Purification of an ethylenically unsaturated alcohol stream, preparation of ethylenically unsaturated aldehydes, in particular prenal, and compounds derived therefrom

Abstract

Organically bound nitrogen is removed from the ethylenically unsaturated alcohol stream by contacting the ethylenically unsaturated alcohol stream with a weakly acidic solid adsorbent. Trace amounts of organically bound nitrogen tend to impair the action of the oxidation catalyst in subsequent oxidation processes using the ethylenically unsaturated alcohol stream.

Description

Technical Field

[0001] The present invention relates to a process for purifying an ethylenically unsaturated alcohol stream, more specifically to a process for removing organically bound nitrogen from an ethylenically unsaturated alcohol stream, and to a process for preparing an ethylenically unsaturated aldehyde from an ethylenically unsaturated alcohol, in particular prenal from prenol, in the presence of an oxidizing agent and a catalytically active metal catalyst. The present invention further relates to a process for preparing 3,7-dimethyl-octa-2,6-dienal (citral), derived menthol and linalool.

Background Art

[0002] Ethylenically unsaturated aldehydes such as prenal (3-methyl-2-buten-1-al) are important chemical intermediates, for example, for the preparation of terpene-based fragrances such as citral and for the preparation of vitamins such as vitamin E. Thus, such ethylenically unsaturated aldehydes are of great technical and economic importance. The literature describes various examples for the preparation of ethylenically unsaturated aldehydes.

[0003] WO 2009 / 106621 A1 pamphlet describes, for example, a process for producing an olefinically unsaturated carbonyl compound such as prenol by oxidative dehydrogenation of prenol and / or isoprenol. The reaction is carried out at a temperature in the range of 50 to 240 °C in an oxygen-containing atmosphere with a supported gold-containing catalyst. For example, p-xylene can act as a solvent.

[0004] WO 2018 / 002040 A1 pamphlet describes a process for preparing an α,β-unsaturated aldehyde by oxidizing an alcohol using oxygen or air as an oxidizing agent in the presence of a catalyst containing platinum on a support. The reaction is carried out in the presence of a liquid phase containing at least 25% by weight of water, based on the total weight of the liquid phase.

[0005] International Publication No. WO 2018 / 172110 A1 pamphlet describes a process for preparing an α,β-unsaturated aldehyde, such as prenal, by oxidizing an alcohol, such as prenol, in the presence of a liquid phase. The aforementioned liquid phase contains less than 0.1 to 25% by weight of water, at least 25% by weight of an alcohol, such as prenol, and an α,β-unsaturated aldehyde, such as prenal. Oxygen and / or hydrogen peroxide can be used as an oxidizing agent. Preferably, the oxidation is carried out in the presence of a catalyst containing a catalytically active metal selected from platinum, palladium, and gold supported on a carrier.

[0006] International Publication No. WO 2019 / 121012 A1 pamphlet describes a process for preparing an α,β-unsaturated aldehyde, such as prenal, by oxidizing an alcohol, such as prenol, in the presence of a liquid phase containing at least 25% by weight of water. Oxygen is used as an oxidizing agent. The oxidation is carried out in the presence of a catalyst containing a catalytically active metal supported on a carrier, in which case the catalytically active metal is mainly located on the outer shell of the catalyst. Preferably, the catalytically active metal is selected from platinum, palladium, and gold.

[0007] International Publication No. WO 2019 / 121011 A1 pamphlet describes a process for preparing prenal (3-methylbut-2-en-1-al) from dimethylvinylcarbinol (2-methylbut-3-en-2-ol), which may optionally further contain prenol. 2-Methyl-3-buten-2-ol is assumed to be isomerized to 3-methyl-2-buten-1-ol and then oxidized to 3-methyl-2-buten-1-al. This process is carried out in the presence of an oxidizing agent and a catalyst. The catalyst preferably contains a catalytically active metal on a carrier, in which case the catalytically active material is preferably selected from platinum, palladium, and gold. Further, this process is carried out at a pH of less than 7, in which case the pH can be adjusted, for example, by adding an acid or a strongly acidic cation exchanger. Suitably, this process is carried out in the presence of a liquid phase containing at least 25% by weight of water.

[0008] These catalysts having noble metals deposited on the support exhibit good alcohol conversion and excellent selectivity and can exhibit a long lifespan depending on the exact nature of the catalyst. However, over time, these catalysts may lose some of their activity and sometimes may become sufficiently deactivated to render the catalyst unusable. At this stage of partial or complete deactivation, the catalyst needs to be regenerated or replaced.

Summary of the Invention

Problems to be Solved by the Invention

[0009] The present invention is based on the insight that trace amounts of organically bound nitrogen, for example nitrogen in the form of amines, tend to impair the action of oxidation catalysts. Isoprenol is produced by the chemical condensation of isobutene and formaldehyde, and isoprenol is further isomerized to prenol. The reaction of isobutene and formaldehyde can be carried out in the presence of a catalyst such as an amine base, for example hexamethylenetetramine (urotropine), as described in, for example, U.S. Patent No. 3,574,773. The amine base also inhibits formic acid formed by the disproportionation of formaldehyde. As a result, the resulting prenol and / or isoprenol stream may contain, for example, organic bound nitrogen impurities in amounts of several ppm.

[0010] However, reliably purifying ethylenically unsaturated alcohols from trace amounts of organically bound nitrogen on an industrial scale is not an easy task.

[0011] Generally, such ethylenically unsaturated alcohols are reactive compounds. This reactivity can pose difficulties, for example, when performing purification steps to remove impurities from such ethylenically unsaturated alcohols. For example, when treated with a solid adsorbent, isoprene is suspected of forming tertiary carbocations that can cause undesirable side reactions. In addition, nitrogen compounds that are present only at low concentrations compete with the abundant alcohol for absorption sites.

