Chemical Engineering July 2021 - 5

Chementator
Polyolefin deconstruction process could provide
new use for post-consumer plastic waste
A
catalytic process to selectively
break carbon-carbon bonds within
the polymer chains of polyethylene
and polypropylene could allow the
use of waste plastics to make biodegradable
surfactant molecules. Researchers led
by the Institute for Cooperative Upcycling of
Plastics (iCOUP) at the U.S. Department of
Energy's Ames National Laboratory (Ames,
Iowa; www.ameslab.gov) developed the
process, which catalytically cleaves polymer
chains into shorter units by introducing organo-aluminum
end groups. The scientists
can then functionalize these end groups to
make biodegradable fatty alcohols, carboxylic
acids or other derivatives.
The transformation (diagram) is enabled by
C-H bond activation and ß-alkyl elimination reactions,
in which a silica-supported zirconium
catalyst forms a metal-alkyl intermediate that
breaks C-C bonds within the polymer chain.
Then, the complex is treated with tri-alkyl aluminum,
forming shorter chain fragments with a
triethylaluminum or tributylaluminum group at
one end. The carboaluminum species can be
derivatized using oxygen or other reagents to
make fatty alcohols or carboxylic acids.
" Using Zr catalysts that are dispersed on
a silica surface, we can essentially reverse
the mechanism used to polymerize olefins
into plastics - instead of forming new
C-C bonds, we are cleaving them, " explains
Aaron Sadow, iCOUP director. " The alkylaluminum
species that are formed allow upcycling
of waste plastics, because they can
be functionalized using known methods. "
A
lthough the oceans contain about
5,000 times more lithium than what
is found on land, the low concentrations
(about 0.2 parts per million
(ppm)), as well as the predominance of other
larger ions (sodium, magnesium and potassium)
makes Li extraction difficult. Now, researchers
from King Abdullah University of
Science and Technology (KAUST; Thuwal,
Saudi Arabia; www.kaust.edu.sa) have developed
an economically viable system that
can extract high-purity lithium from seawater.
As described in a recent issue of Energy
& Environmental Science, the KAUST team
developed an electrochemical cell featuring
a solid-state electrolyte membrane - a ceramic
membrane made from lithium lanthanum
titanium oxide (LLTO). This membrane's
crystal structure has holes just wide enough
to let Li+ ions pass through, while blocking
larger metal ions. The electrochemical cell
C-C Bond Alumination: Tandem Carbon-Carbon Bond Cleavage
and Carbon-Aluminum Bond Formation
Catalytic C-C bond
functionalization
C-C bond cleavage alkyl group metathesis
Polyolefi n deconstruction by
C-C bond alumination
Catalytic
C-C bond
functionalization
Ames National
Laboratory
environmentally-persistent plastics biodegradable surfactants
A technoeconomic analysis conducted at
Argonne National Laboratory suggests the
costs of producing fatty alcohols from waste
plastic would be comparable to conventional
synthesis of these molecules. At iCOUP, fatty
alcohols have been synthesized using polyethylene
shopping bags with no pre-treatment.
The research team is exploring how the
design of the catalyst and support can be
used to control the distribution of chain
lengths in the fatty alcohol products. " We are
trying to figure out how to maximize yields
of C10-C20 chain lengths, because there is
an existing market for those, " Sadow says,
" But there also could be new markets in the
future for longer-chains, like C30s, because
you could produce them from waste plastic
at costs similar to conventionally made C12
chains, for example. "
Harvesting Li from seawater electrochemically
contains three compartments. Seawater
flows into a central feed chamber, where Li+
ions pass through the LLTO membrane into
a side compartment that contains a buffer
solution and a copper cathode coated with
platinum and ruthenium. Meanwhile, negative
ions exit the feed chamber through a
standard anion-exchange membrane, passing
into a third compartment containing a
NaCl solution and a Pt-Ru anode.
The system has been shown to enrich
lithium from seawater from the Red Sea by
43,000 times - boosting the concentration
from 0.2 ppm to more than 9,000 ppm, with
a Li/Mg selectivity of over 45 million. Li3PO4
with a purity of 99.94% - sufficient for battery
manufacturing - is formed by precipitation.
The value of gases produced by the cell
(H2 at the cathode, Cl2 at the anode) would
more than offset the cost of electricity, which
is estimated at $5 per 1 kg of Li extracted.
CHEMICAL ENGINEERING WWW.CHEMENGONLINE.COM
JULY 2021
Edited by:
Gerald Ondrey
EXTRACTING Li
Doosan Heavy Industries
& Construction, Ltd.
(Changwon, South Korea;
www.doosanheavy.com)
has developed technology
for recovering lithium
carbonate from waste
batteries. Li2CO3 is a
key material that is used
in batteries in electronic
devices, such as laptops
and mobile phones.
Conventional methods
for extracting Li2CO3 from
spent batteries involves
heat-treatment, acid
leaching and crystallization,
which usually involve
the use of chemicals such
as sulfuric acid. In contrast,
Doosan's method
does not use any chemicals.
Instead, the battery
materials first undergo a
heat treatment, followed
by an electro-absorption
crystallization process,
which uses only distilled
water to recover the
Li2CO3.The technology
- developed by Doosan
and for which a patent has
been filed - has the benefit
of being simpler and
more economical than
existing methods, and
is also environmentally
friendly since no chemicals
are used.
Starting in the second
half of this year, Doosan
will begin a demonstration
project for a facility
that will process 1,500
ton/yr of spent batteries
and produce Li2CO3 with
a 99% purity. " We plan to
aggressively
target the
domestic used-battery
recycling market, which
is forecast to grow rapidly
to the size of 19,000 tons
by 2029, " says Yongjin
Song, the company's
chief scientific officer.
HYDROGENATION
A few studies have
shown that hydrogenation
catalysis can be
(Continues on p. 6)
5
http://www.doosanheavy.com http://www.ameslab.gov http://www.kaust.edu.sa http://WWW.CHEMENGONLINE.COM
Chemical Engineering July 2021

Table of Contents for the Digital Edition of Chemical Engineering July 2021
