Method for reacting dibutene with pre-distillation

Abstract

The invention relates to a method for reacting dibutene with pre-distillation. The invention relates to a method for reacting dibutenes, in which a feed stream used, which contains at least the linear isomers and branched isomers of the olefins used, is distilled prior to the reaction, and only the high-boiling phase obtained in the distillation is subjected to the reaction: heterogeneously catalyzed hydroformylation, homogeneously catalyzed hydroformylation or homogeneously catalyzed alkoxycarbonylation.

Description

Technical field

[0001] The subject of the present invention is a process for reacting dibutenes, in which the feed stream used is distilled before the reaction, said feed stream containing at least the linear and branched isomers of the olefins used, and only the high-boiling phase obtained in this distillation is subjected to the reaction: heterogeneous catalytic hydroformylation, homogeneous catalytic hydroformylation or homogeneous catalytic alkoxycarbonylation.

[0002] In the context of the present invention, the term "reaction" is to be understood as meaning three different reactions: heterogeneous catalytic hydroformylation, homogeneous catalytic hydroformylation and homogeneous catalytic alkoxycarbonylation. These three reaction types are known organic chemical processes per se, but will be described in more detail in the context of the present invention. Background art

[0003] In hydroformylation, an olefin reacts with synthesis gas, i.e. a mixture of carbon monoxide (CO) and hydrogen (H2), in the presence of a suitable homogeneous catalyst system to form the corresponding aldehyde. Aldehydes are formed in hydroformylation. For example, if dibutenes are used as the olefin, isononanal is formed. Hydroformylation is a process used industrially on a large scale, which is operated in plants where the aldehyde can be produced on a scale of several to several hundred kilotons (kt) per year. The catalyst systems commonly used here are homogeneously dissolved catalyst systems and contain transition metal complexes mainly formed from cobalt or rhodium as the metal and phosphorus-containing ligands. Many such examples can be found in the patent literature. In industrial chemistry, the aldehydes obtained are usually hydrogenated to form alcohols. If isononanal obtained from dibutenes is used here, the hydrogenation produces isononanol (INA).

[0004] In recent years, there has again been a greater interest in heterogeneous catalytic hydroformylation. EP 3632885 A1 discloses an example of the corresponding hydroformylation. In this document, a catalyst system present in heterogeneous form on a monolithic support made of a porous ceramic material is used instead of the known homogeneously dissolved catalyst. The heterogeneous catalyst system is in particular a transition metal complex known or analogous to homogeneous catalytic hydroformylation and mainly formed from cobalt or rhodium as the metal and phosphorus-containing ligands.

[0005] Alkoxycarbonylation is the reaction of an olefin with carbon monoxide and an alcohol to form the resulting ester. Metal-ligand complexes are usually used as catalysts, which are homogeneously dissolved in the reaction mixture and thus also in the product mixture. For example, EP 3750620 A1 discloses the corresponding process. The catalyst systems used in particular contain metals of groups 8 to 10 of the Periodic Table of the Elements (PSE), such as palladium, or their compounds, phosphorus-containing ligands and an acid as a cocatalyst.

[0006] In order to be able to operate the above reaction processes, namely homogeneous catalytic hydroformylation, heterogeneous catalytic hydroformylation or homogeneous catalytic alkoxycarbonylation, in an economically viable manner, it depends on various factors. One of these factors is the reaction rate, which should be as high as possible. Ultimately, more product can be prepared per unit time compared to a reaction with a lower reaction rate. However, it should be noted here that when the reaction rate is increased, other reaction parameters, such as reaction conversion and / or selectivity to the desired product, are not impaired, so that the advantage of a higher reaction rate is not reversed. SUMMARY OF THE INVENTION

[0007] Accordingly, it is an object of the present invention to provide a process for reacting dibutenes which enables a high reaction rate to be achieved while the reaction conversion and / or the selectivity to the desired product are not significantly impaired, the product being an aldehyde in the case of hydroformylation or an ester in the case of alkoxycarbonylation.

