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Intraparticle applications

Application of the Balzhinimaev model requires assumptions about the reactor and its operation so that the necessary heat and material balances can be constructed and the initial and boundary conditions formulated. Intraparticle dynamics are usually neglected by introducing a mean effectiveness factor however, transport between the particle and the gas phase is considered. This means that two heat balances are required. A material balance is needed for each reactive species (S02, 02) and the product (SO3), but only in the gas phase. Kinetic expressions for the Balzhinimaev model are given in Table IV. [Pg.216]

Cocurrent depressurization, purge, and pressure-equalization steps are normally added to increase efficiency of separation and recovery of product. At the end of the adsorption step, the more weakly adsorbed species have been recovered as product, but there is still a significant amount held up in the bed in the inter- and intraparticle void spaces. A cocurrent depressurization step can be added before the blowdown step, which is countercurrent to adsorption. This increases the amount of product produced each cycle. In some applications, the purity of the more strongly adsorbed components has also been shown to be heavily dependent on the cocurrent depressurization step [Cen and Yang, Ina. Eng. Chem. Fundam., 25, 758-767 (1986)]. This cocurrent blowdown is optional because there is always a countercurrent one. Skarstrom developed criteria to determine when the use of both is justified [Skarstrom in Li, Recent Developments in Separation Science, vol. II, CRC Press, Boca Raton, pp. 95-106 (1975)]. [Pg.51]

A pore size distribution was not available for the coconut-shell carbon, but, again according to the manufacturer, approximately 55% of the intraparticle volume of the coal-base carbon was comprised of diameters between 15 and 20 A. (20). The coal-base carbon was designed primarily for adsorption from solution, while the coconut-shell carbon was intended primarily for application in gaseous systems (6). [Pg.121]

Physical Properties. Physical properties of importance include particle size, density, volume fraction of intraparticle and extraparticle voids when packed into adsorbent beds, strength, attrition resistance, and dustiness. These properties can be varied intentionally to tailor adsorbents to specific applications. See also Adsorption Liquid Separation and Molecular Sieves. [Pg.40]

The desorptive process may be analyzed before boiling. The key assumption is that the vapor and adsorbed phases are in equilibrium in the bulk of the bed. This assumption eliminates intraparticle resistances from further consideration and is reasonable for rotary kiln applications. The two remaining resistances are associated with hydrocarbon diffusion out of the bed and with convection from the bed surface to the bulk gases. The flux of species Al from the desorbing bed becomes... [Pg.50]

FCC catalyst development to reduce the effect of vanadium has been aimed at reduction of vanadium mobility the application of special ingredients in the catalyst which function as metal scavengers or metal catchers. In the past (2, 10) transport experiments were used to show that during steam-aging, intraparticle transfer of vanadium occurs and that migrating vanadium can be irreversibly sorbed by a metal trap such as sepiolite (2) in the form of a heat stable vanadate. [Pg.335]

An extension of this one-dimensional heterogeneous model is to consider intraparticle diffusion and temperature gradients, for which the lumped equations for the solid are replaced by second-order diffu-sion/conduction differential equations. Effectiveness factors can be used as applicable and discussed in previous parts of this section and in Sec. 7 of this Handbook (see also Froment and Bischoff, Chemical Reactor Analysis and Design, Wiley, 1990). [Pg.32]

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... [Pg.170]

We can now summarize where slurry reactors are an attractive option in heterogeneous catalytic processes. For any application where a liquid is present and which benefits from small catalyst particles below 200 pm, for example because intraparticle diffusion limitation has to be avoided (see below), the slurry reactor is attractive, provided pressure drops in the order of one to several bars are acceptable. [Pg.470]

Since electroosmotic flow can exist in both the interparticle and intraparticle spaces, numerous studies have focused on the existence of intraparticle flow in CEC. Several groups have investigated the existence of electroosmotic flow in wide-pore materials [41-44], A model was developed to estimate the extent of perfusive flow in CEC packed with macroporous particles [41] by employing the Rice and Whitehead relationship. Results showed the presence of intraparticle EOF in large-pore packings (> 1000 A) at buffer concentrations as low as 1.0 mM. Additional parameters had been investigated [43,44] to control intraparticle flow by the application of pressure to electro-driven flow. Enhancement in mass transfer processes was obtained at low pore flow velocities under the application of pressure. The authors pointed out that macroporous particles could be used as an alternative to very small particles, as smaller particles were difficult to pack uniformly into capillary columns. [Pg.147]

For slowly diffusing solutes, a significant improvement in the separation efficiency can be expected when a high intraparticle EOF is created. At low pore-to-interstitial flow ratio this may be accomplished by, e.g., the application of a high electrical field strength. [Pg.207]

The methods outlined by Satterfield94 for taking into account the effects of intraparticle mass- and heat-transfer resistances on the effective reaction rate are applicable to three-phase reactors and, therefore, they will not be repeated here. The importance of these resistances depends upon the nature of the reaction and... [Pg.8]

The destabilization of colloids through the addition of counterions should be done in conjunction with the application of the complete coagulation process. Four methods are used to bring about this process double-layer compression, charge neutralization, entrapment in a precipitate, and intraparticle bridging. [Pg.563]

The purpose of this review is to discuss IE kinetics in selected systems using the kinetic model developed in this author s research [26-27,45-50]. It is an attempt to demonstrate, in particular, that phenomenological regularities and criteria describing intraparticle diffusion kinetics for conventional ion exchange are not applicable for the selective ion-exchange systems. [Pg.151]

In selective systems application of the Helfferich-Tunitsky criterion [2,5,16,22,23] may result in erroneous estimates of the contribution of film and intraparticle diffusion. This is because the ion diffiisivities in the resin phase that are included in this criterion can undergo very abrupt changes in magnitude with the reversal of exchange direction. This was not taken into account by Helfferich and Tunitsky in the theoretical expressions as they used them for conventional IE. Moreover the criterion neither includes the influence of the equilibrium parameters characterizing the selectivity in the resin phase nor is there any account for co-ion invasion. The effective diffusivity of the kinetic process may be quite different if these fectors are taken into consideration. [Pg.192]

Investigation 10 was a study of fixed-bed reactor models and their application to the data of Hettinger et al. (1955) on catalytic reforming of C7 hydrocarbons. The heuristic posterior density function p 6 Y) proposed by Stewart (1987) was used to estimate the rate and equilibrium parameters of various reaction schemes, two of which were reported in the article. The data were analyzed with and without models for the intraparticle and boundary-layer transport. The detailed transport model led to a two-dimensional differential-algebraic equation system, which was solved via finite-element discretization in the reactor radial coordinate and... [Pg.164]

For more complex reactions, the effect of intraparticle diffusion resistance on rate, selectivity, and yield depends on the particulars of the network. Also, the use of the Thiele modulus-effectiveness factor relationships is not as easily applicable, and numerical solution of the diffusion-reaction equations may be required. [Pg.22]

In order to evaluate the utility of the removal model for additional metals, additional removal studies were conducted using Chromium and Cobalt in place of copper. Chromium removal was studied using solutions made by dissolving CrO, in dilute H2SO4 to produce solutions with chromium concentrations of 80 ppm. The oxidation state of the chromium in the resulting solutions was not determined. Intraparticle diffusivities of Cr, Co", and Cu were calculated with the removal model, and are compared in Figure 7. The removal model for Dowex XFS 4195.02 appears to be generally applicable to most metals. [Pg.168]


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See also in sourсe #XX -- [ Pg.6 , Pg.7 , Pg.63 ]




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