scholarly journals Coupled transport of iodide ions during interdiffusion of aqueous HCl and NaOH

1987 ◽  
Vol 65 (10) ◽  
pp. 2489-2494 ◽  
Author(s):  
Derek G. Leaist
Keyword(s):  
Diffusion Coefficients ◽  
Transport Coefficients ◽  
Multicomponent Diffusion ◽  
Coupled Transport ◽  
Iodide Ions ◽  
Multicomponent Transport ◽  
Transport Of Ions ◽  
Acids And Bases ◽  
Strong Acids

Stokes diaphragm cells have been used to study multicomponent diffusion in aqueous HCl–NaOH–NaI mixtures at 25 °C. The nine quaternary diffusion coefficients for the mixture containing 0.025 mol L−1 of each electrolyte are reported. The measured coefficients are used to analyze coupled transport of iodide ions generated by interdiffusion of aqueous HCl and NaOH. The analysis shows that the gradient in concentration of NaOH is twice as effective at producing flow of iodide ions relative to the HCl gradient, and that the NaI gradient substantially alters the rates of diffusion of HCl and NaOH components. Equations are developed for predicting multicomponent transport coefficients that describe coupled transport of ions driven by interdiffusion of strong acids and bases.

Diffusion with hydrolysis equilibria: transport coefficients of aqueous SO2, NH3, and Na2CO3

1983 ◽  
Vol 61 (7) ◽  
pp. 1494-1499 ◽  
Author(s):  
D. G. Leaist
Keyword(s):  
Chemical Reaction ◽  
Diffusion Coefficients ◽  
Transport Coefficients ◽  
Dilute Solution ◽  
Coupled Transport ◽  
Mobility Data

Practical equations are derived for estimating diffusion coefficients and Onsager transport coefficients of aqueous solutes subject to hydrolysis. The derivation is based on the Nernst–Hartley method which is extended to include chemical reaction of solute with solvent. The derived equations and existing mobility data are used to estimate transport coefficients of aqueous SO2 (20 °C), NH3 (15 °C), and Na2CO3 (25 °C). In dilute solution where hydrolysis is extensive, rates of diffusion of SO2 and NH3 are increased by about 50% and 25%, respectively, relative to unhydrolyzed solute. Because of the carbonate–bicarbonate equilibrium, diffusion in aqueous Na2CO3 is a ternary process characterized by coupled transport of NaOH. In dilute solution the NaOH flux may exceed the flux of Na2CO3.

Multicomponent diffusion in dilute solutions of mixed electrolytes

1980 ◽  
Vol 33 (9) ◽  
pp. 1869 ◽  
Author(s):  
DG Leaist ◽  
PA Lyons
Keyword(s):  
Diffusion Coefficients ◽  
Transport Coefficients ◽  
Ionic Conductivities ◽  
Multicomponent Diffusion ◽  
Mixed Electrolytes ◽  
Dilute Solutions ◽  
Ternary Diffusion ◽  
Mixed Electrolyte ◽  
Coupled Diffusion ◽  
Phenomenological Coefficients

The Onsager-Fuoss theory of ion transport can be used to study multicomponent diffusion in dilute solutions of mixed electrolytes. Precise Lij phenomenological coefficients can be calculated from a knowledge of the solvent properties and limiting ionic conductivities. If activity coefficients for dilute mixed electrolyte systems are available, precise multicomponent diffusion coefficients can also be calculated. Explicit equations are given for calculating both sets of transport coefficients. The equations apply to systems containing an arbitrary number of strong electrolytes and are valid at low total salt concentrations. To illustrate the use of the equations, ternary diffusion in a few aqueous systems is examined in detail. Aqueous mixed electrolyte systems containing H+ exhibit strongly coupled diffusion and highly variable diffusion coefficients. A modified Harned conductimetric experiment is described for the determination of ternary diffusion coefficients in dilute solutions. Results for the system HCl- KCl-H2O are in good agreement with theoretical predictions.

scholarly journals Self-Diffusion Coefficients of Methane/n-Hexane Mixtures at High Pressures: An Evaluation of the Finite-Size Effect and a Comparison of Force Fields

2019 ◽  
Author(s):  
Thiago José Pinheiro dos Santos ◽  
Charlles Abreu ◽  
Bruno Horta ◽  
Frederico W. Tavares
Keyword(s):  
Molecular Dynamics ◽  
Diffusion Coefficients ◽  
High Pressures ◽  
Force Fields ◽  
Transport Coefficients ◽  
Finite Size ◽  
Finite Size Effect ◽  
Self Diffusion ◽  
Analytical Correction ◽  
Dynamics Simulations

Mass transport coefficients play an important role in process design and in compositional grading of oil reservoirs. As experimental measurements of these properties can be costly and hazardous, Molecular Dynamics simulations emerge as an alternative approach. In this work, we used Molecular Dynamics to calculate the self-diffusion coefficients of methane/n-hexane mixtures at different conditions, in both liquid and supercritical phases. We evaluated how the finite box size and the choice of the force field affect the calculated properties at high pressures. Results show a strong dependency between self-diffusion and the simulation box size. The Yeh-Hummer analytical correction [J. Phys. Chem. B, 108, 15873 (2004)] can attenuate this effect, but sometimes makes the results depart from experimental data due to issues concerning the force fields. We have also found that different all-atom and united-atom models can produce biased results due to caging effects and to different dihedral configurations of the n-alkane.

