Thermal decomposition kinetics of guarana seed residue through thermogravimetric analysis under inert and oxidizing atmospheres.

This work aims to analyze the thermal decomposition kinetics of guarana seed residue applying inert and oxidizing atmospheres. Thermal decomposition experiments were carried out in a thermogravimetric analyser using heating rates of 5, 10 and 15 °C/min. Three thermal decomposition stages were identified: dehydration; pyrolysis/oxidative pyrolysis, and carbonization/combustion, respectively. In order to obtain the estimation of the activation energies, the isoconversional method proposed by Vyazovkin (1997) was applied. Besides that, three and six independent parallel reactions schemes were applied for respective atmospheres. The ranges of activation energy were of 52-140 kJ/mol and 71-171 kJ/mol for inert and oxidizing atmosphere, respectively. The modeling of conversion rates presented a good agreement in relation to the experimental data (AD < 4%).

Drying and thermal decomposition kinetics of sugarcane straw by nonisothermal thermogravimetric analysis.

This work aims the study of the drying (25 ±â€¯3 °C-150 °C) and thermal decomposition (150-900 °C) of sugarcane straw kinetics in inert and oxidative atmospheres by nonisothermal thermogravimetry (TG) analysis using heating rates of 2.5, 5 and 10 °C/min. The drying kinetic analysis was carried out using five models, Lewis, Page, Henderson and Pabis, Midilli and Logaritmic, obtaining the activation energy of 1.25 kJ/mol, in which the Page's model showed to be the most accurate description for both atmospheres. The thermal decomposition kinetics was analyzed through three consecutive reactions scheme, obtaining activation energies of 130, 200 and 56 kJ/mol as well as 200, 350 and 100 kJ/mol for both atmospheres, respectively. The consecutive reaction scheme allowed an excellent agreement between experimental and modeled data, providing a quality of fit similar than the obtained with independent parallel reactions scheme.

Combustion reaction kinetics of guarana seed residue applying isoconversional methods and consecutive reaction scheme.

This work aims the study of decomposition kinetics of guarana seed residue using thermogravimetric analyzer under synthetic air atmosphere applying heating rates of 5, 10, and 15°C/min, from room temperature to 900°C. Three thermal decomposition stages were identified: dehydration (25.1-160°C), oxidative pyrolysis (240-370°C), and combustion (350-650°C). The activation energies, reaction model, and pre-exponential factor were determined through four isoconversional methods, master plots, and linearization of the conversion rate equation, respectively. A scheme of two-consecutive reactions was applied validating the kinetic parameters of first-order reaction and two-dimensional diffusion models for the oxidative pyrolysis stage (149.57kJ/mol, 6.97×10(10)1/s) and for combustion stage (77.98kJ/mol, 98.611/s), respectively. The comparison between theoretical and experimental conversion and conversion rate showed good agreement with average deviation lower than 2%, indicating that these results could be used for modeling of guarana seed residue.

Thermal decomposition of sugarcane straw, kinetics and heat of reaction in synthetic air.

The aim of this work was to analyze the thermal decomposition, kinetics and heat of reaction of sugarcane straw in synthetic air by thermogravimetry (TG) and differential scanning calorimetry (DSC). The TG and DSC experiments were carried out using heating rates of 2.5°C/min, 5°C/min, and 10°C/min, and particle diameter of 0.250mm. In the study of the smoldering reaction were identified three consecutive stages, drying, oxidative pyrolysis, and combustion. Thus, the kinetic pathway was composed by six independent parallel reactions, three for each stage after drying, in which the activation energies were 176, 313, 150, 80, 150, and 100kJ/mol. The heat of reaction in synthetic air was completely exothermic releasing 8MJ/kg. The modeled curves of thermal decomposition of sugarcane straw presented good agreement with experimental data. Then, the kinetic parameters obtained could be used to analyze different processes involving smoldering.

Isoconversional kinetic study of the thermal decomposition of sugarcane straw for thermal conversion processes.

The aim of this work was investigate the kinetics of the thermal decomposition reaction of sugarcane straw. The thermal decomposition experiments were conducted at four heating rates (1.25, 2.5, 5 and 10°C/min) in a thermogravimetric analyzer using nitrogen as inert atmosphere. The kinetic analysis was carried out applying the isoconversional method of Friedman, and the activation energies obtained varied from 154.1kJ/mol to 177.8kJ/mol. The reaction model was determined through master plots, corresponding to a two-dimensional diffusion. The pre-exponential factor of 1.82*10(9)s(-1) was determined by linearization of the conversion rate equation as a function of the inverse of absolute temperature, concerning to activation energy of 149.7kJ/mol, which are in the order of magnitude for biomass thermal decomposition reported in literature. Finally, the theoretical and experimental conversion data showed a very good agreement, indicating that these results could be used for future process modeling involving sugarcane straw.