2 research outputs found
Valorization of Lignin Waste: Carbons from Hydrothermal Carbonization of Renewable Lignin as Superior Sorbents for CO<sub>2</sub> 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 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
Highly Porous Renewable Carbons for Enhanced Storage of Energy-Related Gases (H<sub>2</sub> and CO<sub>2</sub>) at High Pressures
Hydrochar,
i.e., hydrothermally carbonized biomass, is generating
great interest as a precursor for the synthesis of advanced carbon
materials owing to economical, sustainability, and availability issues.
Hereby, its versatility to produce adsorbents with a porosity adjusted
to the targeted application, i.e., low or high pressure gas adsorption
applications, is shown. Such tailoring of the porosity is achieved
through the addition of melamine to the mixture hydrochar/KOH used
in the activation process. Thereby, high surface area carbons (>3200
m<sup>2</sup> g<sup>–1</sup>) with a bimodal porosity in the
micromesopore range are obtained, whereas conventional KOH chemical
activation leads to microporous materials (surface area <3100 m<sup>2</sup> g<sup>–1</sup>). The micromesoporous materials thus
synthesized show enhanced ability to store both H<sub>2</sub> and
CO<sub>2</sub> at high pressure (≥20 bar). Indeed, the uptake
capacities recorded at 20 bar, ca. 7 wt % H<sub>2</sub> (−196
°C) and 19–21 mmol CO<sub>2</sub> g<sup>–1</sup> (25 °C) are among the highest ever reported for porous materials.
Furthermore, the micromesoporous sorbents are far from saturation
at 20 bar and achieve much higher CO<sub>2</sub> uptake at 40 bar
(up to 31 mmol of CO<sub>2</sub> g<sup>–1</sup>; 25 °C)
compared to 23 mmol of CO<sub>2</sub> g<sup>–1</sup> for the
microporous materials. In addition, the micromesoporous materials
show enhanced working capacities since the abundant mesoporosity ensures
higher capture at high uptake pressure and the retention of lower
amounts of adsorbed gas at the regeneration pressure used in PSA systems