Adsorptive carbons from pinewood activated with a eutectic mixture of molten chloride salts: Influence of temperature and salt to biomass ratio

The current market searches for technologies allowing for efficient and sustainable production of biomass-based activated carbons for their further application in the adsorption of pollutants. Chemical activation of biomass in a bed of molten salts is a novel and promising technology in that regard. However, an in-depth understanding of the process mechanism is low and optimal production conditions must be substantiated. Therefore, this study investigates the relationship between molten bed process conditions and properties of derived activated carbons. Pinewood shavings (ca. 1 mm) were mixed with three different ratios of an eutectic mixture of ZnCl2–KCl–NaCl (60:20:20 mol %) and subsequently treated at 400, 500 and 600 °C under an inert atmosphere. After washing, the properties of activated carbons were characterised with elemental and proximate analysis, FTIR, gas adsorption (N2, CO2) and adsorption of iodine and methylene blue. The pore size distribution of activated carbons indicates that the presence of molten salts during conversion enhances micropore and mesopore formation. At 400 °C with a salt to biomass ratio of 5, the optimal structural properties of activated carbon with a specific surface area of 844 m2/g, was obtained. Its adsorption capacity of methylene blue (144 mg/g) and iodine (725 mg/g) were also satisfactorily high. This study confirms that optimum parameters for chemical activation with molten salts (temperature and salt to biomass ratio) towards functional materials can be achieved. Further process development may lead to a novel and efficient technology for the production of bio-based activated carbons.