Rhodamine B removal with activated carbons obtained from lignocellulosic waste.

By-products from the wax production process from carnauba palm (leaves), from the extraction of oil from macauba seeds (endocarp) and from pine nut production (shell) have been assessed for activated carbon production, using H3PO4 or CaCl2 for their chemical activation. The resulting activated charcoals have been thoroughly characterized by elemental and thermal analysis, X-ray diffraction, infrared spectroscopy, electron scanning microscopy and N2 adsorption behavior. Subsequently, their adsorption capacity for the removal of rhodamine B (RhB) from aqueous solutions has been evaluated by studying different parameters: contact time, pH, adsorbent dose, initial dye concentration and solution temperature. The adsorption of RhB followed Freundlich's model in all cases. Kinetic studies indicate that the pseudo-second order model can be used for describing the dynamics of the adsorption process. Thermodynamic parameters have also been evaluated, indicating its endothermic and spontaneous nature. Finally, a preliminary analysis of the impact of cellulose content in the carbon precursor materials has been conducted, by using a mixture of native cellulose with one of the lignocellulosic materials.

A kinetic study on microwave-assisted conversion of cellulose and lignocellulosic waste into hydroxymethylfurfural/furfural.

Native cellulose, lignocellulosic materials from Brazil (carnauba palm leaves and macauba pulp and shell) and pine nut shell from Spain have been studied as substrates for the production of HMF and furfural in a conventional microwave oven. In order to promote the dissolution of native cellulose, several ionic liquids, catalysts, organic solvents and water doses have been assessed. The most suitable mixture (5mL of choline chloride/oxalic acid, 2mL of sulfolane, 2mL of water, 0.02g of TiO2 and 0.1g of substrate) has been chosen to conduct kinetic studies at different reaction times (5-60min) and various temperatures (120-200°C) and to evaluate the best conditions for HMF+furfural production according to Seaman's model. The best production yields of HMF+furfural have been attained for native cellulose, with a yield of 53.24% when an ultrasonic pretreatment was used prior to a microwave treatment with stirring.