[0008] This object can be achieved by the process according to the claims. Preferred embodiments are set out in the dependent claims. The process according to the invention is a process for reacting dibutenes, which comprises the following steps:

[0009] a) providing a dibutene feed stream which contains at least the straight-chain and branched isomers of the olefins used;

[0010] b) distilling the provided feed stream to obtain at least one low-boiling phase and a high-boiling phase, where 1 wt% to less than 50 wt%, preferably 5 wt% to 40 wt%, particularly preferably 10 wt% to 30 wt% of the distilled feed stream is obtained as the low-boiling phase, and where the proportion of straight-chain isomers in the low-boiling phase is less than the proportion of straight-chain isomers in the high-boiling phase;

[0011] c) feeding the high-boiling phase from step b) to a reaction unit comprising one or more reactors and carrying out the reaction in the reaction unit, where the reaction is heterogeneous catalytic hydroformylation in the presence of synthesis gas, homogeneous catalytic hydroformylation in the presence of synthesis gas, or homogeneous catalytic alkoxycarbonylation in the presence of carbon monoxide and a C1 to C6 alcohol; and

[0012] d) feeding the low-boiling phase from step b) to a hydrogenation unit consisting of one or more reactors for hydrogenation, where the olefins present in the low-boiling phase are hydrogenated to the corresponding alkanes with a hydrogen-containing gas in the presence of a supported catalyst.

[0013] The key method steps here are step b), i.e., the distillation of the feed stream, and the use of only the high-boiling phase in the reaction of step c). The method according to the invention has the advantage that the reaction rate in the reaction of step c) is higher than that of known methods without such distillation. The reason for this may be that in the said distillation, the relatively less reactive isomers and / or substances inhibiting the reaction are separated from the feed stream through the low-boiling phase and thus not supplied to the reaction.

[0014] The first step a) of the method according to the invention is to provide a feed stream of dibutenes. The feed stream used is generally an industrially available hydrocarbon stream which contains at least different isomers of the respective olefins. Here, these feed streams contain at least linear isomers and branched isomers. It is well known that isomers are olefins having the same number of carbon atoms but different structures. It should be understood that the amount of the respective olefins in the hydrocarbon stream should be high enough to enable the reaction in step c) to be operated in an economically viable manner; preferably, the feed stream should contain at least 5% by weight of the olefins concerned, based on the total weight of the feed stream.

[0015] Higher olefins can be obtained in particular by oligomerization, such as dimerization, trimerization or tetramerization. Suitable hydrocarbon streams are mixtures of isomeric octenes (dibutenes) obtained in the dimerization of butenes. Dibutene refers to a mixture of at least different linear and branched isomers of dibutene, i.e., C8 olefins. Dibutene can be obtained in particular by the oligomerization or dimerization of butenes, optionally after distillative separation from the oligomerization mixture.

[0016] The feed stream provided in step a) may have previously undergone one or more additional method steps to convert specific components of the feed stream or to remove them from the stream. An example is the removal of impurities that may be harmful to the catalyst, such as substances or compounds containing oxygen, nitrogen or sulfur. One possible way to remove such impurities is to pass the feed stream through an adsorption bed, where the impurities remain attached to the adsorbent. Such methods are known and have been published several times.

[0017] The dibutene feed stream provided in step a) is distilled in step b), where a high-boiling phase and a low-boiling phase are obtained. The distillation in step b) is preferably carried out at a top temperature of 40 °C to 100 °C, particularly preferably 45 °C to 80 °C. The pressure at the top in the distillation of step b) is preferably 80 to 450 mbar, particularly preferably 100 to 400 mbar. The bottom temperature in the distillation of step b) is preferably 60 °C to 130 °C, particularly preferably 65 °C to 115 °C. The pressure at the bottom in the distillation of step b) is preferably 100 to 500 mbar, particularly preferably 120 to 450 mbar.

[0018] In distillation, the less reactive isomers and / or reaction-inhibiting substances can be at least partially transferred to the low-boiling phase, so that the reaction in the high-boiling phase in step c) can proceed at a higher reaction rate. In the distillation of step b), 1% to less than 50% by weight, preferably 5% to 40% by weight, particularly preferably 10% to 30% by weight of the feed stream of the distillation is obtained as the low-boiling phase. The separation of the low-boiling phase in distillation can be achieved here in different ways, which are basically familiar to those skilled in the art. For example, a specific amount of the low-boiling phase can be separated by the separation sharpness of distillation, and the separation sharpness can be influenced by the reflux ratio and / or temperature. Separation can also be carried out according to the separated mass, such as a mass flow meter or similar suitable device or internals. The proportion or amount of the feed stream separated as the low-boiling phase in the distillation of step b) can also be set based on other parameters.

[0019] As a result of the distillation in step b), the proportion of the linear isomers in the used dibutenes in the low-boiling phase is less than the proportion of the relevant linear isomers in the high-boiling phase. This can be checked or determined, for example, by NMR or gas chromatography. The branched isomers generally have a lower boiling point and are transferred to the low-boiling phase in a larger proportion. Since the olefins used in the context of the present invention are a mixture of isomeric olefins, it is almost impossible to prevent the linear isomers from also being transferred to the low-boiling phase. However, the distillation should only be carried out under suitable conditions so that the proportion of linear isomers in the high-boiling phase can be higher.

