Hydroformylations commercial applications

Until recently, the hydroformylation using palladium had been scarcely explored as the activity of palladium stayed behind that of more active platinum complexes. The initiating reagents are often very similar to those of platinum, i.e., divalent palladium salts, which under the reaction conditions presumably form monohydrido complexes of palladium(II). A common precursor is (39). The mechanism for palladium catalysts is, therefore, thought to be the same as that for platinum. New cationic complexes of palladium that are highly active as hydroformylation catalysts were discovered by Drent and co-workers at Shell and commercial applications may be expected, involving replacement of cobalt catalysts. 

SLPC or SAPC (supported liquid [or aqueous] phase catalysis [9,10,62,64] see also Section 5.2.5) provide no improvement, probably because of the tremendous stress on the support/transition metal bond during the repeated change between tetrahedral and trigonal-bipyramidal metal carbonyls over the course of a single catalyst cycle. Only recent publications [11,21,26b,28h] report on successful realization of supported homogeneous hydroformylation catalysts, but so far there is no confirmation by practise-soriented tests -not to mention by commercial applications. 

Catalyst decomposition is, overall, receiving little attention in academic work on homogeneous catalysis, and only in recent years has research on decomposition and stabilization of organometallic catalysts started to expand (116), with emphasis on reactions of significant commercial interest such as hydroformylation (117), metathesis 118), crosscoupling, and polymerization 119). Ligand decomposition seems to be a key issue for industrial application, because it affects the total number of turnovers, TON. Phosphine decomposition is an unavoidable side reaction in metal-phosphine complex-catalyzed reactions and the main barrier for commercial application of homogeneous catalysts. There are a few exceptions to this statement for example, the rhodium tppts-catalyzed hydroformylation of propene, a process developed by Ruhrchemie-Rhone Poulenc (now Celanese). 

An example of a noncovalent attachment of a metal-phosphine complex to a solid support is presented in Figure 31, as reported by Bianchini et al. (120). The complex is attached via a sulfonated variant of the "triphos" ligand, which is known for its successful application in several catalytic reactions. The ligand is attached to the silica by an ionic bond, which is stable in the absence of water. The catalyst was used for the hydroformylation of styrene and of hex-1-ene in batch mode and showed moderate activity. The triply coordinated rhodium atom is strongly boimd although the conditions were rather harsh (120 °C, 30 bar) the concentration of leached metal measured by atomic emission spectroscopy was at most at the parts per million level. However, for commercial applications, for example, in a process such as hydroformylation of bulk products, these concentrations should be less than 10 ppb 111,121). 

Amyl alcohols occur in eight isomeric forms and have the empirical formula CjHnOH. All are liquids at ambient conditions except 2,2-dimethylpropanol (neopentyl alcohol), which is a solid. Almost all amyl alcohols are manufactured in the United States by the hydroformylation of butylenes. Yeast fermentation processes for ethanol yield small amounts of 4-methyl-l-butanol (isoamyl alcohol) and 2-methyl-1-butanol (active amyl alcohol, scc-butyl-carbinol) as fusel oil. However, when the amino acids leucine and isoleucine are added to sugar fermentations by yeast, 87% and 80% yields of 4-methyl-l-butanol and 2-methyl-l-butanol, respectively, are obtained (Fieser and Fieser, 1950). These reactions are not suitable for commercial applications because of cost, but they do indicate the close structural relationship between these C5 amino acids and the C5 alcohols. The reactions occur under nitrogen-deficient conditions. If a nitrogen source is readily available, the production of the alcohols is lowered considerably. 

In commercial applications of propene hydroformylation the process underwent several modifications predominantly aimed at improvements in product/catalyst separation. The very first version of the process, which was later named the gas recycle process , effected the removal of the product aldehydes from the catalyst solution by applying a large gas recycle in order to evaporate the aldehydes [146, 196, 197]. The catalyst solution consisted of high-boiling aldehyde condensation products (dimers, trimers, and various other aldehyde consecutive products), in which an excess of TPP and the rhodium complex itself was dissolved [198, 199]. In order to keep the volume of this reaction mixture constant, the reaction conditions had to be maintained in a manner which allowed continuous evaporation of the aldehyde products generated by the hydroformylation reaction... 

