Reactors packed type

Reactor type Packed-bead capillary micro flow reactor Packed-bead bed length 2-10 mm... 

Fig. 6. Examples of types of meshes developed to resolve laminar flow around particles (a) Chimera grid. Reprinted, with permission, from the Annual Review of Fluid Mechanics, Volume 31 1999 by Annual Reviews www.annualreviews.org (b) Unstructured grid with layers of prismatic cells on particle surfaces. Reprinted from Chemical Engineering Science, Vol. 56, Calis et al., CFD Modeling and Experimental Validation of Pressure Drop and Flow Profile in a Novel Structured Catalytic Reactor Packing, pp. 1713-1720, Copyright (2001), with permission from Elsevier.

Various reactor types have been used as the foundation for microreactor designs, including coated wall reactors, packed-bed reactors, structured catalyst reactors, and membrane reactors. 

Deviation from the two ideal flow patterns can be caused by channeling of fluid, by recycling of fluid, or by creation of stagnant regions in the vessel. Figure 11.1 shows this behavior. In all types of process equipment, such as heat exchangers, packed columns, and reactors, this type of flow should be avoided since it always lowers the performance of the unit. 

In a method proposed by Booth et al. (141) for the determination of phylloquinone in various food types, extracted samples are subjected to silica solid-phase extraction followed, in the case of meat or milk samples, by further purification using reversed-phase solid-phase extraction or liquid-phase reduction extraction, respectively. The final test solution is analyzed by NARP-HPLC, and the fluorescent hydroquinone reduction products of phylloquinone and the internal standard are produced online using a postcolumn chemical reactor packed with zinc metal. 2, 3 -Dihydrophylloquinone, a synthetic analog of phylloquinone, is a suitable internal standard for the analysis of vegetable juice, whole milk, and spinach. Another synthetic analog, Ku23), is used for the analysis of bread and beef, because a contaminant in the test solution coelutes with dihydro-phylloquinone. 

Reactors. TWo types of reactors will be discussed, a straight-tkmugh transport reactor, which is also referred to as a riser or circulating fluidized bed, and a packed-bed reactor (PER), which is also referred to as u fixed-bed reactor. 

In our discussion of surface reactions in Chapter 11 we assumed that each point in the interior of the entire catalyst surface was accessible to the same reactant concentration. However, where the reactants diffuse into the pores within the catalyst pellet, the concentration at the pore mouth will be higher than that inside the pore, and we see that the entire catalytic surface is not accessible to the same concentration. To account for variations in concentration throughout the pellet, we introduce a parameter known as the effectiveness factor. In this chapter we will develop models for diffusion and reaction in two-phase systems, which include catalyst pellets and CVD reactors. The types of reactors discussed in this chapter will include packed beds, bubbling fluidized beds, slurry reactors, and trickle beds. After studying this chapter you will be able to describe diffusion and reaction in two- and three-phase systems, determine when internal pore diffusion limits the overall rate of reaction, describe how to go about eliminating this limitation, and develop models for systems in which both diffusion and reaction play a role (e.g., CVD). 

A photograph of different types and sizes of catalyst is shown in Figure 10-5(a). A schematic diagram of a tubular reactor packed with catalytic pellets is showm in Figure I0-5(b). The overall process by w-hich heterogeneous catalytic reactions proceed can be broken down into the sequence of individual steps shown in Table 10-2 and pictured in Figure 10-6 for an i.somerizalion reaction. 

The second reactor setup type is commonly referred to as a biofilm bioreactor. This reactor is filled with packing material onto which a microbial biofilm is allowed to develop and biomass retention is achieved without the need for special membranes. Selected examples of this second type of reactor are provided in Table 7. 

Like enzymes, whole cells are sometimes immobilized by attachment to a surface or by entrapment within a support. One motivation for this is similar to the motivation for using biomass recycle in a continuous process. The cells are grown under optimal conditions for cell growth but are used at conditions optimized for production of a secondary metabolite. A hollow-liber reactor, similar to those used for cross-flow filtration, can be used to entrap the cells while allowing input of the substrate and removal of products. Attachment of the cells to a nonreactive material such as alumina allows a great variety of reactor types including packed beds, fluidized and spouted beds, and air-lift reactors. Packed beds with a biofilm on the packing are commonly used for wastewater treatment. A semicommercial process for beer used an air-lift reactor to achieve reaction times of one day compared to five to seven days for the normal batch process. Unfortunately, the beer suffered from a mismatched flavor profile that was attributed to mass transfer limitations. 