[0020] The distillation in step b) can be carried out in one or more distillation columns. If there is only a single distillation column, the feed stream required for the reaction in step c) is taken out from the distillation column as the bottom stream. If there are multiple distillation columns, only the high-boiling phase from the first distillation column is supplied to the next distillation column, and the low-boiling phase from the last distillation column is supplied to the reaction in step c).

[0021] All known distillation columns are in principle suitable for the distillation of the present invention. These distillation columns usually have internals for improving the separation sharpness. Suitable internals are, for example, trays, unstructured packings (random packings) or structured packings. The trays used are usually bubble-cap trays, sieve trays, valve trays with fixed or movable valves, tunnel trays or trough trays. Unstructured packings are usually random packing beds. The random packings used are usually Raschig rings, Pall rings, Berl saddles, SuperRing / SuperRing Plus or saddle packings. Structured packings are, for example, produced by Sulzer under the Trademark name sales. In addition to the above internal components, other suitable internal components are also known to and can be used by those skilled in the art. In a preferred embodiment, the at least one distillation column comprises 20 to 100 trays, particularly preferably 30 to 80 trays.

[0022] The distillation conditions depend on the feed composition and can vary within a wide range. For extremely pure feed streams that contain only a small proportion or no compounds with more or fewer carbon atoms, usually single-stage distillation is sufficient. At this time, more linear isomers to be reacted in step c) are obtained at the bottom of the distillation column. More branched isomers are obtained at the top of the single-stage distillation and are separated out. If the feed stream used contains a significant amount of compounds with long-chain carbon atoms, multi-stage distillation may be advantageous, where the required feed stream for step c) is taken out as the overhead stream from the second or the last distillation column.

[0023] Then, in step c), the phases obtained by distillation in step b) are supplied to a reaction unit for reaction. The reaction unit for the reaction in step c) can consist of one or more reactors. The one or more reactors can particularly be selected from stirred tank reactors, loop reactors, jet loop reactors, bubble column reactors or combinations thereof. If there are multiple reactors, the reactors can be the same or different. If there are multiple reactors, they can be in parallel or in series, or arranged in a mixed form of parallel and series.

[0024] If the reaction is a homogeneous catalytic reaction, the following process conditions are preferred:

[0025] The olefins used in the method are hydroformylated with syngas in the presence of a homogeneously dissolved catalyst system. The molar ratio between the syngas and the feed mixture should be from 6:1 to 1:1, preferably from 3:1 to 1:1, particularly preferably from 2:1 to 1:1. The hydroformylation can optionally be carried out in the presence of a solvent known to those skilled in the art.

[0026] The homogeneous catalyst system that can be used for hydroformylation can contain Co or Rh, preferably Rh, and preferably a phosphorus-containing ligand. In the case of Co, a phosphorus-containing ligand is not actually absolutely necessary. The corresponding catalyst systems are familiar to those skilled in the art. In a particularly preferred embodiment, the homogeneous catalyst system contains Rh and a phosphorus-containing ligand or consists of Rh and a phosphorus-containing ligand. Suitable ligands for the catalyst system according to the invention are known to those skilled in the art (for example, see the textbook "Rhodium Catalyzed Hydroformylation" (2002) by P.W.N.M van Leeuwen or A. and the textbook by R. Franke, "Hydroformylation – Fundamentals, Processes and Applications in Organic Synthesis" (2016)).

[0027] The phosphorus-containing ligand for the catalyst system according to the invention is preferably a phosphine (e.g., TPP (triphenylphosphine)), a mono-phosphite (e.g., Alkanox 240 (tris(2,4-di-tert-butylphenyl) phosphite)) or a bis-phosphite (e.g., Biphephos). Mixtures of ligands can also be used.

[0028] The temperature of the homogeneous catalytic hydroformylation is preferably from 80 °C to 250 °C, more preferably from 90 °C to 225 °C, and particularly preferably from 100 °C to 210 °C. The pressure of the homogeneous catalytic hydroformylation is preferably from 20 to 350 bar, more preferably from 30 to 325 bar, and particularly preferably from 45 to 300 bar.

