Generalized Mechanochemical Synthesis of Biomass‐Derived Sustainable Carbons for High Performance CO2 Storage

Abstract

Novel mechanochemical activation generates biomass-derived carbons with unprecedented CO₂ storage capacity due to higher porosity than analogous conventionally activated carbons but similar pore size. The mechanochemical activation, or so-called compactivation, process involves compression, at 740 MPa, of mixtures of activating agent (KOH) and biomass hydrochar into pellets/disks prior to thermal activation. Despite the increase in surface area and pore volume of between 25% and 75% compared to conventionally activated carbons, virtually all of the porosity of the biomass (sawdust and lignin) derived mechanochemically activated carbons is from small micropores (5.8–6.5 Å), which results in a dramatic increase in CO₂ storage capacity at 25 °C and low pressure (≤1 bar). The ambient temperature CO₂ uptake for a carbon derived from sawdust at 600 °C and a KOH/carbon ratio of 2, rises from 1.3 to 2.0 mmol g⁻¹ at 0.15 bar, and from 4.3 to 5.8 mmol g⁻¹ at 1 bar, which is the highest ever reported for carbonaceous materials. The mechanochemically activated carbons have a superior CO₂ working capacity for pressure swing adsorption and vacuum swing adsorption processes and, due to a high packing density, they exhibit excellent volumetric CO₂ uptake that is higher than for any material reported to date.