Response surface methodology as an efficient tool for optimizing carbon adsorbents for CO2 capture

Phenol–formaldehyde resins and a low-cost biomass residue, olive stones (OS), were used to prepare five activated carbons for CO2 separation at atmospheric pressure, i.e., in post-combustion processes or from biogas and bio-hydrogen streams. Two phenol–formaldehyde resins were synthesized: Resol, obtained by using alkaline environment, and Novolac, synthesized in the presence of an acid catalyst. Carbon precursors were prepared by mixing both resins with KCl or by mixing the Novolac resin with OS. The precursors were carbonized under an inert atmosphere of N2 at different temperatures. The last stage in the synthesis of the adsorbents involved physical activation with carbon dioxide, which was carried out at different temperatures and burn-off degrees. Response surface methodology (RSM) is proposed as a tool for rapidly optimizing the activation parameters in order to obtain the highest possible CO2 capture capacity of activated carbons. The optimum values of activation temperature and burn-off degree that maximize CO2 uptake by the activated carbons at 35 °C and atmospheric pressure were obtained within the experimental region. A value of CO2 adsorption capacity of 9.3 wt.% was achieved. Activated carbons derived from the Novolac phenol–formaldehyde resin type and from OS showed great potential as adsorbents for CO2 capture at atmospheric pressure.

► RSM is a useful tool to optimize AC production for maximum CO2 capture capacity.
► In the absence of interaction T-B, the effect of B is low or nil at the studied T.
► When interaction exists, B only affects the CO2 uptake at high T.
► AC produced from PF and OS show great potential as CO2 adsorbents.