Methods of controlling hydroformylation processes

Abstract

A method of optimizing the production rate of a hydroformylation process for producing a mixture of normal (N) and iso (I) aldehydes is described. The process involves contacting an olefin with carbon monoxide, hydrogen and a catalyst comprising (A) a transition metal, (B) a monophosphine, and (C) a tetraphosphine having a particular structure.The hydroformylation production rate is increased incrementally by taking at least three of the following actions in order. 1.) Establishing the optimized H2 / CO partial pressure ratio limited to greater than 0.4:1 to less than 2.5:1. 2.) Increasing the partial pressure of syngas at the optimized ratio established in Step 1 limited to a CO partial pressure of 30 psi in at least one reaction zone. 3.) Increasing the partial pressure of olefin in at least one reaction zone limited up to 2% of the olefin feed in the first reaction zone is lost via the purge vent stream of the last reaction zone or the alkane purge stream of an optional olefin recovery process. 4.) Lowering the concentration of monophosphine within the reaction fluid to a lower limit of about 1.5 wt. %. 5.) Increasing the temperature within at least one reaction zone to a limit of about 98 °C. and 6.) Increasing the concentration of transition metal within the reaction fluid up but not to exceed 1200 ppmw in the reaction zone.

Description

[0001] METHODS OF CONTROLLING HYDROFORMYLATION PROCESSES

[0002] FIELD

[0003] The present invention relates to methods to maintain or increase hydroformylation reaction rate for a hydroformylation process comprising a polyphosphine and a monophosphine catalyst system.

[0004] BACKGROUND

[0005] It is known in the art that aldehydes may be readily produced by reacting an olefinically unsaturated compound with carbon monoxide and hydrogen in the presence of a solubilized rhodium-triorganophosphorous ligand complex catalyst and that a preferred type of such processes involves continuous hydroformylation. For example, U.S. Patent No. 3,527,809 discloses the hydroformylation of alpha-olefins to produce aldehydes at low temperatures and pressures. The process employs certain rhodium complexes to effectively catalyze, under a defined set of variables in the presence of select triorganophosphorous ligands, the hydroformylation of olefins with hydrogen and carbon monoxide.

[0006] Among the catalysts described in U.S. Patent No. 3,527,809 are compounds containing rhodium and triarylphosphorous ligands, in particular triarylphosphine ligands exemplified by triphenylphosphine (“TPP”). Commercial hydroformylation processes have successfully employed the rhodium-TPP catalyst for decades, and a key aspect of operation is the use of a large excess of TPP relative to rhodium. For example, industrial propylene hydroformylation processes often operate with TPP concentrations of 10-12 weight percent based on the total mass of the reaction fluid. Such high concentrations of TPP are used to achieve the desired product regioselectivity and to enhance catalyst stability. There are references to the kinetics of such rhodium-monophosphine systems, such as “Propylene Hydroformylation with Rhodium Carbonyls and Triphenylphosphine: II Kinetics of Butyraldehyde Formation”, P. C. d’Oro (et.al.), La Chimica E L’lndustria, v.62, 1980, 572- 579, which state that for a rhodium-TPP system with propylene, the rate is a function of propylene, rhodium, and ligand concentrations (but not CO or H2). However, US 4, 277, 627 A teaches there are limits on the parameters such as reactant partial pressures, ligand concentrations, and temperatures that can lead to catalyst deactivation thus loss of reaction rate. These two references teach that while short-term effects on rate can be determined by kinetic studies, maintaining long term stable rates is more complex.

[0007] US 2021 / 01 14010 teaches a catalyst composition comprising the combination of a monophosphine, a tetraphosphine ligand and a hydroformylation process using it. US 11,130,725 discloses that certain monophosphines enhance the stability of tetraphosphinebased hydroformylation catalysts and / or reduces tetraphosphine usage and WO / 2019 / 231611 teaches that the N / I ratio (discussed below) can be adjusted by changes in the amount of monophosphine present in the mixed polyphosphine and monophospine catalyst system.

[0008] The initial conditions for the hydroformylation process can be developed using kinetic parameters such as described above with practical limitations based on equipment capacities (volume, pressure ratings, ability to agitate, etc.), heat removal limitations, solubilities, product / catalyst separation limitations, and the like as known by those skilled in the art. However, it has been observed that after a period of time, the catalyst activity changes from the initial optimized design. Even in the absence of obvious degradation mechanisms, the catalyst activity may decline due to a number of factors such as poisons introduced via the feeds (e.g., sulfur or halogens), heavies buildup (i.e., accumulation of inerts which occupy reactor volume), and entrainment losses of the catalyst in the productcatalyst separation zone (typically a vaporizer). Although the initial plant operating conditions may have been optimized to reflect fresh catalyst behavior, it would be desirable to have a design wherein the parameters can be re-optimized should the apparent catalyst activity decline. In other cases, market demands may decline, thus the plant may choose to reduce production for a period. When market demand returns, it would be desirable to raise the rates in the most efficient manner. Moreover, plants may occasionally wish to increase production rates beyond normal levels to meet short-term spikes in demand. In such instances it would be desirable to increase the hydroformylation rate in an efficient manner to maximize economic value; moreover, if the change were readily reversible, the facility could quickly return to normal operation.

[0009] Unlike catalysts comprised of rhodium and a single ligand, there are no teachings on how to control the process conditions to optimize performance for the mixed tetraphosphine and monophosphine systems such as described in US 2021 / 0114010. The above references give examples of good operation for each ligand alone and for certain combinations of ligands but do not provide guidance on how to alter the process conditions (reagent partial pressures, temperatures, etc.) to give optimal performance and best economic value.

[0010] Olefin efficiency is an important economic consideration in industrial hydroformylation processes. As apparent catalyst activity declines, the olefin conversion typically drops, and thus higher levels of unconverted olefin may be lost with the product or in reactor vents. Recovery and recycle of unconverted olefin can mitigate some of this loss. Examples of such recovery processes are given in US 6,969,777, WO2017160956, and CN104610032. However, these systems are complex and have limited capacity thus can be overwhelmed should the hydroformylation catalyst activity drop significantly or if the olefin feed rate is too high.

[0011] Additionally, the hydrogenation of olefin to alkane is known to occur in hydroformylation systems. This conversion to undesired byproduct decreases olefin efficiency and should be minimized.

[0012] For hydroformylation processes, product regioselectivity is typically expressed as the ratio of linear (or normal) product to branched (or iso) aldehyde product. As used herein, this ratio of linear (or normal) to branched (or iso) aldehyde product will be referred to as the “N / I ratio” or “N / I”. While the branched product has value, the linear product is often preferred. The ability to vary the N / I over a broad range has been previously described (see for example W02008 / 115740, US 8,741,173, US 8,598,389, and US 11,344,869). However, some facilities may choose to maintain a relatively consistent N / I to simplify purification steps and to meet downstream demands.

[0013] Optimizing the N / I ratio and target aldehyde production rate while maximizing olefin efficiencies and maximizing catalyst life are key economic drivers for industrial hydroformylation processes. Thus, in some cases, optimal economics may be achieved at an intermediate production rate with a high N / I and a high olefin efficiency. Given that catalyst performance may change during extended continuous operation, it would be desirable to have a facile means to optimize the operation of a polyphosphine / monophosphine catalyst such that the desired hydroformylation rate may be achieved at substantially the same N / I ratio while minimizing costs and process inefficiencies. It would be preferable if such methods were reversible such that the plant can adjust to shifting market demands.

[0014] SUMMARY

[0015] The present invention relates to methods to optimize the operation of a hydroformylation process comprising a polyphosphine / monophosphine ligand catalyst. It has been found that a sequence of changes to certain operating parameters allows the hydroformylation rate to be increased or maintained while maintaining a consistent N / i with minimal olefin efficiency losses. The changes are mostly reversible, which would allow the production rate to be slowed should market demands shift.

[0016] In one aspect, a method of optimizing the production rate of a hydroformylation process for producing a mixture of normal (N) and iso (I) aldehydes, the process comprising contacting an olefin with carbon monoxide, hydrogen and a catalyst, the catalyst comprising (A) a transition metal, (B) a monophosphine, and (C) a tetraphosphine having the following structure: wherein each P is a phosphorous atom, and each of R1-R46are independently hydrogen, a Cl to C8 alkyl group, an aryl group, an alkaryl group, or a halogen, the contacting conducted in one or more reaction zones and at hydroformylation conditions to produce a blend of normal (N) and iso (I) aldehydes at a N / I ratio, wherein the hydroformylation production rate may be increased incrementally by taking at least three of the following actions in order: 1. Establishing the optimized H2 / CO partial pressure ratio limited to greater than 0.4: 1 to less than 2.5: 1.

[0017] 2. Increasing the partial pressure of syngas at the optimized ratio established in Step 1 limited to a CO partial pressure of 30 psi in at least one reaction zone.

[0018] 3. Increasing the partial pressure of olefin in at least one reaction zone up to a level not to exceed the point at which more than 2% of the olefin feed being lost via the purge vent stream of the last reaction zone or the alkane purge stream of an optional olefin recovery process.

