Solid sorbents for carbon capture

These have the potential to function as more efficient alternatives to amine gas treating processes for selectively removing CO2 from large, stationary sources including power stations.

[2] Concern over the effects of CO2 with respect to climate change and ocean acidification led governments and industries to investigate the feasibility of technologies that capture the resultant CO2 from entering the carbon cycle.

In such a system, fossil fuels are combusted with air and CO2 is selectively removed from a gas mixture also containing N2, H2O, O2 and trace sulphur, nitrogen and metal impurities.

While exact separation conditions are fuel and technology dependent, in general CO2 is present at low concentrations (4-15% v/v) in gas mixtures near atmospheric pressure and at temperatures of approximately -60 °C.

Owing to the imperfect thermal efficiency of power plants, not all of the heat required to regenerate the sorbent would actually have produced electricity.

For temperature swing adsorption processes, the lower heat capacity of solids has been reported to reduce the sensible energy required for sorbent regeneration.

Sensible energy required for sorbent regeneration cannot be effectively recovered if solids are used, offsetting their significant heat capacity savings.

Lastly, many promising solid adsorbents have been measured only under ideal conditions, which ignores the potentially significant effects H2O can have on working capacity and regeneration energy.

Thus, discovering porous materials that can selectively bind CO2 under flue gas conditions using only a physical adsorption mechanism is an active research area.

Zeolites, a class of porous aluminosilicate solids, are currently used in a wide variety of industrial and commercial applications including CO2 separation.

For example, zeolite Ca-A (5A) has been reported to display both a high capacity and selectivity for CO2 over N2 under conditions relevant for carbon capture from coal flue gas, although it has not been tested in the presence of H2O.

[17] Frequently, porous adsorbents with large surface areas, but only weak adsorption sites, lack sufficient capacity for CO2 under realistic conditions.

Amine impregnated solids are reported to maintain their adsorption capacity and selectivity under humid test conditions better than alternatives.