Catalyst beds thickness

Table 7.2 gives measured industrial catalyst bed thicknesses, m catalyst bed (converter) diameters, m converter input gas rate, NmVhour. 

Fig. 8.3 shows industrial catalyst bed thicknesses. Average bed thicknesses are ... 

Fig. 8.3. Industrial lsl, 2nd and 3rd catalyst bed thicknesses. They are from Table 7.2. They increase from bed 1 through bed 3.

Fig. 8.5. Industrial 1st, 2nd and 3rd catalyst bed gas nominal residence times. They increase with increasing bed number. This is due to the increase in bed thickness with increasing bed number, Fig. 8.3. The points have been calculated from Table 7.2 s industrial catalyst bed thicknesses, converter diameters and converter input gas flowrates.

With these goals in mind, we have studied the distribution of the liquid phase in the course of the hydrogenation reaction in a catalyst bed comprised of 1-mm catalyst beads (Figure 5.4.5). The 2D images shown reflect the distribution of the liquid phase in a 2-mm thick axial slice upon variation of the liquid AMS flow rate. The results show that while the increase in the flow rate leads to larger liquid contents in the bed (and vice versa), a steady state operation of the catalyst bed with unchanging spatial distribution of the liquid is observed if the external conditions remain unchanged. 

In conventional experiments the gas and catalyst are maintained at the same temperature. In microwave experiments the power is deposited within the catalyst, which is cooled by the gas flow and thermal conduction to the surroundings. If the catalyst bed is not thick, the gas is always at a lower temperature than the solid catalyst. The increased loss factor of the catalyst favors the formation of CH3 radicals because they are produced at active 02 sites and these specific sites are preferentially excited by the microwave field. Hence the observed enhancement of C2 selectivity is,... 

The differential reactor uses a thin catalyst bed in which only small changes of concentration and temperature occur (Fig. 3.3-3). The rate of reaction, r, can be obtained from the difference in concentration, Ac, over the catalyst bed or its thickness, Ax, the volumetric throughput, v, or the molar throughput, nges, and the quantity of catalyst, WK, using the material balance ... 

Second, the use of meshed particles versus a pressed wafer will typically lead to nonuniformity of X-ray absorption thickness. This can be directly observed by placing an X-ray sensitive camera behind the sample a sample of a powder pressed into a wafer is spectroscopically more uniform than a catalyst bed of meshed particles. Naturally the contrast becomes more extreme as the meshed particles become larger. Moreover, if the sample is spatially nonuniform then severe constraints are placed on the positional stability of the X-ray beam. Any motion of the position of the X-ray beam will then probe different thicknesses of the sample, with direct consequences on the measured S/N. From the perspective of XAFS spectroscopy, any nonuniformity of the sample thickness could directly affect the accuracy of the measurement of the amplitude of the X-ray absorption coefficient. It is the amplitude that contains information about the coordination number and site disorder. As has been discussed elsewhere (Koningsberger and Prins, 1988), these amplitude distorting effects are given the general heading of "thickness effects." In brief, a thickness effect occurs when part of the incident X-ray beam is not attenuated by the sample. In the case of meshed particles this would be in the form of pinholes in the sample. 

Fig. 1.2. Catalyst pieces in a catalytic S02 oxidation converter. Converters are 15 m high and 12 m in diameter. They typically contain four, Va-l m thick catalyst beds. SOj-bearing gas descends the bed at -3000 Nm3 per minute. Individual pieces of catalyst are shown in Fig. 8.1. They are -0.01 m in diameter and length.

Nominal residence times of gas in a converter s catalyst beds are calculated from measured bed thickness, converter diameter and converter gas input rate. The equation is ... 

Industrial lsl catalyst beds are A to 1 m thick, Fig. 8.3. This thickness gives near equilibrium oxidation under the (i) warm and (ii) strong S02 + 02 conditions in the 1st catalyst bed. More catalyst could be added but this isn t often necessary. Nonattainment of equilibrium is discussed further in Section 18.12. 

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