[0019] 4. Lowering the concentration of monophosphine within the reaction fluid to a lower limit of about 1.5 wt. %.

[0020] 5. Increasing the temperature within at least one reaction zone to a limit of about 98 °C.

[0021] 6. Increasing the concentration of transition metal within the reaction fluid but not to exceed 1200 ppmw in the reaction zone.

[0022] It has surprisingly been discovered that both the N / I and hydroformylation rate are nearly independent of hydrogen partial pressure. However, the rate of alkane byproduct formation is highly dependent on the hydrogen-to-carbon monoxide ratio (H2 / CO ratio). In one aspect, the current invention comprises a step of optimizing the H2 / CO ratio so as to minimize the formation of alkane. Thus, the CO partial pressure is optimized to achieve the desired N / I and then the H2 partial pressure is optimized to minimize alkane formation and adjust for any minor changes in N / I due to H2 partial pressure. The range of the optimized H2 / CO partial pressure ratio is from > 0.4:1 to < 2.5:1, preferably >0.6:1 and most preferably >0.9:1 but less than 2.0: 1, preferably less than 1.5: 1 and most preferably less than 1.04: 1. It has surprisingly been discovered that as long as this ratio is maintained, the syngas pressure (that is, the sum of H2 and CO) can be increased with minimal impact on alkane formation. Without being bound by theory, it appears that the increased CO mitigates the undesired hydrogenation. Delivering a consistent CO:H2 ratio to the hydroformylation unit also simplifies the operation of the upstream syngas unit.

[0023] It has surprisingly been discovered that the hydroformylation rate for the catalyst of the current invention exhibits an initial positive order relationship with CO partial pressure and then becomes negative order at higher pressures (CO partial pressures typically greater than about 30 psi). In one embodiment, the second step of the current invention comprises increasing the CO gas partial pressure with a limit of about 65 psi for syngas. This provides an increase in the hydroformylation rate up to where the reaction order in CO becomes negative (typically at or below 3Opsi CO). Higher CO partial pressures tend to give lower N / I product which limits how much rate increase can be achieved without significant impact on the N / I ratio. Thus, whether the CO partial pressure should be increased or decreased depends on where a system is on the CO partial pressure vs production rate curve, and the magnitude of the pressure change is limited by at least one of (A) the negative order region being reached, in which case further increases in CO partial pressure will result in a decrease in hydroformylation rate; or B) a substantial change in N / I. In one embodiment, the upper limit for CO partial pressure is that point where the catalyst system becomes negative order in CO which has been found to be 20-30psi. The H2 and CO partial pressures can be determined by methods well known in the art such as gas chromatography and can be measured directly in the reactor headspace or an inert purge vent.

[0024] In one embodiment, the third step of the current invention comprises increasing the partial pressure of olefin. In processes where the unreacted olefin in the final reactor is not recovered, the olefin pressure may be increased until the amount of olefin lost in the final reaction zone vent comprises no more than about 2% of the total olefin fed into the first reaction zone. In one embodiment, this may be determined by measuring the partial pressure of the olefin in the vent stream and the flow rate of the vent stream. The olefin partial pressure can be determined by methods well known in the art such as gas chromatography (GC) and can be measured directly in the reactor headspace or an inert purge vent. In another embodiment the concentration of olefin (e.g., mole %) is measured directly in the vent stream by GC and used to calculate the olefin loss based on the flow rate of the vent stream.

[0025] Optionally , an olefin recovery process such as described in US 6,969,777B2, US 10,407,372, and CN113387780A to minimize the loss of unreacted olefin from reactor vents and / or downstream vaporizers or refining processes may be employed. In such systems the olefin partial pressure can be increased until amount of olefin in the alkane purge from the olefin recovery system reaches 2% of the total olefin feed to the first reaction zone.

[0026] In one aspect, the fourth step of the current invention comprises lowering the concentration of the monophosphine. This can be accomplished by purging a portion of the process fluid. In a preferred embodiment, the monophosphine concentration is reduced over time via vaporization along with the crude product. In such an embodiment, monophosphine additions to the process (which would normally be performed to maintain a target concentration) are suspended until a new, lower target concentration is reached. The lower limit of acceptable monophosphine concentration is not less than 1.5 wt.% and most preferably not less than 3 wt.% in the catalyst solution so as to maintain the overall catalyst stability and performance.

[0027] In one aspect, the fifth step of the current invention comprises increasing the temperature of at least one reaction zone. Significant increases in reactor temperatures will increase the formation of heavy byproducts and the degradation rate of the expensive polyphosphine. In one embodiment, the upper limit of reaction zone temperature is 98°C.

[0028] In one aspect, the sixth step of the process of the invention is increasing the transition metal concentration. It is well known that rhodium is quite expensive, thus rhodium additions result in a direct economic cost. In addition, the tetraphosphine ligand degradation rate may be dependent on the transition metal concentration. The tetraphosphine concentration is typically raised as well during transition metal additions, to maintain a tetraphosphine: transition metal mole ratio above 1:1. An increase in tetraphosphine concentration will also tend to increase tetraphosphine ligand degradation. However, the benefit of increased hydroformylation rate may often justify the expense.

[0029] Increasing transition metal (e.g., rhodium) independently will change the tetraphosphine: rhodium and monophosphine: rhodium ratio; thus, depending on the magnitude of the transition metal addition, the N / I behavior may be effected. It is preferred that the tetraphosphine and / or monophosphine be added with or within a short period of time of the addition of the rhodium catalyst precursor described herein (e.g., rhodium dicarbonyl acetylacetonate).

[0030] Based on these factors, the upper limit to the transition metal addition is the point at which the rate of tetraphosphine ligand degradation becomes uneconomical, and / or the concentration of the ligand and / or the resulting active (transition metal): (tetraphosphine) in the reaction fluid from the product: catalyst separation zone (typically a vaporizer) approach their solubility limit. It has been determined that the maximum transition metal concentration of the process of the current invention is less than 1200 ppm.

[0031] In cases where market demand has dropped, the plant may opt to reduce production accordingly. This is typically done by reducing the olefin feed to the process. Another scenario is raw material shortages which necessitate lower production rates. Upon the market demand increasing or improved raw material availability, the plant would desire to have the most efficient process to increase production rate. During the period of lower production, the catalyst performance may have changed due to impurities being introduced, heavies buildup, changes in ligand composition or other factors. Thus, the teaching of the present invention allows the process to restore the desired level of production in the most efficient manner.

[0032] Conducting the process of the invention as described herein optimizes the olefin efficiency, maintains a relatively consistent N / I and allows the hydroformylation rate to be increased or maintained at the desired target. Each step may be taken as needed and the time between steps may vary and is not critical to the invention. A hypothetical example of the process of the invention is shown in Figure 1.

[0033] BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 is a graph showing how the reaction rate and N:I ratio might hypothetically change in response to various steps as outlined in the specification.

[0035] Figure 2 is a graph showing the results of Example 1.

[0036] Figure 3 is a graph showing the results of Example 2.

[0037] Figure 4 is a graph showing the results of Example 3.

[0038] Figure 5 is a graph showing the results of Example 4

[0039] Figure 6 is a graph showing the results of Example 5.

[0040] Figure 7 is a graph showing the results of Example 6.

[0041] Figure 8 is a graph showing the results of Example 7.

[0042] Figure 9 is a graph showing the results of Example 8.

[0043] Figure 10 is a graph showing the results of Example 9.

[0044] DETAILED DESCRIPTION

[0045] All references to the Periodic Table of the Elements and the various groups therein are to the version published in the CRC Handbook of Chemistry and Physics, 72nd Ed. (1991-1992) CRC Press, at page 1-11.

[0046] Unless stated to the contrary, or implicit from the context, all parts and percentages are based on weight and all test methods are current as of the filing date of this application. For purposes of United States patent practice, the contents of any referenced patent, patent application or publication are incorporated by reference in their entirety (or its equivalent US version is so incorporated by reference) especially with respect to the disclosure of definitions (to the extent not inconsistent with any definitions specifically provided in this disclosure) and general knowledge in the art.

[0047] As used herein, "a," "an," "the," "at least one," and "one or more" are used interchangeably. The terms "comprises," “includes,” and variations thereof do not have a limiting meaning where these terms appear in the description and claims. Also herein, the recitations of numerical ranges by endpoints include all numbers subsumed in 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 invention, it is to be understood, consistent with what one of ordinary skill in the art would understand, that a numerical range is intended to include and support all possible sub-ranges that are included in that range. For example, the 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. Also herein, the recitations of numerical ranges and / or numerical values, including such recitations in the claims, can be read to include the term "about." In such instances the term "about" refers to numerical ranges and / or numerical values that are substantially the same as those recited herein.

[0048] As used herein, the terms “ppm” and “ppmw” are used interchangeably and mean parts per million by weight.

