Hydroformylation process for removing dissolved hydrogen

Abstract

The present invention discloses a method for producing aldehydes. The method comprises: hydroformylating olefins to form aldehydes using a hydroformylation catalyst; recovering an effluent stream comprising the aldehyde, hydrogen and the hydroformylation catalyst; conveying the effluent stream to a stripping column; contacting the effluent stream with a stripping gas in the stripping column to produce a stripped effluent stream having a lower hydrogen concentration than the effluent stream; and recovering the stripped effluent stream.

Description

Technical Field

[0001] The present invention relates to a process for hydroformylating olefins to produce aldehydes. In particular, but not exclusively, the present invention relates to a process for hydroformylating a mixture of C8 olefin isomers to produce C9 aldehydes. The present invention also relates to a process for hydroformylating olefins to produce aldehydes, the process comprising removing dissolved hydrogen from the reactor product prior to entering a separation unit. Background Art

[0002] Hydroformylation of olefins is carried out industrially on a large scale to produce aldehydes. Aldehydes are generally intermediate products in the production of alcohols, acids or esters. The known method for producing such products is the low pressure oxo synthesis (LP Oxo) method provided by Dow and Johnson Matthey Davy Technologies. In a typical flow, for example, as described in US4148830 or US5087763, hydroformylation is carried out in the liquid phase using a ligand-rhodium catalyst. The liquid phase reactor effluent leaves the hydroformylation reactor and is fed to a catalyst separation unit, where a liquid catalyst solution is separated from the product aldehyde. The liquid catalyst solution is then returned to the reactor. The liquid catalyst solution generally comprises a solvent, rhodium, a ligand and other components present in the reactor.

[0003] Many variants of molecules that can be used as ligands are known. Ligands used commercially are typically phosphines, such as triphenylphosphine; monophosphites, such as trimethylolpropanephosphite or tris(2,4-di-tert-butylphenyl)phosphite; bisphosphites; or mixtures of any of these. WO2016089602 lists various ligands. Of these 3 types of ligands, monophosphites are considered the most active, but are also considered the ligands that interact the least with rhodium, which is thought to result in less stable catalyst complexes.

[0004] Typical catalyst separation units include a gasifier in which a portion of the reactor effluent is gasified. This results in a gas phase containing the aldehyde product and substantially free of catalyst and a liquid phase containing a liquid catalyst solution. The gas phase is transferred for further processing. Further processing typically includes an aldehyde purification stage in which unconverted olefins and paraffins are removed along with dissolved synthesis gas and other light components. The resulting aldehyde is typically used as an intermediate for other products such as alcohols, acids or esters, which can be typically used as plasticizers.

[0005] The gasification of aldehydes in the reactor effluent in the catalyst separation unit is assisted by lower pressures and higher temperatures in the gasifier. However, liquid catalyst solutions are generally sensitive to various forms of degradation, resulting in loss of activity and rhodium loss. Rhodium is a valuable precious metal, so it is desirable that the consumption of rhodium is as low as possible in order to maintain an economic process. This generally determines the maximum allowable temperature in the gasifier. Evaporation can still be increased by operating the gasifier at low pressure. Lower total pressure means that the partial pressure of aldehydes is lower, which increases the evaporation of aldehydes and is particularly useful for relatively heavy aldehydes. However, lower total pressures (especially vacuum) result in larger equipment volumes and therefore more expensive equipment. At pressures below atmospheric pressure, there is also a risk of air entering the interior of the process. This may result in oxidation of aldehydes and / or ligands, both of which result in increased costs.

[0006] It is therefore desirable to stabilize the catalyst to prevent loss and to allow the use of higher temperatures and pressures above atmospheric pressure.

[0007] US6500991 aims to stabilize the catalyst by cooling the catalyst solution obtained from the gasifier and adding a carbon monoxide containing gas to the liquid, or by adding carbon monoxide to a flash vessel before catalyst separation.

