Process for separating heavy by-products and catalytic ligands (LIGANs) from aldehyde-containing vapor streams.

Abstract

A process for separating heavy by-products and catalytic ligands from a vapor stream comprising aldehydes, heavy by-products, and catalytic ligands is disclosed. The process includes passing the vapor stream to a fractionation unit where the vapor stream is contacted with a liquid aldehyde to remove at least a portion of the catalytic ligands and at least a portion of the heavy by-products from the vapor stream, recovering a liquid bottoms stream from the fractionation unit comprising the removed catalytic ligands, the removed heavy by-products, and a portion of the aldehydes, recovering a scrubbed vapor stream from the fractionation unit, condensing a first portion of the scrubbed vapor stream to produce liquid aldehydes for reflux to the fractionation unit, and recovering a second portion of the scrubbed vapor stream as a product aldehyde stream. Passing the liquid bottoms stream to a separation system to separate at least a portion of the aldehydes from the liquid bottoms stream to produce a recovered aldehyde stream comprising the separated aldehydes and a waste stream comprising the removed catalytic ligands and the removed heavy by-products.

Description

Technical Field

[0001] The present invention relates to a process for separating heavy by-products and catalyst ligands from a vapor stream containing aldehyde. In particular, but not exclusively, the present invention relates to a process for separating heavy by-products and catalyst ligands from a vapor stream containing aldehyde formed by sending a liquid output stream (containing aldehyde, catalyst, catalyst ligand, and heavy by-products) from a hydroformylation process to a vaporizer and recovering the vapor stream from the vaporizer.

Background Art

[0002] The production of aldehydes by hydroformylation of olefins is a well-known process. Aldehydes can be used in various downstream reactions such as hydrogenation of aldehydes to produce aliphatic alcohols, amination of aldehydes to produce aliphatic amines, oxidation of aldehydes to produce aliphatic acids, and aldol condensation reactions to produce acrolein, for example for use in the production of plasticizers. Hydroformylating an olefin to an aldehyde and subsequently hydrogenating the aldehyde to produce an aliphatic alcohol is a well-known use of aldehydes. An example of such a process is the LP Oxo SM process provided by Johnson Matthey and Dow. Hydroformylation is carried out in the liquid phase using a homogeneous rhodium catalyst modified with an organic phosphorus ligand. Examples of such ligands and processes are disclosed in U.S. Patent Nos. 4,148,830, 4,717,775, and 4,769,498. Organic phosphines and phosphites, particularly organic monophosphines, bisphosphines, tetraphosphines, monophosphites, and bisphosphites are preferred organic phosphorus ligands. The present invention may be particularly useful when the ligand has a vapor pressure of at least 0.01 mbar at 160 °C. The present invention may be particularly useful when the ligand contains triphenylphosphine (TPP) or triphenylphosphine oxide (TPPO), particularly when the ligand contains TPP.

[0003] In a typical process, one or more hydroformylation reactors produce a product stream containing an aldehyde and a homogeneous catalyst. The aldehyde is separated from the catalyst by vaporization, the vaporized aldehyde remains in the vapor phase, and the catalyst liquid remains as a liquid for recirculation to one or more hydroformylation reactors. Vaporization is typically operated to prevent excessive carryover of catalyst ligands in the vaporized aldehyde. However, it can be difficult to prevent ligands from being retained at the top of the column in the vaporized aldehyde at concentrations that could be problematic in downstream hydrogenation. For example, carryover ligands can harm the catalyst used in downstream hydrogenation. This can be particularly problematic in liquid-phase hydrogenation, where in gas-phase hydrogenation, the vaporization of the feedstock to hydrogenation can potentially be used to remove the carryover ligands. Even low concentrations of carryover ligands can harm the catalyst. Ligands with a vapor pressure of 0.01 mbar or higher at 160°C can result in unacceptable carryover.

[0004] Various solutions have been proposed to reduce ligand carryover. For example, as described in U.S. Patent No. 5110990, a dispersion such as the product aldehyde can be injected into the vaporized aldehyde stream to condense the vaporized ligand, and then the vaporized ligand can be separated in a vapor-liquid separator. A problem associated with such equipment is that heavy by-products in the aldehyde product vapor are also condensed by the dispersion. Therefore, recirculating the ligand leads to the accumulation of heavy by-products. It has been suggested that careful control of the dispersion can promote ligand condensation while avoiding the condensation of heavy by-products, but this is difficult to achieve in practice and is prone to problems. All modifications result in either problematic ligand carryover due to insufficient ligand condensation, or accumulation of heavy by-products due to over-condensation of these by-products. The accumulation of heavy by-products can be problematic because it may require vaporizer operation at higher temperatures, which can lead to even higher ligand carryover. Using purging from catalyst recirculation to remove accumulated heavy by-products can lead to rhodium loss.

[0005] Further proposed solutions are disclosed in U.S. Patent Application Publication No. 2018305285. In this system, the vaporized aldehyde product stream is brought into contact with a partial condenser to condense phosphorus ligands and by-products in the vaporized aldehyde product stream, and up to 10% by weight of the vaporized aldehyde product stream is condensed. The condensed phosphorus ligands and by-products are separated from the condensed aldehyde in a purification column, and the aldehyde is re-vaporized in the purification column and recycled back into the vaporized aldehyde product stream. In some embodiments, the condensed phosphorus ligands and by-products are not returned to the process, thus avoiding the accumulation of heavy by-products. In some embodiments, the phosphorus ligands may be separated from the heavy by-products in a separate distillation system and recycled. While such systems can avoid the accumulation of heavy by-products, the partial condenser only provides a single theoretical stage, and therefore there are limitations to the achievable ligand removal efficiency from the vaporized aldehyde product stream.

