Estudo e caracterização de ligninas pirolisadas para a obtenção de carbonos grafíticos

Abstract

From an industry demand for the improvement of the quality of work, teaching and research institutions came together to study and characterize graphite carbons synthesized by the pyrolysis process, using lignins as raw materials, due to the coplanar phenolic structure, for use as filters of volatile organic compounds. Three samples of lignin powder were used: a commercial of the company SIGMA-ALDRICH, with a low sulfonate content, extracted by the Kraft method and two other samples extracted from the bagasse of the sugar cane by the Soda method, by LADEBIO and another one extracted at the SENAI Institute of Innovation in Green Chemistry (ISI). All samples were characterized before pyrolysis was started to compare the thermal effect in the samples. To obtain the graphite carbons all samples were pyrolyzed at two temperatures, 400 ° C and 800 ° C, with a heating rate set at 5 ° C / min, using a conventional oven with temperature controller and cooling after pyrolysis being done in the air. The temperatures were chosen after TGA, DTG and DSC thermal analyzes performed on samples as received. The same thermal analyzes showed a significant loss of mass related to the elimination of compounds with low molecular weight and more volatile, as well as the breakdown of compounds bonds and graphitization of the material. These results were corroborated by spectroscopy analyzes in the infrared wavelength region that presented a lower absorption in the pyrolyzed material when compared to the initial sample indicating a loss of functional groups and by Raman spectroscopy that showed characteristic peaks of amorphous graphitic materials. Changes in the morphology of the samples after the pyrolysis were determinated using the MEV-FEG technique. The MEV-EDS test used for the semi-quantitative analysis of the chemical elements showed the presence of sulfur only in the commercial sample and no contaminants were observed in the samples. Pyrolysis altered the structures of the samples, transforming them into graphite carbons.