Chemical Engineering August 2022 - 10

tists are searching for sustainable
ways to make healthy nutritional
products, such as omega-3 fatty
acids, from fast-growing microalgae.
New research at Flinders
University (Adelaide, South Australia;
www.flinders.edu.au) has
discovered a simple, low-cost and
effective way to extract high-value
bioactive substances and other
products from single-cell algae
oil. The researchers focused on
thraustochytrids, because this single-celled
algae can produce over
50% of its weight as triglycerides.
In the study, described in a recent
issue of ACS Sustainable Chemistry
& Engineering, the scientists
reported a way to enrich the saturated
triglycerides produced in
thraustochytrids. The method
involves the direct reaction of elemental
sulfur with the algae-oil
extract. The sulfur copolymerizes
with over 90% of the unsaturated
triglycerides into a class of materials
already used in such applications
as Li-S battery cathodes,
slow-release fertilizers and insulation.
The unreacted oil is enriched
in saturated triglycerides, which
can further be separated by extraction
and use, for example, in
biodiesel-fuel production
PURIFYING PYROLYSIS OIL
Last month, BASF SE (Ludwigshafen,
Germany; www.basf.
com) launched PuriCycle, a new
line of products for the purification
of most complex waste-plasticspyrolysis
feeds. The PuriCycle
portfolio includes new catalysts
and adsorbents that were developed
to selectively remove or
convert a wide range of impurities
in pyrolysis oils and enable
downstream processing of circular
plastics streams. PuriCycle
can help users meet industry
compositional compliance standards,
benefit from high efficiency
purification and upgrading solutions
and increase their flexibility
in the chemical recycling process
of plastics, says BASF.
Purification of pyrolysis oils obtained
from waste plastics is said
to be among the most demanding
technical tasks in chemical plastics
recycling. Impurities, such as
halogen, nitrogen, oxygen and sulfur
compounds - but also higher
levels of reactive components
such as dienes - complicate the
downstream use and impose strict
limitations on the further processing
of such streams in the production
of new materials.
❐
10
Limpet tooth inspires strongest biomaterial
A
n interdisciplinary team of biologists,
chemists and engineers
from the University of Portsmouth
(U.K.; www.port.ac.uk) have become
the first to successfully grow a limpetinspired
biomaterial with extreme strength.
The common limpet (Patella vulgata) is a
small, snail-like mollusk with a tongue covered
with microscopic teeth that are used
for scraping food from rocks. The teeth are
a hard, flexible composite of chitin and goethite
(α-FeO(OH)) that, in 2015, was found
to be the strongest known biomaterial -
much stronger than spider silk and comparable
to man-made substances.
The team has now successfully mimicked
limpet tooth formation in the laboratory and
used it to create a new composite biomaterial,
which is described in a study published
last month in Nature Communications.
" Fully synthetic composites like Kevlar
are widely used, but the manufacturing
processes can be toxic, and the materials
difficult and expensive to recycle, " says
lead author Robin Rumney, from the University's
School of Pharmacy and Biomedical
Sciences. " Here we have a material
that potentially is much more sustainable in
terms of how it's sourced and made, and
at the end of its life can be biodegraded. "
The key to the limpet tooth's strength
is thought to be due to a structure that
combines flexible, tightly packed fibers
of a scaffold material (chitin) interspersed
with fine crystals of goethite. Those fibers
are laced through each other in
much the same way that carbon fibers
are used to strengthen plastic.
The researchers developed methods that
allowed cell populations to grow outside of
their natural environment (ex vivo) on serum-coated
glass, onto which they deposited
chitin and iron oxide. After two weeks,
the material self-organized into structures
that resembled the limpet organ, known
as the radula, which makes the teeth. Ribbons
of teeth could also be grown from
tissue samples and individual teeth from
populations containing stem cells.
After successfully replicating the limpet
tooth formation, the team was then
able to produce samples of biomaterial
0.5-cm wide by mineralizing a sheet of chitin.
Now that proof-of-concept has been
established, the researchers will explore
scaleup and manufacturing possibilities.
Biosynthesis of renewable, high-energydensity,
cyclopropane-based fuels
C
yclopropane-functionalized hydrocarbons
can be excellent
fuels because of their high energy
densities, but organic synthesis
of such fuels is difficult. In work
recently published in the journal Joule,
a research team led by Jay Keasling
at the Joint Bioenergy Institute (JBEI;
Emeryville, Calif.; www.jbei.org) and
Lawrence Berkeley National Laboratory
(Berkeley, Calif.; www.lbl.gov) has demonstrated
a sustainable biosynthetic
route to polycyclopropanated fatty-acid
methyl esters (POP-FAMES). These
compounds can be made into fuels with
energy densities of 50 MJ/L or more (Jet
A, the common kerosene-based aviation
fuel, has about 35 MJ/L).
The potential energy in the strained,
three-carbon-rings in polycyclopropanated
molecules translates into
more energy for combustion than can
be achieved with the larger ring structures
or carbon-carbon chains typically
found in fuels, the researchers point out.
In addition, these structures enable fuel
molecules to pack tightly together in a
small volume, increasing the mass -
and therefore the total energy - of fuel
that fits in a given tank.
To produce POP-FAMES, the scientists
first identified a set of iterative
polyketide synthases (iPKSs) - enzymes
that are capable of producing
the desired polycycloproponatated
structures - in Streptomyces bacteria
species, and expressed them in Streptomyces
coelicolor to obtain POP-fatty
acids. The team further engineered the
bacteria to increase the production of
the POP-fatty acids 22-fold, and finally,
produced the methyl ester derivatives.
Project leader Keasling says, " This
biosynthetic pathway provides a clean
route to highly energy-dense fuels that,
prior to this work, could only be produced
from petroleum using a highly
toxic synthesis process. "
The research team is working on
generating much higher volumes of the
POP-FAMEs for testing in rocket engines
and elsewhere. The ultimate objective
is to engineer the process into a workhorse
bacteria strain that could produce
large quantities of POP molecules from
plant waste food sources (for example,
inedible agricultural residue and brush
cleared for wildfire prevention).
n
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AUGUST 2022
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Chemical Engineering August 2022

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