Abstract
Activated carbons were prepared by chemical activation with KOH, FeCl3 and H3PO4 of the chars obtained via hydrothermal carbonization of grape seeds. The hydrochars prepared at temperatures higher than 200 °C yielded quite similar proximate and ultimate analyses. However, heating value (24.5–31.4 MJ·kg−1) and energy density (1.04–1.33) significantly increased with carbonization temperatures between 180 and 300 °C. All the hydrochars showed negligible BET surface areas, while values between 100 and 845 m2·g−1 were measured by CO2 adsorption at 273 K. Activation of the hydrochars with KOH (activating agent to hydrochar ratio of 3:1 and 750 °C) led to highly porous carbons with around 2200 m2·g−1 BET surface area. Significantly lower values were obtained with FeCl3 (321–417 m2·g−1) and H3PO4 (590–654 m2·g−1), showing these last activated carbons important contributors to mesopores. The resulting materials were tested in the adsorption of sulfamethoxazole from aqueous solution. The adsorption capacity was determined by the porous texture rather than by the surface composition, and analyzed by FTIR and TPD. The adsorption equilibrium data (20 °C) fitted the Langmuir equation well. The KOH-activated carbons yielded fairly high saturation capacity reaching up to 650 mg·g−1.
Highlights
Biomass is a widely available source of energy, important in developing countries, but cannot be considered a technically ideal fuel due to physical and chemical properties, each often having fibrous nature, high moisture content, volatile components, alkali and alkaline earth metallic content and a relatively low bulk density and heating value [1,2,3]
The adsorption capacity was determined by the porous texture rather than by the surface composition, and analyzed by FTIR and Temperature programmed desorption (TPD)
GS-260-40 represents the hydrochar obtained from grape seeds at 260 ◦ C with 40% of dry GS
Summary
Biomass is a widely available source of energy, important in developing countries, but cannot be considered a technically ideal fuel due to physical and chemical properties, each often having fibrous nature, high moisture content, volatile components, alkali and alkaline earth metallic content and a relatively low bulk density and heating value [1,2,3]. A broad range of biological (mainly anaerobic digestion and fermentation) and thermochemical (torrefaction and pyrolysis) treatments are typically used to improve the fuel properties of raw biomass [2,4,5]. From those processes, liquid or gaseous biofuels and even some valuable products are derived. As an alternative to the classical thermochemical methods, hydrothermal carbonization (HTC), referred to as wet torrefaction, is becoming an increasingly attractive way of biomass conversion. It operates in presence of water, at comparatively mild temperatures (180–300 ◦ C) and a corresponding
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