Process for separating heavy by-products and catalyst ligands from a vapor stream comprising aldehydes

Abstract

A method for separating heavy byproducts and catalyst ligands from a vapor stream comprising aldehyde, heavy byproducts, and catalyst ligands is disclosed. The method comprises: passing the vapor stream to a fractionator, where the vapor stream is contacted with liquid aldehyde that removes at least a portion of the catalyst ligands and at least a portion of the heavy byproducts from the vapor stream; recovering a liquid bottoms stream comprising the removed catalyst ligands, the removed heavy byproducts, and some of the aldehyde from the fractionator; recovering a scrubbed vapor stream from the fractionator; condensing a first portion of the scrubbed vapor stream to produce liquid aldehyde for reflux back to the fractionator; and recovering a second portion of the scrubbed vapor stream as a product aldehyde stream. The liquid bottoms stream is passed to a separation system to separate at least some of the aldehyde from the liquid bottoms stream to produce a recovered aldehyde stream comprising the separated aldehyde and a waste stream comprising the removed catalyst ligands and the removed heavy byproducts.

Description

Technical Field

[0001] This invention relates to a method for separating heavy byproducts and catalyst ligands from a vapor stream containing aldehydes. Specifically, but not exclusively, this invention relates to a method for separating heavy byproducts and catalyst ligands from a vapor stream containing aldehydes, the vapor stream being formed by conveying a liquid output stream from a hydroformylation process to an evaporator and recovering the vapor stream from the evaporator, the liquid output stream containing aldehydes, catalyst, catalyst ligands, and heavy byproducts. Background Technology

[0002] The production of aldehydes via the hydroformylation of olefins is a well-known method. Aldehydes can undergo a variety of downstream reactions, including hydrogenation to produce aliphatic alcohols, amination to produce aliphatic amines, oxidation to produce aliphatic acids, and aldol condensation to produce acrolein, which is used in the production of plasticizers, for example. The hydroformylation of olefins to aldehydes, followed by hydrogenation of the aldehydes to prepare aliphatic alcohols, is a well-known use of aldehydes. An example of this method is provided by LP Oxo from Johnson Matthey and Dow. SM Method. Hydroformylation is carried out in the liquid phase using a homogeneous rhodium catalyst modified with an organophosphorus ligand. Examples of such ligands and methods are disclosed in US4148830, US4717775, and US4769498. Organophosphorus and organophosphites, particularly organomonophosphorus, organodiphosphorus, organotetraphosphorus, organomonophosphites, and organodiphosphites, are preferred organophosphorus ligands. The invention can be particularly useful when the ligand has a vapor pressure of at least 0.01 mbar at 160 °C. The invention can be particularly useful when the ligand comprises triphenylphosphine (TPP) or triphenylphosphine oxide (TPPO), especially when the ligand comprises TPP.

[0003] In a typical approach, one or more hydroformylation reactors produce a product stream containing an aldehyde and a homogeneous catalyst. The aldehyde is separated from the catalyst by evaporation; the evaporated aldehyde remains in the gas phase, while the catalyst liquid is retained as a liquid for recycling back to one or more hydroformylation reactors. Evaporation is typically performed to prevent excessive carryover of catalyst ligands in the evaporated aldehyde. However, it can be difficult to prevent ligands from being carried over the evaporated aldehyde at levels that could be problematic in downstream hydrogenation. For example, carried ligands can poison the catalyst used in downstream hydrogenation. This can be particularly problematic in liquid-phase hydrogenation; in gas-phase hydrogenation, evaporation of the hydrogenation feed can potentially be used to remove carried ligands. Even low levels of carried ligands can poison the catalyst. Ligands with a vapor pressure of 0.01 mbar or higher at 160 °C will result in unacceptable carryover.

[0004] Solutions have been proposed to attempt to reduce ligand carryover. These involve spraying a dispersed liquid (such as the product aldehyde) into an evaporating aldehyde stream to condense the evaporated ligands, which can then be separated in a gas-liquid separator, as described, for example, in US5110990. The problem with this arrangement is that heavy byproducts in the aldehyde product vapor are also condensed in the dispersed liquid. Therefore, ligand recycling leads to the accumulation of heavy byproducts. Careful control of the dispersed liquid has been suggested to promote ligand condensation while avoiding the condensation of heavy byproducts; however, this is difficult to achieve in practice and tends to be problematic. Any variation will result in problematic carryover of ligands through insufficient condensation or accumulation of heavy byproducts through excessive condensation of those byproducts. The accumulation of heavy byproducts can be a problem, potentially leading to higher ligand carryover, etc., as the evaporator may then need to operate at higher temperatures. Using purging from the catalyst cycle to remove accumulated heavy byproducts can result in rhodium loss.

[0005] Another proposed solution is disclosed in US2018305285. In this system, the evaporated aldehyde product stream is contacted with a partial condenser to condense the phosphorus ligands and byproducts in the evaporated aldehyde product stream, wherein up to 10% by weight of the evaporated aldehyde product stream is condensed. The condensed phosphorus ligands and byproducts are separated from the condensed aldehyde in a distillation column, where the aldehyde is re-evaporated and recycled to the evaporated aldehyde product stream. In some embodiments, the condensed phosphorus ligands and byproducts are not returned to the process, thus avoiding the accumulation of heavy byproducts. In some embodiments, the phosphorus ligands can be separated and recycled from the heavy byproducts in a separate distillation system. While such a system avoids the accumulation of heavy byproducts, the partial condenser provides only a single theoretical stage and therefore limits the efficiency of removing ligands from the achievable evaporated aldehyde product stream.