[0012] German Patent Application Publication No. 19910504 A1 describes a process for reducing the content of amines, such as monomethylamine, in an N-substituted lactam contaminated with amines, such as N-methyl-2-pyrrolidone, by treating the N-substituted lactam contaminated with amines with an acidic macroporous cation exchanger. At the same time, the metal cations contained as impurities in the N-substituted lactam may be depleted.

[0013] Therefore, there is still a need for an executable process for removing organic bound nitrogen from feed streams such as ethylenically unsaturated alcohol streams. Furthermore, there is still a need for an improved preparation process for ethylenically unsaturated aldehydes.

Means for Solving the Problem

[0014] The object of the present invention is solved by a process for removing organic bound nitrogen from an ethylenically unsaturated alcohol stream by contacting the ethylenically unsaturated alcohol stream with a weakly acidic solid adsorbent.

[0015] By the process of the present invention, organic bound nitrogen is depleted from the ethylenically unsaturated alcohol stream. Therefore, the present invention makes it possible to overcome the above problems in subsequent processes using an ethylenically unsaturated alcohol stream. For example, such subsequent processes include the oxidation of the aforementioned ethylenically unsaturated alcohol.

[0016] Generally, the ethylenically unsaturated alcohol stream is contacted with the weakly acidic solid adsorbent in the substantial absence of an oxidizing agent. Generally, the ethylenically unsaturated alcohol stream is contacted with the weakly acidic solid adsorbent in the absence of a catalytically active metal catalyst.

[0017] As used herein, the term "organically bound nitrogen" is intended to denote any compound containing at least one nitrogen atom directly bonded to one or more carbon atoms. For example, such compounds containing at least one nitrogen atom can be selected from amines such as ethylamine, trimethylamine, aniline, pyridine, or piperidine. A particularly important amine in practice is hexamethylenetetramine (urotropin). The ethylenically unsaturated alcohol stream subjected to the process of the present invention, for example, prenol stream or isoprenol stream, may contain about 5 - 30 ppm of organically bound nitrogen.

[0018] The "ethylenically unsaturated alcohol stream" of the present invention contains an alcohol having a carbon - carbon double bond. For example, the ethylenically unsaturated alcohol stream can be an α,β - unsaturated alcohol or a β,γ - unsaturated alcohol.

[0019] Examples of suitable ethylenically unsaturated alcohols include 3 - buten - 1 - ol, 3 - penten - 1 - ol, 3 - methylbut - 3 - en - 1 - ol, 3 - methylbut - 2 - en - 1 - ol, 3 - hexen - 1 - ol, 3 - methylpent - 3 - en - 1 - ol 3 - ethylbut - 3 - en - 1 - ol, 2 - methylhexen - 1 - en - 5 - ol, 2 - methylhexen - 1 - en - 4 - ol, 2 - phenylbut - 1 - en - 4 - ol, 4 - methylpent - 3 - en - 1 - ol and 2 - cyclohexylbut - 1 - en - 4 - ol, and mixtures thereof.

[0020] In a preferred embodiment, the ethylenically unsaturated alcohol is selected from 3 - methylbut - 2 - en - 1 - ol (prenol), 3 - methylbut - 3 - en - 1 - ol (isoprenol), and mixtures thereof, preferably 3 - methylbut - 2 - en - 1 - ol (prenol).

[0021] According to the present invention, an ethylenically unsaturated alcohol stream is contacted with a weakly acidic solid adsorbent. Such solid adsorbents in the context of the present invention have been found to be able to adsorb organic bound nitrogen in the presence of abundant alcohol while not interfering with reactive carbon-carbon double bonds.

[0022] The weakly acidic adsorbent can comprise an adsorbent material having an acidity sufficient to adsorb organic bound nitrogen from the ethylenically unsaturated alcohol stream.

[0023] In one embodiment, the solid adsorbent is a crosslinked resin having phosphonic acid functional groups.

[0024] Preferably, the resin polymer is a vinyl aromatic copolymer, preferably crosslinked polystyrene, more preferably a polystyrene divinylbenzene copolymer. Other polymers having phosphonic acid functional groups can also be used.

[0025] Preferably, the crosslinked resin having phosphonic acid functional groups is of the macroporous type.

[0026] A preferred solid adsorbent is Purolite S956.

[0027] The resin is typically used in the form of beads and packed into a column. The ethylenically unsaturated alcohol stream passes through the column and contacts the resin beads. During contact, the organic bound nitrogen in the ethylenically unsaturated alcohol stream reacts with the functional groups, protons move to the nitrogen, and an exchange occurs where ionic bonds are formed at the anionic sites of the resin. The contact is maintained until a threshold level, i.e., a breakthrough concentration, is reached. At this breakthrough point, the process reaches equilibrium where further organic bound nitrogen cannot be effectively removed. The flow is stopped and the column is backwashed with water, preferably deionized water or soft water. The reverse flow causes the resin to fluidize and the solids trapped by the beads are loosened and removed.

[0028] In another embodiment, the solid adsorbent is a silica-alumina hydrate. A number of silica-alumina catalyst compositions and their preparation processes are described in the patent literature. For example, refer to U.S. Patent Application Publication No. 4,499,197.

[0029] Preferably, the alumina content of the silica-alumina hydrate is about 10 to about 90 wt% of Al 2 O 3 . The preferred range of the alumina content is about 30 to about 70 wt% of Al 2 O 3 .

[0030] When silicon dioxide is introduced into aluminum oxide, acidic centers are introduced. The number of acidic centers can be controlled by the amount of silicon dioxide introduced. The number of acidic centers increases up to the maximum number of acidic centers according to the amount of introduced silicon dioxide, and after reaching the maximum number of acidic centers, it decreases again when the amount of silicon dioxide is further increased.

