Process for the vapor phase hydrogenation of aldehydes.

Abstract

The present invention relates to a process for the gas phase hydrogenation of aldehydes. In one embodiment, the process includes: (a) providing a liquid aldehyde stream to a vaporization system to produce a gaseous aldehyde stream in the presence of a weakly basic amine, the weakly basic amine having a normal boiling point at least 50° C. higher than the normal boiling point of the aldehyde, the weakly basic amine reacting with an acidic impurity in the liquid aldehyde stream to form an ammonium salt adduct, the ammonium salt adduct and any excess weakly basic amine being removed as a heavy purge from the vaporization system; (b) combining the gaseous aldehyde stream with a hydrogen stream, either by feeding a hydrogen stream to the vaporization system, by adding a hydrogen stream to the gaseous aldehyde stream after step (a), or a combination thereof; (c) providing the combined gaseous aldehyde and hydrogen stream to a gas phase hydrogenation zone; and (d) hydrogenating the gaseous aldehyde in the gas phase hydrogenation zone.

Description

[Technical field]

[0001] The present invention relates generally to a process for the vapor phase hydrogenation (VPH) of aldehydes. [Background technology]

[0002] The use of heterogeneous (packed bed) hydrogenation catalysts for the reduction of aldehydes (and unsaturated aldehydes) to the corresponding alcohols is well known. When utilizing such hydrogenation catalysts, particularly in gas phase hydrogenation, a number of issues must be considered, including, for example, reactivity, selectivity (avoidance of side reactions), and pressure drop across the bed.

[0003] For example, considerable research has been done on the shape and size of hydrogenation catalyst particles to alleviate these problems. US Patent No. 4,673,664 discusses the improvement of pressure in fixed bed reactors by using helical, lobed, or polylobed catalyst particles formed by extrusion, which create additional void space due to their decorative structure. US Patent Application Publication No. 2017 / 0189875 discusses the improvement of pressure drop in fixed bed reactors by using catalyst particles of various decorative shapes, and discusses reactor designs using these particles.

[0004] US Patent No. 6,096,931 teaches the addition of low levels (1-50 ppm nitrogen basis) of amines to the gas phase entering the VPH catalyst zone to modify the behavior of the VPH catalyst itself, presumably by modifying sites on the catalyst itself. To achieve the required levels of amine in the gas phase, the amine must be volatile or the vaporization and VPH temperatures must be high enough to vaporize the amine and avoid condensation on the VPH catalyst. The process then requires separation of the amine after the VPH reaction zone. The presence of amines in the VPH zone and downstream purification processes is likely to produce heavies via amine-catalyzed aldol condensation. This reference is silent about the impact of incoming acidic species with the aldehyde feed and does not offer any remediation for incoming acidity.

[0005] Another issue that needs to be considered is the degradation of solid hydrogenation catalysts used in gas phase hydrogenation. It has been found that as the catalyst is used, the solid catalyst degrades and produces "fines" or "catalyst dust". The exact nature of these "fines" is not defined and may vary depending on the nature of the catalyst and the support. However, the ability of the catalyst to tolerate the production of these fines has not been adequately addressed in the past. The generation of fines from a hydrogenation catalyst can result in an undesirable increase in pressure drop across the catalyst bed. Catalyst beds that start out with good performance but rapidly degrade (i.e., exhibit a rapid increase in pressure drop over time) need to be replaced frequently, which may require plant shutdown and expensive catalyst recovery or catalyst disposal.

[0006] It would be desirable to have a process for the vapor phase hydrogenation of aldehydes that minimizes catalyst degradation, thus improving the catalyst. Summary of the Invention

[0007] In a typical vapor phase hydrogenation (VPH) process, the aldehyde stream passes through a vaporizer before entering the hydrogenation reactor. It has been found that having a mild base present during the vaporization process mitigates at least one cause of catalyst degradation with some catalyst supports. The mild base is believed to neutralize acidic impurities (e.g., carboxylic acids possibly derived from olefin carbonylation, aldehyde oxidation, or heavy ester hydrolysis) that may be present in the aldehyde stream. In addition, the presence of acidic impurities may cause side reactions during the vaporization and hydrogenation process. For example, often the amount of acidic impurities from an upstream hydroformylation process (including any intermediate storage) may be high enough to cause decomposition of the VPH catalyst as well as cause side reactions resulting in reduced yields.

[0008] In one embodiment, the process for the vapor phase hydrogenation of aldehydes comprises: (a) providing a liquid aldehyde stream to a vaporization system to produce a gaseous aldehyde stream in the presence of a weakly basic amine, the weakly basic amine having a normal boiling point at least 50° C. higher than the normal boiling point of the aldehyde, the weakly basic amine reacting with acidic impurities in the liquid aldehyde stream to form an ammonium salt adduct, and the ammonium salt adduct and any excess weakly basic amine being removed from the vaporization system as a heavy purge; (b) combining the gaseous aldehyde stream with a hydrogen stream, either by feeding the hydrogen stream to a vaporization system, by adding the hydrogen stream to the gaseous aldehyde stream after step (a), or a combination thereof; (c) providing a combined gaseous aldehyde and hydrogen stream to a vapor-phase hydrogenation zone; (d) hydrogenating the gaseous aldehyde in a vapor phase hydrogenation zone.

[0009] These and other embodiments are described in greater detail in the Detailed Description. [Brief description of the drawings]

[0010] [Figure 1] FIG. 1 is a system diagram showing process streams and equipment according to one embodiment of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0011] This disclosure generally relates to a process for the gas phase hydrogenation of aldehydes. VPH typically involves contacting at least one aldehyde with hydrogen in the presence of a fixed bed catalyst comprising as components a transition metal and at least one support under heterogeneous VPH conditions sufficient to form at least one alcohol product. Prior to hydrogenation, the liquid aldehyde stream is typically converted to a gaseous aldehyde stream in a vaporization system. In one aspect, the invention includes providing the liquid aldehyde stream to a vaporization system to produce a gaseous aldehyde stream in the presence of a weakly basic amine, the weakly basic amine having a normal boiling point at least 50° C. higher than the normal boiling point of the aldehyde, the weakly basic amine reacting with an acidic impurity in the liquid aldehyde stream to form an ammonium salt adduct, and the ammonium salt adduct and any excess weakly basic amine being removed from the vaporization system as a heavy purge. The gaseous aldehyde stream is combined with a hydrogen stream either by feeding a hydrogen stream to a vaporization system, by adding a hydrogen stream to the gaseous aldehyde stream after vaporization, or a combination thereof. The combined gaseous aldehyde and hydrogen stream is provided to a vapor-phase hydrogenation zone, where the gaseous aldehyde is hydrogenated.

