PROCESS

Abstract

A process for the hydroformylation of olefins to aldehydes is disclosed. The process comprises: hydroformylating one or more olefins with hydrogen and carbon monoxide in the presence of a ligand-rhodium catalyst in a reaction zone; recovering a reactor effluent from the reaction zone, the reactor effluent comprising product aldehyde and the ligand-rhodium catalyst; passing the reactor effluent and a strip gas to a vaporiser, wherein the strip gas comprises carbon monoxide and is formed from a recycle strip gas stream and a make-up strip gas stream, wherein the product aldehyde is vaporised into the strip gas in the vaporiser resulting in a vapour mixture, comprising the strip gas and the product aldehyde, and a liquid mixture, comprising the ligand-rhodium catalyst; recovering the liquid mixture and recycling the ligand-rhodium catalyst to the reaction zone; recovering the vapour mixture and separating the product aldehyde from the vapour mixture.

Claims

1-12. (canceled)

13. A process for the hydroformylation of olefins to aldehydes, the process comprising: a. Hydroformylating one or more olefins with hydrogen and carbon monoxide in the presence of a ligand-rhodium catalyst in a reaction zone; b. Recovering a reactor effluent from the reaction zone, the reactor effluent comprising product aldehyde and the ligand-rhodium catalyst; c. Passing the reactor effluent and a strip gas to a vaporiser, wherein the strip gas comprises carbon monoxide and is formed from a recycle strip gas stream and a make-up strip gas stream, wherein the product aldehyde is vaporised into the strip gas in the vaporiser resulting in a vapour mixture, comprising the strip gas and the product aldehyde, and a liquid mixture, comprising the ligand-rhodium catalyst; d. Recovering the liquid mixture and recycling the ligand-rhodium catalyst to the reaction zone; e. Recovering the vapour mixture and separating the product aldehyde from the vapour mixture to create a product aldehyde stream and the recycle strip gas stream for returning to step (c); f. Purging a portion of the recycle strip gas as a purged strip gas stream; and g. Combining the purged strip gas stream with a hydrogen-containing stream to create a re-formed syngas stream, comprising hydrogen and carbon monoxide, and feeding the re-formed syngas stream to the reaction zone in step (a).

14. The process according to claim 13, wherein the make-up strip gas stream is from 50-100 mol % carbon monoxide.

15. The process according to claim 13, wherein the reaction zone is fed with the re-formed syngas stream and a fresh syngas stream.

16. The process according to claim 13, wherein the process comprises separating a syngas stream into the hydrogen-containing stream and the make-up strip gas stream.

17. The process according to claim 16, wherein the separating of the syngas stream into the hydrogen-containing stream and the make-up strip gas stream is carried out using a membrane separation unit.

18. The process according to claim 17, wherein the concentration of carbon monoxide in the make-up strip gas stream is at least 95 mol %.

19. The process according to claim 16, wherein the molar ratio of hydrogen to carbon monoxide in the syngas stream is from 0.5 to 2.0.

20. The process according to claim 16, wherein the molar ratio of hydrogen to carbon monoxide in the re-formed syngas stream is similar to the molar ratio of hydrogen to carbon monoxide in the syngas stream.

21. The process according to claim 13, wherein the vaporiser is operated at a temperature of from 60 to 160° C.

22. The process according to claim 13, wherein the vaporiser is operated at a pressure of from 0.1 to 2000 kPa.

23. The process according to claim 13, wherein the molar ratio of hydrogen to carbon monoxide in the re-formed syngas stream is from 0.5 to 2.0.

24. The process according to claim 13, wherein the olefin is a C.sub.2 to C.sub.16 olefin and the aldehyde is a C.sub.3 to C.sub.17 aldehyde.

Description

DESCRIPTION OF THE DRAWINGS

[0037] Embodiments of the present invention will now be described, by way of example, and not in any limitative sense, with reference to the accompanying drawings, of which:

[0038] FIG. 1 is a block diagram of a flowsheet embodying the invention; and

[0039] FIG. 2 is a process flow diagram of part of the process of FIG. 1 embodying the invention.

