CN121443574A - Hydroformylation process - Google Patents

Abstract

The process of the present invention is a continuous hydroformylation process comprising (a) removing a crude product from a reactor, (b) sending the crude product to a vaporizer, (c) separating the crude product in the vaporizer to produce a liquid stream comprising catalyst and a vapor phase stream, and (d) maintaining an average partial pressure of CO in the vaporizer of less than 15psia (103 kPa) at a reduced H _{2 2} level.

Description

Hydroformylation process

Background

The present invention relates to a hydroformylation process. More particularly, the present invention relates to such a process wherein the amount of heavies in the catalyst recycle stream is controlled. More particularly, the present invention relates to such a process wherein the loss of catalyst stability is minimized.

It is well known that aldehydes can be produced by reacting olefins with carbon monoxide and hydrogen in the presence of a metal-organophosphorus ligand complex catalyst, and that the preferred process involves continuous hydroformylation and recycling of a catalyst solution containing a metal-organophosphorus ligand complex catalyst, wherein the metal is selected from group 8, group 9 or group 10. Rhodium is the preferred group 9 metal. Examples of such methods are disclosed in US 4,148,830, US 4,717,775 and US 4,769,498. The resulting aldehydes can be used to produce a number of products including alcohols, amines, and acids. It is common practice to use an evaporator after the reaction zone to separate the product from the catalyst.

Hydroformylation catalysts comprising rhodium and an organophosphite ligand are known to be capable of very high reaction rates, see "rhodium catalyzed hydroformylation (Rhodium Catalyzed Hydroformylation)", "van Leeuwen, claver, kluwer Academic pub (2000). Such catalysts are of industrial applicability because they can be used to increase productivity, or to effectively hydroformylate internal olefins and/or branched internal olefins, which react slower than linear alpha olefins. However, it is also known, for example, from U.S. Pat. No.4,774,361, under certain conditions, these catalysts lose rhodium during the liquid recycle hydroformylation. The continuous loss of rhodium can significantly increase catalyst costs because rhodium is too expensive.

Although the exact cause of rhodium loss is not clear, it has been assumed in US 4,774,361 and elsewhere that this loss is exacerbated by the low concentration carbon monoxide (CO) and high temperature environment of typical product separation steps. US 6,500,991 describes a process to mitigate rhodium losses in an organophosphite promoted process by cooling the concentrated catalyst after product removal and then adding CO to the concentrated stream. US 6,500,991 also describes adding CO to the depressurization/flash vessel prior to the separation step. For either option, the total pressure in the separation zone is taught to be less than or equal to 1 bar. Thus, the process of US 6,500,991 attempts to stabilize the catalyst before and after the separation zone without directly addressing the losses that may occur during the harsh environment of the separation step.

US 8,404,903 describes a means for removing aldehyde products at greater than atmospheric pressure while employing relatively moderate temperatures. However, this method provides no means of controlling the CO content other than changing the condenser temperature of the separation zone. Such control is limited to a narrow range of partial pressures of CO and requires expensive refrigeration units to regulate such large gas flows. At the maximum total pressure (100 psia) and mole percent CO (16%) described in US 8,404,903, a maximum CO partial pressure of 16psia is possible, although at this high pressure the separation zone productivity is unacceptably low, even for the removal of relatively volatile C ₅ aldehydes. This is due to the fact that an acceptable balance of evaporator temperature, recycle gas flow and total pressure is required to achieve acceptable product recovery and rhodium loss rates. US 8,404,903 focuses on the first two factors and mentions that the presence of CO in the recycle gas should be beneficial for the stability of the phosphite ligand, but does not mention slowing or preventing rhodium losses. US 8,404,903 is limited by the cooling temperature of the evaporator condenser, which may require a significant capital investment to achieve a low enough process fluid temperature to achieve the desired CO partial pressure.

WO2016089602A1 expands the process taught in US 8,404,903 by adding a CO-rich gas to the recycle gas to increase the CO partial pressure above 16psia while maintaining an acceptable total pressure. The added CO mainly displaces inert gases in the recycle stream, thus achieving a higher CO partial pressure. The patent also teaches that high levels of H ₂ are detrimental to catalyst life and that Table 3 shows in particular the effect of low CO/H ₂ ratios on catalyst stability.

WO2020240194 teaches the use of a membrane unit to separate the synthesis gas supply from the hydroformylation system to produce a CO-rich stream to be fed to the stripping gas evaporator, the improvement being that the H ₂ -rich stream is sent to the hydroformylation zone (in combination with a CO sweep from the evaporator vent). This teaches a means of generating a "highly CO-rich stream" as used in WO2016089602 for higher evaporator CO partial pressures (equal to or higher than 15psia (103 kPa)), and preferably hydrogen partial pressures of no more than 10psi (69 kPa).

US 8,404,903, WO2016089602A1 and WO2020240194 all relate to the use of a recycle gas stream in the evaporator and the use of purge off-gas (e.g. stream 25 in WO2016089602 A1) to control the composition of the stripping gas. In such a system, since CO is largely insoluble in the liquid phase removed from the evaporator condenser, most of the CO is recycled so it accumulates in the recycle gas (as taught in US 8,404,903) and if the WO2016089602A1 method is employed to further increase the CO partial pressure, only a small amount of CO needs to be added. All three methods focus only on controlling the CO partial pressure in the evaporator, but neglecting the accumulation of H ₂. In US 8,404,903, at lower condenser temperatures, the CO fraction rises, but the CO/H2 ratio falls (the relative amount of H ₂ increases faster than CO). WO2016089602A1 partially addresses this problem by directly adding a high CO content stream to increase the CO content to a partial pressure above 16psi, but this requires a total pressure well above 16psia, which is not optimal for higher molecular weight aldehydes.

As taught by van Leeuwen et al (organometallic (Organometalli) cs, 14, 34 (1995)) and Rush et al (kinetics and catalysis (KINETICS AND CATALYSIS), 50, 557 (2009)), for phosphite-based catalysts the reaction rate is positive in the H ₂ partial pressure, so the amount of H ₂ present typically remains high in the reaction zone until the point at which hydrogenation to alkanes becomes significant. There is no teaching of any adverse effect on catalyst stability due to the higher hydrogen content. Rush further teaches that at monophosphite to rhodium ratios exceeding 50:1, up to 250:1, there is no change in hydroformylation behavior, but does not mention any benefit to catalyst life at higher ratios. In US 4,277,627, for example for triphenylphosphine, an enhanced stability based on ligand: rh ratio is taught, but only in connection with the hydroformylation reaction, not in the evaporator for the phosphine.

Both US 4,277,627 and WO2020112373 teach the stabilization of rhodium-based hydroformylation catalysts for olefins, the latter being of particular interest in evaporators in which the olefin concentration is to be expected to be the lowest. However, WO2020112373 requires that unreacted olefin be present throughout the evaporator, which may represent an inefficient and/or substantial recycle of olefin. For highly reactive lower olefins such as ethylene, propylene and 1-butene having highly active hydroformylation catalysts, the amount of unreacted olefin present in the evaporator will be very low.

The ratio of CO to H ₂ in the evaporator stripping gas is a function of how much CO and H ₂ are fed with the stream from the hydroformylation zone (which is itself a function of the CO to H ₂ ratio in the synthesis gas feed in the reaction zone), the purge vent, the evaporator condenser temperature, the total pressure and the inert gases present in the feed stream (e.g., methane, alkanes, etc.), and the amount of any added CO or H ₂. For example, as the inert content increases at a constant total pressure, the CO content in the recycle gas stream will likely become lower. To compensate, the total pressure can be increased, but this will have a negative impact on the aldehyde evaporation process, resulting in catalyst degradation. An alternative is to increase the recycle gas flow to purge more inerts, but such increased flow risks catalyst entrainment losses and requires a larger condenser and recycle blower/compressor.

It has now been found that while a higher partial pressure of CO is desirable for catalyst stability, a lower partial pressure of hydrogen is desirable for CO partial pressures below 15psia and olefin concentrations low. This will be the case in evaporators of processes having lower molecular weight olefins, for example, where most, if not all, of the olefins have been converted (or evaporated). When the total pressure of the evaporator is kept low to enhance product evaporation at lower temperatures, there may be a lower partial pressure of CO, which is generally preferred for catalyst stability. Under these conditions, the CO partial pressure is low enough that an undesirable hydrogen driven catalyst deactivation process occurs in the evaporator.

In cases where it is not possible to have a sufficiently high partial pressure of CO to maintain stability due to equipment or other process limitations, we have found that higher ligand concentrations, especially higher ligand to transition metal ratios, can also be employed to moderate catalyst stability when operating at a partial pressure of CO of less than 15 psi.

In view of the drawbacks of the prior art, there remains a need for a process that is capable of separating aldehydes from rhodium-organophosphite hydroformylation catalysts at lower total pressures while reducing the loss of rhodium and/or catalyst activity with significantly reduced catalyst stabilization achieved by residual olefins and CO.

Disclosure of Invention

The process of the present invention is a continuous hydroformylation process comprising (a) removing a crude product from a reactor, (b) sending the crude product to an evaporator, (c) separating the crude product in the evaporator to produce a liquid stream comprising catalyst and a vapor phase stream, and (d) maintaining an average partial pressure of CO in the evaporator of less than 15psia (103 kPa) at a reduced H ₂ level.

