Effect of macropore convection on mass transfer in a bidisperse adsorbent particle

The importance of adsorption induced convection in the macropores of a bidisperse adsorbent particle is studied for a step change in mole fraction or total pressure at the surface of the particle. Material balance equations for a binary gas mixture are written for both the macropores and the macropores with allowance for convection in the macropores, which is described by Darcy's law. The coupled set o1' partial differential equations is solved by orthogonal collocation. The enhancement in mass transfer as a result of convection is assessed by comparing the fractional uptake curves obtained with and without allowance for convection. Both equilibrium-based and kinetic-based separation processes are considered. The effect of the presence of convection in determining the controlling diffusional resistance (macropore or micropore) is also examined. Due to inclusion of convection no single non-dimensional group alone can determine the relative importance of macropore and micropore resistances. Results show that convection can significantly affect the performance of an equilibrium-based macropore diffusion controlled process and that the enhancement in mass transfer is more for a particle with a high value of Darcy permeability.     

Complexometric titration of copper(II) using nitrosochromotropic acid as a new metal indicator

Summary Nitrosochromotropic acid gives a violet coloured soluble complex with Cu^II in ammonium chloride-ammonium hydroxide buffer solution, which is less stable than Cu^II-EDTA complex. When microquantities of Cu^II solution containing 1 or 2 drops of nitrosochromotropic acid in the ph range 7.25 to 8.00, are titrated with EDTA, a sharp colour change from violet to orange occurs at the end point. The method of titration can be carried out from 20° to 40° C, but the copper complex dissociates at higher temperature and gives low results. The separation of Zn²⁺, Cd²⁺, Co²⁺, Ni²⁺, Pb²⁺ and alkaline earths, is necessary as they interfere in the titrations with EDTA.

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Zusammenfassung Nitrosochromotropsäure bildet mit Kupfer(II) in Ammoniumchlorid-Ammoniak-Pufferlösung einen violett gefärbten löslichen Komplex, der weniger stabil ist als der Kupfer(II)-ÄDTA-Komplex. Mikromengen Kupfer(II) können imph-Bereich von 7,25–8,00 unter Zusatz von 1–2 Tropfen Nitrosochromotropsäurelösung als Indicator mit ÄDTA-Lösung titriert werden, wobei am Endpunkt ein scharfer Umschlag von Violett nach Orange erfolgt. Die Temperatur der Lösung soll 20–40° C betragen; bei höherer Temperatur erhält man zu niedrige Werte, da der Kupferkomplex dann dissoziiert. Zn²⁺, Cd²⁺, Co²⁺, Ni²⁺, Pb²⁺ und Erdalkalien müssen vor der Titration abgetrennt werden.

     

Micro determination of olefinic unsaturation. Reaction of N-bromosuccinimide with olefins in polar medium

Summary A micro method for the determination of olefinic unsaturation in organic compounds has been developed. 2–10 mg sample dissolved in acetic acid is reacted with a known excess of N-bromosuccinimide at room temperature and the excess reagent is back titrated iodometrically. The maximum deviation in the results is ±2%. The compounds containing electron withdrawing groups close to the C=C site are not reactive and hence could not be determined by this procedure.

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Mikrobestimmung der Ungesättigtheit von Olefinen. Reaktion von N-Bromsuccinimid mit Olefinen in polarem Medium

Zusammenfassung 2–10mg der Probe werden in Essigsäure gelöst, mit überschüssigem Reagens versetzt und der Überschuß jodometrisch zurücktitriert. Der maximale Fehler der Ergebnisse beträgt ±2%. Verbindungen, die benachbart zur C=C-Doppelbindung elektronenentziehende Gruppen enthalten, können nicht analysiert werden.

     

Foldamer simulations: novel computational methods and applications to poly-phenylacetylene oligomers

We apply several methods to probe the ensemble kinetic and structural properties of a model system of poly-phenylacetylene (pPA) oligomer folding trajectories. The kinetic methods employed included a brute force accounting of conformations, a Markovian state matrix method, and a nonlinear least squares fit to a minimalist kinetic model used to extract the folding time. Each method gave similar measures for the folding time of the 12-mer chain, calculated to be on the order of 7 ns for the complete folding of the chain from an extended conformation. Utilizing both a linear and a nonlinear scaling relationship between the viscosity and the folding time to correct for a low simulation viscosity, we obtain an upper and a lower bound for the approximate folding time within the range 70 ns相似文献   