[0031] An example of a commercially available silica-alumina hydrate is Siral® available from Sasol Germany Gmbh, Hamburg, Germany. Siral® is based on orthorhombic aluminum oxide hydroxide (boehmite, AlOOH) and is doped with SiO 2 . Various Siral® grades with different ratios of AI 2 O 3 to SiO 2 are available: Siral 1 (AI 2 O 3 / SiO 2 = 99 / 1), Siral 5 (AI 2 O 3 / SiO 2 = 95 / 5), Siral 10 (Al 2 O 3 / SiO 2 = 90 / 10), Siral 20 (AI 2 O 3 / SiO 2 = 80 / 20), Siral 28M (Al2 O 3 / SiO 2 = 72 / 28), Siral 30 (AI 2 O 3 / SiO 2 = 70 / 30), Siral 40 (Al 2 O 3 / SiO 2 = 60 / 40). Siral 40 is particularly preferred.

[0032] In a suitable measurement process, the solid adsorbent is characterized by temperature-programmed desorption of ammonia (TPAD) carried out with an apparatus manufactured by Raczek analyzing technique GmbH, Hannover (Germany). For this purpose, the sample is conditioned at a temperature of 400 °C in a helium stream. Then, a mixture of 10% NH 3 / He is passed over the sample at 70 °C. Physically adsorbed ammonia is removed by flushing with helium at 120 °C for 2 hours. Chemisorbed ammonia is removed by passing helium over the sample heated to 400 °C at a linear heating rate of 15 °C / min. The integrated value of the peak of the amount of ammonia desorbed from the solid adsorbent is reported as the amount of acid sites.

[0033] In one embodiment, the ethylenically unsaturated alcohol stream is passed over a bed of weakly acidic solid adsorbent.

[0034] Suitably, the step of "passed over a bed" described above means that the layer of weakly acidic solid adsorbent ("bed") is provided in a conventional reaction vessel known to those skilled in the art, which can preferably be equipped with a stirring device, for example, in a stirred tank reactor. Then, the ethylenically unsaturated alcohol stream is introduced into the reaction vessel and induced through the reaction vessel to contact the weakly acidic solid adsorbent.

[0035] Alternatively, the weakly acidic solid adsorbent can be provided, for example, in the reaction tube of a tubular reactor, and then the ethylenically unsaturated alcohol stream continuously flows through the aforementioned reaction tube while contacting the weakly acidic solid adsorbent.

[0036] In one embodiment, the ethylenically unsaturated alcohol stream contains less than 2 ppm of organically bound nitrogen after contacting the ethylenically unsaturated alcohol stream with a weakly acidic solid adsorbent. As used herein, "ppm" refers to weight ppm of a compound containing organically bound nitrogen relative to the total weight of the ethylenically unsaturated alcohol stream.

[0037] Suitably, the content of organically bound nitrogen in the ethylenically unsaturated alcohol stream can be determined by Kjeldahl analysis. Alternatively, an oxidative combustion method using a chemiluminescence detector according to DIN 51444 can be used.

[0038] The present invention further relates to a process for preparing an ethylenically unsaturated aldehyde from an ethylenically unsaturated alcohol in the presence of an oxidizing agent and a catalytically active metal catalyst, wherein the ethylenically unsaturated alcohol stream is treated by the above process before contacting with the catalytically active metal catalyst.

[0039] As used herein, the aforementioned process for preparing an ethylenically unsaturated aldehyde is referred to as an "alcohol dehydrogenation process".

[0040] In other words, the ethylenically unsaturated alcohol stream is treated by a process of removing organically bound nitrogen from the ethylenically unsaturated alcohol stream by contacting the ethylenically unsaturated alcohol stream with a weakly acidic solid adsorbent. After the aforementioned treatment, the treated ethylenically unsaturated alcohol stream is then reacted in the presence of an oxidizing agent and a catalytically active metal catalyst as described below.

[0041] This procedure improves the catalytic activity and the catalyst life. Furthermore, the conversion and selectivity of the subsequent oxidation reaction are increased.

[0042] The alcohol dehydrogenation process is carried out in the presence of an oxidizing agent. In a preferred embodiment, the oxidizing agent is selected from oxygen and hydrogen peroxide.

[0043] The oxidizing agent can be a gas mixture containing oxygen in a content range of 2 to 50% by volume, preferably 3 to 40% by volume, more preferably 7 to 18% by volume. In addition to oxygen, the gas mixture may further contain a diluent gas. Appropriately, the diluent gas is an inert gas such as nitrogen, argon, carbon dioxide, etc. For example, the oxidizing agent can be air as an easily available oxidizing medium.

[0044] Preferably, oxygen is used without dilution.

[0045] The alcohol dehydrogenation process is carried out in the presence of a catalytically active metal catalyst.

[0046] Appropriately, the catalytically active metal can be selected from the metals of Groups 8, 9, 10, and 11 of the Periodic Table of the Elements by IUPAC. The elements of Groups 8, 9, 10, and 11 include iron, cobalt, nickel, copper, ruthenium, rhodium, palladium, silver, osmium, iridium, platinum, and gold.

[0047] In a preferred embodiment, the catalytically active metal is selected from platinum, palladium, and gold. Platinum is particularly preferred.

[0048] The catalytically active metal can be used in any form, for example, in an unsupported form or on a support.

[0049] The catalytically active metal can be used in an unsupported form such as powder, mesh, sponge, foam, or net, etc.

[0050] In a preferred embodiment, the catalytically active metal is preferably deposited on a support selected from a carbonaceous material and an oxide material.

[0051] For example, the support may contain aluminum oxide, silicon dioxide, magnesium oxide, or hydrotalcite.