[0012] All references to the Periodic Table of the Elements and the various Groups therein are to the version published in CRC Handbook of Chemistry and Physics, 72nd Ed. (1991-1992) CRC Press, page I-11.

[0013] Unless otherwise stated or implicit from the context, all parts and percentages are by weight and all test methods are 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 the U.S. equivalent thereof is so incorporated by reference), particularly 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.

[0014] As used herein, "a", "an", "the", "at least one", and "one or more" are used interchangeably. The terms "comprise", "include", and variations thereof do not have a limiting meaning when these terms appear in the specification and claims. Thus, for example, an aqueous composition comprising "a" hydrophobic polymer particle can be interpreted to mean that the composition comprises "one or more" hydrophobic polymer particles.

[0015] Also herein, the recitation of numerical ranges by endpoints includes all numbers subsumed within that range (e.g., 1-5 includes 1, 1.5, 2, 2.75, 3, 3.80, 4, 5, etc.). For purposes of the present invention, it is to be understood that numerical ranges are intended to include and support all possible subranges within that range, consistent with what one of ordinary skill in the art would understand. For example, a range of 1-100 is intended to convey 1.01-100, 1-99.99, 1.01-99.99, 40-60, 1-55, etc. Also herein, recitations of numerical ranges and / or values ​​can be read to include the term "about," including such recitations in the claims. In such cases, the term "about" refers to substantially the same numerical ranges and / or values ​​as described herein.

[0016] As used herein, the term "ppmw" means parts per million by weight. When used to assess the concentration of weakly basic amines, the phrase "ppmw (nitrogen basis)" is based on the weight of the amine nitrogen divided by the total weight of the mixture. This makes the analysis independent of the molecular weight of the amine and focuses on the active groups on the weakly basic amine. The amine nitrogen does not include nitrogen moieties that cannot react with acids, such as quaternary amines.

[0017] 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 (which can range from 1 to 20 or more carbons, preferably 1 to 12 carbons), as well as hydroxy, halo, and amino. The permissible substituents can be one or more and the same or different for appropriate organic compounds. It is not intended that this invention be limited in any manner by the permissible substituents of organic compounds.

[0018] As used herein, the term "gas phase hydrogenation" is intended to include, but is not limited to, all gas phase hydrogenation processes that involve the conversion of one or more substituted or unsubstituted aldehyde compounds or a reaction mixture containing one or more substituted or unsubstituted aldehyde compounds to one or more substituted or unsubstituted alcohols or a reaction mixture containing one or more substituted or unsubstituted alcohols using a heterogeneous (solid) catalyst. The alcohols can be asymmetric or non-asymmetric. The starting aldehyde can be unsaturated (conjugated or unconjugated with the aldehyde moiety) and the resulting product can be the corresponding saturated or unsaturated alcohol.

[0019] In one aspect, a process for the gas-phase hydrogenation of aldehydes includes: (a) providing a liquid aldehyde stream to a vaporization system to produce a gaseous aldehyde stream in the presence of a weakly basic amine, the weakly basic amine having a normal boiling point at least 50° C. higher than the normal boiling point of the aldehyde, the weakly basic amine reacting with acidic impurities in the liquid aldehyde stream to form an ammonium salt adduct, and the ammonium salt adduct and any excess weakly basic amine being removed from the vaporization system as a heavy purge; (b) combining the gaseous aldehyde stream with a hydrogen stream, either by providing a hydrogen stream to the vaporization system, by adding a hydrogen stream to the gaseous aldehyde stream after step (a), or a combination thereof; (c) providing the combined gaseous aldehyde and hydrogen stream to a gas-phase hydrogenation zone; and (d) hydrogenating the gaseous aldehyde in the gas-phase hydrogenation zone.

[0020] Simple amines such as trialkylamines are too basic, but simple alkanolamines and heterocyclic nitrogen compounds such as imidazoles are not basic enough to effectively neutralize acidic impurities without producing aldol condensation heavies. This leads to longer catalyst life. In addition, removal of feed acid contributes to reducing side reactions in the VPH process itself. Since alkanolamines and imidazoles exhibit very low volatility, they do not vaporize during the VPH system and are removed (along with any salts) in the vaporizer heavy stream, and therefore do not affect downstream purification. The alkalinity or basicity of weakly basic amines is generally reported as the pKa of the conjugate acid, which is advantageously 5-11 at 25°C. The pKa is preferably 5.0-9.5 at 25°C, and most preferably 6.0-9.0 at 25°C, in some embodiments. In some embodiments, the weakly basic amine has a normal boiling point at least 100°C higher than the normal boiling point of the aldehyde. In some embodiments, the weakly basic amine used in the process of the present invention comprises a trialkanolamine or an imidazole. In some embodiments, the weakly basic amine used in the process of the present invention comprises a triethanolamine or a benzimidazole.

[0021] In some embodiments, the concentration of the weakly basic amine in the combined gaseous aldehyde and hydrogen stream in step (c) (the combined stream fed to the gas-phase hydrogenation zone) is less than 1 ppmw (based on nitrogen).

[0022] In some embodiments, the process further comprises measuring the acid content of the liquid aldehyde stream, and the amount of weakly basic amine added to the vaporization system is between 0.1 and 5 equivalents of weakly basic amine per equivalent of acid, hi some embodiments, the amount of weakly basic amine added to the vaporization system is between 0.1 and 1.5 equivalents of weakly basic amine per equivalent of acid.

[0023] In some embodiments, the liquid aldehyde stream to be vaporized and hydrogenated is provided from the hydroformylation reaction and a product-catalyst separation step, in which the hydroformylation catalyst is separated from the hydroformylation product stream to provide the liquid aldehyde stream.

