Hydroformylation Ruhrchemie/Rhone-Poulenc process

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). 

Biphasic techniques for recovery and recycle are among the recent improvements of homogeneous catalysis - and they are the only developments which have been recently and successfully applied in the chemical industry. They are specially introduced into the hydroformylation (or "oxo") reaction, where they form a fourth generation of oxo processes (Figure 5.1 [1]). They are established as the "Ruhrchemie/Rhone-Poulenc process" (RCH/RP) [2] cf. also Section 5.2.4.1), with annual production rates of approximately 800,000 tonnes y"1 (tpy). 

The synthesis of aldehydes via hydroformylation of alkenes is an important industrial process used to produce in the region of 6 million tonnes a year of aldehydes. These compounds are used as intermediates in the manufacture of plasticizers, soaps, detergents and pharmaceutical products [7], While the majority of aldehydes prepared from alkene hydroformylation are done so in organic solvents, some research in 1975 showed that rhodium complexes with sulfonated phosphine ligands immobilized in water were able to hydroformylate propene with virtually complete retention of rhodium in the aqueous phase [8], Since catalyst loss is a major problem in the production of bulk chemicals of this nature, the process was scaled up, culminating in the Ruhrchemie-Rhone-Poulenc process for hydroformylation of propene, initially on a 120000 tonne per year scale [9], The development of this biphasic process represents one of the major transitions since the discovery of the hydroformylation reaction. The key transitions in this field include [10] ... 

In Chapter 8 we will discuss the hydroformylation of propene using rhodium catalysts. Rhodium is most suited for the hydroformylation of terminal alkenes, as we shall discuss later. In older plants cobalt is still used for the hydroformylation of propene, but the most economic route for propene hydroformylation is the Ruhrchemie/Rhone-Poulenc process using two-phase catalysis with rhodium catalysts. For higher alkenes, cobalt is still the preferred catalyst, although recently major improvements on rhodium (see Chapter 8) and palladium catalysts have been reported [3],... 

The third generation process concerns the Ruhrchemie/Rhone-Poulenc process utilizing a two-phase system containing water-soluble rhodium-tppts in one phase and the product butanal in the organic phase. The process has been in operation since 1984 by Ruhrchemie (or Celanese, nowadays). The system will be discussed in section 8.2.5. Since 1995 this process is also used for the hydroformylation of 1-butene. 

Rhodium-catalyzed biphasic hydroformylation of olefins. The Ruhrchemie-Rhone Poulenc process for manufacturing... 

As mentioned earlier, in the Ruhrchemie-Rhone Poulenc process for propene hydroformylation the pH of the aqueous phase is kept between 5 and 6. This seems to be an optimum in order to avoid acid- and base-catalyzed side reactions of aldehydes and degradation of TPPTS. Nevertheless, it has been observed in this [93] and in many other cases [38,94-96,104,128,131] that the [RhH(CO)(P)3] (P = water-soluble phosphine) catalysts work more actively at higher pH. This is unusual for a reaction in which (seemingly) no charged species are involved. For example, in 1-octene hydroformylation with [ RhCl(COD) 2] + TPPTS catalyst in a biphasic medium the rates increased by two- to five-fold when the pH was changed from 7 to 10 [93,96]. In the same detailed kinetic studies [93,96] it was also established that the rate of 1-octene hydroformylation was a significantly different function of reaction parameters such as catalyst concentration, CO and hydrogen pressure at pH 7 than at pH 10. 

The Ruhrchemie/Rhone-Poulenc process is performed annually on a 600,000 metric ton scale (18). In this process, propylene is hydroformylated to form butyraldehyde. While the solubility of propylene in water (200 ppm) is sufficient for catalysis, the technique cannot be extended to longer-chain olefins, such as 1-octene (<3 ppm solubility) (20). Since the reaction occurs in the aqueous phase (21), the hydrophobicity of the substrate is a paramount concern. We overcame these limitations via the addition of a polar organic co-solvent coupled with subsequent phase splitting induced by dissolution of gaseous CO2. This creates the opportunity to run homogeneous reactions with extremely hydrophobic substrates in an organic/aqueous mixture with a water-soluble catalyst. After C02-induced phase separation, the catalyst-rich aqueous phase and the product-rich organic phase can be easily decanted and the aqueous catalyst recycled. 

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... 

An interesting variation of hydroformylation with a great potential for the industrial preparation of primary amines is hydroaminomethylation. In this process two catalytic reactions are combined, a hydroformylation and a reductive amination of the resulting aldehyde. Although first described more than 60 years ago a really successful procedure was only published recently [78]. To ensure the success of this sequence a rhodium catalyst for the hydroformylation was combined with an iridium catalyst for the imine reduction in a two-phase system, similar to the Ruhrchemie/Rhone-Poulenc process for the hydroformylation. It was demonstrated that less polar solvents such as toluene in combina-... 

Synthesis of water-soluble phosphines is nowadays one of the most active areas in hydroformylation research. The oxo synthesis in a two-phase system with water-soluble catalysts, the Ruhrchemie/Rhone-Poulenc process (RCH/ RP), will be discussed in Section 2.1.1.4. Water-soluble catalysts in general are treated in Section 3.1.1.1. Since the last exhaustive reviews in 1993 and 1992 on water-soluble complexes [38], some progress has been made in this area, which will be discussed in Section 2.1.1.5.3. 

