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  • Author or Editor: A. Araújo x
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Abstract  

A thermogravimetric method is proposed for study of the kinetic parameters of coked HZSM-5 zeolite regeneration. The technique, which makes use of integral thermogravimetric curves, was optimized by microprocessed integrated mathematical methods. The kinetic parameters obtained from the TG curves are the activation energy, the rate constants, the half-life times, and in particular the coke removal time as a function of temperature. The activation energy calculated by using the Flynn and Wall kinetic method was 81.4 kJ mol−1. It was observed that, to remove 99% of the coke from the zeolite in a period of 1 h, it would be necessary to carry out thermo-oxidation at 748 K, with a dry air purge flow of 120 cm3 min−1.

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Abstract  

The coke removal of HZSM-12 zeolite deactivated in the reaction of n-heptane cracking was studied by thermogravimetry using two multiple heating rate integral kinetics models proposed by Ozawa-Flynn-Wall and Vyazovkin to obtain the activation energy of process of thermoxidation of coke. The results obtained by both models presented excellent accordance with the related literature.

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Abstract  

The evaluation of the crystallinity of several samples of ALPO-11 was performed by X-ray diffraction and thermogravimetry. Through XRD, the degrees of crystallinity of the samples were determined by the measurement of the area of the peaks at 2γ ranging from 20.7 to 24.1 degrees. The sample that presented the largest area was considered as 100% crystalline and the areas of the other samples were normalized in relation to this. From TG, the degree of crystallinity was determined considering the mass loss in the temperature range from 453 to 653 K that is related to remotion of di-isopropylamine molecules used during the synthesis procedure. The quantity of diisopropylamine on the material is proportional to the degree of crystallinity.

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Abstract  

A geochemical study was carried out in sediment cores along the Galician Continental Shelf and at the mouth of the Vigo and Pontevedra Rias. Multielemental analysis was performed by Instrumental Neutron Activation Analysis and Energy Dispersive X-ray Fluorescence Spectrometry. Sedimentological and geochemical characterisation (lithogenic, biogenic and anthropogenic elements) indicates different supplies for the fine-grained, deposited sediments. No significant heavy metal enrichment could be detected in coastal sediments despite the current sediment contamination in adjacent Rias. Variations in the accumulation rates suggest different factors controlling the sedimentation processes including sediment sources and geomorphology.

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Abstract  

Environmental quality assessment studies have been conducted with tree species largely distributed in the Atlantic Forest. Leaf and soil samples were collected in the conservation unit Parque Estadual da Serra do Mar (PESM) nearby the industrial complex of Cubatão, São Paulo State, Brazil, and analyzed for chemical elements by instrumental neutron activation analysis. Results were compared to background values obtained in the Parque Estadual Carlos Botelho (PECB). The higher As, Fe, Hg and Zn mass fractions in the tree leaves of PESM indicated anthropogenic influence on this conservation unit.

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Abstract  

In the present work, the thermal decomposition of glimepiride (sulfonylurea hypoglycemic agent) was studied using differential scanning calorimetry (DSC) and thermogravimetry/derivative thermogravimetry (TG/DTG). Isothermal and non-isothermal methods were employed to determine kinetic data of decomposition process. The physical chemical properties and compatibilities of several commonly used pharmaceutical excipients (glycolate starch, microcrystalline cellulose, stearate, lactose and Plasdone) with glimepiride were evaluated using thermoanalytical methods. The 1:1 physical mixtures of these excipients with glimepiride showed physical interaction of the drug with Mg stearate, lactose and Plasdone. On the other hand, IR results did not evidence any chemical modifications. From isothermal experiments, activation energy (E a) can be obtained from slope of lnt vs. 1/T at a constant conversion level. The average value of this energy was 123 kJ mol–1. For non-isothermal method E a can be obtained from plot of logarithms of heating rates, as a function of inverse of temperature, resulting a value of 157 and 150 kJ mol–1, respectively, in air and N2 atmosphere, from the first stage of thermal decomposition.

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