Chemical Engineering August 2023 - 12

duce polylactic-co-glycolic
acid (PLGA), a carbonnegative
polymer with valuable
characteristics: it has
an excellent barrier against
oxygen and moisture, has
good mechanical properties,
is recyclable and is
both home-compostable
and marine-degradable.
This makes PLGA a more
sustainable and costeffective
alternative to, for
example, non-degradable,
fossil-based polymers, the
company says.
Under this agreement,
Avantium and SCGC intend
to further evaluate PLGA in
order to subsequently scale
up production of glycolic
acid monomer and PLGA
polyester in the next two
years to a pilot plant.
TEXTILE DYEING
Archroma (Pratteln, Switzerland;
www.archroma.com)
and Somelos Group (Ronfe,
Braga, Portugal; www.
somelos.pt) have joined
forces to advance sustainable
cotton processing with
a new water-saving dyeing
and finishing process that
generates no wastewater.
Conventional cotton dyeing
and finishing requires
substantial water and
chemical inputs and produces
a large volume of
wastewater. To address
this challenge, the companies
have developed
the New Dry Dyeing/Ox
Finishing Process for the
production of bottoms and
shirting in cotton fabrics.
Based on Archroma's PadOx
dyeing process, which
combines oxidation and
fixation into one step, and
the latest technologies for
washdown effects, including
ozone and laser treatments,
it delivers water
savings of up to 97% compared
to conventional cotton
dyeing and finishing.
The New Dry Dyeing/Ox
Finishing process only uses
water to prepare the dye
and oxidation baths. Archroma
Diresul RDT liquid
pre-reduced sulfur dyes
ensure easy washdown
and direct fixation - with
no need for pre-washing -
(Continues on p. 14)
12
Carbon nanotube coating could expand the
applications for superlubricity
W
hen a sliding interface experiences
a coefficient of friction
(CoF) below 0.01, the situation
is said to have superlubricity. In
the past, superlubricity has been limited to
the microscale in controlled environments,
and to ceramic surfaces with polar-fluid lubrication.
Now,
research from Oak Ridge
National Laboratory (ORNL; Oak Ridge,
Tenn.; www.ornl.gov) demonstrates a path
to expand superlubricity to the most common
bearing system - steel-steel contact
in non-polar oil lubrication. By dramatically
decreasing friction in steel bearings and
other steel-steel moving parts, energy consumption
would be substantially reduced
and equipment lifetimes lengthened because
of less equipment wear.
The ORNL team, led by Jun Qu, first
ORNL
developed a process for growing carbon
nanotubes (CNTs) on a stainless-steel surface
using a chemical vapor deposition
process (see image). The vertically aligned
CNTs are hollow, made from layers of rolled
graphene. When steel with the CNTs on its
surface moves past another steel surface,
fragments of graphene flakes are shaved
from the vertical CNTs and redeposited on
the contact surface. These fragments form
a graphene-rich tribofilm that is capable of
reducing friction between the surfaces to
almost zero. As the fractured carbon nanotubes
release pieces of graphene, the graphene
pieces are " smeared and connected
to the contact area... then both contact surfaces
are covered by some graphene-rich
coating. Now, when they rub each other, it's
graphene on graphene, " Qu says.
The CNTs then function as a sacrificial
lubricant reservoir, allowing the low-friction
graphene to persist. The superlubricity of
the ORNL coating has persisted in tests
for more than 500,000 rubbing cycles. The
team published its results in a recent issue
of Materials Today Nano.
The presence of a small amount of polyalphaolefin
(PAO) lubricant oil is crucial to
achieving superlubricity. " The reason is, without
oil, friction removes the carbon nanotubes
too aggressively. Then the tribofilm
cannot form nicely or survive long, " Qu says.
Electrochemical amalgamation effectively
removes mercury from concentrated H2SO4
I
t is well known that mercury is not only
toxic, but is also highly mobile. As a result,
Hg emissions from both industrial
processes (gold mining, combustion
of fossil fuels, cement production, waste
incineration and more), as well as natural
emissions (volcanic and geothermal activities)
eventually are taken up by organisms
in the food chain.
Existing methods for removing Hg from
aqueous streams, such as precipitation,
ion exchange and solvent extraction, either
require the addition of chemicals and
subsequent generation of large volumes of
contaminated solids, or are limited to either
very low or very high concentrations or
feed volumes, which hampers their general
application. And none of the conventional
methods can handle highly acidic aqueous
solutions, which are common in some metallurgical
processes.
Five years ago, researchers at Chalmers
University of Technology (Gothenburg,
Sweden; www.chalmers.se) demonstrated
an alternative decontamination method that
is suitable for both low and high concentrations
of mercury, and can reduce the mercury
levels " far below " the limits allowed in
drinking water, as reported in Nature Communications
(see Chem. Eng., January
2019, p. 8). The method uses a platinum
cathode, which, when a potential is applied,
extracts the mercury ions from solution to
form a stable PtHg4 alloy. In addition to a
high removal capacity (>88 g Hg per cm3),
the electrodes can easily be regenerated.
Now, the electrochemical amalgamation
method has been demonstrated for removing
mercury from concentrated acid from
a zinc smelter. In both laboratory (50-mL
volume) and pilot tests (20-L volume), more
than 90% of the initial mercury content was
removed from the smelter sample, achieving
high-purity acid with mercury well below
(0.02 mg/kg) the industrial limits of 0.08 mg/
kg (after 80 h). The study, described in a recent
issue of ACS ES&T Engineering, demonstrated
the scalability of the technology.
CHEMICAL ENGINEERING WWW.CHEMENGONLINE.COM
AUGUST 2023
http://www.ornl.gov http://www.archroma.com http://www.somelos.pt http://www.chalmers.se http://WWW.CHEMENGONLINE.COM
Chemical Engineering August 2023

Table of Contents for the Digital Edition of Chemical Engineering August 2023
