Chemical Engineering October 2013 - 11

Edited by Gerald Ondrey
October 2013
A 'new' concept for CO2
capture: birds' lungs
esearchers at the University of California
Irvine (UCI, Irvine CA; www.chem.
uci.edu) have taken a cue from nature in
devising a way to remove carbon dioxide
from fluegas. They are developing a synthetic
membrane based on the design and
function of birds' lungs.
R
" Birds' lungs are the most efficient mass
exchangers in nature and have one of the
highest specific surface areas known, " says
Aaron Esser-Kahn, an assistant chemistry
professor. The reason, he adds, is that the
lungs are rigid and push gas continuously
through thousands of microscopic pores.
" They have larger tubes hierarchically connected
to smaller tubes, which allows them
to maximize surface area while minimizing
pressure, " he says. " Overall, there are three
levels of hierarchy within the lung. "
The researchers make the membrane by
stretching polylactic acid fibers of two different
diameters (100 µm and 300 µm) between
two brass plate headers (diagram). The use
of two diameters allows a tighter and more
efficient pack. This assembly is put into a
mold, which is then filled with liquid polydimethylsiloxane
(PDMS). After the PDMS
sets, the module is heated to about 200°C in
a modest vacuum to depolymerize the fibers,
resulting in a structure similar to a shelland-tube
heat exchanger.
continuous fermentation process for making
biologically derived butanol from a
variety of sugar feedstocks is operating at
what developers call " lab-pilot " scale, producing
2.5 liters per day. Engineering studies
conducted by the research team forecast
that it could be produced for the same cost as
existing sugar-based bioethanol processes.
The technology developer, Optinol Inc.
(San Francisco,
A
Calif.; www.optinol.com),
estimated capital and operating costs for
commercial-scale manufacturing using its
biobutanol process and concluded that it is
feasible to produce biobutanol " at cost parity
with ethanol. "
Optinol has built its process around
a robust, naturally occurring strain of
Clostridium bacteria that converts a range
of feedstocks,
including sugarcane juice,
Note: For more information, circle the 3-digit number
on p. 60, or use the website designation.
In laboratory tests, the researchers have
flowed CO2 through the large-diameter
channels while feeding monoethanolamine
(MEA) countercurrently through the
smaller ones. The CO2 diffuses through the
membrane and is carried away by the MEA.
Esser-Kahn says MEA is used for convenience,
but a commercial unit could use another
carrier gas. So far, the mass transfer is
below that of commercial hollow-fiber membranes.
However, Esser-Kahn says the tests
have proved the concept and he expects to
increase the specific surface area by creating
finer capillaries.
New approach for biobutanol reaches 'lab-pilot' scale
corn starch,
molasses,
cellulosic sugars
and others, into butanol at high conversion
rates. " One of the challenges for genetically
modified organisms [producing bio-based
chemicals] is that they evolve quickly, and
can lose the genetic features that were engineered
into them, " explains Optinol founder
and interim CEO Jack Oswald. " Instead of
engineering a bug to fit a process, we took
the approach of engineering a production
system tailored to the organism. "
The company operates banks of inexpensive
fermentation columns that contain a
cell-growth matrix on which the microbes
thrive. The sugar feed is continuously
flowed through the columns, where it is
converted to butanol. The immobilized-cell
columns are followed by a low-cost extrac(Continues
on p. 14)
Strength with stress
Shear forces usually break
bonds in polymer materials,
but a research team at
Duke University (Durham,
N.C.; www.duke.edu) has
demonstrated for the fi rst
time synthetic polymers capable
of forming new bonds
in the presence of shear
forces that would normally
break down polymer chains.
Termed activated remodeling
via mechanochemistry
(ARM), the concept depends
on a mechanically active
dibromocyclopropane moiety
that is embedded within a
polybutadiene backbone.
The dibromocyclopropane
ring opens as a result of
mechanical stress, forming
a 2,3 dibromoalkene
product that is susceptible
to nucleophilic substitution.
This chemistry provides the
basis for remodeling and
potential self-strengthening
or self-repair through covalent
cross-linking. The
Duke team's results raise
" intriguing possibilities of
localized mechanochemical
self-strengthening to 'at-risk'
regions within a load-bearing
material, " the authors state.
CHEMICAL ENGINEERING WWW.CHE.COM OCTOBER 2013 11
http://www.chem http://www.uci.edu http://www.duke.edu http://www.optinol.com http://WWW.CHE.COM
Chemical Engineering October 2013

Table of Contents for the Digital Edition of Chemical Engineering October 2013
