Long term isothermal aging and thermal analysis of N-CYCAP polyimides

The N-CYCAP polyimides utilize a (2,2) paracyclophane endcap that polymerizes and does not generate volatile gases during the cure process. These polyimides have both high glass temperatures (390 C) and an onset of decomposition in air of 560 C. Thermal oxidative stability (TOS) weight loss studies show that replacing 25 percent by weight of the paraphenylene diamine in the polymer backbone with metaphenylene diamine improves the weight loss characteristics. N-CYCAP neat resin samples performed better than PMR-II-50 when exposed at 343 and 371 C in air for up to 1000 hours. Preliminary composite studies show that both PMR-II-50 and N-CYCAP have better thermal stability when fabricated on T-40R. Higher isothermal aging temperatures of longer aging times are needed to determine the differences in TOS between composite samples of PMR-II-50 and N-CYCAP polyimides

Élimination de métaux par adsorption en réacteur à membranes à lit mobile de particules et en réacteur lit fixe continu - Approche cinétique

Ce travail propose un nouveau procédé d'élimination du Cu2+ par adsorption sur des résines échangeuses d'ions poreuses, mises en œuvre dans un réacteur à membrane à lit mobile de particules. Ce procédé a été étudié sur le plan cinétique pour des solutions synthétiques de Cu(II) dans de l'eau. L'application visée à moyen terme est l'intégration de cette opération unitaire dans une filière de traitement complète des effluents industriels liquides.L'étude cinétique a été réalisée avec une résine cationique forte Mono C-350H en réacteur agité fermé et thermostaté. Les isothermes d'adsorption ont été établies à 21°C et les paramètres de Langmuir et de Freundlich ont été calculés. Une étude de l'influence de la vitesse d'agitation et de la température sur la vitesse réactionnelle apparente a permis de déterminer la zone opératoire correspondant à un régime cinétique. Ce régime est obtenu pour un Reynolds d'agitation supérieur à 4700 et une température inférieure à 60°C. Dans ces conditions, l'ordre de la réaction par rapport au Cu2+ est de un et la constante cinétique exprimée par unité de masse de particules est kwapp=0,03721 lgrés-1min-1 à 21°C. L'énergie d'activation de la réaction a également été déterminée.Par ailleurs, en s'appuyant sur les résultats de l'étude cinétique, les premiers éléments de comparaison d'un réacteur classique à lit fixe et d'un réacteur original à membranes à lit de particules sont présentés. Pour le même débit à traiter, en fixant dans les deux cas un taux de conversion objectif de 95 %, le nouveau procédé permettant d'utiliser des particules de plus faible diamètre conduit à une réduction du volume de particules réactives d'un facteur 4, de la puissance énergétique à fournir au système d'un facteur 3 à 5. Les performances prometteuses de ce procédé restent à valider lors d'une étude pilote.Legislation in France and in Europe is becoming more rigorous for industrial fluid wastes, which is encouraging many industries to find a proper solution to their effluent problems and to include a complete wastewater treatment plant in their process. This paper focuses on effluents containing metallic compounds, which can be toxic. For Cu(II) the maximal allowed concentration is 1 mg/l. Many unit operations can be used to remove metal compounds from industrial waste waters, but the most widely used are scaling followed by settling and/or filtration, adsorption, solvent extraction and incineration. The main drawbacks encountered with these processes are:1. a low yield, 2. high operating and investment costs, 3. sludge production. This paper deals with a new unit operation to be included in a complete treatment line in place of adsorption, for removing metallic compounds. This new operation consists of a membrane moving bed reactor, which uses very fine dispersed adsorbent particles, so as to increase the particles' specific area. The particles are circulated with the water and separated from the treated water by an ultrafiltration hollow fibre or tubular membrane. The potential advantages of the process are the following: use of high specific area particles, production of a permeate without particles or suspended matter, no bed fouling (in comparison with fixed bed adsorption), continuous separation of metallic compounds and particles by the membrane. Moreover, we have chosen porous ion exchange resins as adsorbent particles, thus allowing a further continuous regeneration and recycling of the particles.The aim of this first paper on this new reactor is to introduce a comparison between the performances of a conventional fixed bed reactor and those of the moving bed membrane reactor, for the removal of Cu(II) from pure water. The first step for this study consists of a characterization of the particles/metallic compounds interactions in terms of kinetic rates and adsorption isotherms. Ion exchange is here considered with a chemical engineering approach, as a heterogeneous liquid/solid reaction.Experiments have been carried out in a thermostatted 1 litre stirred batch reactor. The solutions are prepared with CuSO4 . 5H20 in demineralised water. Cu(II) concentrations are measured by spectro-colorimetry using the regulation T90022 from AFNOR. Particles are cationic ion exchange resins referenced as Mono C-350H. Their mean diameter (315 mm) is higher than the membrane pore diameter (0.01 mm). No membrane internal fouling will then occur during particle filtration. Moreover the particle diameter is lower than the inner diameter of the fibres to prevent plugging of the hollow fibre.The adsorption isotherms have been determined at 21°C and the relevant Langmuir and Freundlich parameters are given in Table 2. The influence of stirring velocity and temperature in the reactor on the reaction rate has been studied. For stirring velocities above 100 rpm, the apparent reaction rate is independent of the stirring velocity. That means that the kinetic regime is obtained for stirring Reynolds numbers higher than 4700. The plot of Lnkwapp against T-1, at a constant and high enough stirring velocity to prevent external diffusion limitations, shows two linear areas :- under 60°C, the kinetic regime is obtained, thus allowing the determination of the reaction activation energy (given in Table 3); - above 60°C, the internal diffusion is limiting. In the kinetic controlled area, the reaction was found to be first-order and the rate constant expressed by mass of particles is kwapp=0.03721 lgrés-1 min-1 at 21 °C.Using the kinetic data, it is possible to design and to compare the characteristics of a fixed bed reactor and a moving bed reactor, which would have the same conversion rate (95 %), for the same effluent flow rate to treat (5 m3/h). As a first approximation, we consider operating conditions inducing a kinetic regime. We also consider that the reaction mostly takes place at the particle surface. This assumption allows one to obtain the reaction rate expressed by particle's area for any particle size. At 21 °C, the previously defined reaction rate is ks=4.43x10-5 m3/s.m2. The expression of the conversion rate as a function of ks, the reaction volume and the particle diameter is obtained for each reactor from the mass balance written in terms of Cu(II). The pressure drop expression is also given for the reactors. In the case of the moving bed reactor the increase of dynamic viscosity induced by the presence of particles has been taken into account. For each reactor, a solid retention, particle diameter and fluid velocity corresponding to values widely used industrially have been chosen (see Table 4). For the membrane reactor, we consider hollow fibres with 0.93 mm inner diameter, 1.2 m length and a total filtration area of 50 m2 per module. Calculations have been done for two limit values of the permeation flux: 50 and 100 l/h.m2.A comparison of the two reactors is given in Table 5, which demonstrates the interest of the moving-bed reactor, as it allows one to reduce the volume of adsorbent particles by a factor 4. This result is linked to the high specific surface of the fine dispersed particles. The membrane reactor also induces a high reduction of the pressure drop (by a factor 40) and of the energy consumption (from 4.7 for a one- module plant to 2.6 for a two-module plant). These promising results are encouraging to continue the research on this process with the aim to optimize it. Further studies will include:- comparison of different adsorbent particles and choice of the best available; - validation of this preliminary simulation by experiments on a pilot plant, with synthetic and then industrial waters; - integration of this unit operation in a complete treatment plant

