Accelerating diffusion with mixed solvents

Abstract

The experiments reported here show how diffusion rates in liquids can be increased by as much as an order of magnitude by use of coupled dBusion fluxes in mixed solvents. Solutes whose diffusion can be accelerated in this way include simple electrolytes, essential oils, dyes, and antibiotics. These increases are primarily caused by thermodynamic interactions and can be estimated from solubilities. E. L. CUSSLER and M. M. BREUERUnilever Resemch Isleworth, Middlesex, England SCOPEThis study aims at sharply increasing diffusion rates in liquids by means of coupled diffusion fluxes. Such increases are important because diffusion in liquids is slow and is often the rate-limiting step of an industrial process. Coupled diffusion fluxes occur when the flux of a solute is altered by the concentration gradient of a second solute. For example, the flux of sodium acetate in aqueous solution can be increased nine times by a gradient of acetone.The feature of this work which distinguishes it from past studies is the large magnitude of the coupled diffusion effects observed. These effects are well understood: most of the theoretical work is over ten years old (1, 2) and the experimental observations go back at least to 1892 (3). But past physical chemical studies have concentrated on the accurate experimental verification of the Onsager reciprocal relations and hence required an emphasis on experimental detail (4). Strongly coupled diffusion fluxes are observed in biological systems, but the interpretation of experimental results in these cases is hindered by the inexact knowledge of the chemical composition of the systems used (5). Engineering studies of coupled diffusion have focused on estimation methods which can avoid the tedious experiments characteristic of exact analysis (6-7).In contrast, this work is not interested in accurately studying small effects but aims at approximately predicting and experimentally discovering greatly accelerated diffusion rates. CONCLUSIONS AND SIGNIFICANCEThere are three conclusions from these experiments:1. The diffusion of simple electrolytes can be accelerated by an order of magnitude by means of coupled fluxes in mixed solvents.2. These increased diffusion rates are primarily caused by thermodynamic interactions and can be estimated from solubilities.3. The diffusion of dyes, antibiotics, and essential oils can also be accelerated several hundred percent, but the increases are generally less than those observed for simple electrolytes. While the experiments reported here all involve increases in diffusion rates, parallel experiments could also achieve decreases in these rates.The accelerated diffusion rates reported here offer a means by which the rate of almost any mass transfer process can be increased. In practice, these increases will be useful if the industrial situation fulfills three requirements:1.. the process is diffusion limited; 2. it involves small amounts of valuable materials; and 3. it is restricted to short process times.Such processes occur most commonly in the photogra...

Development Of ABEC Column For Separation Of Tc-99 From Northstar Dissolved Target Solution

“…This higher value is caused by an accelerated diffusion effect, where diffusion is increased by coupled diffusion fluxes due to a higher concentration gradient of other solutes and a higher concentration of K + . 14,15 The D p for Tc in Solution B measured in those experiments is lower than that measured with the 2 cc ABEC cartridge (Figure 10). The Tc Langmuir "a" values were estimated from the breakthrough data in Figures 11 and 12 using Eq.…”

“…Coupled diffusion fluxes occur when the flux of the solute is altered by the concentration gradient of other solutes. 14,15 In addition, the increased diffusivity may be caused by a higher concentration/activity of K + , which coextracts with TcO 4 -. Therefore, it is assumed that in solution A, Tc D p = D b = 2.0 × 10 -3 cm 2 /min.…”

“…This effect is expected due to accelerated diffusion caused by the concentration gradient of other solutes and the higher concentration/activity of K + . [14][15] Breakthrough curves were obtained from Omnifit columns packed with ABEC sorbent using the AKTA system. Solution B containing either 0.00386 mM Tc-99 or 0.00215 mM Tc-99 was loaded on a column with 0.66 cm ID x 0.4 cm length or 0.66 cm ID x 0.8 cm length, respectively, and tests were run at 10 mL/min and RT.…”

An optimal control framework to determine diffusivity versus concentration surfaces in ternary systems of two gases and a non volatile phase

“…However, if acetone is added to the left side of the tank, the rate of diffusion of sodium sulfate is decreased, and, if acetone is added on both sides of the porous membrane, the diffusion of sodium sulfate is increased slightly. This shows that the gradient of acetone strongly influences the diffusion of sodium sulfate (E. L. Cussler & Breuer, 1972).…”

Enhanced protein diffusion in a solvent gradient

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