[0052] In principle, suitable carrier materials are basic, acidic, or otherwise amphoteric carrier materials. Basic materials have been found to be particularly suitable. Aluminum oxide, basic aluminosilicates or hydrotalcites, preferably aluminum oxide and hydrotalcite, have been found to be advantageous in some cases. Carbon-based carrier materials, such as various types of charcoal, are also suitable.

[0053] In a preferred embodiment, the catalytically active metal is platinum on a carrier, in which case the carrier is selected from carbonaceous materials and oxide materials, and the oxide is selected from oxides of Al, Ce, Zr, Ti, V, Cr, Zn, and Mg, preferably oxides of Al, Ce, Zr, and Ti.

[0054] In a particularly preferred embodiment, the catalyst is selected from platinum on carbon (Pt / C) and platinum on aluminum oxide (Pt / Al 2 O 3 ).

[0055] When the catalytically active metal is deposited on a carrier, the total weight of the catalyst herein shall be defined as the sum of the weight of the catalytically active metal and the weight of the carrier.

[0056] The content of the catalytically active metal in the catalyst is not particularly limited per se and can range from 0.1 to 20% by weight, preferably from 0.1 to 15% by weight, more preferably from 0.5 to 10% by weight, based on the total weight of the catalyst.

[0057] Optionally, the catalyst may contain one or more promoters that enhance the activity of the catalytically active metal. Examples of such promoters are bismuth, antimony, lead, cadmium, tin, or tellurium. For example, the promoter may be present on or in the carrier or can be added separately to the process.

[0058] In one embodiment, this process is carried out at a temperature in the range of 1 to 250 °C, preferably 5 to 150 °C, more preferably 20 to 100 °C, most preferably 25 to 80 °C, particularly 30 to 70 °C, particularly 35 to 50 °C.

[0059] In one embodiment, the reaction is carried out in a liquid phase containing at least 25% by weight, preferably at least 30% by weight, more preferably at least 40% by weight, particularly at least 50% by weight of water, based on the total weight of the liquid phase determined at a temperature of 20 °C and a pressure of 1 bara.

[0060] Optionally, the liquid phase may further contain one or more solvents. As used herein, the term "solvent" refers to any component other than reactants, products, oxidants, or water that is liquid at a temperature of 20 °C and a pressure of 1 bara.

[0061] The liquid phase may contain less than 70% by weight, preferably less than 60% by weight, more preferably less than 50% by weight, most preferably less than 40% by weight, particularly less than 30% by weight, particularly less than 20% by weight, particularly less than 10% by weight, based on the total weight of the liquid phase determined at a temperature of 20 °C and a pressure of 1 bara.

[0062] Preferably, the solvent is an aprotic organic solvent. Useful aprotic organic solvents are selected from the following - aliphatic hydrocarbons such as hexane, heptane, octane, nonane, decane and petroleum ether, - aromatic hydrocarbons such as benzene, toluene, xylene and mesitylene, - aliphatic ethers such as 1,2 - dimethoxyethane (DME), diethylene glycol dimethyl ether (diglyme), diethyl ether, dipropyl ether, methyl isobutyl ether, tert - butyl methyl ether, tert - butyl ethyl ether, dimethoxymethane, diethoxymethane, dimethylene glycol dimethyl ether, dimethylene glycol diethyl ether, trimethylene glycol dimethyl ether, trimethylene glycol diethyl ether, and tetramethylene glycol dimethyl ether, - cycloaliphatic hydrocarbons such as cyclohexane and cycloheptane, - Alicyclic C such as tetrahydrofuran (THF), tetrahydropyran, 2-methyltetrahydrofuran, 3-methyltetrahydrofuran, 1,3-dioxolane, 1,4-dioxane, and 1,3,5-trioxane 3 - C 6 - Ether, - Short-chain ketones such as acetone, ethyl methyl ketone, and isobutyl methyl ketone, - C such as methyl acetate, ethyl acetate, methyl propionate, dimethyl oxalate, methyl methoxyacetate, ethylene carbonate, propylene carbonate, ethylene glycol diacetate, and diethylene glycol diacetate 3 - C 6 - Ester, - C such as dimethylformamide (DMF), dimethylacetamide, and N-methylpyrrolidone (NMP) 3 - C 6 - Amide, - Sulfoxides such as dimethyl sulfoxide (DMSO), - C such as acetonitrile and propionitrile 3 - C 6 - Nitrile, and - Their mixtures.

[0063] Preferably, the boiling point of the solvent exceeds 50 °C, more preferably ranges from 50 to 200 °C, most preferably from 65 to 180 °C, particularly from 80 to 160 °C.

[0064] In one embodiment, the liquid phase contains 1 to 75% by weight, preferably 1 to 50% by weight, more preferably 2 to 45% by weight, most preferably 3 to 40% by weight of ethylenically unsaturated alcohol based on the total amount of the liquid phase.

[0065] By this means, it is confirmed that a sufficient amount of the starting material, namely ethylenically unsaturated alcohol, is present in the reaction mixture of the alcohol dehydrogenation process.

[0066] The alcohol dehydrogenation process can be carried out in a reaction vessel customary for such reactions. For example, the alcohol dehydrogenation process can be carried out in continuous mode, semi-batch mode, or batch mode. Suitable reaction vessels are known to those skilled in the art.

[0067] The alcohol dehydrogenation process can be carried out at atmospheric pressure or under pressure. However, preferably, the alcohol dehydrogenation process is carried out under a pressure in the range of 1 to over 15 bara, more preferably 1 to 10 bara.

[0068] When using oxygen as the oxidizing agent, the alcohol dehydrogenation process may suitably be carried out at an oxygen partial pressure in the range of 0.1 to 15 bara, preferably 0.2 to 10 bara, more preferably 0.2 to 8 bara, most preferably 0.2 to 5 bara, particularly 1 to 3 bara, particularly 1 to 2.5 bara, particularly 1.2 to 2 bara.

