Hydroformylation homogeneous catalysts immobilization

Industrial hydroformylation is currently performed in two basic variants the homogeneous processes, where the catalyst and substrate are in the same liquid phase (Shell, UCC, BASF, etc.), and the two-phase process with a water-soluble catalyst (RCH/RP). These processes will be discussed in detail in Section 2.1.1.4. Gas-phase hydroformylation with heterogeneous catalysts plays no role today. The immobilization of homogeneous catalysts will be discussed in Section 3.1.1. Special applications such as SLPC (supported /iquid-phase catalysts) [43] and SAPC (supported aqueous-/7hase catalysts) [44] are not considered further here. Heterogeneous oxo catalysts are not within the scope of this book they are discussed further elsewhere [267]. 

First of all, these properties were used to separate the sulfonated phosphine from the excess of sulfuric acid affer sulfonation by forming a triisooctylammo-nium salt in toluene, which is totally insoluble in water [1], Later it was discovered, that the re-immobilized ligand in toluene as well as the immobilized ligand in water are useful and remarkably stable catalyst systems. As classical homogeneous catalysts they are very active, e. g., for the hydroformylation of higher olefins and olefins with internal double bonds. 

The immobilization of the homogeneous catalyst with the aid of water as liquid support leads to appreciable technical simplifications, as illustrated in Figure 4 for the recycling of the catalyst of an industrial hydroformylation process (A = olefin, B = CO/H2, C and D = butyraldehydes) [22a, 25],... 

Supported Liquid-phase Hydroformylation. - A potentially attractive alternative to chemically anchored hydroformylation catalysts is the use of supported liquid-phase catalyst (SLPC) systems for gas-phase hydroformyl-ations. The homogeneous catalyst is dissolved in a non-volatile solvent and then condensed in the pores of a support, where the strong negative capillary forces effectively immobilize the catalyst, thereby preventing metal loss. In addition one might expect that the environment of the homogeneous system... 

Table I illustrates some of the catalysts we have prepared using polyethylene oligomers. Basically, we have carried out this chemistry with a wide variety of homogeneous catalysts, including various isomerization catalysts, hydrogenation catalysts, hydroformylation catalysts, etc. This approach to catalyst immobilization and recovery seems to be very general. In all cases, we recover 99.9 percent of the catalysts after the first or second cycle whenever we measure it by looking for metal in the filtrate.

IR spectroscopy has proved that SILP catalysts have metalorganic complexes dissolved in the liquid layer, which then worked as a homogeneous catalyst Riisager et al. [12] have made spectroscopic measurements of a rhodirun-sulfoxantphos complex which was immobilized in an SILP system. This SILP catalyst was tested in the continuous-flow fixed-bed hydroformylation of propene. Spectroscopy of the SILP system was performed in situ under conditions closely related to the reaction conditions, that is, imder various gas atmospheres and at 100 °C. The result was that the Rh-sulfoxantphos complex of the SILP catalyst behaved similar to an analogous rhodium-xanthene catalyst dissolved in the homogeneous phase. Analysis of the CO stretching band showed that the catalyst was in equilibrium between a dimeric form and two monomeric forms (Scheme 8.3) and, consequently, that the hydroformylation reactions were indeed homogeneously catalyzed. 

SCCO2 has also been used as a solvent with a silica-immobilized catalyst in metathesis reactions [25]. A heterogeneous catalytic process is developed, in which catalyst leaching is avoided but the reactivity is lower than when using a homogeneous catalyst This application has also been extended to continuous-flow processes for hydrogenation [26], Friedel-Crafts alkylations [27], etherification [28], and hydroformylation [29] reactions. 

The above examples have shown that there is considerable activity in searching for other ways to achieve separation of product and homogeneous catalysts. The improvements needed are the same for all reaction types, also reactions other than hydroformylation. Most of the new techniques have in common that not only the product, but also the starting material and byproducts are separated from the catalyst. This mixture of organic products needs further separation, but as we have seen in Chapter 8 separation of catalyst and byproducts such as heavy ends is an important issue in hydroformylation of simple alkenes. There may be a future for immobilized drop in catalysts as described above in the hydroformylation of fine chemicals. 

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