[0024] FIG. 1 is a system diagram illustrating process streams and apparatus according to one embodiment of the present invention. As shown in FIG. 1, liquid aldehyde stream 1, optionally together with hydrogen gas stream 2, is fed to vaporization system 3. The vaporized aldehyde (along with optional H2) exits vaporization device 3 via stream 1, and any non-volatilized material exits via stream 5. If hydrogen gas is not fed to the vaporization system, in some embodiments, hydrogen gas can be added to the gaseous aldehyde stream 4 exiting vaporization device 3 or to VPH unit 6 (discussed below). Stream 4, including the gaseous aldehyde and any hydrogen added to vaporization system 3, is then subjected to gas-phase hydrogenation in a gas-phase hydrogenation zone within VPH unit 6. In some embodiments, hydrogen can also be provided to VPH unit 6 via stream 7 (or combined with stream 4 prior to entering the VPH unit). Specifically, hydrogen can be provided to VPH unit 6 in a number of ways: (a) hydrogen can be added to vaporization system 3 via stream 2 and then exits with the gaseous aldehyde in stream 4; (b) hydrogen can be added to VPH unit 6 as a separate stream 7; (c) hydrogen can be added to stream 4 prior to entering VPH unit 6; or any combination of (a), (b), and (c). The crude alcohol product and excess H2, unconverted aldehyde, and gaseous inerts exit via stream 8 for further processing, including separating unreacted H2 and / or aldehyde and recycling one or both of them to a previous unit. For example, unreacted hydrogen can be separated and recycled to the process as part of stream 2, stream 7, or another stream. Recycle streams to either vaporization system 3 or VPH unit 6 are not explicitly shown. The weakly basic amines used in the process of the present invention are typically added to stream 1 before vaporization system 3 to allow for good mixing, but may also be added directly to vaporization system 3.

[0025] Liquid aldehyde stream 1 may be directly from a hydroformylation unit or may include recycle streams or aldehydes from other unit operations (e.g., recycled from an aldol condensation or from a purification unit). Any of these processes may generate acidic species that need to be removed before the aldehyde stream enters the vapor-phase hydrogenation zone (e.g., contacts the VPH catalyst).

[0026] Vaporization system 3 can be a simple distillation column, a spray vaporizer, a thin film vaporizer, a hydrogen stripping system, or combinations thereof. If the weakly basic amine is not added to the liquid aldehyde stream, the weakly basic amine can be added from the liquid aldehyde feed to a different tray in the distillation column, typically a few trays below the top tray (in those embodiments where the vaporization system is a distillation column), or as part of the reflux flow, or any combination of these.

[0027] The vaporization system should have a heavies removal stream (e.g., Stream 5 in Figure 1) to remove heavies formed during the hydroformylation process and during storage prior to being fed to the vaporizer system. This process also removes hydroformylation catalyst residues (either entrained or sublimed) and protects the VPH catalyst from condensation with heavy organics. Weakly basic amines and any salts they form with the incoming acidic species are removed along with the heavies in this purge. The resulting purge can be further processed to recover any valuable aldehydes that are recycled and, in some cases, to recover the weakly basic amines for reuse.

[0028] Hydrogen is required for the gas phase hydrogenation of aldehydes and may be provided to a VPH unit as described. Hydrogen may be obtained from any suitable source, including petroleum cracking and refining operations.

[0029] The properties and compositions of aldehyde gas phase hydrogenation catalysts are well known. Catalysts useful in gas phase hydrogenation processes include catalytic metals on supports. The catalytic metals 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), chromium (Cr), osmium (Os), copper (Cu), and mixtures thereof, with preferred metals being palladium, platinum, copper, and nickel.

[0030] Catalyst supports for gas phase hydrogenation catalysts are generally inert solid materials designed to hold the active catalytic metals. Examples include graphite, activated carbon, silica, alumina, and metal oxides such as molybdenum oxide, chromium oxide, zinc oxide, titania, etc. Supports can be made of combinations of different materials and other additives that provide different properties such as improved crush strength, reduced metal leaching, reduced by-products, and ease of extrusion, among others.

[0031] By way of example, the catalytic metal may be impregnated on any solid support, such as inorganic oxides (i.e., alumina, silica, titania, or zirconia), carbon, or ion exchange resins. The catalyst may be supported on or inserted into the pores of a zeolite, glass, or clay. The catalyst may also be dissolved in a liquid film that coats the pores of the zeolite or glass. Such zeolite-supported catalysts are particularly advantageous for producing one or more regioisomeric alcohols with high selectivity, as determined by the pore size of the zeolite. Techniques for supporting catalysts on solids, such as incipient wetness, will be known to those skilled in the art. The solid catalyst thus formed may still be complexed with one or more of the ligands defined above. Descriptions of such solid catalysts can be found, for example, in J. Mol. Cat., 1991, 70, 363-368; Catal. Lett., 1991, 8, 209-214; J. Organomet. Chem., 1991, 403, 221-227; Nature, 1989, 339, 454-455; J. Catal., 1985, 96, 563-573; J. Mol. Cat., 1987, 39, 243-259.

[0032] The nature of the support is not critical to the invention, but it has been observed that some supports are more vulnerable to acid decomposition than others. Zinc oxide appears to be particularly vulnerable, while chromium oxide is not. Acidic impurities can degrade the support, promote metal leaching, or alter the nature of the catalyst surface or pore structure.

[0033] It should be noted that the exact composition and microscopic (pore) structure of the heterogeneous gas phase hydrogenation catalyst is not critical for the present invention, which mainly deals with changes in the properties of the catalyst. The most obvious problem observed is the change in catalyst performance (hydrogenation rate, selectivity, pressure drop, and hot spot location in the bed, etc.). An increase in pressure drop can often be caused by the generation of fines. The nature of the fines, how they are generated, and also how they move in the bed are not critical, other than the change in pressure drop observed, to the extent that catalyst performance and / or catalyst bed performance is adversely affected.

[0034] To determine whether metal leaching or fines generation has occurred during gas phase hydrogenation, the catalyst metal concentration in the catalyst and / or condensed liquid product may be measured using analytical techniques well known to those skilled in the art, with, for example, atomic absorption (AA), inductively coupled plasma (ICP), X-ray diffraction (XRD), and X-ray fluorescence (XRF) being typically preferred.

[0035] One indicator of whether there may be a problem with the catalyst (e.g., fines generation) is the pressure drop across the gas phase hydrogenation reactor, and thus, in some embodiments, the pressure drop across the hydrogenation reaction may be monitored. As used herein, pressure drop refers to the pressure difference between the feed point of the hydrogenation reactor (typically measured at or near the aldehyde feed point) and the exit point of the reactor. As the reaction material passes through the heterogeneous catalyst, the flow experiences resistance due to the catalyst, resulting in a pressure drop as the material passes through the bed. Excessive pressure drop may result in further catalyst bed deterioration (e.g., spallation or attrition), and in the case of gas phase hydrogenation, condensation, channeling, and heat transfer problems are possible. Particle fines tend to increase flow resistance and thus may be the main contributor to increased pressure drop over time, leading to the need for catalyst replacement. The exact nature of fines and how they are generated is often unknown, but they are usually due to catalyst destruction, attrition, chemical / physical erosion (leaching), etc.

[0036] It is known that fines can be generated at the beginning of catalyst life, such as during initial catalyst loading. For purposes of the present invention, the increase in pressure drop can be monitored after an initial "break-in" period. After the initial "break-in" period, the pressure drop remains stable for a period of time and then begins to increase over time, often in an exponential manner.