[0008] EP2297077 describes the use of circulating stripping gas to reduce the partial pressure of aldehyde, but maintains an overall positive pressure. In the catalyst separation unit, the reactor effluent is fed to the gasifier together with the stripping gas, and the two are co-currently passed through the gasifier. The stripping gas is substantially free of aldehyde, and therefore reduces the partial pressure of aldehyde in the gasifier, thereby increasing the driving force of the aldehyde evaporating from the reactor effluent. The gasifier can also be heated to further promote evaporation. Then, the resulting vapor mixture comprising aldehyde and stripping gas is separated from the remaining liquid catalyst solution. The liquid catalyst solution is returned to the reactor, and the vapor mixture is fed to a condenser. In the condenser, the temperature of the vapor mixture is reduced, and the result is that substantially all aldehydes are condensed and separated from the remaining steam. Then, the remaining steam is recompressed to the gasifier inlet pressure and reused as a stripping gas.

[0009] WO2016089602 describes adding carbon monoxide to the gasifier stripping gas in order to reduce catalyst losses. It also suggests that a lower hydrogen partial pressure in the stripping gas can contribute to lower catalyst losses. Carbon monoxide can be obtained by separating the synthesis gas into a hydrogen-containing stream and a supplementary stripping gas stream.

[0010] It has been found that hydrogen dissolved in the reactor effluent stream can develop into the circulating stripping gas and will accumulate if not purged. As a result, a large flow of make-up gas such as carbon monoxide may be required to maintain the hydrogen concentration in the circulating stripping gas at a sufficiently low level. There remains a need for a method that can solve the problem surrounding hydrogen in the reactor effluent stream while minimizing the need for additional synthesis gas feed and energy input and the reduction in equipment size required to produce a CO-rich stream for the stripping gas and to recover the CO-rich gas for purge for useful purposes.

[0011] The present invention seeks to ameliorate some of the problems of the prior art. In particular, but not exclusively, the present invention seeks to provide an improved more cost effective process for the hydroformylation of olefins to aldehydes. Summary of the invention

[0012] According to a first aspect of the present invention, there is provided a method for producing an aldehyde, the method comprising:

[0013] a. hydroformylating olefins using a hydroformylation catalyst to form aldehydes;

[0014] b. recovering an effluent stream comprising aldehyde, hydrogen and hydroformylation catalyst;

[0015] c. conveying the effluent stream to a stripping column;

[0016] d. contacting the effluent stream with a stripping gas in the stripping column to produce a stripped effluent stream having a lower hydrogen concentration than the effluent stream; and

[0017] e. Recovering the stripped effluent stream.

[0018] Therefore, the present invention relates to a stripping tower for removing hydrogen from an effluent stream before the effluent stream enters a catalyst separation unit. As used herein, a stripping tower may include any suitable unit for removing hydrogen from a solution. In the catalyst separation unit, the catalyst is separated from the effluent stream, concentrated in the liquid phase, and preferably recycled to the hydroformylation reactor to participate in the reaction again. Catalyst separation is usually carried out at an elevated temperature and a reduced pressure. Under these conditions, it was found that the presence of hydrogen may be detrimental to catalyst stability. In addition, the hydrogen dissolved in the reactor effluent stream may develop into a circulating stripping gas and will accumulate if not removed. As a result, a large flow of make-up gas such as carbon monoxide is usually required to maintain the hydrogen concentration in the circulating stripping gas at a sufficiently low level.

[0019] The present invention provides for removing dissolved hydrogen from a reactor effluent stream upstream of a catalyst separation unit. By reducing the amount of hydrogen entering the stripping gas as a dissolved gas from the reactor effluent stream, the present invention significantly reduces the purge required in the stripping gas loop to maintain the low hydrogen concentration necessary for catalyst stability. Since less purge is required, the method requires less make-up gas such as carbon monoxide. As a direct result, the method of the present invention reduces the equipment cost in the separation assembly and reduces the recompression requirements for returning the purge to the hydroformylation reactor. Therefore, the present invention provides significant benefits of maintaining catalyst activity, minimizing the need for additional raw materials and allowing smaller equipment. In addition, the gas flow rate required to maintain a low hydrogen partial pressure in the circulating stripping gas is significantly reduced, so the present invention brings a significant reduction in total power consumption and equipment costs. In the proposed scheme, the flow rate of CO-rich gas to the stripping tower is less than 1.5 mol% of the make-up gas required to achieve the same hydrogen content in the circulating gas in an arrangement where the CO-rich gas is directly sent to the loop as make-up gas.

