che_february-2025 - 9

Flow chemistry yields a more sustainable route to isocyanates
T
he wide range of performance properties of polyurethane
foams makes them essential in many
consumer goods. Thus, there is much effort going
into creating a more environmentally friendly production
process for polyurethane's main building blocks,
polyols and isocyanates. While much progress has been
made across the industry to develop bio-based routes to
different polyols, developing new technologies for isocyanates
has proven more elusive, due in part to the presence
of highly toxic phosgene and hydrochloric acid in
conventional petroleum-derived isocyanates production.
Now, a novel flow-chemistry approach is being demonstrated
to enable a biological production pathway for isocyanates,
while avoiding risks associated with phosgene.
Algenesis
Materials' (San Diego, Calif.; www.
algenesislabs.com) patented technology, originally developed
in the laboratory of chemistry professor Michael
Burkart at the University of California San Diego (www.
ucsd.edu), converts algae-based fatty acids into isocyanates
via acyl azides in a continuous-flow process. " Using
flow chemistry, we never accumulate large amounts of
any of the hazardous intermediates. We go right from the
precursor, which is a hydrazine, to the diisocyanate in
flow, " explains Stephen Mayfield, chief executive officer
of Algenesis. The group has used this method to make
some 25 different types of isocyanates, including some
that are very similar in structure and properties to toluene
diisocyanate (TDI) and methylene diphenyl diisocyanate
(MDI), which are widely used in polyurethane foams.
A benefit of the bio-based isocyanates pathway is that
it can provide " different physical properties to the ultimate
polyurethane - lower carbon footprint, novel properties
and biodegradability - than conventional fossil-based
isocyanates, says Mayfield. " What's unique about our
foams is high biological content, while meeting performance
specifications like rebound and tensile strength.
And we are moving toward cost parity for certain consumer
applications - the benefit of algae is they grow
quickly and relatively cheaply, " he adds. In combination
with the company's already-established bio-based polyols
production process, Algenesis' renewable and biodegradable
polyurethane materials have been utilized in
footwear, phone cases and more.
Currently, Algenesis produces several kilograms per
week of renewable isocyanates, and work is ongoing to
scale up to 2 ton/yr in 2025.
The company has also
received a grant from the U.S. Department of Defense to
evaluate plans for a 10-ton/yr facility.
Creating ultrathin gold films with the largest continuous area
T
hin gold films offer a broad range of benefits for
electronics due to their high electrical conductivity
and transparency. Current manufacturing
methods are unable to achieve gold films thinner
than 10 nm, and are also limited in the area and continuity
of films they can produce, due to the formation
of " metal islands " - clusters of atoms on the substrate
that can hinder conductivity, mechanical stability and
substrate coverage. A new high-vacuum deposition
process that takes inspiration from the chemical vapor
deposition of graphene, developed in a collaboration between
Xpanceo (Dubai, U.A.E.; www.xpanceo.com) and
professor Konstantin S. Novoselov from the University of
Manchester (U.K.; www.manchester.ac.uk), overcomes
these challenges, producing films as thin as 3.5 nm with
continuous, unrestricted area - moving a step closer to
atomically thin gold films.
" We developed a graphene-based method for synthesizing
transferable, wafer-scale ultrathin gold films with
exceptional conductivity and transparency. These new
films are ideal for applications like flexible electrodes,
biosensing and thermal management. Unlike traditional
methods, our approach avoids percolation issues and
enables new study techniques to be used on atomically
thin metals, such as plasmonics. This work marks a milestone
whereby two-dimensional (2-D) fabrication techniques
start making their way into the domain of conventional
3-D materials, " says Valentyn Volkov, Xpanceo
co-founder and chief technology officer.
Using traditional production techniques, gold atoms
are evaporated within a vacuum chamber until they form
clusters on the substrate that then merge into a continuous
film around 10-20-nm thick. If they are any thinner,
CHEMICAL ENGINEERING WWW.CHEMENGONLINE.COM
they lack continuous
morphology.
With
Xpanceo's
new method,
gold films are
deposited
onto a copper
substrate
(which itself
is deposited
onto a silicon/
graphene
substrate) and
coated with
polymethyl
methacrylate
(PMMA). The
Nano Lett
PMMA/Au/Cu structure then undergoes electrochemical
delamination from the silicon/graphene layer in potassium
chloride solution, followed by dissolution of the Cu
layer and cleaning, resulting in a free-standing PMMA/Au
film (diagram; source: Nano Lett. 2024, 24, 51, 16,270-
16,275). " These films feature continuous structures and
can be transferred to any substrate via electrochemical
techniques. The films maintain their conductivity under
extreme bending and offer balance between transmittance
and conductivity, " explains Volkov.
According to Volkov, the method allows for the scalable
production of 2-D metallic films greater than 1 m2 in
area using established roll-to-roll techniques - a significant
improvement over current 2-D gold films, which are
typically no more than 0.000001 mm2.
■
FEBRUARY 2025
9
http://www.algenesislabs.com http://www.ucsd.edu http://www.xpanceo.com http://www.manchester.ac.uk http://WWW.CHEMENGONLINE.COM
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