18 March 2011
Plants may help to reduce carbon dioxide in the atmosphere when dead as well as alive, say scientists from Spain.
Carbon capture - the removal of CO2 from waste gases (such as from power plants) - is an important method for reducing CO2 emissions. One such strategy is the use of porous solids, such as zeolites and porous carbons, to absorb CO2 into their pores. However, these materials exhibit poor uptake capacities (about 3mmol CO2/g) and have complex and costly syntheses.
Now, Antonio Fuertes and his group at the National Institute of Carbon, Oviedo, have made a porous carbon material that performs better than other currently available ones, using a simple and inexpensive process. The major difference in this work, however, is that the raw material is sawdust.
The two step synthesis involves hydrothermal carbonisation of the sawdust, creating a hydrochar, which is then activated using potassium hydroxide. The KOH treatment creates pores in the sawdust structure by oxidation of carbon and carbon gasification from K2CO3 decomposition. These pores are responsible for the material's uptake capabilities, bestowing it with a capacity as high as 4.8mmol CO2/g. In addition, Fuertes' material has good selectivity for CO2 over N2, fast adsorption rates and can be easily regenerated.
Magnified image of sawdust before (left) and after (right) being heated and activated, showing the pores
'This type of carbonaceous material gives rise to an activated carbon that possesses textural properties that are appropriate for CO2 capture,' says Fuertes. 'What's more, the fabrication process is not complex and the raw material is abundant and widely available.'
Peter Styring, an expert in carbon capture technologies at the University of Sheffield says that the material has advantages over the currently most popular class of materials. 'They're comparable in terms of performance [to alkanolamines], but in terms of their engineering capabilities, these are superior,' he explains. 'With the alkanolamines, you get problems with corrosion, evaporation and degradation.'
Fuertes says that there is more work to be done before this technology can be commercialised, including investigations into scaling up. For now, he is focusing on other materials, such as nitrogen-doped carbons.