DETAILED DESCRIPTION

[0040] In FIG. 1 an olefin feed 1 is fed to a hydroformylation reaction zone 100. The reaction zone 100 comprises at least one reactor, and possibly two or three reactors, from which a reactor effluent 11 is passed to a catalyst separation unit 101. Liquid ligand-rhodium catalyst solution 12, with the solvent typically comprising heavies such as dimers or trimers, is recycled from the catalyst separation unit 101 to the reaction zone 100. Product aldehyde stream 13 is recovered from the catalyst separation unit 101 and passed to an aldehyde purification unit 102, from which purified aldehyde 15 is recovered. Olefins and paraffins 14 are also recovered from the aldehyde purification unit 102.

[0041] Syngas feed 2 is split into fresh syngas stream 4, which is fed directly to the reaction zone 100 as part of mixed syngas feed stream 10, and syngas stream 3, which is fed to membrane separation unit 200. In membrane separation unit 200, the syngas stream 3 is separated into make-up strip gas stream 5, which is passed to the catalyst separation unit 101, and hydrogen-containing stream 6, which is combined with purged strip gas stream 7 to form re-formed syngas stream 8, which is compressed in compressor 201 and fed 9 to the reaction zone 100 as part of mixed syngas feed stream 10. A purge may be included, for example from one or more of streams 6, 7, 8 or 9, for operational reason, but is preferably avoided so as to avoid loss of reformed syngas.

[0042] More detail of catalyst separation unit 101 is shown in FIG. 2. In FIG. 2 reactor effluent 11 and optionally a small flow of nitrogen 20, to assist stripping of hydrogen, are fed to flash vessel 207. The flash vessel 207 has a vent 21 to a condenser 208. The condenser 208 has a vent 22 and a liquid outlet stream 23, which returns to the flash vessel 207. The flash vessel 207 and condenser 208 operate to remove dissolved syngas, and especially dissolved hydrogen, from the liquid reactor effluent 11. The liquid outlet 24 from the flash vessel 207 is fed to the top of a falling film vaporiser 202 along with a strip gas 28 comprising recycle strip gas 27 and carbon-monoxide rich stream 5. Make-up strip gas stream 5 is produced by feeding syngas stream 3 to a membrane separator 200 to produce make-up strip gas stream 5 and hydrogen-containing stream 6. The outlet 25 of the vaporiser 202 is fed to a vapour/liquid separation vessel 203, from which liquid ligand-rhodium catalyst solution 12 is recovered and recycled to reaction zone 100. The vapour mixture 26 from the vapour/liquid separation vessel 203 is fed to a condenser 204 and then to a further vapour/liquid separation vessel 205. Product aldehyde stream 13 is recovered from the bottom of the further vapour/liquid separation vessel 205 and recycle strip gas 27 is recovered from the top. Recycle strip gas 27 is compressed in recycle compressor 206 before being fed back to the falling film vaporiser 202 as part of the strip gas 28. A purged strip gas stream 7 is purged from the recycle gas stream 27 after the recycle compressor 206 and combined with hydrogen-containing stream 6 to form re-formed syngas stream 8. Re-formed syngas stream 8 is compressed in syngas compressor 201 and fed 9 to the reaction zone 100. FIG. 2 has been described with a falling film vaporiser 202, but other types of vaporiser are equally applicable.

[0043] The following examples have been generated using a commercially available simulation package SimSci ProII v9.3. The use of simulations to evaluate new processes is well-established in the chemical engineering art.