[0029] The pressure of the hydroformylation generally corresponds to the total gas pressure. In the context of the present invention, the total gas pressure means the sum of the pressures exerted by all gaseous substances present, i.e., the pressure of the (total) gas phase. In this process, this particularly corresponds to the sum of the partial pressures of CO and H2, i.e., the total gas pressure is then the synthesis gas pressure.

[0030] The homogeneous catalytic hydroformylation can be operated as a liquid discharge process ("liquid recycle") or a gas discharge process ("gas recycle"). Both of these process variants are known to those skilled in the art and are described in many textbooks. In the context of the present invention, no specific selection of such a process is required because the process can basically be carried out in two ways. In homogeneous catalysis, in all cases it is still important to separate the catalyst system from the reaction effluent. In the case of a liquid effluent, this can be done, for example, by a flash process or membrane separation. In the case of a gaseous effluent, it can be done, for example, by condensation and / or scrubbing. This is also known to those skilled in the art and does not require detailed explanation. The further work-up of the reaction effluent, in particular the separation of the reaction products, is likewise familiar to those skilled in the art and can be carried out, for example, by thermal separation methods such as distillation. In the context of the present invention, thermal separation or thermal separation methods mean separation methods in which separation is based on the boiling point.

[0031] If the reaction is a heterogeneous catalytic hydroformylation, the following process conditions are preferred:

[0032] In the context of the present invention, heterogeneous catalytic hydroformylation is particularly those in which the catalyst system is heterogenized, in particular by immobilization on a support material (see the introductory discussion in WO2015 / 028284A1). Thus, the terms heterogenization and immobilization should be understood to mean that the catalyst system is present in immobilized form by forming a liquid film on the surface and / or in the pores of a solid support material.

[0033] The heterogeneous catalytic hydroformylation is characterized in particular in that the high-boiling phase of step b) passes through the support made of porous ceramic material in gaseous form, and the catalyst system comprising a metal of Group 8 or 9 of the Periodic Table, at least one organophosphorus ligand, and a stabilizer is present in heterogenized form on the support.

[0034] The temperature in the heterogeneous catalytic hydroformylation can be from 65 °C to 200 °C, preferably from 75 °C to 175 °C, particularly preferably from 85 °C to 150 °C. The pressure in the heterogeneous catalytic hydroformylation should be greater than 0 bar, but particularly not greater than 35 bar, preferably not greater than 30 bar, particularly preferably not greater than 25 bar. The molar ratio between the synthesis gas and the feed mixture should be from 6:1 to 1:1, preferably from 5:1 to 3:1. Optionally, the feed mixture can be diluted with an inert gas or a solvent, for example with an alkane present in an industrial hydrocarbon stream, in order to control the reaction.

[0035] The catalyst system used in the hydroformylation process according to the invention preferably comprises a transition metal of Group 8 or 9 of the Periodic Table, in particular iron, ruthenium, iridium, cobalt or rhodium, particularly preferably cobalt and rhodium, at least one organophosphorus ligand, a stabilizer and optionally an ionic liquid.

[0036] The stabilizer is preferably an organic amine compound, particularly preferably an organic amine compound containing at least one 2,2,6,6-tetramethylpiperidine unit.

[0037] The organophosphorus ligand for the catalyst system according to the invention preferably has the general formula (I)

[0038] R'–A–R”–A–R”'(I)

[0039] wherein R', R” and R”' are each an organic group, and each of the two A's is a bridging -O-P(-O)2 group, wherein two of the three oxygen atoms -O- are each bonded to the group R' and the group R”', provided that R' and R”' are two separate organic groups. R' and R”' can be the same or different organic groups. The organic groups R', R” and R”' preferably do not contain terminal trialkoxysilyl groups.

[0040] In a preferred embodiment, R', R'' and R''' in the compound of formula (I) are preferably selected from substituted or unsubstituted 1,1'-biphenyl, 1,1'-binaphthyl and o-phenyl, especially substituted or unsubstituted 1,1'-biphenyl, provided that R' and R''' are not the same. Particularly preferably, the substituted 1,1'-biphenyl has an alkyl and / or alkoxy group at the 3,3' and / or 5,5' positions of the 1,1'-biphenyl basic structure, especially a C1-C4 alkyl group, particularly preferably tert-butyl and / or methyl, and / or preferably a C1-C5 alkoxy group, particularly preferably methoxy. An example of a suitable ligand is Biphephos (6,6'-[(3,3'-di-tert-butyl-5,5'-dimethoxy-1,1'-biphenyl-2,2'-diyl)bis(oxy)]bis(dibenzo[d,f][1,3,2]dioxaphosphepine)).

