Hydroformylation Operations

The operating plants produce aldehydes in the range Cg-Cjg which are either hydrogenated as such to give the corresponding alcohols or subjected to aldol condensation prior to the hydrogenation. In the latter case the resulting alcohols contain double the number of carbon atoms as the aldehyde used for the aldol condensation (e. g. 2-ethylhexanol is made from two moles of n-butyraldehyde via 2-ethylhexenal). 

Certain quantities of aldehydes are often oxidized for carboxylic acids in adjacent plants. 

With only one exception, all industrially applied oxo processes more or less follow the technique which was developed by Ruhrchemie AG in Oberhausen/Germany [895-898, 1015] in co-operation with BASF. The exception is the process developed by Shell, which will be discussed later. The first industrial application dates back to 1940 when plant operations were started in the works of Ruhrchemie by a joint venture of Ruhrchemie, BASF and Henkel. 

All existing oxo plants are operated fully continuously. In general they consist of the following sections  

As mentioned earlier the plants may also contain aldolisation reaction and oxidation units. 

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Figure 3.8. An early example of a hybrid support applied in the rhodium catalysed hydroformylation operated in a continuous flow reactor. Polystyrene containing phosphite ligands were grafted on inorganic silica, such that the catalyst will behave as a homogeneous catalyst when using a compatible solvent...

However, there are technical processes known working even with higher water concentrations, see chapter on industrial hydroformylation operations. 

A double hydroformylation is also employed in the allyl boration process. The aldehyde group of 128 obtained in the first hydroformylation operates in the intramolecular allyl boration to give rise to the vinylpiperidine 130, which on introduction of the next formyl group ring closes to hemiacetal 129 [59a, b]. 

The rate of hydroformylation increases with increasing hydrogen and decreases with increasing carbon monoxide partial pressures (9), suggesting that rates of hydroformylation would be satisfactory at high H2 and low CO partial pressures. In industrial practice, however, high pressures of both H2 and CO ate required in order to stabilize the HCo(CO)4 catalyst at the temperatures necessary for practical rates (10). Commercial processes, for example, operate at >24 MPa (3480 psi) and >140 C. 

Ligand-Modified Rhodium Process. The triphenylphosphine-modified rhodium oxo process, termed the LP Oxo process, is the industry standard for the hydroformylation of ethylene and propylene as of this writing (ca 1995). It employs a triphenylphosphine [603-35-0] (TPP) (1) modified rhodium catalyst. The process operates at low (0.7—3 MPa (100—450 psi)) pressures and low (80—120°C) temperatures. Suitable sources of rhodium are the alkanoate, 2,4-pentanedionate, or nitrate. A low (60—80 kPa (8.7—11.6 psi)) CO partial pressure and high (10—12%) TPP concentration are critical to obtaining a high (eg, 10 1) normal-to-branched aldehyde ratio. The process, first commercialized in 1976 by Union Carbide Corporation in Ponce, Puerto Rico, has been ficensed worldwide by Union Carbide Corporation and Davy Process Technology. 

Propanol has been manufactured by hydroformylation of ethylene (qv) (see Oxo process) followed by hydrogenation of propionaldehyde or propanal and as a by-product of vapor-phase oxidation of propane (see Hydrocarbon oxidation). Celanese operated the only commercial vapor-phase oxidation faciUty at Bishop, Texas. Since this faciUty was shut down ia 1973 (5,6), hydroformylation or 0x0 technology has been the principal process for commercial manufacture of 1-propanol ia the United States and Europe. Sasol ia South Africa makes 1-propanol by Fischer-Tropsch chemistry (7). Some attempts have been made to hydrate propylene ia an anti-Markovnikoff fashion to produce 1-propanol (8—10). However, these attempts have not been commercially successful. 

The hydroformylation reaction is carried out in the Hquid phase using a metal carbonyl catalyst such as HCo(CO)4 (36), HCo(CO)2[P( -C4H2)] (37), or HRh(CO)2[P(CgH3)2]2 (38,39). The phosphine-substituted rhodium compound is the catalyst of choice for new commercial plants that can operate at 353—383 K and 0.7—2 MPa (7—20 atm) (39). The differences among the catalysts are found in their intrinsic activity, their selectivity to straight-chain product, their abiHty to isomerize the olefin feedstock and hydrogenate the product aldehyde to alcohol, and the ease with which they are separated from the reaction medium (36). 

To date, these functionalized ligands have been investigated on the laboratory scale, in batch operations to immobilize rhodium catalyst in hydroformylation. 

