Hydroformylation reactor conditions

A cracker converts isobutyraldehyde at a pass yield of 80% back to propylene, carbon monoxide, and hydrogen by passage over a catalyst with steam. After separation of the water and unreacted isobutyraldehyde the cracked gas is recycled to the hydroformylation reactor. The isobutyraldehyde is recycled to the cracker inlet. The operating conditions of the cracker are 275 °C and 1 bar. 

Most of the 0x0" aldehydes are hydrogenated to alcohols. This hydrogenation is sometimes favoured inside the hydroformylation reactor (32). More often, it is realized in a subsequent reactor using the purified 0x0 aldhydes or after an aldol condensations of these aldehydes. Nickel or copper are very selective catalysts. They are used in the gas phase or in the liquid phase. Purified aldehydes are treated in the liquid phase at 115 C and 80 bar in the presence of nickel. Under more rigorous conditions (200 C and 280 bar), crude 0x0 aldehydes containing small amounts of ester and acetal can be hydrogenated. This supplies further amounts of alcohol by hydrogenolysis. 

Hydroformyl ati on of Polybutadiene - A number of hydroformyl at ion experiments were performed using the automated batch reactor system in order to synthesize the hydroformylated polybutadiene with varying degree of reaction completion (2 to 20% of the total C=C present). The following reaction conditions were employed PBD = 1.55 x 103 mol/m3, RhH(CO) (P(C6HJ3 )3 = 0.58... 

Mitsubishi has patented a triphenylphosphine oxide-modified rhodium catalyst for the hydroformylation of higher alkenes with both alkyl branches and internal bonds. [19] Reaction conditions are 50-300 kg/cm2 of CO/H2 and 100-150 degrees C. The high CO/H2 partial pressures provide stabilization for rhodium in the reactor, but rhodium stability in the vaporizer separation system is a different matter. Mitsubishi adds triphenylphosphine to stabilize rhodium in the vaporizer. After separation, triphenylphosphine is converted to its oxide before the catalyst is returned to the reactor. 

In subsequent work the same supported catalysts were used in different reactor setups [20] (Figure 3.3). A vapour-phase reactor in which the supported catalyst was mounted on a bed was used for the hydroformylation of volatile alkenes such as cis-2-butene and trifluoropropene. The initial activities and selectivity s were similar to those of the homogeneous solutions, i.e. a TOF of 114 and 90% ee in the hydroformylation of trifluoropropene was reported. No rhodium was detected in the product phase, which means less then 0.8% of the loaded rhodium had leached. The results were, however, very sensitive to the conditions applied and, especially at longer reaction times, the catalyst decomposed. In a second approach the polymer supported complex was packed in a stainless steal column and installed in a continuous flow set-up. 

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]. 

However, (Ph3P)2Rh(CO)Cl on alumina or activated carbon were effective hydroformylation catalysts under more severe conditions 108). At 148°C and a pressure of 49 atm (CO 37.5 mol%, H2 37.5, propylene 25), good activity was found. The propylene conversion was 30% at a contact time of 0.92 cm3 of reactor void space/cm3 of feed per minute. Isomer ratios of 1.3 to 1.9 1 n iso were realized. By-product formation was low, with <1% conversion to alcohols plus alkanes and 2.2% high-boiling materials. This system was stable for a 300 hour operating time, with no detectable loss of activity or selectivity. 

Fig.21 Hydroformylation of 1-octene with Co2(CO)8 in SCCO2 (a) and in toluene (b) initial conditions 53 mmol of 1-octene, 106 mmol syngas (H2 CO = 1 1), 0.106 mmol Co2(CO)8, T = 393 K left Reactor pressure as function of time right C Conversion, S Selectivity, la 1-nonanal, lb 2-nonanal, 2 nonanols, 3 octenes (without 1-octene), 4 -octane...

The same dendritic ligands, but used in combination with rhodium, were utilized in hydroformylation reactions [46]. Preliminary experiments with this catalytic system in a nanofiltration membrane reactor, however, showed that this membrane set-up was not compatible with the standard hydroformylation conditions because of its temperature and solvent restrictions. 

As is the case of hydroformylation, the use of rhodium allows much milder conditions to be used. Such a process was started by Monsanto in 1966 it operates at 30-60 bar and 150-200°C and is now the world s largest process for acetic acid production (>5 million tons per year). In view of the corrosive nature of the reagents, Hastalloy or zirconium reactors have to be used. 

