Column-type reactors

A new alternative approach for Stage I screening in liquid phase is the use of bubble column-type reactors. These parallel bubble columns can operate in batch and fed-batch mode regarding the reaction mixture, while a continuous stream of gas is used as reactant (H2, 02, or others) as well as for the intense agitation of the reaction mixture (Figure 11.39). 

Description Ethylene is compressed (6) and introduced to a bubble-column type reactor (1) in which a homogenous catalyst system is introduced together with a solvent. The gaseous products leaving the reactor overhead are cooled in a cooler (2) and cooled in a gas-liquid separator for reflux (3) and further cooled (4) and separated in a second gas-liquid separator (5). 

Generally, immobilized biocatalysts are packed in a column-type reactor this apparatus is called bioreactor , which is an effective item of production equipment apphed to a biocatalyst, such as an inunobilized enzyme. The column apparatus containing the immobilized biocatalyst is the core of the bioreactor. Some typical models are shown in Fig. 22.1. 

For designing a reactor on a larger scale, one merely needs to take into account gas dispersion (see sections 4.6.1 and 4.7.22) and heat transfer. Heat can be transferred via the reactor wall, but heat removal via an evaporating solvent is generally to be preferred (sections 8.3.2 and 8.3.3). Both effects can be controll simultaneously in a bubble column type reactor, by adjusting the gas flow rate. This reactor type has the advantage that there are no internals save the gas distributor. In a stirred reactor, the baffles and the impeller shaft are often liable to fouling. 

Since the reactor or synthesis vessel used in this instrument is a batch-type reactor unlike a column-type reactor used for small-scale DNA synthesis where the entire amount of solid support is suspended into reaction solution to give efficient coupling, it is very essential to have proper fluidization of the large amount of supports. Fluidization in this approach is effected by bubbling dry gas (argon) through the bottom of a reactor, resulting in complete suspension of the support. 

Catalytic desulfurization is at present carried out industrially by at least three of the major types of gas-liquid-particle operations referred to in Section I trickle reactors, bubble-column slurry reactors, and gas-liquid fluidized reactors. 

The expression gas-liquid fluidization, as defined in Section III,B,3, is used for operations in which momentum is transferred to suspended solid particles by cocurrent gas and liquid flow. It may be noted that the expression gas-liquid-solid fluidization has been used for bubble-column slurry reactors (K3) with zero net liquid flow (of the type described in Sections III,B,1 and 1II,V,C). The expression gas-liquid fluidization has also been used for dispersed gas-liquid systems with no solid particles present. 

Laboratory reactor for studying three-phase processes can be divided in reactors with mobile and immobile catalyst particles. Bubble (suspension) column reactors, mechanically stirred tank reactors, ebullated-bed reactors and gas-lift reactors belong the class of reactors with mobile catalyst particles. Fixed-bed reactors with cocurrent (trickle-bed reactor and bubble columns, see Figs. 5.4-7 and 5.4-8 in Section 5.4.1) or countercurrent (packed column, see Fig. 5.4-8) flow of phases are reactors with immobile catalyst particles. A mobile catalyst is usually of the form of finely powdered particles, while coarser catalysts are studied when placing them in a fixed place (possibly moving as in mechanically agitated basket-type reactors). 

The trickle-bed reactor (TBR) and slurry reactor (SR) are the most commonly used for multiphase reactions in the chemical industries. A new reactor type, the monolithic reactor (MR), offers many advantages. Therefore, these three types of reactors are discussed below in more detail. Their general characteristics are given in Table 5.4-44. With respect to slurry reactors, the focus will be on mechanically agitated slurry reactors (MASR) because these are more widely used in fine chemicals manufacture than column slurry reactors. 

The principle of the perfectly-mixed stirred tank has been discussed previously in Sec. 1.2.2, and this provides essential building block for modelling applications. In this section, the concept is applied to tank type reactor systems and stagewise mass transfer applications, such that the resulting model equations often appear in the form of linked sets of first-order difference differential equations. Solution by digital simulation works well for small problems, in which the number of equations are relatively small and where the problem is not compounded by stiffness or by the need for iterative procedures. For these reasons, the dynamic modelling of the continuous distillation columns in this section is intended only as a demonstration of method, rather than as a realistic attempt at solution. For the solution of complex distillation problems, the reader is referred to commercial dynamic simulation packages. 

If the flow-sheet is not part of the documentation for a project, then a simple, but consistent, identification code should be devised. The easiest code is to use an initial letter to identify the type of equipment, followed by digits to identify the particular piece. For example, H—heat exchangers, C—columns, R—reactors. The key to the code should be shown on the flow-sheet. 

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. 

Gas-liquid bubble column This reactor is of tubular shape (Figure 3.5). The liquid phase is agitated by the bubble rise of the gas phase. The gas phase flows through the reactor upward at a constant rate. The liquid phase is continuous. This reactor could be of continuous type, if the liquid is flowing through the reactor continuously or semibatch, if the liquid is stationary in the reactor. 

In some respects, airlift reactors (airlifts) can be regarded as modifications ofthe bubble column. Airlift reactors have separate channels for upward and downward fluid flows, whereas the bubble column has no such separate channels. Thus, fluid mixing in bubble columns is more random than in airlift reactors. There are two major types of airlift reactors, namely, the internal loop (IL) and the external loop (EL). 

Wen and Fan [6] have provided a comprehensive listing of various tracers and experimental techniques for determining the RTD in flow systems. Recent studies [10,11,12] have been performed employing an impulse tracer to determine the RTD in bubble columns and an oscillatory flow electrochemical reactor. The author [13,14] has employed both step-change and an impulse to determine the RTD of nozzle type reactors analysis of the RTD involves an atomic absorption spectrophotometer (AAS), a cine-projector, and a chart recorder. Figures 8-7 and 8-8 show the nozzle-type reactors and the AAS, respectively. Figure 8-9 gives a typical response curve from the AAS. 

The process to produce Delos is simple yet effective. The two key pieces of equipment are a well-stirred tank-type reactor and a separation column. A simplified flow diagram is shown in Figure 2.8. 

Class 1 equipment are also called column-type equipment. Under this category, there are the various multiphase contactors. Gas-liquid contactors include bubble columns, packed bubble columns, internal-loop and external-loop air-lift reactors, sectionalized bubble columns, plate columns, and others. Solid-fluid (liquid or gas) contactors include static mixers, fixed beds, expanded beds, fluidized beds, transport reactors or contactors, and so forth. For instance, fixed-bed geometry is used in unit operations such as ion exchange, adsorptive and chromatographic separations, and drying and in catalytic reactors. Liquid-liquid contactors include spray columns, packed extraction... 

A bubbler-type reactor is incorporated into the chromatographic system upstream of the column. The thoroughly dried carrier gas (high-purity argon containing about... 

Alternatives to the stirred tank have of course been proposed and used extensively for many years. Bubble column and trickle bed type reactors will be discussed below. But first however, let us consider the stirred tank in a little more detail. 

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