[0049] For purposes of this invention, the term "hydrocarbon" is contemplated to include all permissible compounds having at least one hydrogen and one carbon atom. Such permissible compounds may also have one or more heteroatoms. In a broad aspect, the permissible hydrocarbons include acyclic (with or without heteroatoms) and cyclic, branched and unbranched, carbocyclic and heterocyclic, aromatic and nonaromatic organic compounds that can be substituted or unsubstituted.

[0050] As used herein, the term "substituted" is contemplated to include all permissible substituents of organic compounds unless otherwise indicated. In a broad aspect, the 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, alkyloxy, aryl, aryloxy, hydroxyalkyl, aminoalkyl, in which the number of carbons can range from 1 to 20 or more, preferably from 1 to 12, as well as hydroxy, halo, and amino. The permissible substituents can be one or more and the same or different for appropriate organic compounds. This invention is not intended to be limited in any manner by the permissible substituents of organic compounds.

[0051] As used herein, the term "hydroformylation" is contemplated to include, but is not limited to, all hydroformylation processes that involve converting one or more substituted or unsubstituted olefinic compounds or a reaction mixture comprising one or more substituted or unsubstituted olefinic compounds to one or more substituted or unsubstituted aldehydes or a reaction mixture comprising one or more substituted or unsubstituted aldehydes. The aldehydes may be asymmetric or non-asymmetric. Unless otherwise indicated, as used herein, the terms “hydroformylation rate”, “hydroformylation production rate”, and “production rate” are used interchangeably and refer to the total mass or moles of aldehydes produced per unit time. Side reactions such as hydrogenation to hydrocarbons and aldol condensation to heavies are not included in the production rate calculation. Production rate may be expressed in different units based on convention or preference, such as moles of aldehyde per liter of reaction fluid per unit time. In one embodiment, the production rate is calculated and expressed as the total moles of butyraldehydes produced per liter of reaction fluid per hour (moles / L / hr). The terms may be further limited by the amount of a particular aldehyde isomer that is produced such as “rate of linear aldehyde production”, for example, to be specific to one particular aldehyde.

[0052] As used herein, the term “olefin efficiency” is contemplated to comprise the percentage of olefin fed to the process that is transformed to the desired product aldehydes. Transformation of olefin to alkane via hydrogenation and purging of unreacted olefin from reactor vents or from olefin recovery units would have a negative impact on olefin efficiency. Olefin efficiency is typically determined by conducting a mass balance of the system. For example, if 9.8 moles of the desired product aldehydes are produced per unit time for every 10 moles of olefin fed, an olefin efficiency of 98 % would be achieved.

[0053] As used herein, the term “reaction zone” is contemplated to comprise at least one hydroformylation reactor. In some embodiments the reaction zone comprises two or more reactors in series. In some embodiments the reaction zone comprises multiple continuous stirred tank reactors (CSTRs) in series.

[0054] As used herein the terms “optimized H2 / CO ratio” and “optimized H2 / CO partial pressure ratio” are contemplated to include a mixture of hydrogen and carbon monoxide comprised of hydrogen and carbon monoxide as molar ratios measured as partial pressures within the reaction zone rather than the ratio in the feed streams or ratio of feed streams.

[0055] As used herein, the term “optimized syn gas” is contemplated to comprise a mixture of hydrogen and carbon monoxide at the optimized H2 / CO partial pressure ratio as determined by the partial pressures within the reaction zone. Unless otherwise specified, the terms “H2 / CO ratio” or “H2 / CO partial pressure ratio” are referring to the observed gas partial pressures within the reaction zone rather than the ratio in the feed streams which may be different. Thus, increasing the optimized syn gas partial pressure would comprise higher pressures of both hydrogen and carbon monoxide at the optimized H2 / CO ratio. The terms “optimized syn gas pressure” and “partial pressure of optimized syngas” are contemplated to only include the partial pressures of H2 and CO (exclusive of olefin and inerts). Hydrogen and CO partial pressures can be determined by the total pressure and a number of methods including gas chromatography or spectroscopic techniques well known to those skilled in the art.

[0056] As used herein, the terms “optimized aldehyde production” or “optimized aldehyde rate” are used interchangeably and refer to achieving a target aldehyde production rate at an acceptable N / l with high olefin efficiency. In some instances, facilities may choose to slow production due to decreased demand or market conditions; in such cases it is still important to achieve high olefin efficiency and a consistent product mix. Thus, optimized aldehyde production is not the same as maximum hydroformylation rate.

[0057] The terms "reaction fluid," “reaction medium” and “catalyst solution” are used interchangeably herein, and may include, but are not limited to, a mixture comprising: (a) a transition metal -monophosphine complex catalyst (e.g., a rhodium-triphenylphosphine complex catalyst), (b) a transition metal-tetraphosphine complex catalyst (e.g., a rhodiumtetraphosphine complex catalyst), (c) free monophosphine (e.g., triphenylphosphine), (d) free tetraphosphine, (e) aldehyde products formed in the reaction, (f) unreacted reactants, (g) a solvent for said transition metal complex catalysts and said free phosphine ligands, and, optionally (h) monophosphine ligand and tetraphosphine ligand degradation products. The reaction fluid can encompass, but is not limited to, (a) a fluid in a reaction zone, (b) a fluid stream on its way to a separation zone, (c) a fluid in a separation zone, (d) a recycle stream, (e) a fluid withdrawn from a reaction zone or separation zone, (f) a fluid in an external cooler.

[0058] The term “ligand degradation products” is contemplated to include but is not limited to any and all compounds resulting from one or more chemical transformations of at least one of the tetraphosphine and or monophosphine molecules charged to the reaction fluid. Such compounds may include but are not limited to triphosphine or diphosphine compounds derived from rhodium-promoted cleavage of the parent tetraphosphine as well as the smaller phosphine moieties resulting from said cleavage side reactions. Ligand degradation products are also contemplated to include alkyldiarylphosphines which are known to be present in rhodium-triarylphosphine hydroformylation catalyst solutions (see, for example, US Patent No. 4,297,239, col. 5). Ligand degradation products are additionally contemplated to include any and all compounds which result from oxidation of phosphine moieties. For example, ligand degradation products may comprise phosphine oxides derived from monophosphine introduced to the process, from partial or complete oxidation of tetraphosphine introduced to the process, or from the oxidation of phosphine compounds resulting from rhodium-promoted side reactions (e.g., oxidation of triphosphine compounds derived from the parent tetraphosphine).

[0059] As used herein the terms “tetradentate phosphine” and “tetraphosphine” are used interchangeably and are contemplated to comprise compounds containing four phosphine atoms each one of which is bound to three carbon atoms.

[0060] As used herein the terms “monodentate phosphine” and “monophosphine” are used interchange bly and comprise compounds which contain a single phosphine atom bound to three carbon atoms.

[0061] As used herein the terms “rhodium complex”, “rhodium complex catalyst”, and “catalyst complex” are used interchangeably and are contemplated to comprise at least one rhodium atom with ligands bound or coordinated via electron interaction. Examples of such ligands include but are not limited to monophosphine, tetradentate phosphine, carbon monoxide, olefin (e.g., propylene) and hydrogen.

[0062] As used herein, the term “free” phosphine is contemplated to comprise monophosphine or tetraphosphine molecules that are not bound or coordinated to rhodium.

[0063] In general, the present invention is directed to methods for maintaining the N / I ratio of aldehydes produced by a hydroformylation process. The catalyst composition includes two ligands, a monophosphine and a tetraphosphine, and the N / I ratio of the aldehydes produced can be increased or decreased slightly by adding one ligand or other to a reaction zone. Changes in the syngas partial pressure may also shift the N / I, but the goal is to maintain the proportion of linear butyraldehyde in the product generally constant.

[0064] In one aspect, a method of optimizing the production rate of a hydroformylation process for producing normal (N) and iso (I) aldehydes, the process comprising contacting an olefin with carbon monoxide, hydrogen and a catalyst, the catalyst comprising (A) a transition metal, (B) a monophosphine, and (C) a tetraphosphine having the following structure:

[0065] wherein each P is a phosphorous atom, and each of R1-R46are independently hydrogen, a Cl to C8 alkyl group, an aryl group, an alkaryl group, or a halogen, the contacting conducted in one or more reaction zones and at hydroformylation conditions to produce a blend of normal (N) and iso (I) aldehydes at a N / I ratio, wherein the hydroformylation production rate is increased incrementally by taking at least 3, preferably 4, 5, or even all 6 of the following actions, preferably in the order listed:

[0066] 1. Establishing the optimized H2 / CO partial pressure ratio limited to greater than 0.4: 1 to less than 2.5: 1.

[0067] 2. Increasing the partial pressure of syngas at the optimized ratio established in Step 1 limited to a CO partial pressure of 30 psi in at least one reaction zone.

[0068] 3. Increasing the partial pressure of olefin in at least one reaction zone up to a level not to exceed the point at which more than 2% of the olefin feed is being lost via the purge vent stream of the last reaction zone or the alkane purge stream of an optional olefin recovery process.

[0069] 4. Lowering the concentration of monophosphine within the reaction fluid to a lower limit of about 1.5 wt. %.

[0070] 5. Increasing the temperature within at least one reaction zone to a limit of about 98 °C.

