Process for producing alcohols by alkoxycarbonylation of diisobutylene and C4 to C7 olefins and subsequent hydrogenation

Abstract

The present invention provides a process for the alkoxycarbonylation of diisobutylene and C4 to C7 olefins in a common reaction zone. The alkoxycarbonylation is carried out with an alcohol and carbon monoxide in the presence of a homogeneous catalyst system comprising at least one metal of groups 8 to 10 of the Periodic Table of Elements or a compound thereof, a phosphorus-containing ligand and an acid.

Description

[0001] The present invention relates to a process for preparing target alcohols by hydrogenating esters produced by alkoxycarbonylation of diisobutylene and C4 to C7 olefins in a common reaction zone. The alkoxycarbonylation is carried out with alcohol and carbon monoxide in the presence of a homogeneous catalyst system comprising at least one metal from Groups 8 to 10 of the Periodic Table of Elements or a compound thereof, a phosphorus-containing ligand and an acid.

[0002] The preparation of alcohols in industrial chemistry is mainly achieved by hydroformylation to produce aldehydes and subsequent hydrogenation of the aldehydes to alcohols. Although the preparation of alcohols by hydroformylation and subsequent hydrogenation has been an industrially mature and proven process for decades, there is still potential for improvement. One problem with this synthesis route is that the pressures and temperatures in the hydroformylation are generally high and therefore place high technical demands on the equipment used. Ultimately, the equipment must be able to withstand the pressures and temperatures.

[0003] Diisobutene is an industrially relevant product obtained by dimerization of isobutene. Diisobutene consists of the isomers 2,4,4-trimethylpent-1-ene (2,4,4-trimethylpent-1-ene) (hereinafter also referred to as: TMP1) and 2,4,4-trimethylpent-2-ene (2,4,4-trimethylpent-2-ene) (hereinafter also referred to as: TMP2), the mass distribution of TMP1:TMP2 being about 78:22 to 81:19 (equilibrium distribution). Industrial mixtures containing C4 olefins are light petroleum fractions from refineries, C4 fractions from FC crackers or steam crackers, mixtures from Fischer-Tropsch synthesis, mixtures from butane dehydrogenation, and mixtures produced by metathesis or other industrial processes. C5 olefins, i.e. pentenes, are present in light petroleum fractions from refineries or crackers. Higher olefins can be obtained in particular by oligomerization. Both diisobutylene and C4 to C7 olefins can be converted by alkoxycarbonylation into valuable products, such as esters formed in the alkoxycarbonylation.

[0004] The problem of this method is that special preparation equipment must be obtained or built, and these equipment must be operated under the cost incurred thereby. Because the market of petrochemical products is quite changeable in some cases, it is almost impossible to economically operate the special preparation equipment of every kind of described olefin. Another shortcoming is that because all equipment all need maintenance, the resource efficient operation of multiple preparation equipment is almost impossible. This not only needs economic and personnel costs, but also needs a certain amount of energy, such as electricity or heat transfer medium.

[0005] It is therefore an object of the present invention to provide a process for preparing the target alcohols which does not exhibit the above-mentioned problems. In particular, diisobutylene and C4 to C7 olefins can be converted into esters via alkoxycarbonylation and subsequent hydrogenation in a more resource-efficient manner. In addition, alternative synthesis routes should be provided which can relatively easily provide the desired carboxylic acids / salts thereof.

[0006] The basic object is achieved by the method according to claim 1. Preferred embodiments are specified in the dependent claims.

[0007] According to the present invention, the method for preparing the target alcohol comprises at least the following steps:

[0008] a. providing a diisobutylene stream containing 2,4,4-trimethylpent-2-ene and 2,4,4-trimethylpent-1-ene, and providing an olefin stream containing C4 to C7 olefins;

[0009] b. alkoxycarbonylating diisobutylene and C4 to C7 olefins with alcohol and carbon monoxide in the presence of a homogeneous catalyst system comprising at least one metal of Groups 8 to 10 of the Periodic Table of Elements or a compound thereof, a phosphorus-containing ligand and an acid in a common reaction zone to obtain a liquid product mixture comprising at least esters formed by the alkoxycarbonylation, the homogeneous catalyst system, unreacted olefins (i.e., unreacted diisobutylene and unreacted C4 to C7 olefins) and unreacted alcohol;

