Chemical Engineering June 2020 - 8

electrolysis and gas streams
containing CO2.
Conventional production
processes based on fossil
feedstock have reached
technical maturity over the
past decades, but have
large CO2 emissions. " In
contrast, methanol synthesis
in PtL processes offers the
potential to bind CO2 from
biomass, for example, and
to reuse it, " explains Achim
Schaadt, head of the Thermochemical
Processes department
at Fraunhofer ISE.
A number of questions still
need to be answered before
this process can be implemented
on an industrial
scale. For example, a high
CO2 content in the synthesis
gas lead to accelerated
aging of the catalyst and to
lower chemical yields. Furthermore,
fluctuations both
in the amount of H2 produced
by renewables and in
the process for the provision
of CO2 may require dynamic
synthesis operation.
The project is funded by
the German Federal Ministry
for Economic Affairs and
Energy and led by Dechema
e. V. , with industrial partners
CropEnergies AG, Clariant
AG and thyssenkrupp Industrial
Solutions AG.
metal aerogels
A new class of porous materials,
noble metal aerogels
(NMAs) have drawn interest
because of their useful
properties, including selfsupported
architectures,
high surface areas and
numerous optical and catalytic
active sites. However,
current production methods
suffer from long fabrication
times, unavoidable
impurities and uncontrolled
multiscale structures.
Now, chemists from the
Dresden University of Technology
(Germany; www.
tu-dresden.de) have developed
a freeze-thaw method
capable of synthesizing various
NMAs that have clean
surfaces and multiscale
structure. Because of their
hierarchical structures and
unique optical properties, the
NMAs exhibit " outstanding "
performance for the electro(Continues
on p. 9)
8
ChemiCal engineering www.Chemengonline.Com June 2020
Filtering out and detoxifying Cr(VI) from water
EPFL, Alain Herzog
C
hemists from
the Swiss Federal
Institute of
Technology Lausanne
(EPFL; Switzerland;
www.epfl.ch) have developed
" sponges " designed
to capture various target
substances, such as gold,
mercury and lead, dissolved
in solution. Now,
they have developed one for capturing toxic
hexavalent chromium from water. The material
- a composite bead of a metal organic
framework (MOF) on a polymer - not only
has a high adsorption capacity for Cr(VI), but
it also acts as a photocatalyst, whereby the
Cr(VI) is converted to the less toxic Cr(III).
As described in an article published last
month in the Journal of Materials Chemistry
A, the adsorbent sponge is made by first functionalizing
a known Zr-MOF, UiO-66, with double
amino groups. This modification permits
the new material, Zr-BDC-(NH2)2, to serve a
dual-purpose as both adsorbent and photocatalyst,
according to the chemists. Next,
Zr-BDC-(NH2)2 was incorporated into MOF@
polymer beads using polyethersulfone
(PES) that was
chemically modified with
carboxylic acid groups to
improve hydrophilicity.
The researchers have
demonstrated that the
MOFs can extract approximately
208 mg of Cr(VI)
per gram of MOF [photo
before (left) and after
(right)]. Also, shining light on the loaded MOF
then transforms the highly toxic Cr(VI) into
a relatively nontoxic Cr(III). Further developments
are required in order to implement the
technology for decontaminating water outside
of the laboratory.
Hexavalent chromium continues to contaminate
water sources around the world,
with one U.S. company fined just this past
February for having put employees at risk.
Cr(VI) is considered to be extremely toxic,
especially when inhaled or ingested, and
its use is regulated in Europe and in many
countries around the world. It is thought to
be genotoxic, leading to DNA damage and
the formation of cancerous tumors.
New process for safer and continuous
magnesium production to be piloted
B
ecause of its abundance, light
weight and easy alloying, magnesium
metal has great potential for
components in the automotive,
aerospace and military industries. However,
the two existing production processes for
Mg - the Pidgeon process from ore and
electrolytic process from MgCl - both have
major drawbacks with safety and environmental
impact.
Now, a pilot plant currently in the design
phase will demonstrate a new Mg production
process that is continuous, rather than
batch, and that dramatically reduces the
safety and environmental problems compared
to existing processes. The process
developer, Western Magnesium Corp. (Vancouver,
B.C.; www.westmagcorp.com), says
the safety, environmental and economic profile
of the new process could make Mg production
viable in North America. Currently,
85% of Mg comes from China.
The Western Magnesium process begins
with mined dolomite (calcium-magnesium
carbonate), which is crushed and calcined
(thermal decomposition) to make MgO. The
MgO is combined with ferrosilicon, a reductant
that is also used in the Pidgeon process,
and a catalyst, and formed into briquettes.
The briquettes are fed into the top of a newly
designed continuous reactor, where they
are heated, allowing the silicon to react with
oxygen and reduce the magnesium to metal.
The vaporized Mg is collected and removed
from the reactor as molten Mg using a proprietary
Mg-recovery system that was designed
specifically for this process.
" In the Pidgeon process, which occurs
batch-wise, repeated heating and cooling
cycles are needed to remove the Mg and
drive the reaction, so the process is highly
energy-intensive - 40 MWh/ton of Mg, "
explains Paul Sauvé, vice president of operations
at Western Magnesium. " The continuous
nature of our process eliminates the
temperature cycles, so much less energy is
required. " To further raise efficiency and reduce
environmental footprint, the company's
process uses an electric-powered calciner,
heat-recovery systems and a method for recovering
food-grade CO2 from the calcination
step. Finally, in addition to Mg, the process
yields dicalcium silicate, which can be
sold as an aggregate material.
Western Magnesium plans for the pilot plant
operation to be complete in Q3 2021. The pilot
will inform the design of the full-scale plant.
After some refinement, the plant will be capable
of producing 99.8% pure Mg in ingots,
granules or as molten material, Sauvé says.
http://www.epfl.ch http://www.westmagcorp.com http://www.tu-dresden.de http://www.Chemengonline.Com
Chemical Engineering June 2020

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