Paula Manoel Crnkovic

O emprego da termogravimetria para determinar a energia de ativação do processo de combustão de óleos combustíveis

Activation energy (Ea) is a parameter that can be applied to make predictions about the quality of oils to be used in an ICO engine. In this study, Ea was determined by thermogravimetry following two different procedures: ASTM E 1641 and Model-free kinetics. The energies were calculated in the low temperature oxidation (LTO) region for three Brazilian fuel oils (denominated A, B and C) and the results were equal using both methods: 43 kJ mol-1 (a=0.1 to 0.9) for oil A, 48 kJ mol-1 (a=0.1 to 0.5) and 65 kJ mol-1 (a=0.5 to 0.9) for oil B, and 58 kJ mol-1 (a=0.1 to 0.5) and 65 kJ mol-1 (a=0.5 to 0.9) for oil C. It was concluded that, among the oils studied, sample A was potentially the best option concerning the behavior in the LTO region.

O efeito da granulometria na decrepitação durante a decomposição térmica de calcários e carvão

The use of fluidized bed combustors to burn coal is largely studied to permit the addition of limestone to capture SO2. The particle size for coal and limestone is an important parameter in this process. Thermogravimetry (TG) is used to elucidate the combustion and sulfation processes, but the experimental parameters must be evaluated to be representative in fluidized bed combustors. In the present study the effect of particle size is analyzed in the calcination of limestones and the combustion of coal through the thermogravimetric curve for limestone and derivative thermogravimetric curve for coal. Small peaks representing mass losses between 400 and 500 oC are observed due to the jumping of particles out of the crucible. This effect, recognized as decrepitation is observed for mid-sized particles provoked by the release of water vapor trapped within their lattice.

Thermal decomposition kinetics of Brazilian limestones: effect of CO2 partial pressure

The influence of the partial pressure of carbon dioxide (CO2) on the thermal decomposition process of a calcite (CI) and a dolomite (DP) is investigated in this paper using a thermogravimetric analyser. The tests were non-isothermal at five different heating rates in dynamic atmosphere of air with 0% and 15% carbon dioxide (CO2). In the atmosphere without CO2, the average activation energies (E α) were 197.4 kJ mol−1 and 188.1 kJ mol−1 for CI and DP, respectively. For the DP with 15% CO2, two decomposition steps were observed, indicating a change of mechanism. The values of E α for 15% CO2 were 378.7 kJ mol−1 for the CI, and 299.8 kJ mol−1 (first decomposition) and 453.4 kJ mol−1 (second decomposition) for the DP, showing that the determination of E α for DP should in this case be considered separately in those two distinct regions. The results obtained in this study are relevant to understanding the behaviour changes in the thermal decomposition of limestones with CO2 partial pressure when applied to technologies, such as carbon capture and storage (CCS), in which carbon dioxide is present in high concentrations.

Emprego de reagente em suspensão em sistema de injeção em fluxo: determinação espectrofotométrica de sulfato em águas naturais

This paper presents an automatic procedure employing a reagent in the form of a slurry in a flow-injection system. The feasibility of the proposal is demonstrated by sulphate determination in water using the Barium Chloranilate method, which is based on the precipitation of barium sulphate. The release of a stoichiometric amount of highly colored chloranilic ions is monitored at 528 nm. The reaction is carried out in alcoholic medium in order to reduce the solubility of the reagent. A considerable improvement in the sensitivity is attained by adding ferric ions to the released chloranilic ions. An on-line filtration step to separate the excess reagent from the released chloranilic ions was necessary. In addition, a column containing a cation exchange resin was included in the manifold to remove potentially interfering ions. The proposed procedure is suitable for 30 determinations per hour and the relative standard deviation is less than 2%. The analytical curve is linear between 0.0 and 40 mg L-1 and the determination limit is about 2.0 mg L-1SO42-. Accuracy was confirmed by running several samples already analysed by a standard turbidimetric procedure.

Estudo termogravimétrico do efeito da temperatura e da atmosfera na absorção de dióxido de enxofre por calcário

Thermogravimetry was applied to investigate the effects of temperature and atmosphere on conversion of sulfur dioxide (SO2) absorbed by limestone. Ranges of temperature and particle size were studied, typical of fluidized-bed coal combustion. Isothermal experiments were performed at different temperatures (between 750 and 950 oC) under local atmospheric pressure (~ 697 mmHg) in dynamic atmospheres of air and nitrogen. The maximum conversion was 29% higher in nitrogen atmosphere than in air atmosphere. The optimum conversion temperature was found at 831 oC in air atmosphere and at 894 oC in nitrogen atmosphere.

