Reactor dead-end

Remarks Dead-end reactor with a hollow shaft or a nuiltistirrer system possible Internals like disc-donuts or perforated plates can be inserted Internal gas circulation without pumping device possible... 

Another reaction performed in the dead-end reactor discussed before, is the allylic amination of 3-phenyl-2-propenyl-carbonic acid methyl ester with morpholine. [30] First and second generation commercially available DAB-dendrimers were functionalized with diphenylphosphine groups (Figure 4.13). Two different membranes were used, the Nadir UF-PA-5 (ultrafiltration) and the Koch MPF-50 (former SELRO) (nanofiltration), which gave retentions of 99.2% and 99.9% respectively for the second generation functionalized dendrimers. 

Double Michael addition reactions between methyl vinyl ketone (MVK) and ethyl a-cyanoacetate under continuous conditions (dead-end reactor) were performed with a dodecakis (NCN-Pd") catalyst by the van Koten group (12). A high productivity and retention (99.5%) of the catalyst for more than 24 h was observed, but slow deactivation of the system occurred after a stable conversion level had been reached [23]. 

TS) and outer side (shell side, SS) of the membrane. The membrane itself is considered to be catalytically inert. The reactants are converted on the alternatively also catalyst particles, positioned in the tube side of the membrane (e.g., catalyst can be placed in the shell side). The dead-end reactor configuration shown in the figure (i.e. closed shell-side outlet) allows dosing reactants through the membrane in a controlled manner, with predefined flow rates. All reactants dosed have to permeate through the membrane. The products and the unconverted reactants leave the reactor at the tube side outlet. The PBMR shown in Fig. 

Fig.3a-d. Interfacial contact membrane reactors (adapted from [110]). B biocatalyst, S substrate, P product. Shaded area organic phase, white area-, aqueous phase. Dead-end reactor is a hybrid system, combining an emulsion reactor and a membrane module in the same imit, through which the organic phase flows, while aqueous phase is rejected... 

Basically, two different kinds of experiments can be carried out to analyze the kinetics of hydrogen absorbing metallic membranes (Fig. 18.25) (i) permeation experiment (the membrane is positioned between two reaction chambers) and (ii) sorption experiments (the membrane is not positioned between two reaction chambers but in a dead-end reactor). 

Porous composite polyethersulfone/poly(styrene sulfonate) hollow fibres containing palladium nanoparticles have been efficiently used in the liquid-phase reduction of nitrophenol to aminophenol by sodium borohydride in a forced-flow reactor. The crossed-flow and dead-end reactor configuration were compared (Fig. 1.7). 

Glaser and Litt (G4) have proposed, in an extension of the above study, a model for gas-liquid flow through a b d of porous particles. The bed is assumed to consist of two basic structures which influence the fluid flow patterns (1) Void channels external to the packing, with which are associated dead-ended pockets that can hold stagnant pools of liquid and (2) pore channels and pockets, i.e., continuous and dead-ended pockets in the interior of the particles. On this basis, a theoretical model of liquid-phase dispersion in mixed-phase flow is developed. The model uses three bed parameters for the description of axial dispersion (1) Dispersion due to the mixing of streams from various channels of different residence times (2) dispersion from axial diffusion in the void channels and (3) dispersion from diffusion into the pores. The model is not applicable to turbulent flow nor to such low flow rates that molecular diffusion is comparable to Taylor diffusion. The latter region is unlikely to be of practical interest. The model predicts that the reciprocal Peclet number should be directly proportional to nominal liquid velocity, a prediction that has been confirmed by a few determinations of residence-time distribution for a wax desulfurization pilot reactor of 1-in. diameter packed with 10-14 mesh particles. 

In this paper we formulated and solved the time optimal problem for a batch reactor in its final stage for isothermal and nonisothermal policies. The effect of initiator concentration, initiator half-life and activation energy on optimum temperature and optimum time was studied. It was shown that the optimum isothermal policy was influenced by two factors the equilibrium monomer concentration, and the dead end polymerization caused by the depletion of the initiator. When values determine optimum temperature, a faster initiator or higher initiator concentration should be used to reduce reaction time. 

The dead-end setup is by far the easiest apparatus both in construction and use. Reactor and separation unit can be combined and only one pump is needed to pump in the feed. A cross-flow setup, on the other hand, needs a separation unit next to the actual reactor and an additional pump to provide a rapid circulation across the membrane. The major disadvantage of the dead-end filtration is the possibility of concentration polarization, which is defined as an accumulation of retained material on the feed side of the membrane. This effect causes non-optimal membrane performance since losses through membrane defects, which are of course always present, will be amplified by a high surface concentration. In extreme cases concentration polarization can also lead to precipitation of material and membrane fouling. A membrane installed in a cross-flow setup, preferably applied with a turbulent flow, will suffer much less from this... 

Figure 4.2. Dead-end filtration reactor described by Vogt et

Using unmodified Ru-BINAP and Rh-Et-DUPHOS catalysts Jacobs et al. performed hydrogenation reactions of dimethylitaconate (DMI) and methyl-2-acetamidoacrylate (MAA), respectively. [11,47] The continuous hydrogenation reaction was performed in a 100 mL stirred autoclave containing an MPF-60 membrane at the bottom, which also acts as a dead-end membrane reactor. The hydrogenation reactions will be discussed in paragraph 4.6.1. 

