A non-equilibrium thermodynamics approach to model mass and heat transport for water pervaporation through a zeolite membrane

Pervaporation through zeolite membranes involves local heat effects and combined heat and mass transport. The current state-of-the-art Maxwell–Stefan (M–S) models do not take these effects into account. In this study, transport equations for the coupled heat and mass transport through a zeolite membrane are derived from the framework of non-equilibrium thermodynamics (NET). Moreover, the assumption of equilibrium between the adjacent bulk phases at the feed and permeate sides of the zeolite layer is abandoned in favor of local equilibrium. The equations have been used to model pervaporation of water through a 2 m thick NaA type zeolite membrane, deposited on an asymmetric -alumina support, at a feed temperature of 348 K. Assuming a flux of 10 kg m⁻² h⁻¹(0.15 mol m⁻² s⁻¹), the transport through the zeolite layer, as well as the liquid feed side boundary layer and the support layers is modeled. The activity, fugacity, and temperature profiles are calculated with and without taking coupling effects and surfaces into account. The profiles show distinct differences between the two cases. Including the surface effects leads to discontinuities in the activity and temperature at the membrane interfaces. A significantly higher temperature drop of 1.3 K is calculated across the zeolite, compared to 0.4 K when surface and coupling effects are not accounted for. The calculated decrease in temperature over the zeolite layer is dominated by the surfaces. This could indicate that temperature polarization is, to a large extent, a surface effect. The heat flux induces an extra driving force for mass transport, reducing the activity difference over the membrane. A positive jump in activity is observed at the interfaces, revealing the mass transport across the interfaces is governed by the coupling with the heat flux. The support layers contribute significantly to the total mass transport resistance.     

Plated thermocouples for boiling heat transfer studies

Plated thermocouples are developed for the measurement of the temperatures of the inner and outer surfaces of the tube wall during the boiling heat transfer processes. A thin layer of a suitable metal is electroplated on the surface of the tube wall. The entire contacting surface between the plated layer and the base metal serves as the joint of the thermocouple. A wire of the same material as the tube is securely attached to the tube wall by embedding under an electrodeposited layer of the same metal. Another wire of the same material as the plated layer is securely attached to the plated layer by the same technique. There wires serve as the leads of the thermocouple represents the average temperature of the plated portion of the tube surface fairly accurately. The linearity and reproducibility of the temperature-emf relationship are also very good.     

Rate and thermodynamic studies of the interaction between water and iso-butyl cellosolve by ultrasonic methods

Ultrasonic absorption and velocity measurements in aqueous solution of iso-butyl cellosolve (ethylene glycol iso-butyl ether) as a function of the concentration are reported. The two relaxational absorptions have been attributed to the perturbation of the equilibria expressed by AB?A+B and Aα(1/n)A_n where A is the solute, B is the solvent, AB is the complex and A _n is the solute aggregate. The rate constants for each step have been determined. From the concentration dependence of the maximum excess absorption per wave length, the enthalpy change and the volume change for the reaction between the solute and the solvent have been determined for aqueous solutions of butyl cellosolve (ethylene glycol n-butyl ether), iso-butyl cellosolve and propyl cellosolve (ethylene glycol n-propyl ether). The results are consistent with a hydrogen bonding reaction. The effect of the ethers on water structure are considered and it is clear that the fraction of water molecules which can hydrogen bond to the solute decreases with the increasing hydrophobicity of the solute.     

Flow-through determination of sulphate in water using different methods: A comparison

Summary Sulphate was determined in various kinds of environmental samples using a continuous-flow system, a flow-injection system or a flow-through titrimeter. The reagents in the three cases consisted basically of DMSA(III), KNO₃ and Ba(ClO₄)₂. The results of the three methods were evaluated statistically. A comparison of the three methods is given. The advantage of the DSMA(III)-methods is shown in a comparison with the commonly used thorin method.

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Sulfatbestimmung in Wasser mit verschiedenen Methoden in einem Durchflußsystem; ein Vergleich

Zusammenfassung Die Bestimmung von Sulfat in unterschiedlichen Umweltwasserproben wurde mit drei verschiedenen Systemen vorgenommen: mit continuous-flow und flow-injection Durchflußsystemen und mit einem Durchflußtitrimeter. Die Reagentien bei den drei Bestimmungen waren DMSA(III), KNO₃ und Ba(ClO₄)₂. Die Ergebnisse wurden statistisch ausgewertet und die Methoden miteinander verglichen. Die DMSA(III)-Verfahren sind der weit verbreiteten Thorin-Methode vorzuziehen.