An example of the application of a water-soluble hydroformylation catalyst other than in the Ruhrchemie/Rhone-Poulenc process is the synthesis of 1,9- non-anediol according to Kuraray [58]. Hydrodimerization of butadiene (also cata-... 

Starting in 1999, the Ruhrchemie/Rhone-Poulenc process will be operated in plants having a capacity of about 600,000 metric tons per year, which corresponds to over 10% of the aimual world production of C4 products the first licensed plant is operating in Korea (Hanwha Chem. Corp.). On the Ruhrchemie site, a butene hydroformylation plant [to produce n-valeraldehyde (pentanal)j is also operating without problems. 

Another useful separation technique for gas-liquid-liquid systems30 involves catalysts that are only soluble in one of two phases. An outstanding example was cited in Chap. 1. The hydroformylation of propylene to produce bu-tyraldehydes (in the Ruhrchemie/Rhone-Poulenc process) is done by passing propylene gas into an aqueous solution... 

The opposite of entry 2 is the phase combination of entry 5, a fully organic reaction in the presence of an aqueous phase which contains the catalyst. This type of reaction system is the most often used for the technical realization of aqueous-phase organometallic-catalyzed reactions, for instance in the oligomerization of ethylene using the SHOP process (cf. Section 7.1) or in the Ruhrchemie/Rhone-Poulenc process (cf. Section 6.1.1) of propene hydroformylation (see also Section 4.2.2). 

The most important process with the solvent water is the hydroformylation of propene to butyraldehydes, known as the Ruhrchemie/Rhone-Poulenc process. This reaction is catalyzed by a rhodium complex containing the water-soluble ligand triphenylphosphane trisulfonate (TPPTS). The aldehydes are formed with an annual capacity of approx. 3000001. 

The lack of data is obvious and surprising at a time when the Ruhrchemie/ Rhone-Poulenc process has been in operation for more than 20 years. A rigid reaction rate model, established under idealized conditions, becomes complex and complicated when it is transferred to the hydroformylation of lower olefins under conditions relevant to the industrial practice, as the mass transfer phenomena involved in a triphasic system (gas-liquid-liquid) in large reactors have to be taken... 

There have been many approaches to overcome the problem of low space-time yields in biphasic reaction systems with rhodium and other metals, such as the Ruhrchemie/Rhone-Poulenc process. Concerning two-phase hydroformylation of higher alkenes in an aqueous-organic reaction system, the different approaches can be categorized as follows ... 

If the conditions of the Ruhrchemie/Rhone-Poulenc process are applied to linear a-alkenes (LAOs) with 5-12 carbon atoms, the space-time yield of the hydroformylation reaction decreases with increasing chain length of the substrate. Table 1 summarizes the results of the batchwise hydroformylation of LAOs different at 30-80 bar syngas pressure. 

The thermal instability of rhodium-based hydroformylation catalysts has already been overcome commercially in the Ruhrchemie/Rhone-Poulenc process for propene hydroformylation in which the sodium salt of a sulfonated triphe-nylphosphine ligand (TPPTS, la) is used to solubilize the catalyst in the aqueous phase. In this process, the second phase is toluene and the reaction is carried out as a batch process with rapid stirring to intimately mix the two immiscible phases. After reaction, the system is allowed to separate and the organic phase is simply decanted from the aqueous catalyst phase. Both water-soluble polymers and PAMAM dendrimers have been reported as supports for rhodium-catalyzed hydroformylation under aqueous biphase conditions, but reactivities and regioselec-tivities were only comparable to or worse than those obtained with the reference TPPTS ligand. The aqueous biphase approach has found limited application for the hydroformylation of longer-chain alkenes, because of their very low solubility in water leading to prohibitively slow reaction rates, but there have been a variety of approaches directed at the solution of this problem. 

We vrill describe the basics of aqueous two-phase hydroformylation with TPPTS and rhodium complexes thereof [1] as they apply to C3 and C4 olefins according to the Ruhrchemie/Rhone-Poulenc process. Emphasis will be put on the commercial applications and the basic description of the processes. 

For the different hydroformylation processes described above, the catalyst separation and recycling remain a constant preoccupation. This point is particularly crucial when a very expensive metal is used as catalyst (rhodium). The recycling is either operated by chemical transformation or by direct distillation, depending on the catalyst and its stability. In that way, the development of the aqueous biphasic process can be considered as an important breakthrough (4-6). The separation is operated by decantation, which simplifies the process scheme and limits the risks of catalyst decomposition during distillation. Even if the 0x0 Ruhrchemie/Rhone-Poulenc process presents undeniable advantages, this process remains limited to short-chain olefins (C2-C5) because of the low solubility of higher olefins in water which renders the reaction rates too low for viable processes [7]. 

The most important large-scale aqueous-organic biphasic process is the hydroformylation of propene into butanal (Scheme 14) catalyzed by [HRh(CO)-(TPPTSlsl, that is the Ruhrchemie-Rhone Poulenc process (63,139,140). The catalyst is dissolved in water, whereas the substrate and product(s) comprise the organic phase. In the heart of this technology is a continuously stirred tank reactor connected to a phase separator. Complete insolubility of the rhodium-phosphine catalyst in the organic phase together with the lack of surfactant behavior of TPPTS assures a full recovery of rhodium by perfect phase separation. The catalytic reaction takes place at 120°C and 5 MPa (CO H2 = 1.01 1)—such conditions are milder than those of the so-called low pressure oxo processes. Propene reacts... 

---