[0020] Removal of hydrogen from the effluent stream can be accomplished by contacting the effluent stream with a stripping gas. Contact between the effluent stream and the stripping gas can be achieved in any suitable manner. Examples include, but are not limited to, passing the stripping gas and the effluent stream co-currently or countercurrently through a tower containing structured or random packing; or bubbling the stripping gas through a flash vessel containing the effluent stream. In some aspects, the effluent stream can be flashed at a lower pressure in a flash vessel before being introduced into the stripping column.

[0021] In some aspects, the stripping gas comprises carbon monoxide, carbon dioxide, alkanes, or a combination thereof. Preferably, the stripping gas comprises carbon monoxide. The method may include feeding a synthesis gas stream to a separation system, separating the synthesis gas stream into a hydrogen-rich stream and a carbon monoxide-rich stream in the separation system, and using the carbon monoxide-rich stream as a stripping gas. Preferably, the carbon monoxide-rich stream comprises hydrogen in an amount of 0 mol% to 10 mol%; less than 5 mol%; less than 2 mol%. Preferably, the carbon monoxide-rich stream comprises 90 mol% to 100 mol%. Greater than 95 mol%; or greater than 98 mol% carbon monoxide. The separation system may include, for example, a membrane or a cryogenic distillation unit.

[0022] In some aspects, the method includes recovering a spent stripping gas stream from the stripping column, the spent stripping gas stream comprising stripping gas and hydrogen. The spent stripping gas stream can be combined with a hydrogen-rich gas stream to form a reformed synthesis gas stream, which can then be fed to a hydroformylation reactor.

[0023] The method may include separating a syngas stream fed to a separation system from a syngas feed stream fed to a hydroformylation reactor. In some aspects, a recombinant syngas stream may be fed to a hydroformylation reactor by mixing the recombinant syngas stream with the syngas feed stream.

[0024] Preferably, hydrogen should be completely or substantially removed from the stripped effluent stream. In some aspects, the stripped effluent stream comprises hydrogen in an amount of less than 0.5 mol %; less than 0.1 mol %; less than 0.05 mol %; or 0 mol % to 0.02 mol %. The method may also include feeding the stripped effluent stream to an evaporator and recovering a vapor stream from the evaporator, the vapor stream comprising: (1) aldehyde, and (2) a liquid catalyst recycle stream comprising a hydroformylation catalyst for recycling to the hydroformylation reactor. In some aspects, the hydrogen concentration in the evaporator does not exceed 5 mol %; 3 mol %; or 1 mol %. The method may also include feeding a gas comprising carbon monoxide to the evaporator.

[0025] The stripped effluent stream may be passed to a catalyst separation unit for separating a catalyst, such as a ligand-rhodium catalyst, from the effluent of the hydroformylation reaction zone, wherein a recycle stripping gas may be used in a gasifier for separating the product aldehyde from the ligand-rhodium catalyst, wherein the recycle stripping gas may be purged, for example, to prevent accumulation of hydrogen and inert components, wherein make-up carbon monoxide-rich gas, typically from a synthesis gas separation unit, is added to the recycle stripping gas. The purged stripping gas, still rich in carbon monoxide, may be combined with a hydrogen-containing stream, typically also from a synthesis gas separation unit, to form a re-integrated synthesis gas stream, which is fed to the reaction zone.