[0006] Further proposed solutions are disclosed in U.S. Patent No. 4,792,636. This disclosure provides a rhodium complex hydroformylation catalyst containing (i) carbon monoxide and rhodium complexed with a ligand, (ii) an excess ligand, and (iii) at least one optionally substituted C7-C 17 (iv) aldehyde condensate products containing optionally substituted C6-C 16 From the liquid hydroformylation product medium obtained by rhodium-catalyzed hydroformylation of olefins, optionally substituted C7-C 17 A process is provided to recover the aldehyde, and this process is (a) Degassing the liquid hydroformylating medium, (b) The degassed liquid hydroformylated medium is subjected to at least one C7-C 17 Passing the material through an evaporation zone maintained under temperature and pressure conditions that induce aldehyde evaporation, (c) Recovering the liquid catalyst-containing flow from the evaporation zone, (d) Cooling the catalyst-containing flow leaving the evaporation zone, (e)(i) At least one optionally substituted C7~C 17 (ii) an aldehyde, and (iii) a small amount of the aldehyde condensation product, to recover the vapor stream from the evaporation zone. (f) Sending the steam flow to the fractional distillation zone, (g) From the fractional distillation zone, (i) at least one type of C7~C 17 (ii) recover the vapor product stream containing the aldehyde, and the liquid bottom stream containing the ligand and the aldehyde condensate product. (h) Recirculating at least a portion of the cooled catalyst-containing flow from step (d) and the liquid bottom flow from step (g) to the hydroformylation zone.

[0007] At least a portion of the liquid bottom flow can be recycled to the hydroformylation zone. Alternatively, the bottom flow recovered from the fractional distillation zone can be sent to the ligand recovery zone, where the ligands are separated from the aldehyde condensation products, for example, by fractional distillation, and the resulting separated ligands can be recycled to the hydroformylation zone. It is also possible to recycle a portion of the bottom product flow from the fractional distillation zone to the hydroformylation zone, process the remainder in the ligand recovery zone, and then recycle the ligands recovered from there.

[0008] In this scheme, any product aldehydes in the liquid bottom flow can be discarded. Attempts to reduce the concentration of product aldehydes in the liquid bottom flow can be made by operating the bottom of the fractional distillation zone at a higher temperature, but such methods can lead to the formation of excess heavy byproducts and even decomposition in the reboiler of the fractional distillation zone. The formation of heavy byproducts undesirably consumes aldehydes that would otherwise be recovered as the desired product. Any decomposition products can contaminate the aldehyde product leaving the fractional distillation zone. This scheme may also be impractical for shorter-chain aldehydes, where heavy byproducts, along with catalyst ligands, can form close boilers.

[0009] In processes involving distillation columns for separating aldehyde isomers, such as a butanal isomer column for separating n-butanal from i-butanal, all carryover TPP can be removed within the isomer column. For example, the apparatus described in International Publication No. 2017182780 removes carryover TPP in the first butanal isomer column, and therefore TPP will not be present in the feed sent to aldolization and subsequent hydrogenation, which could poison the catalyst. However, such apparatus is not economical when there is no commercial need to separate isomers.

[0010] Therefore, a more efficient and effective system is still needed to prevent ligand carryover in the vaporized aldehyde stream. Preferred embodiments of the present invention aim to overcome one or more of the above-mentioned drawbacks of the prior art. In particular, preferred embodiments of the present invention aim to provide an improved process for separating aldehydes from a hydroformylation product stream containing aldehydes, heavy by-products, and catalytic ligands. [Overview of the project]

[0011] According to a first aspect of the present invention, a process is provided for separating a catalyst ligand from a vapor stream containing an aldehyde, heavy by-products, and a catalyst ligand, the process comprising: sending the vapor stream to a fractional distillation unit, where the vapor stream is brought into contact with a liquid aldehyde to remove at least a portion of the catalyst ligand and at least a portion of the heavy by-products from the vapor stream; recovering a liquid bottom stream containing the removed catalyst ligand, the removed heavy by-products, and a portion of the aldehyde from the fractional distillation unit; recovering a washed vapor stream from the fractional distillation unit; condensing a first portion of the washed vapor stream to produce a liquid aldehyde for reflux to the fractional distillation unit; and recovering a second portion of the washed vapor stream as a product aldehyde stream, wherein the liquid bottom stream is sent to a separation system to separate at least a portion of the aldehyde from the liquid bottom stream to produce a recovered aldehyde stream containing the separated aldehyde, and a waste stream containing the removed catalyst ligand and the removed heavy by-products.

[0012] A more flexible system can be formed by sending the bottom liquid flow to a separation system and separating at least a portion of the aldehyde from the bottom liquid flow. For example, the system can be operated under conditions that reduce the possibility of heavy byproduct formation and potential decomposition, while the separation system can be operated under conditions that maximize the recovery of aldehyde in the recovered aldehyde flow. This can be advantageous because the fractional distillation unit handles a significantly larger flow rate and therefore a larger aldehyde inventory than the separation system, and therefore the formation of heavy byproducts and potential decomposition in the fractional distillation unit can cause more serious problems. Heavy byproducts can be formed in the reboiler, for example, by reactions involving aldehydes. Therefore, the formation of such heavy byproducts represents the loss of the desired aldehyde product. Furthermore, if decomposition occurs, the decomposition products can move upwards in the fractional distillation unit and contaminate the product aldehyde flow. Larger fractional distillation units can operate under more economical conditions, and this flexibility can also enable more economical performance because there is no loss of aldehyde products that would occur in operation under those conditions in conventional processes.

[0013] The second portion of the washed vapor stream can preferably be condensed together with the first portion and recovered as a liquid product aldehyde stream. The second portion of the washed vapor stream can preferably be recovered as a vapor stream by feeding the washed vapor stream into a partial condenser to condense the first portion, and then feeding it into a gas-liquid separator to separate the first and second portions.

[0014] The process preferably includes forming a vapor stream by sending a liquid output stream (containing aldehyde, catalyst, catalyst ligands, and heavy by-products) from the hydroformylation process to a separator, and recovering the vapor stream from the separator. The separator may be, for example, a membrane separator, but is preferably a vaporizer. The vaporizer may include, for example, a series heat exchanger and a knockout drum. The vapor stream preferably contains 50 to 99% by weight of the aldehyde sent to the vaporizer. The vapor stream typically contains a small portion of the catalyst ligands and heavy by-products sent to the vaporizer. For example, the liquid output stream from hydroformylation may contain 5% to 20% by weight of catalyst ligands, and the vapor stream preferably contains 5000 ppmw or less, preferably 2500 ppmw or less of catalyst ligands. As another example, up to 10% by weight of the catalyst ligands entering the vaporizer may be present in the vapor stream. For short-chain olefins such as C3 or less, preferably, 1% by weight or less of the catalyst ligands entering the vaporizer are present in the vapor stream. Preferably, the majority of the catalyst and catalyst ligands are recovered in the liquid stream within the vaporizer, typically at the bottom of the vaporizer, and preferably recycled to the hydroformylation process.