In one embodiment, the step of maintaining the average CO pressure in the evaporator at less than 15psia (103 kPa) comprises one or more of the following three processes:

Feeding a crude product stream comprising one or more products, one or more heavy byproducts, a transition metal-organophosphite ligand complex catalyst, one or more unconverted reactants, and one or more inert lights to an evaporator, and

(B) Removing from the evaporator an overhead gas stream comprising one or more products, one or more unconverted reactants, one or more inert lights, hydrogen, carbon monoxide, and a portion of heavy byproducts, and feeding the overhead gas stream to a condenser, and

(C) Removing a condenser overhead gas stream from the condenser, the condenser overhead gas stream comprising one or more unconverted reactants and one or more inert lights, and

(D) Recycling at least a portion of said condenser overhead gas stream to the evaporator and/or reaction zone, and

(E) Introducing a gas stream comprising CO into the evaporator in addition to the condenser overhead gas stream such that the average CO partial pressure in the evaporator is less than 15psia (103 kPa);

Wherein the molar ratio of CO to H ₂ in the added gas stream is higher than that present in step (b), and

Wherein the total evaporator pressure, the partial pressure of CO and the partial pressure of H ₂ are controlled by the fraction of the condenser overhead gas stream recycled in step (d), and

(F) A liquid recycle catalyst stream comprising transition metal-organophosphite ligand complex catalyst and the balance of the heavy by-product is removed from the evaporator as a tail stream.

Feeding a crude product stream comprising one or more products, one or more heavy byproducts, a transition metal-organophosphite ligand complex catalyst, one or more unconverted reactants, and one or more inert lights to a depressurization zone, wherein a gaseous purge is removed and a liquid phase is sent to an evaporator;

Wherein the depressurization zone removes undissolved H ₂ and optionally inert gas such that the amount of H ₂ introduced into the evaporator is reduced to allow for reduced total evaporator pressure, and

(B) Removing from the evaporator an overhead gas stream as a heel comprising one or more products, one or more unconverted reactants, one or more inert lights, hydrogen, carbon monoxide, and a portion of the heavy byproducts, and feeding said overhead gas stream to a condenser, and

(C) Removing a condenser overhead gas stream from the condenser, the condenser overhead gas stream comprising one or more unconverted reactants and one or more inert lights, and

(D) Recycling at least a portion of said condenser overhead gas stream to the evaporator and/or reaction zone, and

(E) Introducing a gas stream comprising CO into the evaporator in addition to the condenser overhead gas stream such that the average CO partial pressure in the evaporator is less than 15psia (103 kPa);

wherein the total evaporator pressure, the partial pressure of CO and the partial pressure of H ₂ are controlled by the fraction of the condenser overhead gas stream recycled in step (d), and

(F) A liquid recycle catalyst stream comprising transition metal-organophosphite ligand complex catalyst and the balance of the heavy by-product is removed from the evaporator as a tail stream.

Feeding a crude product stream comprising one or more products, one or more transition metal-organophosphite ligand complex catalysts, one or more unconverted reactants, and one or more inert lights to the heavy byproduct evaporator, and

(B) Removing from the evaporator an overhead gas stream comprising one or more products, one or more unconverted reactants, one or more inert lights, hydrogen, carbon monoxide, and a portion of the heavy byproducts, and feeding said overhead gas stream to a condenser, and

(C) Removing the condenser overhead gas stream from the condenser, the condenser overhead gas stream comprising one or more unconverted reactants and one or more inert lights, and

(D) Recycling at least a portion of said condenser overhead gas stream to the evaporator and/or reaction zone, and

(E) Introducing a gas stream comprising CO into the evaporator in addition to the condenser overhead gas stream such that the average CO partial pressure in the evaporator is less than 15psia (103 kPa);

wherein the total evaporator pressure, the partial pressure of CO and the partial pressure of H ₂ are controlled by the fraction of the condenser overhead gas stream recycled in step (d), and

(F) A liquid recycle catalyst stream comprising transition metal-organophosphite ligand complex catalyst and the balance of heavy by-products is removed from the evaporator as a tail stream.

Wherein the ratio of ligand to transition metal in the crude product stream in step (a) is greater than 20:1, the concentration of transition metal in the tail stream in step (f) is less than 100ppm, or both.

For example, for scheme 1, the analyzer measures the CO content (or partial pressure) of the recycle gas (at step (c) or (d)), and if the CO is below the target value, a CO-rich stream is added at step (e) (the stream has a CO: H ₂ ratio that is higher than the CO: H ₂ ratio of the recycle gas). This will cause the system pressure to increase, so the pressure controller will increase the evaporator vent to purge some of the gas, thereby maintaining a constant total pressure. All of this has the effect of increasing CO and decreasing other components (i.e., H ₂). The target CO partial pressure will be a function of equipment limitations such as total pressure, steam temperature (for the evaporator), cooling water and pressure of the CO-rich gas in step (e). The total pressure limit will be a function of other gases such as inert gases from the feed (e.g., N ₂ from the synthesis gas or unintentional hydrogenation of paraffins or olefins from the olefin feed). The stripping gas flow rate is set such that the evaporator temperature remains below the set limit (driven primarily by the available vapor and condenser cooling medium temperatures and avoiding excessive heavies formation and catalyst degradation). The amount of heat input (and temperature) is set by the evaporator feed to heel ("F/T") ratio, which is also a function of the available steam and the avoidance of undesirable side reactions. The prior art teaches that higher partial pressures of CO are preferred and that these pressures are not always economical to achieve, but current solutions also reduce the H ₂ content to achieve comparable catalyst stability. For example, as taught in US 8,404,903, higher condenser temperatures can result in higher aldehyde losses via purging, thus representing a loss of process efficiency, and refrigeration units representing high capital expenditures.

For scheme 2, the flash tank reduces the total amount of high pressure gas introduced into the evaporator and removes a significant amount of H ₂ that may exceed the amount of CO present. Hydrogen has a lower solubility in the liquid matrix than CO and is therefore rich in CO relative to H ₂ in the residual gas introduced into the vaporisation zone via the liquid phase. The flash tank is typically operated at a significantly elevated pressure compared to the evaporator, so the condenser (not shown in fig. 2) can better minimize aldehyde product losses. Removing a majority of the non-condensable gases enables easier operation of the evaporator and reduces the flow lost through the evaporator condenser exhaust gas, which operates at a lower pressure than the flash tank. The reduced flow and lower total pressure promote CO accumulation while maintaining H ₂ concentration and exhaust losses at low levels.

In scheme 3, it was surprisingly found that a higher ligand to rhodium ratio not only provides a higher rate, but also higher stability. Assuming that the rhodium loss rate is due to the formation of catalytically inactive multimetal sites (and thus rhodium concentration may be positive order), lower rhodium concentrations should produce slower deactivation at the expense of lower hydroformylation rates. However, combining a higher rate due to increased ligand concentration with a lower starting rhodium concentration counteracts the rate of decrease due to lower rhodium concentration, so both factors give the same rate, but with higher catalyst stability.

For embodiment 3, higher ligand concentrations may be used up to the point of solubility problem (see mainly in the evaporator bottoms recycle line, such as stream 13 in fig. 1). Changing the concentration of phosphite ligands is typically done simply by adding additional ligands to increase the concentration or allowing the natural ligand to decompose and evaporation losses to continue without the need for conventional replenishment. Direct introduction of an oxidizing agent (e.g., O ₂ or peroxide) may also be used, but is generally not preferred. Also, reducing rhodium concentration is generally not preferred because expensive rhodium will need to be recovered, although it may be slowly reduced by normal entrainment losses through the evaporator, and no conventional periodic rhodium recharge charge is performed. Thus, a preferred embodiment is to initiate the catalyst in the reaction zone at a high ligand to rhodium ratio such as above 20:1, preferably above 40:1, with rhodium concentrations below 100ppm, and preferably below 60ppm, and most preferably below 40ppm.

As process conditions for the evaporation of C ₃ and higher aldehydes, superatmospheric pressure in the evaporator is generally avoided. Thus, surprisingly, good transition metal-organophosphite catalyst stability was observed even at moderate partial pressure of CO in the super-atmospheric environment of the evaporator, while allowing removal of high boiling aldehydes and aldehyde condensation products at moderate temperatures. Lower H ₂ concentrations at these modest CO partial pressures are a key parameter for this discovery, and furthermore, a tradeoff is made between higher rates and higher ligand: transition metal and lower transition metal levels to achieve comparable overall production rates with less transition metal loss.

Drawings

Fig. 1 is a schematic flow chart of one embodiment of the method of the present invention.

Figure 2 is a schematic flow chart of another embodiment of the method of the present invention.

Detailed Description

The hydroformylation process generally comprises contacting CO, H ₂, and at least one olefin in the presence of a catalyst comprising a transition metal and a hydrolyzable ligand as components under hydroformylation conditions sufficient to form at least one aldehyde product. Optional process components include amines and/or water.

All the mentioned periodic Table of the elements and the various groups therein are the versions published in the Handbook of CRC chemistry and Physics (CRC Handbook of CHEMISTRY AND PHYSICS), 72 nd edition, (1991-1992), CRC Press (CRC Press), pages I-11.

Unless stated to the contrary, or implied from the context, all parts and percentages are based on weight and all test methods are up to date by the date of filing of the present application. For purposes of U.S. patent practice, the contents of any reference to a patent, patent application, or publication are incorporated by reference in their entirety (or an equivalent U.S. version thereof is so incorporated by reference), especially with respect to the disclosure of definitions and general knowledge in the art, without inconsistent with any definitions specifically provided in this disclosure.

As used herein, "a", "an", "the", "at least one" and "one or more" are used interchangeably. The terms "comprising," "including," and variations thereof, when used in the specification and claims, are not to be construed as limiting. Thus, for example, an aqueous composition comprising particles of "one" hydrophobic polymer may be interpreted to mean that the composition comprises particles of "one or more" hydrophobic polymers.

