Method for producing alcohols by alkoxycarbonylation of diisobutylene with pre-distillation and subsequent hydrogenation

Abstract

The invention relates to a method for producing alcohols by alkoxycarbonylation of diisobutylene with pre-distillation and subsequent hydrogenation. The invention relates to a method for producing a target alcohol by hydrogenating an ester formed by the alkoxycarbonylation of diisobutylene. The diisobutylene stream used in the alkoxycarbonylation is distilled prior to the alkoxycarbonylation, such that the stream to be alkoxycarbonylated is enriched in 2, 4, 4-trimethylpent-1-ene. 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

Technical Field

[0001] The present invention relates to a process for preparing a target alcohol by hydrogenating an ester formed by alkoxycarbonylation of diisobutylene. The diisobutylene stream used in the alkoxycarbonylation is distilled before the alkoxycarbonylation so that the stream to be alkoxycarbonylated is enriched in 2,4,4-trimethylpent-1-ene. The alkoxycarbonylation is carried out with an 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. Background Art

[0002] The preparation of alcohols in industrial chemistry is mostly carried out by hydroformylation to aldehydes and subsequent hydrogenation of the aldehydes to alcohols. Although the preparation of alcohols by hydroformylation and subsequent hydrogenation is an established and proven process in industry for decades, there is always potential for improvement. One problem with this synthesis route is the generally high pressures and high temperatures present in the hydroformylation, which places relatively high technical demands on the equipment used. Ultimately, the equipment must be able to withstand the pressures and temperatures.

[0003] Diisobutene is a technically relevant product obtained by dimerization of isobutene. Diisobutene consists of the isomers 2,4,4-trimethylpent-1-ene (hereinafter also referred to as: TMP1) and 2,4,4-trimethylpent-2-ene (hereinafter also referred to as: TMP2), wherein the mass distribution of TMP1:TMP2 is about 78:22 to 81:19 (equilibrium distribution). This mixture can be converted into higher-value products in carbonylation processes in particular. In carbonylation processes, such as methoxycarbonylation (where the reaction product is methyl 3,5,5-trimethylhexanoate) or hydroformylation (where the reaction product is 3,5,5-trimethylhexanal), the reactivity of the internal olefin TMP2 is significantly lower than that of the terminal olefin TMP1. Due to insufficient catalyst stability or due to economic factors (e.g. reactor size), it is usually not possible to adjust the reaction conditions or residence times in these carbonylation reactions sufficiently to allow complete reaction of the terminal TMP2. Summary of the invention

[0004] The object of the present invention is therefore to provide a process for preparing the target alcohol which does not have the above-mentioned problems. In particular, the alkoxycarbonylation should be carried out using a diisobutylene stream with a high proportion of 2,4,4-trimethylpent-1-ene. In addition, an alternative synthesis route for preparing the target alcohol should be obtained, by which the desired target alcohol can be obtained relatively easily.

[0005] This object is achieved by the method according to the invention as described in independent claim 1. Preferred embodiments are given in the dependent claims.

[0006] The present invention describes a method for preparing a target alcohol, wherein the method comprises at least the following steps:

[0007] a. supplying a diisobutylene stream comprising 2,4,4-trimethylpent-2-ene and 2,4,4-trimethylpent-1-ene to at least one distillation column and separating the diisobutylene stream into at least one overhead stream and a residue stream, the overhead stream being enriched in 2,4,4-trimethylpent-1-ene compared to the diisobutylene stream used and containing more than 85% by weight of 2,4,4-trimethylpent-1-ene, and the residue stream being depleted in 2,4,4-trimethylpent-1-ene compared to the diisobutylene stream used;

[0008] b. supplying the top stream to an alkoxycarbonylation reaction, whereby 2,4,4-trimethylpent-2-ene and 2,4,4-trimethylpent-1-ene react in a reaction zone with an 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 to obtain a liquid product mixture, wherein the liquid product mixture comprises at least an ester formed by the alkoxycarbonylation reaction, the homogeneous catalyst system, unreacted 2,4,4-trimethylpent-2-ene and 2,4,4-trimethylpent-1-ene and unreacted alcohol;

[0009] c. separating the homogeneous catalyst system from the liquid product mixture to obtain a crude product mixture comprising at least the ester formed by alkoxycarbonylation, unreacted 2,4,4-trimethylpent-2-ene and 2,4,4-trimethylpent-1-ene and unreacted alcohol;

[0010] d. subjecting the crude product mixture to a distillative work-up in at least one distillation column to separate unreacted alcohol and unreacted 2,4,4-trimethylpent-2-ene and 2,4,4-trimethylpent-1-ene, wherein unreacted alcohol and unreacted 2,4,4-trimethylpent-2-ene and 2,4,4-trimethylpent-1-ene are separated and recycled to the alkoxycarbonylation in step b;

[0011] e. hydrogenating the ester obtained in step d with hydrogen in the presence of a heterogeneous catalyst system in a hydrogenation zone to obtain an alcohol mixture comprising at least the target alcohol, the eliminated alcohol and the unreacted ester; and

[0012] f. separating 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.

