Chemical Engineering May 2020 - 7

Chementator
A low-cost way to make PO
without chlorine or wastewater
Chemetry
C
hemetry
Corp. (Moss
Landing,
Calif.; www.
chemetrycorp.com) is
piloting a hybrid electrochemical-catalysis
process
for
making
propylene
oxide (PO)
that eliminates some
of the major production hurdles associated
with chlorohydrin-based PO production.
" The traditional chlorohydrin process produces
about 47 tons of wastewater per ton
of product. With our process, we are able
to eliminate this wastewater stream, producing
effectively nothing, " says Ryan Gilliam,
Chemetry CEO, also highlighting the
fact that the process requires no chlorine
gas and also offers a dramatic reduction in
energy consumption. Chemetry's integrated
pilot facility has been ramping up production
in recent months, and now produces
around 50 kg/d of PO. According to Gilliam,
the technology is economically promising
not only for existing PO producers who want
to expand or retrofit their capacity, but also
for locations where building a smaller-scale
commercial plant is more economical than
purchasing or importing PO.
Fundamentally, the closed-loop process
(diagram) employs copper bromine salts,
which are recycled between the electroPropylene
Oxygen
Hydrogen
PBD
→ PBH
Propylene →
PDB + PBH
Extraction/
Separation
Oxybromination
Saponification
Caustic
NaBr
Electrochemistry
Copper loop
PDB loop
Salt loop
Inputs/outputs
chemical unit and the catalysis units to convert
propylene and oxygen into PO. " Bromine
salts offer many advantages in terms
of kinetics and ease of separation, " explains
Gilliam. Copper bromide salts from the electrochemistry
unit react with propylene in the
catalysis unit, forming a split of propylene
bromohydrin (PBH) and propylene dibromide
(PDB). PBH, the precursor for PO production,
reacts with sodium hydroxide to make
PO. Simultaneously, the PDB goes into a
secondary reactor where it is catalytically
converted to PBH and sent to the saponification
reactor. The copper is oxidized in
the electrochemical cell and carries bromide
back to the catalysis reactor. The closedloop,
zero-discharge nature is a cornerstone
of its advantages to PO producers. " We've
been able to prove that the copper stream is
fully recyclable between catalysis and electrochemistry.
We've been running the same
copper bromide solution over the last six
months in the pilot plant, " adds Gilliam.
Propylene
oxide (PO)
PO
Purification
Edited by:
Gerald Ondrey
Researchers
LIGHT-EMITTING Si
from
Eindhoven
University of Technology
(TUE; the Netherlands;
www.tue.nl) have developed
an alloy with silicon that can
emit light. Together with researchers
from the universities
of Jena, Linz and Munich,
the researchers combined
silicon and germanium in
a hexagonal structure that
is able to emit light - a
breakthrough after 50 years
of work. The findings, published
in a recent issue of Nature,
are a first step towards
revolutionizing computing by
making chips faster.
In contrast to electrons, photons
do not experience resistance.
As they have no mass
or charge, they will scatter
less within the material they
travel through, and therefore
no heat is produced. The energy
consumption will therefore
be reduced. Moreover,
by replacing electrical communication
within a chip by
optical communication, the
speed of on-chip and chip(Continues
on p. 8)
An efficient electrochemical route to triphenylphosphine -
without the waste
A
new electrochemical process
could make triphenylphosphine
(TPP) - an
important reagent in many
organic transformations - more
practical for industrial use. Synthesizing
TPP results in large volumes
of waste in the form of triphenylphosphine
oxide (TPPO), which
is very energy-intensive to handle.
Now, a study led by Christo Sevov,
professor of chemistry at The Ohio
State University (Columbus, Ohio;
www.osu.edu), has demonstrated
the efficient conversion of TPPO
into TPP. " In industry, people avoid
these very simple and reliable reactions
with TPP because of the TPPO
problem. They have to come up with
really circuitous routes to get to the
same products that they could access
in a single step if they had TPP
in greater abundance, or were able
to do something with the waste, " explains
Sevov. Currently, there is only
one large-scale industrial process
for recycling TPPO into TPP, and it
requires massive energy input, multiple
synthetic steps and the use of
toxic substances like phosgene.
Beginning with an electrified aluminum
container acting as the anode
in an electrochemical cell, the aluminum
ions are strategically stripped
from the anode surface and then
utilized as a Lewis-acid activator for
the TPPO. " Everything is self-contained,
and because you are using
the waste of the anode to activate
the substrate, you don't have to add
any super-stoichiometric quantities
of reagents, and you continuously
CHEMICAL ENGINEERING WWW.CHEMENGONLINE.COM MAY 2020
generate the activator as you perform
the electrochemical reaction, " adds
Sevov. This continuous generation is
key, since this type of reaction normally
stalls out after about only 5%
completion, shutting down either because
the anode is passivated or the
selectivity is low.
The team has demonstrated this
conversion using various aluminum
sources - including soda cans and
aluminum mesh fencing. This process
could also unlock other organic
reactions
that
are
not
industrially
practical. " We are also looking at hetero-arenes
and pyridines. If we can
activate these with in-situ-generated
Lewis acids, then we can begin doing
functionalization reactions on these
desirable pharmaceutical platforms, "
adds Sevov.
7
http://www.chemetrycorp.com http://www.tue.nl http://www.osu.edu http://WWW.CHEMENGONLINE.COM
Chemical Engineering May 2020

Table of Contents for the Digital Edition of Chemical Engineering May 2020
