Efeito do campo magnético na precipitação de parafinas

In the oil industry, the paraffination phenomenon is a major problem during oil production, displacement and treatment. Paraffin deposition in subsea flowlines, surface equipment, production string or even in the reservoir, can cause significant and increasing oil losses. To minimize paraffin precipitation, the application of magnetic field in the petroleum path has been suggested based on empiric studies. In this study, we assembled a labscale magnetic conditioner to determine the influence of magnetic field on the physical-chemical properties of two fluids : oil and a paraffin mixture. We observed that magnetic field reduce sample aparent viscosity due to crystal morphology alteration.

Modelagem dos processos químicos em plasmas de misturas gasosas usadas na corrosão de silício. Parte 1: CF4 / O2

The plasma etching of semiconductor surfaces with fluorine-containing compounds has technological interest. Presently, considerable effort is being devoted to understand the chemistry involved. In this work, a numerical modeling analysis of the gas-phase decomposition of CF4/O2 mixtures, in the presence of silicon, was performed. The relative importance of individual processes was determined as well as the effect of the parameters' uncertainties. The results were compared with experimental data. The main etching agent in the system is the fluorine atom. The concentration of the main species, SiF4, CO, CO2 and COF2 depend on the composition of the mixture.

Modelagem dos processos químicos em plasmas de misturas gasosas usadas na corrosão de silício. Parte 2: SF6 / O2

In this work, a numerical modeling analysis of the gas-phase decomposition of SF6 / O2 mixtures, in the presence of silicon, was performed. The relative importance of individual processes and the effect of the parameters' uncertainties were determined. The model was compared with experimental data for the plasma etching of silicon and with the calculated results for the CF4 / O2 system. In both systems the main etching agent is the fluorine atom and the concentration of the major species depends on the composition of the mixture. The etching rate is greater for SF6 / O2.

Extração líquido-líquido em sistemas de fluxo

This review deals with principles of the liquid-liquid extraction, when performed in flow systems. This approach is frequently used for sample treatment to improve the selectivity and/or sensitivity in analytical measurements. The advances in this area are reported, including the use of monosegmented flow systems to perform metal extraction through both two-phase and single phase processes.

Simulação do processo Solvay no laboratório didático

The Solvay Process is an important route for the industrial preparation of sodium carbonate from brine and CO2. However, experiments illustrating such process are performed only in a few chemistry courses, mainly because of the difficulties to precipitate out the intermediate product NaHCO3 within the 3 or 4 hours generally available for laboratory classes. In this article we describe a method that properly simulates the Solvay process using glass apparatus that can be found in any chemistry laboratory. The good yields and purity attainable, associated with the short time (~3 hours) required to get the sodium bicarbonate, account for the suitability of our method for chemistry or chemical engineering undergraduate students laboratory classes.

Troca iônica no estado sólido de európio3+ em zeólita Y: influência do tempo de reação

Rare earth elements supported in zeolites are the most important catalysts in the fluid cracking of petroleum. The solid state ion exchange of Eu3+ in Y zeolite was investigated. First of all, the hydrated EuCl3 was well mixed in a ball mill and was then heated at 300ºC for different times. The quantitative determination of Eu3+ showed that the degree of ion exchange depends on the reaction time at constant temperature, being ~95% in 4 h. The X-ray study showed that the crystallinity of the zeolite is little affected by the exchange procedure. The study of spectroscopic properties of Eu3+, emission spectra and lifetime, give information about the migration and position of the ion in the zeolite cages.

Utilização do resíduo líquido de indústria de processamento de suco de laranja como meio de cultura de Penicillium citrinum: depuração biológica do resíduo e produção de enzima

Penicillium citrinum grown in orange juice processing wastes medium under continuous agitation was studied in order to establish optimal conditions (incubation period, incubation temperature, initial pH and nitrogen addition) for biomass and ribonuclease production, as well as, biological depuration of the wastes. Nitrogen addition to wastes medium increased the biomass and ribonuclease production and provides COD reduction. The soy meal shows to be the best nitrogen source. The conditions for a more favorable enzyme and biomass production and COD reduction were initial pH 6.0 and temperature of 27°C. The maximum value obtained for these parameters on optimal conditions of cultivation was 11 U/mL of enzyme, 4 mg/mL of biomass (dry matter) and 55% of COD reduction, in 96 hours of incubation.

Caracterização de polimorfismo em fármacos por ressonância magnética nuclear no estado sólido

This review aims to present some features about solid state NMR and its application in the field of pharmaceutical chemistry, for the characterization of polymorphism of pharmaceutical molecules.

Termodinâmica estatística de líquidos com o método de Monte Carlo. II. O líquido clorofórmio

Thermodynamic properties and radial distribution functions for liquid chloroform were calculated using the Monte Carlo method implemented with Metropolis algorithm in the NpT ensemble at 298 K and 1 atm. A five site model was developed to represent the chloroform molecules. A force field composed by Lennard-Jones and Coulomb potential functions was used to calculate the intermolecular energy. The partial charges needed to represent the Coulombic interactions were obtained from quantum chemical ab initio calculations. The Lennard-Jones parameters were adjusted to reproduce experimental values for density and enthalpy of vaporization for pure liquid. All thermodynamic results are in excelent agreement with experimental data. The correlation functions calculated are in good accordance with theoretical results avaliable in the literature. The free energy for solvating one chloroform molecule into its own liquid at 298 K and 1 atm was computed as an additional test of the potential model. The result obtained compares well with the experimental value. The medium effects on cis/trans convertion of a hypotetical solute in water TIP4P and chloroform solvents were also accomplished. The results obtained from this investigation are in agreement with estimates of the continuous theory of solvation.