[0015] By sending the vapor stream to a fractional distillation unit that brings the vapor stream into contact with the liquid aldehyde, more efficient separation of ligands from the vapor stream can be achieved. This is because the fractional distillation unit provides opportunities for multiple theoretical stages. Preferably, the fractional distillation unit includes at least two theoretical stages, more preferably at least four theoretical stages. The theoretical stages may include theoretical stages for condensers associated with the fractional distillation unit. Using the liquid aldehyde condensed from the washed vapor stream as reflux to the fractional distillation unit is an efficient source of washing liquid that does not introduce further components into the system.

[0016] The bottom liquid flow is sent to a separation system, such as a distillation column, to separate at least a portion of the aldehyde from the bottom liquid flow, generating a recovered aldehyde flow containing the separated aldehyde and a waste flow containing the removed catalyst ligand and removed heavy by-products. Thus, the separated aldehyde, which is a useful product of hydroformylation, is not lost from the process. By not returning the removed heavy by-products to the process, the present invention prevents the accumulation of heavy by-products in the process. The use of a fractional distillation unit advantageously generates the bottom liquid flow as a separation flow, while also enabling efficient multi-theoretical stage separation to prevent the carryover of excess catalyst ligands to downstream processes. Conventional processes that do not generate a separation flow can lead to the accumulation of heavy by-products, while conventional processes using a single theoretical stage may be less efficient in removing catalyst ligands. Conventional processes in which aldehydes are not recovered from the liquid bottom flow require operation under conditions that result in undesirable aldehyde loss in the liquid bottom flow, or under conditions that minimize aldehydes in the liquid bottom flow but may result in aldehyde loss as a result of heavy byproduct formation in the fractional distillation unit, potentially leading to decomposition in the fractional distillation unit and contamination of the aldehyde product flow by decomposition products. The process of the present invention can also operate at a higher reflux ratio in the fractional distillation unit, thus increasing the proportion of catalyst ligands and heavy byproducts removed from the vapor flow. Without a separation system, a higher reflux ratio would either require harsher conditions, such as a fractional distillation unit reboiler operating at a higher temperature, to prevent higher concentrations of aldehydes in the liquid bottom flow, or result in higher concentrations of aldehyde loss.

[0017] The recovered aldehyde stream is preferably recycled back into the process. The recovered aldehyde stream is preferably recycled upstream of the fractional distillation unit. The recovered aldehyde stream may be recycled back into the fractional distillation unit. Preferably, the vapor stream is recovered from the vaporizer, and the recovered aldehyde stream is preferably recycled back into the vaporizer. If the vaporizer has a knockout drum, the recovered aldehyde stream is preferably recycled back into the knockout drum. If the recovered aldehyde stream is recycled back into the fractional distillation unit, it is preferably recycled back into the fractional distillation unit as a liquid reflux. In some embodiments, the recovered aldehyde stream may be combined with the product aldehyde stream, but this may be undesirable because the recovered aldehyde stream may contain some catalytic ligands due to incomplete separation in the separation system.

[0018] Preferably, the recovered aldehyde stream contains at least 90% by weight, more preferably at least 95% by weight, of aldehyde. A higher aldehyde content in the recovered aldehyde stream may increase the likelihood of using the stream. For example, if the aldehyde content is high, it may be more desirable to combine the recovered aldehyde stream with the product aldehyde stream.

[0019] The waste stream preferably contains 10% by weight or less, and more preferably 7.5% by weight or less, of aldehydes. Therefore, the waste of aldehydes, which are the desired products of this process, is kept low. The present invention advantageously benefits from a low bottom temperature in the fractional distillation unit while achieving such low concentrations of aldehydes in the waste stream. The waste stream is preferably sent to waste, thus ensuring that the removed heavy by-products are not returned to the process where they could accumulate.

[0020] If the separation system includes a distillation column, the distillation column preferably includes a reboiler and a reflux condenser. It may also be advantageous to have a reboiler in the fractional distillation unit. Since the separation system recovers aldehydes from the liquid bottom flow, aldehyde losses are advantageously minimized even in the absence of a reboiler in the fractional distillation unit. However, the aldehydes recovered in the separation system are typically recycled upstream, for example, to an upstream hydrogenation reactor where the aldehydes act as a diluent (potentially meaning that the reactor needs to be larger to handle the additional flow rate). By providing a reboiler in the fractional distillation unit, it is advantageous to be able to send more aldehydes to the liquid bottom flow than would be desirable in the prior art apparatus, for example, at a lower temperature, and advantageously reduce the risk of heavy by-products or decomposition products forming in the reboiler, but nevertheless, it is possible to provide flexibility in operating the reboiler in a way that avoids sending excess amounts of aldehydes to the separation system for recycling. By providing a reboiler in the fractional distillation unit, the present invention can obtain the further advantage of reducing the dilution of the upstream process by recirculated aldehydes, while maintaining the advantage of reducing the formation and decomposition of heavy by-products. Having a reboiler in the fractional distillation unit also allows for an increase in the reflux ratio of the fractional distillation unit, and therefore, an increase in the proportion of catalyst ligands and heavy by-products removed from the vapor flow without increasing the amount of liquid aldehyde in the liquid bottom flow. Thus, it is possible to achieve the removal of more catalyst ligands and heavy by-product components while maintaining the advantages of the present invention described above. Providing a reboiler in the fractional distillation unit in conjunction with a separation system can increase process flexibility, for example, to deal with changes in the composition of the input flow, by providing an additional option for controlling the process. Thus, providing a reboiler can improve process flexibility and ease of operation.

