Valorization of Lignin Waste: Carbons from Hydrothermal
Carbonization of Renewable Lignin as Superior Sorbents for CO<sub>2</sub> and Hydrogen Storage
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Abstract
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 m<sup>2</sup> g<sup>–1</sup> and pore volume of 0.59–1.77 cm<sup>3</sup> g<sup>–1</sup>. Activation at KOH/carbon = 2, generates highly
microporous carbons (≥97% micropore surface area and 93% micropore
volume), which exhibit excellent CO<sub>2</sub> uptake capacity; up
to 4.6 mmol g<sup>–1</sup> at 1 bar and 25 °C, and 17.3
mmol g<sup>–1</sup> at 20 bar and 25 °C, whereas at 0
°C and 1 bar, they store up to 7.4 mmol g<sup>–1</sup>. Activation at KOH/carbon = 4 can generate carbons with surface
area and pore volume of up to 3235 m<sup>2</sup> g<sup>–1</sup> and 1.77 cm<sup>3</sup> g<sup>–1</sup>, 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