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%).

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.

Immobilization of Paecilomyces variotii tannase and properties of the immobilized enzyme.

Tannase produced by Paecilomyces variotii was encapsulated in sodium alginate beads and used for the effective hydrolysis of tannic acid; the efficiency of hydrolysis was comparable to that of the free enzyme. The alginate beads retained 100% of their efficiency in the first three rounds of successive use and 60% in rounds 4 and 5. The response surface methodology showed that the best conditions to hydrolysis of tannic acid by immobilized tannase were: sodium alginate 5.2%, CaCl2 0.55 M and 9 h to curing time. The optimized process resulted in 2.4 times more hydrolysed tannic acid than that obtained before optimization. The optimum pH for the actions of both the encapsulated and the free enzymes was 5.5. The optimum temperature of the reaction was determined to be 40 °C for the free enzyme and 60 °C for the immobilized form. The immobilization process improved the stability at low pH.