Soret-‘shifted’ dew-point temperatures for surfaces exposed to hydrocarbon vapors dilute in compressed nitrogen

Soret-driven species transport causes concentration non-uniformities in the immediate vicinity of ‘cold’ surfaces immersed in undersaturated vapor-containing streams. These concentration non-uniformities, in turn, alter corresponding condensation onset temperatures, often by as much as 30 K (i.e., ca. 3%) in previously studied, near-atmospheric pressure combustion systems [see, e.g., Rosner, D.E. and Nagarajan, R., 1985. Chemical Engineering Science 40 (2), 177]. Because high-pressures often cause remarkable increases in the relevant binary Soret factor, α_T,12, we investigate here the importance of these vapor phase ‘transport’ effects for ‘compressed’ N₂ streams containing dilute quantities of an alkane: C₁₂H₂₆ (n-dodecane) or C₈H₁₈ (n-octane). We invoke the virial equation of state (VES) to predict gas phase non-ideality, and its appreciable effect on previously available ideal gas Soret factors. Our illustrative numerical results, valid for, say, nominally 1000 K N₂ streams up to pressures of over 100 atm, reveal that high-pressure Soret ‘shifts’ in T_dp can amount to ca. 80%, even at surface temperatures above the equilibrium freezing points of these condensates. We conclude that these high-pressure vapor phase transport phenomena will not only influence the interpretation of such hot gas/‘cold’ surface ‘dew-point’ measurements, they will significantly raise the temperatures at which containment or immersed surfaces must be maintained to avoid the ravages of corrosive or insulating inorganic condensates [Rosner, D.E., Chen, B.K., Fryburg, G.C., Kohl, F.J., 1979. Combustion Science and Technology 20, 87; Rosner, D.E., 1988a. Invited paper, Benjamin G. Levich Memorial Issue of Journal of Physico-Chemical Hydrodynamics 10 (5/6), 663]. In principle, the present theory could itself be used to study the pressure dependence of the binary Soret factor—at least for systems with well-characterized saturation vapor pressures.     

PBI-based polymer electrolyte membranes fuel cells: Temperature effects on cell performance and catalyst stability

In this work, it has been shown that the temperature (ranging from 100 to 175 °C) greatly influences the performance of H₃PO₄-doped polybenzimidazole-based high-temperature polymer electrolyte membrane fuel cells by several and complex processes. The temperature, by itself, increases H₃PO₄-doped PBI conductivity and enhances the electrodic reactions as it rises. Nevertheless, high temperatures reduce the level of hydration of the membrane, above 130-140 °C accelerate the self-dehydration of H₃PO₄, and they may boost the process of catalyst particle agglomeration that takes place in strongly acidic H₃PO₄ medium (as checked by multi-cycling sweep voltammetry), reducing the overall electrochemical active surface. The first process seems to have a rapid response to changes in the temperature and controls the cell performance immediately after them. The second process seems to develop slower, and influences the cell performance in the “long-term”. The predominant processes, at each moment and temperature, determine the effect of the temperature on the cell performance, as potentiostatic curves display. “Long-term” polarization curves grow up to 150 °C and decrease at 175 °C. “Short-term” ones continuously increase as the temperature does after “conditioning” the cell at 125 °C. On the contrary, when compared the polarization curves at 175 °C a continuous decrease is observed with the “conditioning” temperature. A discussion of the observed trends is proposed in this work.     

Synthesis and gas permeability of new polynorbornene dicarboximide with fluorine pendant groups

The new exo-N-3,5-bis(trifluoromethyl)phenyl-7-oxanorbornene-5,6-dicarboximide (TFmPhONDI, 2), was synthesized and polymerized via ring opening metathesis polymerization (ROMP) using tricyclohexylphosphine [1,3-bis(2,4,6-trimethylphenyl)-4,5-dihydroimidazolilydene][benzylidene] ruthenium dichloride (I) to produce the corresponding PTFmPhONDI (3). Gas permeability, diffusion and solubility coefficients of PTFmPhONDI (3) were determined by transient permeation for five gases He, CO₂, O₂, N₂ and CH₄. The larger gas permeability and diffusion coefficients of 3 compared to polynorbornene dicarboximides without fluorine pendant groups were attributed to a lower polymer chain packing due to the effect of the CF₃ groups in the lateral phenyl moiety pending at positions 3 and 5.     

