Sarah Arvelos

Anais do I Web Encontro Nacional de Engenharia Química (978-65-5941-255-6) - Desenvolvimento De Um Modelo Matemático Para A Previsão Do Ponto De Turvação De Biodieseis

The goal of this study was to investigate the reaction mechanisms linked with the oxy-fuel combustion of ethanol (C₂H₆O). The oxidation of ethanol in O₂/N₂ and O₂/CO₂ environments were examined using reactive molecular dynamics in the temperature range from 2200 to 3000 K at constant density media and O₂/fuel ratio equals to 0.5. The main reactions were examined to supply a description of the ethanol oxidation behavior, the main products distribution, and the corresponding time evolution behavior in the atomic scale. It has been noted that the oxidation of C₂H₆O was initiated mainly from the same routes in both environments generating the same main species. However, the key reaction pathways were different depending on the media. We noticed an increase of CO formation when N2 was replaced by CO₂ molecules, increasing the net flux of the following reactions: by CO₂ + H ↔ CO + OH and CO₂ + CHO ↔ O=COH + CO. This work also studied the effect of increasing O₂ concentration (O₂/fuel ratio equals to 0.5, 1.0, and 2.0) in O₂/CO₂ combustion. During the simulations, high oxygenated and unstable species were detected such as carbonates and carboxyl radicals. The change of the O₂/fuel ratio from 0.5 to 2.0 lead to an increase of CO₂ formation mainly from O₂ + O=COH ↔ CO₂ + HO₂ and O₂ + CO ↔ CO₂ + O reactions. In addition, the increase of O₂ concentration attenuated the effect of CO₂ and could increase the occurrence of reactions that lead to flame cessation.

The use of molecular simulation has been growing in engineering field moved not just by the advances on computational power but also on the availability of reliable software. One potential use of molecular simulation is related to the screening of materials for a specific application. The reliability of molecular simulation results depends on the trustworthiness of the force field used, what by engineering purposes should be as simple as possible. This work provides an evaluation of the potential accuracy cost of using simple generic force fields to predict the adsorption of CO2, CH4, N2 and their mixtures on MFI. We employed the GCMC technique for this investigation. Different models and force fields to describe adsorbates and adsorbent were tested. The force fields performances were estimated through comparison with available adsorption experimental data. Transferability was evaluated on the prediction of pure and mixtures adsorption on CHA, LTA and FER. The results showed that a simple force field presented similar performance when compared to a more sophisticated one.

Literature reports have shown that supercritical extraction is a promising method to obtain bioactive compounds used to develop drugs based on natural products. This work investigated the yield, antioxidant activity, and phytochemical constituents of the extracts obtained from Vernonia amygdalina Delile leaves with supercritical CO2. The supercritical extraction was examined at temperatures of 40, 50 and 60?C and at pressures of 200 and 250 bar. The supercritical fluid extraction (SFE) method was compared with the classical Soxhlet using different solvents at atmospheric pressure. The overall yield obtained using SFE varied from 0.69 to 1.24%. The extraction conditions which favored the highest yield were 60?C and 250 bar. The overall SFE curves were fitted using three mathematical models. All of them were able to describe satisfactorily the extraction kinetics. Spline model presented the best fit to experimental data and was able to characterize constant and decreasing extraction rate periods. Extracts were characterized by gas chromatography coupled with mass spectrometry technique and some major components were identified. The antioxidant activity tests showed that the SFE extracts had low antioxidant activity exhibiting the estimated concentration of extract required to reduce 50% of the stable free radical DPPH (EC50) values to be between 622.62 and 937.88 ?g mL-1.

A adsorção é considerada um fenômeno complexo por envolver espécies de natureza química e física muito diferentes. Esta complexidade se reflete na natureza do adsorvente, que pode ser considerado um sólido homogêneo ou heterogêneo, nas interações sólido-fluido e nas interações fluido-fluido. Este trabalho visa apresentar a evolução dos modelos que têm sido aplicados na modelagem do equilíbrio de adsorção de gases, ressaltando sua base teórica e suas aplicações.