Adsorção de azul de metileno utilizando carvão ativado produzido a partir do endocarpo do coco babaçu

Abstract

Babaçu (Attalea speciosa) is one of the largest natural resources in the world and one of the main extractive products in Brazil, occupying an area of 18 million hectares and contributing to an economy of some states of the federation, such as Maranhão, Piauí and Tocantins. The fruit has a great industrial potential due to the versatility of its use, in which all parts can be used. Activated carbon is a non-graphitic microcrystalline form of carbon diffused by its high porosity and surface capacity which attributes its ability to adsorb the molecules either in the liquid phase as in the gas phase. Due to these properties, it is an adsorbent of industrial interest with several applications. The production of the coal is carried out by the carbonization by the pyrolysis of a great variety of raw materials, as long as it has a high carbon content. Activation of the precursor material can be physical, using water vapor, CO2, or a mixture of the two gases, or chemical using activating agents such as ZnCl2, H2SO4, H3PO4 or alkali metal compounds. The purpose of the expansion is to increase the surface area of the coal due to the release or creation of new pores, so that it can be used as an adsorbent mean for textile effluents, for example. It is estimated that about 700,000 tons per year of dyestuffs are produced and that about 10 to 20% of these dyestuffs are lost during the process, having as destination the effluent industry. Thus, several studies have appeared that aim at the treatment through the removal of these dyes present in industrial effluents. Among them, adsorption, which is a solid-liquid or solid-gas mass transfer unit operation that exploits the ability of certain solids to concentrate on their surface some substances in solution. It is a simple and effective method for the removal of species in low concentration solutions. For this reason the treatment of industrial liquid effluents is widely used. In this scenario, the objective of this work was to produce and characterize the activated charcoal produced through the endocarp of babaçu coconut, with the purpose of using it as an adsorbent for the removal of the methylene blue dye. The yield of activated carbon was 34.91%. The samples had a granulometry of 0.32 mm for the in natura sample, 0.19 mm for the activated carbon and 0.31 mm for the impregnated sample. The specific mass obtained for each material was 1444.77 kg m-3 for sample in natura, 1421.88 kg m3 for the impregnated sample and 1435 kg m-3 for the activated carbon. For the apparent specific mass and the porosity of the bed the obtained results were of 684,97 and 0,53 for in natura sample, 655,00 and 0,54 for impregnated sample and of 656,40 and 0,54 for the activated carbon, respectively. The values for moisture in wet basis were 8.84% for in natura sample, 1.38% for impregnated sample and 0.34% for activated carbon, for ash content, 1.56% for sample in natura the impregnated sample obtained 4.42% of ashes while the activated carbon presented a percentage of 30,93. For volatile analysis, the values were 84.5% for in natura sample, 52.61% for impregnated sample and 17.83% for activated carbon. In the thermogravimetric curves it was possible to observe three zones of mass loss. The first present only in the in natura samples and the activated carbon, is due to loss of humidity. The second and third peak present in the samples in natura and impregnated, refers to the degradation of hemicellulose and cellulose, not being observed in activated carbon. For the adsorption kinetics tests, the model that best fits the experimental data was the pseudo second order model for all cases. For the adsorption isotherms, the Langmuir model presented the best fit and the maximum adsorbed amount for each model was 9,146 mg g-1 for the adsorption with the in natura sample, 39,252 mg g-1 for the impregnated material and 39,015 mg g-1 for the activated carbon, being these values below the one found in the literature for the adsorption of methylene blue on activated carbon.