[0010] c. removing the homogeneous catalyst system from the liquid product mixture to obtain a crude product mixture, the crude product mixture comprising at least the ester formed by the alkoxycarbonylation, the unreacted olefin and the unreacted alcohol;

[0011] d. treating the crude product mixture by distillation in at least one distillation column to remove the unreacted alcohol and the unreacted olefin to obtain an ester mixture containing the formed esters, wherein the unreacted alcohol and the unreacted olefin are preferably removed and recycled to the alkoxycarbonylation in step b;

[0012] e. hydrogenating the ester obtained in step d with hydrogen in a hydrogenation zone in the presence of a heterogeneous catalyst system to obtain an alcohol mixture comprising at least the target alcohol, the eliminated alcohol and the unreacted ester; and

[0013] f. removing the target alcohol formed in step e in at least one separation process step selected from thermal separation such as distillation, extraction, crystallization and membrane separation.

[0014] The process according to the invention thus involves the simultaneous reaction of diisobutene and C4 to C7 olefins in a single common reaction zone with subsequent hydrogenation to the corresponding target alcohol. This procedure has numerous advantages.

[0015] The method allows a flexible response to the market, in particular to small production volumes. In addition, only one production plant is required, which can be operated more efficiently and therefore in a more resource-saving manner even when market demand fluctuates. The specific boiling sequence also allows the resulting products of the various olefins employed to be separated, while the reactants can be returned directly to the reaction or after further treatment.

[0016] The diisobutene stream provided in step a comprises 2,4,4-trimethylpent-2-ene and 2,4,4-trimethylpent-1-ene. In a preferred embodiment, the proportion of 2,4,4-trimethylpent-1-ene in the diisobutene stream is at least 60 mol%, preferably at least 70 mol%, based on the total diisobutene stream. This stream can be, for example, a diisobutene stream produced by dimerization of isobutene or an isobutene-containing hydrocarbon mixture according to the process disclosed in EP 1 360 160 B1. In addition, the diisobutene stream to be employed here can be obtained as an unreacted residual stream in a carbonylation process such as alkoxycarbonylation or hydroformylation.

[0017] Step a comprises providing not only a diisobutylene stream, but also an olefin stream containing C4 to C7 olefins used in the process according to the invention. In a preferred embodiment, the present invention employs an olefin stream comprising C4 olefins, particularly preferably a C4 olefin stream. The corresponding streams are known to those skilled in the art and can be obtained on a large industrial scale.

[0018] Olefin streams comprising C4 olefins include, for example, light petroleum fractions from an oil refinery, C4 fractions from a FC cracker or steam cracker, mixtures from Fischer-Tropsch synthesis, mixtures from butane dehydrogenation, or streams produced by metathesis or other industrial processes. For example, C4 olefin streams suitable for use in the method according to the invention can be obtained from the C4 fraction of a steam cracker. C5 olefins, i.e. pentenes, are present in light petroleum fractions from an oil refinery or cracker. C6 olefins can be obtained, for example, by dimerization of propylene. C7 olefins can be obtained, for example, by dimerization of propylene and butenes.

[0019] The stream provided in step a, i.e. the diisobutylene stream and the C4 to C7 olefin stream, is sent to the alkoxycarbonylation in step b. The streams can be sent to the alkoxycarbonylation in step b individually and separately or premixed. Preferably, before the alkoxycarbonylation in step b, the diisobutylene stream and the C4 to C7 olefin stream are mixed. A particularly preferred embodiment of the present invention actually provides that before the alkoxycarbonylation in step b, the diisobutylene stream, the C4 to C7 olefin stream, the alcohol and the homogeneous catalyst system are mixed, particularly in a suitable mixing vessel. If there is a recycle stream that is recycled to the reaction, i.e., for example by recycling the catalyst system, the recycle stream can also be sent to the mixing vessel.

[0020] Step b comprises reacting diisobutylene (i.e. 2,4,4-trimethylpent-2-ene and 2,4,4-trimethylpent-1-ene) and C4 to C7 olefins with carbon monoxide (CO) and alcohol to obtain esters. Therefore, the carbon number in the ester is increased by 1 carbon atom from carbon monoxide and the carbon number in the alcohol used is increased compared to the olefins used. Diisobutylene (8 carbon atoms) correspondingly produces an ester having 9 carbon atoms in the acid portion of the ester, plus the carbon atoms of the alcohol in the alcohol portion of the ester. Then C4 to C7 olefins are correspondingly converted into esters having 5 to 8 carbon atoms in the acid portion.