[0006] Another proposed solution is disclosed in US4792636. This disclosure provides a method for recovering optionally substituted C7 to C8 atoms from a liquid hydroformylation product medium. 17 The method for aldehydes, wherein the liquid hydroformylation product medium is substituted with C6 to C6 via optional substitution. 16 The olefin is obtained by rhodium-catalyzed hydroformylation, wherein the liquid hydroformylation product medium comprises (i) a rhodium complex hydroformylation catalyst containing rhodium in a complexation combination with carbon monoxide and a ligand, (ii) an excess ligand, and (iii) at least one optionally substituted C7 to C8 olefin. 17 Aldehydes, and (iv) aldehyde condensation products, the method comprising:

[0007] (a) Degas the liquid by hydroformylation of the medium;

[0008] (b) The degassed liquid hydroformylation medium is kept in a position that facilitates the evaporation of at least one C7 to C8 medium. 17Evaporation zone of aldehydes under temperature and pressure conditions;

[0009] (c) Recovering the catalyst-containing liquid stream from the evaporation zone;

[0010] (d) Cooling the catalyst-containing stream leaving the evaporation zone;

[0011] (e) Recovering from the evaporation zone C7 to C7 containing (i) at least one optionally substituted C7 to C8 17 A vapor stream of aldehyde, (ii) ligand and (iii) a small amount of the aldehyde condensation product;

[0012] (f) The vapor stream is transferred to the fractionation zone;

[0013] (g) Recovering (i) from the fractionation zone containing at least one of the C7 to C8 compounds. 17 (ii) a gaseous product stream of aldehydes, and (ii) a liquid bottom stream containing the ligands and aldehyde condensation products;

[0014] as well as

[0015] (h) Recycle at least a portion of the material from the cooled catalyst-containing stream of step (d) and the liquid bottom stream of step (g) to the hydroformylation zone.

[0016] At least a portion of the liquid bottom stream can be recycled to the hydroformylation zone. Alternatively, the bottom stream recovered from the fractionation zone can be conveyed to a ligand recovery zone, where the ligands are separated from the aldehyde condensation product, for example by fractionation, and the separated ligands can be recycled to the hydroformylation zone. A portion of the bottom product stream from the fractionation zone can also be recycled to the hydroformylation zone, and the residues can be treated in the ligand recovery zone, from which the recovered ligands are recycled.

[0017] In this approach, any aldehyde product in the liquid understream is likely to be wasted. An attempt could be made to reduce the level of aldehyde product in the liquid understream by running the bottom of the fractionation zone at a higher temperature, but this method may result in the formation of excessive heavy byproducts and even cracking in the reboiler of the fractionation zone. The formation of heavy byproducts undesirably consumes the aldehyde, which would otherwise be recovered as the desired product. Any cracking products may contaminate the aldehyde product leaving the fractionation zone. This approach may also be impractical for shorter-chain aldehydes, where heavy byproducts may form near-boiling compounds with catalyst ligands.

[0018] In methods involving distillation columns for separating aldehyde isomers (such as butyraldehyde isomer columns for separating n-butyraldehyde from isobutyraldehyde), any carried TPP can be removed in the isomer column. For example, the arrangement described in WO2017182780 would remove TPP carried in the first butyraldehyde isomer column, so that TPP would not be present in the feed to the aldehyde-alcohol condensation and subsequent hydrogenation, where it could poison the catalyst. However, such an arrangement is unlikely to be economical when there is no commercial need to separate isomers.

[0019] Therefore, a more efficient and effective system is still needed to prevent ligands from being carried over in the evaporated aldehyde product stream. Preferred embodiments of the present invention seek to overcome one or more of the aforementioned disadvantages of the prior art. In particular, preferred embodiments of the present invention seek to provide an improved method for separating aldehydes from a hydroformylation product stream comprising aldehydes, heavy byproducts, and catalyst ligands. Summary of the Invention

[0020] According to a first aspect of the invention, a method is provided for separating a catalyst ligand from a vapor stream comprising an aldehyde, a heavy byproduct, and a catalyst ligand, the method comprising: conveying the vapor stream to a fractionator in which the vapor stream is contacted with a liquid aldehyde, the liquid aldehyde removing at least a portion of the catalyst ligand and at least a portion of the heavy byproduct from the vapor stream; recovering from the fractionator a liquid bottom stream comprising the removed catalyst ligand, the removed heavy byproduct, and some of the aldehyde; recovering from the fractionator a washed vapor stream; condensing a first portion of the washed vapor stream to produce the liquid aldehyde for reflux back to the fractionator; and recovering a second portion of the washed vapor stream as a product aldehyde stream, wherein the liquid bottom stream is conveyed to a separation system to separate at least some of the aldehyde from the liquid bottom stream to produce a recovered aldehyde stream comprising the separated aldehyde and a waste stream comprising the removed catalyst ligand and the removed heavy byproduct.

[0021] A more flexible system is created by feeding the liquid bottom stream to a separation system to separate at least some aldehydes from the liquid bottom stream. For example, this system has the flexibility to operate the fractionator under conditions that reduce the formation of heavy byproducts and the likelihood of potential cracking, while the separation system can operate under conditions that maximize aldehyde recovery from the recovered aldehyde stream. This can be advantageous because the fractionator handles significantly higher flow rates and therefore significantly larger aldehyde stocks compared to the separation system, and thus the formation of heavy byproducts and potential cracking in the fractionator has a greater potential to cause significant problems. Heavy byproducts can form, for example, in the reboiler through reactions involving aldehydes. Therefore, the formation of such heavy byproducts represents a loss of the desired aldehyde product. Furthermore, if cracking occurs, cracking products can move upwards along the fractionator and contaminate the product aldehyde stream. This flexibility also allows for more economical performance, as larger fractionators can operate under more economical conditions without the loss of aldehyde products that would occur when operating under those conditions in existing technology processes.

[0022] The second portion of the washed vapor stream can be condensed, preferably together with the first portion, and recovered as the liquid product aldehyde stream. The second portion of the washed vapor stream can be recovered as a vapor stream, preferably by feeding the washed vapor stream into a partial condenser to condense the first portion, and then passing it through a vapor-liquid separator to separate the first and second portions.

