Cylindrical catalysts

Figure 1.3.2 gives another perspective for scale-down to recycle reactor studies. In this actual case, after preliminary studies in a recycle reactor, a 5-stage adiabatic reactor was envisioned (Betty 1979.) Scaling down the proposed commercial reactor, a 3 diameter tube was designed with elaborate temperature compensation (heating and insulation) for pilot-plant studies (Betty 1968, 1969.) Small squares in the proposed reactor represent side views of cylindrical catalyst cutouts for the recycle reactor... 

Ross (R2) measured liquid-phase holdup and residence-time distribution by a tracer-pulse technique. Experiments were carried out for cocurrent flow in model columns of 2- and 4-in. diameter with air and water as fluid media, as well as in pilot-scale and industrial-scale reactors of 2-in. and 6.5-ft diameters used for the catalytic hydrogenation of petroleum fractions. The columns were packed with commercial cylindrical catalyst pellets of -in. diameter and length. The liquid holdup was from 40 to 50% of total bed volume for nominal liquid velocities from 8 to 200 ft/hr in the model reactors, from 26 to 32% of volume for nominal liquid velocities from 6 to 10.5 ft/hr in the pilot unit, and from 20 to 27 % for nominal liquid velocities from 27.9 to 68.6 ft/hr in the industrial unit. In that work, a few sets of results of residence-time distribution experiments are reported in graphical form, as tracer-response curves. 

Radius of central hole in a cylindrical catalyst Prob. 10.14... 

Our very first experiments with the reactor depicted in Figure 5.4.1 were carried out with a 15% Pt-Y-Al203 single cylindrical catalyst pellet [10-12], The acquisition time of 2D images of an axial slice at that time was about 260 s. Despite this, the first direct MRI visualization of the operation of a model gas-liquid-solid reactor has revealed the existence of large gradients of the liquid phase content within the catalyst pellet upon imbibition of liquid a-methylstyrene (AMS) under conditions... 

Schematic representation of straight cylindrical catalyst pore.

FIGURE 12.1 Representation of a single cylindrical catalyst pore and mass balance for... 

For a better understanding of the obtained effectiveness factors in Table 12.2, the results of the simulation at different conversion degrees (concentrations of CO, H2, and H20 in a cylindrical catalyst pore) are depicted in Figure 12.3. 

No practical catalyst pellet can be described by the geometry of the wafer, yet it will be shown that eqn. (6), albeit with a slightly different interpretation of the Thiele modulus, 0, is of practical value. For a cylindrical catalyst pellet (a shape often used in practice) of radius r and sealed at its flat ends... 

Hollow cylindrical catalyst pellets are sometimes employed in commercial chemical reactors in order to avoid excessive pressure drops across a packed bed of catalyst. A more complex expression for the effectiveness factor is obtained for such geometry. This case was first discussed by Gunn [4]. Figure 2 illustrates the effectiveness factor curves obtained for the slab, sphere and cylinder. 

The reactant A and the product B diffuse into and out of a cylindrical catalyst pore with length L and radius r. The material balance for reactant A at steady state for a differential length dr of the catalyst pore is written as diffusion flux in - diffusion flux out - disappearance by reaction = 0... 

GUNN(I6) discusses the case of the hollow cylindrical catalyst particle. Such catalyst particles reduce the difficulties caused by excessive pressure drops. 

Derive an expression for the effectiveness factor of a cylindrical catalyst pellet, scaled at both ends, in which a first-order chemical reaction occurs. 

Commonly [17], when the length-to-diameter ratio of a cylindrical catalyst is close to 1, the cylindrical catalyst can be simplified as a sphere, the radius of which, Rp, is calculated by 3 Kp/.S p. The one-dimensional, key-component based reaction-diffusion models of methanation system are as follows ... 

Rp and Up are the radius and semi-length of cylindrical catalyst, respectively. Assume a cylindrical ring element with the length dll and the radial thickness dR at the axial position H and the radial position A in the 2D cylindrical system. Introducing the dimensionless variables... 

The kinetic experiments, activity tests, and poisoning experiments were carried out in a gas-flow isothermal fixed bed reactor [6) at the benzene partial pressure of 7.55 kPa hydro gen partial pressure 99.82 kPa thiophene partial pressure 0.032 kPa and the reaction temperatures 403, 427 and 448 K. The size of the commercial cylindrical catalyst pellet was 5x5mm (21% Ni on alumina, supplied by BASF). The nickel oxide containing precursor was activated by reduction with hydrogen at 743 K for 10 hr. 

Figure 4.2.5 Cross section of steatite spheres, coated with a mixed oxide having primary, cylindrical catalyst particles of approximately 200-300 nm in length and 150-180 nm in diameter.

The similarity between the wafer problem (11-12) and the cylindrical catalyst particle problem has already been mentioned. 

Without any prove it is stated here that the geometry factor T falls between the two extremes of 2/3 for the infinitely long slab and of 6/s for the sphere for almost all practical cases. Thus T is almost always close to unity. This holds for any catalyst geometry, hence also for catalyst geometry s commonly found in industry, for example ring-shaped or cylindrical catalyst pellets. For this type of pellet it can be shown (Appendix C) that the geometry factor T equals ... 

Thus for < = 0 the ring-shaped catalyst pellet becomes a cylindrical catalyst pellet. Equation 6.41 is illustrated in Figure 6.10. In this diagram 1 is plotted versus A lines with a constant geometry factor T are drawn. The four comers of the diagram represent... 

Cylindrical catalyst pellets, whether hollow or not, are often given shape by extrusion of a paste of wet catalyst (Chapter 3). During this process the diameter of pores in the radial direction will become smaller, whereas for pores in the longitudinal direction the length will decrease. This can result in a radial effective diffusivity being smaller than the longitudinal one. Thus cylindrical catalyst pellets can be anistropic. 

The following reaction is carried out in a cylindrical catalyst pellet A + 2B- P... 

Petroleum ethcr-carbon dioxide Cylindrical catalyst 2 t... 

Spherical catalyst o Cylindrical catalyst 2 + Cylindrical catalyst 2 X Cylindrical catalyst 2 X Cylindrical catalyst 2 Cylindrical catalyst 2 a Cylindrical catalyst 2 1 Cylindrical catalyst 2 O Cylindrical catalyst 2 +... 

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