[0021] The process includes at least partially condensing the washed vapor stream to produce liquid aldehydes for reflux to a fractional distillation unit. The process may include condensing the majority of the washed vapor stream, for example, by condensing essentially all of the aldehydes in the washed vapor stream in a condenser to produce a condensed stream, which is then divided to produce liquid aldehyde and product aldehyde streams for reflux to a fractional distillation unit. In this case, the product aldehyde stream is recovered as a liquid product aldehyde stream. Condensation may occur in a condenser, preferably subsequently in a knockout drum or other gas-liquid separator, to remove any light components that did not condense with the aldehydes. Alternatively, the process may include partially condensing the aldehydes in the washed vapor stream and separating the condensed aldehydes to produce liquid aldehydes for reflux to a fractional distillation unit from the uncondensable aldehydes recovered as a product aldehyde stream. Thus, the product aldehyde stream becomes a vapor product aldehyde stream. In such embodiments, partial condensation may be performed, preferably in a fractional condenser, preferably subsequently in a knockout drum or other gas-liquid separator, to separate the liquid aldehyde from the steam-product aldehyde stream for reflux to a fractional distillation unit. The steam-product aldehyde stream may then be condensed in a further condenser, preferably subsequently in a knockout drum or other gas-liquid separator, to remove all light components that did not condense with the aldehyde, thereby producing a liquid-product aldehyde stream. Such a device may be particularly attractive as an addition to an existing plant, and therefore the present invention may include methods for modifying a plant to install such a device. An existing plant has an existing condenser for condensing a steam stream, and the existing condenser can preferably be used as a further condenser with little to no modification. The fractional distillation unit and fractional condenser, as well as other equipment related to the present invention, would be installed upstream of the existing condenser.

[0022] Preferably, the vapor stream contains at least 80 wt% aldehyde, more preferably at least 90 wt% aldehyde. The vapor stream may contain at least 0.5 wt% heavy by-products, or at least 1 wt% heavy by-products, or at least 2 wt% heavy by-products. Preferably, the vapor stream contains 10 wt% or less heavy by-products, more preferably 5 wt% or less heavy by-products. The present invention can be particularly advantageous when the vapor stream contains at least 10 ppmw of catalyst ligands, and can be even more advantageous when the vapor stream contains at least 20 ppmw of catalyst ligands. If not removed, such concentrations of catalyst ligands can cause significant poisoning problems in downstream catalysts, particularly downstream hydrogenation catalysts. 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 5000 ppmw or less of catalyst ligands, more preferably 2500 ppmw or less of catalyst ligands. The vapor stream may also contain other contaminants such as olefins, paraffins, alcohols and further contaminants, particularly light (i.e., lighter than aldehyde) contaminants.

[0023] The product aldehyde stream preferably contains 10 ppmw or less of catalyst ligands, more preferably 5 ppmw or less, even more preferably 1 ppmw or less of catalyst ligands. Preferably at least 95 wt%, more preferably at least 97 wt%, even more preferably at least 99 wt%, even more preferably at least 99.5 wt% of the catalyst ligands in the vapor stream are removed in the fractionation apparatus. Such high levels of catalyst ligand removal, and thus low levels of catalyst ligands in the product aldehyde stream, may be possible in an economic way due to the efficiency of removal in the fractionation apparatus.

[0024] The bottoms stream may contain at least 5 wt% of heavy by-products, or at least 10 wt% of heavy by-products. The bottoms stream may contain at least 60 wt% of heavy by-products and may contain at least 80 wt% of heavy by-products. Advantageously, however, the present invention may enable the fractionation device to operate in a manner such that more aldehyde enters the bottoms stream. Thus, the bottoms stream preferably contains 50 wt% or less of heavy by-products. Preferably, the bottoms stream contains at least 25 wt%, more preferably at least 50 wt% of aldehyde. Such higher aldehyde concentrations typically result from milder conditions at the bottom of the fractionation device and are associated with the advantages of reduced heat load and avoidance of the formation and decomposition reactions of undesirable heavy by-products.

[0025] Preferably, the reflux ratio of the fractionation device is at least 0.05, more preferably at least 0.1. The reflux ratio is the mass flow rate of the liquid aldehyde refluxed to the fractionation device divided by the mass flow rate of the aldehyde product stream. The reflux ratio is preferably 0.5 or less. A higher reflux ratio, for example at least 0.1, can be particularly advantageously used in the present invention because the separation system prevents excessive aldehyde losses.

[0026] When a reboiler is used in the fractionation device, the reboiler preferably operates such that the bottom temperature of the fractionation device is at least 90 °C. The reboiler preferably operates such that the bottom temperature of the fractionation device is 140 °C or less. By operating at such temperatures, it is possible to advantageously re-vaporize a portion of the aldehyde and introduce it into the fractionation device while avoiding undesirable losses of aldehyde due to the formation of heavy by-products or the formation of contaminants due to decomposition reactions.

[0027] The above operating conditions can be particularly advantageous when the catalyst ligand is TPP and the aldehyde contains C3 - C6 aldehydes, especially butyraldehyde.

[0028] Preferably, the separation system includes a distillation column. The distillation column preferably operates such that the bottom temperature of the distillation column is higher than the bottom temperature of the fractionation unit. Preferably, the distillation column operates such that the bottom temperature of the distillation column is 140°C or less. The bottom temperature of the distillation column is preferably at least 90°C, more preferably at least 100°C. It is preferable that the bottom temperature of the distillation column is higher than the bottom temperature of the fractionation unit. A lower bottom temperature of the fractionation unit reduces the risk of formation or decomposition of heavy by-products in the fractionation unit that processes higher flow rates of material, while a higher bottom temperature of the distillation column increases the recovery of aldehydes into the recovered aldehyde stream. The bottom temperature of the distillation column is preferably at least 10°C, more preferably at least 20°C, and even more preferably at least 30°C higher than the bottom temperature of the fractionation unit.