[0023] The method preferably involves forming a vapor stream by conveying a liquid output stream from the hydroformylation process to a separator and recovering a vapor stream from the separator, the liquid output stream comprising aldehydes, catalyst, catalyst ligands, and heavy byproducts. The separator can be, for example, a membrane separator, but is preferably an evaporator. The evaporator can, for example, comprise a heat exchanger and a separation drum in series. The vapor stream preferably contains 50% to 99% by weight of the aldehyde conveyed to the evaporator. The vapor stream typically contains a small portion of catalyst ligands and heavy byproducts conveyed to the evaporator. For example, the liquid output stream from hydroformylation may contain 5% to 20% by weight of catalyst ligands, and the vapor stream preferably contains no more than 5000 ppmw, and more preferably no more than 2500 ppmw of catalyst ligands. Alternatively, up to 10% by weight of catalyst ligands entering the evaporator may be in the vapor stream. For short-chain olefins, such as C3 or shorter, preferably no more than 1% by weight of catalyst ligands entering the evaporator may be in the vapor stream. Preferably, the catalyst and most of the catalyst ligands are recovered in the liquid stream in the evaporator, typically at the bottom of the evaporator, and preferably recycled to the hydroformylation process.

[0024] More efficient separation of ligands from the vapor stream can be achieved by directing the vapor stream to a fractionator in which the vapor stream contacts the liquid aldehyde. This is because the fractionator provides the opportunity for multiple theoretical stages. Preferably, the fractionator includes at least two theoretical stages, more preferably at least four theoretical stages. The theoretical stages may include the theoretical stage of a condenser connected to the fractionator. Using the liquid aldehyde condensed from the scrubbed vapor stream as reflux to the fractionator is an effective source of scrub liquid that does not introduce other components into the system.

[0025] The liquid bottom stream is fed to a separation system, such as a distillation column, to separate at least some aldehydes from the liquid bottom stream, thereby producing a recovered aldehyde stream containing the separated aldehydes and a waste stream containing removed catalyst ligands and removed heavy byproducts. Thus, the separated aldehydes (which are valuable products of hydroformylation) are not lost from the process. By not returning the removed heavy byproducts to the process, the present invention prevents the accumulation of heavy byproducts in the process. The use of a fractionator advantageously produces a liquid bottom stream as a separate stream, while also allowing for efficient multi-theoretical-stage separation to prevent excessive carryover of catalyst ligands to downstream processes. Existing methods that do not produce a separate stream can lead to the accumulation of heavy byproducts, while existing methods with a single theoretical stage may be less efficient in removing catalyst ligands. Existing methods that do not recover aldehydes from the liquid understream either require operation under conditions that lead to undesirable aldehyde loss in the liquid understream or under conditions that minimize aldehydes in the liquid understream. However, this can result in aldehyde loss due to the formation of heavy byproducts in the fractionator and potentially lead to contamination of the aldehyde product stream by cracking and cracking products in the fractionator. The method of the present invention can also be operated at a higher reflux ratio in the fractionator, thus increasing the proportion of catalyst ligands and heavy byproducts removed from the vapor stream. Without a separation system, a higher reflux ratio would require a fractionator reboiler operating under more demanding conditions (e.g., elevated temperatures) to prevent higher levels of aldehydes in the liquid understream; or it would result in higher levels of aldehyde loss.

[0026] Preferably, the recovered aldehyde stream is recycled back into the process. The recovered aldehyde stream is preferably recycled upstream of the fractionator. The recovered aldehyde stream can be recycled back to the fractionator. Preferably, the vapor stream has been recovered from the evaporator, and the recovered aldehyde stream is preferably recycled back to the evaporator. When the evaporator includes a separation drum, the recovered aldehyde stream is preferably recycled back to that separation drum. When the recovered aldehyde stream is recycled back to the fractionator, it is preferably recycled back to the fractionator as a liquid reflux. In some embodiments, the recovered aldehyde stream may be combined with the product aldehyde stream; however, this may not be preferred because the recovered aldehyde stream may contain some catalyst ligands due to incomplete separation in the separation system.

[0027] Preferably, the recovered aldehyde stream contains at least 90% by weight, and more preferably at least 95% by weight, aldehyde. A higher aldehyde content in the recovered aldehyde stream can increase the likelihood of using the stream. For example, a higher aldehyde content can improve the desirability of combining the recovered aldehyde stream with the product aldehyde stream.

[0028] The waste stream preferably contains no more than 10% by weight, and more preferably no more than 7.5% by weight, of aldehyde. Therefore, the waste of aldehyde (the desired product of the method) remains low. This invention advantageously achieves such a low level of aldehyde in the waste stream, while also benefiting from the low bottom temperature in the fractionator. It is preferable to feed the waste stream into waste, thereby ensuring that the removed heavy byproducts are not returned to the process where they might accumulate.

[0029] When the separation system includes a distillation column, the distillation column preferably includes a reboiler and a reflux condenser. Having a reboiler on the fractionator may also be advantageous. The separation system recovers aldehydes from the liquid bottom stream, thus aldehyde loss is advantageously minimized even in the absence of a reboiler on the fractionator. However, the aldehydes recovered in the separation system are typically recycled upstream, for example, to an upstream hydrogenation reactor, where the aldehydes will act as a diluent, potentially meaning the reactor needs to be larger to handle the additional flow rate. Providing a reboiler on the fractionator advantageously offers the flexibility to operate the reboiler in such a way that, for example at lower temperatures, more aldehydes enter the liquid bottom stream than would be desirable in prior art arrangements, and it advantageously reduces the risk of heavy byproducts or cracking products forming in the reboiler, while still preventing excessive aldehydes from being transferred to the separation system and recycled. By utilizing a reboiler on the fractionator, the present invention can thus retain the advantages of reduced heavy byproduct formation and cracking, while benefiting from the additional advantage of reduced dilution of upstream processes by recycled aldehydes. Having a reboiler on the fractionator also allows for an increase in the reflux ratio of the fractionator, thus increasing the proportion of catalyst ligands and heavy byproducts removed from the vapor stream without increasing the amount of liquid aldehydes in the bottom liquid stream. Therefore, greater removal of catalyst ligands and heavy byproducts can be achieved while maintaining the advantages of the invention described above. The combination of providing a reboiler on the fractionator with providing a separation system also increases the flexibility of the process in handling variations in the composition of the input stream by providing additional options for controlling the process. Therefore, providing a reboiler improves the flexibility and operability of the method.