[0026] The supplementary stripping gas stream may contain carbon monoxide and is preferably rich in carbon monoxide. Preferably, the supplementary stripping gas stream is 50mol% to 100mol% carbon monoxide, more preferably the supplementary stripping gas stream is 70mol% to 100mol% carbon monoxide, still more preferably the supplementary stripping gas stream is 80mol% to 100mol% carbon monoxide, and most preferably the supplementary stripping gas stream is 97mol% to 100mol% carbon monoxide. Higher concentrations of carbon monoxide are advantageous because they allow a higher concentration of carbon monoxide in the stripping gas. Preferably, the hydrogen-containing stream is 50mol% to 100mol% hydrogen, more preferably the hydrogen-containing stream is 70mol% to 100mol% hydrogen, still more preferably the hydrogen-containing stream is 80mol% to 100mol% hydrogen, and most preferably the hydrogen-containing stream is 95mol% to 100mol% hydrogen. In some embodiments, the partial pressure of carbon monoxide in the vapor mixture leaving the gasifier may be at least 15 psi (103 kPa) and preferably at least 20 psi (138 kPa). For example, the partial pressure of carbon monoxide in the vapor mixture leaving the gasifier may be at least 15 psi (103 kPa) to no more than 200 psi (1379 kPa). The partial pressure of hydrogen in the vapor mixture leaving the gasifier may, for example, be no more than 10 psi (69 kPa). No more than 5 psi (34 kPa); or no more than 1 psi (6.9 kPa).

[0027] The method may include separating the synthesis gas stream into a hydrogen-containing stream and a supplementary stripping gas stream, wherein the synthesis gas stream is separated from the main synthesis gas feed and contains carbon monoxide and hydrogen, and the supplementary stripping gas stream is fed to the stripping section and / or evaporator. As described above, this synthesis gas separation section can be located upstream of the hydrogen stripper. The synthesis gas feed can be sent to the reaction zone after being recombined with the carbon monoxide and hydrogen of the stripping gas in the evaporator and the stripping gas in the hydrogen stripper and the hydrogen-rich gas stream from the synthesis gas separation section to produce the reformed synthesis gas stream. In some embodiments, for example, the synthesis gas feed can reach the device zone boundary of the process, and a part of the synthesis gas feed can be separated into a supplementary stripping gas stream and a hydrogen-containing stream, wherein other parts of the synthesis gas feed can be fed to the reaction zone. In such cases, some synthesis gas feeds effectively bypass the catalyst separation unit. Such an arrangement can be conducive to balancing the demand for synthesis gas feed to the reaction zone and carbon monoxide feed to the stripping gas. In such embodiments, the molar ratio of the portion of the synthesis gas feed separated into the supplemental stripping gas stream and the hydrogen-containing stream to the portion of the synthesis gas feed fed to the reaction zone as a fresh synthesis gas stream may preferably be from 0.01 to 1, more preferably from 0.05 to 0.5, and most preferably from 0.1 to 0.3. The molar ratio may be selected based on the separation efficiency (e.g., membrane separation efficiency, if a membrane is used for the separation). For example, if the supplemental stripping gas stream contains a relatively high level of hydrogen, a higher flow rate of the supplemental stripping gas stream may be used.

[0028] The molar ratio of carbon monoxide fed to the reaction zone to the olefins fed to the reaction zone is preferably about 1. The separation of the synthesis gas stream into a hydrogen-containing stream and a supplementary stripping gas stream is preferably carried out using a membrane separation unit. Such membrane separation units are commercially available from companies such as MTR and Air Products. The membrane separation unit can achieve a very high (such as at least 95mol% or preferably at least 99mol%) concentration of carbon monoxide in the supplementary stripping gas stream in an economical manner. However, such high purity may require a high flow rate of synthesis gas to enter the membrane separation unit, so it is important not to waste carbon monoxide. This is achieved in the present invention by reorganizing the stripping gas stream with a hydrogen-rich stream to produce a reformed synthesis gas stream that is transferred to the reaction zone. Alternatively or in addition, the separation of the synthesis gas stream into a hydrogen-containing stream and a stripping gas stream can be carried out using the COSORB process or a variant thereof, such as described, for example, in The absorption of carbon monoxide in COSORB solutions: absorption rate and capacity JA Hogendoorn, WPM van Swaaij, GF Versteeg, The Chem. Eng. Journ. 59 (1995) 243-252 or US 4950462 or US 5382417. Alternatively or in addition, the separation of the synthesis gas stream into a hydrogen-containing stream and a stripping gas stream can be carried out using cryogenic absorption of liquid nitrogen.