[0029] The pressure in the distillation column is preferably at least 0.3 bara. The pressure in the distillation column is preferably 1.2 bara or less. The pressure in the distillation column is preferably lower than the pressure in the fractionation unit. Preferably, the pressure in the distillation column is at least 0.1 bar, preferably at least 0.2 bar, and more preferably at least 0.5 bar lower than the pressure in the fractionation unit. Lower pressure typically means an increase in equipment size, but the distillation column handles lower flow rates than the fractionation unit and therefore can still be a smaller part of the equipment. Lower pressure is advantageous in that it allows for the separation of more aldehydes into the recovered aldehyde stream without requiring temperatures at which heavy by-product formation or decomposition can occur. Therefore, since the fractionation unit can operate at higher pressures, the fractionation unit can be economically sized, and some of the aldehydes can be flowed into the liquid bottom stream, handling lower flow rates, and therefore a smaller distillation column in any case operates at lower pressures and achieves good aldehyde recovery without aldehyde loss due to heavy by-product formation or contamination by decomposition products.

[0030] The reflux ratio of the distillation column is preferably at least 0.1. Preferably, the reflux ratio of the distillation column is 1.2 or less. Such conditions, particularly the combination of temperature, pressure, and reflux ratio ranges, can be particularly advantageous for recovering aldehydes from the recovered aldehyde stream without aldehyde loss due to the formation of heavy by-products or contamination of the recovered aldehyde stream with catalytic ligands or decomposition products. Such conditions may be particularly suitable when the catalytic ligand is TPP and the aldehyde is a C3-C6 aldehyde.

[0031] The catalyst ligand preferably contains an organophosphorus ligand. The organophosphorus ligand is preferably an organophosphine or organophosphine, particularly an organomonophosphine, organobisphosphine, organotetraphosphine, organomonophosphine, or organobisphosphine. The present invention may be particularly useful when the ligand has a vapor pressure of at least 0.01 mbar at 160°C. The present invention may be particularly useful when the ligand contains triphenylphosphine (TPP) or triphenylphosphine oxide (TPPO), particularly when the ligand contains TPP.

[0032] The aldehyde is preferably a C3-C6 aldehyde. More preferably, the aldehyde includes butyraldehyde or varelualdehyde, and most preferably, the aldehyde includes butyraldehyde.

[0033] In some embodiments, the vapor stream may further contain ligand decomposition products, which themselves may be organic phosphorus compounds such as organic monophosphines, organic bisphosphines, organic tetraphosphines, organic monophosphites, or organic bisphosphites. The ligand decomposition products may be separated together with the catalytic ligands. Some ligand decomposition products may act as catalytic ligands themselves, and therefore, the catalytic ligands may themselves be decomposition products of other catalytic ligands.

[0034] Those skilled in the art will be familiar with the formation of heavy by-products in the chemical processes that form aldehydes. Heavy by-products typically include aldehyde condensation products such as aldehyde dimers and trimers. Aldehyde condensation products may also include tetramers.

[0035] Those skilled in the art will be familiar with various fractionation apparatus designs, including filled bed and tray designs. A fractionation apparatus can be a scrubber.

[0036] The separation system preferably includes fractional distillation equipment such as a distillation column, but it may also be another type of separation system, such as a membrane separation system.

[0037] Preferably, the process involves sending the aldehyde product stream to one or more reactors to hydrogenate the aldehyde to produce an aliphatic alcohol, aminating the aldehyde to produce an aliphatic amine, oxidizing the aldehyde to produce a fatty acid, or producing acrolein by an aldol condensation reaction. Preferably, the process involves purifying the aliphatic alcohol, aliphatic amine, fatty acid, or acrolein by distillation, for example, in one or more columns. Acrolein can preferably be hydrogenated in liquid-phase hydrogenation to an alcohol, preferably 2-ethylhexanol or 2-propylhexanol, most preferably 2-ethylhexanol (preferably then purified). Most preferably, the process involves sending the aldehyde product stream to one or more reactors to hydrogenate the aldehyde to produce an aliphatic alcohol, preferably butanol. Preferably, the process involves purifying the alcohol by distillation, for example, in one or more columns. Hydrogenation is preferably liquid-phase hydrogenation. The present invention may be particularly useful when there is a downstream liquid hydrogenation of either an aldehyde or acrolein produced by the aldol condensation of an aldehyde. This is because the catalyst for liquid hydrogenation is particularly susceptible to poisoning by the catalytic ligand.

[0038] The process preferably includes sending a liquid output stream (containing an aldehyde, catalyst, catalyst ligand, and heavy by-products) from a hydroformylation process to a separator to form a vapor stream, and recovering the vapor stream from the separator. The separator is preferably a vaporizer and may comprise, for example, a heat exchanger and a knockout drum arranged in series. The hydroformylation process preferably includes supplying a catalyst, catalyst ligand, olefin, and carbon monoxide to one or more hydroformylation reactors, reacting the olefin with carbon monoxide to form an aldehyde and heavy by-products, and recovering a liquid output stream containing the aldehyde, catalyst, catalyst ligand, and heavy by-products. The carbon monoxide is preferably contained in the synthesis gas. Therefore, the process preferably comprises supplying a catalyst, a catalyst ligand, an olefin, and carbon monoxide to one or more hydroformylation reactors; reacting the olefin with carbon monoxide to form an aldehyde and heavy by-products; recovering a liquid output stream containing the aldehyde, catalyst, catalyst ligand, and heavy by-products; sending the liquid output stream to a separator and recovering a vapor stream from the separator, wherein the vapor stream contains an aldehyde, preferably at least 50% by weight of an aldehyde, a small portion of the catalyst ligand, and a small portion of the heavy by-products; and sending the vapor stream to a fractional distillation unit, where the vapor stream is brought into contact with the liquid aldehyde, thereby recovering at least the catalyst ligand from the vapor stream. The process includes removing some and at least some of the heavy by-products, recovering the liquid bottom stream containing the removed catalyst ligands, removed heavy by-products, and some of the aldehydes from the fractional distillation unit, recovering the washed vapor stream from the fractional distillation unit, condensing a first portion of the washed vapor stream to produce liquid aldehydes for reflux to the fractional distillation unit, and recovering a second portion of the washed vapor stream as a product aldehyde stream, wherein the liquid bottom stream is sent to a separation system to separate at least some of the 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 removed heavy by-products.