[0071] 6. Increasing the concentration of transition metal within the reaction fluid up but not to exceed 1200 ppmw in the reaction zone. It should be understood that steps 1-5 are readily reversible (i.e., the rate can be decreased by reversing the change) but Step 6 is largely irreversible, although lowering the reactor temperature (reversing Step 5) after Step 6 would allow the production rate to be reduced if desired. It should also be understood that it is contemplated to combine steps (e.g., perform both Steps 1 and 2 at the same time) or to skip a single step and still be within the scope of the current invention. At least 3, preferably 4, more preferably all 5 of the first 5 steps should be employed in the listed order but doing one of the steps in a different order (e.g., Step 4 before Step 2) is contemplated as being within the scope of the invention, but doing so is not expected to be optimal. The time between steps is not prescribed in the present invention and will instead be dictated by the observed performance of the system.

[0072] The monophosphine, in some embodiments, is one or more of the following: triphenylphosphine, tris(o-tolyl)phosphine, trinaphthylphosphine, tri(p-methoxyphenyl) phosphine, tri(m-chlorophenyl)-phosphine, tribenzylphosphine, tricyclohexylphosphine, dicyclohexylphenylphosphine, cyclohexyldiphenylphosphine, and trioctylphosphine. The monophosphine is triphenylphosphine in some embodiments. In some embodiments, the catalyst comprises a mixture of different species of monophosphines.

[0073] In some embodiments, each of R’-R46in the structure for the tetraphosphine are hydrogen. In some embodiments the catalyst comprises one or more of the following tetraphosphines:

[0074]

[0075] In some embodiments, the transition metal comprises rhodium, the monophosphine is triphenylphospine, each of R'-R46are hydrogen, and the olefin comprises propylene.

[0076] In some embodiments, the amount of monophosphine in the reaction zone is greater than 1.5 weight percent based on the total weight of reaction fluid in the reaction zone. The amount of monophosphine in the reaction zone, in some embodiments, is from 1.5 to 13 weight percent based on the total weight of reaction fluid in the reaction zone. The amount of monophosphine in the reaction zone, in some embodiments, is from 4 to 8 weight percent based on the total weight of reaction fluid in the reaction zone. In some embodiments, the amount of tetraphosphine in the reaction zone is greater than 0.06 weight percent based on the total weight of reaction fluid in the reaction zone. The amount of tetraphosphine in the reaction zone, in some embodiments, is from 0.1 to 9 weight percent based on the total weight of reaction fluid in the reaction zone. In some embodiments, the amount of monophosphine in the reaction zone is greater than 1.5 weight percent and the amount of tetraphosphine in the reaction zone is greater than 0.06 weight percent and preferably below 5 weight percent, 2 weight percent, 1 weight percent and most preferably below about 0.4 weight percent, each based on the total weight of reaction fluid in the reaction zone. In some embodiments, the amount of monophosphine in the reaction zone is from 1.5 to 13 weight percent and the amount of tetraphosphine in the reaction zone is from 0. 1 to 9 weight percent, each based on the total weight of reaction fluid in the reaction zone. Hydrogen and carbon monoxide may be obtained from any suitable source, including petroleum cracking and refinery operations.

[0077] It has surprisingly been discovered that CO partial pressure is the dominant variable for both hydroformylation rate and N / I compared to H2 partial pressure. Moreover, excess hydrogen will lower olefin efficiency due to the hydrogenation side reaction forming alkanes (e.g., propane). Thus, the first step of the process of the invention comprises establishing the optimized H2 / CO partial pressure ratio so as to minimize alkane formation and thereby improve olefin efficiency. As discovered and disclosed herein, the optimized H2 / CO partial pressure ratio is preferably within the range of above 0.4: 1, preferably above 0.6: 1, more preferably above 0.7:1, and most preferably above 0.9: 1 to less than 2.5: 1, preferably below 1.5: 1, and most preferably below 1.04: 1.

[0078] Within commercial scale operations, there will likely be variation in the ratio subject to equipment and measurement limitations but generally the ratio is within 20 % of the target value (i.e., for a target of 1.1: 1.0, one might observe values from 0.9: 1 to 1:1.3) but preferably within 10%, or most preferably within 5% of the target value. With the exception of these unintended variations, the optimized H2 / CO partial pressure ratio is maintained throughout all steps of the process of the invention.

[0079] Syngas (from synthesis gas) is the name given to a gas mixture that contains varying amounts of CO and H2. Production methods are well known. Hydrogen and CO typically are the main components of syngas, but syngas may contain CO2 and inert gases such as N2 and Ar. Syngas is commercially available and is often used as a fuel source or as an intermediate for the production of other chemicals. In one aspect, Step 2 of the current invention comprises increasing the optimized syngas partial pressure. To be clear, the partial pressures of both hydrogen and carbon monoxide are increased concomitantly such that the optimized H2 / CO partial pressure ratio is maintained during Step 2 of the current invention.

[0080] The ratio of H2 and CO in the syngas feed to the reaction zone can be varied by methods well known in the art including pressure-swing absorption separation and membrane separation processes. In some cases, the facility may not have the capability to vary the ratio in the feeds thus the optimization in Step 1 may be limited. There is some control of the headspace partial pressures by the reactor headspace vent. It has been found that the headspace composition may differ from that of the feeds thus some control of the headspace partial pressure ratio can be affected by changes in the vent flow, particularly if the vent is sent to a downstream reactor thus not wasted. In a preferred embodiment, a syngas separation unit is employed to send a CO-enriched stream to the hydroformylation zone and an ft-enriched stream to a downstream hydrogenation unit.

[0081] In one aspect / embodiment, Step 3 of the current invention comprises increasing the olefin partial pressure in the reaction zone. In some embodiments, the olefin partial pressure in the reaction zone is increased by increasing the olefin feed rate to at least one reaction zone. Recognizing that partial pressures and concentration are related, the use of higher olefin partial pressure leads to an increased proportion of olefin in the liquid catalyst fluid. It has been discovered and disclosed herein that the hydroformylation rate demonstrated by the catalyst of the current invention has a positive order relationship in regard to olefin concentration. Increasing the olefin partial pressure in the reaction zone therefore will accelerate the hydroformylation reaction, but it may also increase the concentration of olefin in the "off gas" (e.g., inerts purge vent) from the last reaction zone. Since it may be necessary to purge part of the gas stream from the product recovery zone before recycling to the liquid body in order to remove inerts (e.g., alkanes), higher olefin content in the "off gas" means lower olefin efficiency. Thus, increasing the olefin partial pressure in the reaction zone indiscriminately could result in poor olefin efficiency which would negatively impact process economics. In one aspect, Step 3 of the current invention comprises increasing the olefin feed rate to at least one reaction zone up to a level not to exceed the point at which more than 2% of the olefin feed becomes lost via the purge vent stream of the last reaction zone or the alkane purge stream of an optional olefin recovery process. The olefin concentration in the reaction zone headspace or the purge stream can be measured by one or more analytical techniques, such as gas chromatography, and the flow rate of the purge stream can be measured by one or more mass flow meters well known to those skilled in the art.

[0082] In cases where market demand declines and the plant scales back production by reducing the olefin feed, the amount of unreacted olefin in the last reaction zone will typically be very low. When the plant wished to return to normal production levels, the olefin feed may be returned to the original (e.g., plant design) flows rate, which will cause the olefin partial pressure in the reaction zones to increase. However, due to changes in the catalyst or catalyst solution composition, the system may not return to the initial performance. In this case, the process of the present invention would allow the plant to move production back to design production rates in a cost-effective manner.

[0083] In some embodiments, the catalyst of the invention has been utilized for commercial production for about 6 months and the observed aldehyde productivity has declined from the initial target. The process of the invention, wherein the steps are taken in the prescribed order, gives the best results for the optimized plant performance. The time between each step is not critical to the invention but the order is important, particularly for optimal performance.

[0084] In some embodiments, equipment designed to recover unreacted olefins such as propylene from the inerts purge stream may be employed (see for example US 6,969,777, WO2017160956, and CN104610032). In such embodiments, the olefin partial pressure increase is generally limited by the propylene partial pressure in the alkane purge stream from the propylene recovery unit comprising less than or equal to 2% of the total olefin fed to the first reaction zone. The olefin concentration in the olefin recovery purge stream is measured by one or more analytical techniques, such as gas chromatography.

