Cutting-edge chemistry
Find out more
Industrial nitroglycerin made fast and safe
out the
Learn more ab
troglycerin
ni
of
y
chemistr
ast from
with this podc
ld
Chemistr y Wor
0xW
Jo
O
y/
http://bit.l
control the decomposition products. And in the event
of something going very wrong, the resulting explosion
would be much smaller.
The microreactor is a hand-sized clear polymer tile with
an internal channel that meanders across the plane.
The internal channel has two entrances but only one
exit – the reactants are brought together at the start and
then mixed as they move through the microreactor by
turbulence caused by a complex pattern of grooves and
ridges on the sides of the channel.
Structure of nitroglycerin
Did you
know?
High purity
That said, this is not an approach for
bulk production of nitroglycerin. Low
grade product, primarily for the mining and construction
industries, can be made cheaply in bulk already. Where
this approach is a real advantage is in the manufacture
of smaller quantities of nitroglycerin at very high grades
for use in the pharmaceutical industry.
Andrew Turley
Nitrating hydrocarbons
Fraunhofer ict
Nitroglycerin is not only a
powerful explosive but
also a potent drug
(sometimes called
glyceryl trinitrate), widely
used for treating angina
and other heart problems.
Since the invention of nitroglycerin in the mid-19th
century, people have been trying to find safer ways
to manufacture this highly unstable liquid explosive.
Now, researchers at the Fraunhofer Institute for
Chemical Technology (ICT) in Pfintzal, Germany, have
come up with what might be the safest approach
yet – using microreactors to produce nitroglycerin
continuously rather than in batches. This is not only
safer but also quicker, facilitating a 10-fold increase in
production rate.
To scale up production, you simply add more
microreactors in parallel. A single microreactor
might be used to make 10–50 kg of
nitroglycerine per day. But the research
group in Pfinztal has experimented with
production at 2–3 tonnes per week by
‘numbering up’ the microreactors.
Nitroglycerin is made by adding glycerol, a simple
hydrocarbon with three hydroxyl groups, to a mixture
of sulfuric acid and nitric acid. The reaction is
extremely exothermic, and if the temperature gets too
high ‘runaway’ can occur, dramatically increasing the
risk of explosion.
Therefore manufacturers continually cool the reaction
mixture and – in the traditional batch process – add
the glycerol drop-by-drop to the acid to allow time for
the heat to dissipate and maintain an excess of acid,
essential to ensure complete nitration of the all the
hydroxyl groups.
Microreactors
Microreactors can be
used to produce explosive
materials much more
safely
8 | The Mole | September 2012
Switching to a continuous process in a microreactor
means working with much smaller quantities – safer
for several reasons. It makes it easier to control the
overall temperature and the degree of mixing, which
is important to avoid localised temperature variations
and dangerous ‘hotspots’. It also makes it easier to
www.rsc.org/TheMole
Did you
know?
Smart windows store sun’s energy
Polymers and plastics are
often thought of solely as
insulators. However,
polymers like polyaniline
can conduct electricity
due to their conjugated
electronic structure. Find
out more about
conducting polymers at
http://bit.ly/Mzo1IC
The energy storage
smart window can be
bent and flexed and
still do its job
Scientists in China have developed a smart window that
not only heats and cools a building, but can also act as
an energy storage device to power electrical equipment
within the building.
Smart windows are already in use in some buildings;
they are used to reduce energy consumption by keeping
the interiors cool and controlling the light levels within.
An example of this is in museums, where artefacts can
be damaged by too much sunlight.
Changing colour
Now, Zhixiang Wei from the National Centre for Nanoscience and Technology and colleagues have made a
window that combines a supercapacitor with a window
pane that changes colour in response to an electric
current. In bright sunlight, it absorbs and stores energy,
but when it is full to capacity, the window darkens
to limit the amount of light that enters. This controls
the temperature and brightness of the room and the
captured energy can be used to power equipment, such
as television screens. As the electricity is used up, the
energy storage smart window (ESS window) will lighten
and begin to absorb more sunlight to recharge itself.
The ESS window is made of polyaniline nanowire arrays,
which are deposited onto a transparent film that has
been coated with a conductive layer. The nanowires
www.rsc.org/TheMole
are then covered with a gel electrolyte layer to form an
electrode, and two electrodes are sandwiched together
to make a working device.
Flexible devices
Polyaniline has a high capacity and doesn’t cost
much to make, plus it has the added advantages of
being transparent and flexible. ‘Flexible devices are
attracting more and more attention because they are
lightweight, easy to roll up, and can be designed in
a more fashionable way. It is no doubt that a flexible
smart window like ours possesses these properties. For
instance, the ESS window can be rolled up like a curtain
if it is not being used,’ says Wei.
John Rogers, an expert in photonic devices from
the University of Illinois at Urbana-Champaign, US,
was cautiously optimistic about the work. ‘Such
technologies, if they can be made cheaply and in forms
that offer long-lived operation, could be valuable in
contexts ranging from automotives to homes,’ he says.
Have a go�
Electrochromic materials
change colour when an
electric current is applied.
Make your own
electrochromic polymer in
your school lab.
http://bit.ly/SJHvLF
Wei’s team is working on optimising their device by
trying different electrode materials and improving the
window’s electrochromic properties. They are also
looking at integrating a solar cell into the device to store
even more energy.
Holly Sheahan
September 2012 | The Mole | 9