[0029] The molar ratio of hydrogen to carbon monoxide in the synthesis gas stream is preferably 0.5 to 2.0. The most desired ratio of hydrogen to carbon monoxide may depend on the desired hydrogen and carbon monoxide partial pressures in the reaction zone. Preferably, the molar ratio of hydrogen to carbon monoxide in the reformed synthesis gas stream is similar to the molar ratio of hydrogen to carbon monoxide in the synthesis gas stream, for example within 10% of the molar ratio of hydrogen to carbon monoxide in the synthesis gas stream. It is possible that the molar ratio of hydrogen to carbon monoxide in the reformed synthesis gas stream is preferably 0.5 to 2.0. The hydrogen and carbon monoxide partial pressures in the reaction zone may affect the hydroformylation reaction, rate and selectivity. If the molar ratio of hydrogen to carbon monoxide in the reformed synthesis gas stream is similar to the molar ratio of hydrogen to carbon monoxide in the synthesis gas stream, it may be advantageously simpler to control the partial pressures of carbon monoxide and hydrogen in the reaction zone.

[0030] The gasifier is preferably a falling film gasifier, but may be other types of gasifiers including, for example, vessels containing structured or random packing.The stripping gas may be fed to the gasifier in co-current or counter-current to the reactor effluent.

[0031] Because the recirculated stripping gas is at a lower pressure than the stripping gas due to the pressure drop in the process, a compressor is preferably provided to compress the recirculated stripping gas before the recirculated stripping gas is combined with the supplementary stripping gas. A compressor is also preferably provided to compress the reformed synthetic gas stream before it is fed to the reaction zone. Preferably, after compressing the recirculated stripping gas, the purged stripping gas stream is purged from the recirculated stripping gas. In this way, the purged stripping gas stream can be under a pressure suitable for combining with the hydrogen-containing stream to form a reformed synthetic gas stream, which can then be compressed before being fed to the reaction zone, and a separate compressor on the recirculated stripping gas and the purged stripping gas stream is avoided.

[0032] Typically, the reaction zone is operated at about 20 bar (2 MPa), such as 15 bar to 40 bar (1.5 MPa to 4.0 MPa), and the gasifier is operated at about 8 bar (800 kPa), such as 1 bar to 20 bar (100 kPa to 2000 kPa). However, pressures of 50 bar to 235 bar (5 MPa to 23.5 MPa) are also known for operating the reaction zone.

[0033] Preferably, the olefin is C2 to C 16 Olefins, more preferably C4 to C 12 The olefin is preferably a monoolefin. The olefin is preferably an acyclic olefin, such as a linear olefin or a branched olefin. For example, the olefin may be propylene or n-butene. However, the olefin is preferably a C8 olefin, such as octene, dibutylene or oligoethylene. Preferably, the aldehyde has one more carbon than the olefin. Thus, the aldehyde is preferably a C3 to C 17 Aldehyde, more preferably C5 to C 13 Aldehydes and most preferably C9 aldehydes. The skilled person will appreciate that the aldehyde produced depends on the olefin used.

[0034] The present invention can be used with any suitable ligand system that benefits from a carbon monoxide-rich stripping gas. Preferably, the ligand is a phosphine, such as triphenylphosphine; a monophosphite, such as trimethylolpropanephosphite or tris(2,4-di-tert-butylphenyl)phosphite; a bisphosphite; or a mixture of any of these.

[0035] In addition to the product aldehyde and the ligand-rhodium catalyst, the reactor effluent will generally also comprise other components. Such other components may include olefins and paraffins, ligand decomposition products, ligand stabilizers, aldehyde oligomers (sometimes referred to as "heavy components"), water and dissolved gases. In addition to the product aldehyde and the stripping gas, the vapor mixture leaving the gasifier will generally also comprise other components. Such other components may include olefins, paraffins and other light components. Olefins and paraffins will generally be condensed in a condenser, while light components will be retained in the recirculated stripping gas, wherein their levels are controlled by the purging of the stripping gas stream purged.