[0037] Critical pressure drop values ​​will, of course, vary depending on the catalyst system and equipment, but when catalytic reactor efficiency and operation is affected by pressure drop, it becomes an economic decision as to whether to continue with suboptimal performance (e.g., lower rates, lower conversions, higher by-products, dual / swing reactors) or to shut down operation and replace the catalyst. Embodiments of the present invention may advantageously extend the life of the catalyst bed, thus deferring and / or reducing the costs of catalyst purchases, plant shutdowns, and associated catalytic precious metal recovery or disposal.

[0038] For purposes of the present invention, the term "weakly basic amine" includes relatively non-volatile substituted amines and heterocyclic nitrogen compounds as described below. Weakly basic amines function as acid scavengers or acidity moderators to remove acidic components from the aldehyde feed stream in the vaporization system as adducts (typically salts) in the vaporizer bottoms purge. Although it may be preferred to use only one weakly basic amine species at a time in any given VPH process, mixtures of two or more different weakly basic amine species may also be used in any given process, if desired. By adding a weakly basic amine to the vaporization system, acidic components are advantageously removed prior to the hydrogenation zone where such components may cause decomposition of the hydrogenation catalyst as discussed herein.

[0039] Weakly basic amines useful in embodiments of the invention advantageously have two properties: (1) they are weakly basic to avoid heavies formation in the vaporization system, and (2) they are non-volatile to avoid contact and collection (condensation) on the VPH catalyst under hydrogenation conditions. The alkalinity or basicity of the weakly basic amines is generally reported as the pKa of the conjugate acid, which is advantageously between 5 and 11 at 25° C. The pKa is preferably between 5.0 and 9.5 at 25° C. in some preferred embodiments, and between 6.0 and 9.0 at 25° C. in other preferred embodiments. In some embodiments, the weakly basic amines are not strong promoters of heavies formation. In some embodiments, the weakly basic amines can be tested for heavies formation by heating the product aldehyde with the weakly basic amine at an elevated temperature, such as at or near the vaporization temperature of the aldehyde. In some embodiments, the weakly basic amine exhibits less than 1 gram of heavy products formation per liter of test solution (product aldehyde + weakly basic amine in solution, the weakly basic amine typically added at a concentration of 1000 ppmw) per day at the vaporization temperature of the aldehyde. The amount of heavy products formation can be readily determined by gas or liquid chromatography, as known to those skilled in the art.

[0040] With respect to volatility, the volatility of the weakly basic amine should be such that under vaporization conditions of the vapor phase aldehyde, less than 1%, preferably less than 0.1%, and most preferably less than 0.01% of the added weakly basic amine volatilizes. This can be controlled by selecting a weakly basic amine that in some embodiments has a normal boiling point at least 50° C. higher than the aldehyde to be hydrogenated, and in other embodiments has a normal boiling point at least 100° C. higher than the aldehyde.

[0041] The amount of weakly basic amine that volatilizes under vaporization conditions can also be managed by controlling the concentration of the weakly basic amine, so that the amount of excess weakly basic amine (relative to the acidic impurities) reduces the "free" amine to a low level. When there is little free amine, this reduces the partial pressure of the amine, lowering the loss of amine through the vaporization stream. The term "free amine" refers to amine that has not been neutralized or reacted with acidic impurities. For example, at an equimolar ratio of acid to amine, there is little free amine in solution, and therefore the amine partial pressure is very low. This also means that the amount of free acid is very low.

[0042] The amount of weakly basic amine that may be used in any given process of the present invention need only be the minimum amount necessary to provide a basis for at least some minimization of catalyst decomposition as may be found to occur as a result of running the same metal catalyzed hydrogenation process under essentially the same conditions, but in the absence of the weakly basic amine, during harsh conditions such as vaporization separation of the aldehyde product. Thus, in some embodiments, the amount of weakly basic amine added to the vaporization system is 0.1 to 5 equivalents of weakly basic amine relative to the equivalents of acid in the liquid aldehyde stream provided to the vaporization system. In some embodiments, the amount of weakly basic amine added to the vaporization system is 0.5 to 1.5 equivalents of weakly basic amine relative to the equivalents of acid in the liquid aldehyde stream provided to the vaporization system. The acid content of the liquid aldehyde stream provided to the vaporization system is measured by titration.

[0043] Weakly basic amines that may be advantageously used in various embodiments of the present invention are selected from one or more of the following classes:

[0044] One class of weakly basic amines has the structure:

[0045] [ka] In the formula, R 1 , R2 , and R 3 are each independently R 1 , R 2 , and R 3 represents alkyl or aryl substituents such that none of the substituents is hydrogen, at least one being an electron-withdrawing substituent (either alpha or beta to the nitrogen moiety), and preferably at least two being electron-withdrawing substituents. Electron-withdrawing alkyl or aryl substituents include alkyl-substituted or unsubstituted aryl, alkoxylated, alkyl alkoxylated, or carboxylated aryl groups, β-alkoxy or β-alkoxyalkyl (e.g., β-hydroxyethyl, β-hydroxy-α-methylethyl, β-hydroxy-β-methylethyl, and ethoxylated and / or propoxylated adducts thereof). Examples of preferred amines in this class include triethanolamine, methyldiethanolamine, ethyldiethanolamine, dimethylethanolamine, and tri(2-hydroxypropyl)amine, and ethoxylates thereof. Preferred amines are trialkanolamines, such as triethanolamine and tri(2-hydroxypropyl)amine.

[0046] The second class of weakly basic compounds includes heterocyclic nitrogen compounds as described in WO 2019 / 083700. Such heterocyclic nitrogen compounds are well known, as are the methods for their preparation. In many instances, such heterocyclic nitrogen compounds are readily commercially available. Suitable substituted and unsubstituted heterocyclic nitrogen compounds include the acceptable substituted and unsubstituted heterocyclic nitrogen compounds described in Kirk-Othmer, "Encyclopedia of Chemical Technology", Fourth Edition, 1996, the relevant portions of which are incorporated herein by reference.

[0047] Exemplary heterocyclic nitrogen compounds that may be used as weakly basic amines in some embodiments of the present invention include the following diazoles: (a) an imidazole represented by the formula:

[0048] [ka] (b) a pyrazole represented by the formula:

[0049] [ka] and (c) an indazole represented by the formula:

[0050] [ka] In the above formulas (II), (III), and (IV), R 8 , R 9 , R 10 , R 11 , R 12 , and R 13 are the same or different and each represents a hydrogen atom or a monovalent substituent, provided that in one embodiment of the present invention, R 8 and R 9 and R should not both be monovalent hydrocarbon radicals at the same time. 8 and R 11 , or R 8 and R 9 , or R 10 and R 11 , or R 10 and R 12 , or R 12 and R 13 can optionally be taken together to form a substituted or unsubstituted divalent radical that forms a cyclic ring together with the two atoms of the formula to which the adjacent substituents are attached.