Isolation of high quality graphene from Ru by solution phase intercalation

2013 AIP Publishing LL

Acute phase proteins and white blood cell levels for prediction of infectious complications in status epilepticus

ABSTRACT: INTRODUCTION: Infections in status epilepticus (SE) patients result in severe morbidity making early diagnosis crucial. As SE may lead to inflammatory reaction, the value of acute phase proteins and white blood cells (WBC) for diagnosis of infections during SE may be important. We examined the reliability of C-reactive protein (CRP), procalcitonin (PCT), and WBC for diagnosis of infections during SE. METHODS: All consecutive SE patients treated in the ICU from 2005 to 2009 were included. Clinical and microbiological records, measurements of CRP and WBC during SE were analyzed. Subgroup analysis was performed for additional PCT measurements in the first 48 hours of SE. RESULTS: 22.5% of 160 consecutive SE patients had infections during SE. Single levels of CRP and WBC had no association with the presence of infections. Their linear changes over the first three days after SE onset were significantly associated with the presence of infections (p=0.0012 for CRP, p=0.0137 for WBC). Levels of PCT were available for 31 patients and did not differ significantly in patients with and without infections. Sensitivity of PCT and CRP was high (94% and 83%) and the negative predictive value of CRP increased over the first three days to 97%. Specificity was low, without improvement for different cut-offs. CONCLUSIONS: Single levels of CRP and WBC are not reliable for diagnosis of infections during SE, while their linear changes over time significantly correlated with the presence of infections. In addition, low levels of CRP and PCT rule out hospital-acquired infections in SE patient

