Multi-component gas mixture

Mass transport inside the catalyst has been usually described by applying the Fick equation, by means of an effective diffusivity Deff a Based on properties of the interface and neglecting the composition effect, composite diffusivity of the multi-component gas mixture is calculated through the simplified Wilke model [13], The effect of pore-radius distribution on Knudsen diffusivity is taken into account. The effective diffusivity DeffA is given by... 

The sum of the partial pressures p, of n components in a multi-component gas mixture equals the total pressure... 

Sircar, S. (1979). Separation of multi-component gas mixtures. US Patent 4,171,206. 

In gases, the binary MS diffusivities are normally assumed independent of composition. With this approximation, the effective diffusivity of component i in a multi-component gas mixture can be derived from the Stefan-Maxwell equation to give (Treybal, 1980)... 

Diffusivities of Multi-Component Gas Mixtures in Microporous Materials. 273... 

The behaviour of a multi-component gas mixture in a microporous adsorbent is important both theoretically and practically in separation and catalytic processes. Detailed theoretical analysis of the frequency response for the diffusion of multiple adsorbates in microporous material crystals have been... 

Upstream side, where a multi-component gas mixtures (three species H2, CO, N2) is present... 

Neither procedure requires pure compound(s) thus technical products, spray formulations or multi-component pesticide mixtures may be assayed. Both techniques are as sensitive as the chemical procedure(s) used to determine the quantity of pesticide trapped (SVC technique) or lost (volatilization rate technique). In both techniques mixtures must be uniform, of sufficient thickness to attenuate any interactions with the surface and the entraining gas should be unreactive to the test chemicals. 

Porous media finds extensive application in chemical engineering. In certain cases they are simply used to increase the mass transfer rate between two distinct phases, while in certain other cases they are used to disperse the catalyst effectively. Catalytic packed beds are an integral part of any chemical production industry. Solid Oxide Fuel Cells are class of electrochemical devices where porous media finds important application. Over the years many models have been developed to study the transport processes in porous media, starting from simple Fickian approach to complex Dusty Gas Model GDGM). However, very little is done to validate the accuracy of these models under reaction conditions, especially with multi-component species mixtures. 

The most simple and still fairly reliable method to measure multi-component gas adsorption equilibria is the volumetric-chromatographic method. The basic installation for this method is sketched in Figure 1. It basically consists of a gas storage vessel of volume (Vsv) and an adsorption chamber of volume (Vac) filled with adsorbent of mass (m ) and provided with proper tubing and valves to allow gas circulation and evacuation. The gas (mixture) is first prepared in the storage vessel and then expanded to the adsorption vessel where it is partly adsorbed in the sorbent material. 

The volumes in this series deal with the change of energy which accompanies the formation of a multi-component gas, liquid, or supercritical flirid system, usually from its pure components. The process of formation is called mixing, solution or dilution. The difference between a mixing process and a solution or dilution process is that in the former case all components involved in the process are treated equivalently, while in the latter, a distinction is made between a group of components, named solutes, and another group of components, named solvents. The solvent may be a pure component (pitre solvent) or a mixture (mixed solvent). 

When oil and gas are produced simultaneously into a separator a certain amount (mass fraction) of each component (e.g. butane) will be in the vapour phase and the rest in the liquid phase. This can be described using phase diagrams (such as those described in section 4.2) which describe the behaviour of multi-component mixtures at various temperatures and pressures. However to determine how much of each component goes into the gas or liquid phase the equilibrium constants (or equilibrium vapour liquid ratios) K must be known. 

One of the earliest examples of Gibbs energy minimisation applied to a multi-component system was by White et al. (1958) who considered the chemical equilibrium in an ideal gas mixture of O, H and N with the species H, H2, HjO, N, N2, NH, NO, O, O2 and OH being present. The problem here is to find the most stable mixture of species. The Gibbs energy of the mixture was defined using Eq. (9.1) and defining the chemical potential of species i as... 

Computer simulation can also be used for relief sizing (see Annex 4). This may be the only safe alternative in cases where physical properties are non-ideal, multiple reactions occur or there are significant continuing.feed streams or external heating. It will be necessary to choose a computer simulation package which can handle multi-component mixtures comprising both volatile and permanent gas components. 

The direct hydroxylation of benzene and aromatics with a mixture of 02 and H2 have been performed by simultaneously mixing benzene, oxygen and hydrogen in the liquid phase using a very complicated system containing a multi-component catalyst, a solvent and some additives. Besides the possibility of an explosive gas reaction, these hydroxylations gave only very low yields, 0.0014—0.69% of phenol and aromatic alcohols. For example, Pd-containing titanium silicalite zeolites catalyzed... 