Also herein, the recitation of numerical ranges by endpoints includes all numbers subsumed within that range (e.g., 1 to 5 includes 1, 1.5, 2, 2.75, 3, 3.80, 4, 5, etc.). For the purposes of the present invention, it is to be understood that a numerical range is intended to include and support all possible subranges included within that range, consistent with the understanding of those skilled in the art. For example, a range from 1 to 100 is intended to convey from 1.01 to 100, from 1 to 99.99, from 1.01 to 99.99, from 40 to 60, from 1 to 55, etc. Further, in this document, recitations of numerical ranges and/or values, including such recitations in the claims, are to be understood to include the term "about". In such cases, the term "about" refers to a range of values and/or values that are substantially the same as the range of values and/or values described herein.

As used herein, the terms "ppm" and "ppmw" mean parts per million by weight. When referring to the concentration of transition metal in the catalyst solution, it refers to the weight of metal (excluding ligand, if any) divided by the mass of the remainder of the solution (including solvent, free ligand, reactants, and impurities).

For the purposes of the present invention, the term "hydrocarbon" is intended to include all permissible compounds having at least one hydrogen and one carbon atom. Such permissible compounds also have one or more heteroatoms. In a broad aspect, permissible hydrocarbons include acyclic (with or without heteroatoms) and cyclic, branched and unbranched, carbocyclic and heterocyclic, aromatic and nonaromatic organic compounds which can be substituted or unsubstituted.

As used herein, unless otherwise indicated, the term "substituted" is intended to include all permissible substituents of organic compounds. In a broad aspect, permissible substituents include acyclic and cyclic, branched and unbranched, carbocyclic and heterocyclic, aromatic and nonaromatic substituents of organic compounds. Illustrative substituents include, for example, alkyl, alkoxy, aryl, aryloxy, hydroxyalkyl, aminoalkyl, wherein the number of carbons can range from 1 to 20 or more, preferably from 1 to 12, and hydroxy, halo, and amino. For suitable organic compounds, the permissible substituents can be one or more and the same or different. The present invention is not intended to be limited in any way by the permissible substituents of organic compounds.

The terms "reaction fluid", "reaction medium" and "catalyst solution" are used interchangeably herein and may include, but are not limited to, mixtures comprising (a) metal-organophosphorus ligand complex catalyst, (b) free organophosphorus ligand, (c) aldehyde product formed in the reaction, (d) unreacted reactants, (e) solvents for the metal-organophosphorus ligand complex catalyst and the free organophosphorus ligand, and optionally (f) one or more phosphate compounds formed in the reaction (which may be homogeneous or heterogeneous, and these compounds include those that adhere to surfaces of process equipment). The reaction fluid may encompass, but is not limited to, (a) a fluid in the reaction zone, (b) a fluid stream flowing to the separation zone, (c) a fluid in the separation zone, (d) a recycle stream, (e) a fluid discharged from the reaction zone or separation zone, (f) a discharged fluid treated with an aqueous buffer solution, (g) a treated fluid returned to the reaction zone or separation zone, (h) a fluid in an external cooler, and (i) ligand breakdown products and salts thereof.

A "hydrolyzable phosphorus ligand" is a trivalent phosphorus ligand containing at least one P-Z bond, where Z is oxygen, nitrogen, chlorine, fluorine or bromine. Examples include, but are not limited to, phosphites, phosphinites-phosphites, bisphosphites, phosphonites, phosphinites, phosphoramidites, phosphinites-phosphoramidites, bisphosphinamides, fluorophosphites, and the like. The ligand may include a chelating structure and/or may contain multiple P-Z moieties, such as polyphosphites, polyphosphazenes, and the like, and mixed P-Z moieties, such as phosphite-phosphoramidites, fluorophosphites-phosphites, and the like.

As used herein, the term "complex" refers to a coordination compound formed by the combination of one or more electron rich molecules or atoms (i.e., ligands) with one or more electron poor molecules or atoms (i.e., transition metals). For example, organophosphorus ligands useful herein have a phosphorus (III) donor atom with a pair of unshared electrons capable of forming a coordinate covalent bond with the metal. The multi-organophosphorus ligands employable herein have two or more phosphorus (III) donor atoms, each atom having a pair of unshared electrons, each of which is capable of forming a coordinate covalent bond with a transition metal independently or possibly in concert (e.g., via chelation). Carbon monoxide may also be present and complexed with the transition metal. The final composition of the complex catalyst may also contain additional one or more ligands as described above, such as hydrogen, mono-olefins or anions meeting the coordination sites or nuclear charges of the metal.

For the purposes of the present invention, the term "heavy by-product" is used interchangeably with "heavy" and refers to a hydroformylation process liquid by-product having a normal boiling point at least 25 ℃ higher than the normal boiling point of the desired product of the hydroformylation process. In hydroformylation reactions, for example, when the reactants comprise one or more olefins, the desired product typically comprises one or more isomeric aldehydes as well as heavies.

For the purposes of the present invention, the terms "feed ratio heel" and "feed to heel ratio" are used interchangeably and refer to the mass of the reaction fluid entering the separation zone relative to the mass of the concentrated effluent (evaporator heel) exiting the bottom of the separation zone and returning to the first hydroformylation reactor. Referring to fig. 1, this is the mass ratio of stream 4 to stream 13. "feed ratio heel" is an indicator of the rate at which volatiles such as aldehyde products are removed from the reaction fluid. For example, "feed heel ratio" of 2 means that the weight of the reaction fluid entering the separation zone is twice greater than the weight of the concentrated effluent returned to the first reactor.

For the purposes of the present invention, the terms depressurization zone, "knock-out pot," "separation vessel," and "flash vessel" are used interchangeably and refer to the low pressure section between the reaction zone and the evaporator. The flash vessel allows for rapid degassing of the reaction fluid and facilitates control of the evaporator partial pressure. The flash vessel also removes any entrained bubbles from the liquid phase, which may transport more H ₂ than simply dissolving H ₂ in the liquid phase from the hydroformylation reaction zone. Such vessels are typically maintained at a pressure and temperature that is much lower than the pressure and temperature established in the hydroformylation reactor.

For the purposes of the present invention, the term "light weight" refers to a material having a normal boiling point of 25 ℃ or less at atmospheric pressure. As used herein, the term "inert lights" or "light inerts" refers to lights that are substantially unreactive in the process. "reactive lights" refers to lights that are largely reactive in the process. For example, in a hydroformylation process, reactive lights include carbon monoxide and hydrogen, while inert lights include alkanes, such as those present in the olefins fed to the reaction, and other inert gases, such as nitrogen.

"Substantially constant pressure" and like terms mean at a substantially constant pressure or within a pressure differential of 1 bar (100 kPa) or less, preferably 0.5 bar (50 kPa) or less. In other words, in one embodiment of the invention, the maximum pressure differential across the product phase stripper and the product condenser is 1 bar (100 kPa) or less, preferably 0.5 bar (50 kPa) or less.

The terms "evaporator," "stripping gas evaporator," "stripper," and "product phase stripper" are used interchangeably herein and refer to a separation device that employs a stripping gas to aid in separating components of a product-containing stream from a product.

As used herein, the term "average CO partial pressure" means the average carbon monoxide partial pressure measured at the vapor outlet of the vaporizer over a period of at least 10 minutes under steady state operation. It is well known to use Gas Chromatography (GC) to determine mole% CO in a gas composition, and then calculate the CO partial pressure by measuring the total pressure and using raoult's law.

As used herein, the term "average H ₂ partial pressure" means the average hydrogen partial pressure measured at the vapor outlet of the evaporator over a period of at least 10 minutes under steady state operation. It is well known to determine the mole% of H ₂ in a gas composition using Gas Chromatography (GC) and then calculate the hydrogen partial pressure by measuring the total pressure and using Raoult's law.

The hydrogen and carbon monoxide may be obtained from any suitable source including petroleum cracking and refinery operations. Synthesis gas mixtures are the preferred sources of hydrogen and CO for the hydroformylation reaction zone.

Synthesis gas (from synthesis gas) is the name for a gas mixture containing varying amounts of CO and H ₂. The production process is well known. Hydrogen and CO are typically the main components of the synthesis gas, but the synthesis gas may contain CO ₂ and inert gases such as N ₂ and Ar. The molar ratio of H ₂ to CO varies widely, but typically ranges from 1:100 to 100:1, and is preferably between 1:10 and 10:1. Synthesis gas is commercially available and is typically used as a fuel source or as an intermediate in the production of other chemicals. The most preferred H ₂ to CO molar ratio for chemical production is between 3:1 and 1:3, and is generally targeted between about 1:2 and 2:1 for most hydroformylation applications.

Substituted or unsubstituted olefin reactants useful in the hydroformylation process include optically active (prochiral and chiral) and non-optically active (achiral) olefinically unsaturated compounds containing from 2 to 40, preferably from 3 to 30, more preferably from 4 to 20, carbon atoms. These compounds are described in detail in US 7,863,487. Such olefinically unsaturated compounds may be terminally or internally unsaturated and may be of linear, branched or cyclic structure, as well as olefin mixtures, such as olefin mixtures obtained from dimerization of mixed butenes, oligomerization of propylene, butenes, isobutenes, etc. (such as so-called dimerization, trimerization or tetrapropylenes, etc., as disclosed, for example, in US 4,518,809 and 4,528,403).

Prochiral and chiral olefins useful in asymmetric hydroformylation are useful in the production of enantiomeric aldehyde mixtures. Illustrative optically active or prochiral olefin compounds useful in asymmetric hydroformylation are described, for example, in U.S. Pat. nos. 4,329,507, 5,360,938 and 5,491,266.