[0041] The porous ceramic material constituting the carrier is preferably selected from silicate ceramics, oxide ceramics, nitride ceramics, carbide ceramics, silicide ceramics and mixtures thereof. The silicate ceramics are preferably selected from aluminum silicate, magnesium silicate and mixtures thereof, such as bentonite. The oxide ceramics are preferably selected from γ-aluminum oxide, α-aluminum oxide, titanium dioxide, beryllium oxide, zirconium oxide, aluminum titanate, barium titanate, zinc oxide, iron oxide (ferrite) and mixtures thereof. The nitride ceramics are preferably selected from silicon nitride, boron nitride, aluminum nitride and mixtures thereof. The carbide ceramics are preferably selected from silicon carbide, boron carbide, tungsten carbide or mixtures thereof. Also contemplated is a mixture of carbide ceramics and nitride ceramics, i.e., so-called carbonitrides. The silicide ceramics are preferably molybdenum silicide. The carrier according to the invention to which the catalyst system is applied preferably consists of carbide ceramics.

[0042] The carrier can be monolithic, i.e., the carrier can consist of a block (three-dimensional object) of ceramic material. Such a block can be in one-piece form or can consist of a plurality, i.e., at least two separate parts, which can be joined together to form a block and / or can be joined to each other in a fixed or detachable manner. The carrier can also be in the form of granules or pellets. The median particle size (d50) of the carrier can be from 0.1 mm to 7 mm at this time, preferably from 0.3 to 6 mm, particularly preferably from 0.5 mm to 5 mm. The median particle size can be determined by imaging methods, especially by the methods described in standard ISO 13322-1 (version: 2004-12-01) and ISO 13322-2 (version: 2006-11-01). The carrier in the form of granules or pellets can be prepared by methods known to those skilled in the art. This can be achieved, for example, by mechanically crushing a monolith of the carbide material, nitride material, silicide material or mixtures thereof, such as using a jaw crusher, and setting the particle size of the resulting crushed granules by sieving.

[0043] According to the present invention, the support consists of a porous ceramic material, i.e., the ceramic material has pores. Different porosities or pore diameters can be considered in principle. However, the pore diameter is preferably from 0.9 nm to 30 μm, more preferably from 10 nm to 25 μm, and particularly preferably from 70 nm to 20 μm. The pore diameter can be determined by the nitrogen adsorption method or the mercury porosimetry method in accordance with DIN 66133 (version: 1993-06).

[0044] A so-called washcoat can be additionally applied on the support made of ceramic material, which consists of the same or different ceramic materials as the ceramic material of the support, in particular ceramic materials selected from the above-mentioned ceramic materials, preferably silica. The washcoat itself can be porous or non-porous; the washcoat is preferably non-porous. The particle size of the washcoat is preferably from 5 nm to 3 μm, preferably from 7 nm to 700 nm. The washcoat is used to introduce or generate the required pore diameter and / or increase the surface area of the support. The washcoat can be applied in particular by impregnation (dipping) into a washcoat solution containing the ceramic material of the washcoat (optionally also as a precursor). The amount of the washcoat present on the support is ≤20% by weight, preferably ≤15% by weight, and particularly preferably ≤10% by weight, based on the total amount of the support. At this time, the catalyst system is applied to the ceramic support with the applied washcoat thus produced. However, the support preferably does not contain a washcoat.

[0045] In the reaction effluent obtained from heterogeneous catalytic hydroformylation, it is not necessary in principle to remove the catalyst system. The further work-up, i.e., for example, separating the reaction products, is familiar to those skilled in the art and can in principle be carried out by distillation or by other thermal separation methods.

[0046] If the reaction is homogeneous catalytic alkoxycarbonylation, the following process conditions are preferred:

[0047] In alkoxycarbonylation, the olefin of the feed stream used reacts with carbon monoxide (CO) and an alcohol (in this case a C1 to C6 alcohol) in the presence of a homogeneous catalyst system to form an ester.

[0048] Carbon monoxide can be provided directly as a feed mixture, or by adding a carbon monoxide-containing gas (selected from syngas, water gas, producer gas, and other carbon monoxide-containing gases). Carbon monoxide can also be provided in such a way that a carbon monoxide-containing gas is separated into its components in a manner known to those skilled in the art in advance, and then the carbon monoxide is passed through the reaction zone. The carbon monoxide may still contain a certain proportion of hydrogen or other gases, because complete separation is almost impossible to achieve.

