Chemical Engineering January 2018 - 24

Cover Story
HONOR ACHIEVEMENTS
Chemetry:
FIGURE 3. The electrochemical
cell of eShuttle is shown
here
Chemetry
Overall reaction: C2H4 + 2H2O + 2NaCl ➔ H2 + 2NaOH + C2H4Cl2
Membranes
EDC
(C2H4Cl2)
CuCl2
Aqueous
reaction
process
CuCl
C2H4
Anode: Cu+
Catalysis
C2H4 + 2CuCl2 ➔ C2H4Cl2 + 2CuCl
24
➔ Cu2+ + e-
E° = 0.159 ➔ 0.7 V
A
n
o
d
e
A
n
i
o
n
m
e
m
b
r
a
n
e
NaCl
Na+
Cl-
C
a
t
i
o
n
m
e
m
b
r
a
n
e
C
a
t
h
o
d
e
Cathode: 2H2O + 2e-
Electrochemistry
2H2O + 2NaCl + 2CuCl ➔ H2 + 2NaOH + 2CuCl2
H2
NaOH
OH-
Chemetry
eShuttle™ technology
Chemetry's eShuttle technology provides a
breakthrough in the synthesis of chlorinated
organic compounds by eliminating chlorine
generation from the traditional chlor-alkali
process. The first commercial application of
the technology is the chlorine-free synthesis
of ethylene dichloride (EDC), an intermediate
in the production of polyvinyl chloride
(PVC). The next application for this platform,
a process producing propylene oxide,
is now in development.
General description. eShuttle replaces the
chlor-alkali and direct-chlorination processes
with a single, integrated process (Figure 3) that
uses a circulating stream of aqueous copper
chloride to transfer chloride ions from NaCl to
ethylene. Specifically, the process leverages
the redox states of copper to convert CuCl to
CuCl2 at the anode of the electrochemical cell.
The CuCl2 then reacts with ethylene to form
EDC, regenerating the CuCl, which is returned
to the cell. Like the processes it replaces, the
eShuttle technology uses the same feedstocks
- NaCl brine, water and ethylene - to
produce the same products - EDC, caustic,
and H2 - but at much lower energy and operating
cost and without Cl2 gas generation.
The novelty of the technology lies in the
elimination of Cl2 as a chemical intermediate.
By replacing the standard chlor-alkali anode
reaction, 2Cl- → Cl2 + 2e-, with the copper
oxidation reaction, Cu+ → Cu2+ + e-, the
theoretical anodic voltage is decreased by
0.6V. This voltage translates directly to electrical
savings of 25% and significantly lower
operating costs. Moreover, the elimination
of Cl2 as an intermediate reduces the safety
risk and costs associated with Cl2 compression,
storage and transportation.
Cell technology. From a chemical engineering
perspective, one of the most important
advances in the development of the new
cell is the anode structure. Unlike traditional
chlor-alkali cells, which have gas-generating
reactions at both the cathode (H2) and anode
(Cl2), the eShuttle cell does not generate gas
at the anode. This provides two significant
benefits to the cell design. First, the anode
half-cell reaction is strictly an electron-transfer
reaction; it is non-catalytic. As a result,
catalytic coatings are not needed to assist
with any reaction step, including gas desorption.
Secondly, the anode compartment
itself can be much thinner because there are
no issues with two-phase flow. This is important
because a three-compartment cell
would typically lead to a much thicker cell.
However, the thinner anode compartment
actually allows for a cell that is about half the
thickness of the state-of-the-art chlor-alkali
cell. This allows the eShuttle to be readily retrofittable
to existing electrolyzer floor space.
Although a single-phase anolyte does have
benefits, it also presents two key challenges:
mass transfer and pressure balancing. The
gas generation in the chlor-alkali anode provides
effective mass transfer through convective
flows. Without gas generation, a thick,
stagnant boundary layer may form at the
anode surface. Formation of such a boundary
layer can lead to localized depletion of
Cu+1, and diffusion-limited cell performance.
To address
these challenges,
Chemetry
H2O
➔ H2 + 2OH-
E° = -0.83 V
utilized 3-D computational fluid dynamics
(CFD) models to simulate various anode design
concepts. The final design incorporates
optimized electrodes with a bridged, corrugated
mesh that acts as an inline static mixer
for the flow. The design is optimized for high
mass transfer and low pressure drop, and
features an anion exchange membrane that
has low resistance for Cl- transport and yet
blocks the migration of copper species, and
a design that minimizes electrical losses and
cell thickness.
Development and commercialization. The
eShuttle process was transferred from laboratory
to commercial demonstration scale
at Chemetry's facility in Moss Landing, Calif.
with integrated operation beginning in 2014
and extensive production campaigns in 2015.
To bring the process to commercial scale,
Chemetry has developed partnerships with a
number of key suppliers, including FuMA-Tech
for the supply of membranes, Covestro for the
supply of oxygen-depolarized cathodes, and
a specialized laser welding company for cell
fabrication. In 2016, TechnipFMC obtained
rights to license eShuttle for EDC. Recently, a
confidential development partner has signed
a term sheet to install a demonstration-scale
plant at one of its existing production sites.
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JANUARY 2018
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Chemical Engineering January 2018

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