Aqueous biphasic hydroformylation processes

The effect of methylated cydodextrins on the RhH(CO)(TPPTS)3 complex in hydroformylation conditions (50 bar, CO H2 = 1 1, and80°C) were investigated by high-pressure P NMR spectroscopy. It was found that the formation of the stable inclusion complex between methylated P-cyclodextrin and TPPTS influences the TPPTS dissociation equilibrium. The methylated a-cydodextrin does not interact with the TP PTS and the methylated y-cydodextrin can only weakly bind to the TP PTS. These results explain why a decrease in the normal-to-branched aldehydes ratio is always observed when cydodextrins are used as mass-transfer agents in aqueous biphasic hydroformylation processes [104]. 

The POP-Xantphos ligand, which at the present affords the best turnover frequencies and l b ratios is considerably more expensive than the rather simple TPPTS ligand employed in aqueous biphasic hydroformylation. Compared to the classical rhodium-phosphine process, manufacturing costs in the aqueous biphasic process are about 10% lower. Accordingly, requirements for a fairly expensive catalyst will be exceptional if it should be considered in an industrial process, especially if one bears the additional costs for the required ionic liquid in mind. Nevertheless, the prospect of biphasic ionic liquid hydroformylation looks very promising. 

The great number of very different proposals which address widely differing points in the 0x0 process does prove that there is currently no single ideal way of reacting higher olefins in aqueous biphasic hydroformylations. In addition, the 0x0 products, which are under a great deal of cost pressure, tolerate no cost-... 

The aqueous biphasic hydroformylation of propene, namely the Ruhrchemie/ Rhone Poulenc (RCH/RP) process, has been widely used to produce n-butanal and many attempts have been proposed to improve this catalytic system, such as a thermoregulated phase transfer (TRPT) Rh(I) complex catalyst [74]. Moreover, Bonnemann et al. [75] have proved the in situ formation of Rh colloids when such a catalyst was applied to the aqueous biphasic hydroformylation of 1-octene. 

Accompanying Ruhrchemie/Rhone-Poulenc s industrial realization of the aqueous biphasic hydroformylation reaction (cf Sections 2.4.1.1.3 and 2.5.1) and Kuraray s hydrodimerization process (see Section 2.4.4.2), there are some other minor processes for the production of fine chemicals. 

In spite of the importance of the field, the last reviews covering a broad area in hydroformylation are outdated (Falbe 1980, Pruett 1977) and it was felt timely to bring together the recent developments. Only in the area of aqueous biphasic hydroformylation there are several exhausting reviews available. This is the first monograph on hydroformylation of this type and for other processes there not many examples. 

An example of a large scale application of the aqueous biphasic concept is the Ruhrchemie/Rhone-Poulenc process for the hydroformylation of propylene to n-butanal (Eqn. (15)), which employs a water-soluble rhodium(I) complex of trisulphonated triphenylphosphine (tppts) as the catalyst (Cornils and Wiebus, 1996). 

Hydroformylation comprises the state-of-the-art of bulk chemical production via aqueous-biphasic processes. At present five plants produce worldwide some 800,000 tpy of oxo products [1], Another bulk process - the hydrodimerization of butadiene and water, a variant of telomerization - is mn by Kururay with a capacity of 5000 tpy (Equation 5.2 [3 lb,36]). 

With the RCH/RP process, it is possible to hydroformylate propene up to pentenes with satisfying space time yields. On the other hand, heavier aldehydes such as Cio (iso-decanal) or higher from the hydroformylation of nonene(s), decenes, etc. can not be separated from the oxo catalysts by conventional means such as distillation due to thermal instability at the required temperatures and thus especially needs the careful aqueous-biphasic separation technique. There are numerous attempts to overcome the problem of low reactivity of higher alkenes which is due to low miscibility of the alkenes in water [26,27b, 50a,58d]. These proposals can briefly be summarized as ... 

Taking all criteria into consideration, aqueous two-phase techniques are very sound methods for homogeneously catalyzed processes such as hydrogenations or hydroformylations. Of the various alternatives to the conventional (and solvent-free) processes most progress in terms of ecological impact and economics has been attained by the aqueous biphasic approach (Figure 5.20). 

A wide variety of new approaches to the problem of product separation in homogeneous catalysis has been discussed in the preceding chapters. Few of the new approaches has so far been commercialised, with the exceptions of a the use of aqueous biphasic systems for propene hydroformylation (Chapter 5) and the use of a phosphonium based ionic liquid for the Lewis acid catalysed isomerisation of butadiene monoxide to dihydrofuran (see Equation 9.1). This process has been operated by Eastman for the last 8 years without any loss or replenishment of ionic liquid [1], It has the advantage that the product is sufficiently volatile to be distilled from the reactor at the reaction temperature so the process can be run continuously with built in product catalyst separation. Production of lower volatility products by such a process would be more problematic. A side reaction leads to the conversion of butadiene oxide to high molecular weight oligomers. The ionic liquid has been designed to facilitate their separation from the catalyst (see Section 9.7)... 

