Decomposição térmica da casca de soja pura e misturada com NaCl, MgCl2 e ZnCl2

Abstract

There is a growing interest in renewable and sustainable energy sources. Biomass is an important alternative source of energy, with several advantages. Huge amounts of biomass waste are generated worldwide, among them is the soybean hulls. Pyrolysis is an attractive alternative to use of this waste generating appreciable economic value products. Thermogravimetric analysis (TGA) is a widely used analytical technique to observe the thermal decomposition and kinetics of pyrolysis of materials. The main objectives of this work were to determine the physical and chemical properties of soybean hulls and conduct a study on the kinetics of pyrolysis for pure soybean hulls and with the addition of inorganic salts. Thermogravimetric analysis was performed at different heating rates (5, 10, 15, 20 and 25 °C/min) under an inert atmosphere of nitrogen for soybean hulls, to the main components present in biomass (cellulose, hemicellulose and lignin ) and for soybean hulls with addition of some salts (NaCl, ZnCl2 and MgCl2) at concentrations of 10, 20 and 30%. The curves of weight loss (TG) and derived of the weight loss curve (DTG) for the main components present in biomass indicate that cellulose degradation occurs in a temperature range between 240 ° C and 370°C, for hemicellulose occurs between 170 and 350 ° C and for lignin occurs between 250 and 900° C, approximately. TG and DTG curves for soybean hulls with addition salts showed that there was a reduction of the degradation temperature for the samples with added 20 and 30% of ZnCl2 and all samples with addition of MgCl2. For samples with addition of NaCl there was a increased of the degradation temperature The kinetics of decomposition of samples was represented by isoconversional models (model of Flynn-Wall- Ozawa - FWO and the Friedman model) and for independent parallel reaction models. The activation energy for soybean hulls ranged from 110 178 kJ/mol for the FWO model and from 131 212 kJ / mol for the Friedman model. For the soybean hulls with addition of salt, it was observed that only the samples with added 20 and 30% of MgCl2 presented a reduction of the activation energy. Among the results of the kinetic parameters determined by the independent parallel reaction models, cellulose presented the highest activation energy (201.1 204.0 kJ/mol), followed by the hemicellulose (109.5 112.5 kJ/mol) and lignin (57.3 61.3 kJ/mol).