[0051] Monovalent R in formulas (II), (III), and (IV) 8 ~R 13The substituents may be any substituents which do not unduly adversely affect the objectives and processes of the present invention. Examples of such monovalent substituents include hydroxy, cyano, nitro, trifluoromethyl, and substituted or unsubstituted radicals containing 1 to 30 carbon atoms selected from the group consisting of acyl, acyloxycarbonyloxy, oxycarbonyl, silyl, alkoxy, aryloxy, cycloalkoxy, alkyl, aryl, alkaryl, aralkyl, and alicyclic radicals.

[0052] More specifically, exemplary monovalent substituents containing 1 to 30 carbon atoms include, for example, primary, secondary, and tertiary alkyl radicals, such as methyl, ethyl, n-propyl, isopropyl, butyl, sec-butyl, t-butyl, neopentyl, n-hexyl, arnyl, sec-amyl, t-amyl, isooctyl, decyl, octadecyl, and the like; aryl radicals, such as phenyl, naphthyl, and the like; aralkyl radicals, such as benzyl, phenylethyl, and triphenylmethyl, and the like; alkaryl radicals, such as tolyl and xylyl, and the like; cyclopentyl, cyclohexyl, 1-methylcyclohexyl, cyclooctyl, cyclohexyl, and the like; alkoxy radicals such as methoxy, ethoxy, propoxy, t-butoxy, --OCH2CH2OCH3, --O(CH2CH2)2OCH3, --O(CH2CH2)3OCH3; aryloxy radicals such as phenoxy; silyl radicals such as --Si(CH3)3, --Si(OCH3)3, --Si(C3H7)3; acyl radicals such as --C(O)CH3, --C(O)C2H5, --C(O)C6H5; carbonyloxy radicals such as --C(O)OCH3; and oxycarbonyl radicals such as --O(CO)C6H5.

[0053] Optionally, such monovalent substituents may then be optionally substituted with any substituent that does not unduly adversely affect the objectives and processes of the present invention, such as, for example, R 8 , R 9 , R 10 , R 11 , R 12 , and R 13Formulas (II)-(IV) are also intended to encompass compounds having two or more such diazole formulae, for example, two diazole formulae R 8 ~R 13 As a result of any one of the substituents optionally representing a direct bond, or R 8 ~R 13 Any one of the substituents is optionally substituted with a second diazole formula so as to be directly bonded together.

[0054] Furthermore, the adjacent substituent, R 8 and R 11 , or R 8 and R 9 , or R 10 and R 11 , or R 10 and R 12 , or R 12 and R 13 may together form a substituted or unsubstituted divalent bridging group having 3 to 5, preferably 4, carbon atoms which, together with the two atoms shown in the formula to which they are attached, form a 5 to 7 membered cyclic ring. Such divalent bridging groups preferably consist only of carbon atoms, but may contain 1 to 2 nitrogen atoms in addition to the carbon atoms. Examples of substituents which may be present on a substituted divalent bridging group are R 8 , R 9 , R 10 , R 11 , R 12 , and R 13 The hydrocarbon and non-hydrocarbon substituents are the same as those defined herein for embedded image Preferred diazoles are the imidazoles of formula (II) above, especially benzimidazoles.

[0055] Exemplary heterocyclic nitrogen compounds that may be used as weakly basic amines in some embodiments of the present invention also include triazole compounds such as: (a) a 1,2,3-triazole represented by the formula:

[0056] [ka] (b) A 1,2,4-triazole represented by the formula: [ka] (c) 2,1,3-triazole represented by the formula:

[0057] [ka] and (d) 4,1,2-triazoles represented by the following formula: [ka] In the above formulas (V), (VI), (VII), and (VIII), R 8 , R 9 , R 10 , R 11 , and R 12 are the same or different and each represents a hydrogen atom or a monovalent substituent, and adjacent substituents R 8 and R 9 , or R 8 and R 11 , or R 10 and R 11 , or R 10 and R 12 may optionally be taken together to form a substituted or unsubstituted divalent radical that forms a cyclic ring together with the two atoms of the formula to which the adjacent substituents are attached. More specifically, R 8 , R 9 , R 10 , R 11 , and R 12 and the adjacent substituent R 8 and R 9 , R 8 and R 11 , R 10 and R 11 , or R 10 and R 12may be the same as the monovalent substituents and divalent radicals defined for formulae (II)-(IV) above. It should be further understood that formulae (V)-(VIII) are also intended to encompass compounds having two or more such triazole formulae, e.g., two triazole formulae are represented by R 8 , R 9 , R 10 , R 11 , and R 12 As a result of any one of the substituents optionally representing a direct bond, or R 8 , R 9 , R 10 , R 11 , and R 12 Any one of the substituents is optionally substituted with a second triazole formula, resulting in direct bonding together. Preferred triazoles are 1,2,3-triazoles of formula (VIII) above, particularly benzotriazoles. Other exemplary triazoles include 5-methyl-1H-benzotriazole, 5,6-dimethyl-1-H-benzotriazole, 1-hydroxybenzotriazole, 2-(2H-benzotriazol-2-yl)-4-(1,1,3,3-tetramethylbutyl)-phenol, 5-nitrobenzotriazole, bis(1-benzotriazolyl)oxalate, 1-benzotriazolyl 9-fluorenylmethylcarbonate, 1-cyanobenzotriazole, 2-(2H-benzotriazol-2-yl)-hydroquinone, 2-(2-hydroxy-5-methylphenyl)-benzotriazole, 5-hexylbenzotriazole, 5-decylbenzotriazole, 1-ethylbenzotriazole, 1-pentylbenzotriazole, 1-benzylbenzotriazole, 1-dodecylbenzotriazole, and the like.