[0069] The crude product obtained from the alcohol dehydrogenation process can be subjected to conventional purification means known to those skilled in the art, including distillation or chromatography, or combinations thereof. Distillation apparatuses suitable for the purification of the product include, for example, distillation columns such as bubble cap trays, sieve plates, sieve trays, trays optionally provided with packages or packings, or spinning band columns such as thin film evaporators, falling film evaporators, forced circulation evaporators, wiped film (Sambay) evaporators, and combinations thereof.

[0070] According to the present invention, various ethylenically unsaturated aldehydes can be produced. In one embodiment, the ethylenically unsaturated alcohol is 3-methylbut-2-en-1-ol (prenol), and the ethylenically unsaturated aldehyde produced is prenal (3-methyl-2-buten-1-al).

[0071] Prenol, which is useful as a starting material for the present invention, can be obtained by reacting a formaldehyde source with isobutylene to obtain 3-methylbut-3-en-1-ol (isoprenol) and isomerizing the obtained isoprenol.

[0072] In one embodiment, isoprenol is obtained by mixing a formaldehyde source and isobutylene, injecting them into a reactor through at least one nozzle, and reacting the formaldehyde source and isobutylene under supercritical conditions. To achieve the supercritical state, formaldehyde and isobutylene are preferably reacted at a temperature in the range of at least 220°C, for example, 220 - 290°C, and an absolute pressure of at least 200 bar. The reaction of isobutene and formaldehyde can be carried out in the presence of a catalyst such as an amine base, for example, hexamethylenetetramine (urotropin).

[0073] Formaldehyde can be provided as a liquid, for example, as a solution of paraformaldehyde. Preferably, the formaldehyde source is an aqueous formaldehyde solution.

[0074] Further details regarding the reaction of a formaldehyde source with isobutylene to obtain isoprenol can be found in International Publication No. WO 2020 / 049111 A1.

[0075] Separating isoprenol from formaldehyde is not an easy task. This difficulty arises because monomeric formaldehyde (and polymeric formaldehyde) forms hydrates with water and further forms hemiacetals with isoprenol. Hydrates and hemiacetals with different degrees of polymerization of formaldehyde have mixed boiling points.

[0076] However, it has been found that by distilling at a temperature at which the hemiacetal decomposes into formaldehyde and isoprenol, formaldehyde can be substantially completely separated from isoprenol, and as a result, formaldehyde can be easily separated from isoprenol.

[0077] Accordingly, crude isoprenol is purified by distilling the crude isoprenol stream containing isoprenol, water and formaldehyde, or its isoprenol-containing fraction, in a low-boiling-point separation column operated at a pressure of 2 bara or more, preferably 2.5 bara or more, to obtain a distillate stream containing aqueous formaldehyde and a bottom stream containing isoprenol substantially free of formaldehyde.

[0078] In particular, formaldehyde can be substantially completely separated from isoprenol, and an aqueous formaldehyde solution concentrated suitable for recycling to isoprenol synthesis has an equilibrium shifted to the hemiacetal side of formaldehyde and isoprenol, so that as a result, essentially all of the formaldehyde remains at the bottom of the distillation column at the temperature of the first distillation and the hemiacetal decomposes into formaldehyde and isoprenol, so that as a result, formaldehyde can be easily separated from isoprenol. It has been found that it can be obtained in a distillation train involving a second distillation at a temperature at which it can be separated.

[0079] To enable a first distillation at a temperature below the dissociation temperature of isoprenol-formaldehyde and a second distillation at a temperature above the dissociation temperature of isoprenol-formaldehyde, two low-boiling-point separation columns operating at different pressures are envisaged. Accordingly, at a relatively low pressure extending to the first low-boiling-point separation column, a first distillate containing water and low-boiling components substantially free of formaldehyde is obtained. At a relatively high pressure extending to the second low-boiling-point separation column, substantially all of the formaldehyde is separated from the isoprenol. Accordingly, this process can obtain isoprenol substantially free of formaldehyde.

[0080] Accordingly, in a more preferred embodiment, the purification process is (i) feeding the aforementioned stream of crude isoprenol to a first low-boiling-point separation column operated at a pressure of 1.5 bara or less to obtain a first bottom stream containing isoprenol and formaldehyde and a first distillate stream containing water and low-boiling components; (ii) Feeding the first bottom stream to a second low-boiling-point component separation column operated at a pressure of 2 bara or more to obtain a second distillation stream containing aqueous formaldehyde and a second bottom stream containing isoprenol; (iii) Feeding the second bottom stream to a finishing column to obtain pure isoprenol as a distillation stream and a bottom stream containing high-boiling-point components.

[0081] The second distillation stream constitutes concentrated aqueous formaldehyde suitable for recycling to isoprenol synthesis.

[0082] The second low-boiling-point separation column is preferably operated at a pressure of 2.5 bara or more, more preferably 2.8 bara or more, and most preferably 2.9 bara or more. The bottom temperature of the second low-boiling-point component separation column is preferably in the range of 160 to 200 °C, more preferably 170 to 185 °C, and most preferably 175 to 180 °C. The top temperature of the second low-boiling-point component separation column is preferably in the range of 115 to 160 °C, and more preferably in the range of 125 to 145 °C.

[0083] In a particularly preferred embodiment, the second low-boiling-point separation column is operated at a pressure in the range of 2.9 to 3.5 bara, a bottom temperature in the range of 175 to 180 °C, and a top temperature in the range of 130 to 140 °C.

[0084] Further information regarding the process for recovering isoprenol essentially free of formaldehyde can be found in the pamphlet of International Publication No. WO 2022 / 189652 A1.