It has yet to be seen whether the principle of biphasic hydroformylation can be further extended beyond C4 olefins. Bearing in mind the advantages of biphasic operation, two pathways may be considered biphasic operation in the reactor section and subsequent phase separation or a combination of homogeneous hydroformylation reaction with an auxiliary agent. This substance would require a miscibility gap with the products under conditions different from the reaction conditions. Examples of both principal methods have already been published [271, 272]. However, a general solution is not to be expected, as each feed-stock/product pair requires a specially adapted solvent. Novel developments in the field of catalyst separation and reuse of catalyst systems are noted below. 

By comparison between the calculated and measured pressure and heat flux vs. time curves it was shown that the site of this hydroformylation reaction could not be the bulk of the liquid. Only the assumption of a reaction in the liquid boundary layer at the gas-liquid interface gave satisfactory agreement of the data under all experimental conditions. Thus, on this basis scale-up rules for the aqueous bipha-sic hydroformylation and appropriate kinetic models can be developed for optimal reactor design. The principle of both models applied to the general equation (Eq. 10) is shown in Figure 5. 

Some further special technical aspects should be mentioned. The intensive mixture of the two liquid phases is an important condition for obtaining high reaction rates. This mixing can be achieved in bubble columns, tray columns or in stirred-tank reactors. In the few publications on industrially realized two-phase reactions the stirred tank reactor is always cited, but without detailed information on the stirring device. One further possible way to increase the mass transfer between the two liquid phases is by the influence of sonification. Cornils et al. applied this technique in the hydroformylation of hexene or diisobutene and found a considerable increase in the turnover numbers [93]. Another possibility for increasing the mass transfer may be by the use of microemulsions and micellar systems [94], which can be reached by addition of certain surfactants. This aspect is discussed in Sections 3.2.4 and 4.5. The separation of catalyst compounds in two-phase systems in combination with membranes has been studied recently by Muller and Bahrmann [95],... 

Horvath conducted several other interesting experiments with rhodium SAPCs (Table 1) [12]. Clearly, the water-solubility of the olefins does not limit the performance of the SAPCs since the TOFs (turnover frequencies) are essentially independent of olefin carbon number. This has been shown to be true also for carbon numbers as high as 17 [13]. Additionally, Horvath conducted experiments aimed at observing rhodium loss into the organic phase. He concluded that the SAPC does not leach catalytically active rhodium species under hydroformylation conditions. Another critical test for leaching was performed by Horvath. He conducted a 38 h continuous-flow experiment in a trickle-bed reactor and showed no loss of rhodium by elemental analysis. Thus, the combined data from all work shows that... 

For long-term stability, the SAPC must remain assembled. To test for this type of stability, it was investigated whether the components can self-assemble. The rhodium complex HRh(CO)(TPPTS)3, TPPTS and water were loaded into a reactor with cyclohexane and 1-heptene. The reactor was pressurized with approx. 70 bar H2 + CO (CO H2, 1 1) and heated with stirring to 100°C. A second experiment was carried out in a manner similar to the one previously described except that CPG-240 was added also. The components of the SAPC self-assemble to form an SAPC and carry out the hydroformylation reaction [13]. Upon termination of the reaction, the solid collected contained HRh(CO)(TPPTS)3 and TPPTS. This test indicates that, under the conditions of the experiment, the individual components of the SAPC are more stable assembled in an SAPC configuration than separated. Therefore, the reverse, i.e., the separation of the solution and complex from the support, is not likely to happen under reaction conditions. 

The lack of data is obvious and surprising at a time when the Ruhrchemie/ Rhone-Poulenc process has been in operation for more than 20 years. A rigid reaction rate model, established under idealized conditions, becomes complex and complicated when it is transferred to the hydroformylation of lower olefins under conditions relevant to the industrial practice, as the mass transfer phenomena involved in a triphasic system (gas-liquid-liquid) in large reactors have to be taken... 

A highly fluorous C02-philic rhodium catalyst was effectively immobilized in an inverted H20/scC02 system for the prototypical hydroformylation reaction shown in Eq. (5) [57]. Emulsion-type mixtures are formed under the reaction conditions upon stirring, which separate rapidly when stirring is stopped. After removal of the aqueous phase from the bottom of the reactor, a clear supercritical catalyst phase remains in the reactor that can be re-used for subsequent reactions. Recycling is very efficient at moderate catalyst loadings, but noticeable deactivation occurs at very low rhodium concentrations, probably caused by the low pH of the aqueous solution in the presence of C02. 

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