RESUMO
Activated carbons (ACs) from Pinus canariensis cones were developed by KOH chemical activation. The effect of the impregnation KOH/carbonized cones ratio (IR = 1, 2, or 3) and temperature (873, 973, 1073 K) on main chemical, textural, and morphological characteristics of the resulting ACs was systematically examined. CO2 adsorption capacity from gaseous streams was evaluated by gravimetric adsorption tests, and the analysis of breakthrough curves was determined in a packed-bed column at 303 K and atmospheric pressure. Comparison of CO2 adsorption capacities of the ACs at 273 K and 303 K at equilibrium showed that those samples developed at 973 K with IR = 3 (BET surface area ~ 1900 m2 g-1) attained the highest values (6.4 mmol g-1 and 1.9 mmol g-1, respectively), even though the ACs obtained at 1073 K with the same IR exhibited the largest surface area (2200 m2 g-1). Thermodynamic parameters evaluated from CO2 adsorption isotherms determined in the range 273-333 K for the former sample pointed to a physisorption, spontaneous, and exothermic process; isosteric heat of adsorption was also estimated for the range of surface coverage of the equilibrium isotherms. The kinetics of CO2 adsorption onto all the ACs was successfully described by the linear driving force model. The breakthrough curves were properly represented by the Thomas' model, the longest breakthrough time and highest adsorption capacity being also attained for the bed packed with the ACs developed at 973 K with IR = 3. Higher CO2 adsorption capacities of the ACs were directly related to the presence of narrow micropores (< 0.9 nm) induced by the stronger activation conditions. However, an excessively severe combination of the IR and activation temperature exerted a negative influence on CO2 adsorption onto the ACs, likely due to micropores widening.
Assuntos
Carvão Vegetal , Pinus , Adsorção , Dióxido de Carbono , CinéticaRESUMO
Graphene oxide/alginate beads were prepared from lab-synthesized graphene oxide, varying its content within the beads (0.05, 0.125, and 0.25wt.%). Ethanol-drying and lyophilization were compared as drying methods to obtain suitable adsorbents which were later tested to the removal of a model organic molecule (methylene blue). The morphological and textural properties of all the beads were characterized by scanning electron microscopy and N2 adsorption/desorption isotherms at -196°C, respectively. Limited porosity was obtained for all cases (SBET<60m2/g). Uniaxial compression tests were performed to assess the mechanical properties of the beads. Ethanol-dried ones exhibited higher Young's elasticity modulus (E=192kPa) than the lyophilized samples (twice at 0.25wt.% graphene oxide loading), which disclosed breakage points at lower deformation percentages. Adsorption experiments were conducted and dye adsorption isotherms were obtained for the beads with the best removal performance. The experimental data were better fitted by the Langmuir model. The highest maximum adsorption capacity (4.25mmol/g) was obtained for the lyophilized beads with the highest graphene oxide content. Mechanical properties were found to be affected also by the dye adsorption.
Assuntos
Alginatos/química , Grafite/química , Óxidos/química , Adsorção , Físico-Química , Etanol/química , Liofilização , Ácido Glucurônico/química , Ácidos Hexurônicos/química , Tamanho da Partícula , Propriedades de SuperfícieRESUMO
Vinal-derived Activated Carbon (VAC) developed by phosphoric acid activation of sawdust from Prosopis ruscifolia native wood was tested for the adsorption of Ni(II) ions from dilute solutions in both batch and dynamic modes, comparing it with a Commercial Activated Carbon (CAC). Batch experiments were performed to determine adsorption kinetics and equilibrium isotherms for both carbons. It was possible to remove near 6.55 mg Ni g(-1) VAC and 7.65 mg Ni g(-1) CAC after 5 h and 10 h contact time, respectively. A pseudo second order equation fitted well with the kinetics of the process, and Langmuir adsorption model was used to adjust the experimental results concerning the adsorption isotherm. The parameters obtained indicate a stronger interaction between sorbent and sorbate for VAC (K = 26.56 L mmol(-1)) than for CAC (K = 19.54 L mmol(-1)). Continuous experiments were performed in a fixed-bed column packed with the investigated carbons, evaluating the influence of operational parameters such as flow rate, bed height and feed concentration on the breakthrough curves obtained. The breakthrough occurred more slowly for low concentrations of the metal ion in the feed, low flow rates and high bed height. The breakthrough curves were properly represented by Hall's model for both carbon types. Regeneration of the vinal activated carbon in column was tested, obtaining the same breakthrough curve in a new cycle of use. Finally, vinal-derived activated carbon can effectively be used to treat wastewater having until 30 ppm Ni(II).