Catalytic gasification of glycerol in supercritical water

The conversion of glycerol in supercritical water (SCW) was studied at 510-550 °C and a pressure of 350 bars using both a bed of inert and non-porous ZrO2 particles (hydrothermal experiments), and a bed of a 1% Ru/ZrO2 catalyst. Experiments were conducted with a glycerol concentration of 5 wt% in a continuous isothermal fixed-bed reactor at a residence time between 2 and 10 s. Hydrothermolysis of glycerol formed water-soluble products such as acetaldehyde, acetic acid, hydroxyacetone and acrolein, and gases like H2, CO and CO2. The catalyst enhanced the formation of acetic acid, inhibited the formation of acrolein, and promoted gasification of the glycerol decomposition products. Hydrogen and carbon oxides were the main gases produced in the catalytic experiments, with minor amounts of methane and ethylene. Complete glycerol conversion was achieved at a residence time of 8.5 s at 510 °C, and at around 5 s at 550 °C with the 1 wt% Ru/ZrO2 catalyst. The catalyst was not active enough to achieve complete gasification since high yields of primary products like acetic acid and acetaldehyde were still present. Carbon balances were between 80 and 60% in the catalytic experiments, decreasing continuously as the residence time was increased. This was attributed partially to the formation of methanol and acetaldehyde, which were not recovered and analyzed efficiently in our set-up, but also to the formation of carbon deposits. Carbon deposition was not observed on the catalyst particles but on the surface of the inert zirconia particles, especially at high residence time. This was related to the higher concentration of acetic acid and other acidic species in the catalytic experiments, which may polymerize to form tar-like carbon precursors. Because of carbon deposition, hydrogen yields were significantly lower than expected; for instance at 550 °C the hydrogen yield potential was only 50% of the stoichiometric value.

Cristalização e taxa crítica de resfriamento para vitrificação do poli(sebacato de decametileno)

We synthesized Poly(decamethylene sebacate) - P10MS - and studied its overall crystallization rates in a range of temperatures using Differential Scanning Calorimetry in isothermal conditions, which enabled us to identify the crystallization mechanism by means of the Johnson-Mehl-Avrami-Kolmogorov equation. The critical cooling rate (Rc) to vitrify the P10MS was determined using a non-isothermal method proposed by Barandiarán & Colmenero (BC). The value of Rc is around 50-250 K/s, which confirms the experimentally observed difficulty to vitrify this polymer.

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.

Adsorção de íons cobre(II) pela quitosana usando coluna em sistema sob fluxo hidrodinâmico

The adsorption of Cu(II) ions from aqueous solution by chitosan using a column in a closed hydrodynamic flow system is described. The adsorption capacities as a function of contact time of copper(II) ions and chitosan were determined by varying the ionic strength, temperature and the flow of the metal solution. The Langmuir model reproduced the adsorption isothermal data better than the Freundlich model. The experimental kinetic data correlate properly with the second-order kinetic reaction for the whole set of experimental adsorption conditions. The rate constants exercise great influence on the time taken for equilibrium to be established by complexation or electrostatic interaction between the amino groups of chitosan and the metal.

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.

Cinética de redução do catalisador CuO/ZnO/Al2O3

The reduction kinetics of a CuO/ZnO/Al2O3 catalyst by hydrogen was investigated isothermally and by temperature programmed reduction (TPR). Two reducible Cu2+ species were detected; the first one was identified as CuO bulk and the other as Cu2+ strongly interacting with alumina, possibly in the form of copper aluminate. The activation energies for the reduction of these two species were 60 and 90 kJ mol-1, respectively, and the reaction order with respect to hydrogen was one. The isothermal reduction data showed that the isotropic growth model is the most appropriate to describe the reaction rate data for both Cu2+ species.

A thermogravimetric analysis of the combustion of a Brazilian mineral coal

Knowledge of coal combustion kinetics is crucial for burner design. This work aims to contribute on this issue by determining the kinetics of a particular Brazilian bituminous coal. Non-isothermal thermogravimetry was applied for determining both the pre-exponential factor and the activation energy. Coal samples of 10 mg and 775 mm mean size were used in synthetic air atmospheres (21 % O2). Heating rates from 10 to 50 ºC/min were applied until the temperature reached 850 ºC, which was kept constant until burnout. The activation energy for the primary and the secondary combustion resulted, respectively, in 135.1 kJ/mol and 85.1 kJ/mol.

Estudo da adsorção de surfactante catiônico na matriz inorgânica fosfato de nióbio hidratado

This work describes the study the adsorption of a cationic surfactant, cetyl trimethyl ammonium bromide (CTAB) in the hydrous niobium phosphate matrix. The matrix was characterized by powder X-ray diffraction (DRX), thermal analysis (TG), differential scanning calorimetry (DSC), scanning electron microscopy (SEM) and surface area measurements (BET). The Langmuir and Freundlich isothermal models were used in the CTAB adsorption study. The adsorption process wasn`t favorable for the NbOPO4.nH2O in both studied models.

Adsorção de Cr(VI) em esferas reticuladas de quitosana: novas correlações cinéticas e termodinâmicas utilizando microcalorimetria isotérmica contínua

The synthesis and characterization of crosslinked chitosan microbeads and their application in the removal of Cr(VI) are described. New kinetic and thermodynamic parameters of Cr(VI) adsorptions processes were found using continuous isothermal calorimetry. All adsorption processes are exothermic in nature. However, a multivariate statistical analysis have pointed out that adsorption enthalpies were affected by important binary interactions of the initial Cr(VI) in solution and temperature. The adsorption energetic data were well fitted to a kinetic exponential model, which have indicated fractionary adsorption kinetic orders.