[0021] In the alkoxycarbonylation in step b, carbon monoxide can be provided directly in the form of an input mixture, or by adding a gas containing carbon monoxide, the gas containing carbon monoxide being selected from synthesis gas, water gas, generator gas and other gases containing carbon monoxide. Carbon monoxide can also be provided by first separating the gas containing carbon monoxide into its components in a manner known to those skilled in the art and sending the carbon monoxide to the reaction zone. Carbon monoxide may still contain a certain proportion of hydrogen or other gases, because complete separation is almost impossible.

[0022] The alcohol used in the reaction in step b is preferably a monohydric alcohol having 1 to 4 carbon atoms, in particular methanol, ethanol, propanol or butanol. This then gives an ester having a chain length corresponding to the alcohol employed. For example, the use of methanol leads to the formation of methyl esters.

[0023] The molar ratio of the alcohol used in step b, preferably a monohydric alcohol having 1 to 4 carbon atoms, in particular methanol, ethanol, propanol or butanol, to the total amount of all olefins, i.e. diisobutylene and C4 to C7 olefins, alcohol:olefin is 10:1 to 1:1, preferably 8:1 to 1.5:1, particularly preferably 7:1 to 2:1. Therefore, the alcohol is added in at least the same molar amount, but preferably in a molar excess, based on the olefins used.

[0024] The reaction according to the invention in step b is carried out in the presence of a homogeneous catalyst system comprising at least one metal of Groups 8 to 10 of the Periodic Table of Elements (PTE) or a compound thereof, a phosphorus-containing ligand and an acid as a cocatalyst. Obviously, a suitable catalyst must be able to alkoxycarbonylate all olefins (i.e. diisobutylene and C4 to C7 olefins). The content of metals of Groups 8 to 10 of the Periodic Table of Elements, in particular palladium, in the alkoxycarbonylation reaction solution in step b is preferably 100 ppm to 500 ppm, further preferably 150 ppm to 450 ppm, particularly preferably 180 ppm to 350 ppm.

[0025] The metal of the 8th to 10th group of PTE 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 (II) [Pd(cod)2Cl2], bis (dibenzylideneacetone) palladium (0) [Pd(dba)2], tris (dibenzylideneacetone) dipalladium (0) [Pd2(dba)3], bis (acetonitrile) dichloro palladium (II) [Pd(CH3CN)2Cl2], (cinnamyl) dichloro palladium [Pd(cinnamyl)Cl2]. Preferably, the compound [Pd(acac)2] or [Pd(OAc)2] is used. The concentration of the palladium metal in step b is preferably 0.01 mol % to 0.6 mol %, preferably 0.03 mol % to 0.3 mol %, more preferably 0.04 mol % to 0.2 mol %, based on the molar amount of hydrocarbon used.

[0026] Suitable phosphorus-containing ligands for the catalyst system according to the invention preferably have a bidentate structure. Preferred phosphorus-containing ligands for the catalyst system according to the invention are benzene-based diphosphine compounds, such as disclosed in EP 3 121 184 A2, for example. The ligand can be combined with palladium in a preliminary reaction so that the palladium-ligand complex is sent to the reaction zone, or added to the reaction in situ and combined with palladium there. The ligand: metal molar ratio of the reaction in step b can be 1: 1 to 10: 1, preferably 2: 1 to 6: 1, particularly preferably 3: 1 to 5: 1.

[0027] The homogeneous catalyst system further comprises an acid, in particular a Bronsted acid or a Lewis acid. The Lewis acid used is preferably aluminum trifluoromethanesulfonate, aluminum chloride, aluminum hydride, trimethylaluminum, tri(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.

[0028] The suitable Bronsted acid strength is preferably pKa≤±5, more preferably pKa≤±3. The acid strength pKa refers to the pKa measured under standard conditions (25°C, 1.01325 bar). For polyacids, the acid strength pKa in the context of the present invention refers to the pKa of the first protolysis step. The amount of Bronsted acid added is preferably a molar ratio of Bronsted acid: ligand of 1:1 to 15:1, preferably 2:1 to 10:1, and particularly preferably 3:1 to 5:1.

[0029] The Bronsted used may in particular be perchloric acid, sulfuric acid, phosphoric acid, methylphosphonic acid or sulfonic acid. Suitable sulfonic acids are, for example, methanesulfonic acid, trifluoromethanesulfonic acid, tert-butylsulfonic 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.

