Zeolite multicomponent

In order to design a zeoHte membrane-based process a good model description of the multicomponent mass transport properties is required. Moreover, this will reduce the amount of practical work required in the development of zeolite membranes and MRs. Concerning intracrystaUine mass transport, a decent continuum approach is available within a Maxwell-Stefan framework for mass transport [98-100]. The well-defined geometry of zeoHtes, however, gives rise to microscopic effects, like specific adsorption sites and nonisotropic diffusion, which become manifested at the macroscale. It remains challenging to incorporate these microscopic effects into a generalized model and to obtain an accurate multicomponent prediction of a real membrane. 

Pure and multicomponent adsorption equilibrium of carbon dioxide, ethylene, and propane on ZSM-5 zeolites with different Si/Al ratios. 

Zeolite catalysts in many forms are used for important commercial processes. The studies were extended to L zeolites, mordenite, erionite, and dealuminated faujasites and mordenites. More attention is paid now to zeolites with univalent and multivalent cations and to multicomponent catalysts. Among these some important examples are the tellurium-containing catalyst for hydrocarbon dehydrocyclization (42), the difunctional Ni- and Pd-zeolite catalysts for benzene hydrodimerization to phenylcyclohexane (42), the catalyst for the hydrogenation of phenol cyclohexanol (44), the 4% Ni/NaY which forms butanol, 2-ethylhexanol, 2-ethylhexanal, and 2-ethylhexanol from a mixture of n-butyraldehyde and hydrogen. 

In this paper we report experimental and theoretical results on the sorption of methane and krypton on 5A zeolite. The sorption of methane in the 5A cavity is reported to be non-localized (9.), whereas that of krypton is localized at a cavity site and window site (10). The multicomponent form of the isotherm of Schirmer et al. is used to interpret the experimental data and to predict mixture equilibria at other concentrations. 

Pure component loadings for CO2, N2 and O2 on commercial pelleted forms of Linde type 4A, 5A and 13X molecular sieve zeolites were derived from various gravimetric and volumetric measurements. The range of pressures and temperatures over which these measurements were made were at least as broad as those encountered in the breakthrough experiments described here, to permit accurate estimations of heats of adsorption in the manner described by equation (6) above. As mentioned above, the pure component data were correlated to the LRC model, and the CO2 loadings predicted by the multicomponent LRC model compared to actual loadings in the breakthrough runs at bed saturation. 

Ideally, the active sites should all be identical, and isolated from each other. This is seldom the case, because industrial heterogeneous catalysts are often amorphous, multicomponent and multiphase solids, containing many types of active sites. Nevertheless, there is one important exception zeolites. These highly crystalline materials can be synthesized to exacting specifications, including the setup ofidentical active sites at uniform distances. As we shall see, this is one of the key advantages of zeolites, which are the preferred catalysts today for many industrial processes. 

However, during the crystallization of zeolites and related materials, complex multicomponent mixtures, e.g. of silica, alumina, mineralizers, water and organic templates, are hydrothermally... 

Figure 1 shows the result for gas phase conversion of an equimolar heptane - nonane mixture over PtAJSY type zeolite catalyst CBV720 (Si/Al = 13, Zeolyst), and demonstrates it is indispensable to use appropriate expressions for the multicomponent adsorption equilibria. For vapor phase conditions resulting in significant pore filling, the Langmuir + interaction model is appropriate. 

TIME RESOLVED MULTICOMPONENT SORPTION OF LINEAR AND BRANCHED ALKANE ISOMERS ON ZEOLITES, USING NIR SPECTROSCOPY... 

Li J.-M. and Talu O., Effect of structural heto-ogeneity on multicomponent adsorption benzene and p-xylene mixture on silicalite, in M. Suzuki (ed.) Proc. IV Int. Corf, on Fundamentals of Adsorption, (Elsevio", Amsto dam, 1993) pp. 373-380. Meininghaus C. K.W. and Prins R., Sorption of volatile organic compounds on hydrophobic zeolites, Microporous and Mesoporous Materials 35-36 (2000) pp. 349-365. 

