Monolithic reactors three-phase processes

J.A. (2006) Monolithic catalysts for three-phase processes, in Structured Catalysts and Reactors, 2nd edn. 

Obviously, the least experience has been accumulated with monoliths, particularly in three-phase applications. They are also more expensive than the other reactors. Therefore, the use of monoliths can only be economically ju.stified for three-phase processes in which it offers a distinct advantage, like higher yield, improved. selectivity, increased throughput of a plant, or lower overall investment or operating costs. Of particular interest are situations in which a MR substantially simplifies the design or operation of a unit. 

Andersson B, Irandoust S, Cybulski A. Modeling of monolith reactors in three-phase processes. In Cybulski A, Moulijn JA, eds. Structured Catalysts and Reactors. Chemical Industries, Vol. 71. New York Marcel Dekker, 1998 267-304. 

An interesting monolithic configuration has recently been disclosed that can be suitable for three-phase processes carried out in countercurrent mode [10]. This can be particularly important for processes in which both thermodynamic and kinetic factors favor countercurrent operation, such as catalytic hydrodesulfurization. The flooding of a reactor is a considerable limitation for the countercurrent process run in conventional fixed-bed reactors. Flooding will not occur to that extent in the new monolith. A configuration of channels of the new monolith is such that subchannels open to the eentcrline are formed at the walls. The liquid flows downward, being confined in these subchannels and kept there by surface tension forces. The gas flows upward in the center of the channel. The results of studies on the new monolith concept are presented in Chapter 11 of this book. 

V. APPLICATION OF MONOLITH REACTORS IN THREE-PHASE PROCESSES... 

R. K. Edvinsson, Monolith reactors in three-phase processes. PhD dissertation, Chalmers University of Technology, Gdteborg, 1994. 

Modeling of Monolith Reactors in Three-Phase Processes... 

R. Edvinsson, Monolith Reactors in Three-Phase Processes, Ph.D. dissertation Chalmers University of Technology, Coteborg, Sweden, 1994. 

Recently, a novel technology for three-phase processes has been developed the monolith catalyst, sometimes also called the frozen slurry reactor. Similar to catalytic gas-phase processes (Section 4.1), the active catalyst material and the catalyst carrier are flxed to the monolith structure. The gas and liquid flow through the monolith channels. The flow pattern in the vertical channels is iUustrated in Figure 6.14. At low gas velocities, a bubble flow dominates, and the bubble size distribution is even. At higher gas flow rates, larger... 

Cybulski A, Albers R, Moulijn JA. 2006. Monolithic catalysts for three-phase processes. In Cybulski A, Moidiin JA (editors). Structure catalysis and reactors, 2nd edn. Boca Raton, FL Taylor Francis, pp. 355-392. 

In the design of optimal catalytic gas-Hquid reactors, hydrodynamics deserves special attention. Different flow regimes have been observed in co- and countercurrent operation. Segmented flow (often referred to as Taylor flow) with the gas bubbles having a diameter close to the tube diameter appeared to be the most advantageous as far as mass transfer and residence time distribution (RTD) is concerned. Many reviews on three-phase monolithic processes have been pubhshed [37-40]. 

Cybulski et al. [39] have studied the performance of a commercial-scale monolith reactor for liquid-phase methanol synthesis by computer simulations. The authors developed a mathematical model of the monolith reactor and investigated the influence of several design parameters for the actual process. Optimal process conditions were derived for the three-phase methanol synthesis. The optimum catalyst thickness for the monolith was found to be of the same order as the particle size for negligible intraparticle diffusion (50-75 p.m). Recirculation of the solvent with decompression was shown to result in higher CO conversion. It was concluded that the performance of a monolith reactor is fully commensurable with slurry columns, autoclaves, and trickle-bed reactors. 

Hydrogen peroxide is mostly produced on a large scale using the anthraquinone (AQ) autoxidation process. The key step is the selective liquid-phase hydrogenation of the AQs to their corresponding hydroquinones (Scheme 9.8). An industrial process has been designed at Chalmers University and developed and used by Akzo-Nobel on the pilot scale. It involves a three-phase monolith reactor but very few details... 

There have been many review articles and monographs (e.g., Cybulski and Moulijn [2] and Chen et al. [3]) dedicated to this topic. In this chapter, we focus on the design and classical transport-reaction analysis of these reactors (Section 8.2). Then, it is showed how the relevant regimes of operation of a monolith can be identified in terms of ranges of dimensionless parameters, which combine the variables describing the geometry, operation, and physicochemical properties of the system. This can be done analytically as illustrated in Section 8.3. The issue of performance evaluation in isothermal monoliths is also discussed. While most part of the chapter refers to gas-solid or liquid-solid processes. Section 8.4 presents some considerations about three-phase systems. 

Traditionally, monolith reactors have demonstrated their performance in gas-phase reactions, particularly in the treatment of automotive exhaust gases. Today, virtually all vehicles are equipped with catalytic converters. Here we will consider three-phase applications. These have been studied by a few authors and research groups such as Moulijn and coworkers [4,5] and Irandoust and Andersson [6]. Certain industrial processes such as hydrogenation of anthraquinone in the production of hydrogen peroxide are also examples of the monolith reactor technology being established on an industrial scale. Monolith... 

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