[0030] The alkoxycarbonylation in step b is preferably carried out at a temperature of 60° C. to 120° C., further preferably 65° C. to 110° C., particularly preferably 70° C. to 100° C. The alkoxycarbonylation in step b is further preferably carried out at a carbon monoxide pressure of 10 bar to 35 bar, preferably 12.5 to 30 bar, more preferably 15 bar to 25 bar.

[0031] The alkoxycarbonylation in step b takes place in a suitable reaction zone. The reaction zone for the reaction comprises at least one reactor, but may also consist of two or more reactors arranged in parallel or in series. The at least one reactor may in particular be selected from a stirred tank reactor, a loop reactor, a jet loop reactor, a bubble column reactor or a combination thereof. If more than one reactor is used, the reactors may be identical or different.

[0032] The alkoxycarbonylation in step b above yields a liquid product mixture which comprises at least the ester formed by the alkoxycarbonylation, the homogeneous catalyst system, unreacted olefins and unreacted alcohols. In addition, the liquid product mixture may contain low-boiling by-products such as dimethyl ether or formic acid and / or high-boiling components such as ligand decomposition products.

[0033] The product mixture thus obtained is supplied to subsequent step c, to remove the homogeneous catalyst system from the liquid product mixture. Before the supply product mixture, low boiling point components such as a part of unreacted alcohol and / or low boiling point by-products can be removed, for example, by distillation. Alcohol can be recycled to step b, i.e. in the alkoxycarbonylation. The low boiling point by-products can be discharged from the method under the condition of purging so that they do not accumulate in the method. Removing the homogeneous catalyst system obtains a crude product mixture, which at least comprises esters formed by the alkoxycarbonylation, unreacted olefins and at least a portion of unreacted alcohol.

[0034] The removal homogeneous catalyst system in step c can be realized by means of various separation methods to obtain a crude product mixture, for example, by thermal separation or by membrane separation. Suitable methods are familiar to those skilled in the art. In the context of the present invention, the removal homogeneous catalyst system in step c is preferably realized by membrane separation. As is well known, membrane separation produces retentate and permeate. The homogeneous catalyst system will accumulate in the retentate. In this case, the permeate constitutes the aforementioned crude product mixture and is sent to the subsequent distillation treatment step d.

[0035] According to the present invention, the retentate is preferably recycled to the alkoxycarbonylation in step b / the reaction zone for alkoxycarbonylation. This allows the catalyst system to be reused. In the preferred continuous execution of the claimed method, this produces a catalyst cycle, wherein only the smaller catalyst loss associated with the method needs to be compensated at most. If, according to a preferred embodiment, before the alkoxycarbonylation in step b, a diisobutylene stream, an olefin stream, an alcohol and a homogeneous catalyst system are mixed, especially in a suitable mixing vessel, the retentate is sent to the mixing vessel. In the recycling of the retentate, a purge stream that may contain inert alkanes, low-boiling by-products (e.g., ethers), possible decomposition products of the catalyst system or other impurities (e.g., trace water or nitrogen) may be taken out in addition to avoid accumulation in the reaction zone.

[0036] Any suitable membrane material can be used for membrane separation. Preferably, OSN (organic solvent nanofiltration) membrane material is used in the membrane separation in step c of the method of the present invention. Such membrane material preferably consists of at least a separation active layer (also referred to as an active separation layer) and a substructure on which the separation active layer is present. The membrane material of the present invention preferably consists of at least a separation active layer and a substructure.

[0037] The membrane material consisting of at least the separation active layer and the substructure should be acid-stable so that the membrane material is not destroyed by the acid present in the liquid product mixture. In the context of the present invention, the term "acid-stable" means that the membrane material is stable in the presence of the acid of the catalyst system for at least 300 h and maintains separation performance.

[0038] The substructure preferably has a porous structure, which is permeable to the permeate that has passed through the separation active layer. The substructure has a stabilizing function and is used as a support for the separation active layer. The substructure can be composed of any suitable porous material in principle. Suitable materials are familiar to those skilled in the art. However, the prerequisite is that the material is stable for acid and alkali. The substructure can be composed of the same material as the separation active layer. The preferred material for the substructure includes plastics, such as polypropylene (PP), polyethylene (PE) or non-condensation polymers that are not easily hydrolyzed or alcoholyzed, such as polysulfone, polytetrafluoroethylene (PTFE), polyethersulfone (PES), polyvinylidene fluoride (PVDF) or polyacrylonitrile (PAN).

