Preparação de carvão ativado usando casca de arroz em um forno micro-ondas modificado

Abstract

Activated carbon is a highly porous form of pure carbon that can adsorb molecules or ions from fluid media. Activated carbon can be used as water filtration, contaminant removal, gas adsorption, treatment drug, currently biorenewable supercapacitor has been developed and other applications. This study proposes the carbonization of rice husk, with the objective of preparing in detail the activated carbon with physical and chemical activation via microwave radiation processing, comparing the results obtained with those from the literature, adopting a sequence of procedures : modification of the microwave oven, installation of the gas system, preparation of coals with heating ramp and purchase of items. In the preparation of the coals, first the vegetable (N2 atmosphere), the activated in the physical activation (CO2 atmosphere) and activated in the chemical activation with NaOH activating agent, all with temperatures between 500ºC to 600ºC in 60 min. The following analyzes were performed: Thermogravimetry (TGA), Differential Scanning Calorimetry (DSC), Scanning Electron Microscopy (SEM) coupled with Energy Dispersive Spectroscopy (EDS), X-Ray Diffraction (XRD). UV-Vis spectrophotometry was used in methylene blue solution and adsorption area by BET and Langmuir method. Charcoal obtained a yield of almost 40%, activated by physical activation more than 50% and activated by chemical activation, close to 35%. In the TGA measurements, the rice husk showed stages of loss of mass of the existing substances, being 90% with temperature above 520ºC; the DSC thermal events were both endothermic (peak of 120ºC) and exothermic (peak of 340ºC); in the XRD assays, several peaks of Silicon Oxide, Sucrose, Calcite and organic compounds (cellulose) were identified. The charcoal, analyzed in the SEM, showed a brittle material and low porosity; in EDS carbon, oxygen, silicon and potassium were found; XRD showed their presence in addition to iron oxide and other oxides; a dye absorbance was observed in the UV Vis measurements showed a dye absorbance in the solution in the time of 55 min of 0.41 (59% removal); the BET and Langmuir obtained a surface area of 55.8990 m²/g and 85.0025 m²/g, respectively. Activated carbon in the physical activation SEM it is possible to observe a heterogeneous and porous structure; the EDS points out the peaks of Carbon, Oxygen, Silicon and Magnesium; XRD exhibited the same oxides as charcoal; UV-Vis showed an absorbance of more than 0.32 in a time of 55 min (dye removal 68%); BET and Langmuir had surface areas of almost 127 m²/g and 192 m²/g. The activated carbon in the chemical activation SEM was seen quite fragmented in several points and apparently even greater porosity; the EDS presented Carbon, Oxygen, Sodium, Magnesium, Silicon and Potassium; XRD consisted of Silicon Oxide, Calcite, Sodium Chloride; UV-Vis showed absorbance of the solution at 0.045 (95.5% removal of methylene blue) in 55 min; BET close to 190 m²/g and Langmuir close to 288 m²/g. Coals produced using the precursor were successfully obtained with quality.