[0013] An advantage of the process is that the diisobutene stream is distilled before the alkoxycarbonylation, since this allows the proportion of 2,4,4-trimethylpent-1-ene in the top stream of the at least one distillation column to be increased compared to the stream used. Thus, a proportion of 2,4,4-trimethylpent-1-ene in the stream of more than 85% by weight, preferably more than 90% by weight, more preferably more than 95% by weight can be achieved, which is advantageous for the downstream alkoxycarbonylation since 2,4,4-trimethylpent-1-ene has a higher reactivity.

[0014] Step a of the process according to the invention involves the distillation of a diisobutene stream comprising 2,4,4-trimethylpent-2-ene and 2,4,4-trimethylpent-1-ene. In this process, the diisobutene stream is separated into at least one top stream, which is enriched in 2,4,4-trimethylpent-1-ene compared to the diisobutene stream used and preferably comprises more than 85% by weight of 2,4,4-trimethylpent-1-ene, further preferably more than 90% by weight of 2,4,4-trimethylpent-1-ene, particularly preferably more than 95% by weight of 2,4,4-trimethylpent-1-ene, and a residue stream which is depleted in 2,4,4-trimethylpent-1-ene compared to the diisobutene stream used.

[0015] The diisobutene stream used in step a comprises 2,4,4-trimethylpent-2-ene and 2,4,4-trimethylpent-1-ene. This stream may be a diisobutene stream which can be produced by dimerization of isobutene or an isobutene-containing hydrocarbon mixture, as disclosed, for example, in EP 1360160 B1. In addition, the stream to be used here can be obtained as an unreacted residual stream in a carbonylation process, for example in methoxycarbonylation or hydroformylation. It has already been mentioned that the input stream can be supplied to the isomerization and / or the distillation. Therefore, the designations of steps a. and b. in the present claims do not constitute a priority or chronological order. It is understood that both steps must be carried out and that each step is fed by the respective other step. Therefore, which step is considered to be carried out first is of secondary importance.

[0016] The distillation in step a of the process according to the invention is carried out in at least one distillation column. Distillation columns are generally known to those skilled in the art. The distillation unit according to the invention preferably comprises at least one distillation column, more preferably at least two distillation columns. The following description of the characteristics of the distillation columns also always applies to the case where there are more than one distillation column in the distillation unit.

[0017] The at least one distillation column preferably has internals to cope with the separation task. The person skilled in the art is familiar with the corresponding internals. Particularly suitable here are random packings or structured packings, such as those known to the person skilled in the art under the trade names of In a preferred embodiment of the present invention, the at least one distillation column comprises at least 50 theoretical plates, preferably at least 70 theoretical plates, more preferably at least 90 theoretical plates. If two or more distillation columns are present, the distillation columns may have the same or different numbers of theoretical plates.

[0018] The operating parameters of the at least one distillation column are tailored to the separation task and the design of the distillation column. In the process, the at least one distillation column is preferably operated under reduced pressure, particularly preferably at a pressure of 0.2 to 0.9 bar. In the context of the present invention, reduced pressure is always present as long as operation is carried out below an ambient pressure of about 1 bar (i.e. the atmospheric pressure prevailing at the respective location). If there are two or more distillation columns, the distillation columns can be operated at the same or different pressures.

[0019] Also preferably, the bottom temperature of the at least one distillation column is 50 to 100° C. If there are two or more distillation columns, the distillation columns may be operated at the same or different temperatures.

[0020] Another parameter for the design of a distillation column is the reflux ratio. The reflux ratio refers to the ratio of reflux (recycled) to distillate (condensate removed, ie here the top stream K). Thus, the reflux is the condensed portion of the top stream that is recycled to the distillation column. Preferably according to the invention, in the distillation in step a., the reflux ratio of the at least one distillation column is 5 to 15.

[0021] In the at least one distillation column, a top stream which preferably comprises at least 85% by weight of 2,4,4-trimethylpent-1-ene, more preferably at least 90% by weight of 2,4,4-trimethylpent-1-ene, particularly preferably at least 95% by weight of 2,4,4-trimethylpent-1-ene, is produced by the distillation in step a according to the invention. In addition, a residual stream which is depleted in 2,4,4-trimethylpent-1-ene compared to the diisobutene stream used is produced in the distillation.