[0049] The alcohols used in the alkoxycarbonylation are monohydric or polyhydric alcohols (polyhydric alcohol = two or more OH groups) having 1 to 6 carbon atoms. Suitable alcohols for the reaction in step c) are methanol, ethanol, 1-propanol, 1-butanol, 1-pentanol, 1-hexanol, 2-propanol, tert-butanol, 3-pentanol, cyclohexanol, phenol or mixtures thereof. In the alkoxycarbonylation, methanol and ethanol are preferably used. If methanol is used, the reaction is also called methoxycarbonylation. If ethanol is used, the reaction is also called ethoxycarbonylation.

[0050] The homogeneous catalyst system for the alkoxycarbonylation preferably comprises at least one metal of Groups 8 to 10 of the Periodic Table of the Elements (PSE) or a compound thereof, a phosphorus-containing ligand and an acid as a cocatalyst.

[0051] The metal of Groups 8 to 10 of the PSE is preferably palladium. Palladium is preferably used in the form of a precursor compound as a palladium compound coordinated by a phosphorus-containing ligand. Examples of palladium compounds that can be used as precursor compounds are palladium chloride [PdCl2], palladium(II) acetylacetonate [Pd(acac)2], palladium(II) acetate [Pd(OAc)2], dichloro(1,5-cyclooctadiene)palladium [Pd(cod)2Cl2], bis(dibenzylideneacetone)palladium(0) [Pd(dba)2], tris(dibenzylideneacetone)dipalladium(0) [Pd2(dba)3], bis(acetonitrile)dichloropalladium(II) [Pd(CH3CN)2Cl2], dichloro(cinnamyl)palladium [Pd(cinnamyl)Cl2]. The compounds [Pd(acac)2] or [Pd(OAc)2] are preferably used. Based on the molar amount of the hydrocarbon used, the metal concentration of palladium in the alkoxycarbonylation is preferably 0.01 to 0.6 mol%, preferably 0.03 to 0.3 mol%, particularly preferably 0.04 to 0.2 mol%.

[0052] The suitable phosphorus-containing ligands of the catalyst system according to the invention preferably have a bidentate structure. Preferred phosphorus-containing ligands of the catalyst system according to the invention are benzene-based diphosphine compounds, as disclosed in EP 3121184A2. The ligand can be combined with palladium in a preliminary reaction, thereby supplying the palladium-ligand complex to the reaction zone, or added in situ to the reaction and combined with palladium there. In the alkoxycarbonylation, the molar ratio of ligand:metal can be 1:1 to 10:1, preferably 2:1 to 6:1, particularly preferably 3:1 to 5:1.

[0053] In the alkoxycarbonylation, the homogeneous catalyst system further comprises an acid, which can in particular be a Brønsted acid or a Lewis acid. The Lewis acid used can in particular be aluminum trifluoromethanesulfonate, aluminum chloride, aluminum hydride, trimethylaluminum, tris(pentafluorophenyl)borane, boron trifluoride, boron trichloride or a mixture thereof. Among the Lewis acids mentioned, aluminum trifluoromethanesulfonate is preferably used. The Lewis acid is preferably added in a molar ratio of Lewis acid:ligand of 1:1 to 20:1, preferably 2:1 to 15:1, particularly preferably 5:1 to 10:1.

[0054] Suitable Brønsted acids preferably have an acid strength with pKa ≤ 5, particularly preferably an acid strength with pKa ≤ 3. The acid strength pKa refers to the pKa value measured under standard conditions (25 °C, 1.01325 bar). For polyprotic acids, in the context of the present invention, the acid strength pKa is the pKa value of the first proton transfer step. The Brønsted acid is preferably added in a molar ratio of Brønsted acid to ligand of 1:1 to 15:1, preferably 2:1 to 10:1, particularly preferably 3:1 to 5:1.

[0055] The Brønsted acids used can in particular be perchloric acid, sulfuric acid, phosphoric acid, methylphosphonic acid or sulfonic acids. Suitable sulfonic acids are, for example, methanesulfonic acid, trifluoromethanesulfonic acid, tert-butanesulfonic acid, p-toluenesulfonic acid (PTSA), 2-hydroxypropane-2-sulfonic acid, 2,4,6-trimethylbenzenesulfonic acid and dodecylsulfonic acid. Particularly preferred acids are sulfuric acid, methanesulfonic acid, trifluoromethanesulfonic acid and p-toluenesulfonic acid. The acid is preferably sulfuric acid. In contrast, carboxylic acids are less suitable or not suitable at all.

