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Intraparticle conductivity

The reaction of solid particles is inherently an unsteady state process, so that the previously discussed gas to solid convection and intraparticle conduction phenomena have to be applied in a time-dependent manner. [Pg.51]

Rate of intraparticle heat conduction is rate controlling ... [Pg.210]

Such a high reaction rate strongly suggested the potential for mass transport problems. Indeed, a turn-over frequency on the order of 1 s 1 is considered appropriate for the purpose of mechanistic studies normally conducted in the gas phase (ref. 5). At higher rates, various complications including intraparticle diffusion problems, often arise. The situation is even more severe in the liquid phase where the bulk diffusivity of species is considerably reduced. A... [Pg.177]

Such experiments with the different catalyst fractions were conducted in toluene at both 2.0 and 10.0 MPa hydrogen and at 900 RPM. The initial rates of the reaction as well as the initial ee s for these two sets of experiments are shown in Figures 6 and 7. In both cases, essentially constant TOF s as well as constant ee s are obtained, indicating a complete absence of intraparticle control. [Pg.182]

Here we consider a spherical catalyst pellet with negligible intraparticle mass- and negligible heat-transfer resistances. Such a pellet is nonporous with a high thermal conductivity and with external mass and heat transfer resistances only between the surface of the pellet and the bulk fluid. Thus only the external heat- and mass-transfer resistances are considered in developing the pellet equations that calculate the effectiveness factor rj at every point along the length of the reactor. [Pg.430]

Conductive heat transfer is the dominant mode of intraparticle heat transfer. Under low Reynolds number flow situations, conductive heat transfer is also an important mode for fluid heat transfer. This section analyzes the conductive heat transfer characteristics of a... [Pg.130]

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]

Studies with porous catalyst particles conducted during the late 1930s established that, for very rapid reactions, the activity of a catalyst per unit volume declined with increasing particle size. Mathematical analysis of this problem revealed the cause to be insufficient intraparticle mass transfer. The engineering implications of the interaction between diffusional mass transport and reaction rate were pointed out concurrently by Damkohler [4], Zeldovich [5], and Thiele [6]. Thiele, in particular, demonstrated that the fractional reduction in catalyst particle activity due to intraparticle mass transfer, r, is a function of a dimensionless parameter, 0, now known as the Thiele parameter. [Pg.206]

The Biot number Bib for heat transport. Analogous to Bim, this is defined as the ration of the internal to external heat transfer resistance (intraparticle heat conduction versus interphase heat transfer). [Pg.331]

The reaction rates of the thermal reduction and the reoxidation by CO2 are increased by high oxygen anion conductivity and high surface areas. Oxygen anion conductivity is a function of temperature, crystal structure, and defects. Because cycling results in stoichiometric gas-solid reactions, the gas-solid interface can be a crucial parameter depending on the reaction conditions. Whether gas-solid, intraparticle mass transfer, or surface chemical processes are rate-limiting is primarily determined by the reaction temperature and gas flow rates. [Pg.407]

The FT-conversion has been conducted in a fixed bed reactor with the finely powdered catalyst (dp <0.1 mm) covering larger fused silica particles (dp = 0.25-0.4 mm) as an adhering layer, the weight ratio of catalyst to fused silica particles being 1 10. By this means a very isothermal catalyst bed was provided with highly uniform flow of the gas phase, minor pressure drop and no noticeable intraparticle resistance influence. [Pg.159]

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]

Intraparticle mass diffusion and heat conduction for porous catalyst pellets. [Pg.14]

There are many cases where the external mass transfer resistance can be neglected while the external heat resistance in not negligible. In gas-solid systems, external heat transfer resistances are usually much higher than external mass transfer resistances especially for light components. Also there are cases where the intraparticle resistances are appreciable while the intraparticle heat transfer resistance is negligible due to the high thermal conductivity of the metal or metal oxides forming the bulk of the catalyst pellet. [Pg.83]

Heat transfer within catalyst particles occurs by conduction and an effective thermal conductivity /.g for the pellet is used with Fourier s law, to describe the intraparticle heat conduction. [Pg.159]

During sterilization by heat there are two steps in the heat transfer process -heat transfer to the particle surface and intraparticle heat transfer. Due to the poor mixing characteristics of solid beds and the fact that intraparticle heat transfer is limited to conduction, it is more problematic to ensure sterility of a solid substrate than it is to ensure sterility of a liquid medium. In unmixed beds it is highly likely that the effectiveness of the sterilization process will vary with position. [Pg.78]


See other pages where Intraparticle conductivity is mentioned: [Pg.113]    [Pg.113]    [Pg.444]    [Pg.255]    [Pg.457]    [Pg.33]    [Pg.167]    [Pg.167]    [Pg.184]    [Pg.422]    [Pg.29]    [Pg.550]    [Pg.219]    [Pg.336]    [Pg.255]    [Pg.202]    [Pg.109]    [Pg.218]    [Pg.146]    [Pg.506]    [Pg.1148]    [Pg.202]    [Pg.71]    [Pg.173]    [Pg.274]    [Pg.361]    [Pg.422]    [Pg.554]    [Pg.78]    [Pg.378]    [Pg.61]    [Pg.394]    [Pg.242]   
See also in sourсe #XX -- [ Pg.5 ]




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