PROCESS FOR HYDROFORMYLATION WITH REMOVAL OF DISSOLVED HYDROGEN

Abstract

A process for producing an aldehyde is disclosed. The process comprises: hydroformylating an olefin to form the aldehyde using a hydroformylation catalyst; recovering an effluent stream comprising the aldehyde, hydrogen and the hydroformylation catalyst; passing the effluent stream to a stripper; contacting the effluent stream with a strip gas in the stripper to produce a stripped effluent stream having a lower hydrogen concentration than the effluent stream; and recovering the stripped effluent stream.

Claims

1. A process for producing an aldehyde, the process comprising: hydroformylating an olefin to form the aldehyde using a hydroformylation catalyst; recovering an effluent stream comprising the aldehyde, hydrogen and the hydroformylation catalyst; passing the effluent stream to a stripper; contacting the effluent stream with a strip gas in the stripper to produce a stripped effluent stream having a lower hydrogen concentration than the effluent stream; and recovering the stripped effluent stream.

2. A process according to claim 1, wherein the strip gas comprises carbon monoxide.

3. A process according to claim 2, wherein the process comprises: feeding a syngas stream to a separation system; separating the syngas stream into a hydrogen rich stream and a carbon monoxide rich stream in the separation system; and using the carbon monoxide rich stream as the strip gas.

4. A process according to claim 3, wherein the separation system comprises a membrane or a cryogenic distillation unit.

5. A process according to claim 3, wherein the process comprises: recovering a used strip gas stream, comprising the strip gas and hydrogen, from the stripper; combining the used strip gas stream with the hydrogen rich stream to form a recombined syngas stream; and feeding the recombined syngas stream to the hydroformylation section.

6. A process according to claim 3, wherein the process comprises splitting the syngas stream fed to the separation system from a syngas feed stream to the hydroformylation section.

7. A process according to claim 6, wherein the recombined syngas stream is fed to the hydroformylation section by mixing the recombined syngas stream with the syngas feed stream.

8. A process according to claim 1 wherein the hydroformylation catalyst comprises a homogenous metal-ligand catalyst.

9. A process according to claim 8, wherein the homogeneous metal-ligand catalyst comprises rhodium.

10. A process according to claim 8, wherein the metal-ligand catalyst comprises an organophosphite or organophosphine ligand.

11. A process according to claim 10, wherein the organophosphite or organophosphine ligand comprises Normax or triphenylphosphine.

12. A process according to claim 1, wherein the process comprises feeding the stripped effluent stream to a vaporiser and recovering from the vaporiser a vapour stream comprising: (1) the aldehyde, and (2) a liquid catalyst recycle stream comprising the hydroformylation catalyst for recycle to the hydroformylation section.

13. A process according to claim 12, wherein the molar composition of hydrogen in the stripped effluent stream is not more than 5 mol %.

14. A process according to claim 12, wherein the process comprises feeding a gas comprising carbon monoxide to the vaporiser.

Description

DESCRIPTION OF THE DRAWINGS

[0039] 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:

[0040] FIG. 1 is a block diagram of a flowsheet embodying the invention; and

[0041] FIG. 2 is a process flow diagram of part of the process of FIG. 1 embodying the invention.

DETAILED DESCRIPTION

[0042] 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.

[0043] 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.

[0044] More detail of catalyst separation unit 101 is shown in FIG. 2. In FIG. 2, 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 strip gas stream 5, which is passed to stripper 202, and hydrogen-containing stream 6, which is combined and compressed 201 with purged strip gas stream 7 to form re-formed syngas stream 9, which is fed to the reaction zone 100 as part of mixed syngas feed stream 10. Reactor effluent 11 is fed to stripper 202, which operates to produce a stripped effluent stream 12 having a lower hydrogen concentration than effluent stream 11, and which is passed to a catalyst separation unit.

Example 1

[0045] The following examples have been generated using a commercially available simulation package SimSci ProII v10.1. The use of simulations to evaluate new processes is well-established in the chemical engineering art.

[0046] Reactor effluent at 90 C. containing 0.8 mol % dissolved hydrogen is fed to a stripping column operating at 13.5 barg at the top of the column.

[0047] 3.6 mol % of the plant syngas feed at 25 barg is fed to a membrane separation unit, where a CO-rich stream is generated. The CO-rich stream contains 96.4 mol % CO and 0.8 mol % hydrogen. The CO-rich stream with a flow of 1.36 Nm.sup.3/tonne of aldehyde reactor product is fed to the bottom of the stripping column, which contains seven theoretical stages. It is contacted with the reactor effluent inside the column and a stripped effluent stream containing 0.08 mol % hydrogen in predominantly C.sub.8 and C.sub.9 oxygenates is produced at the bottom of the stripping column.

