Chemical Engineering September 2020 - 10

according to the researchers,
which reported the study in
Environmental Science Nano.
The researchers are now working
to create membranes and
fibrous sponges of the material.
'PorouS liquidS'
A new material that promises to
save up to 80% of the energy
used to separate propylene
from propane (by distillation) has
been developed by a team of
researchers from the Karlsruhe
Institute of Technology (KIT;
Germany; www.kit.edu), Leibniz
Universität Hannover, KAUST
and the German Institute of Rubber
Technology e.V. (Hannover).
As described in a recent
issue of Nature Materials, the
researchers have been able
to distribute a metal-organic
framework (MOF) in a liquid for
the first time. To do this, they
started with the solid material
ZIF-67 (zeolitic imidazole
framework), whose atoms form
a MOF with 0.34-nm wide pore
openings. By systematically
modifying the surface of ZIF67
nanoparticles, it becomes
possible to form a dispersion
of the MOF in liquids, such as
cyclohexane, cyclooctane or
mesitylene. Because propylene
is retained in the pores of
this so-called porous liquid, it
can effectively be separated
from smaller molecules that
pass through more quickly.
The researchers also produced
mixed-matrix membranes
from a plastic material
containing up to 47.5% of
the chemically modified ZIF67.
Two such membranes
arranged in series were able
to produce propylene with
99.9% purity from a gas mixture
containing equal parts
of propylene and propane -
even though the molecules differ
in size by just 0.2 nm.
The flowrate was at least
three times higher than alternative
membranes, which
makes the new membranes
even more promising as an
alternative to conventional
distillation separation.
water SPlittiNg
A team of scientists led by Nanyang
Technological University,
Singapore (NTU
Singapore;
www.ntu.edu.sg) have discovered
the parameters that deter(Continues
on p. 11)
10
ChemiCal engineering www.Chemengonline.Com September 2020
A zinc-based catalyst makes
syngas by co-electrolysis
R
B
A
esearchers from the University of
New South Wales (Sydney, Australia;
www.unsw.edu.au), led by professor
Rose Amal, have shown that by making
zinc oxide at very high temperatures using
a technique called flame spray pyrolysis (FSP),
they can create nanoparticles that catalyze the
co-electrolysis of CO2 and water into synthesis
gas (syngas; H2 + CO). The researchers believe
the method is less expensive and more
scalable to the requirements of heavy industry
than the methods available today.
In the process, humidified CO2 is fed to the
electrolyzer. The ZnO catalyst is designed
with two active sites, thereby simultaneously
converting CO2 into CO, and H2O into H2.
The H2-to-CO ratio (H/C ratio) can be varied
by making small adjustments to the way the
nanoparticles are burned by the FSP technique.
This feature makes it possible to tailor
the catalyst to meet the requirements for
end-use applications.
The researchers say past attempts have used
expensive catalyst materials, such as palladium,
but their method is the first instance where an
inexpensive and abundant material has been
successfully applied to waste CO2 conversion.
The next phase of the research is to test the
nanomaterials in a fluegas setting to ensure
that the new catalyst can withstand the harsh
conditions and other chemicals found in industrial
waste gas.
Improved process for treating AMD waste
recovers more rare earth elements
y modifying a traditional treatment
method for acid mine drainage
(AMD), researchers at Penn State
University (PSU; State College, Pa.;
www.psu.edu) were able to both reduce the
amount of chemicals required for treatment
and increase the amount of rare earth elements
(REEs) recovered from the waste.
AMD is an acidic aqueous runoff that occurs
when iron sulfide exposed to air and
water by coal mining activity oxidizes and
generates sulfuric acid. The sulfuric acid solution
dissolves surrounding rocks, drawing
a variety of toxic metals into the water. AMD
is a major environmental hazard for plants,
animals and humans, and is treated traditionally
by collecting the AMD in retention ponds
and neutralizing the acid with hydroxides. This
causes toxic metals to precipitate as a sludge.
The PSU team developed a novel, stagedprecipitation
processes for AMD that incorporates
CO2 mineralization. Adding gaseous CO2
to the AMD produces chemical reactions that
result in the formation of insoluble metal carbonates,
the scientists say. The rare earth elements
bond with the extra carbonate anions and precipitate
out of the water at lower pH values. The
PSU study, published in Chem. Eng. J., represents
the first time CO2 mineralization has been
used to recover REEs from AMD.
The staged precipitation process with CO2
mineralization raised the level of REEs recovered
by 15 percentage points compared to
traditional methods, while also suppressing
the formation of iron precipitates, which can
complicate downstream REE purification.
The PSU researchers say the process
can also be applied for the recovery of critical
elements from other low-concentration
pregnant leach solutions.
Waste-based rubber can be
joined or repaired catalytically
new sustainable rubber that can,
with an amine catalyst, be repaired
and returned to its original strength in
minutes, has been discovered by researchers
from Flinders University (Adelaide,
Australia; www.flinders.edu.au), the University
of Western Australia (Perth), and the University
of Liverpool (U.K.). " This study reveals a new
concept in the repair, adhesion and recycling
of sustainable rubber, " says Justin Chalker, research
leader and professor at Flinders University.
" Too many rubbers, plastics and ceramics
are not recyclable, " says Chalker.
The new rubber can be made from industrial
waste products, such as sulfur and canola
cooking oil, and dicyclopentadiene (DCPD). It
is produced by means of inverse vulcanization,
which is a copolymerization of elemental sulfur
and alkenes. These polymers contain a polysulfide
network that creates many opportunities for
processing, assembly and repair that are not
possible with traditional rubbers, plastics and
thermosets. The researchers have shown that
two surfaces of these sulfur-containing polymers
can be chemically joined at room temperature
through a phosphine- or amine-catalyzed
exchange of the S-S bonds in the polymer.
Rubber bricks made out of these polymers can
be chemically joined by applying the catalyst.
These new polymers have potential applications
in energy storage, adhesives, infrared
optics and environmental remediation.
http://www.unsw.edu.au http://www.kit.edu http://www.psu.edu http://www.flinders.edu.au http://www.ntu.edu.sg http://www.Chemengonline.Com
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