetics, pharmaceutical and
transportation sectors," Zanphorlin said.
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