Authors:G. A. A. Teixeira, A. S. Maia, I. M. G. Santos, A. L. Souza, A. G. Souza, and N. Queiroz
Cloud point (CP), cold filter plugging point (CFPP), and pour point (PP) of biodiesel samples obtained from blends containing different amounts of beef tallow, babassu oil, and soybean oil were investigated by the corresponding conventional techniques and by temperature modulated differential scanning calorimetry (TMDSC). The CP and CFPP values correlate well with the crystallization temperature (Tonset) obtained from the TMDSC curves, being the highest for the biodiesel sample containing the highest amount of methyl stearate. A correspondence between PP and the peak temperature was also noticed, pointing out that pouring ceases after the crystallization of the heavier fatty acid ester. Among the samples of biodiesel, Bio-3 (highest amount of babassu oil) and Bio-4 (highest amount of soybean oil) showed better cold-flow properties, or in other words, lower values of CP, CFPP, and PP. Independently of the composition, the cold-flow properties of all biodiesel samples meet the requirements from the Brazilian National Agency of Petroleum, Natural Gas, and Biofuels (ANP).
Authors:E. F. S. M. Ramalho, I. M. G. Santos, A. S. Maia, A. L. Souza, and A. G. Souza
Chemical composition of oils and fats used in the biodiesel synthesis can influence in processing and storage conditions, due to the presence of unsaturated fatty acids. An important point is the study of the biodiesel thermal stability to evaluate its quality using thermal analysis methods. In this study the thermal stabilities of the poultry fat and of their ethyl (BEF) and methyl (BMF) biodiesels were determined with the use of thermogravimetry (TG/DTG), differential thermal analysis (DTA) and differential scanning calorimetry (DSC), in different atmospheres. The TG/DTG curves of the poultry fat in synthetic air presented three decomposition steps while only one step was observed in nitrogen (N2) atmosphere. The DSC results indicated four exothermic enthalpic transitions in synthetic air and an endothermic transitions in N2 atmosphere attributed to the combustion process and to the volatilization and/or decomposition of the fatty acids, respectively. For both biodiesels the TG/DTG curves in air indicated two mass loss steps. In the DSC curves four exothermic transitions were observed in synthetic air besides an endothermic one in N2 atmosphere.
Authors:G. Souza, I. Pastre, A. Benedetti, C. Ribeiro, and F. Fertonani
Thermogravimetry, Differential Scanning Calorimetry and other analytical
techniques (Energy Dispersive X-ray Analysis; Scanning Electron Microscopy;
Mapping Surface; X-ray Diffraction; Inductively Coupled Plasma Atomic Emission
Spectroscopy and Cold Vapor Generation Atomic Absorption Spectroscopy) have
been used to study the reaction of mercury with platinum foils. The results
suggest that, when heated, the electrodeposited Hg film reacts with Pt to
form intermetallic compounds each having a different stability, indicated
by at least three mass loss steps. Intermetallic compounds such as PtHg4,
PtHg and PtHg2 were characterized by XRD. These intermetallic
compounds were the main products formed on the surface of the samples after
partial removal of bulk mercury via thermal desorption. The Pt(Hg) solid solution
formation caused great surface instability, attributed to the atomic size
factor between Hg and Pt, facilitating the acid solution’s attack to
Authors:A. Moitinho, E. Ionashiro, G. de Souza, and F. Fertonani
Solid-state M-EDTA chelates, where M represents the divalent ions Mg(II), Ca(II), Sr(II) or Ba(II) and EDTA is ethylenediaminetetraacetate
anion, were synthesized. Thermogravimetry, derivative thermogravimetry (TG, DTG), differential scanning calorimetry (DSC)
and X-ray diffraction powder patterns have been used to characterize and to study the thermal behaviour of these chelates.
The results provided information concerning the stoichiometry, crystallinity, thermal stability and thermal decomposition.
