Carbon capture made easy
Gasification plants may be one
of the keys to a hydrogen economy,
if capture and sequestration of carbon
dioxide (CO2) becomes technically
and economically feasible. These plants
would transform fossil fuel feedstock,
including coal, biomass and municipal
wastes, into clean-burning hydrogen
gas where the only byproduct is water.
But there are problems to solve.
In addition to producing hydrogen,
coal gasification produces CO2.
Current methods for CO2 capture
use large volumes of chemical solvents
that must be cycled through dramatic
changes in pressure and temperature
to absorb and then release CO2.
These pressure and temperature
swings use a lot of energy and increase
costs of electricity production by 15
to 30 percent.
Researchers at Pacific Northwest
National Laboratory are developing
a new class of materials for CO2
capture that aims to significantly
reduce the energy penalty for
CO2 capture. The PNNL process
does not require dramatic
pressure and temperature swings,
making it more energy-efficient.
And the concept integrates CO2
capture with a water-gas shift
reaction into a single, more efficient
unit, reducing costs and creating
a near-zero emissions system.
Integrating the process improves
the efficiency of the water-gas shift
reaction, which converts carbon
monoxide to CO2 and hydrogen by
reacting with water vapor, ultimately
producing more CO2 and more
hydrogen, the desired product.
A unique nanomaterial will
be instrumental in the integrated
process. “We are working with a
nano-structured material called
an organic clathrate that can be
engineered to attract CO2 and other
gases into its molecular cages,” said
Laboratory Fellow Pete McGrail, who
is leading the carbon capture work.
Organic clathrates can hold several
gas molecules in each of their cavities.
The material is a solid that could be
packed into an absorber column to
collect CO2 from the gas stream.
“The water-gas shift reaction
of interest takes place at 230 to
260 degrees Celsius,” said Praveen
Thallapally, who is leading the materials
synthesis work. “We have created a new
clathrate material that can absorb
CO2 at 220 degrees Celsius so we
believe it’s possible, with additional
research, to create materials that will
perform at the temperatures necessary
for this application.”
McGrail and his team also are
using molecular dynamics simulations
in their studies. Instead of the timeconsuming
conventional method of
constructing a material, synthesizing
it and evaluating it, they are using
computer simulations to help guide
their materials development and