Produção e modificação de carvões ativados para aplicações ambientais

Abstract

In this work it was investigated the production and characterization of activated carbons from lignocelulosic and synthetic polymeric precursors. From the modification of surface and structural properties it was investigated different applications of these activated carbon as adsorbents. In the first part, activated carbons with molecular sieve properties were produced from resorcinol-formaldehyde xerogels. It was investigated the effect of different organic solvents for the washing and drying steps on the porous structure of the obtained activated carbons. Immersion calorimetry analyses using different probe molecules showed that samples treated with ethanol and water presented molecular sieve properties for compounds with dimensions of ca. 0.7 nm. In the second part, a special form of activated carbon, i.e. briquette, was produced from mixtures of eucalyptus or poplar with rice husk and grape must asbinding agent. The surface of the briquettes was functionalized by the treatment with HNO3 and H2SO4.SO3. Characterization by nitrogen adsorption, TG, IR, acid sites titration and elemental analyses CHN suggested that the acid sites and surface area of the activated briquettes decrease from the more external to the inner layers. Thetreatment with HNO3 reaches all the briquette, with the more external layer more oxidized. On the other hand, H2SO4.SO3 do not react even with the more external layer likely due to its high viscosity. Adsorption with different cationic species, i.e. methylene blue, Cr(III) and Zn(II) showed that briquettes treated with HNO3 are more efficient. Studies with EDS/SEM showed that Zn(II) is adsorbed homogeneously throughout the briquette. In the last part of this work, it was studied a novel anionic exchange resin based on composites of a quaternary ammonium salt dimethyldioctadecylammonium (DMDO, [(C18H37)2(CH3)2)]N+Cl-), using as support micro and mesoporous activated carbon and SiO2 and Al2O3. Nitrogen adsorption and SEM studies suggested thatDMDO is dispersed over the surface occupying the pores of the material. Adsorption isotherms with the anion dichromate Cr2O7 2- showed that the composite with DMDO presented high anionic adsorption capacity. Among the prepared composites, alumina presented the highest efficiency, followed by carbon and silica.