[0056] The homogeneous catalytic alkoxycarbonylation is preferably carried out at a temperature of 25 °C to 140 °C, more preferably at a temperature of 60 °C to 120 °C, particularly preferably at a temperature of 70 °C to 110 °C. The pressure can be 5 to 60 bar, preferably 10 to 40 bar, particularly preferably 15 to 30 bar.

[0057] A product mixture is obtained by the homogeneous catalytic alkoxycarbonylation, which at least comprises the ester formed by the reaction, the homogeneous catalyst system, low boilers, such as low-boiling by-products such as ethers, high boilers, unreacted alcohol and optionally unreacted hydrocarbons. Therefore, the product mixture can be subjected to subsequent catalyst separation. This can be achieved, for example, by membrane separation, whereby the homogeneous catalyst system and the unreacted hydrocarbons and / or unreacted alcohol are enriched in the retentate, while the formed ester is enriched in the permeate. The retentate containing the enriched homogeneous catalyst system can be recycled to the reaction zone.

[0058] The further work-up of the permeate, in particular the separation of the ester as the target product, can be achieved by known methods and is in principle familiar to those skilled in the art. One possible way is a thermal separation method such as distillation.

[0059] The low-boiling phase obtained by distillation in step b) is fed in step d) to a hydrogenation unit consisting of one or more reactors, where the olefins present in the low-boiling phase are hydrogenated to the corresponding alkanes with a hydrogen-containing gas in the presence of a supported catalyst. The hydrogenation is carried out in the hydrogenation unit, which can consist of one or more reactors. The reactors can operate in a once-through or recycle mode. In a preferred embodiment of the invention, the hydrogenation unit comprises at least two reactors. Preferably, the first reactor operates in a recycle mode and the second reactor operates in a once-through mode. Here, the first and second reactors can be connected to each other by overflow. This has the advantage that no pump is required between the first and second reactors.

[0060] The hydrogenation is carried out with a hydrogen-containing gas, preferably with hydrogen. In the hydrogenation, hydrogen is preferably used in a stoichiometric excess, particularly preferably in a stoichiometric excess of 5% to 30%.

[0061] The hydrogenation of the low-boiling phase is carried out on a supported catalyst. Suitable supported catalysts comprise at least one transition metal selected from palladium, platinum, rhodium, ruthenium, nickel or mixtures thereof and a support material selected from alumina, silica, titania, magnesia or mixtures thereof. In a preferred embodiment of the invention, a supported catalyst containing palladium or nickel as the transition metal is used in an optional step in the hydrogenation.

[0062] The hydrogenation is preferably carried out at a temperature of 100 °C to 180 °C, particularly preferably at a temperature of 135 °C to 160 °C. In the hydrogenation, the pressure is preferably 5 to 40 bar gauge, particularly preferably 10 to 30 bar gauge. Here, the pressure is generated particularly by the gas phase, i.e. hydrogen. The hydrogenation is preferably carried out in the liquid phase. After the hydrogenation, phase separation known to those skilled in the art can be carried out in order to separate the gas phase containing unreacted hydrogen and optionally a small amount of hydrocarbons from the liquid phase. Detailed Description

[0063] Examples

[0064] Hydroformylation of Dibutene

[0065] 21.5 tons / hour of dibutene (feed) is distilled in a distillation column having 42 trays at a top temperature of 58 °C and a bottom temperature of 62 °C and a corresponding top pressure of 0.1 bar and a bottom pressure of 0.15 bar. Approximately 20% is separated off as distillate (= low-boiling fraction) (4.44 tons / hour) from the dibutene used. The remaining 80% is withdrawn from the bottom and is thus the high-boiling fraction.

[0066] The composition of the feed stream of the dibutene stream and the bottoms product is investigated by GC (gas chromatography).

[0067] The overview is shown in Table 3:

[0068] Table 3: Proportions of the groups of isomers in the respective dibutene streams

[0069]

[0070] The straight-chain degree of dibutene is described by the ISO index, a value representing the average number of methyl branches in the dimer. For example (for butene as the reactant), 1-octene contributes 0 to the ISO index of the C8 fraction, methylheptene contributes 1, and dimethylhexene contributes 2. The lower the ISO index, the more straight-chain the molecular structure in the respective fraction. The ISO index is calculated according to the following general formula, where the proportions of the individual dimer fractions are based on the total dimer fraction:

[0071]

[0072] Thus, a dimer mixture with an ISO index of 1.0 has exactly one methyl branch per dimer molecule on average.

[0073] The ISO index of the feed is 1.03 and that of the bottoms is 0.88. This indicates that the proportion of straight-chain isomers in the bottoms is higher.