[0039] Preferably, the process comprises recovering a liquid stream from a separator, the liquid stream containing the majority of the catalyst and catalyst ligands, and recirculating the liquid stream to one or more hydroformylation reactors. The catalyst preferably contains rhodium. When the stream is said to contain the majority of the component, the stream 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 amount of the component supplied to the separator; when the stream is said to contain a small portion of the component, the stream may contain 25% by weight or less, more preferably 10% by weight or less, more preferably 5% by weight or less, and even more preferably 1% by weight or less of the amount of the component supplied to the separator.

[0040] A second aspect of the present invention provides an aliphatic alcohol, aliphatic amine, fatty acid, or acrolein obtained by a process according to the first aspect of the present invention. Preferably, the aliphatic alcohol, aliphatic amine, fatty 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, preferably 2-ethylhexanol or 2-propylhexanol, most preferably 2-ethylhexanol, obtained by hydrogenating acrolein obtained by a process according to the first aspect of the present invention is provided.

[0041] It will be understood that features described in relation to one aspect of the present invention may be equally applicable to other aspects of the present invention. Some features may not be applicable to a particular aspect of the present invention and may be excluded from that particular aspect. [Brief explanation of the drawing]

[0042] Now, with reference to the attached diagrams, embodiments of the present invention will be described as examples, not in a restrictive sense.

[0043] [Figure 1] The comparison process is shown. [Figure 2]The comparison process is shown. [Figure 3] The comparison process is shown. [Figure 4] The comparison process is shown. [Figure 5] This is the process according to the present invention. [Figure 6] This is another process according to the present invention. [Figure 7] This is another process according to the present invention. [Figure 8] This is another process according to the present invention.

[0044] The comparison process is a process for comparison with the present invention and does not necessarily have to be a prior art process. [Modes for carrying out the invention]

[0045] The following process examples were simulated using Aveva Simsci ProII. Those skilled in the art will understand that the use of simulation packages is a well-established method for evaluating processes in the chemical field.

[0046] Figure 1 shows a reference process that includes a vaporizer 50 equipped with a heat exchanger 50a and a knockout drum 50b, and a condenser 52, but does not include a fractional distiller. In this process, Rh / TPP catalytic propylene hydroformylation using a liquid catalyst recirculation scheme produces a flow containing 2.5 wt% propylene and propane, 70 wt% butyraldehyde, 15 wt% heavy by-products, 11.9 wt% TPP, with the remainder being non-condensable gases, catalyst, and butanol. This feed 1 is fed into vaporizer 50 operating at 1.2 bara and 130°C, where approximately 70 wt% of the feed is vaporized to produce a vapor flow 2 containing 3.5 wt% propylene and propane, 93.7 wt% butyraldehyde, 2.4 wt% heavy by-products, as well as non-condensable gases, butanol, and approximately 1300 ppmw of TPP. The vapor stream 2 is supplied to a condenser 52 operating at 40°C, generating a liquid / vapor condenser outlet stream 4, which is sent to a knockout drum 53, generating a liquid aldehyde product stream 7 containing approximately 1315 ppmw of TPP. The non-condensable vapor is discharged into the exhaust stream 5. The liquid stream 9 recirculates the catalyst and TPP ligand for hydroformylation.

[0047] Figure 2 shows a process similar to Figure 1, but further including a fractional distillation unit 51. In Figure 2, feed 1 (having the above composition) is fed into a vaporizer 50 equipped with a heat exchanger 50a and a knockout drum 50b to produce a vapor flow 2. The vapor flow 2 is fed into a fractional distillation unit 51 having four theoretical stages. The fractional distillation unit 51 operates at a pressure of 1.1 bara and has a bottom temperature of 78°C. The fractional distillation unit 51 receives reflux of the condensed top distillate (reflux flow 6) to provide a reflux ratio of 0.3. The vapor flow 3 is fed into a condenser 52 operating at 40°C to produce a liquid / vapor condenser outlet flow 4, which is sent to a knockout drum 53. The non-condensable vapor is discharged into an exhaust flow 5, and the remaining liquid is split into reflux 6 and a liquid aldehyde product flow 7 containing less than 1 ppb of TPP. In practice, this concentration of TPP is below the detection limit. The bottom liquid flow 18 of the fractional distillation unit contains approximately 75% by weight of butyraldehyde and is recirculated to the knockout drum 50b of the vaporizer 50. Substantially all of the heavy byproducts vaporized in the vaporizer 50 return to the liquid flow 9 via the bottom liquid flow 18 and the knockout drum 50b, and are returned to the catalyst recirculation. This leads to further accumulation of heavy byproducts in the catalyst solution, and therefore the temperature of the vaporizer 50 must be further increased until the removal of heavy byproducts is equal to the formation of heavy byproducts. In this scenario, the heavy byproducts cannot escape and may continue to accumulate in the catalyst solution until purging is performed, for example, from the liquid flow 9. However, performing such purging is undesirable because it can result in the loss of rhodium, which is costly to replace.

[0048] Therefore, an alternative embodiment may be as shown in Figure 3. In this figure, items with similar numbering are the same as in Figures 1 and 2 and will not be described again here, but the liquid bottom stream 8 is sent to the waste. In this way, heavy by-products do not accumulate. However, as in Figure 2, the entire liquid bottom stream 8 containing about 75 wt% butyraldehyde is sent to the waste. The reflux ratio in the fractional distillation unit 51 needs to be sufficiently large in order to keep the TPP concentration in the aldehyde product stream 7 sufficiently low, so the amount of butyraldehyde that is discarded can be quite large.

[0049] In Figure 4, items with similar numbering are the same as in Figures 1-3 and will not be explained again here, but the fractional distillation unit 51 includes a reboiler 54. The reboiler 54 concentrates the liquid bottom flow 38 by re-vaporizing the aldehyde and returning it to the fractional distillation unit 51. The fractional distillation unit 51 operates at the same reflux ratio as described for Figures 2 and 3, and the liquid aldehyde product flow 7 contains less than 1 ppb of TPP. The reboiler 54 is controlled to provide an aldehyde concentration of 5 wt% in the liquid bottom flow 38 to minimize aldehyde loss. The liquid bottom flow 38 is not recirculated but is purged as wastewater. The reboiler 54 operates at a temperature of 163°C. At such high reboiler temperatures and low aldehyde concentrations, controlling the reboiler can be difficult because the boiling point of the liquid changes significantly with even slight changes in aldehyde concentration. This can lead to unstable reboiler operation. Furthermore, such high temperatures tend to form heavier byproducts, leading to aldehyde loss and, in some cases, decomposition of the heavy byproducts. Such decomposition is undesirable because it can produce lighter byproducts that tend to contaminate the aldehyde product stream.