Solvents are advantageously employed in the hydroformylation process. Any suitable solvent that does not unduly interfere with the hydroformylation process may be used. Suitable solvents for use in the transition metal catalyzed hydroformylation process include, for example, those disclosed in U.S. Pat. Nos. 3,527,809, 4,148,830, 5,312,996, and 5,929,289. In rhodium-catalyzed hydroformylation processes, aldehyde compounds corresponding to the desired aldehyde product to be produced and/or higher boiling aldehyde liquid condensation byproducts (e.g., as may be produced in situ during the hydroformylation process) may be preferably employed as the primary solvent, as described, for example, in US 4,148,380 and US 4,247,486. Due to the nature of the continuous process, the primary solvent will generally ultimately comprise the aldehyde product and higher boiling aldehyde liquid condensation byproducts ("heavies"). The amount of solvent is not particularly critical and need only be sufficient to provide the desired amount of transition metal concentration to the reaction medium. Typically, the amount of solvent ranges from about 5 wt% to about 95 wt% based on the total weight of the reaction fluid. Mixtures of solvents may be employed.

Illustrative metal-organophosphorus ligand complexes that can be used in such hydroformylation reactions include metal-organophosphorus ligand complex catalysts. These catalysts and their methods of preparation are well known in the art and include those disclosed in the patents mentioned herein. Typically, such catalysts may be preformed or formed in situ and comprise a metal in complex combination with an organophosphorus ligand, carbon monoxide and optionally hydrogen. The exact structure of the catalyst is not known.

The metal-organophosphorus ligand complex catalyst may be optically active or non-optically active. The metal may include group 8, 9 and 10 metals selected from rhodium (Rh), cobalt (Co), iridium (Ir), ruthenium (Ru), iron (Fe), nickel (Ni), palladium (Pd), platinum (Pt), osmium (Os) and mixtures thereof, wherein preferred metals are rhodium, cobalt, iridium and ruthenium, more preferably rhodium, cobalt and ruthenium, especially rhodium. Mixtures of these metals may be used. Permissible organophosphorus ligands that make up the metal-organophosphorus ligand complex and free organophosphorus ligand include monoorganophosphorus ligands, diorganophosphorus ligands, triorganophosphorus ligands and higher polyorganophosphorus ligands. Mixtures of ligands may be used in the metal-organophosphorus ligand complex catalyst and/or the free ligand, and such mixtures may be the same or different. In one embodiment of the invention, mixtures of mono-and organopolyphosphite (e.g., bisphosphite) ligands may be used.

The organophosphorus compounds that can act as ligands and/or free ligands of the metal-organophosphorus ligand complex catalyst can be of the achiral (optically inactive) or chiral (optically active) type and are well known in the art. Achiral organophosphorus ligands are preferred.

Among the organophosphorus ligands useful as ligands for metal-organophosphorus ligand complex catalysts, there are mono-, di-, tri-and organopolyphosphites. Such organophosphorus ligands and methods for their preparation are well known in the art.

Representative monoorganophosphites may include those having the formula:

Wherein R ¹⁰ represents a substituted or unsubstituted trivalent hydrocarbon group containing 4 to 40 or more carbon atoms, such as trivalent acyclic and trivalent cyclic groups, for example trivalent alkylene groups such as those derived from 1, 2-trimethylol propane and the like, or trivalent cycloalkylene groups such as those derived from 1,3, 5-trihydroxy cyclohexane and the like. Such monoorganophosphites can be described in more detail in, for example, US 4,567,306.

Representative diorganophosphites may include those having the formula:

Wherein R ²⁰ represents a substituted or unsubstituted divalent hydrocarbon group containing 4 to 40 carbon atoms or more, and W represents a substituted or unsubstituted monovalent hydrocarbon group containing 1 to 18 carbon atoms or more.

Representative substituted and unsubstituted monovalent hydrocarbon groups represented by W in formula (II) above include alkyl groups and aryl groups, and representative substituted and unsubstituted divalent hydrocarbon groups represented by R ²⁰ include divalent acyclic groups and divalent aromatic groups. Illustrative divalent acyclic groups include, for example, alkylene-oxy-alkylene, alkylene-S-alkylene, cycloalkylene, and alkylene-NR ²⁴ -alkylene, where R ²⁴ is hydrogen or a substituted or unsubstituted monovalent hydrocarbon group, such as an alkyl group having 1 to 4 carbon atoms. More preferred divalent acyclic groups are divalent alkylene groups such as more fully disclosed, for example, in U.S. patent 3,415,906 and 4,567,302, and the like. Illustrative divalent aromatic radicals include, for example, arylene, bisarylene, arylene-alkylene-arylene, arylene-oxy-arylene, arylene-NR ²⁴ -arylene, wherein R ²⁴ is as defined above, arylene-S-arylene, arylene-S-alkylene, and the like. More preferably, R ²⁰ is a divalent aromatic group, such as disclosed more fully, for example, in U.S. patent nos. 4,599,206, 4,717,775, 4,835,299, and the like.

More preferred classes of diorganophosphites are those of the formula:

Wherein W is as defined above, each Ar is the same or different and represents a substituted or unsubstituted aryl group, each y is the same or different and has a value of 0 or 1, Q represents a divalent bridging group selected from the group consisting of-C (R ³³)₂-、-O-、-S-、-NR²⁴-、Si(R³⁵)₂ and-CO-, wherein each R ³³ is the same or different and represents hydrogen, an alkyl group having 1 to 12 carbon atoms, phenyl, tolyl, and anisoyl, R ²⁴ is as defined above, each R ³⁵ is the same or different and represents hydrogen or methyl, and m has a value of 0 or 1, such diorganophosphites are described in more detail, for example, in U.S. Pat. Nos. 4,599,206;4,717,775, and 4,835,299.

Representative triorganophosphites may include those having the formula:

Wherein each R ⁴⁶ is the same or different and is a substituted or unsubstituted monovalent hydrocarbon radical, for example, alkyl, cycloalkyl, aryl, alkylaryl, and arylalkyl radicals, which can contain from 1 to 24 carbon atoms. Illustrative triorganophosphites include, for example, trialkyl phosphites, dialkylaryl phosphites, alkyldiaryl phosphites, triaryl phosphites and the like, such as trimethyl phosphite, triethyl phosphite, butyldiethyl phosphite, xylene phosphite, triphenyl phosphite, trinaphthyl phosphite, bis (3, 6, 8-tri-tert-butyl-2-naphthyl) methyl phosphite, bis (3, 6, 8-tri-tert-butyl-2-naphthyl) cyclohexyl phosphite, tris (3, 6-di-tert-butyl-2-naphthyl) phenyl phosphite, bis (3, 6, 8-tri-tert-butyl-2-naphthyl) phenyl phosphite and bis (3, 6, 8-tri-tert-butyl-2-naphthyl) (4-sulfonylphenyl) phosphite and the like. The most preferred triorganophosphite is triphenyl phosphite. Such triorganophosphites are described in more detail, for example, in U.S. Pat. Nos. 3,527,809 and 5,277,532.

Representative organopolyphosphites contain two or more tertiary (trivalent) phosphorus atoms and may include those having the formula:

Wherein X represents a substituted or unsubstituted n-valent organic bridging group containing from 2 to 40 carbon atoms, each R ⁵⁷ is the same or different and represents a divalent organic group containing from 4 to 40 carbon atoms, each R ⁵⁸ is the same or different and represents a substituted or unsubstituted monovalent hydrocarbon group containing from 1 to 24 carbon atoms, a and b can be the same or different and each have a value of from 0 to 6, provided that the sum of a+b is from 2 to 6 and n is equal to a+b. It will be appreciated that when a has a value of 2 or greater, each R ⁵⁷ group may be the same or different. Each R ⁵⁸ group may also be the same or different in any given compound.

Representative n-valent (preferably divalent) organic bridging groups represented by X and representative divalent organic groups represented by R ⁵⁷ described above include acyclic and aromatic groups such as alkylene, alkylene-Q _m -alkylene, cycloalkylene, arylene, bisarylene, arylene-alkylene, and arylene- (CH ₂)_y-Q_m-(CH₂)_y -arylene, and the like, wherein each Q, y and m is defined as above in formula (III): more preferred acyclic groups represented by X and R ⁵⁷ above are divalent alkylene groups, and more preferred aromatic groups represented by X and R ⁵⁷ above are divalent arylene and bisarylene groups such as, for example, monovalent alkyl groups represented by R ⁵⁸ above more fully disclosed in U.S. Pat. Nos. 4,769,498;4,774,361;4,885,401;5,179,055;5,113,022;5,202,297;5,235,113;5,264,616;5,364,950 and 5,527,950.

Illustrative preferred organopolyphosphites may include bisphosphites such as those of formulas (VI) to (VIII) below:

Wherein each R ⁵⁷、R⁵⁸ and X of formulae (VI) to (VIII) is the same as defined above for formula (V). Preferably, each R ⁵⁷ and X represents a divalent hydrocarbon group selected from alkylene, arylene-alkylene-arylene, and bisarylene, and each R ⁵⁸ group represents a monovalent hydrocarbon group selected from alkyl and aryl. Such organic phosphite ligands of formulas (V) to (VIII) may be found, for example, in U.S. patent 4,668,651;4,748,261;4,769,498;4,774,361;4,885,401;5,113,022;5,179,055;5,202,297;5,235,113;5,254,741;5,264,616;5,312,996;5,364,950; and 5,391,801.

