Influence of the purification process on the stability of <Emphasis Type="Italic">Jatropha curcas</Emphasis> biodiesel

The aim of this work was to evaluate the influence of the purification process on the stability of Jatropha curcas biodiesel. The biodiesel was obtained using a variety of purification processes: three wet methods with different drying processes (vacuum oven, conventional oven and anhydrous sodium sulfate) and one dry method (purification with adsorbent magnesium silicate). Biodiesel was characterized through the analysis of carbon residue, acidity index, infrared and gas chromatography. The composition J. curcas oil indicated 56.3 % of unsaturated fatty acids and 43.7 % of saturated fatty acids. Jatropha oil presented high quantity of saturated acids, which are less susceptible at oxidation. The biodiesel sample that was chemically purified (PUsq) presented better purity, indicating be the process more efficient in remove the residues of synthesis. Thermogravimetric curves of purified biodiesel by wet method, PUsq, with chemical drying using anhydrous sodium sulfate, and PUsv, with vacuum drying, showed the highest initial decomposition temperatures, indicating higher thermal stability. The carbon residue and infrared analyses suggested that contamination by catalyst residue is a determining factor in reduction of the oxidative stability of biodiesel. The oxidative stability was evaluated using Rancimat and pressure differential scanning calorimetry. Biodiesel samples showing better oxidative stability were purified using PUsq and PUsv, which obtained stability of 6 h using the Rancimat technique, the minimum limit set by Brazilian legislation, without the addition of antioxidant, suggesting that these methods least influenced the stability of biodiesel.     

A novel method to prepare water dispersible poly(benzimidazobenzophenanthroline) (BBL) by partial substitution of chain ends with poly(ethylene oxide)

Poly(benzimidazobenzophenanthroline) (BBL) was prepared according to literature method and modified with poly(ethylene oxide) in a one pot synthesis. After precipitation in aqueous sodium carbonate solution and subsequent purification, aqueous dispersions were prepared by ultrasonication. Particle sizes in the dispersions ranged from few tens of nanometers to several micrometers and most of the particles had sizes of 50–250 nm. Further studies indicated that the colloidal stability is a combined result of steric stabilization caused by excluded volume interactions of PEO chains on particle surface and electrostatic stabilization by the dissociated carboxylic acid groups on the particle surface. The product could be processed into uniform films 20–30 nm in thickness by spin coating onto gold-plated silicon substrates having aminethiol monolayer as the top most layer.     

Synthesis, characterization, and spectroscopic investigation of benzoxazole conjugated Schiff bases

Two Schiff bases were synthesized by reaction of 2-(4'-aminophenyl)benzoxazole derivatives with 4-N,N-diethylaminobenzaldehyde. UV-visible (UV-vis) and steady-state fluorescence in solution were applied in order to characterize its photophysical behavior. The Schiff bases present absorption in the UV region with fluorescence emission in the blue-green region, with a large Stokes' shift. The UV-vis data indicates that each dye behaves as two different chromophores in solution in the ground state. The fluorescence emission spectra of the dye 5a show that an intramolecular proton transfer (ESIPT) mechanism takes place in the excited state, whereas a twisted internal charge transfer (TICT) state is observed for the dye 5b. Theoretical calculations were performed in order to study the conformation and polarity of the molecules at their ground and excited electronic states. Using density functional theory (DFT) methods at theoretical levels BLYP/Aug-SV(P) for geometry optimizations and B3LYP/6-311++G(2d,p) for single-point energy evaluations, the calculations indicate that the lowest energy conformations are in all cases nonplanar and that the dipole moments of the excited state relaxed structures are much larger than those of the ground state structures, which corroborates the experimental UV-vis absorption results.     

Thermal stability evaluation of methylic biodiesel obtained for different oilseeds

Biodiesel is defined as a mixture of mono- or di-alquil esters of vegetable oil or animal fats. During long-term storage, oxidation caused by contact with air (autoxidation) presents a legitimate concern in relation to monitoring and maintaining fuel quality. Extensive oxidative degradation may compromise the quality by adversely affecting kinematic viscosity, acid value, or peroxide value. The oxidation susceptibility of biodiesel, due to the presence of triacilglycerides of poly-unsaturated fatty acids, was evaluated in this study. Samples of sunflower, castor, and soybean biodiesels were obtained through the transesterification reaction, with the intention of achieving the thermal stability study through thermogravimetrical analyses and differential scanning calorimetry high pressure. It was furthermore observed through thermogravimetry and pressure differential scanning calorimetry curves that castor biodiesel exhibited the highest thermal and oxidative stability.     

