Abstract
A process for separating heavy by-products and catalyst ligand from a vapour stream comprising aldehyde, the heavy by-products and the catalyst ligand the process comprises passing the vapour stream to a fractionator in which the vapour stream is contacted with liquid aldehyde which removes at least a portion of the catalyst ligand and at least a portion of the heavy by-products from the vapour stream, recovering a liquid bottom stream, comprising removed catalyst ligand from the fractionator; recovering a scrubbed vapour stream from the fractionator, condensing a first portion of the scrubbed vapour stream to create the liquid aldehyde, and recovering a second portion of the scrubbed vapour stream as a product aldehyde stream. The liquid bottom stream is passed to a separation system to separate some aldehyde from the liquid bottom stream to create a recovered aldehyde stream, comprising the separated aldehyde.
Claims
1-20. (canceled)
21. A process for separating heavy by-products and catalyst ligand from a vapour stream comprising aldehyde, the heavy by-products and the catalyst ligand, the process comprising: passing the vapour stream to a fractionator in which the vapour stream is contacted with liquid aldehyde which removes at least a portion of the catalyst ligand and at least a portion of the heavy by-products from the vapour stream; recovering a liquid bottom stream, comprising removed catalyst ligand, removed heavy by-products and some of the aldehyde, from the fractionator; recovering a scrubbed vapour stream from the fractionator; condensing a first portion of the scrubbed vapour stream to create the liquid aldehyde, for reflux back to the fractionator; and recovering a second portion of the scrubbed vapour stream as a product aldehyde stream, wherein the liquid bottom stream is passed to a separation system to separate at least some aldehyde from the liquid bottom stream to create a recovered aldehyde stream, comprising the separated aldehyde, and a waste stream comprising the removed catalyst ligand and the removed heavy by-products.
22. The process according to claim 21 wherein the temperature at the bottom of the fractionator is not more than 140 C.
23. The process according to claim 21, wherein the separation system comprises a distillation column.
24. The process according to claim 23 wherein the temperature at the bottom of the distillation column is greater than the temperature at the bottom of the fractionator.
25. The process according to claim 23, wherein the pressure in the distillation column is lower than the pressure in the fractionator.
26. The process according to claim 23, wherein the distillation column is operated such that the temperature at the bottom of the distillation column is not more than 140 C.
27. The process according to claim 21, wherein the fractionator includes a reboiler.
28. The process according to claim 27, wherein the reboiler is operated such that the temperature at the bottom of the fractionator is at least 90 C.
29. The process according to claim 21, wherein the liquid bottom stream comprises at least 50 wt % aldehyde.
30. The process according to claim 21, wherein the recovered aldehyde stream is recycled to a point in the process upstream of the fractionator.
31. The process according to claim 21, wherein the catalyst ligand comprises an organophosphorus ligand.
32. The process according to claim 21, wherein the catalyst ligand comprises triphenylphosphine.
33. The process according to claim 21, wherein the catalyst ligand has a vapour pressure of at least 0.01 mbar at 160 C.
34. The process according to claim 21, wherein the aldehyde is a C.sub.3 to C.sub.6 aldehyde.
35. The process according to claim 21, wherein the process further comprises forming the vapour stream by passing a liquid output stream from a hydroformylation process, the liquid output stream comprising the aldehyde, catalyst, the catalyst ligand and the heavy by-products, to a separator and recovering the vapour stream from the separator.
36. The process according to claim 35, wherein the hydroformylation process comprises feeding catalyst, the catalyst ligand, olefins and carbon monoxide to one or more hydroformylation reactors; reacting the olefins with the carbon monoxide to form the aldehyde and the heavy by-products; and recovering the liquid output stream comprising the aldehyde, the catalyst, the catalyst ligand and the heavy by-products.
37. The process according to claim 21, wherein the process further comprises passing the aldehyde in the aldehyde product stream to one or more reactors for: hydrogenation of the aldehyde to produce an aliphatic alcohol; amination of the aldehyde to produce an aliphatic amine; oxidation of the aldehyde to produce an aliphatic acid; aldol condensation of the aldehyde to produce an acrolein; or aldol condensation of the aldehyde to produce an acrolein followed by hydrogenation of the acrolein to an aliphatic alcohol.
38. The process according to claim 37, wherein the process comprises passing the aldehyde in the aldehyde product stream to one or more reactors for: liquid phase hydrogenation of the aldehyde to produce an aliphatic alcohol; or aldol condensation of the aldehyde to produce an acrolein followed by liquid phase hydrogenation of the acrolein to an aliphatic alcohol.