R ¹⁰、R²⁰、R⁴⁶、R⁵⁷、R⁵⁸, ar, Q, X, m and y in formulae (VI) to (VIII) are as defined above. Most preferably, X represents a divalent aryl- (CH ₂)_y-(Q)_m-(CH₂)_y -aryl) group, wherein each y has a value of 0 or 1, respectively; more preferably, each alkyl group of the R ⁵⁸ groups defined above may contain from 1 to 24 carbon atoms, and each aryl group of the Ar, X, R ⁵⁷ and R ⁵⁸ groups defined above of formulas (VI) to (VIII) may contain from 6 to 18 carbon atoms, and the groups may be the same or different, and the preferred alkylene groups of X may contain from 2 to 18 carbon atoms, and R ⁵⁷ may contain 5 to 18 carbon atoms, further, preferably, the divalent Ar group and the divalent aryl group of X of the above formula are phenylene, wherein the bridging group represented by- (CH ₂)_y-(Q)_m-(CH₂)_y -is bonded to the phenylene at a position ortho to the oxygen atom in the formula, it is also preferred that when present on such phenylene groups, any substituents are bonded at the para and/or ortho positions of the phenylene group relative to the oxygen atom to which the given substituted phenylene group is bonded.

Any of the R ¹⁰、R²⁰、R⁵⁷、R⁵⁸, W, X, Q, and Ar groups of such organophosphites of formulas (I) through (VIII) above may be substituted, if desired, with any suitable substituent containing from 1 to 30 carbon atoms that does not unduly adversely affect the desired results of the process of this invention. Except for corresponding hydrocarbon radicals such as alkyl, aryl, aralkyl, Substituents which may be present on the radicals may include, for example, silyl groups such as- -Si (R ³⁵)₃; amino groups such as- -N (R ¹⁵)₂; phosphino groups such as- -aryl-P (R ¹⁵)₂; acyl groups such as- -C (O) R ¹⁵; acyloxy groups such as- -OC (O) R ¹⁵; amido groups such as- -CON (R ¹⁵)₂ and- -N- (R ¹⁵)COR¹⁵; sulfonyl groups such as- -SO ₂ R¹⁵; alkoxy groups such as- -OR ¹⁵; sulfinyl groups such as- -SOR ¹⁵; phosphono groups such as- -P (O) (R ¹⁵)₂; and halo groups), Nitro, cyano, trifluoromethyl, hydroxy, etc., wherein each R ¹⁵ group independently represents the same or different monovalent hydrocarbon radicals having 1 to 18 carbon atoms (e.g., alkyl, aryl, aralkyl, etc.), Alkylaryl and cyclohexyl), provided that in amino substituents such as-N (R ¹⁵)₂, each R ¹⁵ taken together can also represent a divalent bridging group that forms a heterocyclic group with the nitrogen atom, and in amide substituents such as-C (O) N (R ¹⁵)₂ and-N (R ¹⁵)COR¹⁵, each N-bonded R ¹⁵ can also be hydrogen). it will be appreciated that any of the substituted or unsubstituted hydrocarbyl groups that make up a particular given organophosphite may be the same or different.

More specifically, illustrative substituents include primary, secondary and tertiary alkyl groups such as methyl, ethyl, n-propyl, isopropyl, butyl, sec-butyl, tertiary butyl, neopentyl (neo-pentyl), n-hexyl, pentyl (amyl), sec-pentyl, tertiary pentyl, isooctyl, decyl, octadecyl, and the like; aryl such as phenyl, naphthyl, and the like, aralkyl such as benzyl, phenethyl, triphenylmethyl, and the like, alkylaryl such as tolyl, xylyl, and the like, alicyclic such as cyclopentyl, cyclohexyl, 1-methylcyclohexyl, cyclooctyl, cyclohexylethyl, and the like, alkoxy such as methoxy, ethoxy, propoxy, tert-butoxy 、-OCH₂CH₂OCH₃、-O(CH₂CH₂) ₂OCH₃、-O(CH₂CH₂)₃OCH₃, and the like, aryloxy such as phenoxy, and the like, as well as silyl such as-Si (CH ₃)₃、-Si(OCH₃)₃、-Si(C₃H₇)₃, and the like; amino such as-NH ₂、-N(CH₃)₂、-NHCH₃、-NH(C₂H₅, and the like; arylphosphino such as-P (C ₆H₅)₂, and the like; acyl such as-C (O) CH ₃、-C(O)C₂H₅、-C(O)C₆H₅, carbonyloxy such as-C (O) OCH ₃, and the like; oxycarbonyl such as-O (CO) C ₆H₅, and the like; amide such as-CONH ₂、-CON(CH₃)₂、-NHC(O)CH₃, and the like; sulfonyl such as-S (O) ₂C₂H₅, and the like; sulfinyl such as-S (O) CH ₃, thio (sulfoyl) such as-SCH ₃、-SC₂H₅、-SC₆H₅, and the like; phosphono such as -P(O)(C₆H₅)₂、--P(O)(CH₃)₂、--P(O)(C₂H₅)₂、-P(O)(C₃H₇)₂、-P(O)(C₄H₉)₂、-P(O)(C₆H₁₃)₂、-P(O)CH₃(C₆H₅)、--P(O)(H)(C₆H₅), and the like.

Specific illustrative examples of such organophosphite ligands include the following: tris (2, 4-di-tert-butylphenyl) phosphite, 2-tert-butyl-4-methoxyphenyl (3, 3 '-di-tert-butyl-5, 5' -dimethoxy-1, 1 '-biphenyl-2, 2' -diyl) phosphite, methyl (3, 3 '-di-tert-butyl-5, 5' -dimethoxy-1, 1 '-biphenyl-2, 2' -diyl) phosphite, 6'- [ [3,3' -bis (1, 1-dimethylethyl) -5,5 '-dimethoxy- [1,1' -biphenyl ] -2,2 '-diyl ] bis (oxy) ] bis-dibenzo [ d, f ] [1,3,2] dioxaphosphine, 6' - [ [3,3', 5' -tetrakis (1, 1-dimethylethyl) -1,1 '-biphenyl ] -2,2' -diyl ] bis [ d, f ] [1,3,2] -dioxaphosphine, (2R) -bis [2,2'- (3, 3',5 '-dimethoxy- [1, 2' -biphenyl ] -2,2 '-diyl ] bis [ d, f ] [1,3,2] dioxaphosphine, (4R) -bis [3, 5' -dimethoxy- [1,2 '-diyl ] [2,2' -diphenyl ] -2,2 '-diyl ] [2, 4' -bis (oxy) ], f ] [1,3,2] dioxaphosph-6-yl ] oxy ] -3- (1, 1-dimethylethyl) -5-methoxyphenyl ] methyl ] -4-methoxy, methylenebis-2, 1-phenylenetetra [2, 4-bis (1, 1-dimethylethyl) phenyl ] phosphite, and [1,1 '-biphenyl ] -2,2' -diyl-tetrakis [2- (1, 1-dimethylethyl) -4-methoxyphenyl ] phosphite.

In one embodiment, the organic phosphite ligands include organobisphosphite ligands. In one embodiment, the ligand is a bidentate phosphoramidite ligand, such as a bidentate phosphoramidite ligand of the type disclosed in, for example, WO 00/56451 Al.

The metal-organophosphorus ligand complex catalyst may be in homogeneous or heterogeneous form. For example, preformed rhodium carbonyl-organophosphorus ligand catalysts may be prepared and introduced into the hydroformylation reaction mixture. More preferably, the rhodium-organophosphorus ligand complex catalyst may be derived from a rhodium catalyst precursor, which may be introduced into the reaction medium to form the active catalyst in situ. For example, rhodium catalyst precursors such as rhodium dicarbonyl acetylacetonate, rh ₂O₃、Rh₄(CO)₁₂、Rh₆(CO)₁₆、Rh(NO₃)₃, and the like can be introduced into the reaction mixture along with the organophosphorus ligand for in situ formation of the active catalyst. In a preferred embodiment rhodium dicarbonyl acetylacetonate is used as rhodium precursor and reacted with an organophosphorus ligand in the presence of a solvent to form a catalytic rhodium-organophosphorus ligand complex precursor which is introduced into the reactor together with an excess (free) organophosphorus ligand for in situ formation of the active catalyst. In any event, carbon monoxide, hydrogen and organophosphorus ligands are ligands capable of complexing with the metal and active metal-organophosphorus ligand catalysts are present in the reaction mixture under the conditions employed in the hydroformylation reaction. The carbonyl and organophosphorus ligands can be complexed with rhodium in situ prior to or during the hydroformylation process.

By way of illustration, a preferred catalyst precursor composition consists essentially of a solubilized rhodium carbonyl organophosphite ligand complex precursor, a solvent, and optionally free organophosphite ligand. Preferred catalyst precursor compositions can be prepared by forming a solution of rhodium dicarbonyl acetylacetonate, an organic solvent, and an organic phosphite ligand. As evidenced by the release of carbon monoxide gas, the organophosphorus ligand readily replaces one of the carbonyl ligands of the rhodium acetylacetonate complex precursor.

Thus, the metal-organophosphorus ligand complex catalyst advantageously comprises a metal complexed with carbon monoxide and an organophosphorus ligand, said ligand being bonded (complexed) to the metal in a chelating and/or non-chelating manner.

Mixtures of catalysts may be employed. The amount of metal-organophosphorus ligand complex catalyst present in the reaction fluid need only be the minimum amount necessary to provide the given metal concentration to be employed, and will at least provide the basis for the catalytic amount of metal necessary to catalyze the particular hydroformylation process involved (as disclosed, for example, in the above-identified patents). In general, for most processes, a concentration of catalytic metal (e.g., rhodium) in the range of from 5ppmw to 100ppmw calculated as free metal in the reaction medium should be sufficient, while it is generally preferred to employ from 10ppmw to 80ppmw of metal and more preferably from 20ppmw to 60ppmw of metal.