Self-Diffusion of Sodium, Chloride and Iodide Ions in Methanol-Water Mixture

1986 ◽  
Vol 41 (7) ◽  
pp. 939-943 ◽  
Author(s):  
E. Hawlicka
Keyword(s):  
Sodium Chloride ◽  
Diffusion Coefficients ◽  
Solvent Composition ◽  
The Self ◽  
Water Mixture ◽  
Preferential Hydration ◽  
Water Solutions ◽  
Iodide Ions ◽  
Self Diffusion

The self-diffusion coefficients of Na+, Cl- and I- in methanol-water solutions at 35 ± 0.01 °C have been measured in their dependence on the salt molarity in the range 1 · 10-4- 1 · 10-2 mol dm -3. The ionic self-diffusion coefficients in infinitely diluted solutions have been computed. The influence of the solvent composition on the solvation of the ions is discussed. A preferential hydration of Na+, Cl- and I- ions in water-methanol mixtures has been found.

scholarly journals Transport Properties for Pharmaceutical Controlled-Release Systems: A Brief Review of the Importance of Their Study in Biological Systems

Biomolecules ◽  
2018 ◽  
Vol 8 (4) ◽  
pp. 178 ◽  
Author(s):  
Ana C. F. Ribeiro ◽  
Miguel A. Esteso
Keyword(s):  
Controlled Release ◽  
Transport Properties ◽  
Diffusion Coefficients ◽  
Drug Carrier ◽  
Strong Association ◽  
Mutual Diffusion ◽  
Mixed Electrolytes ◽  
Coupled Transport ◽  
Concentration Gradients ◽  
Enhanced Solubility

: The goal of this work was to comprehensive study the transport properties of controlled-release systems for the safe and reliable delivery of drugs. Special emphasis has been placed on the measurement of the diffusion of drugs, alone or in combination with carrier molecules for enhanced solubility and facilitated transport. These studies have provided detailed comprehensive information—both kinetic and thermodynamic—for the design and operation of systems for the controlled release and delivery of drugs. Cyclodextrins are among the most important carriers used in these systems. The basis for their popularity is the ability of these materials to solubilize poorly soluble drugs, generally resulting in striking increases in their water solubilities. The techniques used in these investigations include pulse voltammetry, nuclear magnetic resonance (NMR) and Raman spectroscopy, ultrasonic relaxation, and dissolution kinetics. Transport in these systems is a mutual diffusion process involving coupled fluxes of drugs and carrier molecules driven by concentration gradients. Owing to a strong association in these multicomponent systems, it is not uncommon for a diffusing solute to drive substantial coupled fluxes of other solutes, mixed electrolytes, or polymers. Thus, diffusion data, including cross-diffusion coefficients for coupled transport, are essential in order to understand the rates of many processes involving mass transport driven by chemical concentration gradients, as crystal growth and dissolution, solubilization, membrane transport, and diffusion-limited chemical reactions are all relevant to the design of controlled-release systems. While numerous studies have been carried out on these systems, few have considered the transport behavior for controlled-release systems. To remedy this situation, we decided to measure mutual diffusion coefficients for coupled diffusion in a variety of drug–carrier solutions. In summary, the main objective of the present work was to understand the physical chemistry of carrier-mediated transport phenomena in systems of controlled drug release.

scholarly journals Experimental study of multicomponent diffusion in low permeable sediments

2019 ◽  
Vol 98 ◽  
pp. 10002
Author(s):  
Vladimir Lekhov ◽  
Alexei Lekhov
Keyword(s):  
Diffusion Coefficients ◽  
Average Length ◽  
Effective Diffusion ◽  
Length Distribution ◽  
Large Degree ◽  
Multicomponent Diffusion ◽  
Distribution Coefficients ◽  
Disposal Site ◽  
Special Equipment ◽  
Permeable Sediments

Diffusion coefficients for Na+ and distribution coefficients for Cs+, Ba2+, Ni2+, CO2+, Sr2+ were measured on low permeable samples (3 cm diameter, average length 7 cm) from the deep disposal site Siberian Chemical Combine (SSC) using the end-diffusion technique. The direction of diffusion was perpendicular to bedding. Special equipment for experiment were designed and constructed. Two types of concentration observation were used. For non-sorbing Na+ in time used EC sensors and length distribution of sorbed elements. The synthetic solution used in the experiments was a model of low-activity contaminant of the SSC, and consist NaNO3 (25 g/l) and nitrate compounds: Cs+, Ba2+, Ni2+, Co2+, Sr2+ (100 mg/l each). The measured values of the effective diffusion coefficients De) for Na+ from 7.60×10-7 to 1.51×10-5 m2/day and volumetric dimensionless distribution coefficients (Kdρ) are: Cs+ from 0.21 to 22.1, Ba2+ from 1.1 to 1.45, Ni2+ from 0.3 to 16.4, Co2+ from 1.98 to 24.7, Sr2+ from 1.9 to 14.3. The values of the diffusion coefficient show a large degree of variability. The diffusion coefficients of non-sorbing Na+ measured in this study are in good agreement with pore-scale diffusion simulation on microtomography data.

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