[0058] Exemplary heterocyclic nitrogen compounds that may be used as weakly basic amines in some embodiments of the present invention also include diazine compounds such as: (a) 1,2-diazines represented by the formula:

[0059] [ka] (b) 1,3-diazines represented by the formula:

[0060] [ka] and (c) 1,4-diazines represented by the following formula:

[0061] [ka] In the above formulas (IX), (X), and (XI), R 14 , R 15 , R 16 , R 17 , and R 18 are the same or different and each represents a hydrogen atom or a monovalent substituent, and adjacent substituents R 14 and R 15 , or R 15 and R 16 , or R 16 and R 17 , or R 14 and R 18 may optionally be taken together to form a substituted or unsubstituted divalent radical that forms a cyclic ring together with the two atoms of the formula to which the adjacent substituents are attached. More specifically, the monovalent substituent R 14 , R 15 , R 16 , R 17 , and R 18 and adjacent substituent R 14 and R 15 , or R 15 and R 16 , or R 16 and R 17 , or R 14 and R 18 may be the same as the monovalent substituents and divalent radicals defined for formulae (II)-(IV) above. It should be further understood that formulae (IX)-(XI) are also intended to encompass compounds having two or more such diazine formulae, e.g., two diazine formulae are represented by R 14 ~R 18As a result of any one of the substituents optionally representing a direct bond, or R 14 ~R 18 Any one of the substituents is optionally substituted with a second diazine formula so that they are directly bonded together. Examples of such diazine compounds are pyridazine, pyrimidine, pyrazine, etc.

[0062] Exemplary heterocyclic nitrogen compounds that may be used as weakly basic amines in some embodiments of the present invention also include triazine compounds, such as 1,3,5-triazine, represented by the formula:

[0063] [ka] In the above formula (XII), R 15 , R 17 , and R 18 are the same or different and each represents a hydrogen atom or a monovalent substituent. More specifically, the monovalent substituent R 15 , R 17 , and R 18 may be the same as the monovalent substituents defined for formulae (II)-(IV) above. It should be further understood that formula (XII) is also intended to encompass compounds having two or more such triazine formulae, for example, two triazine formulae R 15 , R 17 , and R 18 As a result of any one of the substituents optionally representing a direct bond, or R 15 , R 17 , and R 18 Any one of the substituents is optionally substituted with a second triazine formula so that they are directly bonded together. Examples of such triazine compounds include 1,3,5-triazine.

[0064] It is to be understood that in some embodiments of the present invention, the heterocyclic nitrogen compounds that may be used as weakly basic amines contain at least one unfunctionalized nitrogen that has a lone pair of electrons that can form a complex or adduct with an acid moiety. In other words, ionic ammonium salts (either alkylated or protonated) such as those described in U.S. Pat. No. 6,995,293(B2) are not heterocyclic nitrogen stabilizers because these quaternary ammonium salts do not have a free nitrogen lone pair of electrons.

[0065] R of the heterocyclic nitrogen compounds of the above formulae (II) to (XII) 8 ~R 18 Any of the radicals may be substituted, if desired, with any suitable substituent containing from 1 to 30 carbon atoms which does not unduly adversely affect the desired outcome of the process of the invention. Possible substituents on such radicals include, for example, --N(R 19 )2, amino radicals such as --aryl--P(R 19 )2, phosphine radicals such as --C(O)R 19 Acyl radicals such as --OC(O)R 19 Acyloxy radicals such as --CON(R 19 )2 and --N(R 19 )COR 19 Amide radicals such as --SO2R 19 Sulfonyl radicals such as --OR 19 Alkoxy radicals such as --SOR 19 Sulfinyl radicals such as --SR 19 sulfenyl radicals such as --SO3M, --PO3M, --N(R 6 )3X 1 and —COM, an ionic radical selected from the group consisting of M, X 1 , and R 6are as defined above), as well as nitro, cyano, trifluoromethyl, and hydroxy radicals, where each R 19 The radicals independently represent the same or different monovalent hydrocarbon radicals having 1 to 18 carbon atoms (e.g., alkyl, aryl, aralkyl, alkaryl, and cyclohexyl radicals), provided that -N(R 19 In the amino substituents such as 2, each R 19 may also represent a divalent bridging group which, taken together, forms a heterocyclic radical with the nitrogen atom. Of course, it should be understood that any of the substituted or unsubstituted substituent radicals which make up a particular weakly basic amine may be the same or different.

[0066] Illustrative specific examples include imidazole and substituted imidazoles, such as 1-methylimidazole, 1-ethylimidazole, 1-n-propylimidazole, 1-isopropylimidazole, 1-butylimidazole, 2-methylimidazole, 2-ethylimidazole, 2-n-propylimidazole, 2-isopropylimidazole, 2-n-butylimidazole, 2-n-hexylimidazole, 2-n-heptylimidazole, 2-n-octylimidazole, 2-n-nonylimidazole, 2-n-decyl-imidazole, 2-n-undecylimidazole, 2-n-dodecylimidazole, 2-n-tridecylimidazole, 2-n-tetradecylimidazole, 2-n-pentadecylimidazole, 2-n-hexadecylimidazole, 2-n-heptadecylimidazole, 2-(2-ethyl pentyl)imidazole, 2-ethyl-4-methylimidazole, 2-phenylimidazole, 1-benzyl-2-methylimidazole, 2,4,5-triphenylimidazole, 2-(2-propylhexyl)imidazole, 4-methylimidazole, 4-ethylimidazole, 3-n-propylimidazole, 4-isopropylimidazole, 4-butylimidazole, 4,5-dimethylimidazole , 4,5-diethylimidazole, 1-methyl-2-ethylimidazole, 1-methyl-4-ethylimidazole, 2-ethyl-4-methylimidazole, 1-benzyl-2-methylimidazole, 1-phenylimidazole, 2-phenylimidazole, 4-phenylimidazole, 2,4,5-triphenylimidazole, 1,2-trimethyleneimidazole, 1,5-trimethyleneimidazole, 4,5-trimethyleneimidazole, and polar substituted imidazoles such as 1-hydroxymethylimidazole, 2-hydroxymethylimidazole, 4-hydroxymethylimidazole, 1-(2-hydroxyethyl)imidazole, 2-(2-hydroxyethyl)imidazole, 4-2(hydroxyethyl)imidazole, 1-carboxymethylimidazole, 2-carboxymethylimidazole, 4-carboxymethylimidazole, 1-(2-carboxyethyl)imidazole, 4-(2-carboxyethyl)imidazole, 4-(2-carboxyethyl)imidazole, 4-(2-carboxy-2-hydroxyethyl)imidazole, and the like.