[0085] In one aspect, the fourth step of the process of the invention comprises lowering the concentration of the monophosphine. In one embodiment, a catalyst solution comprising rhodium, one or more equivalents of tetraphosphine, and a monophosphine is subjected to conditions in the catalyst-product separation zone that volatilize at least some of the free monophosphine along with the product aldehydes. In some embodiments, the monophosphine that is removed with the product is replenished so as to maintain a near constant concentration of monophosphine in the process fluid. Such monophosphine additions may be made batch wise, or on a continuous basis. It has surprisingly been discovered that there is a negative order relationship between monophosphine concentration and hydroformylation rate. Stated another way, lowering the concentration of the monophosphine in the reaction fluid via volatilization (e.g., vaporization) and suspending monophosphine additions will increase the observed production rate. While the tetraphosphine and the transition metal catalysts are high molecular weight compounds of exceptionally low volatility, the volatility of monophosphines is known, and the ability to regulate their concentration within a reaction fluid is known to those of ordinary skill in the art. For example, U.S. Patent No. 5,110,990 describes how to minimize volatilization of monophosphines in a reaction fluid such that one of skill in the art would understand that volatilization of monophosphine in a reaction fluid can be promoted by not implementing the procedures described in that patent. The lower limit of monophosphine concentration in the process of the invention is < 1.5 wt. %. Monophosphine concentration may be measured by one or more analytical techniques, such as high-performance liquid chromatography (HPLC). In one embodiment, as Step 4 is being done, the process of Step 2 can be repeated. It has been found that when the monophosphine level is dropping and the production rate is increasing, the N / I will also tend to increase. As previously described, an unintended consequence of Step 2 (i.e., increasing the CO partial pressure) was a potentially lower N / I. Thus, Step 2 may be used to counter the higher N / I from Step 4.

[0086] In one aspect, the fifth step of the process of the invention comprises increasing the temperature in at least one reaction zone. It is known to the skilled person that hydroformylation rate will generally increase with higher temperatures. It is also known that higher temperatures often have unintended negative consequences, including but not limited to increased formation of heavy byproducts, accelerated ligand degradation rate, and shortened catalyst life. Increasing the degradation of the tetraphosphine would negatively impact process economics. It has been determined and disclosed herein that in the process of the invention, the temperatures in the reaction zone should not be increased beyond 98 °C.

[0087] In another aspect, the sixth step of the process comprises increasing the transition metal concentration in the reaction fluid subject to ligand degradation rate and tetraphosphine: metal molar ratio and solubility limitations described above. The highest concentration of transition metal in the process of the current invention is 1200 ppmw.

[0088] A solvent advantageously is employed in the hydroformylation process. Any suitable solvent that does not unduly interfere with the hydroformylation process can be used. By way of illustration, suitable solvents for rhodium catalyzed hydroformylation processes include those disclosed, for example, in US Patents 3,527,809; 4,148,830; 5,312,996; and 5,929,289. In rhodium catalyzed hydroformylation processes, it may be preferred to employ, as a primary solvent, aldehyde compounds corresponding to the aldehyde products desired to be produced and / or higher boiling aldehyde liquid condensation by-products, for example, as might be produced in situ during the hydroformylation process, as described for example in US 4,148,830 and US 4,247,486. The primary solvent will normally eventually comprise both aldehyde products and higher boiling aldehyde liquid condensation by-products (“heavies”), due to the nature of the continuous process. The amount of solvent is not especially critical and need only be sufficient to provide the reaction medium with the desired amount of transition metal concentration. Typically, the amount of solvent ranges from about 5 percent to about 95 percent by weight, based on the total weight of the reaction fluid. Mixtures of solvents may be employed. The catalyst of this invention comprises a transition metal, monophosphine, and a tetraphosphine. In certain particularly useful embodiments, the catalyst comprises rhodium a monophosphine, and a tetraphosphine. The most desirable catalyst is free of metal-bound halogens such as chlorine, and contains hydrogen, carbon monoxide and at least one of the monophosphine and tetraphosphine complexed with rhodium metal to produce a catalyst soluble in the aforementioned liquid phase and stable under the conditions of the reaction.

[0089] The transition metal can 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, with preferred metals being rhodium, cobalt, iridium and ruthenium, more preferably rhodium, cobalt and ruthenium, especially rhodium.

[0090] The number of available coordination sites on such metals is well known in the art. Thus, the catalytic species, which may comprise a complex catalyst mixture, may comprise monomeric, dimeric, or higher nuclearity forms, which are preferably characterized by at least one organophosphine-containing molecule complexed per one molecule of metal, e.g., rhodium. For instance, it is considered that the catalytic species of the preferred catalyst employed in a hydroformylation reaction may be complexed with carbon monoxide and hydrogen in addition to the tetraphosphine and / or organophosphine ligands in view of the carbon monoxide and hydrogen gas employed by the hydroformylation reaction. The exact structure of the catalytic complex is not known and there may be more than one active catalyst structure or resting states as noted above.

[0091] In certain preferred embodiments, the transition metal is rhodium. Rhodium can be introduced into the liquid phase as a preformed catalyst, e.g., a stable crystalline solid, rhodium hydridocarbonyl-tris(triphenyl phosphine), RhH(CO)(PPh3)3. The rhodium can be introduced to the liquid body as a precursor form which is converted in situ into the catalyst. Examples of such precursor form are rhodium carbonyl triphenylphosphine acetylacetonate, RI12O3, Rh4(CO)i2, Rhe(CO)i6, and rhodium dicarbonyl acetylacetonate. Both the catalyst compounds which will provide active species in the reaction medium, and their preparation are known by the art, see Brown et al., Journal of the Chemical Society, 1970, pp. 2753- 2764.

[0092] The rhodium complex catalysts may be in homogeneous or heterogeneous form. For instance, preformed rhodium hydrido-carbonyl-phosphine ligand catalysts may be prepared and introduced into a hydroformylation reaction mixture. More preferably, the rhodiumphosphine ligand complex catalysts can be derived from a rhodium catalyst precursor that may be introduced into the reaction medium for in situ formation of the active catalyst. For example, rhodium catalyst precursors such as rhodium dicarbonyl acetylacetonate, RhOs. Rh4(CO)i2, Rh6(CO) 16, Rh(NO3)s and the like may be introduced into the reaction mixture along with the monophosphine and or tetraphosphine for the in-situ formation of the active catalyst. In a preferred embodiment, rhodium dicarbonyl acetylacetonate is employed as a rhodium precursor and combined with at least one of the monophosphine and tetraphosphine in a solvent and introduced into the reactor along with syn gas for the in-situ formation of the active catalyst. Additional monophosphine and or tetraphosphine may be added as necessary to achieve and maintain the desired concentrations. In any event, it is sufficient that carbon monoxide, hydrogen, monophosphine and tetraphosphine are all ligands that are capable of being complexed with the metal and that at least one active metal-ligand catalyst is present in the reaction mixture under the conditions used in the hydroformylation reaction.

[0093] In some embodiments, a catalyst composition is formed in a mix tank by combining the rhodium catalyst precursor with monophosphine and / or tetraphosphine. If the rhodium catalyst precursor is only combined with one of the two ligands prior to addition to the reactor, the other ligand can be added separately to the reactor to form the catalyst composition in the reactor.

[0094] The amount of rhodium complex catalyst present in the reaction fluid need only be that minimum amount necessary to produce the desired production rate. In general, rhodium concentrations in the range of from 50 ppmw to 1200 ppmw, calculated as free metal in the reaction fluid in a hydroformylation reactor, should be sufficient for most processes, while it is generally preferred to employ from 150 to 800 ppmw of metal, and more preferably from 150 to 500 ppmw of rhodium.

[0095] In some embodiments, the catalyst composition (whether formed entirely in a mix tank or formed in the reactor) comprises at least 40 moles of monophosphine per mole of transition metal (preferably rhodium). In some embodiments, the catalyst composition comprises from 40 to 350 moles of monophosphine per mole of transition metal (rhodium). In some embodiments, the catalyst composition comprises at least 1 mole of tetraphosphine per mole of transition metal (rhodium). In some embodiments, the amount of tetraphosphine in the catalyst composition comprises from 1 to 10 moles of tetraphosphine per mole of transition metal (rhodium). The amount of moles of monophosphine or tetraphosphine is measured by high performance liquid chromatography (HPLC) as described in the Examples. In most cases, the levels of the phosphine ligands are reported as weight percent since the typical methods are calibrated for weight percent but can be readily converted to moles based on the molecular weight to assess the ligand: transition metal ratio. The amount of moles of transition metals such as rhodium can be readily measured by analytical techniques such as atomic absorption, inductively coupled plasma or x-ray fluorescence.

[0096] While tetraphosphine ligand can conceivably degrade to one or more monophosphine compounds, the amount of monophosphine in the catalyst compositions and the reaction fluid according to embodiments of the present invention are much greater than would be expected to potentially appear through degradation. In other words, the vast majority of the monophosphine in the catalyst composition or reaction fluid is added or charged to the catalyst composition or reaction fluid to provide the specified amount (e.g., not derived from the tetraphosphine present in the catalyst composition or reaction fluid).

[0097] For commercial operations, ligand concentrations are typically maintained by periodic or continuous additions. To do so, the concentrations of ligands in the reaction fluid are routinely measured by one or more analytical techniques; high performance liquid chromatography (HPLC) is typically preferred. Unless otherwise indicated herein, when referring to the amount of ligand in a reaction, the ligand concentration is determined by HPLC as described in the Examples. Ligand concentrations in such analyses are often reported as weight percent; thus, it is often convenient to use these units for continuous operation.

