Assessing the Potential of Biochars Prepared by Steam-Assisted Slow Pyrolysis for CO₂ Adsorption and Separation

The potentialities in the use of biochars prepared by steam-assisted slow pyrolysis as adsorbents of gases of strategic interest (N₂, CO₂, and CH₄) and their mixtures were explored. The biochars prepared from Populus nigra wood and cellulose fibers exhibited a narrow microporosity, with average pore sizes ranging between 0.55 and 0.6 nm. The micropore volume increased with the pyrolysis temperature, allowing CO₂ and CH₄ uptakes at room temperature between 1.5 and 2.5 mmol/g and between 0.1 and 0.5 mmol/g, respectively. These values are in line with those from the literature on biomass-derived carbon-based materials, exhibiting much higher porous features than those reported herein. As for the separation of CO₂/N₂ and CO₂/CH₄ gas mixtures, data showed that the prepared biochars exhibited good selectivities for CO₂ over both N₂ and CH₄: between ca. 34 and 119 for a CO₂/N₂ mixture in typical post-combustion conditions (15:85, v/v) and between 14 and 34 for a CO₂/CH₄ mixture typical of natural gas upgrading (30:70, v/v).