[0048] The stripped effluent stream leaving the stripping column is then fed to the catalyst separation unit operating at 12 barg, where the product oxygenates are contacted with 3,240 Nm.sup.3/tonne of aldehyde reactor product of cycle gas at 140 C. to vaporise most of the reactor product leaving the catalyst solution to be recycled back to the reactors. The concentration of hydrogen in the cycle gas is 1.56 mol %.

[0049] The purged strip gas stream leaving the top of the stripping column is cooled to 45 C. to remove condensable hydrocarbons and return them to the stripper column. The cooled purged strip gas is then combined with the hydrogen-rich gas from the membrane separation unit, recompressed to 25 barg to be returned to the reactors.

[0050] For the purposes of comparison and to illustrate the benefits of the invention, an arrangement from prior art was also simulated using the same commercially available simulation package SimSci ProII v10.1.

[0051] Reactor effluent of the same composition as described above, also at 90 C. and also containing 0.8 mol % dissolved hydrogen is fed directly to the catalyst separation unit operating at 12 barg, where the product oxygenates are contacted with 3,240 Nm.sup.3/tonne of aldehyde reactor product of cycle gas at 140 C. to vaporise most of the reactor product leaving the catalyst solution to be recycled back to the reactors.

[0052] A CO-rich make-up stream is generated by sending all of the plant feed syngas to a membrane separation unit. The CO-rich make-up stream of 37.14 Nm.sup.3/tonne of aldehyde reactor product is produced and added to the cycle gas. A purge of 38.79 Nm.sup.3/tonne of aldehyde reactor product is removed from the cycle gas to purge hydrogen and inert components. The cycle gas contains 1.94 mol % of hydrogen.

[0053] The example demonstrates that the process of the present invention achieves a low hydrogen concentration in cycle gas using a much lower flow of CO-rich gas than required in the arrangement disclosed in prior art, thereby reducing energy consumption and equipment size.

Example 2

[0054] General procedure: All tests were conducted in a multiwell heating block fitted with six 100 mL autoclaves, with several tests run in duplicate for increased accuracy. The temperature was controlled using an internal thermocouple and double checked against one autoclave with an internal thermocouple to measure the process temperature as a cross check. Phosphorous ligand (in a molar excess) and rhodium stock solution (prepared by dissolving Rh(acac) (CO).sub.2 in toluene; 50 mL of solution charged) were transferred into a 100 ml autoclave before sealing and purging with syn gas (CO:H.sub.2 molar ratio=1:1; 3100 psi(g)). All autoclaves were then pressurised with syn gas and left to form the active catalyst in situ, then left to cool to ambient temperature. Once cool, a sample (1.5 ml) from the autoclave was taken for rhodium analysis via ICP-OES analysis. The autoclave was then purged with the appropriate test gas (syn gas, CO, H.sub.2 or N.sub.2), and then pressurised to the test pressure with the test gas (as outlined in Table 1, below). The reactions were then run for their allotted time period, before removing the autoclaves from the heating block and allowing to cool to room temperature. On the completion of the test, a further sample was removed from the autoclave to analyse for rhodium concentration via ICP-OES to look for soluble rhodium loss during the course of the experiment. The percentage loss of rhodium was then calculated=((1[Rh].sub.Final)/[Rh].sub.Initial)100.

[0055] The loss of rhodium with time have been inputted into Table 1, below, showing dependency on the different gas compositions are varying pressures. Entries 1 and 2 show high losses of rhodium under a syn gas atmosphere at 120 C., with a minor improvement at the higher pressure (90%). Under nitrogen at identical conditions (Entry 3) shows a significant improvement to the rhodium loss with only 5% loss of rhodium. In a CO only atmosphere (Entry 4), no rhodium loss was evident. This clearly shows the benefit of operating in the absence of hydrogen, but also the increased stabilising effect of CO versus nitrogen.

[0056] When operating at higher temperatures (130 C., Entries 5-8), higher pressures were investigated in an attempt to increase stability of the rhodium catalyst. Using a 1:1 syn gas composition (Entry 5), losses were 93%. Operation at higher pressures with high H.sub.2:CO ratios (entry 6) reduced the losses to 69%. Complete loss of rhodium was observed in a hydrogen only atmosphere (Entry 7). However, even under these forcing conditions, the rhodium loss under a pure CO atmosphere was only 12% (Entry 8). Although losses were reduced when using a high H.sub.2:CO atmosphere (Entry 6), it is assumed that the high partial pressure of CO has a stabilising effect on the catalyst solution. However, the results from both sets of experiment show a clear benefit to loss of rhodium from the catalyst solution when using a CO only atmosphere.

TABLE-US-00001 TABLE 1 Rx Tem- % Time perature CO pp H.sub.2 pp N.sub.2 pp Rh Entry (hours) ( C.) (psi(g)) (psi(g)) (psi(g)) loss 1 64 120 2 2 92.78 2 64 120 4 4 89.53 3 64 120 8 5.38 4 64 120 8 0.00 5 120 130 50 50 91.76 6 120 130 112 224 68.86 7 120 130 100 99.16 8 120 130 100 12.22

[0057] 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.