[0036] The product aldehyde stream is preferably a liquid product aldehyde stream.

[0037] Reaction zone is understood to describe one or more hydroformylation reactors. Typically, the reaction zone will include one, two or three reactors. The reactors may be connected in series, for example. A feed stream (such as a fresh synthesis gas stream and a reformed synthesis gas stream) may be provided to one or more reactors, and a reactor effluent may be collected from one or more reactors, which is transferred to a gasifier.

[0038] Where a component such as a product aldehyde is said to be vaporized (such as vaporized into a stripping gas), it is understood that a majority of the component is so vaporized. A small portion of the component may remain in the liquid phase, for example in equilibrium with the vaporized component in the vapor phase. It is possible that at least 50 mol%, preferably at least 60 mol% and more preferably at least 70 mol% of the component is so vaporized. It is possible that substantially all of the components are so vaporized. Similarly, where a component such as a product aldehyde is said to be separated, such as from a vapor mixture, it is understood that a majority of the component is so separated. A small portion of the component may remain. It is possible that at least 75 mol%, preferably at least 90 mol% and more preferably at least 95 mol% of the component is so separated. It is possible that substantially all of the components are so separated. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] Embodiments of the present invention will now be described by way of example and not in any limiting manner with reference to the accompanying drawings, in which:

[0040] Figure 1 is a block diagram embodying the process of the present invention; and

[0041] Figure 2 The present invention is embodied Figure 1 A process flow diagram of a portion of a method. DETAILED DESCRIPTION

[0042] exist Figure 1In the embodiment of the present invention, an olefin feed 1 is fed to a hydroformylation reaction zone 100. The reaction zone 100 includes at least one reactor, and possibly two or three reactors, from which the reactor effluent 11 is passed to a catalyst separation unit 101. A liquid ligand-rhodium catalyst solution 12 (wherein the solvent typically contains heavy components, such as dimers or trimers) is recycled from the catalyst separation unit 101 to the reaction zone 100. A product aldehyde stream 13 is recovered from the catalyst separation unit 101 and passed to an aldehyde purification unit 102 from which purified aldehydes 15 are recovered. Olefins and paraffins 14 are also recovered from the aldehyde purification unit 102.

[0043] The syngas feed 2 is divided into a fresh syngas stream 4, which is fed directly to the reaction zone 100 as part of a mixed syngas feed stream 10, and a syngas stream 3, which is fed to a membrane separation unit 200. In the membrane separation unit 200, the syngas stream 3 is separated into a supplemental stripping gas stream 5, which is passed to the catalyst separation unit 101, and a hydrogen-containing gas stream 6, which is combined with a purged stripping gas stream 7 to form a recombined syngas stream 8, which is compressed in a compressor 201 and fed 9 to the reaction zone 100 as part of the mixed syngas feed stream 10. For operational reasons, a purge, for example from one or more of streams 6, 7, 8 or 9, may be included, but is preferably avoided to avoid loss of recombined syngas.

[0044] Further details of the catalyst separation unit 101 are shown in Figure 2 In. Figure 2 In the embodiment, the syngas feed 2 is divided into a fresh syngas stream 4, which is directly fed to the reaction zone 100 as part of the mixed syngas feed stream 10, and a syngas stream 3, which is fed to the membrane separation unit 200. In the membrane separation unit 200, the syngas stream 3 is separated into a stripping gas stream 5 and a hydrogen-containing stream 6, the stripping gas stream 5 is passed to the stripper 202, the hydrogen-containing stream 6 is combined with the purged stripping gas stream 7 and compressed 201 to form a recombined syngas stream 9, which is fed to the reaction zone 100 as part of the mixed syngas feed stream 10. The reactor effluent 11 is fed to the stripper 202, which operates to produce a stripped effluent stream 12 having a lower hydrogen concentration than the effluent stream 11, and is passed to the catalyst separation unit.

