Monolithic loop reactor

Figure 9.4 Monolithic loop reactor (MLR). (Reprinted from...

Heiszwolf JJ, Engelvaart LB, Gvd Eijnden M, Kreutzer MT, Kapteijn F, Moulijn JA. Hydrodynamic aspects of the monolithic loop reactor. Chem Eng Sci 2001 56 805-812. 

FIGURE 17 Monolithic loop reactors. Left, continuous mode right, batch mode. 

Monolithic Loop Reactor A novel MLR was developed af Air Products and Chemicals (Figure 17) (144). The reactor contains a monolithic catalyst operating under cocurrent downflow condifions. Because the residence time in the monolith is short and the heat of reaction has to be removed, the liquid is continually circulated via an external heat exchanger until the desired conversion is reached. The concept was patented for the hydrogenation of dinifrofoluene fo give toluenediamine (37). 

Boger et al. (42) analyzed the performance of MLRs with internal density-driven circulation (internal monolith loop reactor, IMLR) and foimd them to be superior to slurry reactors. 

Figure 6.2 Monolith loop-reactor configurations. From Heiszwolfet al. [6].

Borchers, 0., A monolith loop reactor as an attractive alternative to slurry reactors. Cat. Today 2003, 79-80, 441-451. 

Vandu, C. Ellenberger,). Krishna, R., Hydrodynamics and mass transfer in an upflow monolith loop reactor. Chem. Eng. Prog. 2005, 44, 363 374. 

Broekhuis, R.R., Machado, R.M., and Nordquist, A.F. (2001), The ejector-driven monolith loop reactor Experiments and modeling, Catalysis Today, 69(1-4) 87-93. 

Guettel and Turek [56] compared four reactor types, namely, fixed bed, slurry bubble column, monolith loop, and microstructured. A one-dimensional (no axial mixing) modeling approach was used to make the comparisons. One of their conclusions was... 

Eisenbeis C, Guettel R, Knnz U, Tnrek T. Monolith loop reactor for hydrogenation of glucose. Catal Today 2009 147 S342-6. 

Reactors with a packed bed of catalyst are identical to those for gas-liquid reactions filled with inert packing. Trickle-bed reactors are probably the most commonly used reactors with a fixed bed of catalyst. A draft-tube reactor (loop reactor) can contain a catalytic packing (see Fig. 5.4-9) inside the central tube. Stmctured catalysts similar to structural packings in distillation and absorption columns or in static mixers, which are characterized by a low pressure drop, can also be inserted into the draft tube. Recently, a monolithic reactor (Fig. 5.4-11) has been developed, which is an alternative to the trickle-bed reactor. The monolith catalyst has the shape of a block with straight narrow channels on the walls of which catalytic species are deposited. The already extremely low pressure drop by friction is compensated by gravity forces. Consequently, the pressure in the gas phase is constant over the whole height of the reactor. If needed, the gas can be recirculated internally without the necessity of using an external pump. 

Bubble column Loop reactor Packed column Plate column Monolithic reactor... 

The reactor design must account for heat removal as well as chemical reaction. For monoliths, the unique situation exists that because of the low-pressure drop, external heat removal in a liquid loop is feasible 38,39). Alternatively, structured packings can be applied that improve radial transport 124,126). 

Reactor Stirred tank Bubble column Jet-loop 3-Phase fluid bed Trickle-bed 3-Phase Monolith... 

Except the recycle loop reactor, real reactors, either packed beds or monoliths, are neither plug flow nor mixed flow reactors. However, in small laboratory reactors, heat conduction tln-ough the solid phase probably makes the temperature to be unifonn as in mixed flow. Conversely, the concentration profiles are those of plug flow. Real LO curves are thus intennediate between tliose of plug and mixed flow. 

Experiments with laboratory monoliths of small cross-section area can lead to biased results due to an uneven flow distribution in the channels, especially close to the reactor wall. The wash-coat of the outer broken chaimels should be scraped away, and the void between the reactor wall and the monolith should be carefully plugged. To minimize wall effects, the diameter of the monolith should be ten tunes the chaimel diameter at least. Plug flow must prevail in a packed bed of crushed catalyst. The bed length and radius should be more than 50 and 10 particle diameters respectively, the flow resistance of the bed support must be unifonn throughout its cross-section, and the particle size distribution must be as narrow as possible. Otherwise, there can be oy-passes or dead vohunes. These hydrodynamic problems are overcome in a recycle loop reactor because the same physical and chemical conditions prevail everywhere. 

Very short contact time available monolith with low pressure drop or fluidized/loop reactors with recycle ... 

Slurry reactor, trickle bed reactor, loop reactor, catalytic monolith, or other structured reactor... 

Kinetics can be screened in a screw impeller-stirred reactor (SISR) [7] (Figure 9.8). The reactor system comprises a screw impeller that pumps the liquid upwards, and the high exit velocity of the liquid results in an effective foam formation in the top section of the reactor. A slug flow (Chapter 6) is thus established in the monolith channels. Consequently, the liquid and gas are pumped from the lower section to the upper section of the reactor, over and over again. In fact, the concept resembles that of a loop reactor. Cylindrical monoliths are placed in the stator of an SISR (Figure 9.8), and a foam of gas and liquid is forced through the monolith channels by a screw. 

Reactor style Modular, loop type Integral type, monolithic... 

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