[0085] The obtained isoprenol undergoes catalytic isomerization to obtain prenol.

[0086] The isomerization of isoprenol to 3-methyl-2-buten-1-ol (prenol) can be carried out over a supported noble metal, preferably in the presence of hydrogen. Preferred catalysts are fixed bed catalysts comprising palladium supported on silicon dioxide and selenium or tellurium or a mixture of selenium and tellurium. The isomerization is carried out at a temperature of 50 to 150 °C to produce a reaction mixture of prenol and isoprenol. Isoprenol can be recycled. Further details are described in WO 2008 / 037693 pamphlet.

[0087] The prenal produced by the present invention is a useful intermediate in the preparation of citral. Citral is a mixture of the isomeric compounds neral and geranial.

[0088] 3,7-Dimethyl-octa-2,6-dienal (citral) can be prepared by obtaining prenal by the above process, which process further comprises condensing prenal with prenol to obtain the diprenyl acetal of prenal, and subjecting the diprenyl acetal of prenal to cleavage conditions to obtain citral via prenyl (3-methyl-butadienyl) ether and 2,4,4-trimethyl-3-formyl-1,5-hexadiene.

[0089] In particular, 3,7-dimethyl-octa-2,6-dienal (citral) is a) condensing prenal with prenol in a reaction column in the presence of at least one catalyst while removing an acetal fraction containing the diprenyl acetal of prenal from the reaction column; and b) subjecting the acetal fraction in a cleavage column to cleavage conditions in the presence of at least one catalyst while removing a cleavage fraction containing at least one of prenyl (3-methyl-butadienyl) ether and 2,4,4-trimethyl-3-formyl-1,5-hexadiene and optionally citral from the cleavage column. c) Reacting the fraction remaining after decomposition in a plug flow reactor to obtain citral, and can be prepared by a process comprising:

[0090] The overall reaction sequence is shown by the following reaction scheme.

Chemical formula

[0091] In step a), using a catalyst, unsaturated acetal 3-methyl-2-butenal-diprenyl acetal (hereinafter referred to as "diprenyl acetal of prenal" or "diprenyl acetal") is generated from prenol and prenal. For this purpose, in the presence of a catalytic amount of an acid, prenal is reacted with prenol while separating the water generated during the reaction in a reaction column. In step b), the 3-methyl-2-butenal diprenyl acetal (diprenyl acetal) obtained in step a) is decomposed in a decomposition column in the presence of a catalyst while removing 3-methyl-2-buten-1-ol (prenol) to obtain prenyl (3-methylbutadienyl) ether. By the Claisen rearrangement of the obtained prenyl (3-methylbutadienyl) ether, 2,4,4-trimethyl-3-formyl-1,5-hexadiene is obtained, and subsequently a Cope rearrangement occurs to obtain 3,7-dimethyl-2,6-octadienal (citral).

[0092] Step a) is carried out in the presence of a catalyst, preferably an acid. In one embodiment, the catalyst in step a) is nitric acid.

[0093] Preferably, in step b), the acetal fraction is continuously subjected to decomposition conditions in a decomposition column. "Decomposition conditions" refer to reaction conditions selected such that the diprenyl acetal contained in the acetal fraction can be decomposed into prenyl (3-methylbutadienyl) ether and then rearranged to 2,4,4-trimethyl-3-formyl-1,5-hexadiene and citral.

[0094] The acetal fraction contains diprenyl acetal as the main component. The acetal fraction does not necessarily consist of pure diprenyl acetal and may also contain prenol, prenal and citral components.

[0095] Step b) is carried out in the presence of a catalyst, preferably an acid catalyst. Suitable acid catalysts are selected from non-volatile protonic acids such as sulfuric acid, p-toluenesulfonic acid and phosphoric acid.

[0096] Suitably, the continuous decomposition in the decomposition column of step b) can be carried out at the bottom or sump of a distillation column functioning as the decomposition column. Preferably, the acetal fraction and / or the catalyst are introduced into the bottom of the distillation column, the sump of the distillation column, or the evaporator of the distillation column.

[0097] If necessary, a high-boiling inert compound can be introduced into the sump of the decomposition column to ensure the minimum filling level of the sump and the evaporator. Suitable high-boiling inert compounds are selected from liquid compounds that are inert under the reaction conditions and have a higher boiling point than citral and diprenyl acetal. For example, the high-boiling inert compound can be selected from hydrocarbons such as tetradecane, pentadecane, hexadecane, octadecane, eicosane, or ethers such as diethylene glycol dibutyl ether, white oil, kerosene, or mixtures thereof.

[0098] Suitably, the distillation conditions are selected such that diprenyl acetal is mainly retained in the bottom or sump of the distillation column. During the decomposition reaction, a decomposition fraction is continuously withdrawn from the decomposition column, and the decomposition fraction contains at least one of prenyl (3-methyl-butadienyl) ether and 2,4,4-trimethyl-3-formyl-1,5-hexadiene, and optionally citral. For the sake of simplicity, prenyl (3-methyl-butadienyl) ether, 2,4,4-trimethyl-3-formyl-1,5-hexadiene and citral are collectively referred to as "citral components". This is because the former is an intermediate in the reaction pathway to citral and can be converted to citral in subsequent step c).

[0099] Furthermore, the prenol formed during the decomposition reaction in step b) is generally continuously removed from the reaction mixture at the upper part of the decomposition column.

[0100] The decomposition fraction together with the formed prenol can be taken out from the upper part of the distillation column.

[0101] Alternatively and preferably, it is also possible to take out the decomposition fraction in the form of a liquid or a vapor at the side outlet of the distillation column.

