In a packed bed

Once fluidized, the bed behaves as if it were a fluid. A level is maintained and a static pressure head is generated. No flow of soHds through a side outlet occurs in a packed bed however, flow through the opening does occur after a fluidized state has been achieved (Fig. Ic). 

Olefin Amination (Method 6). The most recent technology for the production of lower alkylamines is olefin amination (14). This is 2eohte-cataly2ed reaction of ammonia with an olefin, eg, isobutylene, and is practiced in a packed-bed reactor system in the vapor phase. 

There are three types of Hquid content in a packed bed (/) in a submerged bed, there is Hquid filling the larger channels, pores, and interstitial spaces (2) in a drained bed, there is Hquid held by capillary action and surface tension at points of particle contact, or near-contact, as weU as a zone saturated with Hquid corresponding to a capillary height in the bed at the Hquid discharge face of the cake and (3) essentially undrainable Hquid exists within the body of each particle or in fine, deep pores without free access to the surface except perhaps by diffusion or compaction. 

The equations for flow and adsorption in a packed bed or chromatography column give a quasilinear equation. 

A technique for calculating radial temperature gradients in a packed bed is given by Smith Chemical Engineering Kinetics, McGraw-HiU, New York, 1956). 

The total voidage i in a packed bed (outside and inside particles) is... 

FIG. 16-9 General scheme of adsorbent particles in a packed bed showing the locations of mass transfer and dispersive mechanisms. Numerals correspond to mimhered paragraphs in the text 1, pore diffusion 2, solid diffusion 3, reaction kinetics at phase boundary 4, external mass transfer 5, fluid mixing. 

The actual name dry scrubbing was first publicized by Teller [U.S. Patent no. 3,721,066 (1973)]. He worked both with classical Army-type soda-lime and with his patented water-activated form of the alkaline feldspar nepheline syenite as a flow agent and feedstock sorbent for HF and SO9 in hot, sticky fumes from glass melting furnaces. He claimed capture of more than 99 percent of 180 ppm HF and SO9 for more than 20 hours in a packed bed of 200 X 325 mesh hydrated nephehne syenite at 42,000/hr. 

Usually they are employed as porous pellets in a packed bed. Some exceptions are platinum for the oxidation of ammonia, which is in the form of several layers of fine-mesh wire gauze, and catalysts deposited on membranes. Pore surfaces can be several hundred mVg and pore diameters of the order of 100 A. The entire structure may be or catalytic material (silica or alumina, for instance, sometimes exert catalytic properties) or an active ingredient may be deposited on a porous refractory carrier as a thin film. In such cases the mass of expensive catalytic material, such as Pt or Pd, may be only a fraction of 1 percent. 

The Rowe-Claxton empirical equation has been found to conform to many experimental studies of heat transfer in a packed bed, such as the reactor typically used in the catalytic processes described earlier. It is first necessary in this situation to define die voidage of the system, AV, where... 

Flow distribution in a packed bed received attention after Schwartz and Smith (1953) published their paper on the subject. Their main conclusion was that the velocity profile for gases flowing through a packed bed is not flat, but has a maximum value approximately one pellet diameter from the pipe wall. This maximum velocity can be 100 % higher than the velocity at the center. To even out the velocity profile to less than 20 % deviation, more than 30 particles must fit across the pipe diameter. 

On this table, the Arrhenius number E/RT was designated by e, but this symbol is already used in this book for the empty fraction in a packed bed. The correct symbol for E/RT = y is used here. On the last line in this table the derivative of the heat removal rate is given ... 

To identify the pertinent HETP equation that describes dispersion in a packed bed, the following logical procedure will require to be carried out. 

Liquid distribution in a packed bed is a function of the internal vapoi/liquid traffic, the type of packing employed, and the quality of the liquid distributors mounted above the packed bed. Vapor distribution is controlled by the internal vapor/liquid traffic, by the type of packing employed, and by the quality of the vapor distributors located below the packed beds. 

As well as being active, the immobilised enzyme also needs to be stable (active for a long period) and the support must promote this. The support must also have appropriate mechanical characteristics it should not disintegrate if used in a stirred tank reactor it should produce even flow (without channelling) in a packed bed reactor. Hie cost of the support is also important. 

Fluidised beds have been used previously for the industrial-scale recovery of the antibiotics streptomycin and novobiocin.30 However, more recently, considerable interest has been shown in the use of fluidised beds for the direct extraction of proteins from whole fermentation broths.31 In a packed bed, the adsorbent particles are packed within the contactor. The voidage, that is, the inter-particle space, is minimal and thus feedstock clarification is mandatory to avoid clogging of the bed. In a fluidised/expanded bed, the adsorbent bed is allowed to expand by irrigation with feedstock. Bed voidage is increased, allowing the passage of particulates in the feed. The diameters of the adsorbent beads are exaggerated for illustrative clarity. 

Flame-Sprayed Raney Nickel Plates vs. Pellets of Precipitated Catalyst in a Packed Bed. Experiments HGR-13 and HGR-14 demonstrated that the performance of the plates sprayed with Raney nickel catalyst was significantly better than that of the precipitated nickel catalyst pellets. The sprayed plates yielded higher production of methane per pound of catalyst, longer catalyst life or lower rate of deactivation, lower CO concentration in the product gas, and lower pressure drop across the catalyst bed. 

The Peclet numbers decrease when the dispersion coefficients increase. In the Reynolds number range of 10-200, in a packed bed of pellets, Peii = 2 and PeH = 0.5 (119, 120). The dispersions in the transverse... 

The absorption of reactants (or desorption of products) in trickle-bed operation is a process step identical to that occurring in a packed-bed absorption process unaccompanied by chemical reaction in the liquid phase. The information on mass-transfer rates in such systems that is available in standard texts (N2, S6) is applicable to calculations regarding trickle beds. This information will not be reviewed in this paper, but it should be noted that it has been obtained almost exclusively for the more efficient types of packing material usually employed in absorption columns, such as rings, saddles, and spirals, and that there is an apparent lack of similar information for the particles of the shapes normally used in gas-liquid-particle operations, such as spheres and cylinders. 

The pressure drop in a packed bed depends on the particle Reynolds number. When (Re)p is small, Equation (3.17) becomes... 

Constant-Pressure Scaleups for Packed Beds. A scaleup with constant pressure drop can be achieved in a packed bed just by increasing the diameter to keep a constant gas velocity m. This gives... 

Examples 9.1 and 9.2 used a distributed parameter model (simultaneous PDEs) for the phthalic anhydride reaction in a packed bed. Axial... 

Consider an observed reaction of the form A + B P + Q occurring in a packed-bed reactor. 

Suppose that catalyst pellets in the shape of right-circular cylinders have a measured effectiveness factor of r] when used in a packed-bed reactor for a first-order reaction. In an effort to increase catalyst activity, it is proposed to use a pellet with a central hole of radius i /, < Rp. Determine the best value for RhjRp based on an effective diffusivity model similar to Equation (10.33). Assume isothermal operation ignore any diffusion limitations in the central hole, and assume that the ends of the cylinder are sealed to diffusion. You may assume that k, Rp, and eff are known. 

Example 11.10 Determine phase concentrations for a liquid-liquid reaction in a packed-bed reactor. The reactive component is dilute in both phases. It enters the reactor in one phase but undergoes a pseudo-first-order reaction in the other phase. All parameters are constant. 

Radial dispersion coefficient for heat in a packed-bed 9.3 Axial dispersion coefficient for temperature in PDE Sec. 9.1 model... 

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