Static bed reactor

The most satisfactory and meaningful catalyst activity tests are those involving the cracking of a standard cracking stock in small-scale static-bed reactors. Small laboratory-scale fluidized-bed test units have been described, but generally speaking these are more difficult to operate satisfactorily than fixed-bed units. Powdered catalysts are generally tested in pelleted form or in a nonfluidized static bed of powder. 

Fig. 4. Apparatus for testing granular or powdered cracking catalysts in static-bed reactor (Shankland and Schmitkons, 23).

Fig. S.l. Static bed reactor (From C. D. Harrington and A. E. Ruehle, Uramum Production Technology, copyright 1959, D. Van Nostrand, Princeton. New...

The catalyst is employed in bead, pellet, or microspherical form and can be used as a fixed bed, moving bed, or fluid bed. The fixed-bed process was the first process used commercially and employs a static bed of catalyst in several reactors, which allows a continuous flow of feedstock to be maintained. The cycle of operations consists of (/) the flow of feedstock through the catalyst bed (2) the discontinuance of feedstock flow and removal of coke from the catalyst by burning and (J) the insertion of the reactor back on-stream. The moving-bed process uses a reaction vessel, in which cracking takes place, and a kiln, in which the spent catalyst is regenerated and catalyst movement between the vessels is provided by various means. 

The models of Chapter 9 contain at least one empirical parameter. This parameter is used to account for complex flow fields that are not deterministic, time-invariant, and calculable. We are specifically concerned with packed-bed reactors, turbulent-flow reactors, and static mixers (also known as motionless mixers). We begin with packed-bed reactors because they are ubiquitous within the petrochemical industry and because their mathematical treatment closely parallels that of the laminar flow reactors in Chapter 8. 

Static mixing catalysts Operation Monolithic reactors Microreactors Heat exchange reactors Supersonic gas/liquid reactor Jet-impingement reactor Rotating packed-bed reactor... 

Reactors with a packed bed of catalyst are identical to those for gas-liquid reactions filled with inert packing. Trickle-bed reactors are probably the most commonly used reactors with a fixed bed of catalyst. A draft-tube reactor (loop reactor) can contain a catalytic packing (see Fig. 5.4-9) inside the central tube. Stmctured catalysts similar to structural packings in distillation and absorption columns or in static mixers, which are characterized by a low pressure drop, can also be inserted into the draft tube. Recently, a monolithic reactor (Fig. 5.4-11) has been developed, which is an alternative to the trickle-bed reactor. The monolith catalyst has the shape of a block with straight narrow channels on the walls of which catalytic species are deposited. The already extremely low pressure drop by friction is compensated by gravity forces. Consequently, the pressure in the gas phase is constant over the whole height of the reactor. If needed, the gas can be recirculated internally without the necessity of using an external pump. 

A glass tube fixed-bed reactor was used as a closed static reactor. The cyclotron produced nC-radioisotope (Ti/2=20.4 min) was used for nC-labeled methanol production by radiochemical process. The nC-labeled methanol (shortly nC-methanol, - 3pmol, -600 MBq) was then introduced into 250 mg of zeolite at ambient temperature by He gas flow. Afterwards, equivalent volume of liquid methyl iodide was injected into nC-methanol to have mixture of methanol and methyl iodide and introduced into catalyst for investigation of methyl iodide influence. After adsorption (2 min), the catalyst was heated up to the required temperature. 

General Concept. The development of the fixed-bed process was based upon the idea of using a static bed of catalyst and maintaining a continuous flow of hydrocarbon vapor by the use of multiple reactors (17). Each reactor was submitted to a cycle of operations consisting of ... 

If the reactants are in the gas phase, the reactor may be either static or dynamic. Small static reactors are convenient for basic research where either the reactants are expensive (e.g. isotopically labelled molecules) or the reaction slow. Dynamic reactors, where reactants flow through the catalyst bed, provide a better simulation of practical use in a fixed bed reactor the catalyst remains in place, and it is in the form of large particles or pellets. 

The holdup of a phase is usually defined as the volume of the phase per unit reactor volume. However, for a fixed-bed reactor, the gas and liquid holdups are often defined on the basis of void volume of the reactor. In a fixed-bed reactor, the liquid and sometimes gas holdups are divided into two parts dynamic holdup, which depends largely on the gas and liquid flow rates and the properties of the fluids and the packing material, and static holdup, which depends to a major extent on the nature of the packing (e.g., porosity of the packing) and the fluids properties. The relationships between the holdups of various phases and the system variables for a variety of three-phase reactors are discussed in Chaps. 6 through 9. 

Several points about this model should be noted. First, it takes into account both macromixing as well as micromixing (in the rippled films at the junctions) iir the trickle-bed reactor to correlate the RTD and, second, it assumes that the mixing at the static junctions is achieved by hydrodynamic effects, rather than by diffusion effects, as is often postulated.13-29 The model is not tested against the data from porous packing, where a significant portion of the static liquid holdup is due to the liquid in the pores of the packings. 

Woodbury, B. L., et al. (1998). Evaluation of reversible fixed-film static-bed bio-denitrifica-tion reactors. Water Science TechnoL, Wastewater Nutrient Removal Proc. 199819th Biennial Conf. Int. Assoc, on Water Quality, Part 1, June 21-26, Vancouver, Canada, 38, 1, 311-318. Elsevier Science Ltd., Exeter, England. 

The feed enters the top of the static vertical bed reactor. Level sensors automatically interrupt the loading when the reactor is filled to the proper level. Whenever the wood feed level drops below a second selected level, the load auger automatically runs until the full load level is reached. 

The physical arrangement involves a method of containing the solid reactant while the fluid phase is passed over the solid in such a way that intimate contact is possible between the flowing fluid and the resident solid. This physical arrangement is familiar from the static bed plug flow catalytic reactor and is now applied here to a reactor where solid interactions with a fluid phase, including adsorption, are studied. The interactions between the phases involved in a catalytic TS-PFR have been described above. The non-catalytic interactions are now considered as they take place in a TS-PF-SSR. The differences between the two reactor types lie in hardware requirements and in the mode of operation. 

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