Cure kinetics of a diglycidyl ether of bisphenol a epoxy network (n = 0) with isophorone diamine

The study of the cure reaction of a diglycidyl ether of bisphenol A epoxy network with isophorone diamine is interesting for evaluating the industrial behavior of this material. The total enthalpy of reaction, the glass‐transition temperature, and the partial enthalpies at different curing temperatures have been determined with differential scanning calorimetry in dynamic and isothermal modes. With these experimental data, the degree of conversion and the reaction rate have been obtained. A kinetic model introduces the mechanisms occurring during an epoxy chemical cure reaction. A modification of the kinetic model accounting for the influence of the diffusion of the reactive groups at high conversions is used. A thermodynamic study has allowed the calculation of the enthalpy, entropy, and Gibbs free energy. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2007     

Effect of refining on the phenolic composition of crude olive oils

By definition, virgin olive oil is consumed unrefined, although a great proportion of the olive oil produced has to be refined to render it edible. Phenolic compounds are among the substances eliminated during the refining process; in the present work these were characterized by HPLC, and their evolution during the different refining steps was studied. The complete refining process removed most polyphenols from oils, but the behavior of individual compounds at each step also was observed. o-Diphenols (hydroxytyrosol, catechol, and hydroxytyrosol acetate) and flavonoids (luteolin and apigenin) were eliminated first during the alkaline treatment. Tyrosol and 4-ethylphenol remained in the oil until the deodorization step. A large amount of phenolic compounds was discovered in the refining by-products such as soapstocks and deodorization distillates. In the latter streams, the concentrations of tyrosol and 4-ethylphenol reached up to 149 and 3720 mg/kg by-product, respectively. This high level of 4-ethylphenol and its well-known strong off-odor can interfere during further processing of the deodorization distillates, and this must be taken into account when deciding what is to become of them. Similarly, the results of this work open the possibility of recovering phenolic compounds from the “second centrifugation olive oils” by adding a new washing step prior to the refining process. By including this new step, the most polar polyphenols, hydroxytyrosol and tyrosol, will diffuse from oil to water and a concentration of up to 1400 mg/L of hydroxytyrosol may be achieved.     

Synthesis,characterization, and metal complexation of poly(N‐phenylmaleimide‐co‐acrylic acid) and poly(N‐phenylmaleimide‐co‐acrylamide) as polychelatogens in aqueous solution

We carried out the free‐radical copolymerization of N‐phenylmaleimide with acrylic acid and acrylamide with an equimolar feed monomer ratio. We carried out the synthesis of the copolymers in dioxane at 70°C with benzoyl peroxide as the initiator and a total monomer concentration of 2.5M. The copolymer compositions were obtained by elemental analysis and ¹H‐NMR spectroscopy. The hydrophilic polymers were characterized by elemental analysis, Fourier transform infrared spectroscopy, ¹H‐NMR spectroscopy, and thermal analysis. Additionally, viscosimetric measurements of the copolymers were performed. Hydrophilic poly(N‐phenylmaleimide‐co‐acrylic acid) and poly(N‐phenylmaleimide‐co‐acrylamide) were used for the separation of a series of metal ions in the aqueous phase with the liquid‐phase polymer‐based retention method in the heterogeneous phase. The method is based on the retention of inorganic ions by the polymer in conjunction with membrane filtration and subsequent separation of low‐molecular‐mass species from the formed polymer/metal‐ion complex. The polymer could bind several metal ions, such as Cr(III), Co (II), Zn(II), Ni(II), Cu(II), Cd(II), and Fe(III) inorganic ions, in aqueous solution at pH values of 3, 5, and 7. The interaction of the inorganic ions with the hydrophilic polymer was determined as a function of pH and a filtration factor. Hydrophilic polymeric reagents with strong metal‐complexing properties were synthesized and used to separate those complexed from noncomplexed ions in the heterogeneous phase. The polymers exhibited a high retention capability at pH values of 5 and 7. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci, 2006     

A simple model to predict the removal of oil suspensions from water using the electrocoagulation technique