[0039] The separation active layer according to the invention preferably consists of a PAEK (polyaryletherketone) polymer. PAEK has a specific feature that in the repeating unit, the aromatic groups are alternately connected via ether functions and ketone functions. The separation active layer preferably according to the invention consists of PEEK (polyetheretherketone). As the separation active layer, it is particularly preferred to use a PEEK polymer with a sulfonation degree of less than 20%, particularly preferably a sulfonation degree of less than 10%. The corresponding PEEK polymers and their preparation are described in WO 2015 / 110843 A1.

[0040] The membrane separation in step c is preferably carried out at a temperature of 25° C. to 100° C., further preferably 30° C. to 80° C., particularly preferably 40° C. to 70° C. In order to bring the product mixture to the preferred main temperature for membrane separation, the product mixture can be cooled. In addition to active cooling using a coolant, cooling can also be achieved via a heat exchanger, in which thermal energy is transferred to another stream, thereby cooling the product mixture and heating the other stream.

[0041] In the membrane separation in step c, the transmembrane pressure (transmembrane pressure) (TMP) is preferably 10 bar to 60 bar, further preferably 15 bar to 55 bar, particularly preferably 20 bar to 50 bar. The permeate side pressure here can be higher than atmospheric pressure, preferably up to 15 bar, preferably 3 bar to 7 bar. The difference between TMP and the permeate side pressure produces the retentate side pressure. In a preferred embodiment, especially in the case of pressure ratio and permeate side pressure, care should be taken to ensure that the pressure is set according to the hydrocarbon used, the alcohol used and the temperature in the system, so as to avoid evaporation after passing through the membrane. Evaporation may lead to unstable operation.

[0042] In the subsequent step d, the crude product mixture / permeate of the membrane separation is subjected to a distillation treatment in at least one distillation column to remove unreacted alcohol and unreacted olefins, i.e., unreacted diisobutylene and unreacted C4 to C7 olefins. This gives an ester mixture comprising the formed esters. Thus, the ester mixture contains esters formed from diisobutylene and C4 to C7 olefins.

[0043] In the distillation treatment of the crude product mixture / permeate in step d, unreacted alcohol and unreacted olefins, i.e., unreacted diisobutylene and unreacted C4 to C7 olefins, are obtained at the top of at least one distillation column. The mixture of esters thus formed accumulates at the bottom of at least one distillation column. The top stream containing the unreacted alcohol and unreacted olefins removed in at least one distillation column can be recycled to the alkoxycarbonylation / reaction zone in step b). If the components used have undergone mixing before alkoxycarbonylation, the top stream is supplied to the mixing according to definition. This allows the method of the present invention to be operated continuously with the highest possible yield. A purge can be taken out from the recycled top stream to discharge low-boiling by-products from the method.

[0044] The distillation treatment for removing unreacted alcohol and unreacted olefin in step d can be carried out in a distillation column. It is conceivable to carry out the distillation treatment for removing unreacted alcohol and unreacted olefin in step d in two or more distillation columns. However, this will require significantly higher equipment costs. Therefore, it is preferred to carry out the distillation treatment in step d in a single distillation column.

[0045] In the distillation treatment in step d, the pressure in the distillation column is preferably 0.3 to 2 bar, more preferably 0.4 to 1 bar, particularly preferably 0.5 to 0.7 bar. In the distillation treatment in step d, the temperature in the bottom of the distillation column is preferably 80° C. to 160° C. In the distillation treatment in step d, the temperature at the top of the distillation column is preferably 30° C. to 80° C. In addition, it is preferred that the reflux ratio in the distillation column is 1 to 2. The distillation column used for the removal in step d preferably comprises 10 to 30 theoretical plates. The distillation column may contain a high-performance structured packing. Suitable high-performance structured packings are known to those skilled in the art.

[0046] As described above, the distillation process results in an ester mixture comprising esters formed from diisobutylene and C4 to C7 olefins. In order to obtain both esters in the highest possible purity, a further distillation step may be carried out to separate the esters of the ester mixture from one another. The esters from the C4 to C7 olefins will be obtained at the top of the distillation column, while the esters from the diisobutylene will be obtained at the bottom of the distillation column.