[0045] Example 1

[0046] The following examples were generated using the commercially available simulation package SimSci ProII v10.1. The use of simulation to evaluate new processes is well established in the field of chemical engineering.

[0047] The reactor effluent containing 0.8 mol% dissolved hydrogen was fed at 90°C to a stripping column operating at 13.5 barg overhead.

[0048] 3.6 mol% of the plant syngas feed was fed to a membrane separation unit at 25 barg, where a CO-rich stream was produced. The CO-rich stream contained 96.4 mol% CO and 0.8 mol% hydrogen. 3 A CO-rich stream of 100 mol% / ton of aldehyde reactor product is fed to the bottom of a stripper comprising seven theoretical stages. It contacts the reactor effluent in the column and produces a stripped effluent stream containing 0.08 mol% hydrogen in mainly C8 and C9 oxygenates at the bottom of the stripper.

[0049] The stripped effluent stream exiting the stripper is then fed to a catalyst separation unit operating at 12 barg where the product oxygenates are separated from 3240 Nm 3 The circulating gas of 100 mol / ton of aldehyde reactor product was contacted at 140°C to evaporate most of the reactor product, leaving the catalyst solution and recycled back to the reactor. The hydrogen concentration in the circulating gas was 1.56 mol%.

[0050] The purged stripping gas stream leaving the top of the stripper is cooled to 45°C to remove condensable hydrocarbons and returned to the stripper. The cooled purged stripping gas is then combined with the hydrogen-rich gas from the membrane separation unit and recompressed to 25 barg for return to the reactor.

[0051] For comparison and to illustrate the benefits of the present invention, an arrangement from the prior art was also simulated using the same commercially available simulation package SimSci ProII v10.1.

[0052] The reactor effluent of the same composition as above, also at 90°C and also containing 0.8 mol% dissolved hydrogen, was fed directly to a catalyst separation unit operating at 12 barg where the product oxygenates were mixed with 3240 Nm 3 / ton of aldehyde reactor product is contacted with recycle gas at 140°C to vaporize most of the reactor product, leaving the catalyst solution to be recycled back to the reactor.

[0053] A CO-rich make-up stream is generated by sending all of the plant feed syngas to a membrane separation unit. 3 / ton of aldehyde reactor product and add it to the recycle gas. 38.79 Nm 3 / ton of aldehyde reactor product purge gas to purge hydrogen and inert components. The recycle gas contains 1.94 mol% hydrogen.

[0054] This example shows that the process of the present invention achieves a low hydrogen concentration in the cycle gas using a much lower CO-rich gas stream than required in arrangements disclosed in the prior art, thereby reducing energy consumption and equipment size.

[0055] Example 2

[0056] General procedure: All tests were performed in a porous heating block equipped with six 100 mL autoclaves, and several tests were repeated for increased accuracy. Temperature was controlled using an internal thermocouple, and double-checked with respect to one autoclave with an internal thermocouple to measure the process temperature as a cross-check. Phosphorus ligand (molar excess) and rhodium stock solution (prepared by dissolving Rh(acac)(CO)2 in toluene; 50 mL of added solution) were transferred to a 100 mL autoclave, which was then sealed and purged with synthesis gas (CO:H2 molar ratio = 1:1; 3×100 psi(g)). All autoclaves were then pressurized with synthesis gas and the active catalyst was formed in situ, and then allowed to cool to ambient temperature. Once cooled, a sample (1.5 ml) was removed from the autoclave for rhodium analysis via ICP-OES analysis. The autoclave was then purged with a suitable test gas (synthesis gas, CO, H2 or N2), and then pressurized to the test pressure with the test gas (as outlined in Table 1 below). The reaction was then allowed to proceed for the allotted time period before the autoclave was removed from the heating block and cooled to room temperature. At the completion of the test, another sample was removed from the autoclave to analyze the rhodium concentration via ICP-OES to look for soluble rhodium losses during the experiment. The percent rhodium loss was then calculated as ((1-[Rh] 最终 ) / [Rh] 初始 )×100.