[0067] In some embodiments, preferred heterocyclic nitrogen compounds for use as weakly basic amines include benzimidazoles, such as those represented by the formula:

[0068] [ka] In the above formula (XIII), R 20 , R 21 , R 22 , R 23 , R 24 , and R 25 are the same or different and each represents a hydrogen atom or a monovalent substituent, provided that R 20 and R 21 and R cannot both be monovalent hydrocarbon radicals at the same time. 20 , R 21 , R 22 , R 23 , R 24 , and R 25 can be the same as the monovalent substituents defined for formulae (II)-(IV) above. Of course, it should be further understood that formula (XIII) is also intended to encompass compounds having two or more such benzimidazole formulae, e.g., two benzimidazole formulae R 20 ~R 25 Any one of the substituents, e.g., R 21As a result, optionally represents a direct bond, or R 20 ~R 25 Any one of the substituents, e.g., R 21 are optionally substituted with a second benzimidazole formula, for example a di-, bi-, or bis-benzimidazole, as a result of which the two benzimidazole groups are directly linked together.

[0069] Examples of such benzimidazoles include benzimidazole and substituted benzimidazoles such as 1-methylbenzimidazole, 1-ethylbenzimidazole, 1-n-propylbenzimidazole, 1-isopropylbenzimidazole, 1-butylbenzimidazole, 1-benzylbenzimidazole, 2-benzylbenzimidazole, 2-methylbenzimidazole, 2-ethylbenzimidazole, 2-n-propylbenzimidazole, 2-isopropylbenzimidazole, 2-n-butyl 2-n-hexylbenzimidazole, 2-n-heptylbenzimidazole, 2-n-octylbenzimidazole, 2-n-nonylbenzimidazole, 2-n-decylbenzimidazole, 2-n-undecylbenzimidazole, 2-n-dodecylbenzimidazole, 2-n-tridecylbenzimidazole, 2-n-tetradecylbenzimidazole, 2-n-pentadecylbenzimidazole, 2-n-hexadecylbenzimidazole, 2-n-heptadecylbenzimidazole , 2-(2-ethylpentyl)benzimidazole, 2-(2-propylhexyl)benzimidazole, 2-phenylbenzimidazole, 2-phenylbenzimidazole, 1-benzylimidazole, 1-cyclohexylbenzimidazole, 1-octylbenzimidazole, 1-dodecylbenzimidazole, 1-hexyldecylbenzimidazole, 5,6-dimethylbenzimidazole, 1-methyl-5,6-dimethylbenzimidazole, 4-methylbenzimidazole, 4-ethylbenzimidazole benzimidazole, 3-n-propylbenzimidazole, 4-isopropylbenzimidazole, 4-butylbenzimidazole, 4,5-dimethylbenzimidazole, 4,5-diethylbenzimidazole, 1-methyl-2-ethylbenzimidazole, 1-methyl-4-ethylbenzimidazole, 1-phenylbenzimidazole, and 4-phenylbenzimidazole, 5-bromobenzotriazole, 6-bromobenzotriazole, 5-chlorobenzotriazole, 6-chlorobenzotriazole, 5-chloro-1,6-dimethylbenzotriazole, 5-chloro-6-methylbenzotriazole, 6-chloro-5-methylbenzotriazole, 5-chloro-6-methyl-1-phenylbenzotriazole, 4,5,6,7-tetrachlorobenzotriazole, 1-(2-iodoethyl)benzotriazole, 5-chloro-6-fluorobenzotriazole, 5-trifluoromethylbenzotriazole, 6-trifluoromethylbenzotriazole, and the like, as well as polar substituted benzimidazoles such as 1-acetylbenzimidazole, 1-benzoylbenzimidazole, 1-hydroxymethylbenzimidazole, 2-hydroxymethylbenzimidazole, 4-hydroxymethylbenzimidazole, 1-(2-hydroxyethyl)benzimidazole, 2-(2-hydroxyethyl)benzimidazole, 4-2(hydroxyethyl)benzimidazole, 1-Carboxymethylbenzimidazole, 2-Carboxymethylbenzimidazole, 4-Carboxymethylbenzimidazole, 1-(2-carboxyethyl)benzimidazole, 4-(2-carboxyethyl)benzimidazole, 4-(2-carboxyethyl)benzimidazole, 4-(2-carboxy-2-hydroxyethyl)benzimidazole, 1-ethyl-5,6-dimethylbenzimidazole, 1-iso Examples of the 5,6-dimethoxybenzimidazole include propyl-5,6-benzimidazole, 1-isopropyl-5,6-benzimidazole, 5,6-dimethoxybenzyl nidazole, 4,5-trimethylenebenzimidazole, naphtho[1,2-d]imidazole, naphtho[2,3-d]imidazole, 1-methyl-4-methoxybenzimidazole, 1-methyl-5-methoxybenzimidazole, and 1-methyl-5,6-dimethoxybenzimidazole. For example, 2,2'-ethylenebibenzimidazole, 2,2'-heptamethylenebibenzimidazole, 2,2'-hexamethylenebibenzimidazole, 2,2'(iminodiethylidene)-bibenzimidazole, 2,2'-(methyliminodiethylidene)bibenzimidazole, 2,2'-octamethylenebibenzimidazole, 2,2'-pentamethylenebibenzimidazole, 2,2-p-phenylenebibenzimidazole, 2,2'-trimethylenebibenzimidazole, 2,2'-methylenebis(5,Also included are bi-, di-, and bisbenzimidazoles such as 5,5',6,6'-tetramethyl-2,2'-bibenzimidazole, 1,2-bis(5,6-dimethyl-2-benzimidazolyl)ethanol hydrochloride, etc. Among these, the most preferred heterocyclic nitrogen compound is benzimidazole.

[0070] The amount of weakly basic amines that are vaporized and carried over with the vaporized aldehyde stream heading to the VPH catalyst should be minimized, since non-volatile weakly basic amines may condense on the VPH catalyst or have other undesirable downstream effects, including purification and product alcohol purity. Preferably, the amount of amine present in the vapor phase exiting the vaporization system should be less than 1 ppmw (on a nitrogen basis). This level can be controlled by the amount of weakly basic amine added, the acid / amine ratio (i.e., avoiding a high excess of amine relative to the moles of acid present), and the vaporization conditions (temperature, pressure, and purge rate). The amount of amine in the vapor phase exiting the vaporization system is determined by gas chromatography using techniques known to those skilled in the art based on the teachings herein.

[0071] As the aldehyde product is vaporized from the aldehyde feed to the vaporization system, the concentration of non-volatile components in the remaining material (e.g., aldehyde heavies and weakly basic amine (and any acid additives)) increases accordingly. Thus, the upper amount of weakly basic amine to be added is governed by its solubility limit (and also the solubility limit of any acid additives) in the non-volatile liquid purge from the vaporization system. Solubility depends on the vaporization separation temperature, as well as the particular amine itself. In some embodiments, alkanolamines may be preferred because they are typically highly soluble liquids or low melting solids in the aldehyde heavies stream at ambient temperatures.