[0098] In some embodiments wherein R]-R46in the tetraphosphine shown above are each hydrogen and the amount of tetraphosphine in the reaction fluid in a reactor of a hydroformylation process is from 0. 1 to 5 weight percent based on the total weight of the reaction fluid in the reactor. By way of illustration, a preferred catalyst precursor composition consists essentially of a solubilized rhodium complex precursor, at least one of the monophosphine and tetraphosphine, and a solvent. The monophosphine and or the tetraphosphine will readily replace one of the carbonyl ligands of the rhodium acetylacetonate complex precursor as witnessed by the evolution of carbon monoxide gas. Upon introduction of the catalyst precursor composition to the reactor, additional monophosphine or tetraphosphine may optionally then be added to achieve the target concentrations within the reaction fluid.

[0099] Accordingly, the rhodium- ligand complex catalysts in the reaction fluid of a hydroformylation reactor advantageously comprise rhodium complexed with carbon monoxide and at least one of monophosphine and tetraphosphine. In one embodiment, mixtures of rhodium- ligand complexes are employed. For example, the catalyst additionally comprises rhodium complexed with carbon monoxide and tetradentate phosphine in a chelated and / or non-chelated fashion. The catalyst additionally comprises rhodium complexed with one or more monophosphine molecules and carbon monoxide. The exact structure of the catalytic complex is not known and there may be more than one active catalyst structure or resting state as noted above.

[0100] In addition to the rhodium complex catalyst, free monophosphine (i.e., monophosphine that is not complexed with the metal) will also be present in the reaction fluid and may also be present in a catalyst composition prior to being provided to a reactor depending on the particular composition. The significance of free ligand is taught in US 3,527,809, GB 1,338,225, and Brown et al., supra., pages 2759 and 2761. In some embodiments, the hydroformylation process of this invention may involve from 1.5 weight percent or higher of free monophosphine in the reaction medium. The reaction fluid may also contain free tetradentate phosphine. In some such embodiments, the concentration of free tetradentate phosphine may range from 0.1 to 5 moles per mole of rhodium.

[0101] The monophosphine compounds that may serve as ligands in embodiments of the present invention are compounds of Formula I: (Formula I) wherein P is a phosphorous atom, and each of Y1- Y3are independently an aryl group, an alkaryl group, a cycloalkyl group, a benzyl group, a C3 to C8 alkyl group, an alkoxyl group of 1-8 carbons, an aryloxy group, or a halogen. Illustrative examples include but are not limited to triphenylphosphine, tris(o-tolyl)phosphine, trinaphthylphosphine, tri(p- methoxyphenyl) phosphine, tri(m-chlorophenyl)-phosphine, tribenzylphosphine, tricyclohexylphosphine, dicyclohexylphenylphosphine, cyclohexyldiphenylphosphine, trioctylphosphine, and the like. In some embodiments, the monophosphine compounds can be sterically hindered phosphines such as those described in U.S. Patent No. 4,283,562 and U.S. Patent No. 5,741,945. For example, in some such embodiments, Y'-Y3in Formula I can independently be a substituted or unsubstituted C3 to C8 alkyl, a substituted or unsubstituted C5 to C8 cycloalkyl group, or a substituted or unsubstituted C6 to C12 aryl group.

[0102] Mixtures of monophosphines can be used in some embodiments. The tetraphosphine compounds that may serve as the ligands in embodiments of the present invention are compounds of Formula II: wherein each P is a phosphorous atom, and each of R'-R46are independently hydrogen, a Cl to C8 alkyl group, an aryl group, an alkaryl group, a haloalkyl group, or a halogen. In a preferred embodiment, each of R'-R46is hydrogen. Other examples of tetraphosphines that can be used in some embodiments are described elsewhere in the present specification.

[0103] Mixtures of tetraphosphines can be used in some embodiments.

[0104] Hydroformylation processes, and conditions for their operation, are well known. In a typical embodiment, an olefin (e.g., propylene) is hydroformylated in a continuous or semi-continuous fashion, with the product being separated in a separation zone, and the concentrated catalyst solution being recycled back into one or more reactors. The recycle procedure generally involves withdrawing a portion of the liquid reaction medium containing the catalyst and aldehyde product from the hydroformylation reactor, i.e., reaction zone, either continuously or intermittently, and recovering the aldehyde product therefrom by use of a composite membrane, such as disclosed in US 5,430,194 and US 5,681,473, or by the more conventional and preferred method of distilling it, i.e. vaporization separation, in one or more stages under normal, reduced or elevated pressure, as appropriate, in a separate distillation zone, the non-volatilized metal catalyst containing residue being recycled to the reaction zone as disclosed, for example, in US 5,288,918. Condensation of the volatilized materials, and separation and further recovery thereof, e.g., by further distillation, can be carried out in any conventional manner, the crude aldehyde product can be passed on for further purification and isomer separation, if desired, and any recovered reactants, e.g., olefinic starting material and syngas, can be recycled in any desired manner to the hydroformylation zone (reactor). The recovered metal catalyst containing retentate of such membrane separation or recovered non- volatilized metal catalyst containing residue of such vaporization separation can be recycled, to the hydroformylation zone (reactor) in any conventional manner desired.

[0105] In a preferred embodiment, the hydroformylation reaction fluid comprises at least some amount of five main ingredients or components, i.e., a solvent, the aldehyde product, free triphenylphosphine ligand, free tetraphosphine ligand, and rhodium catalyst complexes comprised of rhodium and one or more of tetraphosphine and monophosphine. The hydroformylation reaction mixture compositions can and normally will contain additional ingredients such as those that have either been deliberately employed in the hydroformylation process or formed in situ during said process. Examples of such additional ingredients include unreacted olefin starting material, carbon monoxide and hydrogen gases, and in situ formed by-products, ligand degradation compounds, and high boiling liquid aldehyde condensation by-products, as well as other inert co-solvent type materials or hydrocarbon additives, if employed.

[0106] The hydroformylation process may be carried out using one or more suitable reactors such as, for example, a continuous stirred tank reactor (CSTR), Venturi reactor, bubble column reactor, or a slurry reactor. The optimum size and shape of the reactor will depend on the type of reactor used. The reaction zone employed may be a single vessel or may comprise two or more discrete vessels. The separation zone employed may be a single vessel or may comprise two or more discrete vessels. The reaction zone(s) and separation zone(s) employed herein may exist in the same vessel or in different vessels. For example, reactive separation techniques such as reactive distillation, and reactive membrane separation may occur in the reaction zone(s).

[0107] The hydroformylation process can be conducted with recycling of unconsumed starting materials if desired. The reaction can be conducted in a single reaction zone or in a plurality of reaction zones, and in series or in parallel. The reaction steps may be affected by the incremental addition of one of the starting materials to the other. Also, the reaction steps can be combined by the joint addition of the starting materials. The starting materials may be added to each or all of the reaction zones in series. When complete conversion is not desired or not obtainable, the starting materials can be separated from the product, for example by distillation, and the starting materials then recycled back into the reaction zone.

[0108] The hydroformylation process may be conducted in either glass lined, stainless steel or similar type reaction equipment. The reaction zone may be fitted with one or more internal and / or external heat exchanger(s) in order to control undue temperature fluctuations, or to prevent any possible "runaway" reaction temperatures.

[0109] The hydroformylation process of this invention may be conducted in one or more steps or stages. The exact number of reaction steps or stages will be governed by the best compromise between capital costs and achieving high catalyst selectivity, activity, lifetime and ease of operability, as well as the intrinsic reactivity of the starting materials in question and the stability of the starting materials and the desired reaction product to the reaction conditions.

[0110] In one embodiment, the hydroformylation process useful in this invention may be carried out in a multistage reactor such as described, for example, in US 5,728,893. Such multistage reactors can be designed with internal, physical barriers that create more than one theoretical reactive stage per vessel.

[0111] It is generally preferred to carry out the hydroformylation process in a continuous manner. Continuous hydroformylation processes are well known in the art. The continuous process can be carried out in a single pass mode, i.e., wherein a vaporous mixture comprising unreacted olefinic starting material(s) and vaporized aldehyde product is removed from the liquid reaction mixture from whence the aldehyde product is recovered and make-up olefinic starting material(s), carbon monoxide and hydrogen are supplied to the liquid reaction medium for the next single pass through without recycling the unreacted olefinic starting material(s). Such types of recycle procedure are well known in the art and may involve the liquid recycling of the metal-organophosphorus complex catalyst fluid separated from the desired aldehyde reaction product(s), such as disclosed, for example, in US 4,148,830 or a gas recycle procedure such as disclosed, for example, in US 4,247,486, as well as a combination of both a liquid and gas recycle procedure if desired. The most preferred hydroformylation process comprises a continuous liquid catalyst recycle process. Suitable liquid catalyst recycle procedures are disclosed, for example, in US Patents 4,668,651; 4,774,361; 5,102,505 and 5,110,990.

