Reaction engineering column reactor

FIG. 19-31 Some examples of bubble column reactor types, (a) Conventional bubble column with no internals. (6) Tray bubble column, (c) Packed bubble column with the packing being either an inert or a catalyst. [From Mills, Ramachandran, and Chaudhari, Multiphase Reaction Engineeringfor Fine Chemicals and Pharmaceuticals, Reviews in Chemical Engineering, 8(1-2), 1992, Figs. 2, 3, and 4.]... 

The rapid development of biotechnology during the 1980s provided new opportunities for the application of reaction engineering principles. In biochemical systems, reactions are catalyzed by enzymes. These biocatalysts may be dispersed in an aqueous phase or in a reverse micelle, supported on a polymeric carrier, or contained within whole cells. The reactors used are most often stirred tanks, bubble columns, or hollow fibers. If the kinetics for the enzymatic process is known, then the effects of reaction conditions and mass transfer phenomena can be analyzed quite successfully using classical reactor models. Where living cells are present, the growth of the cell mass as well as the kinetics of the desired reaction must be modeled [16, 17]. 

The symposium upon which this volume is based focused on three areas in reaction engineering fluidized bed reactors, bubble column reactors, and packed bed reactors. Each area comprises a section of this book. Professor J. R. Grace chaired and coordinated the fluidized bed sessions Professors Y. T. Shah and A. Bishop, the bubble column reactor session and Professor A. Varma, the packed bed reactor session. Each section in this book opens with a brief review chapter by the session chairman that includes an overview of the chapters in each session. 

Bubble column reactors (BCR) are widely used in chemical process industries to carry out gas-liquid and gas--liquid-solid reactions, the solid suspended in the liquid phase being most frequently a finely divided catalyst (slurry reactor). The main advantages of BCR are their simple construction, the absence of any moving parts, ease of maintenance, good mass transfer and excellent heat transfer properties. These favorable properties have lead to their application in various fields production of various chemical intermediates, petroleum engineering, Fischer-Tropsch synthesis, fermentations and waste water treatment. 

After completing reaction-engineering work, it is first necessary to evolve a reactor configuration before one can start evaluating whether such hardware can perform the expected duties. In the case of bubble columns, evolving reactor hardware involves at least the following (also see Fig. 11.2) ... 

From reaction engineering it is known that in the case of an infinite number of vessels with a continuous feed stream, all fluid elements have the same residence time in the total system. This corresponds to a plug flow of an ideal tube reactor without any dispersiom Here the real chromatography column is replaced by a vessel cascade to quantify the separation efficiency. 

In engineering terms, polymer-supported species can be treated like any other heterogeneous system they can be used very flexibly in batch or column reactors, and in general are suitable for both gas or liquid phase reactions. Depending upon which mode of operation is chosen, a particular polymer structure and morphology might be more effective (see below). 

Table 12.1 Comparison of reaction engineering models for the Fischer-Tropsch synthesis in slurry bubble column reactor.

The connection between thermodynamics and chemical reaction engineering is very strong. First of all, we need to establish whether the conversions we desire at the temperatures and pressures involved are achievable—whether we reached the limits of thermodynamic equilibrium or are still left with room to maneuver. The second connection is the relation between the chemical and phase equilibria. If we are to design a reactor for a multiphase reaction, the phase equilibria become an immediate problem that we have to solve. The more novel connection comes later, when we intend to combine reaction with separation. A good a priori estimation in designing systans with a multitude of functionalities, such as a distillation column reactor or a monbrane reactor, requires the solution of the chemical reaction problems along with the phase equilibria and other defining constraints that come into play. 

Kastaneck F, Zahradnik J, Kratochvil J, Cermak J. Modeling of large-scale bubble column reactors for nonideal gas-liquid systems. In Doraiswamy LK, Mashelkar RA, eds. Frontiers in Chemical Reaction Engineering. New York Wiley Eastern, 1984, pp 330-344. 

Multi-environment systems with two flowing phases. These systems are perhaps of most interest in reaction engineering applications since they include the most frequently used multiphase reactors. Gas-liquid bubble columns, ebullated beds, three-phase fluidized beds, gas-lift slurry reactors, trickle-bed reactors, pneumatic transport reactors, etc. fall into this category. Some of the developments presented in Section 6.1.1 can be extended to treat these systems. The multivariable joint p.d.f. has to be defined taking into the account that the system has multiple inlets and outlets, i.e. by following the rules established in Section 3 by the appropriate extension of eqs. (9) and (10). However, this approach has not been presented or used to date. The main reason is that the transforms do not have a readily useable analytical form and are functions of many system... 

A hybrid CFD-reaction engineering framework for multiphase reactor modelling basic concept and application to bubble column reactors. Chem. Eng. Sci., 58, 3077 -3089. 

ToweU GD, Ackermann GH Axial mixing of liquid and gas in large bubble column reactors. In 2nd international symposium on chemical reaction engineering, Amsterdam, 1972, p. B 3-1. 

A number of reaction engineering models in literature have already utdized the concepts of TBC or single-bubble-class (SBC) together with the axial dispersion models to couple the hydrodynamics, mass transfer, and reaction in bubble column reactors. While some researchers claim that there is less difference in the SBC and TBC model predictions, others believe that the TBC model prediction is in better agreement with experiments. We find that the difference is actually relevant to the submodels for hydrodynamics, mass transfer, and reaction kinetic as well as gas contraction, and in particular the gas holdup model and whether the system is limited by reaction or mass transfer. Then a new reactor model is developed to replace the empirical... 

Dream reactions can be performed using chemical micro process engineering, e.g., via direct routes from hazardous elements [18]. The direct fluorination starting from elemental fluorine was performed both on aromatics and aliphatics, avoiding the circuitous Anthraquinone process. While the direct fluorination needs hours in a laboratory bubble column, it is completed within seconds or even milliseconds when using a miniature bubble column. Conversions with the volatile and explosive diazomethane, commonly used for methylation, have been conducted safely as well with micro-reactors in a continuous mode. 

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