Diffiisivity molecular

An alternate method for gas diffiisivity of binary gas mixtures at low pressures is the method of Hirschfelder et al. The method requires several molecular parameters and, when evaluated, gives an average absolute error of about 10 percent. The method is discussed in detail in the Data Vrediction Manual. 

Ctf/D = ratio of therm diffiisivity to molecular diffiisivity, dimensionless... 

Effects of isotopic mass on molecular and atomic velocities and diffiisivity... 

Saffman, P. G. (1960). On the effect of molecular diffiisivity in turbulent diffusion. J. Fluid Mech. 8, 273-283. 

Phenols are organic acids. Their dissociation in water is very fast, that is, for most processes we can consider the acid-base equilibrium as an instantaneous equilibrium. The question arises whether the dissociation influences the air-water exchange velocity, and if yes, under which conditions. Before going into much detail you try to get a first approximate answer based on the information which you have at hand for the two compounds, 2-nitrophenols and 4-nitrophenols. Specifically, you want to answer the question whether for these two substances air-water exchange is affected by dissociation at pH =7. Use u10 = lm s-1 and the usual approximations for the molecular diffiisivities. Would your answer be modified for pH=9.5 ... 

Numerous other models have been proposed to explain the deviation of dry oxidation from linear-parabolic kinetics. For example, field-assisted oxidant diffiision during the oxidation of metals was proposed by Cabrera and Mott (75) and used by Deal and Grove (69) to explain the results for thin oxides. Ghez and van der Meulen (76) proposed the dissociation of molecular oxygen into atomic oxygen at the Si-Si02 interface and the re-... 

DP = pore mass molecular diffiisivity, T = fluid temperature, K... 

The effective diffiisivities of DCB in SC C02 for these runs are optimized to De = 4 10 9 m /s. The corresponding tortuosity factors amount to Dm/Dc = 2.3 and 2.5 when estimating the molecular diffusivity by means of the correlation of [10]. These values are in reasonable agreement with respect to those found in the literature. For example in a related study of... 

Copper ions exchanged microporous molecular sieves, in particular Cu-ZSM-5, are active catalysts for the selective catalytic reduction of NO and N2O with hydrocarbons in the presence of O2 (HC-SCR). It has been reported that the catalytic activity may be controlled by intra-crystalline diffiisivity and by geometry-limited diffusion depending on the hydrocarbon molecular size and the zeolite pore size [1]. Therefore, it is of interest to prepare Cu-Al-MCM-41 mesoporous molecular sieves and to compare their activity with that of Cu-ZSM-5. 

Most of the microscopic techniques are restricted to relatively small and rapidly diffusing species since a measurable mean molecular displacement must be achieved within a short time. In general the microscopic techniques show reasonable consistency with other micro techniques but, as the length scale of the measurement increases, the apparent diffiisivities decrease and show increasing discrepancies between different techniques. 

The MSC membranes are produced by carbonization of PAN, polymide, and phenolic resins. They contain nanopores, which allow some of the molecules of a feed gas mixture to enter the pore structure at the high pressure side, adsorb, and then diffiise to the low pressure side of the membrane, while excluding the other molecules of the feed gas. Thus, separation is based on the difference in the molecular sizes of the feed gas components. The smaller molecules preferentially diffuse through the MSC membrane as shown by Table 4 [16,17]. 

To confinn the silicalite pore fitting predictions above, diffiision simulations was carried out using the Solids Diffiision module in the Acceirys Insight II Molecular Modeling package. (Acceirys is a wholly owned subsidiary of Pharmacopeia Inc., headquartered in San Diego, CA.)... 

Table 1. Energetics and Predictions from Modeling Molecular Diffiision in Silicalite.

Figure 5. Contribution of Surtace Diffiisivity to Molecular Diffiisivity...

Adsorption equilibrium and adsorption dynamics on MSC were evaluated for each organics in supercritical CO2 fluid mixed with adsorbate by chromatographic measurement. The dependencies of adsorption equilibrium constants, K, and micropore diffiisivity, D, of toluene, benzene and m-xylene, on molarity of toluene with each parameters of temperature or pressure were obtained. It was found that the values of K and D for an organic substance depended on the amount adsorbed of other organics strongly. The state of the molecule could be observed by the molecular simulation. As for the amount adsorbed, the simulation is small, in comparison with the experiment. 

It has been demonstrated that the combined application of various NMR techniques for observing molecular rotations and migrations on different time scales can contribute to a deeper understanding of the elementary steps of molecular diffusion in zeolite catalysts. The NMR results (self-diffusion coefficients, anisotropic diffiisivities, jump lengths, and residence times) can be correlated with corresponding neutron scattering data and sorption kinetics as well as molecular dynamics calculations, thus giving a comprehensive picture of molecular motions in porous solids. 

In addition, a complete model will also take into account the molecular diffiision through the (stagnant) porous stainless steel support. 

The basic objective of the theoretical analyses is to obtain the effective rate constant for bimolecular reaction between rodlike polymers when the reaction is limited by slow diffusion, in terms of the polymer diffiisivities. The latter are dependent on the concentration and polymer length, and consequently the rate constant is obtained as a function of these variables. This is then useful for predicting the time evolution of the molecular weight distribution using a population balance analysis [48-50]. 

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