[0074] Hydroformylation was carried out separately in a 100 mL autoclave with the feed and the bottoms. The catalyst used here was rhodium (20 ppm Rh), with a 5-fold molar excess of the ligand (tris(2,4-di-tert-butylphenyl) phosphite (TDTBPP)) (total phosphorus:rhodium ratio). The temperature was about 140 °C. In addition, the hydroformylation was carried out separately at a syngas pressure (CO / H2 ratio = 1:1 (vol%)) of about 235 bar. The solvent used in each case was 150 mL of toluene. Samples were taken separately at 10 minutes, 30 minutes, 60 minutes, and 180 minutes after the start of the reaction, and the reaction conversion (conversion = molar amount at time t / molar amount (at the start of the reaction)) was studied. The results of the hydroformylation are shown in Table 4.

[0075] Table 4: Reaction conversions in the hydroformylation of the dibutene streams

[0076]

[0077] It can be learned from Table 4 that a significant acceleration of the reaction can be achieved by pre-distillation. The conversion is up to 20% higher in each case when using the bottoms stream compared to the feed.

Claims

1. A method for reacting dibutylene, comprising the steps of: a) providing a dibutene feed stream, said feed stream comprising at least the linear and branched isomers of the olefin used; b) distilling the feed stream provided to obtain at least one low boiler phase and a high boiler phase, wherein 1% by weight to less than 50% by weight, preferably 5% by weight to 40% by weight, particularly preferably 10% by weight to 30% by weight of the distilled feed stream is obtained as low boiler phase, and wherein the proportion of linear isomers in the low boiler phase is less than the proportion of linear isomers in the high boiler phase; c) supplying the high boiler phase from step b) to a reaction unit comprising one or more reactors and carrying out a reaction in said reaction unit, wherein the reaction is a heterogeneously catalyzed hydroformylation in the presence of synthesis gas, a homogeneously catalyzed hydroformylation in the presence of synthesis gas, or a homogeneously catalyzed alkoxycarbonylation in the presence of carbon monoxide and a C1 to C6 alcohol; and d) supplying the low boiler phase from step b) to a hydrogenation unit consisting of one or more reactors for hydrogenation, wherein the olefins present in the low boiler phase are hydrogenated to the corresponding alkanes in the presence of a supported catalyst using a hydrogen-containing gas.

2. The process according to claim 1, wherein the reaction is a homogeneously catalyzed hydroformylation or a homogeneously catalyzed alkoxycarbonylation in the presence of carbon monoxide and methanol or ethanol.

3. The process according to claim 2, wherein the homogeneous catalyst system in the hydroformylation comprises Co or Rh, and preferably a phosphorus-containing ligand.

4. The process according to claim 2, wherein the homogeneous catalyst system in the alkoxycarbonylation comprises a metal or a compound thereof from Groups 8 to 10 of the Periodic Table of Elements (PSE), a phosphorus-containing ligand and an acid as a promoter.

5. The process according to claim 1, wherein the low boiler phase obtained in step b) is subjected to a hydrogenation.

6. The process according to claim 5, wherein the hydrogenation of step d) is carried out at a temperature of 100°C to 180°C.

7. The process according to claim 5 or 6, wherein hydrogen is used in a stoichiometric excess, preferably in a stoichiometric excess of 5% to 30%, in the hydrogenation in step d).

8. The process according to any one of claims 5 to 7, wherein a supported catalyst is used in the hydrogenation in step d), the supported catalyst comprising at least one transition metal selected from palladium, platinum, rhodium, ruthenium, nickel or a mixture thereof and a support material selected from aluminum oxide, silicon dioxide, titanium dioxide, magnesium oxide or a mixture thereof.

9. The process according to any one of the preceding claims, wherein the distillation of step b) is carried out at a top temperature of 40 to 100°C, preferably 45 to 80°C.

10. The process according to any of the preceding claims, wherein the top pressure of the distillation in step b) is from 80 to 450 mbar, preferably from 100 to 400 mbar.

11. The process according to any one of the preceding claims, wherein the bottom temperature of the distillation in step b) is from 60°C to 130°C, preferably from 65°C to 115°C.

12. The process according to any of the preceding claims, wherein the bottom pressure of the distillation in step b) is from 100 to 500 mbar, preferably from 120 to 450 mbar.

13. The process according to any of the preceding claims, wherein in step b), at least one distillation column comprises 20 to 100 trays, preferably 30 to 80 trays.

14. The process according to claim 1, wherein in step b) 5 to 40% by weight of the distilled feed stream are obtained as low boiler phase.

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