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Abstract  

HZSM-5 zeolite was screened as catalyst for high density polyethylene degradation at 450‡C, under nitrogen static atmosphere. Two different samples were studied in this condition: HDPE alone and mixed with HZSM-5. The reactor was connected on line to an HP 5890-II gas Chromatograph. Sample degradation was investigated using a Perkin-Elmer Delta 7 Thermobalance, from room temperature to 800‡C, with heating rates of 5.0, 10.0 and 20.0‡C min−1. From TG curves, the activation energies, calculated using an integral kinetic method, decreased 60.6% in the presence of the zeolite.

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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 acid properties of the Ca/NaY zeolite were investigated by means ofn-butylamine desorption and thermal decomposition, using both thermogravimetry (TG) and differential scanning calorimetry (DSC). The total acidity of the zeolite was calculated from the TG data, while DSC was used with the Borchardt-Daniels kinetic model to determine the relative acid strength of the catalyst, given in J per acid site. The enthalpies of these processes are proportional to the acid site strength in each specific temperature range.

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Abstract  

The use of catalysts in numerous important processes is widespread throughout the chemical and petroleum-processing industries. Thermal analytical techniques can be used to evaluate important properties and processes associated with solid catalysts. This paper presents examples carried out in our laboratory of the general application of TG and DSC to the acidity, activity and regeneration of solid catalysts.

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Journal of Radioanalytical and Nuclear Chemistry
Authors: H. Oliveira, E. Fernandes, M. Bacchi, G. Sarriés, and F. Tagliaferro

Abstract  

Inorganic components were surveyed of some Brazilian cigarette tobacco by INAA. Sixteen different brands were taken from the consumer market and analyzed for As, Ba, Br, Ca, Ce, Co, Cr, Cs, Eu, Fe, K, La, Na, Rb, Sc, Sm, Sr and Zn elements. Comparisons between the results from this work and those originated from several cigarette tobacco producing countries, indicate significant variation in the levels of some elements.

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Abstract  

Soil as an impurity in sugarcane is a serious problem for the ethanol industry, increasing production and maintenance costs and reducing the productivity. Fe, Hf, Sc and Th determined by INAA were used as tracers to assess the amount of soil in sugarcane from truckloads as well as in the juice extraction process. Quality control tools were applied to results identifying the need for stratification according to soil type and moisture. Soil levels of truckloads had high variability indicating potential for improving cut and loading operations. Samples from the juice extraction process allowed tracking the soil in the mill tandem.

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Abstract  

In a preliminary study performed with the waste rocks from the future uranium mine to be explored in Brazil, 106 samples were taken from the eight main lithologies found in the massif and analysed by instrumental neutron activation analysis (INAA) for 20 elements. For samples from the same lithology, a high variability in the concentration of most of the elements was found (coefficient of variation larger than 20%), which might be attributed to either insufficient homogenisation of minerals or to local variation within lithology. The hypothesis that the variability within the lithology does not have an influence to the total variability was tested by analysing 5 replicates of the 5 most contrasting samples from the predominant lithology (plagioclase-microcline-gneiss), chosen after applying statistical evaluation (principal components and cluster analyses). Results indicated that homogenisation of samples was adequate due to low variation among replicates. The hypothesis tested was rejected with a confidence level higher than 99% for all the elements, corroborating the large intra-lithology variability.

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