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.

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.

scholarly journals Thermodynamically Coupled Transport in Simple Catalytic Reactions

2008 ◽  
Vol 6 (1) ◽  
Author(s):  
Yasar Demirel
Keyword(s):  
Chemical Reaction ◽  
Chemical Potential ◽  
Numerical Solutions ◽  
Nonlinear Differential Equations ◽  
Transport Coefficients ◽  
Reaction Diffusion ◽  
Catalytic Reactions ◽  
Coupled Transport ◽  
Reaction Diffusion Systems ◽  
Considerable Work

Considerable work published on chemical reaction-diffusion systems investigates mainly mathematically coupled nonlinear differential equations. This study presents the modeling of a simple elementary chemical reaction with thermodynamically and mathematically coupled heat and mass transport with external mass and heat transfer resistances. The thermodynamic coupling refers that a flow occurs without or against its primary thermodynamic driving force, which may be a gradient of temperature or chemical potential. The modeling is based on the linear nonequilibrium thermodynamics approach and phenomenological equations by assuming that the system is in the vicinity of global equilibrium. This approach does not need detailed coupling mechanisms. The modeling equations contain the cross coefficients controlling the coupling between heat and mass flows in terms of transport coefficients and surface conditions. These coefficients need to be determined for rigorous analysis of chemical reaction systems with thermodynamically coupled transport phenomena. Some representative numerical solutions of the modeling equations are presented to display the effect of coupling on concentration and temperatures in time and space for simple exothermic catalytic reactions.

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.

scholarly journals Phase Equilibrium and Interdiffusion in Poly(Vinyl Methyl Ether)-Water System

Polymers ◽  
2020 ◽  
Vol 12 (11) ◽  
pp. 2445 ◽  
Author(s):  
Uliana V. Nikulova ◽  
Anatoly E. Chalykh
Keyword(s):  
Phase Equilibrium ◽  
Methyl Ether ◽  
Diffusion Coefficients ◽  
Water System ◽  
State Diagram ◽  
Pair Interaction ◽  
Dilute Solution ◽  
Vinyl Methyl ◽  
Vinyl Methyl Ether ◽  
Kinetics Of

The phase state diagram of the poly(vinyl methyl ether)-water system in a wide concentration range was obtained by the optical interferometry method. It was shown that this system was characterized by a complicated phase equilibrium with two lower critical solution temperatures, one of which was located in the concentrated region at 21 °C, and the other one in the region of a dilute solution at 31 °C. In the framework of the Flory–Huggins theory, pair interaction parameters were calculated for different parts of the binodal curves, and an attempt was made to reverse simulate the diagram in different conditions. It was suggested that the unusual character of the diagram was associated with the formation of a complicated complex between PVME and water in the middle region of the compositions. Concentration profiles for different temperatures were constructed. For the first time for this system, the numerical values of the diffusion coefficients of poly(vinyl methyl ether) (PVME) into water and water in PVME were obtained. Concentration and temperature dependences of diffusion coefficients were constructed and analyzed. The kinetics of water sorption in PVME was plotted, the clustering integral was calculated, and the approximate number of molecules in a water cluster was estimated. It was shown that in the dilute solution region upon passing through the binodal curve, the interphase disappeared immediately, and the remaining fluctuation of the concentration decreased in size with time. The kinetics of this process was estimated from the change in the size of such a particle.

Role of Variable Conductance on Heat and Mass Transport Mechanism Using Generalized Theory

2020 ◽  
Vol 13 (2) ◽  
Author(s):  
Imran Haider Qureshi ◽  
Ahmed Elmoasry ◽  
Jawdat Alebraheem ◽  
M. Nawaz
Keyword(s):  
Thermal Conductivity ◽  
Heat Conduction ◽  
Chemical Reaction ◽  
Diffusion Coefficients ◽  
Mass Diffusion ◽  
Memory Effects ◽  
Temperature Dependent ◽  
Newton's Law ◽  
Newton’S Law ◽  
The Impact

Abstract Fourier law of heat conduction, its analog Fick's first law, and Newton's law of viscosity are classical laws that are not capable of exhibiting memory effects. Conservation laws based on these classical laws do not give predictions about memory effects on the transport phenomena. Recently, proposed novel laws are called Cattaneo–Christov heat flux. Models are based on the generalization of classical laws of heat conduction, mass diffusion, and Newton's law of viscosity. This investigation considers this generalized theory to model the impact of relaxation phenomenon on the transport of momentum, heat, and mass in Maxwell fluid (viscoelastic fluid) of temperature-dependent viscosity and thermal conductivity in the presence of temperature-dependent mass diffusion coefficients. It is observed from the simulations that memory effects play a key role in controlling momentum, thermal and concentration boundary layer thicknesses. It is also noted that the rate of diffusion of heat and mass has shown an increasing trend when thermal conductivity and mass diffusion coefficients are increased via rise in temperature of the fluid. The generative chemical reaction on the transport of specie relative to the impact on the transport of specie when it is compared with the impact of destructive chemical reaction on the transport of specie.