[0030] This method includes at least partially condensing a scrubbed vapor stream to produce liquid aldehydes for reflux back to a fractionator. The method may include condensing a majority of the scrubbed vapor stream, for example by condensing substantially all the aldehydes in the scrubbed vapor stream in a condenser to produce a condensate stream, which is then separated to produce liquid aldehydes and a product aldehyde stream for reflux back to the fractionator. In this case, the product aldehyde stream is recovered as a liquid product aldehyde stream. Condensation may be carried out in a condenser, preferably followed by a separation drum or other vapor-liquid separator to remove any light components that have not been condensed with the aldehydes. Alternatively, the method may include partially condensing the aldehydes in the scrubbed vapor stream and separating the condensed aldehydes to produce liquid aldehydes for reflux back to the fractionator from the uncondensed aldehydes recovered as a product aldehyde stream. Thus, the product aldehyde stream will be a vapor product aldehyde stream. In such embodiments, partial condensation is preferably carried out in a partial condenser, preferably followed by a separation drum or other vapor-liquid separator to separate the liquid aldehydes for reflux back to the fractionator from the vapor product aldehyde stream. The vapor product aldehyde stream can then be condensed in a separate condenser, preferably subsequently in a separating drum or other vapor-liquid separator, to remove any light components that were not condensed with the aldehyde, thereby producing a liquid product aldehyde stream. This arrangement can be particularly attractive as a retrofit of existing equipment, and therefore the invention may include a method for re-attracting equipment to install such an arrangement. Existing equipment will have an existing condenser to condense the vapor stream, and the existing condenser can be used as an additional condenser, preferably without significant modification. Fractionators and partial condensers, as well as other equipment relevant to the invention, will be installed upstream of the existing condenser.

[0031] Preferably, the vapor stream contains at least 80% by weight of aldehyde, more preferably at least 90% by weight of aldehyde. The vapor stream may contain at least 0.5% by weight of heavy byproducts, or at least 1% by weight of heavy byproducts, or at least 2% by weight of heavy byproducts. Preferably, the vapor stream contains no more than 10% by weight of heavy byproducts, more preferably no more than 5% by weight of heavy byproducts. The invention can be particularly advantageous when the vapor stream contains at least 10 ppmw of catalyst ligands, and even more so when the vapor stream contains at least 20 ppmw of catalyst ligands. Such levels of catalyst ligands can cause significant poisoning problems in downstream catalysts (particularly downstream hydrogenation catalysts) if not removed. The vapor stream may contain at least 100 ppmw or at least 200 ppmw of catalyst ligands or at least 500 ppmw of catalyst ligands. Preferably, the vapor stream contains no more than 5000 ppmw of catalyst ligands, and more preferably no more than 2500 ppmw of catalyst ligands. The vapor stream may also contain other contaminants, such as olefins, alkanes, alcohols and other contaminants, especially light (i.e., lighter than aldehydes) contaminants.

[0032] The product aldehyde stream preferably contains no more than 10 ppmw of catalyst ligand, more preferably no more than 5 ppmw, and even more preferably no more than 1 ppmw of catalyst ligand. Preferably at least 95% by weight, more preferably at least 97% by weight, even more preferably at least 99% by weight, and even more preferably at least 99.5% by weight of the catalyst ligand in the vapor stream is removed in a fractionator. Due to the removal efficiency in the fractionator, such high levels of catalyst ligand removal and therefore low levels of catalyst ligand in the product aldehyde stream can be achieved in an economical manner.

[0033] The liquid bottom stream may contain at least 5% by weight of heavy byproducts, or at least 10% by weight of heavy byproducts. The liquid bottom stream may contain at least 60% by weight of heavy byproducts, and may contain at least 80% by weight of heavy byproducts. However, advantageously, the invention allows the fractionator to operate in a manner that allows more aldehydes to enter the liquid bottom stream. Therefore, the liquid bottom stream preferably contains no more than 50% by weight of heavy byproducts. Preferably, the liquid bottom stream contains at least 25% by weight, and more preferably at least 50% by weight of aldehydes. Higher aldehyde concentrations (such as those typically produced by the milder conditions at the bottom of the fractionator) have the associated advantages of reduced heat load and avoidance of the formation and cracking reactions of undesirable heavy byproducts.

[0034] Preferably, the reflux ratio of the fractionator is at least 0.05, and more preferably at least 0.1. The reflux ratio is the mass flow rate of the liquid aldehyde refluxed to the fractionator divided by the mass flow rate of the aldehyde product stream. The reflux ratio is preferably no more than 0.5. Higher reflux ratios, such as at least 0.1, can be used particularly advantageously in this invention because the separation system prevents excessive aldehyde loss.

[0035] When a reboiler is used on a fractionator, the reboiler is preferably operated such that the temperature at the bottom of the fractionator is at least 90°C. The reboiler is preferably operated such that the temperature at the bottom of the fractionator does not exceed 140°C. Operating at such temperatures advantageously allows some aldehydes to be redistilled into the fractionator while avoiding undesirable aldehyde losses through the formation of heavy byproducts or contaminants from the cracking reaction.

[0036] The above operating conditions can be particularly advantageous when the catalyst ligand is TPP and the aldehyde includes C3-C6 aldehydes, especially butyraldehyde.

[0037] Preferably, the separation system includes a distillation column. The distillation column is preferably operated such that the temperature at the bottom of the distillation column is higher than the temperature at the bottom of the fractionator. The distillation column is preferably operated such that the temperature at the bottom of the distillation column does not exceed 140°C. The temperature at the bottom of the distillation column is preferably at least 90°C, and more preferably at least 100°C. The temperature at the bottom of the distillation column is preferably higher than the temperature at the bottom of the fractionator. The lower temperature at the bottom of the fractionator reduces the risk of formation or cracking of heavy byproducts in the fractionator, which handles a higher feed stream, while the higher temperature at the bottom of the distillation column increases the recovery of aldehydes into the recovered aldehyde stream. The temperature at the bottom of the distillation column is preferably at least 10°C higher than the temperature at the bottom of the fractionator, more preferably at least 20°C higher, and even more preferably at least 30°C higher.