     

Thermal particle base methods in fluid flow and heat transfer

Journal of Thermal Analysis and Calorimetry -     

Charge distribution in the water molecule--a comparison of methods

The charge distribution in the water molecule has been analyzed using a broad variety of basis sets, four different quantum mechanical methods (Hartree-Fock, Becke3LYP, MP2, and QCISD), and six population analysis methods (Mulliken, NPA, AIM, CHELPG, Merz-Kollman, and Resp). The influence of the molecular structure on the calculated atomic charges has been studied using small perturbations of the experimentally determined structure.     

Experimental studies of flow boiling heat transfer by using nanofluids

Journal of Thermal Analysis and Calorimetry - Flow boiling heat transfer widely utilized in numerous industrial applications such as boiler tubes, evaporators and cooling of reactors in a nuclear...     

Pairwise decomposition of residue interaction energies using semiempirical quantum mechanical methods in studies of protein-ligand interaction

Pairwise decomposition of the interaction energy between molecules is shown to be a powerful tool that can increase our understanding of macromolecular recognition processes. Herein we calculate the pairwise decomposition of the interaction energy between the protein human carbonic anhydrase II (HCAII) and the fluorine-substituted ligand N-(4-sulfamylbenzoyl)benzylamine (SBB) using semiempirical quantum mechanics based methods. We dissect the interaction between the ligand and the protein by dividing the ligand and the protein into subsystems to understand the structure-activity relationships as a result of fluorine substitution. In particular, the off-diagonal elements of the Fock matrix that is composed of the interaction between the ionic core and the valence electrons and the exchange energy between the subsystems or atoms of interest is examined in detail. Our analysis reveals that the fluorine-substituted benzylamine group of SBB does not directly affect the binding energy. Rather, we find that the strength of the interaction between Thr199 of HCAII and the sulfamylbenzoyl group of SBB affects the binding affinity between the protein and the ligand. These observations underline the importance of the sulfonamide group in binding affinity as shown by previous experiments (Maren, T. H.; Wiley: C. E. J. Med. Chem. 1968, 11, 228-232). Moreover, our calculations qualitatively agree with the structural aspects of these protein-ligand complexes as determined by X-ray crystallography.     

Mechanistic studies and methods to prevent aglycon transfer of thioglycosides

Thioglycosides have been employed extensively for the synthesis of complex oligosaccharides, carbohydrate libraries, and mimetics of O-glycosides. While very useful, aglycon transfer is a problematic side reaction with thioglycosides. In this paper, a series of mechanistic studies are described. The aglycon transfer process is shown to affect both armed and disarmed thioglycosides, cause anomerization of the carbon-sulfur bond of a thioglycoside, and destroy the product of a glycosylation reaction. The results indicate that the aglycon transfer process can be a major problem for a wide range of thioglycosides. This side reaction is especially important to consider when carrying out complex reactions such as solid-phase glycosylations, one-pot or orthogonal multicomponent glycosylations, and construction of carbohydrate libraries. To prevent transfer, a number of modified aglycons were examined. The 2,6-dimethylphenyl (DMP) aglycon was found to effectively block transfer in a variety of model studies and glycosylation reactions. The DMP group can be installed in one step from a commercially available thiol (2,6-dimethylthiophenol) and is useable as a glycosyl donor. On the basis of these features, the DMP group is proposed as a convenient and improved aglycon for thioglycosides.     

A review on heat transfer characteristics of cryogenic heat pipes

Journal of Thermal Analysis and Calorimetry - Heat pipes are broadly applied for thermal management of devices with high heat flux. Due to the dependency of their efficient operating range on the...     

Vibrational spectroscopic studies of the interaction of water with serine

The vibrational dynamics of water around serine was investigated by using Raman spectroscopy and inelastic incoherent neutron scattering. Experiments with serine in deuterium oxide were performed to assist the assignment. The study shows that for the serine, the exchange of protons-deuterons on the active -NH3+ and -OH groups were relatively easy, whereas there were hardly any exchanged on the -CH or -CH2- groups. The main features of the spectra for hydrated samples (versus the dry samples) were altered considerably; new sharp peaks in the measured spectra appeared, indicating that the hydrogen bonding between water and serine had disturbed the structure of the serine molecule.     

