Low-pressure-oxo processes’

Ethanol s use as a chemical iatemiediate (Table 8) suffered considerably from its replacement ia the production of acetaldehyde, butyraldehyde, acetic acid, and ethyUiexanol. The switch from the ethanol route to those products has depressed demand for ethanol by more than 300 x 10 L (80 x 10 gal) siace 1970. This decrease reflects newer technologies for the manufacture of acetaldehyde and acetic acid, which is the largest use for acetaldehyde, by direct routes usiag ethylene, butane (173), and methanol. Oxo processes (qv) such as Union Carbide s Low Pressure Oxo process for the production of butanol and ethyUiexanol have totaUy replaced the processes based on acetaldehyde. For example, U.S. consumption of ethanol for acetaldehyde manufacture declined steadily from 50% ia 1962 to 37% ia 1964 and none ia 1990. Butadiene was made from ethanol on a large scale duriag World War II, but this route is no longer competitive with butadiene derived from petroleum operations. 

Eventually, the spent catalyst solution has to leave the oxo loop for work-up. The Ruhrchemie works of Celanese AG in Oberhausen (Germany) operate several rhodium-based oxo processes besides the well-known Ruhrchemie/Rhone-Poulenc process (RCF1/RP, the described low pressure oxo process with TPPTS-modified Rh catalyst), there are the Ruhrchemie process with an unmodified Rh catalyst at high pressure (comparable to the late ICI process [76] this variant is for the benefit of a high iso/n ratio... 

Union Carbide invented the industrial use of highly active ligand-modified rhodium complexes.90-93 [RhH(CO)(PPh3)3], the most widely used catalyst, operates under mild reaction conditions (90-120°C, 10-50 atm). This process, therefore, is also called low-pressure oxo process. Important features of the rhodium-catalyzed hydroformylation are the high selectivity to n-aldehydes (about 92%) and the formation of very low amounts of alcohols and alkanes. Purification of the reactants, however, is necessary because of low catalyst concentrations. 

Three significant commercial processes for the production of amyl alcohols include separation from fusel oils, chlorination of C-5 alkanes with subsequent hydrolysis to produce a mixture of seven of the eight isomers (Pennsalt). and a low pressure oxo process, or hydroformylalion, of C-4 olefins followed by hydrogenation of the resultant C-5 aldehydes. 

The production of 2-ethylhexanol from propylene by the rhodium catalyzed, low pressure oxo process is accomplished in three chemical steps. The first step of the process (described in section on n-butanol manufacture) converts propylene to normal butyraldehyde by hydroformylation in the presence of a rhodium catalyst. In a second step, the normal aldehyde is aldoled to form 2-ethylhexena1. 2-Ethylhexenal is then hydrogenated to 2-ethylhexanol and refined in the third and final step(see Figure 3). 

Fig. 10.5. Low-pressure oxo process. (Chem Systems Report No. 98/99 S13. Copyright Nexant Chem Systems, Inc. and used by permission of the copyright owner.)...

The low-pressure oxo process based on rhodium complex catalysts has largely replaced the older, high-pressure process, which used cobalt carbonyls as catalyst. The low-pressure process is operated at about 100°C and 200psig. A new generation oxo process with bisphosphite modified rhodium catalyst is shown schematically in Fig. 10.5. 

The low pressure oxo process was jointly developed by Union Carbide, Davy Powergas (Davy McKee), and Johnson Matthey. The latter two companies possess the rights of the Wilkinson patents. The catalyst is a rhodium complex, with a large excess of triphenylphosphine. Temperature and pressure have to be controlled very carefully because the linearity strongly depends on these parameters. Ligand and rhodium (300 ppm) are very sensitive to impurities and the feed must be very thoroughly purified. The rhodium stays in the reactor, apart from a small purification cycle, employed for the reactivation of inactive rhodium... 

Kvaerner Process Technology/ Union Carbide Corp. 2-Ethylhexanol Propylene Rhodium-catalyzed, low pressure oxo process high efficiency with minimal coproducts 14 1997... 

Brewester, EAV, Low pressure Oxo process features rhodium catalyst Chan. Engng, 83 (24) 90-91 (1976). Low pressure Oxo process yields a better product mix , Chan. Engng, 84 (26) 110-115 (1977). 

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]. 

Two-phase hydroformylation of alkenes is an example of the development of a low-pressure oxo process operating at a syngas pressure of 20-50 bar. As can be seen in Table 2, the conversion rate seems to reach a maximum between 30 and 80 bar in the hydroformylation of n-l-hexene. By increasing the syngas pressure from 25 to 270 bar the n/iso-ratio decreases from 98 2 to 92 8. Whereas the increase of... 

Union Carbide and Davy McKee, in conjunction with Johnson Mat-they Corp., developed a low pressure oxo process (LP Oxo) using a modified rhodium catalyst. UCC/Davy McKee actively license this process to other operators that use it primarily for production of n-butanol and 2-ethylhexanol. New developments have focused on improvements in the rhodium-based catalyst and the addition of a liquid recycle variation of the LP Oxo process for production of 2-propyl hepatanol from refinery mixed C4 streams. 

Anon. (1977) Low-pressure oxo process yields a better product mix. Chem. Eng., 84(26) 110-115. 

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... 

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