In addition to the metal-organophosphorus ligand complex catalyst, free organophosphorus ligand (i.e., ligand that does not complex with the metal) may also be present in the reaction medium. The free organophosphorus ligand may correspond to any of the organophosphorus ligands defined above. The free organophosphorus ligand is preferably the same organophosphorus ligand as the metal-organophosphorus ligand complex catalyst employed. However, such ligands need not be identical in any given process. The hydroformylation process of this invention may involve from 0.1 mole or less to 100 moles or more of free organophosphorus ligand per mole of metal in the reaction medium. Preferably, the hydroformylation process is carried out in the presence of from 1 to 50 moles of organophosphorus ligand per mole of metal in the reaction medium. More preferably, for organopolyphosphite, 1.1 mole to 4 moles of organopolyphosphite ligand per mole of metal is used. The amount of organophosphorus ligand is the sum of the amount of organophosphorus ligand present that binds (complexes) to the metal and the amount of free organophosphorus ligand present. If desired, additional organophosphorus ligand can be supplied to the reaction medium of the hydroformylation process at any time and in any suitable manner, e.g., to maintain a predetermined level of free ligand in the reaction medium.

The use of aqueous buffer solutions (such as in extraction systems) to prevent and/or reduce hydrolytic degradation of organophosphite ligands and deactivation of metal-organophosphite ligand complexes is well known and disclosed, for example, in US 5,741,942 and US 5,741,944. Mixtures of buffers may be employed.

Optionally, an organic nitrogen compound may be added to the hydroformylation reaction fluid to scavenge acidic hydrolysis byproducts formed upon hydrolysis of the organophosphorus ligand, as taught, for example, in US 4,567,306 and US 5,731,472. Such organic nitrogen compounds can be used to react with and neutralize the acidic compounds by forming conversion product salts therewith, thereby preventing the catalytic metal from complexing with acidic hydrolysis byproducts and thus helping to preserve the activity of the catalyst when present in the reaction zone under reaction conditions.

Optionally, a polymer additive may be used to help mitigate catalyst instability, particularly in the evaporation zone. Examples of these polymers are given in US 4,774,361 and US 11,111,198.

Hydroformylation processes and their operating conditions are well known. The hydroformylation process may be asymmetric or asymmetric, with the preferred process being asymmetric, and the hydroformylation process may be carried out in any batch, continuous or semi-continuous manner, and may involve any desired catalyst liquid and/or gas recycle operation.

The hydroformylation reaction conditions employed will be controlled by the type of aldehyde product desired. For example, the total gas pressure of the hydrogen, carbon monoxide and olefin starting compound of the hydroformylation process may be in the range of from 1kPa to 69,000 kPa. In general, however, it is preferred to operate the process at a total gas pressure of hydrogen, carbon monoxide and olefin starting compounds of less than 14,000kpa and more preferably less than 3,400 kpa. The minimum total pressure is limited primarily by the amount of reactants required to obtain the desired reaction rate. More specifically, the carbon monoxide partial pressure of the hydroformylation process is preferably 1 to 6,900kPa, and more preferably 21 to 5,500kPa, and the hydrogen partial pressure is preferably 34 to 3,400kPa, and more preferably 69 to 2,100kPa. In general, the molar ratio of gaseous H ₂ to CO may be in the range of 1:10 to 100:1 or higher, with a more preferred molar ratio of 1:10 to 10:1.

In general, the hydroformylation process can be carried out at any operable reaction temperature. Advantageously, the hydroformylation process is carried out at a reaction temperature of from-25 ℃ to 200 ℃, preferably from 50 ℃ to 120 ℃.

The hydroformylation process may be carried out using one or more suitable reactors, such as a fixed bed reactor, a fluidized bed reactor, a Continuous Stirred Tank Reactor (CSTR) or a slurry reactor. The optimal size and shape of the catalyst will depend on the type of reactor used. The reaction zone employed may be a single vessel or may comprise two or more separate vessels.

The hydroformylation process of the present invention may be carried out in one or more steps or stages. The exact number of reaction steps or stages will depend on the best compromise between capital costs and achieving high catalyst selectivity, activity, lifetime and ease of operation, as well as the inherent reactivity of the starting materials in question and the stability of the starting materials and the desired reaction products to the reaction conditions.

In one embodiment, the hydroformylation that can be used in the present invention can be carried out in a multistage reactor, such as described, for example, in US 5,728,893. Such multistage reactors may be designed with internal physical barriers that create more than one theoretical reaction stage in each vessel.

It is generally preferred to carry out the hydroformylation process in a continuous manner. Continuous hydroformylation processes are well known in the art, with the most preferred hydroformylation process comprising a continuous liquid catalyst recycle process. Suitable liquid catalyst recycling processes are disclosed, for example, in U.S. Pat. Nos. 4,668,651, 4,774,361, 5,102,505, and 5,110,990.

FIG. 1 illustrates an integrated hydroformylation process of the present invention. Referring to fig. 1, an olefin feed stream 1 comprising one or more olefin compounds and optionally one or more inert lights is fed to a hydroformylation reactor system 3 comprising one or more hydroformylation reactors (oxo reactors). At the same time, a gaseous feed stream 2 comprising carbon monoxide, hydrogen and optionally one or more gaseous inert substances is also fed to the hydroformylation reactor system 3. For simplicity, the hydroformylation reactor system is shown as a single unit in fig. 1, but it advantageously comprises a series of serially connected hydroformylation reactors.

A recycle catalyst stream 13 comprising a transition metal-organic monophosphite ligand complex, preferably rhodium-organic monophosphite ligand complex, and optionally free or uncomplexed organic monophosphite ligand, solubilized and dissolved in a liquid heavy byproduct phase is also fed to the hydroformylation reaction system 3 wherein hydroformylation of olefins occurs to produce a hydroformylation crude product stream 4 comprising one or more aldehyde products, one or more heavy byproducts, one or more unconverted olefin reactants, a transition metal-organic phosphite ligand complex catalyst, free organic phosphite ligand, and light products including inert light products, carbon monoxide and optionally hydrogen. In one embodiment of the invention, the hydroformylation raw product stream 4 is a stream comprising a liquid and a gas which may be partially dissolved in the liquid. A reactor vent stream (not shown) comprising primarily light components, including inert lights, hydrogen, and carbon monoxide, may be taken overhead from any one or more of the reactors in the reactor system as a gaseous stream from the reactor system 3.

The liquid hydroformylation product stream 4 is fed to a stripping gas evaporator unit 6 from which an overhead gas stream 7 is obtained, which overhead gas stream comprises one or more aldehyde products, one or more unconverted olefin reactants, a portion of the heavy by-products and light products comprising one or more inert light products, carbon monoxide and optionally hydrogen. The overhead gas stream 7 from the stripping gas vaporizer is fed to a product condenser 9 from which a condenser overhead gas stream 10 is obtained, which comprises a portion of the one or more olefin reactants and a portion of the inert lights, carbon monoxide and optionally hydrogen. From condenser 9 a liquid product stream 8 is obtained comprising one or more aldehyde products, a portion of the heavy by-products from the overhead gas stream from the evaporator and the balance unconverted olefin reactant. The condenser overhead gas stream 10 is split into a recycle stream 16 and a stream 15, which is sent back to the stripping gas evaporator 6 via blower 11, and which can be recycled to the hydroformylation reactor system 3, or combusted, or used as fuel, or for another downstream process. Recycle stream 16 comprises one or more unconverted olefin reactants and lights including one or more inert lights, carbon monoxide, and optionally hydrogen. Stream 15 comprises one or more unconverted olefin reactants and lights comprising one or more inert lights, carbon monoxide and optionally hydrogen. A recycle catalyst stream 13 is obtained from the stripping gas evaporator 6 as an evaporator tail stream comprising the balance of heavy by-products, transition metal-organophosphite ligand complex catalyst, and optionally free organophosphite ligand. The recycle catalyst stream 13 is recycled back to the oxo reactor system 3 as a liquid catalyst stream.

Stream 12 can be used to add CO directly to evaporator 6 and/or anywhere in stream 16 before entering evaporator 6 via stream 14. The partial pressure of CO in the evaporator may be measured directly in the evaporator or indirectly by analyzing one or more suitable evaporator input and/or output streams, such as suitably selected streams 7, 10, 14, 15 and/or 16.

Without the addition of CO, the CO partial pressure in the overhead gas recycle stream will vary as a function of the operating temperature of condenser 9. In this case, manipulation of the operating temperature of condenser 9 provides little control over the amount of CO required to be recycled to evaporator 6 to stabilize the hydroformylation catalyst, and does not provide sufficient amounts of CO to achieve the desired CO partial pressure of, for example, greater than 5psia (34 kPa) to 15psia (103 kPa) higher. It is therefore a feature of the present invention to add CO to the evaporator 6, for example via line 14 as shown in fig. 1. However, the CO addition via line 12 must be balanced with the increase in total pressure of the evaporator to avoid the problem of reduced evaporation of the aldehyde product, and thus the adjustment of the 15/16 split ratio must be accompanied by a change in the flow rate of stream 12. By adjusting this ratio, the CO partial pressure can be maintained up to 15psia (110 kPa), while the total pressure remains constant and low enough to facilitate removal of products and heavies. The use of the CO-rich stream 12 and the exhaust stream 15 reduces the H ₂ content even at reduced total pressure, which increases catalyst stability in the evaporator without the need to change the temperature of the condenser (9).

