Multiphase chemical reactor

A number of successful devices have been in use for finding mass-transfer coefficients, some of which are sketched in Fig. 23-29, and all of which have known or adjustable interfacial areas. Such laboratoiy testing is reviewed, for example, by Danckwerts (Ga.s-Liquid Reac-tion.s, McGraw-Hih, 1970) and Charpentier (in Ginetto and Silveston, eds., Multiphase Chemical Reactor Theory, De.sign, Scaleup, Hemisphere, 1986). 

Two complementai y reviews of this subject are by Shah et al. AIChE Journal, 28, 353-379 [1982]) and Deckwer (in de Lasa, ed.. Chemical Reactor Design andTechnology, Martinus Nijhoff, 1985, pp. 411-461). Useful comments are made by Doraiswamy and Sharma (Heterogeneous Reactions, Wiley, 1984). Charpentier (in Gianetto and Silveston, eds.. Multiphase Chemical Reactors, Hemisphere, 1986, pp. 104—151) emphasizes parameters of trickle bed and stirred tank reactors. Recommendations based on the literature are made for several design parameters namely, bubble diameter and velocity of rise, gas holdup, interfacial area, mass-transfer coefficients k a and /cl but not /cg, axial liquid-phase dispersion coefficient, and heat-transfer coefficient to the wall. The effect of vessel diameter on these parameters is insignificant when D > 0.15 m (0.49 ft), except for the dispersion coefficient. Application of these correlations is to (1) chlorination of toluene in the presence of FeCl,3 catalyst, (2) absorption of SO9 in aqueous potassium carbonate with arsenite catalyst, and (3) reaction of butene with sulfuric acid to butanol. 

Gianetto, A., and P.L. Silveston (editors), Multiphase Chemical Reactors Theory, Design, Scale-up, Hemisphere, Washington, 1986. 

Rodrigues, A.E., J.M. Calo, and N.H. Sweed (editors), Multiphase Chemical Reactors Volume 1 Fundamentals Volume 2 Design Methods, Sijthoff and Noordhoff, Alphen aan den Rijn, The Netherlands, 1981. 

Figure S. 2. Trickle Bed Reactor for Hydrotreating 20.000B/D of Light Catalytic Cracker Oil at 370 C and 27 atm CGianetto Silveston, Multiphase Chemical Reactors, 533-563, 1986. ...

We have in fact had to make many approximations to obtain even these complicated expressions, and it is evident that numerical solutions to most multiphase chemical reactor problems can only be obtained after considerable computations and approximations. 

An example of an incredibly complex multiphase chemical reactor is iron ore refining in a blast furnace. As sketched in Figure 12-22, it involves gas, liquid, and solid phases in countercurrent flows with complex temperature profiles and heat generation and removal processes. 

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. 

Multiphase chemical reactors are used for reactions involving at least two reactant species. Normally each of the reactants enters the reactor in a different phase. Typically one reactant is introduced in the liquid phase and the other in the gas phase. More than one phase is present in the reactor. Any phase may participate in the reaction as a reactant or as a product however one phase, generally a solid phase, may act as a catalyst. 

A. Gianetto and P.L. Silveston, Multiphase chemical reactors, Hemisphere Publishing Corporation, New-York (1986). 

Understanding of a multiphase chemical reactor involves chemical (catalysis) kinetics, hydrodynamics and heat/mass transfers at scales... 

Additional information on mechanically agitated gas-liquid-solid reactors can be obtained in van t Riet and Tramper (Basic Bioreactor Design, Marcel Dekker, 1991), Ramachandran and Chaudhari (Three-Phase Catalytic Reactors, Gordon and Breach, 1983), and Gianetto and Silveston (Multiphase Chemical Reactors, Hemisphere, 1986). Examples... 

For more details see Shah (Gas-Liquid-Solid Reactor Design, McGraw-Hill, 1979) and Hofmann [Hydrodynamics and Hydrodynamic Models of Fixed Bed Reactors, in Gianetto and Silveston (eds.), Multiphase Chemical Reactors, Hemisphere 1986]. 

Baldi, G., "NATO Advanced Study Institute on Multiphase Chemical Reactors", Vimeiro, Portugal, August 18-30, 1980. 

For the proper modeling of the performance of a multiphase chemical reactor, the RTD s of various fluid phases are of vital importance. The RTD curves allow... 

The situation may become even more complicated if a second liquid phase is present it may either serve as the reaction space containing the catalyst while the product as well as a part of the reactants exist in the first liquid phase, or it may act as a solvent into which a desired intermediate is extracted from the reacting liquid phase (cf. Section 3.1.1.1). To describe quantitatively the course of a homogeneous catalytic reaction in a multiphase chemical reactor it is necessary to combine the following information in a suitable reactor model ... 

The area averaging theory described in this section is based on the papers by [229, 243, 44, 46, 47, 22, 10, 24, 115, 135, 16[. The main object in this section is to provide the necessary theorems to derive the cross-sectional averaged equations that coincide with the conventional ID multiphase chemical reactor model from first principles. To formulate these theorems we chose to adopt the same concepts as were used deriving the corresponding single phase equations... 

Based on these observations [93] proposed a modified model containing two time constants, one for the liquid shear induced turbulence and a second one for the bubble induced turbulence. The basic assumption made in this model development is that the shear-induced turbulent kinetic energy and the bubble-induced turbulent kinetic energy may be linearly superposed in accordance with the hypothesis of [128, 129]. Note, however, that [82] observed experimentally that this assumption is only valid for void fractions less than 1 %, whereas for higher values there is an amplification in the turbulence attributed to the interactions between the bubbles. The application of this model to the high void fraction flows occurring in operating multiphase chemical reactors like stirred tanks and bubble columns is thus questionable. 

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