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.

Concentration Oscillations During Diffusion With Slow First-Order Chemical Reaction in Aqueous Solutions of trans-Dichloro-bis(ethane-1,2-diamine)cobalt(III) Chloride, trans-[Co(en)2Cl2]Cl

1988 ◽  
Vol 41 (4) ◽  
pp. 469 ◽  
Author(s):  
DG Leaist
Keyword(s):  
Aqueous Solutions ◽  
Chemical Reaction ◽  
Diffusion Coefficients ◽  
Potassium Acetate ◽  
Potassium Sulfate ◽  
Rate Equations ◽  
Ternary Diffusion ◽  
Mixed Electrolyte ◽  
First Order ◽  
First Order Chemical Reaction

The rate equations for diffusion and chemical reaction have been solved for isothermal diffusion with the first-order reactionA → Bin stirred diaphragm cells. Provided pseudo-steady-state conditions are established in the diaphragms, the concentration differences across the diaphragm for the reactant and product are predicted to show damped oscillations in time for certain values of the solute diffusivities. Diffusion coefficients have been determined for aqueous solutions of trans-dichlorobis (ethane-1,2-diamine)cobalt(III) chloride in which the 1 : 1 salt slowly converts into a 1:2 salt through the reaction [Co(en)2Cl2]+ + Cl - → [Co(en)2Cl]2+ +2Cl- with k = 3.6×10-5 s-1 at 25°C. Supplementary ternary diffusion coefficients have been determined for aqueous solutions of potassium acetate + potassium sulfate, a ternary mixed electrolyte with ionic mobilities similar to those of the aqueous cobalt salts.

Proton-Coupled Transport of Ammonia in Aqueous Hydrochloric Acid

1985 ◽  
Vol 38 (2) ◽  
pp. 249 ◽  
Author(s):  
DG Leaist
Keyword(s):  
Diffusion Coefficient ◽  
Hydrochloric Acid ◽  
Aqueous Ammonia ◽  
Transport Coefficients ◽  
Ammonia Concentration ◽  
Ammonium Ion ◽  
Coupled Transport ◽  
Ternary Diffusion ◽  
A Value ◽  
Hydrochloric Acid Solutions

Ternary diffusion in aqueous ammonia + hydrochloric acid solutions has been measured at 25°C. It is shown that the transport coefficients can be successfully predicted from the mobilities of H+, Cl -, NH4+, and un- ionized ammonia species present in the solutions. When an ammonia concentration gradient is prepared in a solution containing excess acid, the region of the solution with the higher ammonia concentration is depleted in H+ by formation of ammonium ion: NH3+H+ ↔ NH4+. As highly mobile H+ diffuses up the ammonia gradient, there is counterflow of NH4+ in order to maintain electroneutrality . This mechanism leads to rapid diffusion of the ammonia component as NH4+. Binary diffusion coefficients of aqueous ammonia have also been measured. Extrapolation gives 2.08(�0.01) × 10-2m2 s-1 for the limiting diffusion coefficient of un-ionized ammonia, a value 6% greater than the limiting diffusion coefficient of the ammonium ion.

Coupled multi-ion electrodiffusion analysis for clay soils

2004 ◽  
Vol 41 (2) ◽  
pp. 287-298 ◽  
Author(s):  
Christian Jungnickel ◽  
David Smith ◽  
Stephen Fityus
Keyword(s):  
Diffusion Coefficients ◽  
Reactive Transport ◽  
Clayey Soil ◽  
Transport Model ◽  
Ion Pairing ◽  
Diffusion Cell ◽  
Coupled Transport ◽  
Exchange Reactions ◽  
Clay Liners ◽  
Ion Species

For a well-engineered compacted clay landfill liner, diffusive transport through the liner is the main mass transport mechanism from the landfill. Therefore, accurate estimates of diffusion coefficients for clay liners are essential for the engineering design of liner systems. A long-standing problem has been the effect of ion pairing on the estimation of diffusion coefficients for multicomponent ionic solutions migrating through clay liners. This paper considers the solution of a fully coupled set of transport equations describing the simultaneous diffusion of several ion species through a clayey soil. The analysis takes into account the diffusion coefficient for each ion species, ion pairing (as required by electroneutrality of the solution), and time-dependent first-order ion and (or) ligand exchange reactions with the clay particles. The behaviour of a double-reservoir diffusion cell, often employed for the estimation of diffusion coefficients in the laboratory, is analyzed using the coupled transport model. A detailed theoretical analysis is made of sodium fluoride transport through saturated kaolinitic clay.Key words: multi-ion diffusion, finite element analysis, reactive transport, kaolinite, double-reservoir diffusion cell.

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