Example 1

[0044] In the process of FIG. 2, 333 kmol/hr of reactor effluent 11 at 20 bara (2 MPa) and 85° C. is fed to flash vessel 207 operating at 10 bara (1 MPa), where the majority of the dissolved syngas components will flash off. Reactor effluent 11 contains mainly dissolved syngas, C.sub.8 olefins, C.sub.8 paraffins, C.sub.9 aldehydes, and catalyst solution. A small 1 kmol/h flow of nitrogen 20 is also fed to flash vessel 207 to assist the removal of dissolved hydrogen. The vent 21 from the flash vessel 207 is fed to condenser 208 to recover the heavier C.sub.8 and C.sub.9 components. The liquid outlet stream 23 from the condenser 208 is returned to the flash vessel 207. The liquid outlet 24 from the flash vessel 207 is fed to the top of falling film vaporiser 202 operating at 1.5 bara (0.15 MPa). Also, strip gas 28 is fed to the top of the falling film vaporiser 202. The liquid reactor effluent and strip gas pass co-currently through the falling film vaporiser 202. The falling film vaporiser 202 is heated in order to evaporate a significant fraction of the C.sub.8 and C.sub.9 components. The outlet 25 of the falling film vaporiser 202 is fed to a vapour/liquid separation vessel 203. The liquid collected in vapour/liquid separation vessel 203 comprises the liquid ligand-rhodium catalyst solution 12 and a minor fraction of C.sub.8 and C.sub.9 components. The vapour mixture 26 from vapour/liquid separation vessel 203 is fed to condenser 204 where the majority of the C.sub.8 and C.sub.9 components are condensed and subsequently separated from the remaining vapour phase in further vapour/liquid separation vessel 205. The liquid thus obtained containing the C.sub.9 aldehydes, olefins and paraffins, is removed from further vapour/liquid separation vessel 205 and forwarded in product aldehyde stream 13 for further processing. The vent from further vapour/liquid separation vessel 205 is recycle strip gas 27, which is fed to recycle compressor 206. The recycle compressor 206 serves to overcome the small pressure drop in the strip gas cycle. A purged recycle gas stream 7 is taken from the recycle strip gas 27 in order to maintain a constant flow rate in the strip gas loop. A make-up flow provided by make-up strip gas stream 5 is added to create strip gas 28.

[0045] A syngas stream 3 with a flowrate of 100 kmol/h syngas at 30 bara (3 MPa), with 2 mol % methane and the remainder hydrogen and carbon monoxide in a 1/1 molar ratio, is fed to the membrane separator 200. The membrane separator 200 produces, as a permeate flow, hydrogen-containing stream 6 having a flowrate of 45.6 kmol/h and, as a retentate flow, make-up strip gas stream 5. Hydrogen-containing stream 6 contains 96.77 mol % hydrogen, whilst make-up strip gas stream 5 contains 87.3 mol % carbon monoxide. The strip gas recycle flow is controlled to a constant flow of 2050 kmol/h after taking the purge of purged strip gas stream 7 and before the introduction of the make-up strip gas stream 5 as make-up. With the condenser 204 cooling to 40° C., the resulting carbon monoxide partial pressure in the strip gas 28 is 17.5 psi (120 kPa) and the hydrogen partial pressure is 2.2 psi (15 kPa). The hydrogen to carbon monoxide ratio in the re-formed syngas 8 is 0.99 mol/mol.

Example 2

[0046] As per example 1 but the syngas stream 3 flowrate is reduced to 50 kmol/h. The resulting carbon monoxide partial pressure in the strip gas 28 is now 17.0 psi (117 kPa) and the hydrogen partial pressure is 2.5 psi (17 kPa). The hydrogen to carbon monoxide ratio in the re-formed syngas 8 is 0.97 mol/mol.

Example 3

[0047] As per example 1 but the syngas stream 3 flowrate is reduced to 20 kmol/h. The resulting carbon monoxide partial pressure in the strip gas 28 is now 16.1 psi (111 kPa) and the hydrogen partial pressure is 3.2 psi (22 kPa). The hydrogen to carbon monoxide ratio in the re-formed syngas 8 is 0.93 mol/mol.

[0048] The examples demonstrate that the process of the present invention can create a high partial pressure of carbon monoxide and a low partial pressure of hydrogen in the strip gas 28, whilst still supplying a re-formed syngas 8 with a hydrogen to carbon monoxide ratio similar to that in the syngas stream 3 fed to the membrane separator 200. The carbon monoxide in the syngas stream 3 is therefore effectively used twice in the process, firstly in the strip gas 28 and then in the re-formed syngas 8 fed to the hydroformylation reaction zone. The result is that the advantages of high carbon monoxide partial pressure in the strip gas 28 are realised, while not wasting any carbon monoxide in the syngas stream 3.

[0049] It will be appreciated by persons skilled in the art that the above embodiments have been described by way of example only, and not in any limitative sense, and that various alterations and modifications are possible without departure from the scope of the invention as defined by the appended claims.