Pinewood Activation with Eutectic Mixture of Chloride Salts Towards High Adsorptive Carbons: Influence of Temperature and Salt to Biomass Ratio

The current market searches for technologies allowing for efficient and sustainable production of biomass-based carbonaceous materials and their further application in adsorption of pollutants. Chemical activation of biomass in a bed of molten salts is a novel and promising technology. However, 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 derived carbon properties. For this purpose, pinewood shavings (ca. 1 mm) were mixed with three different ratios of an eutectic mixture of ZnCl 2 -KCl-NaCl (60:20:20 mol %) and subsequently treated at 400, 500 and 600 °C under an inert atmosphere. To assess the properties of obtained carbonaceous products, after washing, they were characterised with elemental and proximate analysis, FTIR, gas adsorption (N 2 , CO 2) and absorption of iodine and methylene blue. The pore size distribution of chars indicates that the presence of molten salts during conversion enhances micropore and mesopore formation. Most favourable structural properties of pinewood char with a specific surface area of 844 m 2 /g, were obtained at 400 °C and a salt to biomass weight ratio of 5. 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 efficient pathway to produce bio-based carbon materials.