BASF is operating a semicommercial plant for the production of adipic acid via this route.A new route to adipic acid occurs via a sequential carbonylation, isomerization, hydroformylation reactions.The following illustrates these steps ... 

The first stage of the process is a hydroformylation (oxo) reaction from which the main product is n-butyraldehyde. The feeds to this reactor are synthesis gas (CO/H2 mixture) and propylene in the molar ratio 2 1, and the recycled products of isobutyraldehyde cracking. The reactor operates at 130°C and 350 bar, using cobalt carbonyl as catalyst in solution. The main reaction products are n- and isobutyraldehyde in the ratio of 4 1, the former being the required product for subsequent conversion to 2-ethylhexanol. In addition, 3 per cent of the propylene feed is converted to propane whilst some does not react. 

For the hydroformylation reactor prepare a control scheme to ensure safe operation. 

As demonstrated by Hoffmann and coworkers, hydroformylation can also be combined with an allylboration and a second hydroformylation, which allows the formation of carbocycles and also heterocycles [213]. A good regioselectivity in favor of the linear aldehyde was obtained by use of the biphephos ligand [214]. Reaction of the allylboronate 6/2-76 having an B-configuration with CO/H2 in the presence of catalytic amounts of Rh(CO)2(acac) and biphephos led to the lactol 6/2-80 via 6/2-77-79 (Scheme 6/2.17). In a separate operation, 6/2-80 was oxidized to give the lactone 6/2-81 using tetrabutyl ammonium perruthenate/N-methylmorpholine N-oxide. 

Gas Recycle technology has been licensed worldwide by Union Carbide-Davy for the hydroformylation of propene.[9] It has also been operated by Union Carbide for ethene hydroformylation. Its use with butene is feasible, but at the margin of operability. Liquid Recycle, described below, is a better option for butene. 

When a catalyst has sufficiently deactivated to justify taking some action is determined by economics. Both Gas and Liquid Recycle hydroformylation plants may be operated to give essentially constant production rates as the catalyst deactivates. Hydroformylation is approximately first order in both rhodium and alkene concentration. As the rhodium catalyst deactivates, the alkene concentration may be allowed to increase to compensate for the declining catalyst activity. Action is taken when the alkene efficiency declines to the point where it approximates or exceeds the cost of catalyst replacement or reactivation. 

Up to now only limited kinetic data and thus rate models (and even mechanistic details) of aqueous phase operation are available. Thus, in many cases only estimates and experimentally found data are at the disposal for reaction engineers work (e.g.[25]). The state of the art of the hydroformylation of higher alkenes (>C -) comprises additions of supplementary solvents/diluents or extraction fluids, surface-active agents (detergents), intensity and mode of stirring ([22b], power of agitation (cf. Figure 5.5) operation in... 

Quite new ideas for the reactor design of aqueous multiphase fluid/fluid reactions have been reported by researchers from Oxeno. In packed tubular reactors and under unconventional reaction conditions they observed very high space-time yields which increased the rate compared with conventional operation by a factor of 10 due to a combination of mass transfer area and kinetics [29]. Thus the old question of aqueous-biphase hydroformylation "Where does the reaction takes place " - i.e., at the interphase or the bulk of the liquid phase [23,56h] - is again questionable, at least under the conditions (packed tubular reactors, other hydrodynamic conditions, in mini plants, and in the unusual,and costly presence of ethylene glycol) and not in harsh industrial operation. The considerable reduction of the laminar boundary layer in highly loaded packed tubular reactors increases the mass transfer coefficients, thus Oxeno claim the successful hydroformylation of 1-octene [25a,26,29c,49a,49e,58d,58f], The search for a new reactor design may also include operation in microreactors [59]. 

Various other biphasic solutions to the separation problem are considered in other chapters of this book, but an especially attractive alternative was introduced by Horvath and co-workers in 1994.[1] He coined the term catalysis in the fluorous biphase and the process uses the temperature dependent miscibility of fluorinated solvents (organic solvents in which most or all of the hydrogen atoms have been replaced by fluorine atoms) with normal organic solvents, to provide a possible answer to the biphasic hydroformylation of long-chain alkenes. At temperatures close to the operating temperature of many catalytic reactions (60-120°C), the fluorous and organic solvents mix, but at temperatures near ambient they phase separate cleanly. Since that time, many other reactions have been demonstrated under fluorous biphasic conditions and these form the basis of this chapter. The subject has been comprehensively reviewed, [2-6] so this chapter gives an overview and finishes with some process considerations. 

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