Otimização de um mecanismo fotoquímico para a simulação da atmosfera urbana brasileira

A photochemical reaction mechanism for the description of air quality in Brazilian urban regions is described and evaluated by comparison with chamber experiments. The mechanism was developed for use in ozone modeling and application of control strategies. The oxidation of ethanol and methyl-ter-butyl-ether is also considered. Using this chemical model, a trajectory simulation of Brazil Avenue, Rio de Janeiro, was performed. The model predicts that ozone should reach a maximum of 22.4 ppb at 14:57 h. This value is in good agreement with the experimental measurements of 22.5 ppb for 14:00 h and 22.3 ppb for 15:00 h.

Efeito da substituição por átomos de flúor no equilíbrio conformacional de chalcona

Chalcone (1) and its fluorinated derivatives 2-4, as well as their cyclic analogues 5-10, were synthesized through an aldol condensation reaction between the corresponding ketone and aldehyde. These compounds were characterized by IR, EIMS and ¹H and 13C NMR spectral data. Modern NMR techniques allowed us to conclude that the compounds obtained show E configuration. These techniques were also employed to investigate the equilibrium involving the s-cis and s-trans conformations of 1-4, with this equilibrium being dependent on the fluorine substitution on both aromatic rings, A or B. IR studies indicated that the yield of the s-cis conformation in the fluorinated derivatives is 57.4±1.4; 88.1±0.4 and 66.4±0.7%, for 2, 3 and 4, respectively, based on previous ¹H NMR calculations for chalcone. Theoretical calculations, using the MMX method, were employed to justify the variation of chemical shifts for the fluorinated derivatives and cyclic analogues. These chemical shifts are consequence of the anisotropic effect showed by the carbonyl group on these compounds.

Fotoquímica de chalconas fluoradas no estado sólido

Chalcone and its fluorinated derivatives were synthesized and photolyzed in the solid state. UV irradiation of chalcone and its monosubstituted fluorine derivatives (3- and 4-fluorchalcone) resulted in a mixture of anti-head-head (gamma-truxinic), sin-head-tail (alpha-truxilic) and anti-head-tail (epsilon-truxilic) dimers. On the other hand, upon irradiation of 3,4- and 3,5-difluorchalcone a stereoselective formation of the alpha-truxilic photodimer was observed, whereas for 2-substituted chalcones (2,3difluorchalcone, 2,5-difluorchalcone, 2,6-difluorchalcone and 2,3,4-trifluorchalcone) the beta-truxilic dimer was stereoselectively obtained. 2',3',4',5',6'-pentafluorchalcone was the less reactive of all chalcones studied and at least one of the possible photodimers, i.e the anti-head-head isomer, was identified. Irradiation of polyfluorinated chalcones such as 2,3,5,6-tetrafluor-, 2,3,4,5,6-pentafluor-, and 2,2',3,3',4,4',5,5',6,6'-decafluorchalcone led only to polymerization and/or decomposition products.

Propelente sólido compósito polibutadiênico: I- influência do agente de ligação

In the Brazilian Complete Spacial Mission, the research of Vehicle Satellite Launcher is important. The solid propellant composite used in this vehicle is made with ammonium perchlorate, aluminiun powder and hydroxy terminated polibutadiene resin. In the propellant the bonding agent has a function to promote the interaction between solids and polimeric matrix, improving mechanical properties as stress, strain, aging characteristics and moisture embrittlement. Due its importance in propellant, bonding agent is consider as industrial secret and the literature about it is generic, without greater informations.

Efeito da concentração do catalisador acetilacetonato férrico na cura de poliuretano à base de polibutadieno líquido hidroxilado (PBLH) e diisocianato de isoforona (IPDI)

The reaction between hydroxy-terminated polybutadiene and isophorone diisocyanate constitutes the base of the curing process of the most composite solid propellant used in the propulsion of solid rocket propellant. In this work, differential scanning calorimetry and viscosity measurements were used to evaluate the effect of the ferric acetylacetonate catalyst concentration on the reaction between HTBR and IPDI. These analyses show one exotherm, which shifts to lower temperatures as the catalyst concentration increases. The viscosity analyses show that the increase of temperature causes, at first, a reduction in the mixture viscosity, reaching a minimum range called gelification region (increasing the crosslinking density).

Estudo da geometria da uréia por métodos ab initio e simulação computacional de líquidos

A study was carried out on the urea geometries using ab initio calculation and Monte Carlo computational simulation of liquids. The ab initio calculated results showed that urea has a non-planar conformation in the gas phase in which the hydrogen atoms are out of the plane formed by the heavy atoms. Free energies associated to the rotation of the amino groups of urea in water were obtained using the Monte Carlo method in which the thermodynamic perturbation theory is implemented. The magnitude of the free energy obtained from this simulation did not permit us to conclude that urea is non-planar in water.