Derivatlzatlon reactions are carried out In various types of detectors. Open reactors (straight, colled, knotted) are used with fast reactions, while packed reactors or air-segmented systems are to be preferred for slower reactions. The use of reactors packed with an active material (enzymatic or non-enzymatlc reactor) taking part In the derlvatizatlon is becoming more and more frequent. Post-column liquid-liquid extraction is basically used to remove the excess of derivatlzatlon reagent which might Interfere with the detection of the reaction product. 

As an example related to the energy consumption. Figure 3 shows the comparison of 5 different NTP reactors for the removal of 200 ppmv benzene as a model VOC. Regardless of the reactor type, gas-phase homogeneous NTPs (i.e. DBD, SD and pulsed corona) showed similar performances. The PDC reactor packed with l,0wt%-Ag/TiO2 catalyst indicated much... 

Gas-liquid reactions are most often conducted in stirred-tank systems with flow of both gas and liquid through the reactors, or in bubble eolumns, or in packed columns—with countercurrent flow typical in the last two. For the most part the analysis given is independent of the specific configuration of the reaetor (bubbles are still with us and still important in design), but correlations for transport eoeffieients may vary with the individual reactor and type of operation. 

The catalytic dehydrogenation of cyclohexane in an FAU-type zeolite-membrane reactor packed with a 1 wt.% Pt/ AI2O3 catalyst has been studied by Jeong et al. [247,248]. The conversion of cyclohexane in the membrane reactor is... 

As can be seen in Table 19.2, and with some more details in Table 19.3 (this last table shows a short list of some relevant membranes used in the ethyl acetate production research together with separation factors and fluxes obtained), zeolite-based membranes (mordenite and zeolite A) were also tested by De La Iglesia et al. (2007) in an ISU-type continuous membrane reactor packed with Amberlyst 15. Both membranes were capable of shifting the equilibrium (in <1 day) and, in particular, mordenite membranes allowed conversions of approximately 90% and high separation factors of H20/ethanol and H20/acetic acid (>170). Moreover, because of the lower content in aluminum, under acid conditions, mordenite membranes were more stable than zeolite A. Hence, mordenite was also used by De La Iglesia et al. (2006), in another work, to prepare two-layered mordenite-ZSM-5 composite membranes, as shown in Figure 19.15. A tubular alumina tube was used as support. As a result, the feasibility of coupling the separation characteristics of the mordenite layer with the catalytic behavior of the H-ZSM-5 layer was demonstrated. 

Catalytic activities for thiophene HDS were measured at atmospheric pressure in a flow-type reactor packed with 0.2g of catalyst. The solids were first sulfid with a H2S/H2 (10/90) mixture at a flow rate of lOOml/min at 673 K for 2h and then cooled down to 573 K. After purification by vacuum distillation, thiophene was introduced in the reactor at constant pressure (SO torr) in a flow of purified hydrogen (20 ml/min.). The reaction products were analyzed by gaz chromatography. 

Several bioreactor designs are used to produce bioproducts, and include, but are not limited to batch reactors, fed-batch reactors, continuous cultivation reactors, plug flow reactors, recycle bioreactor systems, immobilized cell reactors, biofilm reactors, packed bed reactors, fluidized-bed reactors, and dialysis cultivation reactors (Williams 2002). These reactor types can contain either mixed or pure cultures, and can stimulate heterotrophic and/or phototrophic cellular functions depending on the specific reactor design. Additionally, these reactor schemes can be used to produce products directly, or to harvest biomass or other products for downstream processes. Due to the complex nature of bioreactors, particularly anaerobic digesters, the use of metagenomics is helpful to understand the physiology of such systems. 

Packed reactors. A packed reactor is more popular with very corrosive applications. A designer needs to allow for good distribution and avoid overly large packing and bed depth. Packing types include various kinds of rings and saddles. 

Oxidation Step. A review of mechanistic studies of partial oxidation of propylene has appeared (58). The oxidation process flow sheet (Fig. 2) shows equipment and typical operating conditions. The reactors are of the fixed-bed shell-and-tube type (about 3—5 mlong and 2.5 cm in diameter) with a molten salt coolant on the shell side. The tubes are packed with catalyst, a small amount of inert material at the top serving as a preheater section for the feed gases. Vaporized propylene is mixed with steam and ak and fed to the first-stage reactor. The feed composition is typically 5—7% propylene, 10—30%... 

Flow Reactors Fast reactions and those in the gas phase are generally done in tubular flow reaclors, just as they are often done on the commercial scale. Some heterogeneous reactors are shown in Fig. 23-29 the item in Fig. 23-29g is suited to liquid/liquid as well as gas/liquid. Stirred tanks, bubble and packed towers, and other commercial types are also used. The operadon of such units can sometimes be predicted from independent data of chemical and mass transfer rates, correlations of interfacial areas, droplet sizes, and other data. 

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