[0038] The pressure of the distillation column is preferably at least 0.3 bara. The pressure of the distillation column is preferably no more than 1.2 bara. The pressure in the distillation column is preferably lower than the pressure in the fractionator. Preferably, the pressure in the distillation column is at least 0.1 bar lower than the pressure in the fractionator, more preferably at least 0.2 bar, and even more preferably at least 0.5 bar. Lower pressure generally means increased equipment size, but the flow rate handled by the distillation column is lower than that of the fractionator, so it can still be a smaller unit. Lower pressure advantageously allows more aldehyde to be separated into the recovered aldehyde stream without the need for the formation of heavy byproducts or the temperatures at which cracking may occur. Therefore, the fractionator can operate at higher pressures, allowing the fractionator to have an economical size, allowing some aldehyde to slip into the liquid bottom stream, and enabling the distillation column, which handles lower flow rates and is therefore smaller in any case, to operate at lower pressures to achieve good aldehyde recovery without aldehyde loss through cracking products to the formation or contamination of heavy byproducts.

[0039] The reflux ratio of the distillation column is preferably at least 0.1. The reflux ratio of the distillation column is preferably no more than 1.2. Such conditions, particularly combinations of temperature, pressure, and reflux ratio ranges, may be particularly advantageous for recovering aldehydes from the recovered aldehyde stream without loss of aldehydes to the formation of heavy byproducts or contamination of the recovered aldehyde stream with catalyst ligands or cracking products. These conditions may be particularly suitable when the catalyst ligand is TPP and the aldehyde is a C3-C6 aldehyde.

[0040] The catalyst ligand preferably comprises an organophosphorus ligand. The organophosphorus ligand is preferably an organophosphine or an organophosphite, particularly an organomonophosphine, organodiphosphine, organotetraphosphine, organomonophosphite, or organodiphosphite. The invention can be particularly useful when the ligand has a vapor pressure of at least 0.01 mbar at 160°C. The invention can be particularly useful when the ligand comprises triphenylphosphine (TPP) or triphenylphosphine oxide (TPPO), especially when the ligand comprises TPP.

[0041] The aldehyde is preferably a C3 to C6 aldehyde. More preferably, the aldehyde includes butyraldehyde or pentanaldehyde, and most preferably, the aldehyde includes butyraldehyde.

[0042] In some embodiments, the vapor stream may also contain ligand decomposition products, which may themselves be organophosphorus compounds, such as organomonophosphine, organodiphosphine, organotetraphosphine, organomonophosphite, or organodiphosphite. The ligand decomposition products can be separated from the catalyst ligand. Some ligand decomposition products may themselves act as catalyst ligands, and the catalyst ligand may therefore itself be a decomposition product of another catalyst ligand.

[0043] Those skilled in the art will be familiar with the formation of heavy byproducts in the chemical process of aldehyde formation. Heavy byproducts typically include aldehyde condensation products, including aldehyde dimers and aldehyde trimers. Aldehyde condensation products may also include tetramers.

[0044] Technicians will become aware of various fractionator designs, including packed bed and tray designs. A fractionator can also be a scrubber.

[0045] The separation system preferably includes a fractionator, such as a distillation column, but may be another type of separation system, such as a membrane separation system.

[0046] Preferably, the method includes feeding the aldehyde product 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, or aldol condensation to produce acrolein. Preferably, the method includes purifying the aliphatic alcohol, aliphatic amine, aliphatic acid, or acrolein, for example by distillation in one or more columns. Acrolein can be hydrogenated, preferably in liquid-phase hydrogenation, to an alcohol, preferably 2-ethylhexanol or 2-propylhexanol, and most preferably 2-ethylhexanol, and then preferably purified. Most preferably, the method includes feeding the aldehyde product to one or more reactors for hydrogenation of the aldehyde to produce an aliphatic alcohol, preferably butanol. The method preferably includes purifying the alcohol, for example by distillation in one or more columns. Hydrogenation is preferably liquid-phase hydrogenation. The invention can be particularly advantageous when there is downstream liquid hydrogenation of an aldehyde or acrolein produced by aldol condensation of an aldehyde, because the catalyst used for liquid hydrogenation may be particularly susceptible to poisoning by catalyst ligands.

[0047] The method preferably includes forming a vapor stream by conveying a liquid output stream from the hydroformylation process to a separator and recovering the vapor stream from the separator, the liquid output stream comprising aldehydes, catalyst, catalyst ligands, and heavy byproducts. The separator is preferably an evaporator, which may, for example, include a heat exchanger and a separation drum arranged in series. The hydroformylation process preferably includes feeding a catalyst, catalyst ligands, olefins, and carbon monoxide into one or more hydroformylation reactors; reacting the olefins with carbon monoxide to form aldehydes and heavy byproducts; and recovering the liquid output stream comprising aldehydes, catalyst, catalyst ligands, and heavy byproducts. Carbon monoxide is preferably contained in the syngas. Therefore, the method preferably includes feeding a catalyst, catalyst ligands, olefins, and carbon monoxide into one or more hydroformylation reactors; reacting the olefins with carbon monoxide to form aldehydes and heavy byproducts; recovering a liquid output stream containing aldehydes, catalyst, catalyst ligands, and heavy byproducts; conveying the liquid output stream to a separator, from which a vapor stream containing aldehydes (preferably at least 50% by weight), a small fraction of the catalyst ligands, and a small fraction of the heavy byproducts is recovered; and conveying the vapor stream to a fractionator, in which the vapor stream contacts a liquid aldehyde, which removes at least [amount] of the catalyst ligands from the vapor stream. A portion and at least a portion of heavy byproducts; recovery from a fractionator of a liquid bottom stream containing removed catalyst ligands, removed heavy byproducts and some aldehydes; recovery from a fractionator of a washed vapor stream; condensation of a first portion of the washed vapor stream to produce liquid aldehydes for reflux back to the fractionator; and recovery of a second portion of the washed vapor stream as a product aldehyde stream, wherein the liquid bottom stream is fed to a separation system to separate at least some aldehydes from the liquid bottom stream to produce a recovered aldehyde stream containing the separated aldehydes and a waste stream containing the removed catalyst ligands and the removed heavy byproducts.

