Continuous multiphase reactors

Multiphase reactors can be batch, fed-batch, or continuous. Most of the design equations derived in this chapter are general and apply to any of the operating modes. Unsteady operation of nominally continuous processes is treated in Chapter 14. 

Reactor type Triple-feed continuous multiphase chip reactor system Micro-channel width depth length Not given in [28]... 

Our treatment of Chemical Reaction Engineering begins in Chapters 1 and 2 and continues in Chapters 11-24. After an introduction (Chapter 11) surveying the field, the next five Chapters (12-16) are devoted to performance and design characteristics of four ideal reactor models (batch, CSTR, plug-flow, and laminar-flow), and to the characteristics of various types of ideal flow involved in continuous-flow reactors. Chapter 17 deals with comparisons and combinations of ideal reactors. Chapter 18 deals with ideal reactors for complex (multireaction) systems. Chapters 19 and 20 treat nonideal flow and reactor considerations taking this into account. Chapters 21-24 provide an introduction to reactors for multiphase systems, including fixed-bed catalytic reactors, fluidized-bed reactors, and reactors for gas-solid and gas-liquid reactions. 

This situation describes an emulsion reactor in which reacting drops (such as oil drops in water or water drops in oil) flow through the CSTR with stirring to make the residence time of each drop obey the CSTR equation. A spray tower (liquid drops in vapor) or bubble column or sparger (vapor bubbles in a continuous liquid phase) are also segregated-flow situations, but these are not always mixed. We wiU consider these and other multiphase reactors in Chapter 12. 

In Chapter 12 we will consider multiphase reactors in which drops or bubbles carry one phase to another continuous fluid phase. In fact, these reactors frequently have a sohd also present as catalyst or reactant or product to create a three-phase reactor. We need the ideas developed in this chapter to discuss these even more complicated reactors. 

For the following continuous multiphase chemical reactors construct a table indicating the phases, whether they are mixed or unmixed, the major reactions, and in what phase(s) the reaction is occurring. A sketch may be helpful. 

A second consideration is the operating mode continuous, batch, or semi-continuous. An extensive textbook on theory, design and scale-up of multiphase reactors was published by Gianetto and Silveston in 1986 [22], supplementing "Three-phase catalytic... 

Knowledge of these types of reactors is important because some industrial reactors approach the idealized types or may be simulated by a number of ideal reactors. In this chapter, we will review the above reactors and their applications in the chemical process industries. Additionally, multiphase reactors such as the fixed and fluidized beds are reviewed. In Chapter 5, the numerical method of analysis will be used to model the concentration-time profiles of various reactions in a batch reactor, and provide sizing of the batch, semi-batch, continuous flow stirred tank, and plug flow reactors for both isothermal and adiabatic conditions. 

Emulsion Polymerization in a CSTR. Emulsion polymerization is usually carried out isothermally in batch or continuous stirred tank reactors. Temperature control is much easier than for bulk or solution polymerization because the small (. 5 Jim) polymer particles, which are the locus of reaction, are suspended in a continuous aqueous medium as shown in Figure 5. This complex, multiphase reactor also shows multiple steady states under isothermal conditions. Gerrens and coworkers at BASF seem to be the first to report these phenomena both computationally and experimentally. Figure 6 (taken from ref. (253)) plots the autocatalytic behavior of the reaction rate for styrene polymerization vs. monomer conversion in the reactor. The intersection... 

HYDRODYNAMIC STABILITY OF MULTIPHASE REACTORS TABLE I continued)... 

The most important parameter governing stability is the dispersion coefficient of the dispersed phase such as bubbles, drops, and particles. The published information is not sufficient. A comprehensive research program is needed for the measurement of dispersion in all multiphase reactors over a wide range of terminal velocities, column diameters, column heights, sparger designs, phase velocities, and continuous-phase physical properties. 

The multiphase reactors discussed in this edition of the book are the slurry reactor, fluidized bed, and the trickle bed reactor. The trickle bed reactor which has reaction and transport steps similar to the slurry reactor is discussed in the first edition of the book and on the CD-ROM along with the bubbling fluidized bed. In slurry reactors, the catalyst is suspended in the liquid and gas is bubbled through the liquid. A slurry reactor may be operated in either a semibafch or continuous mode. 

Multiphase Reactors Reactions between gas-liquid, liquid-liquid, and gas-liquid-solid phases are often tested in CSTRs. Other laboratory types are suggested by the commercial units depicted in appropriate sketches in Sec. 19 and in Fig. 7-17 [Charpentier, Mass Transfer Rates in Gas-Liquid Absorbers and Reactors, in Drew et al. (eds.), Advances in Chemical Engineering, vol. 11, Academic Press, 1981]. Liquids can be reacted with gases of low solubilities in stirred vessels, with the liquid charged first and the gas fed continuously at the rate of reaction or dissolution. Some of these reactors are designed to have known interfacial areas. Most equipment for gas absorption without reaction is adaptable to absorption with reaction. The many types of equipment for liquid-liquid extraction also are adaptable to reactions of immiscible liquid phases. 

Further details on these relations are given in many textbooks on thermodynamics (e.g., [125]) and will not be repeated here. However, before we continue our derivation of the basic energy equation, the improved descriptions of the thermodynamic variables that can be embedded in single - and multiphase reactor models with limited costs are pointed out. 

As in the case of other multiphase reactors discussed in this chapter, topical material divides itself rather naturally into three major aspects hydrodynamics, transport, and reaction processes. We will stay with fairly simple approaches, particularly in the area of hydrodynamics and correlations. An extensive amount of research continues to this day on trickle beds, so we cannot attempt to present the latest word. 

Reactions between components of a gas and a liquid, the kinetics of which were discussed in Chapter 6, are carried out in a variet> of equipment, often having confusing names. The variety stems from a number of conditions that have to be fulfilled simultaneously efficient contact between gas and liquid—and eventually a solid catalyst, limitation of pressure drop, ease of removal of heat, low cost of construction and operation. Depending on whether the main mass transfer resistance is located in the gas or in the liquid, multiphase reactors or absorbers are operated either with a distributed gas phase and continuous liquid phase or vice versa. Whether co- or countercurrent flow of gas and liquid is used depends on the availability of driving forces for mass and heat transfer and reaction. 

The work is organized in two parts in the first part kinetics is presented focusing on the reaction rates, the influence of different variables and the determination of specific rate parameters for different reactions both homogeneous and heterogeneous. This section is complemented with the classical kinetic theory and in particular with many examples and exercises. The second part introduces students to the distinction between ideal and non-ideal reactors and presents the basic equations of batch and continuous ideal reactors, as well as specih c isothermal and non-isothermal systems. The main emphasis however is on both qualitative and quantitative interpretation by comparing and combining reactors with and without diffusion and mass transfer effects, complemented with several examples and exercises. Finally, non-ideal and multiphase systems are presented, as well as specific topics of biomass thermal processes and heterogeneous reactor analyses. The work closes with a unique section on the application of theory in laboratory practice with kinetic and reactor experiments. 

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