[0112] In one embodiment, the aldehyde product mixtures may be separated from the other components of the crude reaction mixtures in which the aldehyde mixtures are produced by any suitable method such as, for example, solvent extraction, crystallization, distillation, vaporization, wiped film evaporation, falling film evaporation, phase separation, filtration, or any combination thereof. It may be desired to remove the aldehyde products from the crude reaction mixture as they are formed through the use of trapping agents as described in WO 88 / 08835. One method for separating the aldehyde mixtures from the other components of the crude reaction mixtures is by membrane separation, which is described, for example in US Patents 5,430,194 and 5,681,473.

[0113] As indicated above, desired aldehydes may be recovered from the reaction mixtures. For example, the recovery techniques disclosed in US Patents 4,148,830 and 4,247,486 can be used. For instance, in a continuous liquid catalyst recycle process the portion of the liquid reaction mixture (containing aldehyde product, catalyst, etc.), i.e., reaction fluid, removed from the reaction zone can be passed to a separation zone, e.g., vaporizer / separator, wherein the desired aldehyde product can be separated via distillation, in one or more stages, under normal, reduced or elevated pressure, from the liquid reaction fluid, condensed and collected in a product receiver, and further purified if desired. The remaining non- volatilized catalyst containing liquid reaction mixture may then be recycled back to the reactor as may, if desired, any other volatile materials, e.g., unreacted olefin, together with any hydrogen and carbon monoxide dissolved in the liquid reaction after separation thereof from the condensed aldehyde product, e.g., by distillation in any conventional manner.

[0114] More particularly, distillation and separation of the desired aldehyde product from the metal-organophosphorous complex catalyst containing reaction fluid may take place at any suitable temperature desired. In general, it is preferred that such distillation take place at relatively low temperatures, such as below 150 °C, and more preferably at a temperature in the range of from 50 °C to 140 °C. In one embodiment, such aldehyde distillation takes place under reduced pressure, e.g., a total gas pressure that is substantially lower than the total gas pressure employed during hydroformylation when low boiling aldehydes (e.g., C4 to Ce) are involved or under vacuum when high boiling aldehydes (e.g. C7 or greater) are involved. For instance, a common practice is to subject the liquid reaction product medium removed from the hydroformylation reactor to a pressure reduction so as to volatilize a substantial portion of the unreacted gases dissolved in the liquid medium that now contains a much lower synthesis gas concentration than is present in the reaction medium to the distillation zone, e.g., vaporizer / separator, wherein the desired aldehyde product is distilled. In genera], distillation pressures ranging from vacuum pressures on up to total gas pressure of 340 kPa should be sufficient for most purposes. These separation processes typically have a process purge vent to remove excess syngas and inerts such as N2 and hydrocarbons including hydrogenated olefins.

[0115] In one embodiment, flowing gases may be used in the separation zone to facilitate the aldehyde distillation. Such strip gas vaporizers are described for example in US 8,404,903.

[0116] The increased concentrations, high temperatures, and low partial pressures that occur in the separation zone may negatively affect the catalyst, both in terms of catalyst deactivation and / or increased ligand degradation.

[0117] Illustrative non-optically active aldehyde products of hydroformylation processes according to embodiments of the present invention will depend on the olefin used as a reactant and can include e.g., , n-butyraldehyde, isobutyraldehyde, n-valeraldehyde, 2- methyl 1 -butyraldehyde, hexanal, hydroxyhexanal, 2-methyl 1-heptanal, nonanal, 2-methyl- 1-octanal, decanal, adipaldehyde, 2-methylglutaraldehyde, 2-methyladipaldehyde, 3- hydroxypropionaldehyde, and the like.

[0118] In some embodiments where propylene is the olefin that undergoes the hydroformylation reaction, the product is a mixture of n-butyraldehyde and 2- methylpropionaldehyde. As previously noted, the ratio of linear (N) to branched (I) isomers such as the n-butyraldehyde to 2-methylpropionaldehyde (isobutyraldehyde) ratio is conventionally described as the N / I ratio or simply N / I. With longer-chain olefins, the ratio of terminal aldehyde to the sum of the branched (internal) aldehydes is referred to herein as the N / I ratio.

[0119] As shown in the following table, each step of the process of the invention can be effectively implemented within the range defined by the lower and upper limits. It should be understood that with the exception of #6, all can be readily reversed, and the effects will be in the opposite direction indicated below. In addition, with #6, some of the other variables may be scaled back such as #5 (temperature). The time between each step will be a function of the particular catalyst and system performance and is not critical to the operation of the present invention.

[0120] Table 1

[0121] Step 6 (changing the rhodium concentration) is the least preferred option in most cases since the price of rhodium is very high thus represents a high running capital cost. In addition, it has been found that the tetraphosphine ligand degradation rate is higher at higher transition metal concentrations which represents another cost penalty. However, in systems where a catalyst purge is used to remove heavies and / or where inherent rhodium losses (e.g., via entrainment) may be high, foregoing rhodium makeup charges may allow for Step 6 to be reversed in a timely fashion.

[0122] In some embodiments, after Step 6, the process can be repeated starting at Step 1 or other subsequent steps. As noted above, at or during Step 4, Step 2 may be repeated. The time between each step is not critical to the operation of the present invention and can be quite substantial.

[0123] Some embodiments of the invention will now be described in more detail in the following Examples.

[0124] EXAMPLES

[0125] All parts and percentages in the following examples are by weight unless otherwise indicated. The concentration of Ligand A is expressed as either weight percent of the solution, or as equivalents (i.e., moles of Ligand A per mole of rhodium). Pressures in the following examples are given as pounds per square inch gauge unless otherwise indicated. All manipulations such as preparation of catalyst solutions are done under inert atmosphere unless otherwise indicated. Comparative Experiments are not embodiments of the invention.

[0126] Gas compositions (mole %) are measured by gas chromatography (GC) and partial pressures are then calculated based on the total pressure using Raoult’s law. The terms “PPH2”, “PPCO”, and “PPC3=” refer to partial pressures of H2, CO, and propylene, respectively. Tetradentate phosphine concentration is measured by High Pressure Liquid Chromatography (HPLC). In order to prevent oxidation during analysis, the phosphines are derivatized to stable phosphine sulfides by mixing with a sulfur-saturated diluent (50: 50 by volume acetonitrile : THF saturated with elemental sulfur).

[0127] External standard HPLC analyses are performed on an Agilent 1200 Infinity Series HPLC equipped with an UHPLC SB-C8 3.0mm, 1.8 um guard column followed by a Zorbax SB-C8 analytical column (3.0 xl50 mm). Solvent gradient is 55 % water with a balance of acetonitrile for 4 minutes; then adjusted to 20: 80 water: acetonitrile for 22 minutes, and finally back to the original composition for the remainder of the 35-minute run. Solvent flow rate is 1.00 mL / min throughout, with the column temperature maintained at 40° C. Two microliters of sample are injected into the system; the multi-wavelength UV detector is set at 240 nm.

[0128] Preparation of Ligand A

[0129] The tetradentate phosphine compound Ligand A used in these examples is prepared as set forth in WO / 2019 / 231611 and has the following structure:

[0130] Ligand B is triphenylphosphine (TPP).

[0131] General Procedure A;

[0132] A liquid recycle reactor system is employed that consists of two 1 -liter stainless steel stirred tank reactors connected in series. Each reactor is equipped with an agitator, sparger, silicon oil shell, and pneumatic level control. Reactors 1 and 2 are further connected via lines to transfer any unreacted gases, and to allow a portion of the liquid solution containing aldehyde product and catalyst to be pumped from reactor 1 to reactor 2. Hence, the unreacted olefin of reactor 1 may be further hydroformylated in reactor 2. Reactor 2 has a vent for removal of unreacted gases. A portion of the reactor 2 solution is continuously pumped to a catalyst separation zone comprising two vaporizers in series. Each vaporizer consists of a heated zone followed by a vessel for vapor / liquid disengagement (separator). The vaporized components are condensed and collected in a product receiver. The nonvolatile liquid effluent from the second vaporizer, which includes the catalyst, is recycled to Reactor 1. The pressures and temperatures of the vaporizers are varied to achieve the desired product separation. A pneumatic level controller maintains the liquid level in each of the separators. Reaction production rates are expressed as moles of aldehyde produced per volume of catalyst solution per unit time (moles / L-hour). Product selectivity is expressed as N / I.

[0133] General Procedure B -

[0134] A continuous reaction system is employed comprising 90 mL Fisher-Porter tubes equipped with mass flow controllers for accurate control of gas flows. The tubes are charged with catalyst solutions, gases are continuously introduced via a sparger at the bottom of the reactor. The off gas is sent to a process analyzer to allow quantitation of components. This reactor design is described in detail in US 5,731,472, the teachings of which are incorporated by reference.

[0135] EXAMPLE 1: General Procedure A is followed with the exception of a single reactor and vaporizer (temperature =110 - 135° C and 11 psig) being employed. The catalyst solution is comprised of 304 ppm Rh, 5.5wt. % TPP and an average of 0.31 wt. % Ligand A. Partial pressures of 20 psi CO and 82 psi propylene are established. All parameters are kept constant except for FL partial pressure. The production rate is determined at each condition and the results are shown in Figure 2.