For safety reasons, the cycling operation is interrupted during the weekend. After an interruption, always happening at the end of a discharge phase, several cycles are necessary to join the continuous curve representative of the evolution of the behaviour of the tank. This phenomenon tends to demonstrate the importance of the kinetics of the multi-component adsorption equilibrium in the case of a complex mixture of gas. 

Multi-component hydrocarbon standards to provide accurate calibration of instruments (generally gas chromatographs) used to monitor the concentrations of a wide range of volatile organic hydrocarbon compounds (VOCs) in ambient air. These standards currently contain 30 different hydrocarbon species that are important to photochemical ozone formation, with concentrations ranging down to a few parts per billion by molar value. They are disseminated widely in the United Kingdom and the rest of Europe as calibration standards, and as test mixtures for assessment of the quality of international ambient hydrocarbon measurements (often under the auspices of the European Commission - EC). 

Equations and Solutions. The governing equations that describe a one dimensional, premixed, laminar, unbounded flame for a multi-component ideal gas mixture are (2, 3 4) ... 

The multi-component diffusivities in the gas mixture can be approximated by the modified Stefan-Maxwell equations(8,9) i.e ... 

Such questions are answered empirically all too often. A more fundamental approach is needed. In the area of gas-phase kinetics, the developments in the chemistry of large sets of elementary reactions and diffusion in multi-component mixtures in a combustion context are now finding applications in chemical engineering, as mentioned above. In the area of gas-solid reactions, the information flow will be in the opposite direction. A need exists... 

The dusty gas model (DGM) [21] is used most frequently to describe multi component transport in between the two limiting cases of Knudsen and molecular diffusion. This theory treats the porous media as one component in the gas mixture, consisting of giant molecules held fixed in space. The most important aspect of the theory is the statement that gas transport through porous media (or tubes) can be divided into three independent modes or mechanisms ... 

Especially, for AOPs it is essential to note that the absorbance A is an additive property (cf. Braun et al, 1991), with the consequence that the individual compounds of a wastewater or a gas mixture may compete for the absorption of the incident spectral radiant power. Hence, the concentrations C of any radiation absorbing species i present in water or air must be considered as well as their individual molar absorption coefficients Therefore, the Beer-Lambert law changes to Eq. 3-8, which describes the absorbance A of a multi-component mixture at a specified wavelength X. 

Experimentally measured pure-component adsorption characteristics of O2, N2, CO2, and SO2 on H-mordenite were correlated to predict the behavior of multicomponent mixture of these gases. These correlations, based upon the relationships developed by Myers and Prausnitz, were successfully substantiated experimentally. The CO2 and SO2, which are the predominantly adsorbed components, controlled the fate of the multi-component sorption. This prevailed even at the concentration levels where the pure-component data indicate comparable affinity for both the strongly and the weakly adsorbed species. Hence, indications are that adsorption may be effectively useful in exhaust gas cleanup processes. The temperature sensitivity of the pure components contributes significantly to the selectivity of the sieve for the various components, and the data obtained indicate that this also tends to favor the desired applications in pollution combat. 

The Dusty Gas Model (DGM) is one of the most suitable models to describe transport through membranes [11]. It is derived for porous materials from the generalised Maxwell-Stefan equations for mass transport in multi-component mixtures [1,2,47]. The advantage of this model is that convective motion, momentum transfer as well as drag effects are directly incorporated in the equations (see also Section 9.2.4.2 and Fig. 9.12). Although this model is fundamentally more correct than a description in terms of the classical Pick model, DGM/Maxwell-Stefan models )deld implicit transport equations which are more difficult to solve and in many cases the explicit Pick t)q>e models give an adequate approximation. For binary mixtures the DGM model can be solved explicitly and the Fickian type of equations are obtained. Surface diffusion is... 

Fig. 6.25. Yield of CO2 as a function of catalyst temperature in the oxidation of trimethylamine over single- and multi-component noble metal catalysts. (A) 2 atm.% Ir/La203 ( ) 2 atm.% Pt/Sn02 ( ) 2 atm.% Au/Fe203 (O) 2 atm.% Au/Fe203-2 atm.% Ir/La203 ( ) mechanical mixture of 2wt% Pt/Sn02 and 2wt% Ir/La203 reactant gas, trimethylamine 100ppm in air SV = 10, OOOmlgJ t (adapted from [516])...

Redox non-innocent ligands have also been employed in other kinds of processes. For example, a nickel-based system has been used in the purification of ethene gas streams [41]. The two forms (reduced and oxidized) of the dithiolene complex have different affinities for olefin, leading to separation of ethene from gas mixtures (Scheme 14). Intermediate 47 is obtained after electrochemical oxidation of the anionic nickel complex 46. The oxidized complex 47 reacts selectively with ethylene to form the adduct 48, thus the non-olefinic contamination of the multi-component stream... 

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