Diffusion co- and counter

Abstract Infrared spectroscopic methodsfor the measurement of adsorption and adsorption kinetics of some aromatics (benzene, ethylbenzene, p-xylene), pyridine, and paraffins in solid microporous materials such as zeolites (MOR, ZSM-5, silicalite-1) are described as well as the evaluation of the spectroscopically obtained data. The adsorption isotherms are of the Langmuir-Freundlich type. Isosteric heats of adsorption, transport diffusivities, and activation energies of diffusion as deduced from the spectroscopic measurements are compared with literature data as far as available, and they are found to be in reasonable agreement with results provided by independent techniques. Special attention is paid to sorption and sorption kinetics of binary mixtures, especially the problems of co- and counter-diffusion. ... 

Infrared "Macro"- and "Mkro"-Spectroscopic Investigations of Adsorption, Desorption, Diffusion, and Co- and Counter-Diffusion in Zeolites... 

In Fig. 8, a set of uptake curves for ethylbenzene adsorbed and desorbed at various temperatures after various partial pressure changes has already been shown. The diffusivities of benzene and p-xylene derived from IR measurements in the same way as described for ethylbenzene are collected in Tables 3 and 4. Table 3 includes data for single-component diffusion as well as for co-and counter-diffusion (see Sect. 2.2.4.1)... 

Experiments devoted to the phenomena of co- and counter-diffusion using the micro-FTIR technique were basically performed in the same way as... 

Terada et al. (2007) used a multipopulation model to compare co- and counter-diffusion biofilms for autotrophic nitrogen removal, which is a process that depends on coexistence between aerobic and anaerobic ammonia-oxidizers. They showed that the counter-diffusion biofilm outperformed the co-diffusion biofilm for biofilm thicknesses between 450 and 1400 pm. The counter-diffusion biofilm had a wider application range and was expected to work better for applications with fluctuations in loading rates. 

Chimie, C.R. (2005) Infrared spectroscopic investigation of diffusion, co-diffusion and counter-diffusion of hydrocarbon molecules in zeolites. Elsevier, Comptes Rendus Chimie, 8, 303-319. 

The FTIR technique has proven to be a powerful method for investigating adsorption, desorption, and diffusion of single components or binary mixtures in microporous solids such as zeolites. In the latter case of mixtures, the phenomena of codiffusion and counter-diffusion became accessible to measurement, which was not possible with methods of investigation based on changes of weight, volume, or pressure. Even with the powerful and most important NMR techniques (see Chap. 3 of the present volume), the study of multicomponent (e.g., H2-D2) self-diffusion rather than co- and counterdiffusion experiments is possible (see Sect. 1 and [6]). The only prerequisite for the IR method is that the IR spectra, which are contributed by the components of the mixture, can be sufficiently decomposed. This, however, was easily achieved for all systems studied so far, owing to appropriate computer programs nowadays available. Certainly, the computational methods... 

Syron, E., Kelly, H. and Casey, E. 2009. Studies on the effect of concentration of a self-inhibitory substrate on biofllm reaction rate under co-diffusion and counter-diffusion configurations. Journal of Membrane Science, 335,76-82. 

Terada, A., Lackner, S.,Tsuneda, S. and Smets, B. F. 2007. Redox-stratification controlled biofilm (ReSCoBi) for completely autotrophic nitrogen removal The effect of CO- versus counter-diffusion on reactor performance. Biotechnology and Bioengineering, 97,40-51. 

The evaluation of the f i parameters can be performed by relating these coefficients to the self-diffusion coefficient of co- and counter-ions in a polyelectrolyte solution. 

In fact, instead of looking at the polyion motion referred to its environment it is possible to imagine the converse situation of self-diffusion of co- and counter-ions where the ionic atmosphere is at motion and the polyion is kept stationary. The electrical forces experienced in the two processes are identical. This argument is easily confirmed making use of Equation (9) and writing into the alternative form... 

Figure 7.47 Inclusion of iodine vapour into the THF inclusion compound of 7.65. (a) initial state, (b0 early stage with only the ends of he crystal stained by iodine and (c) final state with channels fully occupied. The inclusion of iodine from both ends implies counter-diffusion of thf and I2. (Copyright Wiley VCH Verlag GmbH Co. Reproduced by permission).

Figure 11.7 Comparison of co-current and counter-current porous membrane reactors for decomposition of ammonia with a hydrogen permselectivity determined by Knudsen diffusion at 627 C [Collins ct al., 19931...

Examples of accompanying chemical reactions influencing film and intraparticle diffusion rate control is afforded by instances where a counter-ion can react with the functional group or with the co-ion, for example ... 

Fig. Ill-13. The change in the concentration of co-ions, +, counter-ions, ri, and the total ion concentration, n = ri +n, in the diffuse part of the EDL...

In an aqueous medium, proteins and solid surfaces are usually charged. In both systems the charge is neutralized by counter- and co-ions, that are partly physically bound and partly diffusely distributed. The charge distribution in and around a protein molecule and at a sorbent surface is schematically represented in Figure 3. 

The Co " " ions then diffuse inward to the scale-alloy interface. In this mechanism the rate is controlled by the counter fluxes of Co " " and Co " " ions ... 

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