Industrial hydroformylation

Of course, there is still a large amount of research to be done to develop further the very preliminary character of the above described economic evaluation of an ionic liquid hydroformylation process. Only on the basis of more detailed data it will be possible to decide whether we will see an industrial hydroformylation plant using ionic liquids in the future. 

In today s industry, hydroformylation is the largest volume homogeneous catal)4ic process employing organometaUic catalysts [1], The simplest representation of this process (Scheme 4.1) is the reaction of a terminal alkene with CO and H2 to afford linear and branched aldehydes. 

Industrial hydroformylation of allyl alcohol employs [RhH(CO)(PPh3)3] as catalyst (Kuraray see also 4.1.1.4). In an aqueous solution K[Ru(EDTA-H)C1] catalyzed both the water gas shift and hydroformylation under 10 bar CO at 100-130 °C. The major product was y-hydroxybutyraldehyde (35%) but large amounts of y-butyrolactone and dihydroftiran were also produced [151]. 

Slaugh and Mullineaux (1) disclosed a low pressure hydroformylation process using trialkylphosphines in combination with rhodium catalysts for the preparation of aldehydes as early as 1966. Trialkylphosphines have seen much use in industrial hydroformylation processes but they typically produce a limited range of products and frequently are very oxygen sensitive. 

This is an industrial hydroformylation for synthesizing aliphatic aldehydes, RCHO. 

The crucial problem associated with the use of homogeneous rhodium catalysts in industrial hydroformylation is catalyst recovery. Because of the high cost of rhodium, it is necessary to recover rhodium at the ppm level to ensure economical operation. A highly successful solution to this problem was the development and application of the aqueous biphasic catalysis concept. 

In a typical industrial hydroformylation process, the rhodium to phosphorus molar ratio is between 1 50 to 1 100, while the partial pressure of CO is about... 

In an industrial hydroformylation reaction with a rhodium catalyst in the presence of excess phosphine and high pressures of CO, what would probably be the minimum number of catalytic cycles and intermediates ... 

Three types of homogeneous transit ion-metal complexes are used in industrial hydroformylation processes. In order of both their present commcrical importance and their historic development, these arc ... 

Cobalt catalysts completely dominated industrial hydroformylation rmtil the early 1970s, when rhodium catalysts were commercialized. Most aldehydes produced are hydrogenated to alcohols or oxidized to carboxylic acids. Esterification of the alcohols with phthalic anhydride produces dialkyl phtha-late plasticizers that are primarily used for polyvinyl chloride plastics - the largest single end-use. Detergents and surfactants make up the next largest category, followed by solvents, lubricants, and chemical intermediates. 

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]. 

Although the oxo synthesis has been applied industrially almost 50 years, its reaction mechanism has not been clarified in every detail. Some aspects of the proposed reaction pathway are still under investigation. Among industrial hydroformylation catalysts, major differences are observed between modified and unmodified systems and therefore they will be discussed separately. 

A convenient catalyst precursor is RhH(CO)(PPh3)3. Under ambient conditions this will slowly convert 1-alkenes into the expected aldehydes, while internal alkenes hardly react. At higher temperatures pressures of 10 bar or more are required. Unless a large excess of ligand is present the catalyst will also have some isomerization activity for 1-alkenes. The internal alkenes thus formed, however, will not be hydroformylated. Accordingly, the 2-alkene concentration will increase while the 1-alkene concentration will decrease this will slow down the rate of hydroformylation. This makes the rhodium triphenylphosphine catalyst less suited for the conversion of alkenes other than propene, for which isomerization is immaterial. To date, industrial hydroformylation of higher alkenes is still carried out with cobalt catalysts. 

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],... 

The industrial hydroformylation of short-chained olefins such as propene and butenes is nowadays almost exclusively performed by so-called LPO (low-pressure oxo) processes, which are rhodium-based. In other words, the former high-pressure technology based on cobalt has been replaced by the low-pressure processes, which cover nearly 80% of total C4 capacity due to their obvious advantages (cf. [8]). Nevertheless, some cobalt processes are still in operation for propene hydroformylation, for example as second stages in combination with a low-pressure process serving as the first stage [8, 9]. 

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