Enthalpy and heat capacity parameters of ammonium bromide interaction with hexamethylphosphotriamide in water

Thermal effects of solution of ammonium bromide in hexamethylphosphotriamide (HMPT)-water mixtures at 4° C, 15°C, and 46°C in the region of minor additions of the nonaqueous component were investigated for the first time by calorimetry. Variations of heat capacity in the course of solution were calculated using previous data for 25°C and 40°C. The curves of the heat capacity of solution (transfer) and temperature variation of transfer entropy versus composition have a minimum near the region of the existence of the 1:20 HMPT:water clathrate. The enthalpy, heat capacity, and temperature variations of the entropy coefficients of electrolyte amide pair and three-particle interactions in water were calculated in terms of MacMillan-Mayer theory. Within the framework of the group additivity method it is shown that the heat capacity coefficient of the bromide ion-HMPT pair interaction is negative and dictates temperature variations of enthalpy for ammonium bromide and tetraalkylammonium interactions with HMPT in water.     

A comparison of some integral methods

The integral methods proposed to compute the kinetic parameters of heterogeneous reactions under non-isothermal conditions are usually worked by the help of the least squares method and the obtained correlation coefficient is taken as a criterion to choose the best integral method.An analysis of several experimental data by mean of three different integral methods was performed by us and the results pointed out that this criterion, by itself, is not enough to provide reliable information on the kinetic parameters.It appears, thus, that the use of an integral method or another is a simple matter of researcher's choice.

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Zusammenfassung Integrationsmethoden zur Berechnung kinetischer Parameter von heterogenen Reaktionen unter nicht isothermen Bedingungen werden im allgemeinen nach der Methode der kleinsten Quadrate erarbeitet und der ermittelte Korrelationskoeffizient dient als ein Kriterium für die Auswahl der besten Integrationsmethode.Mittels drei verschiedenen Integrationsmethoden wurde eine Analyse verschiedener experimenteller Daten durchgeführt. Die Ergebnisse zeigen, daß dieses Kriterium allein nicht ausreicht, um ausreichende Informationen über die kinetischen Parameter zu liefern.Es scheint deshalb, daß die Verwendung der einen oder anderen Integrationsmethode einfach eine Wahl des Anwenders darstellt.

     

Electrochemical studies of the tetrabutyl- and tetramethyl-ammonium ion transfer across the water-1,2-dichloroethane interface: A comparison with the water—nitrobenzene interface

The results of electrochemical studies on the reaction of tetrabutyl- and tetramethylammonium (TBA⁺ and TMA⁺) ion transfer from water to 1,2-dichloroethane are presented in this paper and are compared with se of the water—nitrobenzene interface. The TMA⁺ ion transfer has been studied by the chronopotentiometric cyclic voltammetry methods and that of the TBA⁺ ion by the chronopotentiometric method only.It has been found that the reactions are diffusion controlled over the current density range up to about 1O μA cm^?2 and at polarization rates up to 0.15V s^?1. Diffusion coefficients of the studied ions have been detemined, as well as their formal potentials with respect to an ion-selective tetrabutylammonium electrode to a partition electrode containing tetraethylammonium picrate whose potential is close to zero. In additon, kinetic parameters of the transfer reaction have been determined for the tetrabutylammonium ion from data obtained at current densities over 10 μA cm^?2 (irreversible range).     

A general variance model in methods comparison

Valid statistical tests of paired data require correct models of how measurement variance depends on analyte concentration. One often‐used assumption is that the variance is constant across the range; another is that the coefficient of variation is constant. But in many data sets, neither of these holds. A variance model containing both a constant variance and a constant coefficient of variation term is recommended as an often‐useful additional analysis tool for methods comparison. The more general variance model is fitted to a simulated data set, and one from a clinical chemistry methods comparison. It is used to provide more reliable average versus difference plots, to fit weighted Deming regressions, and to provide valid paired data analyses. The calculations are implemented in r software. Copyright © 2013 John Wiley & Sons, Ltd.     

Intramolecular electron-hole transfer in binuclear transition metal compounds-theoretical methods and model studies

A theoretical framework for intramolecular electron or hole migration is developed starting from the convenient canonical molecular orbitals of an ordinary Hartree-Fock (HF) calculation. The necessary unitary transformations from the canonical MO basis via localized orbitals to a transfer Fockian are presented. A simple procedure for the consideration of relaxation and correlation effects during the time evolution is developed. Computational results for the hole migration between different metal 3d electron-hole pairs in bis(-pentadienyl)dinickel (1) are discussed. The contribution of the direct transfer channel as well as the participation of ligand and channels in the various propagation processes are analyzed.