[0050] In Figure 5, the process according to the present invention includes a separation system 155 after the fractional distillation unit 151. A feed stream 101 having the same source and composition as feed stream 1 described above is fed to a vaporizer 150 equipped with a heat exchanger 150a and a knockout drum 150b to produce a steam stream 102, which is sent to the fractional distillation unit 151 as described above with respect to feed stream 1, vaporizer 50, steam stream 2, and fractional distillation unit 51 in the previous figures. The fractional distillation unit 151 operates at a reflux ratio of 0.3 and a bottom temperature of 78°C. As in Figures 2 to 4, the washed steam stream 103 is recovered from the top of the fractional distillation unit 151 and sent to the condenser 152. The condenser 152 condenses most of the washed steam stream 103, including substantially all of the aldehydes in the washed steam stream 103, to produce a liquid / steam condenser outlet stream 104, which is sent to the knockout drum 153, from which the non-condensable steam is discharged into the exhaust stream 105. The remaining liquid is split into reflux stream 106 and liquid aldehyde product stream 107. Liquid aldehyde stream 107 contains less than 1 ppb of TPP. Liquid bottom stream 108 contains 75 wt% butyraldehyde. Liquid bottom stream 108 is sent to a separation system, which in this embodiment includes a further fractionation unit in the form of a distillation column 155 operating at 0.5 bara, a reflux ratio of 0.1, and a bottom temperature of 124°C for the distillation column 155. The distillation column 155 comprises a reboiler 156, a condenser 158, and a knockout drum 157. Waste stream 188 is recovered from the bottom of the distillation column 155. Waste stream contains 5 wt% butyraldehyde. Waste stream 188 is sent to waste. From the top of the distillation column 155, a recovered aldehyde stream 118 containing butyraldehyde and possibly trace amounts of TPP and heavy by-products is recovered. In this embodiment, the recovered aldehyde stream 118 is recycled to the knockout drum 150b of the vaporizer 150. The recovered aldehyde stream 118 may also be recycled at other points in the process. In some embodiments, the recovered aldehyde stream 118 may be combined with the product aldehyde stream 107.

[0051] The concentration of butyraldehyde in the waste stream 118 in this embodiment is the same as in the embodiment described above in relation to Figure 4. However, this concentration is achieved at a bottom temperature of 78°C in the fractional distillation unit 151 and a bottom temperature of 124°C in the distillation column 155, compared to a temperature of 163°C in the reboiler 54 of the fractional distillation unit 51 in Figure 4. Lower temperatures may be advantageous, for example, by reducing the heat load and therefore the operating cost, by reducing aldehyde loss due to the formation of heavy by-products, and / or by reducing contamination from decomposition products. This process also has the advantage that the distillation column 155 is physically separated from the fractional distillation unit 151 and therefore can operate independently of the fractional distillation unit 151, unlike the reboiler 54 in Figure 4. By supplying the liquid bottom flow 108 from the fractionation unit 151 to the distillation column 155, the distillation column 155 can operate almost independently of the fractionation unit 151, and therefore any difficulties in operating the reboiler 156 in the distillation column 155 do not affect the operation of the fractionation unit 151. This allows for the separation of cumbersome equipment from the main series of operations, thereby simplifying the main series of operations.

[0052] The results of the above examples are summarized in the table below.

[0053] [Table 1]

[0054] The process described in Figure 5 clearly demonstrates that, compared to other processes, it requires a lower load while achieving excellent aldehyde product flow 107 specifications, reducing the risk of aldehyde loss due to the formation of heavy by-products, lowering the risk of contamination, and improving operability.

[0055] In Figure 6, items with similar numbering are the same as in previous figures and will not be explained again here, but the process is similar to the process in Figure 5, except that this time the fractional distillation unit 151 includes a reboiler 154. Therefore, the resulting liquid bottom flow 138 may have a lower aldehyde content compared to the flow 108 in Figure 5. Advantageously, the presence of the reboiler 154 in the fractional distillation unit 151 and the reboiler 156 in the distillation column 155 provides greater operational flexibility. This allows for an optimal balance between maintaining the bottom temperature of the fractional distillation unit 151 low enough to prevent the formation and decomposition of heavy by-products and maintaining it high enough to somewhat reduce the aldehyde content in the liquid bottom flow 138. The distillation column 155 recovers the aldehyde from the liquid bottom flow 138, and the recovered aldehyde flow 118 is typically recirculated to the knockout drum 150b of the vaporizer 150, from where it is recirculated to the hydroformylation reactor. This recirculation prevents aldehyde loss, thus achieving the advantage of the present invention of preventing aldehyde loss during purging while using a temperature that reduces aldehyde loss due to the formation of heavy by-products and contamination by decomposition products. However, recirculating large amounts of aldehyde through the upstream hydroformylation reactor can undesirably dilute the reactants in the hydroformylation reactor. Having a reboiler 154 in the fractionation unit 151 and a reboiler 156 in the distillation column 155 is advantageous in that it can enable optimal mitigation of contamination by the formation and decomposition of heavy by-products while avoiding excessive dilution by recirculated aldehydes.

[0056] In Figure 7, items with similar numbering are the same as in previous figures and will not be explained again here, but the washed steam stream 103 is sent to the fractional condenser 162. The fractional condenser 162 condenses some of the aldehydes, which are returned to the fractional distillation unit 151 as reflux 166. The steam outlet stream 163 from the fractional condenser 162 is sent to a further condenser 152, where substantially all of the remaining aldehydes are condensed. The outlet stream 104 from the further condenser 152 is sent to a knockout drum 153, where it is separated into a steam exhaust stream 105 and a liquid product aldehyde stream 107. Such a device may be particularly attractive as an add-on because the plant has an existing condenser that condenses steam from the vaporizer 150, and this can be used as a further condenser 152 without significant modification. The fractional distillation unit 151 and fractional condenser 162 are then installed between the existing vaporizer 150 and the further condenser 152. The fractional reducer 162 shown in Figure 7 can also be used in other embodiments of the present invention, such as those described in relation to Figures 5, 6, or 8.

