Ruhrchemie water-soluble rhodium catalyst

Reaction in two-phase liquid-liquid systems. The Ruhrchemie process for the manufacture of butyraldehyde from propylene uses a water-soluble rhodium catalyst, while the product butyraldehyde forms an immiscible organic layer. Separation of the product from the catalyst is thus easily accomplished (see Section 5.2.5). 

Ruhrchemie AG was the first to seize upon the idea of applying a water-soluble rhodium catalyst and thus commercialize a process which has been elaborated on a laboratory scale by Rhone-Poulenc earlier [13, 14]. It took only two years of intensive research to develop the technical concept and to erect the first plant, which went on-stream in 1984 [15]. By 1987 the second unit was already built and today the total capacity for n-butyraldehyde amounts to more than 350000 tons per year [16, 17]. An additional plant for the production of n-pentanal from n-butene was brought on-stream in 1995 (see Section 6.1.3.1.8). 

Hydroformylation or oxosynthesis is a well-known homogeneous, transition metal catalyzed reaction which has known considerable and continuous development since its discovery by Otto Roelen in the laboratories of Ruhrchemie AG in 1938 [1], This reaction, which can be considered as the addition of a formyl group and hydrogen to a double bond, has been successfully applied in the industrial context by using two basic processes the homogeneous process where the rhodium or cobalt catalyst and the substrate are in the same phase (Shell, UCC, BASF, RCH processes) [2] and the aqueous/organic biphasic process where the water-soluble rhodium catalyst and the organic compounds are in two different phases (Ruhr-chemie/Rhone-Poulenc process) [3]. 

Rhone-Poulenc and Ruhrchemie (now Hoechst) developed a process in the 1980s based on a water soluble rhodium catalyst modified with triphenylphosphine sulphonate ligand that can produce normal to iso ratios as high as 20. Previous phosphine modified rhodium catalysts were oil soluble. 

Ruhrchemie AG was the first to seize upon the idea of applying a water-soluble rhodium catalyst and thus commercializing a process which had been elaborated on a laboratory scale by Rhone-Poulenc earlier [15, 16]. 

In the 1980s, the RCH/RP (Ruhrchemie/Rhone-Poulenc) process came on stream utilizing a two-phase system containing a water-soluble rhodium catalyst in aqueous phase and the product aldehyde in organic phase. Based on this character of easy separation of two phases, RCH/RP process not only maintains... 

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). 

For instance, catalysis in liquid/liquid two phases is generally referred to as biphasic catalysis and has widened the practical scope of homogeneous catalysis the catalyst is present in one liquid phase, while reactants and products are present in the other liquid phase. Thus, the catalyst can be separated by simple phase separation. Celanese is operating a 300 000 t/a plant for propylene hydroformylation using a water-soluble rhodium phosphine complex in a biphasic mode of operation at the Ruhrchemie site in Oberhausen [142],... 

An important development in the past 15 years in hydroformylation technology was the introduction of biphasic homogeneous catalysis. Kuntz (62) expressed the basic idea of a new generation of water-soluble oxo catalysts with triphenylphosphane trisulfonate (tppts as the sodium salt) as a ligand for a rhodium-complex-catalyzed hydroformylation process. Ruhrchemie AG adapted the idea on the basis of research done at Rhone-Poulenc and developed it into an industrially viable process, which was... 

The idea of applying water-soluble rhodium complexes as catalysts for the hydroformylation reaction [212, 213] was taken up and commercialized by Ruhrchemie AG for the hydroformylation of propene [269]. After only two years of development on the laboratory scale the first plant was erected in 1984, followed by rapid further increases in capacity to more than 600000 tons/year today [214]. An additional unit for the production of n-pentanal from n-butene has been brought onstream in 1995 [271, 294]. 