39. The process according to claim 37, wherein the process comprises purifying the aliphatic alcohol, aliphatic amine, aliphatic acid, or acrolein.
40. An aliphatic alcohol, aliphatic amine, aliphatic acid, or an acrolein obtained by a process according to claim 37.
Description
DESCRIPTION OF THE DRAWINGS
[0053] 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:
[0054] FIG. 1 shows a comparative process;
[0055] FIG. 2 shows a comparative process;
[0056] FIG. 3 shows a comparative process;
[0057] FIG. 4 shows a comparative process;
[0058] FIG. 5 is a process according to the invention;
[0059] FIG. 6 is another process according to the invention;
[0060] FIG. 7 is another process according to the invention; and
[0061] FIG. 8 is another process according to the invention.
[0062] A comparative process is one for the purposes of comparing with the invention and may not be a prior art process.
DETAILED DESCRIPTION
[0063] The following process examples were simulated using Aveva Simsci ProII. The skilled person will appreciate that the use of simulation packages is a well-established method for evaluating processes in the chemical field.
[0064] FIG. 1 shows a reference process which includes vaporiser 50, which comprises a heat exchanger 50a and a knock-out drum 50b, and condenser 52 but no fractionator. In this process, a Rh/TPP catalysed propylene hydroformylation using a liquid catalyst recycle scheme produces a flow containing 2.5 wt % propylene and propane, 70 wt % butyraldehyde, 15 wt % heavy by-products, 11.9 wt % TPP, with a balance of incondensable gases, catalyst and butanol. This feed 1 is fed to vaporiser 50 operating at 1.2 bara and 130 C., where approximately 70 wt % of the feed is vaporised, producing vapour stream 2 containing 3.5 wt % propylene and propane, 93.7 wt % butyraldehyde, 2.4 wt % heavy by-products, along with incondensable gases, butanol and about 1300 ppmw of TPP. Vapour stream 2 is fed to condenser 52 operating at 40 C., producing a liquid/vapour condenser outlet stream 4 which is passed to a knock-out drum 53, producing liquid aldehyde product stream 7 which contains approximately 1315 ppmw of TPP. Uncondensed vapours are vented in vent stream 5. A liquid stream 9 recycles the catalyst and TPP ligand to the hydroformylation.
[0065] FIG. 2 shows a process as in FIG. 1 but further including fractionator 51. In FIG. 2, feed 1 (with the composition as described above) is fed to vaporiser 50, comprising heat exchanger 50a and knock-out drum 50b, producing vapour stream 2. Vapour stream 2 is fed to fractionator 51 which has four theoretical stages. The fractionator 51 operates at a pressure of 1.1 bara and has a bottom temperature of 78 C. Fractionator 51 receives a reflux of condensed overheads (reflux stream 6) to provide a reflux ratio of 0.3. Fractionator vapour stream 3 is fed to condenser 52 operating at 40 C., producing a liquid/vapour condenser outlet stream 4 which is passed to a knock-out drum 53. Uncondensed vapours are vented in vent stream 5 and remaining liquid is split into reflux stream 6 and liquid aldehyde product stream 7, which contains less than 1 ppb of TPP. In practice, this level of TPP is below detection limits. Fractionator liquid bottom stream 18 contains approximately 75 wt % butyraldehyde and is recycled to the knock-out drum 50b of the vaporiser 50. Substantially all the heavy by-products vaporised in vaporiser 50 will return via liquid bottom stream 18 and knock-out drum 50b to liquid stream 9 and return to the catalyst recycle. This will lead to further accumulation of heavy by-products in the catalyst solution, and hence further elevation of the temperature of vaporiser 50 will be required until the heavy by-products removal equals the heavy by-products formation. In this scenario, the heavy by-products cannot escape and may continue to accumulate until a purge is taken from the catalyst solution, for example from liquid stream 9. However, taking such a purge is undesirable because it can lead to loss of rhodium, which is expensive to replace.
[0066] An alternative may therefore be as shown in FIG. 3. In that figure, where like numbered items are as in FIGS. 1 and 2 and not described again here, the liquid bottom stream 8, is sent to waste. In that way, heavy by-products do not accumulate. However, the entire liquid bottom stream 8, which as in FIG. 2 comprises approximately 75 wt % butyraldehyde, is sent to waste. The amount of butyraldehyde wasted may be quite substantial as the reflux ratio in fractionator 51 needs to be sufficiently large to keep the TPP level in aldehyde product stream 7 sufficiently low.
