Catalyst bed configurations

The three principal catalyst bed configurations are the pellet bed, the monolith, and the metallic wire meshes. An open structure with large openings is needed to fulfill the requirement of a low pressure drop even at the very high space velocities of 200,000 hr-1. On the other hand, packings with small diameters would provide more external surface area to fulfill the requirement for rapid mass transfer from the g .s stream to the solid surface. The compromise between these two ideals results in a rather narrow range of dimensions pellets are from to 1 in. in diameter, monoliths have 6 to 20 channels/in., and metallic meshes have diameters of about 0.004 to 0.03 in. 

Fig. 25 RON of the product mixture as a function of MCH conversion, calculated by the method of ref. 14. Standard errors for this method are 1R0N. For the product distribution obtained on the three Pt/HY + Ir/Si02 catalyst bed configurations illustrated in Fig. 24. Conversion was varied by changing temperature. Total pressure = 2 MPa H2/feed molar ratio = 40. Adapted from ref. 100.

Processes 4, 5 and 6 are all essentially one step oxidations of SO2 to SO3 and hence sulphuric acid. The first pair are modified versions of the traditional Contact and Chamber processes for sulphuric acid manufacture, with the principal change being in their ability to accept dilute SO2 gas streams as the feedstock. The use of Activated Carbon as an air oxidation catalyst has clearly received international attention, with success or failure depending to a large extent on subtle modifications in catalyst preparation and catalyst presentation to the reactant gases. Virtually every type of catalyst bed configuration has been explored. 

Figure 13 Monolith catalyst bed configuration used in demonstration of autothermal reforming of hydrocarbons. The monolith catalyst bed through which the hydrocarbon, oxygen, and steam mixture (A) passes is No. 2, and the pellet steam reforming bed is No. 4. (From Ref. 11.)...

Reactor design and catalyst bed configuration are key factors for controlling thermal reactions. 

Ma, L. and Trimm, D. Alternative catalyst bed configurations for the autothermic conversion of methane to hydrogen. Applied Catalysis A General, 138(2) 265-273, 1996. 

GP 2] [R 3a] A Shell Series catalyst was measured in a fixed-bed configuration and deposited in micro channels electrophoretically (20 vol.-% ethylene, 80 vol.-% oxygen 0.3 MPa 230 °C) [101]. The selectivity was lower in the micro channels (51%) than in the fixed bed (57%) at a conversion of 17%. In a further investigation, a sputtered silver catalyst (cesium promoted) was better than both systems (68%) at higher conversion (25%). 

The packing itself may consist of spherical, cylindrical, or randomly shaped pellets, wire screens or gauzes, crushed particles, or a variety of other physical configurations. The particles usually are 0.25 to 1.0 cm in diameter. The structure of the catalyst pellets is such that the internal surface area far exceeds the superficial (external) surface area, so that the contact area is, in principle, independent of pellet size. To make effective use of the internal surface area, one must use a pellet size that minimizes diffusional resistance within the catalyst pellet but that also gives rise to an appropriate pressure drop across the catalyst bed. Some considerations which are important in the handling and use of catalysts for fixed bed operation in industrial situations are discussed in the Catalyst Handbook (1). 

The MTG process can be performed in a fixed-bed reactor or in a fluidized-bed reactor. The fixed bed configuration is technically less demanding. However, for strongly exothermic processes such as the MTG process, the release of heat is a severe problem that results in hot spots and overheating of the reactor. In a fluidized-bed reactor, a gas passes upward through the catalyst bed and... 

The catalyst, which may be an activated natural or synthetic material, is employed in bead, pellet or microspherical form and can be used as a fixed bed, moving-bed, or fluid-bed configurations. Moving bed units often employ catalysts in the form of beads or cylinders (1/8 to 1/4-inch diameter). Fluid bed units usually employ the catalyst in much smaller form where particle sizes may be of the order of 50 pm (50 X 10 4 cm). 

If the system consists of a series of adiabatic reactors, there are two basic configurations. The first has heat exchangers or furnaces between each of the reactors to cool or heat the reactor effluent before it enters the next reactor. The second configuration uses cold shot cooling. Some of the cold reactor feed is bypassed around the upstream reac-tor(s) and mixed with the hot effluent from the reactor to lower the inlet temperature to the downstream catalyst bed. 

Figure 1. Point-plane dc reactor configuration with catalyst bed.

Case histories for the deactivation of commercial Hopcalite and chhromia/alumina catalysts in the oxidation of volatile organic compounds (V0C) are presented. Feeds of pure hydrocarbons, chloro-carbons, and mixtures of the two are considered. Both fixed- and fluid-bed configurations have been studied. Deactivation with mixed feeds is a severe test of V0C catalyst capabilities. There seems here no clear distinction between between the type of reactor, but significant differences between activity and selectivity do exist. A simple model for predicting fixed-bed operation is presented. 

Typically, the reactor was loaded with a preheat section in the bottom for an upflow configuration. The preheat section, which contained 1.5 L of Harshaw Tab Alumina rested on stainless steel wool. The 1-L catalyst bed was placed on top of the alumina preheat section. The small volume at the top of the reactor was filled with additional alumina topped with stainless steel wool to retain the catalyst in the reactor. The thermocouples were inserted at the designated locations in an axial thermowell which runs through the center of the catalyst bed. 

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