[0048] Preferably, the method includes recovering a liquid stream from a separator, the liquid stream containing the catalyst and a majority of the catalyst ligands, and recycling the liquid stream to one or more hydroformylation reactors. The catalyst preferably contains rhodium. When the stream contains the majority of the component, it may contain at least 75% by weight, preferably at least 90% by weight, more preferably at least 95% by weight, and even more preferably at least 99% by weight of the component fed to the separator, and when the stream contains a small portion of the component, it may contain no more than 25% by weight, more preferably no more than 10% by weight, more preferably no more than 5% by weight, and even more preferably no more than 1% by weight of the component fed to the separator.

[0049] According to a second aspect of the invention, an aliphatic alcohol, aliphatic amine, aliphatic acid, or acrolein is provided, obtained by the method according to the first aspect of the invention. Preferably, the aliphatic alcohol, aliphatic amine, aliphatic acid, or acrolein is an aliphatic alcohol, most preferably butanol. Preferably, the aliphatic alcohol consists essentially of butanol. In another preferred aspect, an aliphatic alcohol is provided, preferably 2-ethylhexanol or 2-propylhexanol, and most preferably 2-ethylhexanol, which is obtained by hydrogenation of acrolein obtained by the method according to the first aspect of the invention.

[0050] It should be understood that features described with respect to one aspect of the invention are equally applicable to another aspect of the invention. Some features may not be applicable to a particular aspect of the invention and may be excluded from that particular aspect. Attached Figure Description

[0051] Embodiments of the invention will now be described by way of example, and not in any limiting way, with reference to the accompanying drawings, in which:

[0052] Figure 1 The comparison method is shown;

[0053] Figure 2 The comparison method is shown;

[0054] Figure 3 The comparison method is shown;

[0055] Figure 4 The comparison method is shown;

[0056] Figure 5 This is a method according to the present invention;

[0057] Figure 6 This is another method according to the present invention;

[0058] Figure 7 It is another method according to the invention; and

[0059] Figure 8 This is another method according to the present invention.

[0060] The comparison method is used for comparison with the present invention and may not be a prior art method. Detailed Implementation

[0061] The following method examples were simulated using Aveva Simsci Pro II. Those skilled in the art will understand that the use of simulation packages is a recognized method for evaluating methods in the field of chemistry.

[0062] Figure 1A reference method is shown, comprising an evaporator 50 and a condenser 52, but without a fractionator. The evaporator includes a heat exchanger 50a and a separation drum 50b. In this method, Rh / TPP-catalyzed hydroformylation of propylene using a liquid catalyst recycling scheme produces a stream containing 2.5 wt% propylene and propane, 70 wt% butyraldehyde, 15 wt% heavy byproducts, 11.9 wt% TPP, and the remainder being non-condensable gases, catalyst, and butanol. This feed 1 is fed into an evaporator 50 operating at 1.2 bara and 130 °C, where approximately 70 wt% of the feed is evaporated, producing a vapor stream 2 containing 3.5 wt% propylene and propane, 93.7 wt% butyraldehyde, 2.4 wt% heavy byproducts, and non-condensable gases, butanol, and approximately 1300 ppmw of TPP. Vapor stream 2 is fed into condenser 52, which operates at 40°C, generating a liquid / vapor condenser outlet stream 4, which is conveyed to separation drum 53 to produce a liquid aldehyde product stream 7 containing approximately 1315 ppmw of TPP. Uncondensed vapor is discharged as exhaust stream 5. Liquid stream 9 recycles the catalyst and TPP ligands to hydroformylation.

[0063] Figure 2 As shown Figure 1 The method described herein also includes fractionator 51. Figure 2 In this process, feed 1 (having the composition as described above) is fed into evaporator 50, which includes heat exchanger 50a and separation drum 50b, producing vapor stream 2. Vapor stream 2 is fed into fractionator 51, which has four theoretical stages. Fractionator 51 operates at a pressure of 1.1 bara and has a bottom temperature of 78°C. Fractionator 51 receives reflux (reflux stream 6) of condensed overhead distillate to provide a reflux ratio of 0.3. Fractionator vapor stream 3 is fed into condenser 52, which operates at 40°C, producing liquid / vapor condenser outlet stream 4, which is conveyed to separation drum 53. Uncondensed vapor is discharged as discharge stream 5, and the remaining liquid is separated into reflux stream 6 and liquid aldehyde product stream 7, which contains less than 1 ppb of TPP. During implementation, this TPP level is below the detection limit. Fractionator liquid bottom stream 18 contains approximately 75% by weight of butyraldehyde and is recycled to separation drum 50b of evaporator 50. Essentially all the heavy byproducts evaporated in evaporator 50 will be returned to liquid stream 9 via liquid bottom stream 18 and separation drum 50b, and then back to catalyst recycling. This will lead to further accumulation of heavy byproducts in the catalyst solution, thus requiring a further increase in the temperature of evaporator 50 until the removal of heavy byproducts equals the formation of heavy byproducts. In this case, the heavy byproducts cannot escape and may continue to accumulate until they are removed from the catalyst solution (e.g., from liquid stream 9). However, such removal is undesirable because it results in the loss of rhodium, and rhodium replacement is expensive.

[0064] Therefore, an alternative could be as follows: Figure 3 As shown in the figure. In this figure, similar numbered items are... Figure 1 and Figure 2 The same as described herein, and will not be described again here, is that the liquid bottom stream 8 is sent to the waste. In this way, heavy byproducts do not accumulate. However, as... Figure 2 The entire liquid bottom stream 8, containing approximately 75% by weight of butyraldehyde, is sent to waste. Because the reflux ratio in fractionator 51 needs to be sufficiently large to maintain a sufficiently low TPP level in the aldehyde product stream 7, the amount of butyraldehyde wasted can be considerable.