[0047] The present process is suitable for the alkoxycarbonylation of diisobutylene and C4 olefins with alcohols, preferably alcohols having 1 to 4 carbon atoms, and subsequent hydrolysis or saponification. In the context of the present invention, certain combinations of olefins and alcohols are particularly preferred:

[0048] In a preferred embodiment, the process involves the alkoxycarbonylation of diisobutylene and C4 olefins (i.e. 1-butene, cis- and / or trans-2-butene, isobutylene or a mixture thereof) with methanol. The ester formed by diisobutylene and methanol in the alkoxycarbonylation is 3,5,5-trimethylhexanoic acid methyl ester. The alkoxycarbonylation of different butenes with methanol can form methyl valerate, methyl 2-methylbutyrate and / or methyl 3-methylbutyrate. Thus, a mixture of butenes is also used to obtain a mixture of the esters.

[0049] In a preferred embodiment, the method involves the alkoxycarbonylation of diisobutylene and C4 olefins (i.e. 1-butene, cis- and / or trans-2-butene, isobutylene or a mixture thereof) with ethanol. The ester formed by diisobutylene and ethanol in the alkoxycarbonylation is 3,5,5-trimethylhexanoic acid ethyl ester. The alkoxycarbonylation of different butenes with ethanol can form ethyl valerate, ethyl 2-methylbutyrate and / or ethyl 3-methylbutyrate. Therefore, the use of a mixture of butenes also results in a mixture of the esters.

[0050] The ester produced in step b and removed and optionally purified in step d is then subjected to hydrogenation in step e. The hydrogen employed cleaves the ester groups, thereby forming the target alcohol and allows recovery of the alcohol incorporated in the ester formation in step b. Thus, hydrogenation yields an alcohol mixture comprising at least the target alcohol, the eliminated alcohol and the unreacted ester.

[0051] As described above, the process according to the invention forms a mixture of esters containing esters formed from diisobutylene and esters formed from C4 to C7 olefins. In the hydrogenation in step e, this ester mixture can be used to obtain each target alcohol in a reaction in a single reaction zone. However, the esters obtained from diisobutylene and the esters obtained from C4 to C7 olefins can also be separated from each other in advance and hydrogenated separately from each other in their own dedicated reaction zones. The simultaneous hydrogenation of the two esters has the advantage of reducing equipment costs and is preferred according to the invention.

[0052] The alcohol recovered during the hydrogenation in step e can be removed from the resulting alcohol mixture in a subsequent process step and recycled to the first reaction zone.

[0053] Hydrogenation is a well-known reaction. Typical hydrogenation conditions are known to those skilled in the art and are disclosed in, for example, EP 1 042 260 A1. In step e, the hydrogenation according to the present invention is preferably carried out at a pressure of 10 to 300 bar, further preferably at a pressure of 100 to 280 bar, particularly preferably at a pressure of 150 to 270 bar. The hydrogenation temperature is preferably 100° C. to 300° C., preferably 150° C. to 280° C., particularly preferably 180° C. to 220° C. In the hydrogenation, the offgas can be additionally taken out to remove low-boiling components, for example impurities, such as nitrogen or low-boiling by-products.

[0054] The hydrogenation of step e is carried out in the presence of a heterogeneous catalyst system. Typical catalyst systems are known, for example, from EP1 338 557 A1. The heterogeneous catalyst system preferably comprises a metal selected from copper, rhodium, ruthenium, rhenium or a compound of these metals. In addition, a catalyst system based on copper-chromium oxide is also suitable. Particularly preferred catalyst systems contain copper and / or zinc as active components, which are applied to a support material. Porous silicon dioxide and / or aluminum oxide are suitable as support materials.

[0055] The hydrogen required for the hydrogenation can be supplied directly as feedstock. It is also possible to supply the hydrogen by first separating the hydrogen-containing gas into its components in a manner known to the person skilled in the art and conveying the hydrogen to the hydrogenation zone. The hydrogen may still contain a certain proportion of carbon monoxide or other gases, since complete separation is hardly possible.

[0056] In the subsequent step f of removing the target alcohol formed in step e from the remaining alcohol mixture, the alcohol mixture from the hydrogenation in step e is subjected to at least one separation process step selected from thermal separation such as distillation, extraction, crystallization or further membrane separation. The separation process is preferably distillation. Suitable process conditions are known to those skilled in the art. Multistage distillation can also be carried out.