[0136] The minor changes in reaction production rate and N / I suggest that H2 partial pressure is not a key variable for hydroformylation rate and thus the H2 / CO partial pressure ratio should be optimized to limit propane generation which negatively impacts olefin efficiency (Step 1 of the process of the invention).

[0137] EXAMPLE 2: The procedure of Example 1 is followed, with the exception of catalyst concentrations (290 ppm Rh, 5.9 wt. % TPP, and an average of 0.24 wt. % Ligand A). Partial pressures of 24 psi H and 79 psi propylene are established. All parameters are kept constant except for CO partial pressure. The results are shown in Figure 3.

[0138] It is clear from the data that the PPCO affects the hydroformylation rate and the N / I. Moreover, it is shown that at higher H2 / CO partial pressure ratios, the propane selectivity increases. In other words, higher partial pressure of CO appears to inhibit propane formation; thus, if both H2 and CO are increased at the optimized H2 / CO partial pressure ratio, the benefit of higher CO partial pressure mitigates the negative impact of higher H2 partial pressure for propane formation.

[0139] EXAMPLE 3: Using the data in Example 1, Example 2 and Example 5 which will follow, the relationship between syngas partial pressure ratio (H2 / CO) and propane selectivity may be established. The result is shown in Figure 4.

[0140] As shown in Figure 3, increasing H2 provides minimal increase in hydroformylation rate, but the data of Figure 5 show that higher H2 / CO ratios have a strong, undesired effect on propane selectivity. Thus, it is important to optimize the H2 / CO partial pressure ratio (Step 1 of the process of the invention). The optimized syn gas partial pressure may vary (Step 2 of the process of the invention) as long as the H2 / CO partial pressure ratio is maintained within the indicated range of Step 1.

[0141] EXAMPLE 4 : General Procedure A is followed, and all parameters are kept constant except for the H2 / CO ratio. The hydroformylation rate is determined at each condition and the results are shown in Figure 5. The reaction rate is positive order with respect to CO (reaction rate increases with increasing PPCO) until the PPCO reaches approximately 20 psi, then it becomes slightly negative order at higher PPCO. Since Examples 1 and 2 show that increasing H2 partial pressure has little impact on production rate and N / I, the changes may be attributed to variation in the CO partial pressure.

[0142] The data shows that the PPCO is a key variable for both hydroformylation rate and N / I. If higher reaction rates are needed and the partial pressure of CO is less than about 20 psi, then the partial pressure of syngas should be increased while maintaining the optimized syngas ratio.

[0143] EXAMPLE 5: The procedure of Example 1 is followed with the exception of the partial pressure of CO being held constant at 12 psi and the partial pressure of H2 at 14 psi while the partial pressure of propylene is varied. The results are shown in Figure 6.

[0144] The data shows a direct correlation of the production rate with the concentration of propylene and a modest correlation with N / I and olefin partial pressure but no significant correlation with alkane formation.

[0145] Example 6: General Procedure A is employed. The catalyst solution is comprised of 305 ppm rhodium, 5.2 wt. % TPP and Ligand A (0.39 wt. %). The solution is further comprised of 53% n-butyraldehyde, 2% isobutyraldehyde, 0.65% butyraldehyde dimers, 16 % butyraldehyde trimers, and 5.9 wt. % heavier components such as is common in continuous propylene hydroformylation. The hydrogen partial pressure averages 13.9 psi and the CO partial pressure averages 13.7 psi. TPP concentration is initially held constant via periodic additions. After 320 days, TPP additions are suspended; all other conditions are held constant. The TPP concentration drops slowly due to vaporization and / or oxidation over the next 110 days. On day 430, TPP addition is resumed. The results are shown in Figure 7.

[0146] As the TPP concentration declines, the reaction rate increases. When the TPP concentration is restored, the reaction rate returns to the original value.

[0147] EXAMPLE 7: General Procedure A is followed with the exception of the reactor temperatures being raised from 92°C to 102 °C on day 140; on day 160 the reactor temperatures are returned to 90 °C. The impact of higher reactor temperature on Ligand A degradation is shown in Figure 8.

[0148] The effect of temperature on the polyphosphine ligand usage rate is significant, and would represent an economic penalty (e.g., tripling the cost associated with the polyphosphine ligand). This highlights the importance of the upper temperature limit of Step 5.

[0149] EXMAPLE 8: The procedure of Example 6 is followed with the exception of varying reactor temperatures. The results are shown in Figure 9.

[0150] Raising the temperature causes the heavies selectivity to increase which is an undesirable inefficiency (e.g., about 0.08 % more heavies are formed at 100 °C compared to 90 °C).

[0151] EXAMPLE 9: General Procedure A is followed. The rhodium concentration is initially 328 ppm and is then increased to 438 ppm on day 195 (an increase of 27 %). The results are shown in Figure 10.

[0152] The production rate increases by 29% and there is no immediate impact on the rates of Ligand A usage, propane formation or heavies formation. However, adding rhodium is a direct capital cost and cannot be readily reversed, should a lower production rate be acceptable at a later date.

[0153] EXAMPLES 10 a-f : Hydroformylation is conducted using General Procedure B. The reactor is charged with a solution comprising tetraglyme (20 mL) and Ligand A (0.45 wt. %). The solution further comprises varying concentrations of Ligand B and rhodium as shown in Table 2. Initial reaction conditions are established as shown for Example 10a in Table 2 with a target H2 / CO partial pressure ratio. The resulting catalyst performance is determined and then the Example 10b condition is established while maintaining the other variables constant. This series of process changes and performance measurements are continued sequentially through each of Examples 10 c- lOf. The results are summarized in Table 2. Table 2.

[0154] By the implementation of this scheme, if the performance of the initial catalyst declines or if increased productivity is desired to meet short-term market demands, these changes can provide a nearly 90% production rate increase while maintaining N / I with minimal additional heavies and propane formation.

Claims

WHAT IS CLAIMED IS:

1. A method of optimizing the production rate of a hydroformylation process for producing a mixture of normal (N) and iso (I) aldehydes, the process comprising contacting an olefin with carbon monoxide, hydrogen and a catalyst, the catalyst comprising (A) a transition metal, (B) a monophosphine, and (C) a tetraphosphine having the following structure:wherein each P is a phosphorous atom, and each of R’-R46are independently hydrogen, a Cl to C8 alkyl group, an aryl group, an alkaryl group, or a halogen, the contacting conducted in one or more reaction zones and at hydroformylation conditions to produce a blend of normal (N) and iso (I) aldehydes at a N / I ratio, wherein the hydroformylation production rate is increased incrementally by taking at least three of the following actions in order:

1. establishing the optimized H2 / CO partial pressure ratio limited to greater than 0.4: 1 to less than 2.5:1;2. increasing the partial pressure of syngas at the optimized ratio established in Step 1 limited to a CO partial pressure of 30 psi in at least one reaction zone;3. increasing the partial pressure of olefin in at least one reaction zone up to a level not to exceed the point at which more than 2% of the olefin feed is being lost via the purge vent stream of the last reaction zone or the alkane purge stream of an optional olefin recovery process;4. lowering the concentration of monophosphine within the reaction fluid to a lower limit of about 1.5 wt. %;.

5. increasing the temperature within at least one reaction zone to a limit of about 98 °C;6. increasing the concentration of transition metal within the reaction fluid up but not to exceed 1200 ppmw in the reaction zone.

2. The method of Claim 1 wherein the optimized H2 / CO partial pressure ratio is limited to above 0.6: 1 to less than 2.0: 1.

3. The method of a Claim 1 wherein the optimized H2 / CO partial pressure ratio is limited to above 0.7:1 to less than 1.5:

14. The method of claim 1 wherein the target H2 / CO partial pressure ratio in the reaction zone is from 0.9 to 1.04.

5. The method of claim 1, wherein the monophosphine is triphenylphosphine.

6. The method of claim 1 or claim 2, wherein the transition metal comprises rhodium.

7. The method of any of the preceding claims, wherein each of R'-R46are hydrogen.

8. The method of any of the preceding claims, wherein the olefin is propylene.

9. The method of any of the preceding claims, wherein the amount of monophosphine in the reaction zone is greater than or equal to 0.5 and less than or equal to 18 weight percent based on the total weight of reaction fluid in the reaction zone, or more preferably greater than or equal 1.5 and less than or equal to 13 % or most preferred greater than or equal 3.5% but less than or equal to 7%.

10. The process of the preceding claims wherein at least 4 of the first 5 steps are employed in the specified order.

11. The process of the preceding claims wherein two are more of the steps are combined together.

12. The process of claim 1 wherein all six steps are conducted in the order listed.

13. The method of any of the preceding claims, wherein the amount of tetraphosphine in the reaction zone is from 0.1 wt. % to 0.4 wt. %.

14. The method of any of the preceding claims, wherein the amount of tetraphosphine in the reaction zone is greater than 1.0 mole of tetraphosphine ligand to mole of transition metal.

15. The method of any of the preceding claims wherein the hydroformylation process has been operated for at least 6 months before the sequence of steps in Claim 1 is initiated.

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