[0102] In step c), the decomposition fraction is reacted in a plug flow reactor to obtain citral. For this purpose, the decomposition fraction is induced through a plug flow reactor at a temperature suitable for carrying out the rearrangement reaction to produce citral. By using a combination of a highly back-mixed decomposition column and a plug flow reactor, the selectivity and yield of the decomposition reaction can be increased. All the catalysts required for the decomposition reaction are preferably introduced into the decomposition column in step b), and preferably, the catalyst is not introduced into the plug flow reactor.

[0103] In one embodiment, the prenol removed in step b) is recycled to step a). Thereby, an improved yield can be achieved in the process of the present invention.

[0104] In one aspect, therefore, the present invention provides A) a step of reacting a formaldehyde source with isobutylene to obtain 3-methylbut-3-en-1-ol (isoprenol), and a step of obtaining prenol by isomerizing at least a part of the obtained isoprenol; and B) a step of preparing prenal (3-methylbut-2-en-1-al) from 3-methylbut-2-en-1-ol (prenol) using the above process, and / or a step of preparing prenal using the above process via isoprenal (3-methylbut-3-en-1-al) generated from isoprenol; and C) a step of condensing prenal with prenol to obtain the diprenyl acetal of prenal, and a step of subjecting the diprenyl acetal of prenal to decomposition conditions to obtain citral via prenyl (3-methyl-butadienyl) ether and 2,4,4-trimethyl-3-formyl-1,5-hexadiene, and relates to an improved preparation process of citral (3,7-dimethyl-octa-2,6-dienal).

[0105] Step A can be carried out as described above or by other methods known in the art. Preferably, it can be carried out by distilling at a temperature at which the hemiformaldehyde is decomposed into formaldehyde and isoprenol, so that formaldehyde can be easily separated from isoprenol. More preferably, it can be carried out by distilling a crude isoprenol stream containing isoprenol, water and formaldehyde, or an isoprenol-containing fraction thereof, in a low-boiling separation column operated at a pressure of 2 bara or more, preferably 2.5 bara or more, to obtain a distillate stream containing aqueous formaldehyde and a bottom stream containing isoprenol essentially free of formaldehyde.

[0106] Step B involves the oxidative dehydrogenation of prenol and / or isoprenol. The conversion of isoprenol by a catalytically active metal catalyst forms a reaction mixture of 3-methylbut-3-en-1-al and 3-methylbut-2-en-1-al. Subsequently, the former isomer can be isomerized under a base catalyst to obtain the desired 3-methylbut-2-en-1-al.

[0107] Step C can be carried out as described above, for example, via steps a) to c).

[0108] The citral thus obtained is a useful intermediate for, for example, menthol or linalool.

[0109] Menthol is - a step of catalytically hydrogenating -citral to obtain citronellal, - a step of cyclizing citronellal in the presence of an acidic catalyst to obtain isopulegol; - a step of catalytically hydrogenating isopulegol to obtain menthol, and can be prepared from citral via a process comprising the steps.

[0110] The overall reaction sequence is shown by the following reaction scheme.

Chemical formula

[0111] Hydrogenating citral to obtain citronellal can be achieved by hydrogenation in the presence of a rhodium phosphine catalyst.

[0112] Cyclizing citronellal to isopulegol can be achieved by cyclization in the presence of a Lewis acidic aluminum-containing catalyst such as a bis(diarylphenoxy)aluminum compound, and this catalyst can be used in the presence of an auxiliary agent such as a carboxylic acid anhydride. Isopulegol is recovered from the reaction product containing the catalyst by distillation separation to obtain an upper product rich in isopulegol and a bottom product depleted in isopulegol. The catalyst can be regenerated from the bottom product. The isopulegol thus obtained by cyclizing citronellal can be further purified by a suitable separation and / or purification method, particularly crystallization, to remove at least most of the undesirable impurities or by-products.

[0113] The hydrogenation of isopulegol can be achieved by hydrogenation in the presence of a heterogeneous nickel-containing catalyst, preferably a heterogeneous nickel and copper-containing catalyst.

[0114] Further details regarding the reaction sequence from citral to menthol can be found in U.S. Patent Application Publication No. 2013 / 46118A1, which is incorporated herein by reference.

[0115] In one aspect, therefore, the present invention relates to an improved process for the preparation of menthol by using the above process to produce citral and then producing menthol from citral. Menthol can be prepared as described herein or by other processes known in the art.

[0116] Linalool can be prepared from citral by a process that includes catalytically hydrogenating citral to obtain nerol and / or geraniol and isomerizing the same.

[0117] Obtaining nerol and / or geraniol by hydrogenating citral can be achieved by hydrogenation in the presence of a supported ruthenium, rhodium, osmium, iridium or platinum catalyst, preferably a ruthenium catalyst supported on carbon black.

[0118] Isomerizing nerol and / or geraniol to obtain linalool can be achieved by isomerization in the presence of a tungsten catalyst, particularly a dioxotungsten(VI) complex. Further details regarding the isomerization of nerol and / or geraniol can be found in U.S. Patent No. 7,126,033B2.

[0119] In one aspect, therefore, the present invention relates to an improved process for the preparation of linalool by using the above process to produce citral and then producing linalool from citral. Linalool can be prepared as described herein or by other processes known in the art.

[0120] The present invention can be further explained and illustrated based on the following figures and examples. However, it will be understood that these figures and examples are included for illustrative purposes only and are in no way intended to limit the scope of the present invention.

Brief Description of the Drawings

[0121]

Figure 1

Figure 2

Mode for Carrying Out the Invention

Examples

[0122] Example 1 - Removal of urotropin from a prenol stream using various adsorbents For various adsorbents, the ability to remove urotropin from prenol is tested. For this purpose, the corresponding adsorbent is mixed with water at room temperature and stirred for 15 minutes for washing. Then, the water-wet adsorbent is stirred with a small amount of prenol (nitrogen-free) for 5 minutes. Next, the prenol-wet adsorbent is transferred to a column, and the untreated prenol feed is passed through the column (from top to bottom). The results are shown in Table 1.

