REACTOR FOR CARRYING OUT A GAS-LIQUID TWO-PHASE HIGH-PRESSURE REACTION WITH A FOAMING MEDIUM

Abstract

A reactor for performing a gas/liquid biphasic high-pressure reaction with a foaming medium, comprising an interior formed by a cylindrical, vertically oriented elongate shell, a bottom and a cap, wherein the interior is divided by internals into a backmixed zone and a zone of limited backmixing, wherein the backmixed zone and the zone of limited backmixing are consecutively traversable by the reaction mixture, wherein the backmixed zone comprises means for introducing gas and liquid and a gas outlet and also comprises at least one mixing apparatus selected from a stirrer, a jet nozzle and means for injecting the gas, and the zone of limited backmixing comprises a reaction product outlet, a first cylindrical internal element which in the interior extends in the longitudinal direction of the reactor and which delimits the zone of limited backmixing from the backmixed zone, backmixing-preventing second internal elements in the form of random packings, structured packings or liquid-permeable trays arranged in the zone of limited backmixing and a riser tube whose lower end is arranged within the backmixed zone and whose upper end opens into the zone of limited backmixing so that liquid from the backmixed zone can ascend into the zone of limited backmixing via the riser tube, wherein flow into the zone of limited backmixing enters from below. The reactor is configured such that the high-pressure reaction space is optimally utilized and contamination of workup steps or subsequent reactions arranged downstream of the high-pressure reaction with foam is substantially avoided. The invention further relates to a process for performing a continuous gas/liquid biphasic high-pressure reaction in the reactor.

Claims

1. A reactor for performing a gas/liquid biphasic high-pressure reaction with a foaming medium, comprising: an interior formed by a cylindrical, vertically oriented elongate shell, a bottom and a cap, wherein the interior is divided by internals into a backmixed zone and a zone of limited backmixing, wherein the backmixed zone and the zone of limited backmixing are consecutively traversable by the reaction mixture, wherein the backmixed zone comprises means for introducing gas and liquid and a gas outlet and also comprises at least one mixing apparatus selected from a stirrer, a jet nozzle and means for injecting the gas, and the zone of limited backmixing comprises a reaction product outlet; a first cylindrical internal element which in the interior extends in the longitudinal direction of the reactor and which delimits the zone of limited backmixing from the backmixed zone; backmixing-preventing second internal elements in the form of random packings, structured packings or liquid-permeable trays arranged in the zone of limited backmixing; a riser tube whose lower end is arranged within the backmixed zone and whose upper end opens into the zone of limited backmixing so that liquid from the backmixed zone can ascend into the zone of limited backmixing via the riser tube; and an internal element which is arranged at the lower end of the riser tube and which prevents entry of gas into the riser tube, which internal element is selected from a deflection weir and a U-tube, wherein flow into the zone of limited backmixing enters from below.

2. The reactor according to claim 1, wherein the volume ratio of the backmixed zone to the zone of limited backmixing is in the range from 0.25:1 to 4:1.

3. The reactor according to claim 1, comprising at least one third internal element which is arranged in the upper half of the backmixed zone and has a surface which promotes the propensity to coalescence of foaming media.

4. The reactor according to claim 1, wherein the first internal element is arranged concentrically to the shell so that the zone of limited backmixing has a circular horizontal cross section.

5. A process for performing a continuous gas/liquid biphasic high-pressure reaction in which in a reactor according to claim 1 a gas and a liquid are introduced into the backmixed zone, said liquid is allowed to ascend from the backmixed zone into the zone of limited backmixing through the riser tube, unconverted gas is at least partially discharged via the gas outlet and a reaction product is withdrawn at the reaction product outlet.

6. The process according to claim 5 for preforming a homogeneous rhodium hydrogenation catalyst comprising at least one CO ligand, wherein the liquid comprises a dissolved CO-deficient rhodium hydrogenation catalyst and wherein the gas comprises hydrogen and carbon monoxide, wherein the reaction of the CO-deficient rhodium hydrogenation catalyst with the gas affords a hydrogenation-active rhodium hydrogenation catalyst.

7. The process according to claim 6, wherein the CO-deficient rhodium hydrogenation catalyst comprises at least one chiral ligand.

8. The process according to claim 6, wherein the liquid comprises a compound of formula (IV) ##STR00008## wherein Z in formula (IV) represents a CHR.sup.3R.sup.4 group and wherein the variables R.sup.1, R.sup.2, R.sup.3, R.sup.4 independently of one another and especially jointly are as follows: R.sup.1, R.sup.2: are identical or different and represent phenyl which is unsubstituted or bears 1, 2 or 3 substituents selected from methyl and methoxy; R.sup.3 represents C.sub.1- to C.sub.4-alkyl, especially methyl; R.sup.4 represents C.sub.1- to C.sub.4-alkyl bearing a P(═O)R.sup.4aR.sup.4b group; wherein R.sup.4a, R.sup.4b: are identical or different and represent phenyl which is unsubstituted or bears 1, 2 or 3 substituents selected from methyl and methoxy.

9. The process according to claim 6, wherein the reaction product of the preforming is supplied to an asymmetric hydrogenation reaction together with a substrate to be hydrogenated to afford a hydrogenation reaction mixture and a hydrogenation product is separated from the hydrogenation reaction mixture to afford a residue comprising CO-deficient rhodium hydrogenation catalyst which is supplied to the preforming.

10. A process for producing optically active menthol in which optically active citronellal of formula (VI) ##STR00009## wherein * denotes the asymmetric center; is produced by the process according to claim 9, wherein the hydrogenation reaction comprises the asymmetric hydrogenation of geranial of formula (Va-1) or of neral of formula (Vb-1) ##STR00010## or a mixture comprising neral and geranial, the optically active citronellal of formula (VI) is subjected to a cyclization to afford optically active isopulegol and the optically active isopulegol is hydrogenated to afford optically active menthol.

11. The process of claim 6, wherein the chiral ligand is chiraphos.

12. The process of claim 8, wherein R.sup.1 and R.sup.2 each represent unsubstituted phenyl.

13. The process of claim 8, wherein R.sup.4 represents a CH.sub.2—P(═O)R.sup.4aR.sup.4b or CH(CH.sub.3)—P(═O)R.sup.4aR.sup.4b group.

14. The process of claim 8, wherein R.sup.4a and R.sup.4b each represent unsubstituted phenyl.

Description

[0095] The invention is elucidated in more detail by the accompanying FIGURE.

[0096] FIG. 1

[0097] FIG. 1 is a schematic diagram of a reactor according to the invention.

[0098] The reactor comprises a backmixed zone 101 and a zone of limited backmixing 102 whose backmixing is limited by internal trays. An injection nozzle (not shown) is used to supply a gas and a liquid from the conduit 103 to the backmixed zone 101.

[0099] The backmixed zone 101 has a gas outlet 104 through which unconverted gas is discharged. Liquid ascends from the backmixed zone 101 into the zone of limited backmixing 102 via the riser tube 105 whose lower end is arranged below the liquid level. Reaction product is discharged via the reaction product outlet 106.

[0100] The backmixed zone is in the form of a loop reactor having an external circuit 107. Arranged in the lower region of the backmixed zone is a takeoff through which the reaction mixture is returned into conduit 103 and thus to the backmixed zone 101 via the external circuit 107 using a pump (not shown).

[0101] The reactor comprises a deflection weir 108 which substantially prevents entry of gas into the riser tube 105.

[0102] The backmixed zone 101 may comprise a stirrer 109 instead of the external circuit 107.