The synthesis of aldehydes by hydroformylation of alkenes is an important industrial process discovered in 1938. The use of biphasic catalysis, which is a well-established method for the separation of the product and the recovery of the catalyst, was developed for this reaction in the Ruhrchemie-Rhdne-Poulenc process a water-soluble rhodium complex is used as catalyst - the reaction proceeding in water - and the organic layer is formed simply by the alkene reagent and the aldehyde products. Butanal is manufactured this way, but owing to the low solubility of longer olefins in water, this process is limited to C2-C5 olefins. To overcome this limitation, ionic liquids have been studied as a reaction solvent for this biphasic reaction. 

As water is immiscible with most organic substrates, most reactions involving water are done with liquid-liquid biphasic systems. The use of biphasic organometallic catalysts to catalyze aqueous-phase reactions is a novel method to address this issue. The catalyst in such reactions is a water-soluble transition metal complex with substrates that are partially water-soluble. The Ruhrchemie-Rhone-Poulenc process, which involves hydrofor-mylation of propylene to n-butanol, is an example of biphasic organometallic catalysts being used on an industrial scale (Comils and Kuntz, 1995). The catalyst employed is a water-soluble Rhodium (I) complex of trisulfonated triphenylphosphine (tppts) (see Fig. 5.3). 

Although rhodium recovery is efficient it is difficult to separate it from heavies that are formed in small amounts. Over time these heavies tend to result in some catalyst deactivation. One solution to this problem has been developed by Ruhrchemie/Rhone-Poulenc. In this process sulfonated triphenyl phosphine is used as the ligand, which imparts water solubility to the catalyst. The reaction is two-phase, a lower aqueous phase containing the catalyst and an upper organic phase. Fortunately the catalyst appears to sit at the interface enabling reaction to proceed efficiently. At the end of... 

A breakthrough occurred in the mid-seventies when Union Carbide and Celanese introduced Rh/phosphine catalysts in commercial processes. This catalyst is based on the work by Wilkinson s group he received the Nobel prize for his work in 1973. Rhodium-based catalysts are much more active than cobalt catalysts and, under certain conditions, at least for 1-alkenes, they are also more selective. The processes for the hydroformylation of higher alkenes (detergent alcohols) still rely on cobalt catalysis. A new development is the use of water-soluble complexes obtained through sulphonation of the Ligands (Ruhrchemie). 

Water soluble ligands greatly facilitate catalyst separation. Examples are (22-XLI)174 and (22-XLII),175 which are used in hydroformylations and hydrogenation catalysis, respectively. Rhodium complexes of the sulfonated phosphine (22-XLI) are used in the production of butyraldehyde, a large-scale process developed by Ruhrchemie/Rhone-Poulenc.174... 

Only limited data are available for the kinetics of oxo synthesis with the water-soluble catalyst HRh(CO)(TPPTS)3. The hydroformylation of 1-octene was studied in a two-phase system in presence of ethanol as a co-solvent to enhance the solubility of the olefin in the aqueous phase [115]. A rate expression was developed which was nearly identical to that of the homogeneous system, the exception being a slight correction for low hydrogen partial pressures. The lack of data is obvious and surprising at this time, when the Ruhrchemie/ Rhone-Pou-lenc process has been in operation for more than ten years [116]. Other kinetic studies on rhodium-catalyzed hydroformylation have been published, too. They involve rhodium catalysts such as [Rh(nbd)Cl]2 (nbd = norbomadiene) [117] or [Rh(SBu )(CO)P(OMe)3]2 [118], or phosphites as ligands [119, 120]. 

The Ruhrchemie/Rhone-Poulenc Oxo process (Figure 4.1, Scheme 4.1) was developed for the synthesis of butyraldehyde from propylene and synthesis gas, where the water-soluble tris(m-sulfonated-phenyl)phosphine (TPPTS)-modified rhodium catalyst operates in the aqueous phase [14]. 

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. 

Rhone-Poulenc and Ruhrchemie developed a two-phase process utilizing a water soluble modified rhodium catalyst. 

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