A simple model has been developed to predict the removal of hydrocarbon fractions from wastewater using sacrificial Al anodes. The model was successfully applied to the interpretation of experimental data obtained in a laboratory electrochemical cell operated in a batchwise manner. The adsorption equilibrium of organic matter on Al hydroxide was modelled using three equations, with the best results obtained using a Langmuir-type equation. The model was able to describe the effects of current density and pollutant concentration on the efficiency of wastewater treatment. Different values were obtained for the parameters depending on the nature of the hydrocarbon suspension. Aluminium hydroxide showed a far higher affinity for the oil/kerosene suspension but exhibited a higher capacity to remove heavy oil suspensions. The removal rates of pollutants were found to depend on the initial concentration and the current density. When the current density was sufficient to destabilise the emulsion, the zeta potential of the clear fraction measured at pH 7.0 became positive. This change was also characterised by a significant reduction in turbidity. Furthermore, the application of higher current densities did not allow further treatment of the water. However, the efficiency of emulsion destabilisation was found to depend on the concentration and current densities that were too low were ineffective.     

Influence of the acidity level on the electropolymerization of N-vinylcarbazole: Electrochemical study and characterization of poly(3,6-N-vinylcarbazole)

Poly(3,6-N-vinylcarbazole) films were prepared by electrochemical oxidation of N-vinylcarbazole on a Pt electrode using acetonitrile as solvent and tetraethylammonium tetrafluoroborate as electrolyte. The electrosynthesis was carried out by electrical potential cycling in the presence of two different bases: tetraethylammonium benzoate (Bz⁻) and tetraethylammonium phthalate (Ph⁻). These salts were expected to modify the acidity level of the electrolyte since they can act as scavengers for the protons released during the polymerization, when the reaction takes place in the carbazole unit.Products were characterized by cyclic voltammetry, scanning electron microscopy, FTIR spectroscopy, thermogravimetric analysis, differential scanning calorimetry, absorption spectroscopy and four-probe electrical conductivity measurements. Both bases influenced significantly the chemical structure and morphology of the deposited materials. The presence of Ph⁻ in the electrolyte decreases the cross-linking of the electrodeposited polymer, leading to a poly(3,6-N-vinylcarbazole) bearing a more uniform morphology, higher thermal stability and electrical conductivity compared to those of the polymers obtained in the presence of Bz⁻ and without acidity control.     

Nonionic water‐soluble polymer: Preparation,characterization, and application of poly(1‐vinyl‐2‐pyrrolidone‐co‐hydroxyethylmethacrylate) as a polychelatogen

The free‐radical copolymerization of water‐soluble poly(1‐vinyl‐2‐pyrrolidone‐co‐hydroxyethylmethacrylate) was carried out with a feed monomer ratio of 75:25 mol %, and the total monomer concentration was 2.67M. The synthesis of the copolymer was carried out in dioxane at 70°C with benzoyl peroxide as the initiator. The copolymer composition was obtained with elemental analysis and ¹H‐NMR spectroscopy. The water‐soluble polymer was characterized with elemental analysis, Fourier transform infrared, ¹H‐ and ¹³C‐NMR spectroscopy, and thermal analysis. Additionally, viscosimetric measurements of the copolymer were performed. The thermal behavior of the copolymer and its complexes were investigated with differential scanning calorimetry (DSC) and thermogravimetry techniques under a nitrogen atmosphere. The copolymer showed high thermal stability and a glass transition in the DSC curves. The separation of various metal ions by the water‐soluble poly(1‐vinyl‐2‐pyrrolidone‐co‐hydroxyethylmethacrylate) reagent in the aqueous phase with liquid‐phase polymer‐based retention was investigated. The method was based on the retention of inorganic ions by this polymer in a membrane filtration cell and subsequent separation of low‐molar‐mass species from the polymer/metal‐ion complex formed. Poly(1‐vinyl‐2‐pyrrolidone‐co‐hydroxyethylmethacrylate) could bind metal ions such as Cr(III), Co(II), Zn(II), Ni(II), Cu(II), Cd(II), and Fe(III) in aqueous solutions at pHs 3, 5, and 7. The retention percentage for all the metal ions in the polymer was increased at pH 7, at which the maximum retention capacity could be observed. The interaction of inorganic ions with the hydrophilic polymer was determined as a function of the pH and filtration factor. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 178–185, 2006