Trickle-bed cell

Davison et al. [73] produced hydrogen peroxide in a trickle-bed cell design (Fig. 15) with graphite chips and reticulated vitreous carbon (RVC) cathodes in 2 M NaOH electrolyte. Using graphite chips as the cathode, the current efficiency was 100% for H2O2 evolution at potentials more positive than - 0.7 V vs. SCE. Under identical conditions the RVC cathodes exhibited similar behavior up to -0.7 V. 

Fig. 15. Two-compartment trickle-bed cell used for hydrogen peroxide synthesis. (Adapted from [73]).

Dow Chemical developed a modification of the trickle-bed cell, in which a liquid permeable membrane separated two chambers [72]. As shown in Fig. 17, a packed-... 

Fig. 17. Diaphragm flow controlled trickle-bed cell used by Dow Chemical Co. for the alkaline synthesis of hydrogen peroxide. (Adapted from [72]).

The trickle bed cell (Figure 3) was investigated by Davison et. aL [39] using graphite chips and Reticulated Vitreous Carbon (RVC) cathodes in 2M NaOH electrolyte. At potentials more positive than -0.7V vs. SCE, current efficiencies for low catholyte flowrates were 100%, but at more negative potentials, the current... 

A modification of the trickle bed cell (Figure 5.) was recently developed by Dow Chemical [24]. The cell contained two chambers separated by a liquid... 

A promising start has been made in packed tube CFD simulation, especially at lower Re and for reduced geometries such as unit cells and bed segments. Applications to transport and catalyst particle assessment are active areas of research. We look forward to the insights that these simulations promise, to more streamlined and easier application of the CFD methods, and to wider applications such as two-phase flow in trickle beds. 

There are a few other kinds of industrial plants. An air-lift tower fermenter was developed by ICI for the production of single-cell protein from methanol which employs an external loop for heat removal. Trickle beds for the treatment of waste waters employ packing structures or packing elements of 4-6 cm dia and porosities above 50%. Microbial films are formed on the packing that react with the organic substrate and the air as the liquid flows down and the air up. 

UOP then carried out pilot-scale tests at still higher pressures in a fully automated explosion cell to reproduce vendor work and to study conditions and kinetics. Design was based on direct hydrogen peroxide synthesis using a mini-trickle bed reactor with a micro mixer. 

Haggin J. Trickle-bed electrolytic cell for peroxide developed. Chem Eng News 1984 12 16. 

Activation energy, stability in trickle-bed reactors, 76 Activation overpotential, cross-flow monolith fuel cell reactor, 182 Activity balance, deactivation of non-adiabatic packed-bed reactors, 394 Adiabatic reactors stability, 337-58 trickle-bed, safe operation, 61-81 Adsorption equilibrium, countercurrent moving-bed catalytic reactor, 273 Adsorption isotherms, countercurrent moving-bed catalytic reactor, 278,279f... 

We focus on heterogeneous catalysis with single and multiple reactant phases, as these are the most common in practice. Examples include environmental catalysis, fat hardening, hydrodesulfurization of oil streams, hydrogenation of fine chemicals, and selective conversions catalyzed by immobilized enzymes or cells in biotechnology. The most popular reactors used in industry for multiphase applications are slurry bubble columns and trickle-bed reactors. They are shovm in Figure 1. 

Three-parameter PDE model (Van Swaaij et aL106) This model is largely used to correlate the RTD curves from a trickle-bed reactor. The model is based on the same concept as the crossflow or modified mixing-cell model, except that axial dispersion in the mobile phase is also considered. The model, therefore, contains three arbitrary parameters, two of which are the same as those used in the cross-flow model and the third one is the axial dispersion coefficient (or the Peclet number in dimensionless form) in the mobile phase (see Fig. 3-11). 

Three-parameter mixing-cell model (Van Swaaij et aL106) This is a stagewise model for liquid-phase backmixing in a trickle-bed reactor. According to this model, an elementary mixing pattern for trickle flow is expressed as106... 

Trickle bed reactors Slurry reactors Three-phase fluidized beds No Little Little Modeling on basis of unit cell approach + development of correspondence rules for macroscopic system behavior Modeling of the effect of the solids phase on interfacial transport phenomena Modeling of the effect of the solids phase on interfacial transport phenomena -I- development of refined models for particle-particle and particle-wall interaction... 

It should also be observed that the catalytic cell reactor (described in Section II.D), which is intended to be an alternative reactor to trickle beds for liquid-phase hydrogenations, is a further-developed electrochemical filter-press cell based on the firm Electro Cell AB s concept with respect to the preparation of thin, porous electrodes. 

Figure 1 can represent a wide range of other practical situations. The continuous phase may be liquid or gas. the latter representing special cases such as "sol id-state fermentations (e.g.. composting, trickle-bed reactors, and Koji" processes) while the disprsed phase may be one or more of the following phases solid (e.g.. microbial cells, immobi lized-enzyme... 

Also, Valerius et al. [28, 29] show by exact formulation that the balance of the solid-phase (catalyst) actually is a balance of the liquid phase and/or gas phase in the catalyst pellet. Nevertheless, this text will follow the international trend and designate the trickle-bed reactor balance equations for the gas/liquid phase in the catalyst grain as balance for the solid phase or catalyst . The complex hydrodynamic relations in trickle-bed reactors together with the various assumptions or neglects result in widely different structured mathematical models. Two basic types of models, the differential models and the cascade or cell models, are most frequently used in the literature. 

Figure 11.8 Design concepts of three further cells for metal recovery from dilute solutions of metal ions, (a) Cell with circulating bed cathode, (b) The Swiss-roll cell, (c) The trickle tower cell...

This review puts its focus on high-throughput preparation of heterogeneous catalysts, that is, solid-state materials that are apphed in fixed-bed reactors for gas-phase reactions and in trickle-bed or stirred-tank reactors for liquid or gas-hquid reactions, respectively. Other fields of catalysis are not discussed since very different catalytic systems are used. We refer to the following reviews for homogeneous catalysis (2, 3), where combinatorial catalysis deals mainly with variation of ligands and for electrochemical catalysis [4,5], where catalysts are prepared as arrays of thin films in electrochemical cells. 

This technique has been successfully used to characterize multispecies population in a laboratory-scale trickle bed bioreactor used for the biodegradation of a mixture of polyalkylated benzenes. Interestingly, the in situ hybridization results revealed that the aromatic-degrading cells constitute less than 10% while 60% of the cells were saprophytes and about 30% were inactive cells [119,120]. These saprophytes were believed to utilize intermediate compounds and cell lysis products. 

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