Authors:E. Milaré, J. Turquetti, G. Souza, A. Benedetti, and F. Fertonani
Thermogravimetry (TG), cyclic
voltammetry (CV) and other analytical techniques were used to study the reactions
of mercury with Pt–30% Ir alloy. The results allowed to suggest that
an electrodeposited mercury film interacts with the substrate and when subjected
to heat or electrochemical removal at least four mass loss steps or five peaks
appeared during the mercury desorption process. The first two steps were attributed
to Hg(0) removal probably from the bulk and from the adsorbed monolayer which
wets the electrode surface. These two processes are responsible for peaks
D and F in the cyclic voltammograms. The last two peaks (G, H) in CV were
ascribed to the intermetallic compound decomposition. In TG curves, the last
two steps were attributed to the PtHg4 (third step),
and PtHg2 decomposition followed by Hg removal from
the subsurface. The PtHg2 was formed by an eutectoide
reaction: PtHg→PtHg2+Hg(Pt–Ir). The Hg diffused
to the subsurface was not detectable by cyclic voltammetry.
Authors:G. A. A. Teixeira, A. S. Maia, R. Rosenhaim, I. M. G. Santos, A. L. Souza, A. G. Souza, and N. Queiroz
Biodiesel can be obtained from various fatty acid sources. Each raw material has a different chemical composition that leads to different properties. Owing to these properties, the mixture of different proportions of raw materials can lead to biodiesels with best features in relation to physicochemical parameters such as viscosity, oxidative stability and flow properties, generating a fuel whose characteristics meet the requirements of the current legislation of the Brazilian National Agency of Petroleum, Natural Gas and Biofuels (ANP). The objective of this study was to determine the physicochemical properties of biodiesel samples produced from mixtures of beef tallow, babassu oil, and soybean oil. The thermo-oxidative stability was evaluated using thermogravimetry (TG/DTG) and differential scanning calorimetry (DSC). The results showed that all samples were in accordance to the ANP specifications. The biodiesel obtained from a mixture containing 50% of babassu oil had lower values of pour point, cold filter plugging point, and freezing point. This biodiesel also showed a higher thermo-oxidative stability in synthetic air and in oxygen atmospheres.
Authors:E. F. S. M. Ramalho, A. R. Albuquerque, A. L. Souza, A. K. Barro, A. S. Maia, I. M. G. Santos, and A. G. Souza
The poultry fat methylic (BMF) and ethylic (BEF) biodiesels were synthesized through transesterification by homogeneous basic catalysis. The chromatographic analyses showed the palmitic, stearic, oleic, and linoleic esters as majority components. Owing to its considerable amount of polyunsaturated fat acids, poultry fat usually leads to a biodiesel with low oxidative stability. In this study, the oxidation of their ethylic and methylic biodiesels was evaluated by Rancimat, PDSC, and PetroOxy. The OSI (Rancimat) was of 0.47 and 0.40 h for the ethylic and methylic biodiesel, respectively. In PDSC, both fuels presented an OT of about 120–123 °C. PetroOxy analysis indicated an OxyStab of 11 min for BEF and higher than 11 min for BMF. There was no correspondence among the oxidative stabilities of the employed techniques [OT(BEF) ≈ OT(BMF), OSI(BEF) > OSI(BMF), and OxyStab(BEF) < OxyStab(BMF)]. The discussion of these results was based on the indicator measured by each technique: enthalpic events are observed by PDSC; conductivity of volatile secondary oxidation products is measured by Rancimat; reduction of the oxygen pressure is determined by PetroOxy. This discussion showed that these different indicators do not reflect the same stage of the oxidative process as energy is release at the beginning of the propagation step, oxygen pressure decreases during the propagation step, and oxidation products are formed during the termination step.
Authors:Adney Luís A. da Silva, Guilherme G. G. Castro, and Mariana M. V. M. Souza
Lanthanum strontium chromite (LSC) powders were synthesized by the combustion method, using five different fuels (urea, glycine, ethylene glycol, α-alanine, and citric acid). The ignition of the reagent mixture with urea takes a longer time, and more gases are released by combustion. A calcination step is essential for a good crystallization of the perovskite phase. X-ray diffraction patterns showed formation of perovskite phase and a small amount of SrCrO4 for the sample synthesized with urea after calcination. The crystallite sizes are in the range of 23–33 nm. Scanning electron microscopy revealed the porosity of the powders and the presence of agglomerates, formed by fine particles of different shapes. Thermogravimetric analysis showed a large mass loss for the sample synthesized with citric acid, probably caused by the absence of ignition, with primary polymerization of the precursor reagents.