Diffusion Coefficient of Organics

Several other empirical relations for diffusion coefficients have been suggested Olson and Walton (01) have devised a means for estimating diffusion coefficients of organic liquids in water solution from surface-tension measurements. Hill (H5) has proposed a method based on Andrade s theory of liquids which allows for the concentration dependence of the diffusion coefficient in a binary liquid mixture. The formula of Arnold (A2, T6, p. 102) does not seem generally useful inasmuch as it contains two constants ( abnormality factors ) characteristic of the solute and of the solvent. 

For B = A, the tracer diffusion coefficient equals the self-diffusion coefficient, D lba= Dla- 1° Table 6-6 the self-diffusion coefficient of water and some diffusion coefficients of organic solutes in water at infinite dilution calculated with Eq. (6-31) are compared with experimental values (Reid et al., 1987). The experimental value for sucrose is from Cussler (1997). 

Thble 9-7 Diffusion coefficients of organic compounds in LDPE and partition coefficients between LDPE und methanol or ethanol( ) at 23 °C. 

Figure 9-8 Diffusion coefficients of organic compounds in LDPE depending on their relative molecular mass, Mr. C-6 to C-24 are hexane to tetracosan 1 undecalactone, 2 phenylethyl alcohol. 3 isoamyl acetate. 4 diphenyl methane, 5 diphenyl ether, A 7-OH to 18-OH are alcohols (heptanol to 1-octadecanol).

The data available on the molecular diffusion coefficient of organic vapors in air are meager, but they indicate (in accordance with approximate theory) an inverse proportionality to the square root of molecular weight. The rate of mass transfer by molecular diffusion will be proportional to the diffusion coefficient and to the SVC, itself proportional to vapor pressure times molecular weight (M). We should expect, therefore, under standard conditions of ventilation, that the rate of loss will be proportional to vapor pressure X The ratio of observed rate to... 

Hilal SH, Karickhoff SW, Carreira LA. Prediction of the vapor pressure boiling point, heat of vaporization and diffusion coefficient of organic compounds. QSAR Combin Sci 2003 22 565-74. 

Diffusion coefficients of organic solvents in supercritical CO2 are typically one to two times higher than in conventional organic solvents. 

Thus we have two models represented by Equations 4.81 and 4.82 for the film and penetration theories, respectively, to choose from. In making a choice, note that one is often concerned with the ratio of diffusivities of the two reactants of a two-phase system (see Chapter 14), and not the diffusivity of just one diffusing component. Because the diffusion coefficients of organic compounds in many of the solvents normally used do not greatly differ from one another, the difference... 

Biotechnological processes, such as pulping, are best carried out at elevated temperatures. The increase in temperature has a significant influence on the bioavailability and solubility of organic compounds, and is accompanied by a decrease in viscosity and an increase in the diffusion coefficient of organic compounds. Consequently, higher reaction rates due to smaller boundary layers are expected. The bioavailability of insoluble environmental pollutants can also be improved dramatically at elevated temperatures allowing efficient bioremediation (37). 

PGSE methods were introduced in 1965 by Stejskal and Tanner and, since then, have been widely used. In the 1970s this approach was used to determine diffusion coefficients of organic molecules. In the following decade, variants of the technique were applied to problems in polymer chemistry. "" Since then, diffusion data on dendrimers " and peptides, " as well as on molecules in various environments, e.g., in porous silica and zeolites,have been obtained. Recent applications of PGSE methods in coordination and/or organometallic chemistry have emerged. ... 

Klask, U. (1998) Diffusion coefficients in fluids — Determination of binary diffusion coefficients of organic substances in supercritical cEirbon dioxide with the Taylor dispersion method (in German), Doctoral dissertation. University of Bochum, Germany published 1999 by Shaker, Aachen. 

Since a very large variety of chemicals exist for which knowledge of permeation rates might become relevant, it would be helpful to have a theoretical method for a systematic estimation of the relevant parameters. Partition coefficients and diffusion coefficients of organic compounds in... 

The determination of R (see Eq. 7.25) by a measurement of the partition coefficient k in the laboratory, by some type of sorption experiment for the determination of adsorbed solid-phase concentration versus solution-phase concentration in equilibrium (so-called isopleths or isotherm), however, supplies values of R which are not comparable with the actual in field retardation factors in a mineral liner, because the specific surface susceptible to the pollutant is very different in both cases. Therefore, based on diffusion coefBcients in free aqueous solutions, the effective diffusion coefficients of organic substances for water-saturated mineral liners were estimated by using a tortuosity factor F= 1/3 (Muller et al. 1997a). Table 7.6 shows the results for various soil materials. 

Table 7.6. Diffusion coefficients of organic substances at 20 °C in dilute aqueous solution and effective diffusion coefficient in soil water of mineral liners calculated with r= 1/3 and diffusion coefficient in the HOPE geomembrane at a small concentration. The units for the diffusion coefficient should be considered (Muller etal. 1997a)...

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