Organic compounds -- part of the class 532-570 series – Organic compounds – Oxygen containing
Reexamination Certificate
2002-12-16
2004-11-23
Richter, Johann (Department: 1621)
Organic compounds -- part of the class 532-570 series
Organic compounds
Oxygen containing
C568S454000
Reexamination Certificate
active
06822122
ABSTRACT:
The present invention relates to a process for the hydroformylation of olefins having from 2 to 8 carbon atoms.
Hydroformylation or the oxo process is an important industrial process and is employed for preparing aldehydes from olefins and synthesis gas, i.e. a mixture of carbon monoxide and hydrogen. Hydroformylation is carried out in the presence of catalysts which are homogeneously dissolved in the reaction medium. Catalysts used are generally compounds or complexes of metals of transition group VIII, usually Co or Rh compounds or complexes which may be unmodified or modified with, for example, amine- or phosphine-containing compounds.
In the hydroformylation of lower olefins, virtually complete conversion of the olefin used can be achieved only when there is a sufficiently large reaction space in the hydroformylation reactor. In order to achieve an acceptable space-time yield, the reaction is generally carried out to only partial conversion based on the olefin used. The hydroformylation product is separated off from the output stream from the reactor and the remaining constituents of the output stream are recirculated to the hydroformylation reactor together with fresh carbon monoxide and hydrogen. However, the gaseous inert components, i.e. gases which do not react in the hydroformylation, for example nitrogen, methane, argon, etc., which have been introduced with the synthesis gas and/or olefin are also returned to the reactor together with the recycle stream. To prevent the concentration of the inert components from rising continually in the hydroformylation reactor and reaching values at which the hydroformylation reaction ceases, a substream of the recycled stream or part of the gas phase in the hydroformylation reactor has to be bled from the process in order to remove the inert components introduced with the synthesis gas and/or the olefin-containing feed from the system.
M. Beller et al., Journal of Molecular Catalysis A: 104 (1995), 46-48 and the accompanying
FIG. 3
, describe a typical gas recycle process for the hydroformylation of lower olefins. Carefully purified propylene and synthesis gas (
1
,
2
) are introduced together with circulating gas into the reactor (
3
). The gaseous output from the reactor passes through a demister (
4
) for precipitating entrained droplets of liquid products. The gaseous hydroformylation product is condensed in a condenser (
5
) and collected in a separation vessel (
6
) from which the circulating gas is taken off via a demister (
7
) and a compressor (
8
) and recirculated to the reactor (
3
). A substream or bleed stream (vent) is discharged. The crude hydroformylation product from the separation vessel (
6
) is passed to work-up.
The bleed stream comprises not only the inert components but also considerable amounts of unreacted olefin and other components of value, which are thus lost to the reaction. To keep the bleed stream and the olefin losses associated therewith small, use is generally made of a synthesis gas of high purity. However, this pure synthesis gas is significantly more expensive than synthesis gases of lower purity. Synthesis gases of lower purity, i.e. those having a high content of inert components, cannot be used in industrial hydroformylation processes without special measures for the abovementioned reasons. To prevent the concentration of inert components in the hydroformylation reactor reaching unacceptable levels, the bleed stream would have to be so large that the accompanying loss of unreacted olefin would cancel out the savings made by using the cheaper feed stock.
JP 08092146-A describes a process for the hydroformylation of C
2
-C
6
-olefins. The waste gas obtained in the distillation to separate off the catalyst is compressed in order to liquefy the aldehyde present therein.
JP 08208552-A describes a hydroformylation process in which the waste gas streams obtained are subjected to scrubbing with the high-boiling by-products of the hydroformylation to recover the products of value present therein.
It is an object of the present invention to provide a process for the hydroformylation of lower olefins which allows the use of synthesis gas in which inert gas is present, without significant amounts of starting materials being lost via the bleed stream.
We have found that this object is achieved by a process for the hydroformylation of olefins having from 2 to 8 carbon atoms, in which
a) an olefin-containing feed and a gas mixture comprising hydrogen and carbon monoxide are fed into a reaction zone and reacted in the presence of a hydroformylation catalyst, homogeneously dissolved in the reaction medium,
b) the crude hydroformylation product is separated from the output stream from the reaction zone, a gaseous bleed stream is discharged and the remainder of the output stream is recirculated to the reaction zone, wherein
c) the bleed stream is brought into intimate contact with a scrubbing liquid to remove unreacted olefins present in the bleed stream, where the scrubbing liquid is degassed hydroformylation product, and the olefin-laden scrubbing liquid together with the crude hydroformylation product is passed to work-up.
The gaseous bleed stream can be taken off at any point on the circuit comprising hydroformylation reactor, separation of crude hydroformylation product and recirculation of the reactor output which has been freed of the hydroformylation product. The bleed stream can, for example, be taken from the gas phase of the reaction zone. Part of the recirculated reactor output which has been freed of hydroformylation product is branched off and discharged as bleed stream.
The size of the bleed stream is generally calculated so that, averaged over time, all gaseous inert components such as nitrogen, methane, argon, etc., introduced with the olefin-containing feed and the synthesis gas are removed from the system.
The bleed stream comprises, before it is brought into contact with the scrubbing liquid, variable amounts of unreacted olefin, hydroformylation product, saturated hydrocarbons (in particular the alkane corresponding to the olefin used) and gaseous inert components such as nitrogen, methane and argon, etc., depending on the point at which it is taken off.
The gaseous bleed stream is, before it is discharged from the process, brought into intimate contact with a scrubbing liquid to remove unreacted olefins and any other products of value, such as hydroformylation products or alkanes present in the bleed stream. According to the present invention, the scrubbing liquid used is degassed hydroformylation product, preferably the hydroformylation product which has been obtained in the work-up of the output from the reactor and has been largely freed of unreacted olefins, i.e. the alkanal and/or alkanol having one more carbon atom than the olefin reacted. For the present purposes, “degassed” means that the hydroformylation product can take up, i.e. dissolved, olefins under the pressure and temperature conditions under which it is brought into contact with the bleed stream. In other words, “degassed” is intended to mean that the alkanal and/or alkanol used as scrubbing liquid is not saturated with olefin. The scrubbing liquid laden with the olefins (and any other products of value) is then passed to the work-up section of the process of the present invention.
The scrubbing liquid can be brought into contact with the gaseous bleed stream in any apparatus suitable for scrubbing a gas by means of a liquid. The gas and liquid are advantageously brought into contact in a column in which the bleed stream is introduced into the bottom or the lower part of the column and the scrubbing liquid is introduced at the top or in the upper part of the column and is passed through the column in countercurrent to the bleed stream. To create a large surface area, the column is preferably provided with internals such as trickle trays or packing such as Raschig rings, spirals or saddles, or other internals. The gas and liquid are brought into contact according to the countercurrent principle, with the laden scrubbi
Krokoszinski Roland
McAtee Michael
Müller Rolf
Richter Wolfgang
BASF - Aktiengesellschaft
Keil & Weinkauf
Richter Johann
Witherspoon Sikarl A.
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