Depending on the line 16/line 15 split, a significant amount of CO added via line 12 will be recycled via line 16. The amount of H ₂ will also be similarly dispensed. This circulation reduces the total flow from line 12 required to maintain the partial pressure of CO in the stripping gas vaporizer due to the relatively low solubility of CO in the liquid product outlet stream as compared to conventional vaporizers. However, although the partial pressure of CO will increase in such a recycle process, the hydrogen content will also increase unless the ratio of H ₂ to CO in line 12 is lower than the ratio of CO and H ₂ entering the process via line 4. The flow rate in line 12 is adjusted to maintain the observed partial pressure of CO in the evaporator within the desired range while reducing the H ₂ content. The line may also be used to introduce CO-containing stripping gas during start-up, where appropriate gas from upstream processes may not be available. In various embodiments of the invention, a stream corresponding to stream 12 can be added anywhere in the evaporator. However, it is preferred that the CO be introduced into the vaporizer by mixing the make-up CO feed stream with stripping gas 16 prior to entering the vaporizer as stream 14.

Stream 12 is advantageously a CO-containing stream and is preferably substantially free of sulfur or halide containing impurities and oxygen (O ₂). The source of stream 12 may be the same as the source of CO and H ₂ in the hydroformylation reaction zone, but is preferably enriched in CO using conventional techniques such as pressure swing adsorption, membrane separation or other known techniques. The concentration techniques may be fed with fresh synthesis gas and/or a vent gas from the hydroformylation unit. In general, the higher the CO content in stream 12, the smaller the flow of exhaust stream 15, which results in lower exhaust losses. In other words, the higher CO content in stream 12 changes the line 16/line 15 split ratio to reduce exhaust flow (and thus exhaust losses). Conversely, if lines 4 and 12 contain a large amount of hydrogen, the line 16/line 15 split ratio is adjusted to be lower (the line 15 flow rate is higher).

The reaction fluid from the hydroformylation reactor may be fed directly into the stripping gas evaporator. The stripping gas evaporator is shown in fig. 1 as a single unit 6, but the evaporator may comprise a series of sequentially connected evaporators operating at different pressures.

As shown in fig. 2, the reaction fluid may be first fed to flash vessel 17 to reduce pressure and remove undissolved, reactive and inert gases, after which the remaining liquid may be fed to the stripping gas evaporator via line 4c. For example, a flash vessel operating at a pressure between the pressure of the reactor (3) and the pressure of the evaporator (6) can remove gases (such as hydrogen, CO ₂, methane, nitrogen, argon, etc.) before they enter the evaporator. This not only allows the concentration of these gases to be reduced rapidly, but also helps to prevent them from accumulating in the circulating stripping gas. This accumulation of gas would require a higher fresh CO feed rate (stream 12) and purge flow rate (stream 15) to achieve the desired CO partial pressure and low H ₂ partial pressure in the evaporator. An optional cooler 18 can be present on stream 4 prior to knock out drum 17 to reduce aldehyde and olefin losses via stream 19, or a condenser (not shown) can be present on stream 19 to recover and recycle volatile aldehydes and olefins. Thus, the use of a flash vessel prior to the evaporator can expand the feasible operating pressure of the evaporator (i.e., allow for lower total pressure) and more economical operation can be achieved.

The composition of the reaction fluid from the hydroformylation reactor (excluding the transition metal-organophosphorus ligand complex catalyst and any free ligand) advantageously comprises from about 38 to about 58 wt% of one or more aldehyde products, from about 16 to about 36 wt% of heavy byproducts, from about 2 to about 22 wt% of unconverted olefin reactant, from about 1 to about 22 wt% of inert lights, from about 0.02 to about 0.5 wt% carbon monoxide and less than about 100ppmw hydrogen, adding up to 100 wt%.

Evaporator hardware may be conventional in design and many examples are known to those skilled in the art. The evaporator is advantageously designed to include a series of vertical tubes within the heat exchanger. The optimal evaporator size (number, diameter and length of tubes) is determined by the capacity of the apparatus and can be readily determined by one skilled in the art. Examples of evaporators and their use are described in US 8,404,903.

In order to maintain the CO partial pressure of the present invention, it may be necessary to vent a portion of the recycled stripping gas by means of vent stream 15. Aldehydes, unreacted olefins and paraffins entrained in the vent stream may be recovered by condensation. Condensation may be performed in any suitable condenser using any suitable heat transfer fluid. Examples of such fluids include, for example, cold water, brine or other salt solutions, DOWTHERM brand heat transfer fluid, or other heat exchange fluids, including mixtures thereof.

Since the stripping gas evaporator and the product condenser can be operated at substantially constant pressure, substantial compression of the gaseous stream is not required in some embodiments of the process of the present invention. A blower or fan may be adapted to circulate the recycle gas from the product condenser to the stripper. The blower or fan involves significantly less capital expenditure and maintenance costs than the compression unit, however, the compression unit may be used if desired. Typically, the stripper and product condenser are operated at a pressure of 1.5 bar absolute (150 kPa) to 4 bar absolute (400 kPa), preferably 2 bar to 3 bar absolute (200 kPa to 300 kPa).

By adding a CO-containing stream via line 12, for example as shown in fig. 1, and adjusting the 16/15 ratio, the CO partial pressure in the stripping gas evaporator is advantageously maintained in the range of greater than 5psia (34 kPa) to less than 15psia (103 kPa). In one embodiment of the invention, the evaporator is operated at a temperature that is high enough to remove at least a portion of the heavies from the product fluid in the gaseous overhead stream, but low enough to ensure stability of the catalyst and organophosphorus ligand in the evaporator. Preferably, the evaporator process outlet temperature is at least 70 ℃, and more preferably at least 85 ℃. Preferably, the evaporator process outlet temperature is no more than 120 ℃, and more preferably no more than 110 ℃. The total evaporator pressure is advantageously at least 5psia (69 kPa), and preferably at least 20psia (138 kPa), and most preferably at least 25psia (172 kPa). The total evaporator pressure is advantageously no more than 40psia (276 kPa), and preferably no more than 35psia (241 kPa), and most preferably no more than 30psia (207 kPa). The CO partial pressure is less than 15psia (103 kPa), preferably less than 12psia (83 kPa), and most preferably less than 10psia (69 kPa), but should be greater than 5psia (34 kPa). The evaporator is advantageously operated at a mass ratio of crude liquid product feed to liquid heel in the range of from about 1.5/1 to 5/1, preferably from 2/1 to about 3/1. The mass ratio of crude liquid product feed to recycle gas feed to the evaporator is preferably greater than 0.1/1, more preferably greater than about 0.25/1, but preferably less than 2/1, and more preferably less than about 1/1. In one embodiment of the invention, the H ₂ partial pressure is at most 10:90, preferably 5:95, and most preferably 2:98, respectively, relative to the CO partial pressure in the evaporator. In a preferred embodiment, the H ₂ partial pressure is less than 1% of the total pressure in the evaporator. In one embodiment, the invention is a process as described herein, wherein the stripping gas evaporator is operated substantially at constant pressure with the product condenser.

The overhead gas stream from the evaporator is fed to a condenser. Any desired cooling medium may be employed with the condenser, and the type of cooling medium is not particularly critical. In one embodiment of the invention, the condenser is cooled with conventional water. Water is a preferred cooling medium at operating temperatures in the range of from above freezing (i.e., greater than 0 ℃) to about 50 ℃, preferably from about 34 ℃ to about 45 ℃.

The overhead stream from the condenser is advantageously split into a gaseous vent stream and a gaseous recycle stream to the evaporator. In one embodiment of the invention, the gas recycle stream from the condenser to the evaporator comprises less than 5wt% aldehyde product.

The use of synthesis gas containing about 50mol% H ₂ in the recycle stream increases the total pressure of the evaporator and therefore purified CO is preferred. If synthesis gas is used, it need not have the same H ₂/CO ratio as the synthesis gas fed to the hydroformylation unit, as little of this synthesis gas will be present in stream 13 to be recycled back to the hydroformylation system. In one embodiment, the source of this CO-containing stream 12 comprises a reactor vent stream that has been passed through a condenser to remove a majority of condensibles such as aldehyde products and olefin feed, optionally in combination with a membrane separator or other separation device to further enrich the stream with CO.

Advantageously, the process of the present invention results in lower rhodium losses and thus lower catalyst costs than a comparative process that does not maintain the indicated partial pressure of CO and reduced H ₂ content. In one embodiment of the invention, the crude product stream is obtained by contacting CO, H ₂, an olefin, and a catalyst comprising rhodium and an organophosphite ligand in a reaction zone under hydroformylation reaction conditions to produce an aldehyde product in the crude product stream. In one embodiment of the invention, the method further comprises removing from the evaporator as a tail stream a liquid recycle catalyst stream comprising a transition metal-organophosphite ligand complex catalyst and heavy byproducts.

Illustrative non-optically active aldehyde products include, for example, propionaldehyde, n-butyraldehyde, isobutyraldehyde, n-valeraldehyde, 2-methyl-1-butyraldehyde, hexanal, hydroxyhexanal, 2-methyl-1-heptanal, nonanal, 2-methyl-1-octanal, decanal, hexanal, 2-methylpentanal, 2-methylhexanal, 3-hydroxypropional, 6-hydroxyhexanal, enals, such as 2-pentenal, 3-pentenal and 4-pentenal, alkyl 5-formylpentanoate, 2-methyl-1-nonanal, 2-methyl-1-decanal, 3-propyl-1-undecanol, pentadecanol, 3-propyl-1-hexadecanol, eicosanal, 2-methyl-1-ditridecanalal, eicosanalal, 2-methyl-1-octanal, 2-methyl-1-triacontaneal, and the like.

