Reactor plug-flow fixed-bed

Additional information on the plug flow fixed bed reactors and on the heat and mass balance equations can be found in the Handbook of Heterogeneous Catalysis[15] and in the classical books devoted to chemical engineering kinetics.113,141... 

In the inertial microbalance, the mass located at the tip of an oscillating tapered quartz element is detected as a change in its vibrational frequency. The design of this equipment provides a packed bed of catalyst through which all the gas is forced to flow, and the classical methods of testing for differential operation in an ideal plug-flow fixed-bed reactor can therefore be applied. 

Example 3.4. Balances for Plug-Flow Fixed-Bed Reactors... 

Deactivation rate constants for the zeolite catalysts were obtained from the time-on-stream activity data (Fig. 1) by using the following expression developed for the case of a first order catalyst deactivation in plug flow fixed bed reactor [20]. 

An operational variation reminiscent of combined MT and TM reactors is the use of a plug-flow, fixed-bed reactor followed in series by a packed inert membrane reactor, as shown in Figure 24.If (Wu and Liu, 1992). 

J.J.P. Biermann, P.P. Coelen, H. Den Daas, RJ.J.G. Janssen, The use of a heat-flow differential scanning calorimeter as a plug-flow fixed bed reactor in heterogeneous catalysis. Thermochim. Acta 144, 329-337 (1989)... 

An isothermal, plug flow, fixed bed reforming pilot plant (shown in Fig. 14) was used to generate the kinetic data. The reactor was U shaped and contained roughly 70 ml of catalyst. Five sample taps were spaced along the reactor length to determine compositions over a wide range of catalyst contact times. The reactor assembly was immersed in a fluidized sand bath to maintain isothermal conditions. 

The transient isotope-switching apparatus has been described previously. The reactor was a plug-flow, fixed-bed quartz microreactor, 8 mm in diameter, with a total volume of 0.8 cc. Approximately 0.4 g of catalyst was supported in the middle of the reactor on a fused quartz frit. Temperature in the catalyst bed was measured with a chromel-alumel thermocouple shielded in a quartz jacket. The reactant gas stream was controlled by a mass flow control switching system capable of switching one or more of the reactants to its isotopically labelled counterpart in approximately 1 s. The partial pressures and flow rates of the reactants are not altered by this switch so that the steady-state concentrations of reactants and products in the gas phase, and on the catalyst surface, are not disturbed. 

FIGURE 18.8 Simplified representation of a plug-flow (fixed-bed) trickle-bed reactor. 

A sample (0.050 g) of the catalyst was diluted with 8 g SiC to achieve plug-flow conditions in the continuous flow fixed bed reactor. The catalyst was sulfided in situ with a mixture of 10% H2S in H2 at 648 K and 1.0 MPa for 4 h. After... 

Continuous reactors fall into two categories, plug flow, which includes fixed-bed reactors, and mixed flow, usually a continuous stirred tank reactor. 

Applications of the organic solvents in fluidized-bed reactors have also been investigated, particularly with immobilized cells (Table 5). This type of reactor has several advantages over a fixed-bed reactor, namely, reduced coalescence of the emulsion particles, lower pressure at high flow rate, and less channeling and plugging. 

Equations 12.7.48 and 12.7.39 provide the simplest one-dimensional mathematical model of tubular fixed bed reactor behavior. They neglect longitudinal dispersion of both matter and energy and, in essence, are completely equivalent to the plug flow model for homogeneous reactors that was examined in some detail in Chapters 8 to 10. Various simplifications in these equations will occur for different constraints on the energy transfer to or from the reactor. Normally, equations 12.7.48 and 12.7.39... 

D-Pantolactone and L-pantolactone are used as chiral intermediates in chemical synthesis, whereas pantoic acid is used as a vitamin B2 complex. All can be obtained from racemic mixtures by consecutive enzymatic hydrolysis and extraction. Subsequently, the desired hydrolysed enantiomer is lactonized, extracted and crystallized (Figure 4.6). The nondesired enantiomer is reracemized and recycled into the plug-flow reactor [33,34]. Herewith, a conversion of 90-95% is reached, meaning that the resolution of racemic mixtures is an alternative to a possible chiral synthesis. The applied y-lactonase from Fusarium oxysporum in the form of resting whole cells immobilized in calcium alginate beads retains more than 90% of its initial activity even after 180 days of continuous use. The biotransformation yielding D-pantolactone in a fixed-bed reactor skips several steps here that are necessary in the chemical resolution. Hence, the illustrated process carried out by Fuji Chemical Industries Co., Ltd is an elegant way for resolution of racemic mixtures. 

Figure 4.16 Pressurized fixed-bed reactor synthesis of L-aspartic acid from fumarate applying a plug flow reactor followed by a crystallization step for downstream processing...

Ideal flow is studied and represented using the classic dispersion or dispersed plug-flow model of Levenspiel (1962). Recall the material balance of a fixed-bed reactor with perfect radial mixing (eq. (3.285)) ... 

In more recently introduced equipment, the calcination and loading of the catalyst samples can be performed under shallow-bed conditions. For example, the equipment developed by Zhang et al. (51) (Fig. 9) allows a calcination of the powder in a horizontal tube inside a heater at temperatures of up to 1000 K. After loading of the catalyst with probe molecules or reactants, the powder is added to an MAS NMR rotor at the bottom of the equipment, sealed with a rotor cap from a plug rack, and transferred to the NMR spectrometer. As in the case of the former approaches, the samples prepared in the equipment of Zhang et al. 151) can be used for ex situ as well as in situ NMR investigations under batch reaction conditions. Furthermore, this equipment is suitable for ex situ investigations of solid-catalyzed reactions under flow conditions. In this case, the horizontal tube inside the heater is used as a fixed-bed reactor. 

The apparatus consisted of a flow reactor containing the coal and an oxygen absorber. A fixed bed reactor was used for studies on large coal particles, while a spout reactor was used for studies on small coal particles. Both reactors had a volume of about 400 cc. and were designed so that both wall and end effects were eliminated. Experimental residence time distributions indicated that the fixed bed reactor approximated a plug flow reactor, while the fluidized bed spout reactor had perfect mixing. 

The catalyst may be held in a packed bed and the reactants passed over the catalyst. A packed bed flow reactor is commonly called a fixed bed reactor and the term plug-flow is also used to indicate that no attempt is made to back-mix the reaction mixture as it passes through the catalyst bed. The main modes of operation of a flow reactor are differential involving a small amount of reaction so that the composition of the mixture is approximately constant throughout the catalyst bed, or integral involving a more substantial amount of reaction such that the composition of material in contact with the final section of the catalyst bed is different from that entering the bed. 

Immobilized Enzyme Reactor (Fixed-Bed Reactor with Plug-Flow)... 

The reactor equation for a fixed-bed reactor with plug flow is Eq. (5.13). 

Removal of the metal contaminants is not usually economical, or efficient, during rapid regeneration. In fact, the deposited metals are believed to form sulfates during removal of carbon and sulfur compounds by combustion that produce a permanent poisoning effect. Thus, if fixed-bed reactors are to be used for residuum or heavy oil hydrodesulfurization (in place of the more usual distillate hydro-desulfurization) it may be necessary to first process the heavier feedstocks to remove the metals (especially vanadium and nickel) and so decrease the extent of catalyst bed plugging. Precautions should also be taken to ensure that plugging of the bed does not lead to the formation of channels within the catalyst bed which will also reduce the efficiency of the process and may even lead to pressure variances within the reactor because of the distorted flow patterns with eventual damage. 

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