[0072] The addition of the weakly basic amine to the aldehyde that vaporizes the aldehyde feed can be carried out in any suitable manner desired. For example, the weakly basic amine can be added to the aldehyde stream removed from the hydroformylation reaction zone at any time before or during the vaporization of the aldehyde. However, the weakly basic amine selected for use should not have a substantial detrimental effect on the aldehyde itself, so the weakly basic amine can be added directly to the crude aldehyde immediately after the hydroformylation product-catalyst separation step. In fact, it may be desirable to add the weakly basic amine, especially the heterocyclic nitrogen compound, to the crude aldehyde as soon as possible so that the weakly basic amine is present immediately from the start of the hydrogenation process.

[0073] With respect to the aldehyde feedstock that may be provided as a liquid aldehyde stream in the process of the present invention, exemplary non-optically active aldehyde starting materials include propionaldehyde, n-butyraldehyde, isobutyraldehyde, n-valeraldehyde, 2-methyl-1-butyraldehyde, hexanal, hydroxyhexanal, 2-methylvaleraldehyde, heptanal, 2-methyl-1-hexanal, octanal, , 2-methyl-1-heptanal, nonanal, 2-methyl-1-octanal, 2-ethyl-1-heptanal, 3-propyl-1-hexanal, decanal, adipaldehyde, 2-methylglutaraldehyde, 2-methyladipaldehyde, 3-methyladipaldehyde, 3-hydroxypropionaldehyde, 6-hydroxyhexanal, alkenals such as 2-, 3-, and 4-pentenal.

[0074] Alcohols obtained from embodiments of the present invention have many uses, including as solvents and feedstocks for other products.

[0075] Some embodiments of the invention are described in more detail in the following examples. EXAMPLES

[0076] All parts and percentages in the following examples are by weight unless otherwise indicated. Pressures are listed as absolute pressures unless otherwise indicated.

[0077] The following examples are given to illustrate the present invention and should not be construed as limiting the scope of the invention.

[0078] Comparative example A Analysis of the butyraldehyde feed to a commercial-scale VPH vaporization system reveals a variety of butyric acid levels using conventional GC or titration methods. These levels range from 200-5000 ppmw (based on total organic feed). In addition, analysis of the resulting vaporization stream reveals that a significant amount of the feed acid was volatilized and still present in the feed going to the VPH catalyst. Vapor-Liquid Equilibirum (VLE) modeling indicates that the butyric acid should have made it down to the vaporizer heavies, but for some reason, a significant portion was still migrating to the VPH bed.

[0079] Comparative example B A sample of zinc oxide (ZnO) based VPH catalyst is exposed to butyric acid-containing vaporized aldehyde under typical hydrogenation conditions similar to the levels found in Comparative Example A. A solid is observed to deposit on the cooler downstream equipment, presumably via sublimation from the catalyst. This solid is analyzed by TGA and FT-IR and found to be Zn(butyrate)2 by comparison to authentic material.

[0080] Comparative example C A sample of ZnO-based VPH catalyst from a commercial-scale VPH reactor is examined by SEM and compared to a catalyst that had not been loaded into the reactor. Voids and new crystals are visible within the body of the spent catalyst. The latter was determined to be ZnO, likely from migration of volatile Zn(butyrate)2 and subsequent hydrolysis to ZnO. The new crystals are clearly different (larger) than the original fresh catalyst, showing voids consistent with a change in the morphology of the catalyst support and loss of catalyst integrity.

[0081] Comparative Examples AC demonstrate the detrimental effect of butyric acid vaporizers on heterogeneous catalysts.

[0082] Example 1 A simple flash model in ASPEN for 1000 ppmw (94 ppmw on a nitrogen basis) of triethanolamine (a weakly basic amine) in a crude butyraldehyde stream containing no butyric acid indicates that approximately 1.4 ppmw (on a nitrogen basis) of triethanolamine will be present in the vapor phase. This indicates that only a small amount of triethanolamine will remain with the vaporized aldehyde stream. This represents an upper limit since less free amine will be present in the vaporization system during operation since much of the weakly basic amine is used in neutralizing the acids to reduce the free acids to very low levels. Thus, the amount of triethanolamine in the vapor phase is predicted to be much less than the levels of free acid typically found in the VPH feed prior to neutralization (typically 200-5000 ppmw). Based on this data, the amount of free triethanolamine in the overhead vaporizer stream can be calculated by reducing the feed to more closely match the moles of acidity present, thus neutralizing the free acid without affecting the VPH catalyst.

Claims

1. 1. A process for the vapor phase hydrogenation of aldehydes comprising the steps of: (a) providing a liquid aldehyde stream to a vaporization system to produce a gaseous aldehyde stream in the presence of a weakly basic amine, the weakly basic amine having a normal boiling point at least 50° C. higher than the normal boiling point of the aldehyde, the weakly basic amine reacting with acidic impurities in the liquid aldehyde stream to form an ammonium salt adduct, and the ammonium salt adduct and any excess weakly basic amine being removed from the vaporization system as a heavy purge; (b) combining the gaseous aldehyde stream with a hydrogen stream, either by feeding a hydrogen stream to the vaporization system, by adding a hydrogen stream to the gaseous aldehyde stream after step (a), or a combination thereof; (c) providing said combined gaseous aldehyde and hydrogen stream to a vapor-phase hydrogenation zone; (d) hydrogenating said gaseous aldehyde in said vapor phase hydrogenation zone.

2. 2. The process of claim 1, wherein the weakly basic amine comprises a trialkanolamine or an imidazole.

3. 3. The process of claim 2, wherein the weakly basic amine comprises triethanolamine or benzimidazole.

4. 4. The process of any one of claims 1 to 3, wherein the weakly basic amine concentration in the combined gaseous aldehyde and hydrogen stream in step (c) is less than 1 ppmw (based on nitrogen).

5. 4. The process of any one of claims 1 to 3, further comprising measuring the acid content of the liquid aldehyde stream, and wherein the amount of weakly basic amine added to the vaporization system is from 0.1 to 5 equivalents of weakly basic amine per equivalent of acid.

6. 4. The process of any one of claims 1 to 3, wherein the liquid aldehyde stream is provided from a hydroformylation reaction and a product-catalyst separation step, and in the product-catalyst separation step, a hydroformylation catalyst is separated from the hydroformylation product stream to provide the liquid aldehyde stream.

7. 4. The process according to claim 1, wherein the basicity of the weakly basic amine, determined as the pKa of its conjugate acid, is from 5 to 11 at a temperature of 25° C.

8. The process of any one of claims 1 to 3, wherein the weakly basic amine has a normal boiling point at least 100°C higher than the normal boiling point of the aldehyde.

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