Dead-block coders, 7 691 Dead-burned dolomite, 15 27, 53 Dead-end filtration, 11 388 15 827, 829 Dead end hydrogenation reactor, 10 811, 812... 

Two types of continuous membrane reactors have been applied for oligomer- or polymer-bound homogeneous catalytic conversions and recycling of the catalysts. In the so-called dead-end-filtration reactor the catalyst is compartmentalized in the reactor and is retained by the horizontally situated nanofiltration membrane. Reactants are continuously pumped into the reactor, whereas products and unreacted materials cross the membrane for further processing [57]. 

Complete Mix Reactor - The complete mix reactor is also labeled a completely stirred tank reactor. It is a container that has an inhnite diffusion coefficient, such that any chemical that enters the reactor is immediately mixed in with the solvent. In Example 2.8, we used the complete mix reactor assumption to estimate the concentration of three atmospheric pollutants that resulted from an oil spill. We will use a complete mix reactor (in this chapter) to simulate the development of high salt content in dead-end lakes. A series of complete mix reactors may be placed in series to simulate the overall mixing of a one-dimensional system, such as a river. In fact, most computational transport models are a series of complete mix reactors. 

Figure 11.9 Different arrangements and modes of operation for membrane bioreactors Continuous Stirred Tank Reactor (CSTR) with recirculation arrangement (a), dead-end cell (b), tubular with entrapped enzyme (c).

Membrane reactors allow a different option for the separation of biocatalysts from substrates and products and for retention in the reactor. Size-specific pores allow the substrate and product molecules, but not the enzyme molecules, to pass the membrane. Membrane reactors can be operated as CSTRs with dead-end filtration (Figure 5.5e) or as loop or recycle reactors (Figure 5.5f) with tangential (crossflow) filtration. 

Fig. 3 Schematic representation of batch-wise passive membrane dialysis (A) and continuous membrane filtration dead-end-filtration (B) and loop reactor (C)...

In general, two types of CFMRs are applied in homogeneous catalysis the dead-end-filtration reactor (Fig. 3B) and the loop reactor (Fig. 3C) [19]. In the dead-end-filtration reactor the nanosized catalyst is compartmentalized in the reactor and is retained by nanofiltration membranes. Reactants are continuously pumped into the reactor, whereas small molecules (products and substrates) cross the perpendicularly positioned membrane due to the pressure exerted. Unreacted materials can be processed by adding them back into the reactor in this set-up. Concentration polarization of the catalyst near to the membrane surface can occur using this technique. In contrast, when a loop reactor is used, such behavior is prevented, since the solution is continuously circulated through the reactor and no pressure is exerted in the direction of the parallel-positioned membrane, so small particles cross the membrane laterally. 

A specific feature of the membrane reactor is the fact that a dead end configuration regarding the shell side was implemented. This means that all gas... 

Fig. 12.17. Comparison between experimental results obtained in a conventional (co-feed) fixed-bed reactor (FBR) and in a membrane reactor (MR) where the oxygen was dosed from the shell side over the membrane wall in a dead-end configuration. Conditions xo2° = 0.004 xc2H6° = 0.007 GHSV = 38 000 hr1.

Surface aeration is usually employed for slow reactions or for batch processes. It can be used in semicontinuous systems when it is desirable to recirculate the gas from the headspace. This is frequently the case in hydrogenation and is referred to as dead-end hydrogenation. In this system, gas is fed continuously to the reactor at the rate at which hydrogen is being consumed no compression costs to overcome the static head of liquid or external recirculation is needed. Feeding gas from the headspace may be preferred when there is a possibility of plugging sparger holes with reaction products. Surface aerators are also extensively used for waste-water treatment. There are two types of surface aerators the brush aerator, and the most commonly used turbine aerator. 

In filtration unit operation, especially in microfiltration, one usually differentiates between dead-end filtration (with cake formation) and cross-flow filtration [25] (Fig. 5). The cross-flow filter can have different geometries (Fig. 6) phase membranes, tubular membranes, or pleated membranes, of which the tubular and pleated ones are already accepted as cross-flow geometries in reactor technology, as mentioned above. In filtration engineering the cross-flow term means that the filtrate flows perpendicularly to the suspension stream. Cross-flow may not be considered a sufficiently illustrative term here [25]. A better term would be parallel filtration, but the term cross-flow filtration has been accepted generally and may be difficult to change at present. 

In a general way, most of ceramic membrane modules operate in a cross-flow filtration mode [28] as shown in Figure 6.18. However, as discussed hereafter, a dead-end filtration mode may be used in some specific applications. Membrane modules constitute basic units from which all sorts of filtration plants can be designed not only for current liquid applications but also for gas and vapor separation, membrane reactors, and contactors, which represent the future applications of ceramic membranes. In liquid filtration, hydrodynamics in each module can be described as one incoming flow on the feed side gf, which results in two... 

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