Co-cultivation of Aspergillus nidulans Recombinant Strains Produces an Enzymatic Cocktail as Alternative to Alkaline Sugarcane Bagasse Pretreatment

Plant materials represent a strategic energy source because they can give rise to sustainable biofuels through the fermentation of their carbohydrates. A clear example of a plant-derived biofuel resource is the sugar cane bagasse exhibiting 60–80% of fermentable sugars in its composition. However, the current methods of plant bioconversion employ severe and harmful chemical/physical pretreatments raising biofuel cost production and environmental degradation. Replacing these methods with co-cultivated enzymatic cocktails is an alternative. Here we propose a pretreatment for sugarcane bagasse using a multi-enzymatic cocktail from the co-cultivation of four Aspergillus nidulans recombinant strains. The co-cultivation resulted in the simultaneous production of GH51 arabinofuranosidase (AbfA), GH11 endo-1,4-xylanase (XlnA), GH43 endo-1,5-arabinanase (AbnA) and GH12 xyloglucan specific endo-β-1,4-glucanase (XegA). This core set of recombinant enzymes was more efficient than the alternative alkaline method in maintaining the cellulose integrity and exposing this cellulose to the following saccharification process. Thermogravimetric and differential thermal analysis revealed residual byproducts on the alkali pretreated biomass, which were not found in the enzymatic pretreatment. Therefore, the enzymatic pretreatment was residue-free and seemed to be more efficient than the applied alkaline method, which makes it suitable for bioethanol production.

Metodologia para o estudo da porosidade de dolomita em ensaio de sulfatação interrompida

The aim of this work is to propose a methodology to evaluate the evolution of the pore blockage of limestone during the sulfation reaction. The experiments were performed for a national limestone (dolomite) with average particle size of 545 μm in interrupted sulfation tests were conducted at seven different times and at three different temperatures of the process. The empirical data were obtained from porosimetry tests to establish BET surface area, volume and average size of pore and distribution of pore sizes of the sulfated samples. Thermogravimetric tests were performed to evaluate the preparation methodology of the samples used in the porosimetry tests.

DETERMINAÇÃO DOS PARÂMETROS DE ARRHENIUS DA REAÇÃO DE SORÇÃO DO DIÓXIDO DE ENXOFRE POR CALCÁRIO

Sulfur emission in coal power generation is a matter of great environmental concern and limestone sorbents are widely used for reducing such emissions. Thermogravimetry was applied to determine the effects of the type of limestone (calcite and dolomite), particle size (530 and 650 µm) and atmosphere (air and nitrogen) on the kinetics of SO2 sorption by limestone. Isothermal experiments were performed for different temperatures (650 to 950 oC), at local atmospheric pressure. The apparent activation energies, as indicated by the slope of the Arrhenius plot, resulted between 3.03 and 4.45 kJ mol-1 for the calcite, and 11.24 kJ mol-1 for the dolomite.

Investigation into the physical–chemical properties of chemically pretreated sugarcane bagasse

Enzymatic hydrolysis is one of the major steps involved in the conversion of sugarcane bagasse into ethanol. Pretreatments break down macrostructures in order to improve the enzyme access to the targeted glycosidic bonds. This study reports on the use of thermoanalytic techniques together with other different techniques for the verification of the structural and morphological changes occurred in sugarcane bagasse subjected to acid and alkaline pretreatments. The techniques evaluated differences in the BET and BJH surface areas, diameter and pore volume investigated by porosimetry, scanning electron microscopy and wettability. Thermal analysis (TG/DTG and DTA) was also used to evaluate the thermal degradation of hemicelluloses, cellulose and lignin contents that remained in the samples after pretreatments. The results show that chemical pretreatments were effective in the degradation of lignocellulosic samples and significant morphological changes occurred after the pretreatments. Acid and alkaline pretreatments caused an increase in the surface area, diameter and volume of pores. Wettability also revealed important effects regarding surface changes of the biomasses. In summary, all tested pretreatments were effective to chemically degrade the macrostructures of sugarcane bagasse that hinder enzymatic hydrolysis in, for instance, the second-generation ethanol production.Graphical Abstract

Physical-chemical characterization of biomass samples for application iin pyrolysis process

The use of lignocellulosic biomass as an energy source has considerably increased. Due to the diverse natures of biomass materials, their properties widely range and exhibit different behaviors in thermal processes. The most important properties that provide information about a fuel are heating values, ash composition, proximate (determination of moisture, ash, volatile and fixed carbon content), and ultimate analysis (C, H, N, S and O composition). Moreover, the kinetic study of the thermal behavior of a fuel can be useful for the understanding of the complex decomposition process of each material. This study focuses on the physical-chemical characterization of six lignocellulosic biomasses, namely coffee husk, tucuma seed, sugar cane bagasse, peanut shell, rice husk and pine sawdust, widely available in Brazil. A thermogravimetric analyzer was used to study their decomposition behavior in a pyrolytic environment. Non-isothermal thermogravimetric data were used and the application of a model-free isoconversional method enabled the evaluation of the activation energy (Ea) of the biofuels. The curves also show that the behavior during thermal decomposition varies from one biomass to another and these differences imply the importance of a comprehensive characterization study of fuels for the development and optimization of reactors. The knowledge on biomass properties enables the prediction of environmental impacts and technical aspects related to thermal processes. Therefore, thermal decomposition behavior is a consequence of the feedstock physical-chemical characteristic, which also provides valuable information regarding features of the complex reactions that occur throughout the pyrolysis of the biomass.