Phenol transformation photosensitised by quinoid compounds

The phototransformation of phenol in aqueous solution was studied with different quinoid compounds, which are usually detected on atmospheric particulate matter: 2-ethylanthraquinone (EtAQ), benzanthracene-7,12-dione (BAD), 5,12-naphthacenequinone (NQ), 9,10-anthraquinone (AQ), and 2,6-dihydroxyanthraquinone (DAQ). All the studied quinones were able to sensitise the phototransformation of phenol. Under blue-light irradiation the approximated, polychromatic quantum yields for phenol photodegradation were in the order AQ > BAD > EtAQ > NQ > DAQ. Quantum mechanical calculations showed that AQ and DAQ have a very different spin distribution in the triplet state (largely located on the carbonyl oxygen and delocalised over the aromatic ring, respectively) that could account for the difference in reactivity. The spin distribution of EtAQ is similar to that of AQ. Under simulated sunlight, EtAQ induced the highest rate of phenol degradation. Radiation-excited EtAQ would oxidise both ground-state EtAQ and phenol; a kinetic model that excludes the ˙OH radical and singlet oxygen as reactive species is supported by the experimental data. Quinones were also able to oxidise nitrite to nitrogen dioxide, thereby inducing phenol nitration. Such a process is a potential source of nitrogen dioxide and nitrophenols in the atmospheric aerosols.     

Synthesis and properties of 2-amino-5-(3,5,6-trichloro-1,4-benzoquinon-2-yl)thiazoles

The reaction of thiourea of N-substituted thioureas with 2-(2-N,N-diethylaminoethenyl)-3,5,6-trichloro-1,4-benzoquinone leads, through the formation of 2,5-dihydroxy-3,4,6,7-tetrachlorocoumaran, to 2-amino-5-(2,5-dihydroxy-3,4,6-trichlorophenyl)thiazoles (which exist in the form of betaines), the oxidation of which leads to 2-amino-5-(3,5,6-trichloro-1,4-benzoquinon-2-yl)thiazoles.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 5, pp. 692–698, May, 1988.     

Fixed point limit behavior ofN-mode truncated Navier-Stokes equations asN increases

The fixed point behavior ofN-mode truncations of the Navier-Stokes equations on a two-dimensional torus is investigated asN increases. FromN=44 on the behavior does not undergo any qualitative change. Furthermore, the bifurcations occur at critical parameter values which clearly tend to stabilize asN approaches 100.     

Ring — chain tautomerism and reactions of 4-aryl-4-hydroxy-2,3-dimethyl-3,4-dihydrophthalazinones

It has been established by IR spectroscopy that the N,N-dimethylhydrazides of 2-aroylbenzoic and benzil-o-carboxylic acids, with the exception of 2-mesitoylbenzoic acid, have the ring structure of 4-aryl- or 4-benzoyl-4-hydroxy-2,3-dimethyl-3,4-dihydrophthalazinones. The action of electrophilic agents on 4-hydroxy-2,3-dimethyl-4-phenyl-3,4-dihydrophthal-azinone under mild conditions leads to N₍₃₎-demethylation with the formation of 2-methyl-4-phenylphthalazinone.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 8, pp. 1124–1126, August, 1973.     

Symmetry breaking on a model of five-mode truncated Navier-Stokes equations

A symmetryless model of nonlinear first-order differential equations, obtained by perturbing a known model of five-mode truncated Navier-Stokes equations, is studied. Some interesting phenomena, such as the existence of an infinite sequence of bifurcations in a very narrow range of the parameter and the simultaneous presence of a strange attractor either with two fixed attracting points or with a periodic attracting orbit, are shown. Furthermore, two new sequences of period doubling bifurcations are found in the unperturbed model.