Alloy oxidation as a route to chemically active nanocomposites of gold atoms in a reducible oxide matrix

While nanoparticles are being pursued actively for a number of applications, dispersed atomic species have been explored far less in functional materials architectures, primarily because composites comprising dispersed atoms are challenging to synthesize and difficult to stabilize against sintering or coarsening. Here we show that room temperature oxidation of Au–Sn alloys produces nanostructures whose surface is terminated by a reducible amorphous oxide that contains atomically dispersed Au. Analysis of the oxidation process shows that the dispersal of Au in the oxide can be explained by predominant oxygen anion diffusion and kinetically limitedmetalmass transport, which restrict phase separation due to a preferential oxidation of Sn. Nanostructures prepared by oxidation of nanoscale Au–Sn alloys with intermediate Au content (30–50%) show high activity in a CO-oxidation probe reaction due to a cooperative mechanism involving Au atoms as sites for CO adsorption and reaction to CO2 embedded in a reducible oxide that serves as a renewable oxygen reservoir. Our results demonstrate a reliable approach toward nanocomposites involving oxide-embedded, atomically dispersed noble metal species

Alloy oxidation as a route to chemically active nanocomposites of gold atoms in a reducible oxide matrix

While nanoparticles are being pursued actively for a number of applications, dispersed atomic species have been explored far less in functional materials architectures, primarily because composites comprising dispersed atoms are challenging to synthesize and difficult to stabilize against sintering or coarsening. Here we show that room temperature oxidation of Au–Sn alloys produces nanostructures whose surface is terminated by a reducible amorphous oxide that contains atomically dispersed Au. Analysis of the oxidation process shows that the dispersal of Au in the oxide can be explained by predominant oxygen anion diffusion and kinetically limitedmetalmass transport, which restrict phase separation due to a preferential oxidation of Sn. Nanostructures prepared by oxidation of nanoscale Au–Sn alloys with intermediate Au content (30–50%) show high activity in a CO-oxidation probe reaction due to a cooperative mechanism involving Au atoms as sites for CO adsorption and reaction to CO2 embedded in a reducible oxide that serves as a renewable oxygen reservoir. Our results demonstrate a reliable approach toward nanocomposites involving oxide-embedded, atomically dispersed noble metal species

Diagnosing serious infections in acutely ill children in ambulatory care (ERNIE 2 study protocol, part A): diagnostic accuracy of a clinical decision tree and added value of a point-of-care C-reactive protein test and oxygen saturation

Background: Acute illness is the most common presentation of children to ambulatory care. In contrast, serious infections are rare and often present at an early stage. To avoid complications or death, early recognition and adequate referral are essential. In a recent large study children were included prospectively to construct a symptom-based decision tree with a sensitivity and negative predictive value of nearly 100%. To reduce the number of false positives, point-of-care tests might be useful, providing an immediate result at bedside. The most probable candidate is C-reactive protein, as well as a pulse oximetry. Methods: This is a diagnostic accuracy study of signs, symptoms and point-of-care tests for serious infections. Acutely ill children presenting to a family physician or paediatrician will be included consecutively in Flanders, Belgium. Children testing positive on the decision tree will get a point-of-care C-reactive protein test. Children testing negative will randomly either receive a point-of-care C-reactive protein test or usual care. The outcome of interest is hospital admission more than 24 hours with a serious infection within 10 days. Aiming to include over 6500 children, we will report the diagnostic accuracy of the decision tree (+/- the point-of-care C-reactive protein test or pulse oximetry) in sensitivity, specificity, positive and negative likelihood ratios, and positive and negative predictive values. New diagnostic algorithms will be constructed through classification and regression tree and multiple logistic regression analysis. Discussion: We aim to improve detection of serious infections, and present a practical tool for diagnostic triage of acutely ill children in primary care. We also aim to reduce the number of investigations and admissions in children with non-serious infections

Hydrogen evolution in aqueous solutions containing dissolved H2S: Evidence of direct electroactive contribution of H2S

International audienceThis paper compares the cathodic reactions occurring on steel in an oxygen-free aqueous solution containing dissolved H 2 S or dissolved CO 2. It is well admitted that the rate of the cathodic reaction is enhanced in aqueous solutions containing dissolved CO 2 , in comparison with strong acid solutions at the same pH [1-6]. In a previous paper [7], the authors have shown that this phenomenon appears only in the mass transfer limitation region, where the transport of carbonic acid is added to the transport of proton. In the case of H 2 S containing solutions, this chemical mechanism is no more sufficient to explain the cathodic polarization curves. An additional electrochemical reaction is clearly observed, with strong links with H 2 S concentration