Cálculo do volume na equação de van der Waals pelo método de cardano

Analytical solutions of a cubic equation with real coefficients are established using the Cardano method. The method is first applied to simple third order equation. Calculation of volume in the van der Waals equation of state is afterwards established. These results are exemplified to calculate the volumes below and above critical temperatures. Analytical and numerical values for the compressibility factor are presented as a function of the pressure. As a final example, coexistence volumes in the liquid-vapor equilibrium are calculated. The Cardano approach is very simple to apply, requiring only elementary operations, indicating an attractive method to be used in teaching elementary thermodynamics.

Análise térmica aplicada a fármacos e formulações farmacêuticas na indústria farmacêutica

Several matters of the pharmaceutical demonstrate the great importance of thermal analysis application, especially TG and DSC for the pharmaceutical industry future, namely: characterization of the drugs with the thermal events definition, in studies of drug purity, in the polymorphs identification, in compatibility studies of solid dosage pharmaceutical formulations, in drugs and pharmaceutical formulations thermal stability, and in determination of shelf life for isothermal degradation kinetics by extrapolation using the Arrhenius equation. Thus, the test results obtained from thermal analysis are directly related to the quality of a pharmaceutical product, whether the stability or bioavailability of the pharmaceutical product.

Rheological and thermal characteristics of wheat gluten biopolymers plasticized with glycerol

The objective this work was to obtain bioplastics from mixtures of wheat gluten and glycerol by two different processes and evaluate their respective rheological properties. The mixtures and their respective bioplastics were obtained through direct batch mixing under approximately adiabatic and isothermal conditions. The bioplastics showed high values for the storage (G') and loss (G") moduli, suggesting a stronger protein network formed in both processes. The temperature onset and the percentage of weight loss to be estimated were found to be near in both bioplastics. The bioplastics have demonstrated to be materials of interesting potential of use as biodegradable barrier materials.

Investigação eletroquímica e calorimétrica da interação de novos agentes antitumorais biscatiônicos com DNA

Biscationic amidines bind in the DNA minor groove and present biological activity against a range of infectious diseases. Two new biscationic compounds (bis-α,ω-S-thioureido, amino and sulfide analogues) were synthesized in good yields and fully characterized, and their interaction with DNA was also investigated. Isothermal titration calorimetry (ITC) was used to measure the thermodynamic properties of binding interactions between DNA and these ligands. A double stranded calf thymus DNA immobilized on an electrode surface was used to study the possible DNA-interacting abilities of these compounds towards dsDNA in situ. A remarkable interaction of these compounds with DNA was demonstrated and their potential application as anticancer agents was furthered.

Holocene Varved Lake Sediments as Records of Palaeoenvironmental Change and Geomagnetic Palaeosecular Variation in Eastern Finland

This dissertation discusses Holocene palaeoenvironmental and palaeomagnetic secular variation (PSV) records reconstructed from sediments preserved in Lake Lehmilampi (63º37´N, 29º06´E) and Lake Kortejärvi (63º37´N, 28º56´E) in eastern Finland. Several piston and freeze cores were obtained from both lakes for varve and magnetic analyses. Sediment samples were impregnated in low-viscosity epoxy and physical parameters of varves, including varve thickness and relative grey-scale values, were recorded using x-ray densitometry combined with semiautomatic digital image analysis. On average, varve records of Lehmilampi and Kortejärvi cover 5122 and 3902 years, respectively. Past solar activity, as estimated by residual ₁₄C data, compares favourably with varve thicknesses from Lehmilampi during the last 2000 years. This indicates the potential of clastic-organic varves to record sensitively climatic variations. Bulk magnetic parameters, including magnetic susceptibility together with natural, anhysteretic and isothermal remanent magnetizations, were measured to describe mineral magnetic properties and geomagnetic palaeosecular variation recorded in the sediments. Main stages in the development of the investigated lakes are reflected in the variations in the mineral magnetic records, sediment lithology and composition. Similar variations in magnetic parameters and sediment organic matter suggest contribution of bacterial magnetite in the magnetic assemblages of Lehmilampi. Inclination and relative declination records yielded largely consistent results, attesting to the great potential of these sediments to preserve directional palaeosecular variation in high resolution. The PSV data from Lehmilampi and Kortejärvi were stacked into North Karelian PSV stack, which may be used for dating homogenous lake sediments in the same regional context. Reconstructed millennial variations in relative palaeointensity results are approximately in agreement with those seen in the absolute palaeointensity data from Europe. Centennial variations in the relative palaeointensity, however, are influenced by environmental changes. Caution is recommended when using varved lake sediments in reconstructing relative palaeointensity.

Comparison of the dehydration kinetics of solid state compounds of 2-methoxybenzylidenepyruvate with some divalent metal ions

Divalent metal complexes of ligand 2-methoxybenzylidenepyruvate with Fe, Co, Ni, Cu and Zn as well as sodium salt were synthesized and investigated in the solid state. TG curves of these compounds were obtained with masses sample of 1 and 5mg under nitrogen atmosphere. Different heating rates were used to characterize and study these compounds from the kinetic point of view. The activation energy and pre-exponential factor were obtained applying the Wall-Flynn-Ozawa method to the TG curves. The obtained data were evaluated and the values of activation energy (Ea / kJ mol-1) was plotted in function of the conversion degree (α). The results show that due to mass sample, different activation energies were obtained. The results are discussed mainly taking into account the linear dependence between the activation energy and the pre exponential factor, where was verified the effect of kinetic compensation (KCE) and possible linear relations between the dehydrations steps of these compounds.