[0057] The alcohol used in step b and recovered via hydrogenation can also be removed in at least one separation process step and recycled to the reaction zone. During the recycling, a purge stream can be withdrawn in order to remove hydrogenation by-products such as inert alkanes, aldehydes, acetals, ethers, ketones or carbons from the process. In addition, if diisobutene and two esters of C4 to C7 olefins are hydrogenated together, the target alcohol can also be separated from one another.

Claims

1. A method for preparing a target alcohol, wherein the method comprises at least the following steps: a. providing a diisobutylene stream containing 2,4,4-trimethylpent-2-ene and 2,4,4-trimethylpent-1-ene, and providing an olefin stream containing C4 to C7 olefins; b. alkoxycarbonylating diisobutylene and C4 to C7 olefins with alcohol and carbon monoxide in a common reaction zone in the presence of a homogeneous catalyst system comprising at least one metal from Groups 8 to 10 of the Periodic Table of Elements or a compound thereof, a phosphorus-containing ligand and an acid to obtain a liquid product mixture comprising at least an ester formed by the alkoxycarbonylation, the homogeneous catalyst system, unreacted olefins and unreacted alcohol; c. removing the homogeneous catalyst system from the liquid product mixture to obtain a crude product mixture, the crude product mixture comprising at least the ester formed by the alkoxycarbonylation, the unreacted olefin and the unreacted alcohol; d. treating the crude product mixture by distillation in at least one distillation column to remove the unreacted alcohol and the unreacted olefin to obtain an ester mixture containing the formed esters; e. hydrogenating the ester obtained in step d with hydrogen in a hydrogenation zone in the presence of a heterogeneous catalyst system to obtain an alcohol mixture comprising at least the target alcohol, the eliminated alcohol and the unreacted ester; and f. removing the target alcohol formed in step e in at least one separation process step selected from thermal separation such as distillation, extraction, crystallization and membrane separation.

2. The process according to claim 1, wherein the alkoxycarbonylation in step b is carried out at a temperature of 60 to 120°C, preferably 65 to 110°C, particularly preferably 70 to 100°C.

3. The process according to claim 1 or 2, wherein the alkoxycarbonylation in step b is carried out at a carbon monoxide pressure of 10 bar to 35 bar, preferably 12.5 bar to 30 bar, particularly preferably 15 bar to 25 bar.

4. The method according to any one of the preceding claims, wherein the content of the metal of Group 8 to 10 of the Periodic Table of the Elements, in particular palladium, in the alkoxycarbonylation reaction solution in step b is 100 ppm to 500 ppm, preferably 150 ppm to 450 ppm, particularly preferably 180 ppm to 350 ppm. 5 . The process according to claim 1 , wherein the alcohol is a monohydric alcohol having 1 to 4 carbon atoms, in particular methanol, ethanol, propanol or butanol.

6. The process according to any of the preceding claims, wherein the proportion of 2,4,4-trimethylpent-1-ene in the diisobutene stream is at least 60 mol%, preferably at least 70 mol%.

7. The process according to any one of the preceding claims, wherein the removal of the homogeneous catalyst system in step c is achieved by membrane separation.

8. The process of claim 7, wherein the homogeneous catalyst system accumulates in the retentate.

9. The process according to any one of the preceding claims, wherein the diisobutylene stream, the olefin stream, the alcohol and the homogeneous catalyst system are preliminarily mixed in a mixing vessel before being sent to the reaction zone.

10. The process according to any one of the preceding claims, wherein the distillation treatment in step d. is carried out in a single distillation column. 11 . The process according to claim 10 , wherein the pressure in the distillation column is 0.3 bar to 2 bar, preferably 0.4 bar to 1 bar, particularly preferably 0.5 bar to 0.7 bar.

12. The process according to claim 10 or 11, wherein the temperature in the bottom of the distillation column is 80 to 160°C.

13. The method according to any one of claims 10 to 12, wherein the temperature at the top of the distillation column is 30°C to 80°C.

14. A process according to any one of the preceding claims, wherein C4 olefins and methanol are employed, with the result that the ester mixture obtained is a mixture of methyl 3,5,5-trimethylhexanoate and methyl valerate, methyl 2-methylbutyrate, methyl 3-methylbutyrate or mixtures thereof.

15. The process according to any one of the preceding claims, wherein unreacted alcohol and unreacted olefin are separated in step d and recycled to the alkoxycarbonylation in step b.