[0067] In FIG. 4, where like numbered items are as in FIGS. 1 to 3 and not described again here, the fractionator 51 includes a reboiler 54. The reboiler 54 concentrates the liquid bottom stream 38 by re-vaporising aldehyde and returning it to the fractionator 51. Fractionator 51 is operated at the same reflux ratio as described for FIGS. 2 and 3, and liquid aldehyde product stream 7 comprises less than 1 ppb TPP. Reboiler 54 is controlled to provide an aldehyde concentration of 5 wt % in liquid bottom stream 38, to minimize losses of aldehyde. Liquid bottom stream 38 is not recycled but purged as waste liquid. Reboiler 54 is operated at a temperature of 163 C. At such high reboiler temperature and low aldehyde concentration, the reboiler may be difficult to control, as the boiling point of the liquid will vary significantly with only small changes in the aldehyde concentration. This may result in unstable reboiler operation. Additionally, such high temperatures are likely to result in additional heavy by-product formation, resulting in loss of aldehyde, and possibly cracking of heavy by-products. Such cracking is undesirable as it can create light by-products, which are likely to contaminate the aldehyde product stream 7.
[0068] In FIG. 5, a process according to the invention includes a separation system 155 after the fractionator 151. Feed stream 101 having the same source and composition as feed stream 1 above is fed to a vaporiser 150, comprising heat exchanger 150a and knock-out drum 150b, to create vapour stream 102, which is passed to fractionator 151 as described above in relation to feed stream 1, vaporiser 50, vapour stream 2 and fractionator 51 of the previous figures. Fractionator 151 is operated at a reflux ratio of 0.3 and with a bottom temperature of 78 C. In a similar way to FIGS. 2 to 4, a scrubbed vapour stream 103 is recovered from the top of fractionator 151 and passed to condenser 152. Condenser 152 condenses most of the scrubbed vapour stream 103, including essentially all of the aldehyde in the scrubbed vapour stream 103, to produce a liquid/vapour condenser outlet stream 104, which is passed to a knock-out drum 153, from which uncondensed vapours are vented in a vent stream 105. The remaining liquid is split into a reflux stream 106 and a liquid aldehyde product stream 107. Liquid aldehyde stream 107 includes less than 1 ppb TPP. The liquid bottom stream 108 comprises 75 wt % butyraldehyde. The liquid bottom stream 108 is passed to a separation system, which in this embodiment comprises a further fractionator in the form of distillation column 155 operating at 0.5 bara, a reflux ratio of 0.1 and a temperature of 124 C. in the bottom of the distillation column 155. The distillation column 155 comprises a reboiler 156 and a condenser 158 and knock-out drum 157. A waste stream 188 is recovered from the bottom of the distillation column 155. The waste stream includes 5 wt % butyraldehyde. The waste stream 188 is sent to waste. From the top of the distillation column 155 a recovered aldehyde stream 118 is recovered, comprising butyraldehyde and possibly trace amounts of TPP and heavy by-products. In this embodiment the recovered aldehyde stream 118 is recycled to the knock-out drum 150b of the vaporiser 150. The recovered aldehyde stream 118 could also be recycled elsewhere in the process. In some embodiments the recovered aldehyde stream 118 may be combined with the product aldehyde stream 107.
[0069] The level of butyraldehyde in the waste stream 118 in this embodiment is the same as in the embodiment described above in relation to FIG. 4. However, it is achieved with a bottom temperature of 78 C. in fractionator 151 and a bottom temperature of 124 C. in distillation column 155, compared with a temperature of 163 C. in the reboiler 54 of fractionator 51 in FIG. 4. The lower temperatures may be advantageous, for example by reducing heat duties, and hence operating cost, by reducing aldehyde loss due to heavy by-product formation and/or by reducing contamination from cracking products. The process also has the advantage that the distillation column 155 is physically separated from the fractionator 151 and therefore can operate independently from the fractionator 151, unlike the reboiler 54 of FIG. 4. By feeding the liquid bottom stream 108 from the fractionator 151 into the distillation column 155, the distillation column 155 can operate almost independently from the fractionator 151, and hence any difficulty operating reboiler 156 on the distillation column 155 will not affect the operation of the fractionator 151. This may allow separation of difficult equipment from the main operation train and thereby facilitates ease of operation of the main train.
[0070] Results of the above examples are collected in the table below.
