Activated carbon from bio-based feedstock
CSIC is using selected biomass residues such as pistachio shells or eucalyptus sawdust as carbon precursors.
Activated carbon is one of the most used carbon materials worldwide. It has been used since the Ancient Age, for medical applications as well as for water purifying and odor removal, as recommended by Hippocrates around 400 BC. Nowadays, it is a key component in supercapacitors, an energy storage device used in transport applications for regenerative breaking or start-stop systems. This activated carbon can be produced from a wide variety or materials, where coal and biomass are the most employed precursors. The use of biomass for the preparation of activated carbon is a matter of great interest. Classically activated carbons from biomass origin had been produced from coconut shell and some other carbon-rich residues such as cherry stones. The general process implies two steps, heating of the biomass (conveniently milled and sieved) under inert gases (pyrolysis step) to produce a carbon-rich material and heating this product under controlled oxidizing conditions to generate porosity (activation process). Biomass residues are an ideal source for the preparation of carbon materials on account of their renewable nature and the fact that their disposal (landfilling or burning) represents an environmental problem. In fact, this kind of practices are mandatory in a circular economy that helps us to preserve our planet and its resources. Several biomass residues have been used so far to produce activated carbon, but in general most of the classic studies lack of strict control over the porosity of the material. Moreover, the efficient transformation of biomass into high added-value materials is still a challenge.
In the XXI century we are facing a climate and energetic emergency that can only be solved with scientific knowledge. In MAST3RBoost project we want to develop ultraporous materials for hydrogen storage and our team at CSIC are developing new activated carbons to fulfill the requirements of the project. The group leaded by Dr. Marta Sevilla is using selected biomass residues such as pistachio shells or eucalyptus sawdust as carbon precursors. These two residues are abundant, since pistachio consumption is increasing as it is considered a very good product in terms of nutrition, sometimes referred as green gold, while eucalyptus sawdust is extensively produced in paper factories. We are studying in depth different transformation processes in order to produce carbon materials with the targeted porosity at the highest possible yield, that implies a precise optimization for each type of precursor. The aim of the project is to develop materials with high capacity for the adsorption of hydrogen, and therefore we need to produce materials with a high porosity that should be of the correct size. To achieve a high porosity development and, therefore, a high surface area, we are exploring the use carbon dioxide, which allows us to capitalize on this undesired greenhouse gas. By controlling the synthesis conditions, we have been able so far to prepare activated carbons with very high surface areas up to 2900 m2 g-1, which means that 2.5 g of this material has the same area as the Real Madrid’s football field. Besides, these materials possess very tiny pores which we expect to be highly efficient in hydrogen storage. And this is the point at which we are now, to check if these materials are really capable to store a significant amount of hydrogen.