As outlined in Chapter 5, Section 5.2.3.2 various approaches to overcoming the low rates of the hydroformylation of long chain alkenes in aqueous biphasic systems have been proposed. Some of these, such as the use of microemulsions [24-26] or pH dependent solubility [27], have provided improvements often at the expense of complicating the separation process. Perhaps the most promising new approaches involve the introduction of new reactor designs where improved mixing allows for... 

Aqueous two-phase hydrogenation may be a method of choice for synthetic purposes when no incompatibility problems between water and the substrates, products, or catalyst arise. It has already been proven by the success of the Ruhrchemie-Rhone-Poulenc hydroformylation process, that the catalyst can be retained in the aqueous phase with very high efficiency, and that aqueous-organic biphasic processes using organometallic catalysts are suitable for indus-... 

The limitations of hydroformylation reactions in water are the same as those of hydrogenation reactions, i.e. the poor solubility of the substrates (see Section 8.2.1). While aqueous-organic biphasic hydroformylation works well for alkenes with chain lengths up to C7, the solubility of longer chain alkenes is too low for viable processes. Although simple alkenes are poorly soluble, many functional alkenes have solubilities in water that are sufficiently high to avoid mass transfer problems, but at the same time this can impede separation. 

During the years many studies were directed to find optimal catalysts and conditions for aqueous (or aqueous/organic biphasic) hydroformylation. By nature of research, not all of them led to industrial breakthroughs but all contributed to the foundations of today s practical processes and future developments. These investigations will not be treated in detail, however, a selection of them is listed in Table 4.1. 

In conclusion it can be said, that micellar effects offer useful possibilities to tune the reactivity and separation characteristics of aqueous/organic biphasic hydroformylations. Nevertheless, the added sensitivity of the systems to small changes in process variables and the added cost of surfactants and/or specially synthetized ligands have to be justified by high added value products or on grounds of process cost savings. Whether this will happen on industrial scale (perhaps in the hydroformylation of higher olefins) remains to be seen. 

The latest development in industrial alkene hydroformylation is the introduction by Rurhchemie of water-soluble sulfonated triphenylphosphine ligands.94 Hydroformylation is carried out in an aqueous biphasic system in the presence of Rh(I) and the trisodium salt of tris(m-sulfophenyl)phosphine (TPPTN). High butyraldehyde selectivity (95%) and simple product separation make this process more economical than previous technologies. 

The prototype industrial process based on this concept is the Ruhrchemie-Rhone Poulenc process for the hydroformylation of propylene to butanal94,219,220 (see Section 7.3.1). Because of the use of appropriately modified water-soluble ligands, the catalyst resides and operates in the aqueous phase. The particular features of this process are the positive energy balance and easy catalyst recovery, namely, the simply circulation of the aqueous catalyst solution. New types of water-soluble Ir and Rh complexes with tris(hydroxymethyl)phosphine222 were described, and the biphasic hydroformylation of 1-hexene was accomplished in ionic liquids.223 A cationic sugar-substituted Rh complex displays high regioselectivity to branched aldehydes.224... 

Figure 4.24 a A general process schematic for aqueous biphasic catalysis, and examples ofwater-soluble phosphine ligands b the catalytic cycle for the Ruhrchemie/Rhone-Poulenc hydroformylation of propene. 

Kuntz subsequently showed that the RhCl (tppts) 3 catalyzed the hydroformylation of propylene in an aqueous biphasic system [29]. These results were further developed, in collaboration with Ruhrchemie, to become what is known as the Ruhrchemie/Rhone-Poulenc two-phase process for the hydroformylation of propylene to n-butanal [18, 19, 22, 30]. Ruhrchemie developed a method for the large scale production of tppts by sulfonation of triphenylphosphine with 30% oleum at 20 °C for 24 h. The product is obtained in 95% purity by dilution with water, extraction with a water insoluble amine, such as tri(isooctylamine), and pH-controlled re-extraction of the sodium salt of tppts into water with a 5% aqueous solution of NaOH. The first commercial plant came on stream in 1984, with a capacity of 100000 tons per annum of butanal. Today the capacity is ca. 400000 tpa and a cumulative production of millions of tons. Typical reaction conditions are T=120°C, P=50bar, CO/H2 = 1.01, tppts/Rh = 50-100, [Rh] = 10-1000 ppm. The RhH(CO) (tppts)3 catalyst is prepared in situ from e.g. rhodium 2-ethylhexanoate and tppts in water. 

In the Kuraray process for the production of nonane-1,9-diol two steps involve the use of aqueous biphasic catalysis Pd/tppms catalyzed telomerization of butadiene with water as a reactant and Rh/tppms catalyzed hydroformylation (Fig. 7.14) [51]. 

Because of the generally excellent solubility of metal catalysts in RTILs, many of the reactions studied in these media are homogeneously metal catalysed. For example, rhodium catalysed hydroformylation reactions have been studied at length and a wide variety of phosphine ligands used. This particular reaction in RTILs has just been the subject of an extensive review. In most cases, only minimal leaching of the catalyst out of the ionic liquid phase is observed and the catalysts can be very effectively recycled. These efforts are necessary because the industrial aqueous-biphasic process (Chapter 10) only works effectively for smaller olefins and therefore alternative approaches are needed for more hydrophobic, higher-mass olefins. 

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