Organic compounds -- part of the class 532-570 series – Organic compounds – Oxygen containing
Patent
1998-05-29
2000-08-08
Kumar, Shailendra
Organic compounds -- part of the class 532-570 series
Organic compounds
Oxygen containing
568451, C07C 4550
Patent
active
061004324
DESCRIPTION:
BRIEF SUMMARY
DESCRIPTION
The present invention relates to a process for the purification of a substantially liquid effluent containing aldehydes and unconverted olefins coming from a hydroformylation reactor following low-pressure hydroformylation of C.sub.3 -C.sub.20 olefins or olefin mixtures containing different isomers of the respective olefins, said hydroformylation being catalyzed by means of a phosphorous rhodium catalyst homogeneously dissolved in the reaction medium and carried out at a temperature of from 50.degree. to 150.degree. C. and a pressure of from 2 to 30 bar.
The hydroformylation of olefins to form the corresponding aldehydes is of very great economical significance, since the aldehydes prepared in this way are in turn starting materials for a large number of commercial products such as solvents or plasticizer alcohols. Hydroformylation processes are accordingly subjected to intensive research world-wide, in order to achieve further economical improvements, for example in the energy balance of the process, to increase its selectivity, and to protect the homogeneous rhodium catalyst.
The so-called liquid-discharge process is generally used for the hydroformylation of C.sub.3 -C.sub.20 olefins to produce the corresponding aldehydes (U.S. Pat. No. 4,148,830, EP-A 16,286) in which the substantially liquid--except for the synthesis gas used in excess to effect hydroformylation--effluent from the hydroformylation reactor is depressurized in a let-down vessel, the effluent, on account of the pressure drop, being separated into a liquid phase containing the catalyst, solvent, high-boiling by-products and a minor amount of aldehyde and unconverted olefin and a gas phase containing, in addition to the excess synthesis gas, the major portion of aldehyde formed and the unconverted olefin. The liquid phase is then recycled to the reactor as return stream and the gas phase is withdrawn, the synthesis gas separated therefrom and the mixture subsequently separated into aldehyde and olefins by distillation. The liquid return stream contains amounts of aldehyde and olefin which are small compared with the gas stream withdrawn from the let-down tank but which are not negligible with respect to the economic value of the process. Apart from the fact that it is uneconomical to circulate a specific amount of aldehyde in such manner constantly, the recycled aldehyde tends to form high-boiling condensation products under the hydroformylation conditions. Although the latter are good solvents for said hydroformylation, it is desirable, for economical reasons, to keep the reformation of such high-boiling by-products within narrow limits. Recycling of residual amounts of olefin dissolved in the liquid return stream can also be disadvantageous when the starting material used for the hydroformylation is not a pure olefin but a hydrocarbon mixture containing, in addition to the olefin to be converted, other isomeric olefins and saturated hydrocarbons.
For the aforementioned reasons it would be advantageous to distil the liquid phase separated in the let-down vessel prior to recycling to the hydroformylation reactor, to effect separation of residual amounts of aldehyde or olefin. Such a procedure is however uneconomical, since to effect distillation of the liquid phase from the let-down vessel said liquid phase must be heated strongly. Prior to recycling to the hydroformylation reactor the said heated liquid phase would have to be cooled down, since otherwise the temperature in the hydroformylation reactor would rise to unduly high values due to the heat of reaction liberated in the hydroformylation reactor. Thus such a process would be very unsatisfactory when regarded from the energy balance point of view.
In the prior art (EP-A 404,193, EP-A 484,976) the liquid phase separated in the let-down tank is used as absorbent for those unconverted olefins which become gaseous in the let-down tank. For this purpose the gas phase is passed, in an absorption column, through the (cooled) liquid phase having a temperature not higher than th
REFERENCES:
patent: 3455091 (1969-07-01), Herber et al.
patent: 4148830 (1979-04-01), Pruett et al.
patent: 5001274 (1991-03-01), Bunning
Borgel Franz
Krokoszinski Roland
Muller Rolf
BASF - Aktiengesellschaft
Kumar Shailendra
Padmanabhan Sreeni
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