Chemical Engineering December 2010 - 12

ChementatoR
Microbes convert stack gases to fuels and chemicals
A
demonstration plant for a biological
process that produces ethanol and 2,3
butanediol (2,3-BD) from the offgases of
industrial plants will be started up in the
third quarter of 2011 at a steel mill operated
by Bao Steel (Shanghai). Developed by
LanzaTech (Auckland, New Zealand; www.
lanzatech.co.nz), the process will produce
about 100,000 gal/yr of ethanol from a slipstream
of stack gases, says Mike Schultz,
the company's director of process development.
He adds that negotiations are under
way with Bao for a 50-million-gal/yr commercial
plant that would start up toward
the end of 2012.
LanzaTech's process (flowsheet) converts
carbon monoxide to ethanol by means of a
specially cultivated strain of the Clostridium
bacterium. The steel mill's waste gases
mainly consist of CO, plus some H2, CO2,
CH4 and O2. Particulate matter is filtered
from the gases, then the O2 is removed catalytically,
since the bacterium is anaerobic.
The rest of the gas mixture is sparged into
the aqueous solution of bacteria and converted
to ethanol in a continuous process, at
35-40°C. Hydrogen (needed for the process)
is generated via a biological, water-gas-shift
reaction, although if H2 is present in the gas
stream this reaction is mitigated and can
lead to additional ethanol production, says
Schultz. The CO2 is inert and simply passes
through the reactor. A hybrid recovery system
separates the ethanol and the coproduct
2,3-BD from the fermentation broth, which
is recycled to the process.
Schultz says the process is competitive
with processes that convert biomass to
ethanol, with the advantage that it uses
waste gases rather than crops. Such gases
are often flared (as in the case of the steel
mill) or burned for process heat. Schultz
notes that 2,3-BD is an intermediate for
such chemicals as butylenes, butadiene and
methyl ethyl ketone. He adds that LanzaTech
is working in the laboratory on a microbial
process that converts CO directly to
butanol or fatty acids. Last month, the company
also announced plans to work with Pacific
Northwest National Laboratory (Richland,
Wash.; www.pnl.gov) to develop 2,3-BD
as a drop-in jet fuel.
New catalyst approach for methane-to-ethylene conversion
A
nanotechnology-based, bottom-up
approach to synthesizing catalysts
for converting natural gas to ethylene
could enable an alternative to the
steam-cracking of crude oil, an energyintensive
process conventionally used
to produce ethylene, the world's most
valuable commodity chemical. Scientists
at the startup Siluria Technologies
Inc. (San Francisco, Calif.; www.siluria.
com) have developed a synthetic method
that allows them to manipulate catalyst
surface morphology such that the oxidative
coupling of methane (OCM) reaction
proceeds with high performance at
low temperatures.
An industrially viable OCM method
has been sought for decades, but past
efforts have been unsuccessful because
the high temperatures needed for activating
methane reduce the reaction's
selectivity. With many previously studied
catalysts, methyl free radicals leave
the catalyst surface before conversion
to the desired ethylene product. Nonselective
oxidation to CO2 is common. A
methane-based route to ethylene could
introduce feedstock flexibility and uncouple
the price of crude oil from that
of commodity chemicals.
Marrying molecular biology with industrial
chemistry, Siluria's catalyst
synthesis process uses proteins on the
surface of a genetically modified bacteriophage
(bacteria-infecting virus)
as nucleation sites for growing nanoscale
wires of catalyst material. By
growing the catalyst nanowires on an
engineered biological template, Siluria
is able to access crystal structures
and surface morphologies not formed
through conventional crystallization of
the material. The novel crystal structures,
in turn, give rise to catalyst active
sites with unique properties that
are critical to achieve the selectivity
and yield required for an economically
viable OCM process.
12 ChemiCal engineering www.Che.Com DeCember 2010
(Continued from p. 11)
a scheme that combines
thionyl chloride with a variety
of organic reagents, such as
pyridine, N,N-dimethylformamide
(DmF), pyrimidine
and imidazole, to selectively
dissolve either gold or palladium,
depending on the
solvents chosen and their
concentrations. no combination
of solvents dissolves
platinum, giving the solvent
system the ability to separate
au or Pd from Pt in mixed
metal catalysts. So far, the
researchers have used the
solvent system to separate
au and Pd from Pt, and to
remove au from a mixture of
au and Pd.
" Conventional top-down catalyst
synthesis generates the most thermodynamically
favorable crystal structures,
but unfortunately, those are
not the most effective in catalyzing
OCM, " explains Siluria president Alex
Tkachenko. " We've developed a synthetic
method for producing catalyst
material with specialized surface properties,
which turns out to be critical for
an effective OCM process and delivering
on the promise of methane activation
to produce chemicals. "
The catalyst materials are proprietary,
doped metal oxides of early transition
metals that are designed for compatibility
with existing petrochemical industry
infrastructure. Siluria has developed a
library of compounds with a range of
crystal structures, and has tested their
behavior in catalyzing the OCM reaction.
The company aims to achieve the
catalyst performance required for commercialization
in 2011, Tkachenko says.
http://lanzatech.co.nz http://www.pnl.gov http://www.siluria http://www.Che.Com
Chemical Engineering December 2010

Table of Contents for the Digital Edition of Chemical Engineering December 2010
