Researchers Radu
Custelcean (top) and Charles Seipp study crystals that had absorbed
carbon dioxide from ambient air(Credit:
ORNL)
When we hear about carbon capture technology, it
typically takes the form of sponge-like materials that are used
to trap excess carbon dioxide at the places it is released, such
as industrial smoke stacks. Scientists from the US Department of
Energy's Oak Ridge National Laboratory, however, have created a
means of drawing it right out of the ambient air – and the
technology involves using a liquid to turn the CO2 gas into
crystals.
The researchers started out investigating methods of
removing environmental contaminants such as sulfate, chromate
and phosphate from water. In order to so, they synthesized a
compound known as
guanidine. It binds with such pollutants, forming insoluble
crystals that can subsequently be removed from the water.
However, they also discovered that when an aqueous
solution of guanidine was left open to the air, it drew CO2
from that air and
converted it into prism-like carbonate crystals.
In most carbon-capture scenarios, the captured CO2
needs to be converted back into a gas, so it can be piped into
underground storage reservoirs. In some cases, this involves
heating it as high as 900 ºC (1,652 ºF) – this obviously
requires a lot of energy, potentially creating as much CO2 as
has been captured. The guanidine crystals, though, only need to
be heated to 80-120 ºC (176-248 ºF) – the scientists are looking
into using solar energy as the heat source.
This heating turns the captured carbon back into a
gas that can be piped away, and returns the guanidine to its
liquid form. It can then be reused, to capture more carbon
dioxide.