Illustrative optically active aldehyde products include (enantiomer) aldehyde compounds prepared by the asymmetric hydroformylation process of this invention, such as S-2- (p-isobutylphenyl) -propanal, S-2- (6-methoxy-2-naphthyl) propanal, S-2- (3-benzoylphenyl) -propanal, S-2- (3-fluoro-4-phenyl) phenylpropionaldehyde and S-2- (2-methylacetaldehyde) -5-benzoylthiophene.

Detailed description of the invention

All parts and percentages in the following examples are by weight unless otherwise indicated. Unless otherwise indicated, the pressures in the examples below are given in absolute pressure. Unless otherwise indicated, all manipulations (such as preparation of the catalyst solution) were performed under an inert atmosphere. The comparative experiments are not embodiments of the present invention.

Rhodium analysis is performed by air/acetylene Atomic Absorption (AA) or by Inductively Coupled Plasma (ICP). It has been found that air/acetylene AA does not reliably quantify clustered rhodium, but nevertheless this approach can be used to indicate "rhodium loss" (e.g., rhodium is clustered or otherwise no longer in solution and may not be as active). Due to the high temperature of the plasma, ICP is considered to detect all rhodium in the sample, regardless of its form, so a decrease in rhodium as measured by ICP indicates that a portion of rhodium is no longer in solution. A color change (starting from a colorless or pale yellow solution), darkening or formation of a black film or solid is also indicative of catalyst degradation.

The gas composition (mole%) was measured by Gas Chromatography (GC), and then the partial pressure was calculated based on the total pressure using raoult's law. It should be understood that the stripping gas typically contains trace components (e.g.,. Ltoreq.0.5 psia) in addition to those listed.

General procedure A-single pass gas stripping reactor

Unless otherwise indicated, the examples and comparative experiments were conducted in a 90mL flow-through Fisher port reactor equipped with means for precise control of temperature and gas flow. The reactor off-gas was analyzed by online GC to determine partial pressure. Mixing in a flow-through reactor is achieved by continuous gas flow through a distributor at the bottom of the reactor. The reactor design is described in detail in US 5,731,472, the teachings of which are incorporated herein by reference.

Examples 1 to 4 and comparative examples:

According to general procedure a, solutions of rhodium and ligand a in tetraglyme at different concentrations were charged to each reactor. After overnight contact with 1:1:0.1 CO: H ₂: propylene gas at 75 ℃, the reactor was flushed with N ₂ for about 60 minutes and then sealed at a partial pressure of 2psi CO at the set pressure. After 2 and 7 days, the reactor was sampled to determine the rhodium loss of AA and the results are summarized in table I.

These conditions are intended to simulate worst case conditions in a vaporizer with low CO and trace amounts of residual hydrogen and olefins. There are two generally accepted criteria for catalyst stability, appearance (black and/or cloudy solution indicates cluster formation) and actual metal analysis, where the transition metal element is no longer in solution. As shown in table 1, low ligand/rhodium ratios (less than 20) exhibited characteristic formation of "rhodium black", but improved (lower) AA rhodium loss compared to the control. Increasing the ligand to metal ratio gives improved stability by two criteria. The best results were obtained by combining both high ligand/rhodium values with reduced total rhodium levels.

Claims (11)

1. A continuous hydroformylation process, the continuous hydroformylation process comprising:

(A) Feeding a reaction fluid to an evaporator having an average CO partial pressure, the reaction fluid comprising one or more products, one or more heavy byproducts, a transition metal-organophosphite ligand complex catalyst, one or more unconverted reactants, and one or more inert lights;

(B) Removing an overhead gas stream from the evaporator, the overhead gas stream comprising one or more products, one or more unconverted reactants, one or more inert lights, and a portion of the heavy byproducts, and feeding the overhead gas stream to a condenser;

(C) Removing a condenser overhead gas stream from the condenser, the condenser overhead gas stream comprising one or more unconverted reactants and one or more inert lights;

(D) Recycling at least a portion of the condenser overhead gas stream to the evaporator and/or reaction zone;

(E) Removing from said evaporator as a tail stream a liquid recycle catalyst stream comprising said transition metal-organophosphite ligand complex catalyst and the balance of said heavy by-products;

wherein the average CO partial pressure in the evaporator is maintained at less than 15psia (110 kPa).

2. The continuous hydroformylation process according to claim 1 wherein the average partial pressure of CO in the evaporator is maintained at less than 15psia by:

a. Feeding a crude product stream to an evaporator, the crude product stream comprising one or more products, one or more heavy byproducts, a transition metal-organophosphite ligand complex catalyst, one or more unconverted reactants, and one or more inert lights;

b. Removing an overhead gas stream from the evaporator, the overhead gas stream comprising one or more products, one or more unconverted reactants, one or more inert lights, hydrogen, carbon monoxide, and a portion of the heavy byproducts, and feeding the overhead gas stream to a condenser;

c. Removing a condenser overhead gas stream from the condenser, the condenser overhead gas stream comprising one or more unconverted reactants and one or more inert lights;

d. Recycling at least a portion of the condenser overhead gas stream to the evaporator and/or reaction zone;

e. Introducing a gas stream comprising CO into said evaporator in addition to said condenser overhead gas stream such that said average CO partial pressure in said evaporator is less than 15psia (103 kPa), wherein the molar ratio of CO to H ₂ in said added gas stream is higher than that present in step b, and wherein the total evaporator pressure, CO partial pressure and H ₂ partial pressure are controlled by the fraction of said condenser overhead gas stream recycled in step d;

f. A liquid recycle catalyst stream comprising transition metal-organophosphite ligand complex catalyst and balance of the heavy by-product is removed from the evaporator as a tail stream.

3. The continuous hydroformylation process according to claim 1 wherein the average partial pressure of CO in the evaporator is maintained at less than 15psia by:

a. Feeding a crude product stream comprising one or more products, one or more heavy byproducts, a transition metal-organophosphite ligand complex catalyst, one or more unconverted reactants, and one or more inert lights into a depressurization zone, wherein a gaseous purge is removed and a liquid phase is sent to an evaporator, wherein the depressurization zone removes undissolved H ₂ and optionally inert gas such that the amount of H ₂ introduced into the evaporator is reduced to allow for reduced total evaporator pressure;

b. Removing an overhead gas stream from the evaporator, the overhead gas stream comprising one or more products, one or more unconverted reactants, one or more inert lights, hydrogen, carbon monoxide, and a portion of the heavy byproducts, and feeding the overhead gas stream to a condenser;

c. Removing a condenser overhead gas stream from the condenser, the condenser overhead gas stream comprising one or more unconverted reactants and one or more inert lights;

d. Recycling at least a portion of the condenser overhead gas stream to the evaporator and/or reaction zone;

e. Introducing a gas stream comprising CO into said evaporator in addition to said condenser overhead gas stream such that said average CO partial pressure in said evaporator is less than 15psia (103 kPa), wherein said evaporator total pressure, CO partial pressure and H ₂ partial pressure are controlled by the fraction of said condenser overhead gas stream recycled in step d;

f. A liquid recycle catalyst stream comprising transition metal-organophosphite ligand complex catalyst and balance of the heavy by-product is removed from the evaporator as a tail stream.

4. The continuous hydroformylation process according to claim 1 wherein the average partial pressure of CO in the evaporator is maintained at less than 15psia by:

a. Feeding a crude product stream to an evaporator, the crude product stream comprising one or more products, one or more heavy byproducts, a transition metal-organophosphite ligand complex catalyst, one or more unconverted reactants, and one or more inert lights;

b. Removing an overhead gas stream from the evaporator, the overhead gas stream comprising one or more products, one or more unconverted reactants, one or more inert lights, hydrogen, carbon monoxide, and a portion of the heavy byproducts, and feeding the overhead gas stream to a condenser;

c. Removing a condenser overhead gas stream from the condenser, the condenser overhead gas stream comprising one or more unconverted reactants and one or more inert lights;

d. Recycling at least a portion of the condenser overhead gas stream to the evaporator and/or reaction zone;

e. Introducing a gas stream comprising CO into said evaporator in addition to said condenser overhead gas stream such that said average CO partial pressure in said evaporator is less than 15psia (103 kPa), wherein said evaporator total pressure, CO partial pressure and H ₂ partial pressure are controlled by the fraction of said condenser overhead gas stream recycled in step d;

f. Removing from the evaporator a liquid recycle catalyst stream comprising the transition metal-organophosphite ligand complex catalyst and the balance of the heavy by-product as a tail stream, wherein the ligand to rhodium ratio of the crude product stream in step (a) is greater than 20:1, the transition metal concentration in the tail stream in step f is less than 100ppm, or both.

5. The continuous hydroformylation process according to claim 1 wherein the average partial pressure of CO in the evaporator is maintained at less than 15psia by two or more of the processes described in claims 2,3 and 4.

6. The process of any one of the preceding claims, wherein the transition metal is rhodium.

7. The method of any one of the preceding claims, wherein the metal concentration in step (a) is from 5ppmw to 80ppmw.

8. The method of any one of the preceding claims, wherein the ratio of ligand to transition metal is higher than 25:1.

9. The process of any one of the preceding claims, wherein the ligand is a monophosphite ligand.

10. The process of any of the preceding claims, wherein the CO partial pressure in the evaporator is less than 12psia (83 kPa) but greater than 5psia (34 kPa).

11. The process of any of the preceding claims, wherein the H ₂ partial pressure in the evaporator is less than 0.2psi (1.4 kPa).