Organic compounds -- part of the class 532-570 series – Organic compounds – Oxygen containing
Reexamination Certificate
2002-08-08
2004-04-27
Richter, Johann (Department: 1621)
Organic compounds -- part of the class 532-570 series
Organic compounds
Oxygen containing
C568S438000, C568S492000
Reexamination Certificate
active
06727391
ABSTRACT:
The present invention relates to a process for working up a liquid hydroformylation output from a continuous hydroformylation reaction, which output comprises at least one aldehyde as hydroformylation product, unreacted olefins, dissolved synthesis gas, the homogeneously dissolved hydroformylation catalyst and by-products of the hydroformylation reaction.
The hydroformylation of olefins to the corresponding aldehydes is of tremendous economic importance, since the aldehydes prepared in this way are in turn starting materials for many industrial products such as solvents or plasticizer alcohols. Accordingly, there has been a great deal of research worldwide on hydroformylation processes, for example to improve the energy balance of the process, to increase the selectivity and to subject the homogeneous rhodium catalyst to less stress.
The hydroformylation of C
2
-C
20
-olefins is generally carried out using the liquid output process as is known from EP-A-114 611, U.S. Pat. No. 4,148,830 or EP-A-016 286, in which the essentially liquid output from the hydroformylation reaction is depressurized into an expansion vessel. As a result of the drop in pressure, the output is separated into a liquid phase comprising the catalyst, solvents, high-boiling by-products and a small amount of aldehyde and unreacted olefin and a gas phase comprising the excess synthesis gas together with the major part of the aldehyde formed and of the unreacted olefin. The liquid phase is returned to the reactor as recycle stream and the gas phase is taken off. The gas phase is separated into the synthesis gas plus the unreacted olefins and the aldehyde, which is separated from unreacted olefin by distillation. The synthesis gas and the unreacted olefins are recirculated to the reactor.
WO 97/07086 describes a modified process in which the liquid phase from the expansion vessel is fed into the upper part of a column and the gas phase is introduced into the lower part of the column, so that the liquid phase is treated in countercurrent with the gas phase. This improves the separation of product and high-boiling components. This separation is advantageously carried out at a pressure which is as low as possible so that the separation of product and high boilers can be carried out at temperatures which do not damage the catalyst.
The disadvantage of this process is that large compressors with high energy consumption have to be used in order to compress the excess synthesis gas, unreacted olefins and low-boiling by-products to the reaction pressure and to recirculate them to the reactor.
It is an object of the present invention to provide a more economical process for the hydroformylation of olefins, in which the abovementioned disadvantages in the further work-up of the liquid hydroformulation output from the hydroformylation reactor are circumvented.
We have found that this object is achieved by a process comprising a two-stage flash distillation of the hydroformylation output.
The present invention accordingly provides a process for working up a liquid output from a continuous hydroformylation, which comprises aldehydes, high-boiling by-products, a homogeneously dissolved hydroformylation catalyst, unreacted olefins, low-boiling by-products and dissolved synthesis gas, wherein
a) the liquid hydroformylation output is depressurized in a first depressurization stage to a pressure which is from 2 to 20 bar below the reactor pressure, resulting in separation into a liquid phase and a gas phase, and
b) the liquid phase obtained in the first depressurization stage is depressurized in a second depressurization stage to a pressure which is lower than the pressure of the first depressurization stage, resulting in separation into a liquid phase comprising essentially high-boiling by-products of the hydroformylation, the homogeneously dissolved hydroformylation catalyst and small amounts of hydroformylation product and unreacted olefin and a gas phase comprising essentially the major part of the hydroformylation product, unreacted olefin and low-boiling by-products.
The process of the present invention is suitable for the work-up of liquid outputs from the rhodium-catalyzed hydroformylation of olefins. Olefins employed are generally ones having from 2 to 20 carbon atoms, in particular from 2 to 10 carbon atoms and particularly preferably from 2 to 5 carbon atoms, or mixtures thereof. The olefins used can be unsubstituted or have one or two substituents which are inert under the hydroformylation conditions, for example an ester group, a nitrile group, an alkoxy group or a hydroxy group.
The rhodium catalysts used are generally complexes which bear one or more organophosphorus compounds as ligands and are homogeneously soluble in the reaction medium of the hydroformylation reaction. Examples of such ligands are phosphine ligands selected from the group consisting of triarylphosphines, in particular triphenylphosphine, C
1
-C
6
-alkyldiarylphosphines or arylalkyldiphosphines. Catalysts which can be used are described, for example, in WO 97/07086 and in the patent publications cited therein.
The hydroformylation is generally carried out at from 50 to 150° C. and a pressure in the range from 5 to 50 bar.
At the specified temperature and the specified pressure, the synthesis gas, namely a carbon monoxide/hydrogen mixture having a CO/H
2
molar ratio of generally from 20/80 to 80/20, preferably from 40/60 to 60/40, which is used in excess for the hydroformylation is dissolved in the liquid hydroformylation output to an extent corresponding to its solubility. Part of the synthesis gas can be suspended in the hydroformylation output in the form of small gas bubbles.
The liquid part of the output from the hydroformylation reaction comprises, as significant constituents, the rhodium catalyst, the hydroformylation product, i.e. the aldehyde(s) produced from the olefin or olefin mixture used, and also condensation products of these aldehydes which have boiling points higher than that of the hydroformylation product, as can be formed as by-products during the course of the hydroformylation and have been described, for example, in U.S. Pat. No. 4,158,830, together with low-boiling components such as, in particular, the alkanes corresponding to the olefins. The liquid output may further comprise a high-boiling, inert solvent such as toluene or xylene.
The details of the hydroformylation process and the rhodium catalyst used provided above serve to place the process of the present invention in its technical context. It may be pointed out at this point that the hydroformylation preceding the process of the present invention can be carried out by customary liquid output hydroformylation processes known per se from the prior art, for example as described in EP-A-0 16 286, EP-A-188 246 or U.S. Pat. No. 4,148,830.
The liquid hydroformylation output is preferably firstly heated to a temperature which is from 5 to 50° C., preferably from 10 to 30° C., above the reactor temperature. This heating is carried out in the customary manner, generally by means of heat exchangers.
The heated or unheated hydroformylation output is then, in a first depressurization stage, depressurized into a vessel (expansion vessel) to a pressure which is from 2 to 20 bar, preferably from 5 to 15 bar, below the reactor pressure. The pressure in the expansion vessel is then generally in the range from 2 to 40 bar, preferably from 2 to 20 bar.
In the first depressurization stage, the hydroformylation output is separated into a liquid phase and a gas phase. The gas phase comprises essentially excess synthesis gas, unreacted olefin and possibly the alkane corresponding to the olefin. The gas phase is generally, usually after compression to the reactor pressure, recirculated to the reactor. The liquid phase comprises essentially the hydroformylation product, condensation products of the hydroformylation product which have higher boiling points, the catalyst and possibly a solvent such as toluene or xylene.
The liquid phase separated out in the first depressurization stage is
Geissler Bernhard
Krokoszinski Roland
Müller Rolf
Walczuch Karl-Heinz
BASF - Aktiengesellschaft
Keil & Weinkauf
Richter Johann
Witherspoon Sikarl A.
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