Valorization of Lignin Waste: Carbons from Hydrothermal Carbonization of Renewable Lignin as Superior Sorbents for CO2 and Hydrogen Storage

This report presents the preparation of renewable carbons from hydrothermally carbonized lignin waste. The hydrothermally carbonized mineral-free lignin-derived hydrochar was activated with KOH to yield carbons with surface area of 1157–3235 m2 g–1 and pore volume of 0.59–1.77 cm3 g–1. Activation at KOH/carbon = 2, generates highly microporous carbons (≥97% micropore surface area and 93% micropore volume), which exhibit excellent CO2 uptake capacity; up to 4.6 mmol g–1 at 1 bar and 25 °C, and 17.3 mmol g–1 at 20 bar and 25 °C, whereas at 0 °C and 1 bar, they store up to 7.4 mmol g–1. Activation at KOH/carbon = 4 can generate carbons with surface area and pore volume of up to 3235 m2 g–1 and 1.77 cm3 g–1, respectively, which have hydrogen uptake of up to 6.2 wt % at −196 °C and 20 bar. The simplicity of hydrothermal carbonization in generating hydrochars suitable for activation from readily available lignin waste, without the need for a demineralization step, makes these carbons attractive as gas storage materials for energy related applications. Furthermore, the lignin-derived carbons offer advantages with respect to attainable porosity and gas storage capacity compared to other forms of biomass (e.g., cellulose)-derived carbons.