[0057] The loss of rhodium over time has been entered into Table 1 below, which shows the dependence on different gas compositions at varying pressures. Entries 1 and 2 show high losses of rhodium under syngas atmosphere at 120°C, with a small improvement (~90%) at higher pressures. Under nitrogen, a significant improvement in rhodium loss is shown under the same conditions (entry 3), with only 5% rhodium loss. In a CO only atmosphere (entry 4), there is no significant rhodium loss. This clearly shows the benefit of operating in the absence of hydrogen, and the stabilizing effect of the increase in CO relative to nitrogen.

[0058] When operating at higher temperatures (130°C, entries 5-8), higher pressures were investigated in an attempt to increase the stability of the rhodium catalyst. Using a 1:1 syngas composition (entry 5), the loss was 93%. Operating at a higher pressure with a high H2:CO ratio (entry 6) reduced the loss to 69%. Complete loss of rhodium was observed in a hydrogen-only atmosphere (entry 7). However, even under these forced conditions, the rhodium loss under a pure CO atmosphere was only 12% (entry 8). Although the loss was reduced when a high H2:CO atmosphere was used (entry 6), it is assumed that the high CO partial pressure has a stabilizing effect on the catalyst solution. However, the results from two sets of experiments show a clear benefit in losing rhodium from the catalyst solution when a CO-only atmosphere is used.

[0059] Table 1 :

[0060]

[0061] It will be appreciated by those skilled in the art that the above embodiments are described by way of example only and not in any limiting manner, and that changes and modifications may be made without departing from the scope of the present invention as defined in the appended claims.

Claims

1. A method for producing an aldehyde, the method comprising: hydroformylating an olefin using a hydroformylation catalyst to form the aldehyde; recovering an effluent stream comprising the aldehyde, hydrogen, and the hydroformylation catalyst; passing the effluent stream to a stripping column; contacting the effluent stream with a stripping gas in the stripping column to produce a stripped effluent stream having a lower hydrogen concentration than the effluent stream; and recovering the stripped effluent stream, wherein the stripping gas comprises carbon monoxide, and The method comprises: feeding a synthesis gas stream to a separation system; separating the synthesis gas 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 stripping gas.

2. The process according to claim 1, wherein the separation system comprises a membrane or a cryogenic distillation unit.

3. A method according to claim 1 or claim 2, wherein the method comprises: recovering a spent stripping gas stream comprising the stripping gas and hydrogen from the stripping column; combining the spent stripping gas stream with the hydrogen-rich gas stream to form a reformed syngas stream; and feeding the reformed syngas stream to a hydroformylation section.

4. A process according to claim 1 or claim 2, wherein the process comprises separating the synthesis gas stream fed to the separation system from a synthesis gas feed stream fed to a hydroformylation section.

5. The process of claim 3, wherein the process comprises separating the synthesis gas stream fed to the separation system from a synthesis gas feed stream fed to the hydroformylation section.

6. The process according to claim 5, wherein the reformed synthesis gas stream is fed to the hydroformylation section by mixing the reformed synthesis gas stream with the synthesis gas feed stream.

7. The process of claim 1 wherein the hydroformylation catalyst comprises a homogeneous metal-ligand catalyst.

8. The method of claim 7, wherein the homogeneous metal-ligand catalyst comprises rhodium.

9. The method of claim 7 or 8, wherein the metal-ligand catalyst comprises an organophosphite or organophosphine ligand.

10. The method of claim 9, wherein the organophosphite or organophosphine ligand comprises Normax or triphenylphosphine.

11. The process of claim 1 , wherein the process comprises feeding the stripped effluent stream to an evaporator and recovering a vapor stream from the evaporator, the vapor stream comprising: (1) the aldehyde, and (2) a liquid catalyst recycle stream comprising the hydroformylation catalyst for recycle to the hydroformylation stage.

12. The process according to claim 11, wherein the molar composition of hydrogen in the stripped effluent stream does not exceed 5 mol%.

13. A process according to claim 11 or 12, wherein the process comprises feeding a gas comprising carbon monoxide to the vaporiser.

Images