TABLE-US-00001 Units FIG. 1 FIG. 2 FIG. 4 FIG. 5 TPP in aldehyde ppmw 1,315 <1 ppb <1 ppb <1 ppb product stream Heavy by-products in in ppmw 24,600 <1 ppb <1 ppb <1 ppb aldehyde product stream Reboiler duty for MW 0.57 fractionator Reboiler duty for MW 0.42 distillation column Fractionator bottom/ C. 163 78 reboiler temperature Distillation column C. 124 reboiler temperature
[0071] It is clear that the process described with respect to FIG. 5 is able to achieve an excellent aldehyde product stream 107 specification with reduced risk of aldehyde loss due to heavy by-product formation, reduced risk of contamination and increased operability, while requiring a lower duty versus the other processes.
[0072] In FIG. 6, where like numbered items are as in previous figures and not described again here, the process is similar to that of FIG. 5, but this time including a reboiler 154 on the fractionator 151. The resulting liquid bottom stream 138 may thus have reduced aldehyde content compared to stream 108 in FIG. 5. Advantageously, the presence of reboiler 154 on fractionator 151 and reboiler 156 on distillation column 155 results in greater flexibility of operation. It may for example allow an optimised balance to be struck between keeping the bottom temperature of the fractionator 151 low enough to prevent heavy by-product formation and cracking reactions, but high enough to somewhat reduce aldehyde content in the liquid bottom stream 138. Although the distillation column 155 will recover aldehyde from the liquid bottom stream 138, the recovered aldehyde stream 118 is typically recycled to the knock-out drum 150b of the vaporiser 150, from where it is recycled to the hydroformylation reactor. That recycle prevents aldehyde loss, and so the advantage of the invention in preventing aldehyde loss in purges whilst also using temperatures that mitigates aldehyde loss to heavy by-product formation and contamination by cracking products is achieved, but recycling large amounts of aldehyde through an upstream hydroformylation reactor may undesirably dilute the reactants in the hydroformylation reactor. Having the reboiler 154 on fractionator 151 and the reboiler 156 on distillation column 155 may advantageously allow optimal mitigating of heavy by-product formation and contamination by cracking whilst avoiding excessive dilution by recycled aldehyde.
[0073] In FIG. 7, where like numbered items are as in previous figures and not described again here, the scrubbed vapour stream 103 is passed to a partial condenser 162. The partial condenser 162 condenses some of the aldehyde, which is returned to the fractionator 151 as reflux stream 166. The vapour outlet stream 163 from the partial condenser 162 is passed to a further condenser 152, where essentially all of the remaining aldehyde is condensed. The outlet 104 from the further condenser 152 is passed to knock-out drum 153, where it is separated into a vapour vent stream 105 and a liquid product aldehyde stream 107. Such an arrangement may be particularly attractive as a retrofit, as the plant will have an existing condenser to condense the vapour from the vaporiser 150, which can be used as the further condenser 152 without significant modification. The fractionator 151 and partial condenser 162 are then installed between the existing vaporiser 150 and further condenser 152. The partial condenser 162 depicted in FIG. 7 could equally be used in other embodiments of the invention, for example those described in relation to FIG. 5, 6 or 8.
[0074] In FIG. 8, like numbered items are as in the process of previous figures and their description is not repeated. A stream 201 comprising propylene, carbon monoxide, rhodium and TPP is fed to a hydroformylation reactor 250. In the hydroformylation reactor 250, the propylene reacts with the carbon monoxide to form butyraldehyde, which exits the hydroformylation reactor 250 in liquid output stream 101, which is the feed stream to vaporiser 150, comprising heat exchanger 150a and knock-out drum 150b. From vaporiser 150 the vapour stream 102 and the liquid stream 109 are recovered. The liquid stream 109, comprising rhodium and TPP, is recycled to the hydroformylation reactor 250. The vapour stream 102 is processed in the fractionator 151 as described in relation to previous figures. The liquid product aldehyde stream 107 is sent to a hydrogenation reactor 251, along with a hydrogen-containing stream 202. In the hydrogenation reactor 251, the butyraldehyde from the liquid product aldehyde stream 107 reacts with hydrogen from the hydrogen stream 202 to form butanol, which is recovered in butanol product stream 207. The butanol product stream 207 may then be subject to purification steps, typically distillation, to recover a butanol product of a desired level of purity.
[0075] 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. For example, the olefin may be butylene and the aldehyde may be valeraldehyde. As another example, the hydrogenation reactor 251 may be replaced with an amination reactor to produce an aliphatic amine, an oxidation reactor to produce an aliphatic acid, or an aldol condensation reaction to produce an acrolein, which may then be fed to a hydrogenation reactor to make an alcohol, with the hydrogen stream 202 being replaced with other reactant streams as will be apparent to the skilled person. While the vaporiser 150 comprises heat exchanger 150a and knock-out drum 150b, other designs of vaporiser could for example be used to create vapour stream 102.