[0123]

Table 1

[0124] The examples show that Purolite S956 and Siral 40 exhibit remarkable behavior regarding the removal of urotropin (organic-bound nitrogen) from a prenol stream ("ethylenically unsaturated alcohol stream").

[0125] Example 2 - Removal of urotropin from a prenol stream using Siral 40 A prenol stream with an initial urotropin content of 35 ppm is passed through a column of 1 g of Siral 40 (inner diameter 15 mm, length 250 mm) at the flow rates shown in Table 2. Every 30 minutes, a sample is taken and the urotropin content of the treated prenol is determined by an oxidative combustion method using a chemiluminescence detector. The results are shown in Table 2.

[0126]

Table 2

[0127] As can be seen from the results in Table 2, in the process of the present invention, hexamine can be significantly removed from prenol using Siral 40 as an adsorbent without causing breakthrough during the test period.

[0128] Example 3 - Oxygen Consumption in the Liquid Phase Oxidation of Prenol 103 g of a Pt / Al 2 O 3 catalyst (0.9 wt% Pt) was charged into the reactor. Using a metering pump, a feed stream containing 97 g / h of prenol and 7 g / h of water was metered into the reactor. The specification of prenol (hexamine content) varied throughout reaction periods 1 to 7 as shown in Table 3 (see Figure 1). The reaction was carried out for 59 d at an inlet pressure of 3.9 bara and an outlet pressure of 3.6 bara, and an inlet temperature of 45 °C and an outlet temperature of 48 °C. The oxygen consumption was quantitatively determined by the decrease in the oxygen flow rate in L / h using a flow meter. The oxygen consumption is a measure of the catalyst activity.

[0129] [Table 3]

[0130] The data in Table 3 and Figure 1 show that when using the prenol stream pretreated in the adsorption step according to the present invention (periods 2 and 4 - 7), the decrease in oxygen consumption is not as significant as compared to the unpretreated prenol stream (periods 1 and 3).

[0131] Example 4 - Selectivity for Prenol A fixed-bed reactor containing a heterogeneous catalyst was charged with i) an unsaturated alcohol treated with an adsorbent for nitrogen removal, or ii) an unsaturated alcohol treated with an untreated feed containing up to 35 ppm of nitrogen. In both cases, the reaction was carried out at 80 °C and 1.5 bar for several hours to compare the results regarding catalytic activity and selectivity. The results are shown in Figure 2. From Figure 2, it can be seen that when organic-bound nitrogen was removed from the prenol feed stream prior to the reaction, the conversion to prenal was higher and the selectivity was also higher compared to the untreated prenol feed stream.

Claims

1. A process for removing organically bound nitrogen from an ethylenically unsaturated alcohol stream by contacting the stream with a weakly acidic solid adsorbent.

2. The process according to claim 1, wherein the solid adsorbent is a crosslinked resin having a phosphonic acid functional group.

3. The process according to claim 1, wherein the solid adsorbent is silica-alumina hydrate.

4. The process according to claim 1, wherein the ethylenically unsaturated alcohol stream is flowed across the bed of the weakly acidic solid adsorbent.

5. The process according to claim 1, wherein the ethylenically unsaturated alcohol stream contains less than 2 ppm of organically bound nitrogen after contacting the ethylenically unsaturated alcohol stream with a weakly acidic solid adsorbent.

6. A process for preparing an ethylenically unsaturated aldehyde from an ethylenically unsaturated alcohol in the presence of an oxidizing agent and a catalytically active metal catalyst, wherein the ethylenically unsaturated alcohol stream is treated by the process described in claim 1 before contact with the catalytically active metal catalyst.

7. The process according to claim 6, wherein the catalytic active metal is selected from platinum, palladium, and gold.

8. The process according to claim 6, wherein the catalytically active metal is deposited on a carrier.

9. The process according to claim 8, wherein the carrier is selected from carbonaceous materials and oxide materials.

10. The process according to claim 6, wherein the oxidizing agent is selected from oxygen and hydrogen peroxide.

11. The process according to claim 6, wherein the process is carried out at a temperature in the range of 1 to 250°C.

12. The process according to claim 1, wherein the reaction is carried out in the presence of a liquid phase containing at least 25% by weight of water.

13. The process according to claim 12, wherein the liquid phase comprises 1 to 75% by weight of the ethylenically unsaturated alcohol based on the total amount of the liquid phase.

14. The process according to claim 6, wherein the ethylenically unsaturated alcohol is 3-methylbuto-2-ene-1-ol (prenol), and the ethylenically unsaturated aldehyde is 3-methylbuto-2-ene-1-al (prenal).

15. The process according to claim 14, wherein prenol is obtained by reacting a formaldehyde source with isobutylene to obtain 3-methylbuto-3-en-1-ol (isoprenol), and then isomerizing at least a portion of the obtained isoprenol.

16. A process for preparing 3,7-dimethyl-octa-2,6-dienal (citral), further comprising the steps of obtaining plenal by the process described in Claim 14, condensing the plenal with prenol to obtain a diprenyl acetal of plenal, and subjecting the diprenyl acetal of plenal to decomposition conditions to obtain citral via prenyl(3-methyl-butadienyl) ether and 2,4,4-trimethyl-3-formyl-1,5-hexadiene.

17. A menthol preparation process comprising the steps of preparing citral by the process described in claim 16, and reacting the citral to obtain menthol.

18. A linalool preparation process comprising the steps of preparing citral by the process described in claim 16 and reacting the citral to obtain linalool.

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