[0065] exist Figure 4 In the middle, similar numbered items are similar to Figures 1 to 3 The same as described herein and will not be described again, fractionator 51 includes reboiler 54. Reboiler 54 concentrates the liquid bottom stream 38 by re-evaporating the aldehyde and returning it to fractionator 51. Fractionator 51 is compatible with... Figure 2 and Figure 3 The same reflux ratio operation is performed, and the liquid aldehyde product stream 7 contains less than 1 ppb of TPP. The reboiler 54 is controlled to provide an aldehyde concentration of 5% by weight in the liquid bottom stream 38 to minimize aldehyde loss. The liquid bottom stream 38 is not recirculated but discharged as waste. The reboiler 54 operates at a temperature of 163°C. At such a high reboiler temperature and low aldehyde concentration, the reboiler can be difficult to control because the boiling point of the liquid will vary significantly with small changes in the aldehyde concentration. This can lead to unstable reboiler operation. Additionally, such high temperatures can lead to the formation of additional heavy byproducts, resulting in aldehyde loss, and may also lead to the cracking of these heavy byproducts. This cracking is undesirable because it produces light byproducts that can contaminate the aldehyde product stream 7.

[0066] exist Figure 5 The method according to the invention includes a separation system 155 following a fractionator 151. A feed stream 101 having the same source and composition as the feed stream 1 described above is fed into an evaporator 150 including a heat exchanger 150a and a separation drum 150b to generate a vapor stream 102, which, as described above with respect to the feed stream 1, evaporator 50, vapor stream 2, and fractionator 51 in the previous figures, is conveyed to the fractionator 151. The fractionator 151 operates with a reflux ratio of 0.3 and a bottom temperature of 78°C. Figures 2 to 4Similarly, the washed vapor stream 103 is recovered from the top of fractionator 151 and conveyed to condenser 152. Condenser 152 condenses most of the washed vapor stream 103, including substantially all of the aldehydes in the washed vapor stream 103, to produce a liquid / vapor condenser outlet stream 104, which is conveyed to separation drum 153, from which uncondensed vapors are discharged as discharge stream 105. The remaining liquid is separated into a reflux stream 106 and a liquid aldehyde product stream 107. Liquid aldehyde stream 107 contains less than 1 ppb of TPP. Liquid bottom stream 108 contains 75% by weight of butyraldehyde. Liquid bottom stream 108 is conveyed to a separation system, in this embodiment, which includes another fractionator in the form of distillation column 155 operating at a reflux ratio of 0.5 bara, a bottom temperature of 124°C, and operating at the bottom temperature of distillation column 155. Distillation column 155 includes a reboiler 156, a condenser 158, and a separation drum 157. Waste stream 188 is recovered from the bottom of distillation column 155. The waste stream contains 5% by weight butyraldehyde. Waste stream 188 is fed into waste. The recovered aldehyde stream 118, containing butyraldehyde and possibly trace amounts of TPP and heavy byproducts, is recovered from the top of distillation column 155. In this embodiment, the recovered aldehyde stream 118 is recycled to the separation drum 150b of evaporator 150. The recovered aldehyde stream 118 may also be recycled elsewhere in the process. In some embodiments, the recovered aldehyde stream 118 may be combined with product aldehyde stream 107.

[0067] In this implementation scheme, the butyraldehyde level in waste stream 118 is related to the above regarding Figure 4 The same as in the described implementation scheme. However, with Figure 4 Compared to the 163°C temperature in the reboiler 54 of fractionator 51, it achieves a bottom temperature of 78°C in fractionator 151 and a bottom temperature of 124°C in distillation column 155. The lower temperature can be advantageous, for example, by reducing heat load and thus operating costs, by reducing aldehyde losses due to the formation of heavy byproducts, and / or by reducing contamination from cracking products. The method also has the advantage that distillation column 155 is physically separated from fractionator 151 and can therefore operate independently of fractionator 151, which is consistent with... Figure 4 The reboiler 54 is different. By supplying the liquid bottom stream 108 from the fractionator 151 to the distillation column 155, the distillation column 155 can operate almost independently of the fractionator 151, and therefore any difficulties in operating the reboiler 156 on the distillation column 155 will not affect the operation of the fractionator 151. This allows difficult equipment to be separated from the main operating column, thus facilitating the operation of the main column.

[0068] The results of the above examples are collected in the table below.

[0069]

[0070]

[0071] It is clear that, regarding Figure 5 The described method enables excellent aldehyde product stream specification 107, with reduced risk of aldehyde loss due to heavy byproduct formation, reduced contamination risk and improved operability, while requiring a lower load compared to other methods.

[0072] exist Figure 6 In the diagram, similar numbered items are the same as those in the previous diagram and will not be described again here. The method is the same as... Figure 5 The method is similar, but this time it includes a reboiler 154 on the fractionator 151. With Figure 5 Compared to stream 108, the resulting liquid bottom stream 138 can therefore have a reduced aldehyde content. Advantageously, the presence of a reboiler 154 on fractionator 151 and a reboiler 156 on distillation column 155 results in greater operational flexibility. This allows, for example, an optimized balance to be achieved between keeping the bottom temperature of fractionator 151 low enough to prevent the formation of heavy byproducts and cracking reactions, but keeping the bottom temperature of fractionator 151 high enough to reduce the aldehyde content in liquid bottom stream 138 to some extent. Although distillation column 155 recovers aldehydes from liquid bottom stream 138, the recovered aldehyde stream 118 is typically recycled to the separation drum 150b of evaporator 150, from where it is recycled to the hydroformylation reactor. This recycling prevents aldehyde loss, thus achieving the advantages of this invention in preventing aldehyde loss during purging. It also utilizes temperatures that mitigate aldehyde loss to the formation and contamination of heavy byproducts via cracking products. However, recycling large quantities of aldehyde through the upstream hydroformylation reactor may undesirably dilute the reactants in the hydroformylation reactor. Having a reboiler 154 on the fractionator 151 and a reboiler 156 on the distillation column 155 advantageously allows for optimal mitigation of heavy byproduct formation and contamination via cracking, while avoiding excessive dilution by the recycled aldehyde.

