Presentation on "Carbon Dioxide Sequestration" given by Prof Fredrik Glasser from University of Aberdeen in the Solid Adsorption Technical Session at the UKCCSRC Biannual Meeting in Cambridge on 2-3 April 2014

1. Carbon Dioxide Sequestration
J-L. Galvez-Martos, J.Morrison,
G. Jauffret and F.P. Glasser
University of Aberdeen

2. Human activity and CO2 releases
• We live an energy- rich lifestyle and moreover
are “hooked” on fossil fuel sources of energy
• Other sources, such as nuclear, wind, wave
and tidal, hydro, solar, geothermal.... all have
some undesirable features, e.g., intermittency.
• They are inconsistent with a “push button”
approach to supply
• As pragmatists, we concentrate on mitigation

3. Addressing the challenge.
• We address the challenge in the construction
sector. The work is supported by GORD (Gulf
Organisation for Research and Development)
and embraces a holistic approach, including
energy required to live and work , as well as
eventual demolition and re-use of materials.

4. Concept -1
• Capture and convert CO2 to stable and useful
solids.
• Mg (OH)2 has been obtained from sea water for a
century simply by raising the pH. CO2 is often
uptaken during precipitation. Calcination to
~500°C gives MgO.
- But this has not proven to be a satisfactory
low energy process and MgO is not, in our view, a
good starting point for materials development.
Instead , we precipitate magnesium
hydroxycarbonate hydrates (MHCH phases)

5. Prospects for decarbonising our lifestyle
•Increase photosynthesis: fix more
carbon
•Sequester carbon in various ways,
e.g., CO2 pumped underground
(passive storage)
•Convert CO2 to useful solids by
organic and inorganic routes.
•Eventually, decarbonate society

6. Preparation of MHCH phases
MHCH phases are best made by a two
stage process.
1. Dissolving CO2 in slightly alkaline
solution at 1 bar pressure, ~10-50*C
2. Mixing the CO2 -containing solution
with a second solution containing
Mg and collecting the MHCH
precipitate

7. Reactor for MHCH Synthesis
Mass flow
controller
Overhead
stirrer
Peristaltic pumps
Laptop with control
software
pH meter
Balances (5 kg maximum)
Reactor 1
Reactor 2
To and from
temp.
controller

8. Reactants
• The Mg source is typically reject water from a
desalination plant using sea water intake. We
use a simulate with ~1M NaCl and ~0.1M Mg
• CO2 comes directly from a fixed source, such
as exhaust gas from a power plant or a
cement works but is conveniently modelled
using tank CO2.

9. Products
• The preferred solid products are mainly
hydromagnesite, Mg5[(OH)2|(CO3)4|.4H2O]
and nesquehonite, Mg[CO3].3H2O
• Both occur in nature, hence the mineral
names: their crystal structures are known
• Numerous other phases occur in nature, only
a few of which are known as synthetics

10. Products
30 microns
30 microns
Nesquehonite needles at 1000x magnification Hydromagnesite grains at 1000x magnification

11. Structure of Nesquehonite , MgCO3.3H2O

12. Specimen Calculations
OH / CO2 ratio
1.0 1.2 1.4 1.6 1.8 2.0
Temperature,degC
30
40
50
60
NQ ONLY
NQ AND HM
HM ONLY
predicted phase boundaries
NQ
HM
NQ and HM
Modelled phase diagram showing experimental points
of phase precipitation

13. Specimen Calculation
OH : CO2 ratio
1.0 1.2 1.4 1.6 1.8 2.0
T,degC
25
30
35
40
45
50
55
60
65
80
80
60
6040
40
20
20
1.0 1.2 1.4 1.6 1.8 2.0
30
40
50
60
NQ
NQ
and
HM
HM
Phase Diagram predicted by GEM over a range of
temperatures and OH : CO2 ratios, showing magnesium
recovery contours

14. Calculation vs experiment
• Thermodynamic calculations are not necessarily
completely reliable and require experimental
verification. Example, metastable formation of
dypingite in place of hydromagnesite
• Nevertheless, calculation greatly shortens the
time taken to explore the impacts of changing
temperature, species activities, concentrations,
etc.
• Example: calculation of the impact of increasing
NaCl salinity on yields has proven surprisingly
accurate.

15. Product Properties
Properties of self-cemented NQ
• Thermal conductivity: ~ 0.21 W.m-1.K-1
• Compressive strength: ~ 5 MPa
• Bulk density: ~ 0.75 g.cm-3
• Density of nesquehonite: ~ 1.84 g.cm-3
• Porosity: ~ 59 %

16. Next steps
• Convert reactor to semi- continoous operation
• Make larger (kg) batches for property
measurements and property-structure
correlations
• Continue process optimisation by combining
experiment and calculations
• Develop new applications / products

17. Conclusions
• We see prospects for converting CO2 to a
useful product containing (as for NQ) 32%
carbon dioxide.
• Product is non- toxic, fire retardant and at
end of life, easily recycled.
• Carbon capture to form useful engineered
materials is a very real prospect