Julio Cezar de Oliveira Freitas

Characterization and comparative study of pyrolysis kinetics of the rice husk and the elephant grass

A comparative evaluation of different biomasses allows the choice that presents the best potential as fuel for energy production. The knowledge of the thermal and kinetics parameters of the biomass in the process of thermal conversion is fundamental as their chemical and physical characterization. Various methodologies have been developed for the determination of kinetic parameters as apparent activation energy and reaction order from the thermogravimetric analysis. In this work, the apparent activation energy needed to break the bonds of hemicelluloses and cellulose of rice husk and elephant grass during the thermal conversion was evaluated according to the kinetics models of Flynn and Wall and Model Free Kinetics developed by Vyazovkin. The biomass elephant grass and rice husk were characterized for moisture, ash and volatile matter by ASTM E871, ASTM E1755, ASTM E872, respectively, and fixed carbon by difference. The percentage of carbon, hydrogen, nitrogen, and oxygen were determined by ultimate analysis. The elephant grass showed to be more suitable for production of bio-oil through pyrolysis due to the higher percentage of volatile, less ash content and less energy required to break the bonds of hemicellulose and cellulose than rice husk in the thermal conversion process.

Influência da adição de diatomita nas propriedades de pastas geopoliméricas: volume de filtrado, tempo de espessamento e resistência à compressão

Today, the diversity of available materials for use in engineering is very large, resulting in an increasing of specific materials for each type of application. The geopolymers have been studied for various decades. They are inorganic polymers that can provide cementing characteristics that emerge as a new class of high performance materials, capable of totally or partially replace the Portland cement in various applications. In this work, we studied the influence of the addition of diatomite on geopolymeric pastes based on metakaolin. The use of a new raw material abundant in nature and low value like the diatomite is another alternative as silica source to produce geopolymers. The diatomite is an amorphous silica and in this work it was used as an additive to improve some important properties in cement pastes based in geopolymers. The effect of adding of the diatomite the geopolymeric properties of the slurries was evaluated by comparing them with the properties of the geo-polymer based on metakaolin. To analyze the effects of diatomite concentrations in geopolymeric pastes, filtrate tests were performed, thickening time and compressive strength. Also presents the results of X-ray diffraction (XRD) and scanning electron microscopy (SEM) in order to gather information for a better understanding of the geopolymers cement microstructure. The results showed that the addition of diatomite changed drastically the microstructure and mechanical properties of geopolymer pastes. With the increasing in the concentration of diatomite, the filtrate volume decreases, independent on the temperature