Hydroformylation three-phase

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. 

In a first approximation, the new methods correspond to the conventional solvent techniques of supported catalysts (cf Section 3.1.1.3), liquid biphasic catalysis (cf Section 3.1.1.1), and thermomorphic ( smart ) catalysts. One major difference relates to the number of reaction phases and the mass transfer between them. Owing to their miscibility with reaction gases, the use of an SCF will reduce the number of phases and potential mass transfer barriers in processes such as hydrogenation, carbonylations, oxidation, etc. For example, hydroformylation in a conventional liquid biphasic system is in fact a three-phase reaction (g/1/1), whereas it is a two-phase process (sc/1) if an SCF is used. The resulting elimination of mass transfer limitations can lead to increased reaction rates and selectiv-ities and can also facilitate continuous flow processes. Most importantly, however, the techniques summarized in Table 2 can provide entirely new solutions to catalyst immobilization which are not available with the established set of liquid solvents. 

As was mentioned earlier in this chapter, it is not necessary to transfer every reaction mixture into a thermodynamically stable one-phase system. Often the presence of one organised surfactant phase in equilibrium with one or two excess phases is sufficient to give an appropriate reaction rate. In such two- or three-phase systems the reaction occurs in the surfactants phase while the coexisting phases act as reservoir for the reactants. This approach has been demonstrated for alkylation of phenol [28] and for rhodium catalysed hydroformylation of dodecene [50]. A major practical advantage with the multi-phase systems is that substantially less surfactant is needed. This reduces costs and simplifies the work-up. 

Several chemical engineering factors affect the biphasic hydroformylation of 1-dodecene in a gas-hquid-Hquid three-phase reachon system. In previous research [1], effects of temperature, total pressure, H2/CO molar raho, catalyst and ligand concentration, olefin concentration, surfactant concentration, and organic/ aqueous-phase volume ratio on the hydroformylation kinetics were studied with... 

It is rather difficult to establish a reasonably accurate mathematical model of a gas-liquid-liquid three-phase reactor for biphasic hydroformylation, because of the complexity in formulating all the necessary mechanisms such as phase dispersion and distribution, multiphase flow, interphase mass transfer, micromixing, and the hydroformylation reaction. Besides, the task is further complicated by turbulence in multiphase flow and the complex domain of stirred-tank reactors. 

Three phase catalytic slurry reactors are characterized by a continuous liquid phase in which a gas phase is dispersed and a solid (catalyst) is suspended. They are commonly used for catalytic hydrogenation, oxidation, halogenation or polymerization reactions such as edible oil hydrogenation, olefin oxidation or hydroformylation etc. But also fermenters can be included into this category of multiphase reactors. 

The isomerizing hydroformylation of frans-4-octene has been executed in PC/dodecane/p-xylene with varying compositions of the three solvents. The phase diagram with the corresponding working points is presented in Fig. 7. 

The reaction of [RhCl(COD)2] and four equivalents of P(CH20H)3 in THF gave cis-[RhH2 P(CH20H)3 4], which actively catalyzed the biphasic hydroformylation of 1-pentene [74]. In a water/benzene mixture, at 100 °C and 40 bar syngas this substrate was quantitatively converted to hexanal (43 % yield) and 2-methylpentanal (57 %) in 20 h. At the [substrate]/[catalyst] ratio of 90 this is equivalent to a minimum TOP of 4.5 h" . The catalyst was recycled in the aqueous phase three times with no changes in its activity or selectivity. 

The same general principles and the same phosphines (18) can be used for still another variation of catalyst recovery which was demonstrated in the hydroformylation of 1-tetradecene [143], The reaction, catalyzed by the Rh/18 catdyst, was mn in a homogeneous methanolic solution and gave slightly better results than the Rh/PPhs catalyst under identical conditions. After the reaction most of the methanol was distilled off and the remaining solution was extracted with water. The catalyst-containing aqueous phase was evaporated to dryness, the catalyst was taken up in methanol and reused. No loss of activity and selectivity was observed in three recycles. 

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