Three-phase reactions

DEF. A eutectic reaction is a three-phase reaction, by which, on cooling, a liquid transforms into two solid phases at the same time. It is a phase reaction, of course, but a special one. If the bottom of a liquid-phase field closes with a V, the bottom of the V is a eutectic point. 

DEF. A eutectoid reaction is a three-phase reaction by which,... 

Irandoust, S., Cybulski, A., and Moulijn, J.A. (1998) The use of monolithic reactors for three-phase reactions, in Structured Catalysts and Reactors,... 

So far only propene and butene are hydroformylated commercially using the RCH/RP process. A reason which has been postulated for this is the decreasing solubility in water with increasing number of C atoms in both the starting alkene and the reaction products (Figure 5.4) and the associated mass-transfer problems in the relatively complicated gas-liquid-liquid, three-phase reaction. 

The HTE characteristics that apply for gas-phase reactions (i.e., measurement under nondiffusion-limited conditions, equal distribution of gas flows and temperature, avoidance of crosscontamination, etc.) also apply for catalytic reactions in the liquid-phase. In addition, in liquid phase reactions mass-transport phenomena of the reactants are a vital point, especially if one of the reactants is a gas. It is worth spending some time to reflect on the topic of mass transfer related to liquid-gas-phase reactions. As we discussed before, for gas-phase catalysis, a crucial point is the measurement of catalysts under conditions where mass transport is not limiting the reaction and yields true microkinetic data. As an additional factor for mass transport in liquid-gas-phase reactions, the rate of reaction gas saturation of the liquid can also determine the kinetics of the reaction [81], In order to avoid mass-transport limitations with regard to gas/liquid mass transport, the transfer rate of the gas into the liquid (saturation of the liquid with gas) must be higher than the consumption of the reactant gas by the reaction. Otherwise, it is not possible to obtain true kinetic data of the catalytic reaction, which allow a comparison of the different catalyst candidates on a microkinetic basis, as only the gas uptake of the liquid will govern the result of the experiment (see Figure 11.32a). In three-phase reactions (gas-liquid-solid), the transport of the reactants to the surface of the solid (and the transport from the resulting products from this surface) will also... 

Figure 2.10. Examples of binary systems characterized by complete mutual solubility in the liquid state and, depending on temperature and/or composition, partial solubility in the solid state and presenting (in certain composition ranges) an invariant (three-phase) reaction (eutectic in the Cu-Ag, peritectic in the Ru-Ni and Re-Co and eutectoidal in Ti-W (one) and in Th-Zr (two)).

The experimental optimization of Nafion ionomer loading within a catalyst layer has attracted widespread attention in the fuel cell community, mainly due to its critical role in dictating the reaction sites and mass transport of reactants and products [15,128-134]. Nafion ionomer is a key component in the CL, helping to increase the three-phase reaction sites and platinum utilization to retain moisture, as well as to prevent membrane dehydration, especially at low current densities. Optimal Nafion content in the electrode is necessary to achieve high performance. 

Identify three-phase reactions in binary component systems. 

Three two-phase regions must originate upon every three-phase isotherm that is, six boundary lines must radiate from each three phase reaction horizontal. 

Figure 2.7 Cu-Zn phase diagram, illustrating a number of three-phase reactions. From K. M. Ralls, T. H. Courtney, and J. Wulff, Introduction to Materials Science and Engineering. Copyright 1976 by John Wiley Sons, Inc. This material is used by permission of John Wiley Sons, Inc.

Pclllctlcr, J.C., Khan, A., and Tang, Z., A tandem three-phase reaction for preparing secoundary amines with minimal side products, Org. Lett., 2002, 4, 26, 4611. 

In parallel, the three-phase reaction system was improved. It was found that the reaction was strongly enhanced when performed in the presence of a phase-transfer catalyst as achiral additive [35-40], Epoxidation of chalcone 9 with 10 mol% TBAB led to >99% conversion within 7 min and high enantioselectivity of 94% ee (Scheme 14.3) [35]. In the absence of TBAB the asymmetric poly-L-leucine-catalyzed epoxidation afforded only 2% conversion after 1.5 h. It was also reported that the amount of catalyst could be further reduced. 

Cybulski A, Moulijn JA. The use of monolithic catalysts for three-phase reactions. In Moulijn JA, Cybulski A, eds. Structured Catalysts and Reactors. New York Marcel Dekker, 1998 239-266. 

In the industry, many processes are performed as three-phase reactions, gas, liquid, and solid. Typically a slurry reactor is used for such purposes, as shown in Figure 4.1.10. In such a reactor, the catalyst is usually present in the form of a solid distributed in a liquid, which can be a solvent and reactant concomitant. The gas, as reactant, is also pressed into the reactor. 

Figure 4.1.10 A slurry reactor for a three-phase reaction, between a liquid and a solid, catalyzed by a solid catalyst.

Reactions involving gas, liquid, and solid are often encountered in the chemical process industry. The most common occurrence of this type of reaction is in hydroprocessing operations, in which a variety of reactions between hydrogen, an oil phase, and a catalyst have been examined. Other common three-phase catalytic reactions are oxidation and hydration reactions. Some three-phase reactions, such as coal liquefaction, involve a solid reactant. These and numerous other similar gas-liquid solid reactions, as well as a large number of gas-liquid reactions, are carried out in a vessel or a reactor which contains all three phases simultaneously. The subject of this monograph is the design of such gas-liquid -solid reactors. 

A three-phase reaction involves a solid, C, which is slurried in an inert solvent in which it is soluble and a gas, A, which is bubbled through the slurry. The reaction is A + C -> Products, and is assumed to be instantaneous. There is no gas-side resistance to mass transfer. The average diameter of the solids can be considered to be much less than the thickness of the liquid film. The following data are available for the system under consideration ... 

---