Joule heating in packed capillaries used in capillary electrochromatography

Effective heat dissipation is critical for reproducible and efficient separations in electrically driven separation systems. Flow rate, retention kinetics, and analyte diffusion rates are some of the characteristics that are affected by variation in the temperature of the mobile phase inside the column. In this study, we examine the issue of Joule heating in packed capillary columns used in capillary electrochromatography (CEC). As almost all commonly used CEC packings are poor thermal conductors, it is assumed that the packing particles do not conduct heat and heat transfer is solely through the mobile phase flowing through the system. The electrical conductivity of various mobile phases was measured at different temperatures by a conductivity meter and the temperature coefficient for each mobile phase was calculated. This was followed by measurement of the electrical current at several applied voltages to calculate the conductivity of the solution within the column as a function of the applied voltage. An overall increase in the conductivity is attributed to Joule heating within the column, while a constant conductivity means good heat dissipation. A plot of conductivity versus applied voltage was used as the indicator of poor heat dissipation. Using theories that have been proposed earlier for modeling of Joule heating effects in capillary electrophoresis (CE), we estimated the temperature within CEC columns. Under mobile and stationary phase conditions typically used in CEC, heat dissipation was found to be not always efficient. Elevated temperatures within the columns in excess of 23 degrees C above ambient temperature were calculated for packed columns, and about 35 degrees C for an open column, under a given set of conditions. The results agree with recently published experimental findings with nuclear magnetic resonance (NMR) thermometry, and Raman spectroscopic measurements.     

Pressure induced phase transitions in Ga1 − x In x P

We have theoretically investigated the effect of pressure on the structural stability of GaP?:?InP mixed system. The three-body-potential (TBP) model has been used. The TBP model consists of long-range as well as short-range interactions; the long-range part includes the modified Coulomb force as well as a three-body term; the short-range part in TBP defines the van der Waals and overlap repulsive interactions. We observe a pressure-induced structural phase transformation from ZnS (B3) to NaCl (B1) type phase in Ga _1?x In _x P. Our calculated transition pressures for the initial GaP and final InP compound semiconductors are in good agreement with other reported data.     

Electrochemical studies of novel olivine-layered (LiFePO4-Li2MnO3) dual composite as an alternative cathode material for lithium-ion batteries

Journal of Solid State Electrochemistry - In the present work, olivine-layered composites, i.e., LiFePO4-Li2MnO3, are successfully synthesized in the form of a single monolithic electrode and layer...     

Approximate controllability of retarded semilinear stochastic system with non local conditions

This paper deals with the approximate controllability of retarded semilinear stochastic system with nonlocal conditions in Hilbert Spaces under the assumption that the corresponding linear system is approximately controllable. The control function for this system is suitably constructed by using the infinite dimensional controllability operator. With this control function, the sufficient conditions for the approximate controllability of the proposed problem in Hilbert Space are established. The results are obtained by using Banach fixed point theorem. Finally, two examples are provided to illustrate the application of the obtained results.     

Phase Transfer Catalyzed Peroxidation of Car Boxylic Acids with Potassium Persulfate

Aqueous solution of potassium persulfate converts water-insoluble carboxylic acids in ether (or dichloromethane), to peracids in a yield of 80–90% under the catalytic influence of benzyltriethylammonium chloride (BTEAC) or polyethyleneglycol (PEG-400). The reaction is further catalyzed kinetically in presence of a sulfonated polymer.     

Effect of ionic liquid on polyaniline chemically synthesised under falling-pH conditions

This study investigates the effect of the ionic liquid 1-butyl-3-methyl imidazolium chloride ([bmim]Cl) on the morphological, structural, and electronic properties of polyaniline (PANI) products synthesised by the falling-pH method. Products were characterised by SEM, FT-IR, UVVIS, N₂-physisorption, and conductivity measurements. The [bmim]Cl addition strongly influenced the PANI morphology, specific surface area, porosity, and conductivity. Depending on the [bmim]Cl: ANI ratio and the synthesis pH, a wide range of PANI nanostructures could be prepared, with rod-like, and fibre-like elongated structures being the dominant morphology under most experimental conditions. Samples prepared in the presence of [bmim]Cl exhibit specific areas of ca 22–35 m² g^?1. The conductivity of the final products depends on the [bmim]Cl: ANI ratio. Temperature dependence of conductivity in the temperature range from 77 K to 300 K was also studied.