[0073] exist Figure 7In this configuration, where similar numbered items are identical to those in the previous figures and are not described again here, the washed vapor stream 103 is conveyed to a partial condenser 162. The partial condenser 162 condenses some of the aldehyde, which is returned to the fractionator 151 as a reflux stream 166. The vapor outlet stream 163 from the partial condenser 162 is conveyed to another condenser 152, where substantially all of the remaining aldehyde is condensed. The outlet 104 from the other condenser 152 is conveyed to a separation drum 153, where it is separated into a vapor discharge stream 105 and a liquid product aldehyde stream 107. This arrangement can be particularly attractive as a retrofit, as the existing condenser for condensing vapor from the evaporator 150 can be used as another condenser 152 without significant modification. The fractionator 151 and the partial condenser 162 are then installed between the existing evaporator 150 and the other condenser 152. Figure 7 The portion of the condenser 162 depicted can also be used in other embodiments of the invention, such as those relating to... Figure 5 , Figure 6 or Figure 8 The implementation schemes described.

[0074] exist Figure 8 In this diagram, similar numbered items are identical to those in the methods described in the previous figures, and their descriptions are not repeated. A stream 201 containing propylene, carbon monoxide, rhodium, and TPP is fed into a hydroformylation reactor 250. In the hydroformylation reactor 250, propylene reacts with carbon monoxide to form butyraldehyde, which exits the hydroformylation reactor 250 in a liquid output stream 101 (which is the feed stream) to an evaporator 150, which includes a heat exchanger 150a and a separation drum 150b. Vapor stream 102 and liquid stream 109 are recovered from the evaporator 150. The liquid stream 109 containing rhodium and TPP is recycled back to the hydroformylation reactor 250. Vapor stream 102 is treated in a fractionator 151 as described with respect to the previous figures. The liquid product aldehyde stream 107 is fed together with the hydrogen-containing stream 202 to a hydrogen-containing reactor 251. In hydrogenation reactor 251, butyraldehyde from liquid product aldehyde stream 107 reacts with hydrogen from hydrogen stream 202 to form butanol, which is recovered in butanol product stream 207. Butanol product stream 207 can then be subjected to a purification step, typically distillation, to recover butanol product of the desired purity level.

[0075] Those skilled in the art will understand that the above embodiments are described by way of example only and not by any means of limitation, and that changes and modifications can be made without departing from the scope of the invention as defined by the appended claims. For example, the olefin can be butene, and the aldehyde can be pentanal. As another example, the hydrogenation reactor 251 can be replaced by an amination reactor to produce aliphatic amines, by an oxidation reactor to produce aliphatic acids, or by an aldol condensation reaction to produce acrolein, which can then be fed to the hydrogenation reactor to prepare alcohols, with other reaction streams replacing hydrogen stream 202, as will be apparent to those skilled in the art. Although the evaporator 150 includes a heat exchanger 150a and a separation drum 150b, other designs of the evaporator can be used, for example, to generate vapor stream 102.

Claims

1. A method for separating the heavy byproduct and the catalyst ligand from a vapor stream comprising an aldehyde, a heavy byproduct, and a catalyst ligand, the method comprising: The vapor stream is fed to a fractionator, in which it contacts a liquid aldehyde, which removes at least a portion of the catalyst ligand and at least a portion of the heavy byproduct from the vapor stream; a liquid bottom stream containing the removed catalyst ligand, the removed heavy byproduct, and some of the aldehyde is recovered from the fractionator; a washed vapor stream is recovered from the fractionator; a first portion of the washed vapor stream is condensed to produce the liquid aldehyde, which is then refluxed back to the fractionator; And a second portion of the washed vapor stream is recovered as a product aldehyde stream, wherein the liquid bottom stream is conveyed to a separation system to separate at least some aldehydes from the liquid bottom stream to produce a recovered aldehyde stream containing the separated aldehydes and a waste stream containing the removed catalyst ligands and the removed heavy byproducts.

2. The method according to claim 1, wherein the temperature at the bottom of the fractionator does not exceed 140°C.

3. The method according to claim 1 or claim 2, wherein the separation system comprises a distillation column.

4. The method of claim 3, wherein the temperature at the bottom of the distillation column is higher than the temperature at the bottom of the fractionator.

5. The method of claim 3, wherein the pressure in the distillation column is lower than the pressure in the fractionator.

6. The method of claim 3, wherein the distillation column is operated such that the temperature at the bottom of the distillation column does not exceed 140°C.

7. The method according to claim 1 or claim 2, wherein the fractionator includes a reboiler.

8. The method of claim 7, wherein the reboiler is operated such that the temperature at the bottom of the fractionator is at least 90°C.

9. The method of claim 1 or claim 2, wherein the liquid bottom stream contains at least 50% by weight of aldehyde.

10. The method of claim 1 or claim 2, wherein the recovered aldehyde stream is recycled to a point upstream of the fractionator in the process.

11. The method according to claim 1 or claim 2, wherein the catalyst ligand comprises an organophosphorus ligand.

12. The method according to claim 1 or claim 2, wherein the catalyst ligand comprises triphenylphosphine.

13. The method according to claim 1 or claim 2, wherein the catalyst ligand has a vapor pressure of at least 0.01 mbar at 160°C.

14. The method according to claim 1 or claim 2, wherein the aldehyde is a C3 to C6 aldehyde.

15. The method of claim 1 or claim 2, wherein the method further comprises forming the vapor stream by conveying a liquid output stream from the hydroformylation process to a separator and recovering the vapor stream from the separator, the liquid output stream comprising the aldehyde, the catalyst, the catalyst ligand, and the heavy byproduct.

16. The method of claim 15, wherein the hydroformylation process comprises feeding a catalyst, the catalyst ligand, an olefin, and carbon monoxide into one or more hydroformylation reactors; reacting the olefin with the carbon monoxide to form the aldehyde and the heavy byproduct; and recovering the liquid output stream comprising the aldehyde, the catalyst, the catalyst ligand, and the heavy byproduct.

17. The method of claim 1 or claim 2, wherein the method further comprises transferring the aldehyde in the aldehyde product stream to one or more reactors for: hydrogenating 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 acrolein; or aldol condensation of the aldehyde to produce acrolein, followed by hydrogenation of the acrolein to an aliphatic alcohol.

18. The method of claim 17, wherein the method comprises transferring 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 acrolein, followed by liquid-phase hydrogenation of the acrolein to an aliphatic alcohol.

19. The method of claim 17, wherein the method comprises purifying the aliphatic alcohol, the aliphatic amine, the aliphatic acid, or the acrolein.

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