Diffusivity of Organics

For slow diffusion of organic ions, one of the most suitable methods for the determination of quasi-diffusion in the grain is the use of the calculation of mean sorption time t [108]... 

The application of the above methods of calculation has shown that the quasi-diffusion of organic counterions is profundly affected by both the amount of the crosslinking agent in a crosslinked polyelectrolyte and the method of formation of the crosslinked structure [109-112]. Fig. 28 shows the dependence of diffusion coefficients for streptomycin ions on the amount of the crosslinking... 

Table 15, Quasi-diffusion of organic ions in ma-croporous (KU-23) and gel (SDV-T) sulfonated cation exchangers...

Table 16. Coefficients of quasi-diffusion of organic ions in a CS-KU-23 composite in comparison with the corresponding values for KU-23 micrograins...

The Wilke-Chang equation gives satisfactory predictions for the diffusivity of organic compounds in water but not for water in organic solvents. 

RJ Kokes, FA Long. Diffusion of organic vapors into polyvinyl acetate. J Am Chem Soc 75 6142-6149, 1953. 

Whereas batch equilibrium tests are designed to study equilibrium sorption of solid phase particles with various pollutants, singly or in combination with other pollutants, solid phase column-leaching tests study both sorption and diffusion of organic pollutants through the subsurface environment [10,11,127, 141,142]. 

Saleem, M. Asfour, A.A. De Kee, D. 1989, Diffusion of organic penetrants through low density polyethylene (LDPE) films Effect of size and shape of the penetrant molecules. J. Appl. Polym. Sci. 37 617-625. 

Very few experimentally determined diffusivities of organic substances in water are available in the documented literature. If experimentally determined diffusivity values are not available, Hayduk and Laudie (1974) recommend the following equation for estimating this parameter ... 

The thermal movement of molecules often serves as a prototype of random motion. In fact, molecular diffusion is the result of the random walk of atoms and molecules through gaseous, liquid, solid, or mixed media. This section deals with molecular diffusion of organic substances in gases (particularly air) and in aqueous solutions. Diffusion in porous media (i.e., mixes of gases or liquids with solids) and in other media will be discussed in the following section. 

The peculiar way in which the result on the far right-hand side of Eq. 18-43 is expressed makes it easier to understand the semiempirical relation proposed by Fuller et al. (1966) for the diffusivities of organic molecules in air ... 

Flynn, J. H., A collection of kinetic data for the diffusion of organic compounds in polyolefins , Polymer, 23, 1325-1344 (1982). 

Figure 2.16 Pressure permeation (reverse osmosis) of iso-octane and methyl ethyl ketone through crosslinked 265-p.m-thick natural rubber membranes. The change in the concentration gradient in the membrane as the applied pressure is increased is illustrated by the inserts. At high applied pressures, the concentration gradient and the permeation fluxes approach their limiting values [4]. Reprinted from Pressure-induced Diffusion of Organic Liquids Through Highly Swollen Polymer Membranes, D.R. Paul and O.M. Ebra-Lima, J. Appl. Polym. Sci. 14, 2201 Copyright 1970. This material is used by permission of John Wiley Sons, Inc.

D.R. Paul and O.M. Ebra-Lima, Pressure-induced Diffusion of Organic Liquids Through Highly Swollen Polymer Membranes, J. Appl. Polym. Sci. 14, 2201 (1970). 

Part VI encompasses descriptions of strong molecule-surface interactions (organics on silicon) and molecule-molecule interactions (molecules on metals). In particular, the chapter by J. V. Barth focuses on cooperative effects and the diffusivity of organic molecules on various metal surfaces. G. P. Lopinski and D. D. M. Wayner deal with functionalizing molecular interaction on Silicon surfaces. Finally, J. Reimers and coworkers describe the self-assembly of organic molecules on Silicon, mostly from a chemistry point of view. 

After that, neutralised waters are subjected to biochemical purification. The mechanism of biochemical purification can be conventionally divided into three stages 1) the movement of organic material in the liquid to the surface of the microbe cell 2) the diffusion of organic material through semipermeable membranes with the help of carrier molecules, or special coferments 3) the metabolism of diffused products. The third stage in the microbe cell consists of two simultaneous and interconnected processes the oxidation of organic substances and the synthesis of cytoplasm, i.e. bacterial cell. 

This model approach, which produces curves much like those in Fig. 4.5, is applicable to the intraparticle diffusion of organic adsorptives in natural colloids that are approximately spherical.40 It can be coupled to an appropriate adsorption... 

In the last two decades Vrentas, Duda and their co-workers have published a substantial number of papers (61-67) on the free-volume model of diffusion in polymer-solvent systems they developed in the late 70 s (68-72). This model, which is often cited and used in the literature, underwent a number of modifications over the years and appears to apply well to the diffusion of organic solvents in rubbery and glassy polymers. 

Berens, A.R., and Hopfenberg, H.B., 1982, Diffusion of organic vapors at low concentrations in glassy PVC, polystyrene and PMM A. Journal of Membrane Science 10,283-303. 

In the natural environment, the diffusion of organic chemicals can be retarded by sorption to soil and sediment grains. To account for this process, Eq. (70) is modified to consider the accumulation of mass in the sorbed phase ... 

Fuiita H, "Diffusion of Organic Vapours in Polymers above the Glass Temperature", in "Diffusion in Polymers" (see Gen Ref) (1968), Chap. 3, pp 75-106. 

These diffusion limitations are particularly pronounced with HMORIO (Si/Al ratio of 10) catalysts, which can be explained by the quasi absence of mesopores (26, 27). With the other samples and especially with HMOR90, mesopores created by dealumination allow a quasi tridimensional diffusion of organic molecules in the pore system, decreasing or suppressing diffusion limitations. These diffusion limitations are also responsible for the abnormally low value of TOF per protonic site found with HMORIO catalysts for hydrodealkylation and for disproportionation, i.e. for the other primary reactions involving acid catalytic sites. 

Finally, the rate of response of a coated sensor is temperature dependent. When measurements are made under conditions of equilibrium between free and sorbed analyte, changes in kinetics present no problem unless the response becomes too slow for a chosen application. In some cases, however, the rate of response can be used to identify the species being detected an example is the molecular size-dependent diffusion of organic solvents into some polymer films [35]. In this case, failure to accurately measure and/or control temperature could lead to misidentification of the analyte. 

The creation of a secondary porosity can significantly decrease the toxicity of coke molecules. This has been shown for the transformation of methanol into short-chdn alkenes over HMOR catalysts i.e. the toxicity of coke molecules is more than 10 times lower in dealuminated samples, as mesopores created by dealumination allow a quasi-tridirectional diffusion of organic molecules [23]. This positive effect of mesopores was also observed in liquid phase alkylation of toluene with 1-heptene [42]. 

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