Some authors have used the emission of adventitious carbon at a fixed value of 285.0 eV. (Some others prefer 284.4, 284.5 or 284.6 eV without real justification). This practice is not recommended because of the complexity associated with the possible differential charging of carbon impurities. Moreover it is not unusual to observe multicomponent Cjs peaks in zeolite spectra [11] and the span in binding energy expands over 8 eV in the literature. 

Important for practical implemetation of zeolitic membranes is the acquisition of permeation data of single components and mixtures and the interpretation of these data in the form of macroscopic models. These models describe the permeation flux of components as a function of partial pressure, composition and temperature. Once good models exist separation units can be designed for the separation of multicomponent mixtures. 

As have been seen above adsorption plays an important role in permeation through microporous membranes. So, single and multicomponent adsorption isotherms are required for a successful modelling of the permeation behaviour. An extensive treatment of the recent state of the art of zeolite permeation modelling is given by Van de Graaf et al. [70]. A shortened treatment follows here. 

There are several models to describe intracrystalline diffusion (step 3) in microporous media. Diffusion in zeolites is extensively described in Ref. 30. For the modeling of permeation through zeolitic membranes, such a model should take the concentration dependence of zeolitic diffusion into account. Moreover, it should be easy applicable to multicomponent systems. In Section III.C, several models will be discussed. 

Table 2 Single- and Multicomponent Diffusivities of Ethane and Ethene, Calculated Using the Maxwell-Stefan Model for Zeolitic Diffusion...

The lack of methods for a fast and reliable assessment of membrane quality is stiU one of the outstanding issues in zeolite membrane development. The usual meaning of the term quality relates to the ability of the membrane to carry out a given separation, therefore, is a system-specific property and the universal membrane quality test does not exist. In general, specific permeation measurements at different temperatures, either of single gases (or vapors) or of multicomponent mixtures in the gas or liquid (pervaporation) phase, provide extremely useful information on the effective pore structure of the membrane, on the... 

Although Knudsen diffusion, shape selectivity, and molecular sieving play an important role in the separation of mixtures, the mechanisms which control the majority of the multicomponent separations in zeolite membranes are surface diffusion, and sometimes, capillary condensation. In addition, molecular simulations and modeling of M-S diffusion in zeolites [69,70] show that the slower moving molecules are also sped up in some mixtures [71,72] in the presence of fast-diffusing molecules and other times, slower molecules inhibit diffusion of faster molecules because molecules have difficulty passing one another in zeolite pores [73]. 

Krishna R and Paschek D. Seh-diffusivities in multicomponent mixtures in zeolites. Phys Chem Chem Phys 2002 4 1891-1898. 

Dong J, Lin YS, and Liu W. Multicomponent hydrogen/hydrocarbon separation by MFI-type zeolite membranes. AIChE J 2000 46(10) 1957-1966. 

Synthesis and Photochromism of 6-Nitrospiropyran A Green Chemistry Preparation for Organic Chemistry Laboratory. Abstr. Pap.—Am. Chem. Soc. 2006, 231, CHED-283. (e) Wetter, E. Levy, I. J. Multicomponent Zeolite-Catalyzed Synthesis of p-Acetamido Ketones A Green Chemistry Laboratory Experience. Abstr. Pap.—Am. Chem. Soc. 2006, 231, CHED-272. (f) Hamel, L. J. Levy, I. J. Analyzing Green Chemistry A... 

A common practice is to develop a specific model for the adsorptive process of interest and use simplistic descriptions (models or empirical) of pure and multicomponent gas adsorption equilibria and kinetics in order to describe the effects of various operating variables to obtain an optimum design. The effort is always closely tied to experimental verification and empirical fine-tuning using actual process data from pilot plants. A comprehensive set of data on pure and multicomponent adsorption equilibria of the components of SMROG on an activated carbon and a 5A zeolite is available in published literature.73... 

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