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- Author or Editor: F. Souza x
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Abstract
The reason of comparing thermal behaviour and kinetics of some nickel compounds, is justified by the influence of anion on it, besides supplying information on the stability of the salts. In this work, Ni(TMS)2·6H2O, Ni(TFA)2·3H2O and Ni(Ac)2·2H2O, were synthesized and characterized by microanalysis, atomic absorption molar, conductance and thermal analysis. Thermogravimetric curves indicate that the decomposition of the salts occurs in the range 295–1169 K and the NiO is the final residue. Non-isothermal kinetic evaluation from thermogravimetric data was used to determine energies of activation and pre-exponential factors.
Abstract
Stability of drugs and products has a great practical interest, which is facing to strict regulation. Thermal studies, besides the determination of the thermal properties of the investigated product allow the verification of possible interactions between the drug substances and excipients. The objective of this work was to obtain solid pre-formulates of paracetamol (PC) by spray drying (SPDR), as well as to investigate their thermal behavior. Dynamic and isotherm TG, conventional DSC and DSC-photovisual coupled methods were used to characterize the conventional and pre-formulated mixtures obtained by SPDR. The results of both DSC investigations showed slight alterations in melting temperatures, which suggests incompatibilities. The TG decomposition data of the mixtures evidenced that the dry process via SPDR leads to stability enhancement of the pre-formulated mixtures.
Lanthanide Lanthanide nitrate complexes with 2-azacyclononanone
Thermal and kinetic studies
Abstract
Thermal behavior of rare earth nitrate complexes with 2-azacyclononanone (AZA) with Ln(NO3)3·3(AZA) composition (where Ln=Gd, Er and Ho) was analyzed in kinetic point of view. Kinetic parameters were calculated from thermogravimetric data. All obtained results were similar. The first decomposition step was representative to the loss of ligand and the residue was essentially Ln2O3. Furthermore, a reaction path was proposed for the thermal decomposition of the Ln(NO3)3·3(AZA).
Abstract
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.
Abstract
Biodiesel oxidation is a complex process widely influenced by the chemical composition of the biofuel and storage conditions. Several oxidation products can be formed from these processes, depending on type and amount of the unsaturated fatty acid esters. In this work, fatty acid methyl and ethyl esters were obtained by base-catalyzed transesterification of soybean oil and physicochemically characterized according to standards from ASTM, EN, and ABNT. The thermal and oxidative stabilities of biodiesel samples were investigated during the storage process by pressure differential scanning calorimetry (PDSC) and by viscosity measurements. Absolute viscosities of biodiesels after accelerated aging were also determined. The viscosity increased as the aging temperature and time were raised. The results showed that oxidation induction can occur during storage, decreasing the biodiesel stability. PDSC analysis showed that during storage under climate simulation the values of high-pressure oxidative induction times (HPOIT) were reduced for both FAEE and FAME.
Abstract
This work presents the characterization and the kinetic compensation effect of corn biodiesel obtained by the methanol and ethanol routes. The biodiesel was characterized by physico-chemical analyses, gas chromatography, nuclear magnetic resonance and thermal analysis. The physico-chemical properties indicated that the biodiesel samples meet the specifications of the Brazilian National Agency of Petroleum, Natural Gas and Biofuels (ANP) standards. The analyses by IR and 1H NMR spectroscopy indicated the ester formation. Gas chromatography indicated that biodiesel was obtained with an ester content above 97%. The kinetic parameters were determined with three different heating rates, and it was observed that both the methanol and ethanol biodiesel obeyed the kinetic compensation effect.
Abstract
The babassu (Orbignya Phalerata Mart.) biodiesel has lauric esters as main constituents, resulting in high oxidative stability and low cloud and freezing points. In order to reduce these side effects, the saturated ethyl esters content was reduced by means of winterization process. The TMDSC and PDSC techniques were used to verify the thermal and oxidative stabilities of the ethyl babassu biodiesel. During the heating stage, the winterized solid phase of ethyl esters presented an endothermic transition associated to the solidification process. This behavior was not observed for the liquid winterized FAEE, confirming the efficiency of the winterization process.
Abstract
The influence of drying processes in the biodiesel oxidation was investigated by means of the oxidative induction time obtained from differential scanning calorimetry data. For this purpose, corn biodiesel was dried by different methods including: chemical (anhydrous sodium sulfate) and thermal (induction heating, heating under vacuum and with microwave irradiation). The drying efficiency was evaluated by monitoring IR absorption in the 3,500–3,200 cm−1 range and by the AOCS Bc 2-49 method. In general, the oxidative induction times increased inversely to the heating degree, except that of microwave irradiation, which was selective to water evaporation and caused low impact over the unsaturation of biodiesel. The DSC technique was shown to be a powerful tool to evaluate with high level of differentiation the influence of the drying process on the oxidative stability of biodiesel.