The concept of biphasic catalysis requires that the catalyst and product phases separate rapidly to achieve a practical approach to the recovery and recycling of the catalyst. It is obvious that simple aqueous/hydrocarbon systems form two phases under nearly all operating conditions and thus provide rapid product-catalyst separation. Ultimately, however, the application of water-soluble catalysts is limited to low-molecular-mass substrates which have appreciable water-solubility. The problem is illustrated by the data in Table 1, which gives the solubility of some simple alkenes in water at room temperature [1], Although hydrocarbon (alkene)-solubility in water increases at higher temperature, most alkenes do not have sufficient solubility to give practical reaction rates in catalytic applications. The addition of salts further decreases the solubility of hydrocarbons in water. Substrate solubility in water is a significant issue and it is no accident that so-far the practiced and proposed commercial applications of water-soluble catalysts for hydroformylation are limited to propene and butene. 

Other important commercial applications of hydroformylation include the production of long-chain alcohols from C5-C17 isomeric linear alkenes. " These long-chain alcohols serve as intermediates for lubricants, plasticizers and detergents. The hydroformylation of ethene to propanal is another important Oxo Process. ... 

Other Systems. - The commercial application of Rh hydroformylation catalysts is currently limited to alkenes of relatively low molecular weights where the product can be removed by distillation. Similar constraints apply to SLPC systems and for chemically immobilized systems low activites can be expected for high molecular weight alkenes because of problems connected with reactant diffusion. A number of publications have appeared over the past five years which address 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. 

As recently reported, the efficiency of SAPC over a much wider hydration range will facilitate its use in industry. Two major commercial applications of SAPC are expected first, many fine chemicals and pharmaceuticals could be produced in better conditions due to high enantioselectivity and secondly, hydroformylation of liquid olefins in continuous fixed-bed reactors under mild conditions with relatively high productivity and selectivity is possible. 

Table I. Survey of commercial applications of Rh-catalyzed hydroformylation processes...

As far as it is possible to judge from the published data, the approach developed by Ding and coworkers to heterogenize hydroformylation is an interesting method to achieve robust processes that can be used on an industrial scale. The buoyant patent activity would suggest that developers believe in the possibility of commercial applications. 

Thus the catalyst has to favor first of all CO insertion over pure hydrogenation. This selectivity issue is mainly addressed by the choice of central transition metal for the hydroformylation catalysis. Obviously, all metals active in hydroformylation show a pronounced tendency to form metal carbonyl complexes. However, only Rh and Co complexes show sufficiently high hydroformylation activity for commercial applications, with rhodium being 1000-10000-fold more active, but also about 1000-fold more expensive, than cobalt (Moulijn, Makkee, and van Diepen, 2001). 

The catalyst has to favor CO insertion over pure hydrogenation, which is addressed by selection of the central transition metal for the hydroformylation catalysis. Only Rh and Co complexes show sufficiently high hydroformylation activity for commercial applications. 

Since none of the commercially available nano- or ultrafiltration membranes so far shows real long-term resistance against organic solvents under the reaction conditions needed for a commercially interesting hydroformylation process and since no prices are available for bulk quantities of membranes for larger scale applications, considerations about the feasibility of such processes are difficult and would be highly speculative. 

Industrial Applications. Several large scale industrial processes are based on some of the reactions listed above, and more are under development. Most notable among those currently in use is the already mentioned Wacker process for acetaldehyde production. Similarly, the production of vinyl acetate from ethylene and acetic acid has been commercialized. Major processes nearing commercialization are hydroformylations catalyzed by phosphine-cobalt or phosphine-rhodium complexes and the carbonylation of methanol to acetic acid catalyzed by (< 3P) 2RhCOCl. 

Other Uses of Ethylene Oxide. About 2 percent of ethylene oxide is consumed in miscellaneous applications, such as its use as a raw material in manufacture of choline, ethylene chlorohydrin, hydroxyethyl starch, and hydrox-yethyl cellulose and its direct use as a fumigant/ sterilant. Production of 1,3-propanediol via hydroformylation of ethylene oxide was begun on a commercial scale in 1999. 1,3-Propanediol is a raw material for polytrimethylene terephthalate, which finds uses in fibers, injection molding, and in film. Use of ethylene oxide in making 1,3-propanediol is expected to be as much as 185 million lb by 2004, up from 12 million lb in 1999. 

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