[0057] In Figure 8, items with similar numbering correspond to the processes in previous figures, and their descriptions are not repeated. A stream 201 containing propylene, carbon monoxide, rhodium, and TPP is supplied to the 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 supply stream to the vaporizer 150, equipped with a heat exchanger 150a and a knockout drum 150b. A vapor stream 102 and a liquid stream 109 are recovered from the vaporizer 150. The liquid stream 109 containing rhodium and TPP is recycled back into the hydroformylation reactor 250. The vapor stream 102 is processed in the fractional distillation unit 151 as described in relation to previous figures. The liquid product aldehyde stream 107, along with the hydrogen-containing stream 202, is sent to the hydrogenation reactor 251. In the hydrogenation reactor 251, butyraldehyde from the liquid product aldehyde stream 107 reacts with hydrogen from the hydrogen stream 202 to form butanol, which is recovered in the butanol product stream 207. The butanol product stream 207 is then subjected to a purification step, typically by distillation, to recover butanol of the desired purity.

[0058] The embodiments described above are provided as examples only, and not in any restrictive sense, and it will be understood by those skilled in the art that various changes and modifications are possible without departing from the scope of the invention as defined by the appended claims. For example, the olefin may be butylene, and the aldehyde may be varelualdehyde. In another example, the hydrogenation reactor 251 may be replaced with an amination reactor for producing an aliphatic amine, an oxidation reactor for producing an aliphatic acid, or an aldol condensation reaction for producing acrolein which can then be fed to the hydrogenation reactor to produce an alcohol, and the hydrogen stream 202 may be replaced with other reaction streams as will be apparent to those skilled in the art. The vaporizer 150 comprises a heat exchanger 150a and a knockout drum 150b, but other designs of the vaporizer may be used, for example, to produce a vapor stream 102.

Claims

1. A process for separating heavy by-products and catalyst ligands from a vapor stream containing an aldehyde, the heavy by-products, and the catalyst ligands, The vapor stream is formed by sending a liquid output stream containing the aldehyde, catalyst, catalyst ligand, and heavy by-product from the hydroformylation process to a separator, and then recovering it from the separator. The process includes: sending the vapor stream to a fractional distillation unit that contacts the vapor stream with a liquid aldehyde; removing at least a portion of the catalyst ligand and at least a portion of the heavy by-products from the vapor stream; recovering a liquid bottom stream containing the removed catalyst ligand, the removed heavy by-products, and a portion of the aldehyde from the fractional distillation unit; recovering a washed vapor stream from the fractional distillation unit; condensing a first portion of the washed vapor stream to generate the liquid aldehyde for reflux to the fractional distillation unit; and recovering a second portion of the washed vapor stream as a product aldehyde stream. A process comprising: sending the liquid bottom flow to a separation system to separate at least some of the aldehydes from the liquid bottom flow to produce a recovered aldehyde flow containing the separated aldehydes, and a waste flow containing the removed catalyst ligands and the removed heavy by-products.

2. The process according to claim 1, wherein the bottom temperature of the fractional distillation apparatus is 140°C or less.

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

4. The process according to claim 3, wherein the bottom temperature of the distillation column is higher than the bottom temperature of the fractional distillation apparatus.

5. The process according to claim 3 or 4, wherein the pressure in the distillation column is lower than the pressure in the fractional distillation apparatus.

6. The process according to any one of claims 3 to 5, wherein the distillation column operates such that the bottom temperature of the distillation column is 140°C or less.

7. The process according to any one of claims 1 to 6, wherein the fractionation apparatus includes a reboiler.

8. The process according to claim 7, wherein the reboiler operates such that the bottom temperature of the fractional distillation apparatus is at least 90°C.

9. The process according to any one of claims 1 to 8, wherein the liquid bottom flow contains at least 50% by weight of an aldehyde.

10. The process according to any one of claims 1 to 9, wherein the recovered aldehyde stream is recycled to a point in the process upstream of the fractional distillation apparatus.

11. The process according to any one of claims 1 to 10, wherein the catalyst ligand includes an organophosphorus ligand.

12. The process according to any one of claims 1 to 11, wherein the catalyst ligand comprises triphenylphosphine.

13. The process according to any one of claims 1 to 12, wherein the catalyst ligand has a vapor pressure of at least 0.01 mbar at 160°C.

14. The aforementioned aldehyde is C ３ ~C ６ The process according to any one of claims 1 to 13, wherein the result is an aldehyde.

15. The hydroformylation process according to claim 1, comprising: supplying a catalyst, a catalyst ligand, an olefin, and carbon monoxide to one or more hydroformylation reactors; reacting the olefin with the carbon monoxide to form the aldehyde and the heavy by-products; and recovering the liquid output stream containing the aldehyde, the catalyst, the catalyst ligand, and the heavy by-products.

16. The process according to any one of claims 1 to 15, further comprising: sending the aldehyde in the aldehyde product stream to one or more reactors to hydrogenate the aldehyde to produce an aliphatic alcohol; aminating the aldehyde to produce an aliphatic amine; oxidizing the aldehyde to produce a fatty acid; aldol condensing the aldehyde to produce acrolein; or aldol condensing the aldehyde to produce acrolein, followed by hydrogenating the acrolein to an aliphatic alcohol.

17. The process according to claim 16, wherein the process comprises sending the aldehyde in the aldehyde product stream to one or more reactors to liquid-phase hydrogenate the aldehyde to produce an aliphatic alcohol, or aldol condensing the aldehyde to produce acrolein, and then liquid-phase hydrogenating the acrolein to an aliphatic alcohol.

18. The process according to claim 16 or 17, comprising purifying the aliphatic alcohol, the aliphatic amine, the fatty acid, or the acrolein.

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