Chemical Engineering June 2019 - 8

both the lowest capital expenditures
(capex) and the lowest
operating expenditures (opex)
per metric ton of ammonia
produced in comparison to
competitive
offerings. The
Ammonia 6000 design avoids
expensive air-separation and
nitrogen-wash units and utilizes
an intelligent equipment
layout with optimized and reduced
equipment count and
sizes, all of which help to leverage
economies of scale and
contribute to reduced capex,
says KBR.
NEW MEMBRANE
Researchers from the Massachusetts
Institute of Technology
(MIT; www.mit.edu) have
developed a new type of polymer
membrane - described
in a recent issue of Advanced
Materials - that can " dramatically "
improve the efficiency of
natural-gas purification. Existing
membranes are typically
made using linear strands of
polymer, says Zachary Smith,
the Joseph R. Mares Career
Development Professor of
Chemical Engineering at MIT,
who led this research effort.
" These are long-chain polymers,
which look like cooked
spaghetti noodles at a molecular
level, " he says. " You can
make these cooked spaghetti
noodles more rigid, and in so
doing you create spaces between
the noodles that change
the packing structure and the
spacing through which molecules
can permeate. "
However, such materials are
not sufficiently porous to allow
CO2 molecules to permeate
through them at a fast-enough
rate to compete with existing
purification processes. Instead
of using long chains of polymers,
the researchers have designed
membranes in which the
strands look like hairbrushes,
with tiny bristles on each strand.
These bristles allow the polymers
to separate gases much
more effectively.
In laboratory experiments, the
membrane was able to withstand
CO2 feed pressures of
up to 51 bars without suffering
plasticization, the researchers
report. This compares to around
34 bars for the best-performing
materials. The membrane is
(Continues on p. 9)
8
Electrochemical separation
and compression of hydrogen
H
ydrogen gas is used widely in industry,
including in metal annealing,
float-glass production and silicon
wafer manufacturing, among
others, but greater than 80% of the H2 used
for these processes is typically vented or
flared as waste. A new electrochemical system
allows facilities that use H2 to recover
the gas by separating and purifying it from a
waste gas stream, while also compressing
the gas for re-use.
Skyre Inc. (East Hartford, Conn.; www.
skyre-inc.com) has developed a proprietary
high-pressure electrochemical module,
modeled after proton-exchange-membrane
(PEM) fuel cells, to separate pure
hydrogen from H2-containing mixed-gas
waste streams. Known as H2Renew, the
device works by introducing a mixed gas
stream to one side of a cation-exchange
membrane and applying an electric potential.
When H2 contacts a platinum-group
metal catalyst in the membrane, it separates
into protons (which pass through the
membrane) and electrons (which complete
the electrochemical circuit). As protons
and electrons recombine on the other side
of the cell, pure H2 builds up and is compressed
to high pressure.
" The system works like an electrochemical
filter that effectively separates hydrogen
from other gases and impurities, and is able
to compress the gas simultaneously without
any moving parts, " says Skyre CEO Trent
Molter. Recovering hydrogen that would
have been wasted can reduce the costs of
H2 by one half compared to purchasing new
cylinders or tubes of H2, or generating the
gas onsite, Molter says.
H2Renew can produce H2 with purities
up to 99.999% and pressures up to 13,000
psi. In addition to H2-recycling applications,
H2Renew can also be used for compression
applications and for separating H2 from helium,
which has become expensive recently
due to a shortage of supply.
Based on similar technology, Skyre has
also developed an electrochemical cell for
converting carbon dioxide
into
fuels and chemicals.
High-strength Al alloy for 3-D printing is moving
into commercial production
T
he first high-strength, wrought-aluminum
alloy powder designed for
use in additive manufacturing (3-D
printing) applications is moving into
commercial production. The powder was
developed by HRL Laboratories (Malibu,
Calif.; www.hrl.com) for use in laser powder-bed
fusion 3-D printers. The company
recently announced that the material has
been registered by the Aluminum Association
(Arlington, Va.; www.aluminum.org).
The alloy material was originally described
in a 2017 Nature paper.
High-strength wrought aluminum alloys in
the 7000 and 2000 series have been used
for decades because of their strength and
low-cost alloying additives (Zn, Mg and Cu),
explains HRL's Zak Eckel. These alloys are
used widely, from aircraft components and
industrial equipment to sporting goods,
but they have not been successfully 3-Dprinted
before.
The main barrier to 3-D-printing of highstrength
Al alloys from metal powder is that
rapid melting and solidification of the feed
material in 3-D printing gives rise to suboptimal
crystal structure in the metal product.
Because aluminum's coefficient of thermal
expansion and other properties strain the
crystal structure, cracks develop easily in the
solidified aluminum.
Grain refinement in metal alloys refers
to strategies to control the nucleation and
growth of crystal structures with desired
properties. With its Al 7A77.60L alloy, HRL
has developed a targeted grain-refinement
method that controls the solidification of the
metal in additive manufacturing to avoid the
cracking phenomenon in the end product.
" We have developed an inoculant selection
method, based on matched lattices,
to grow aluminum grains in a way that will
generate the strength and other required
properties in the product, " says HRL metallurgist
Hunter Martin. By functionalizing
the melt pool from which solid Al can grow
when solidifying in 3-D printers, we avoid
large, columnar grains, Martin explains.
Using zirconium, we create many points
for aluminum crystal growth to occur in the
desired way.
HRL is hoping to use the commercial powder
to attract strategic customers looking for
the performance and cost benefits of highstrength
Al-alloy systems combined with the
freedom of additive manufacturing. Among
the initial applications of 3-D-printed Al-alloy
parts is replacement parts in aging, highvalue
equipment for which tooling for components
no longer exists.
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JUNE 2019
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Chemical Engineering June 2019

Table of Contents for the Digital Edition of Chemical Engineering June 2019