[0022] The residual stream obtained additionally in the distillation in step a can be withdrawn as a bottom stream or side stream of the at least one distillation column. If two distillation columns are present, the residual stream is obtained in the last distillation column, regardless of whether it is withdrawn as a side stream or a bottom stream. If the residual stream is withdrawn as a side stream, it can in principle be arranged at the same height as or below the inlet of the diisobutene stream used. It should be understood that the inflow and outflow must be arranged at a sufficient distance from one another. The residual stream preferably contains 80 to 92% by weight of 2,4,4-trimethylpent-2-ene, regardless of whether it is withdrawn as a side stream or a bottom stream.

[0023] If a residual stream from the distillation in step a is withdrawn as a bottom stream of the at least one distillation column, a purge stream is preferably withdrawn from the residual stream, which purge stream comprises high boilers formed during the isomerization, for example dimers or oligomers of 2,4,4-trimethylpent-2-ene and / or 2,4,4-trimethylpent-1-ene. The separated high boilers can be incinerated to produce energy or can be hydrogenated to prepare valuable alkanes therefrom.

[0024] If the residual stream from the distillation in step a is taken off as a side stream of the at least one distillation column, a stream comprising high boilers formed during the isomerization, for example dimers or oligomers of 2,4,4-trimethylpent-2-ene and / or 2,4,4-trimethylpent-1-ene, is preferably obtained at the bottom of the at least one distillation column. The separated high boilers can be incinerated to produce energy or can be hydrogenated to prepare valuable alkanes therefrom.

[0025] As is known, distillation columns are heated at the bottom in order to be able to perform the separation task. The energy can be provided by heating steam, which is usually provided at the chemical production site. In addition, part of the bottoms is passed through a heat exchanger (bottom evaporator), heated there, and then returned to the bottoms of the distillation column. In order to reduce the energy requirement and / or CO 2 Discharge, heat integration can be provided in the distillation in step a. Heat integration means that the energy formed or present in the process is used elsewhere. In the present case, the condensation energy (to be released) generated at the top of at least one distillation column of the distillation unit is particularly suitable. In a preferred embodiment of the invention, heat integration is carried out in step a. so that at least part of the condensation energy at the top is used to heat the bottom.

[0026] Another possible way for heat integration is so-called vapor compression, in which at least a portion of the vapor (tower top stream) is compressed, i.e. brought to a higher pressure level and optionally heated. The vapor compressed and optionally heated in this way is supplied to a heat exchanger (tower bottom evaporator) to thereby heat the bottom. This utilizes the heat of condensation of the vapor.

[0027] Another possibility is to use a heat pump. The heat pump is operated with a working medium, for example n-butane or water. The condensation energy is therefore first transferred to the working medium in a heat exchanger, from which it is transferred to the bottom of the distillation in another suitable heat exchanger. The working medium is usually conveyed to the bottom heat exchanger via a compressor. In principle, two-stage or more heat pumps can also be used in which there are more than one compressor stage. In the case of a two-stage heat pump, not only one working medium but two working media are present, wherein the energy exchange between the first and second working media also takes place in the heat exchanger. In the case of a multi-stage configuration, there are correspondingly multiple working media.

[0028] The top stream obtained from the distillation in step a is supplied to the subsequent alkoxycarbonylation step b and reacted there. In a preferred embodiment, the residual stream, likewise obtained from the distillation in step a, is supplied to an isomerization, wherein 2,4,4-trimethylpent-2-ene is at least partially isomerized to 2,4,4-trimethylpent-1-ene using a heterogeneous catalyst based on zeolites or ion exchange resins. Thus, the isomerization can be carried out with a residual stream which is depleted in 2,4,4-trimethylpent-1-ene compared to the diisobutylene stream used in step a and which is taken off from the distillation in step a.

[0029] The advantage of carrying out the isomerization before the distillation in step a is the use of a heterogeneous catalyst system. Such a catalyst system does not have to be separated from the isomerization stream, but remains in the reaction vessel or reactor. The catalyst systems based on zeolites or ion exchange resins preferred according to the invention can also achieve high conversions.

[0030] Isomerization can be carried out in principle in various suitable reactors. Isomerization can be carried out in a single reactor or in a plurality of reactors connected in parallel or in series. It can also be carried out in batches or in a continuously operated manner. Isomerization is preferably carried out in one or more continuously operated reactors, which are generally used for solid / liquid contact reactions. When a continuously operated flow reactor is used, a fixed bed is generally, but not exclusively, used. When a fixed bed flow reactor is used, the liquid can flow upward or downward. In most cases, it is preferred that the liquid flows downward. In addition, the reactor can be operated by product recirculation or straight-through mode. Concepts different from fixed bed reactors are, for example, reactors in which ion exchangers or zeolites are present in the form of suspension in the liquid phase.

[0031] The reactors used for the isomerization can be tubular reactors or tube bundle reactors, in particular those with an inner tube diameter of 10 to 60 mm. The aspect ratio of the catalyst bed can be varied depending on the geometry of the reactor or its filling level. Thus, with identical contact volume and loading (LHSV), different empty tube velocities can be achieved and the heat transfer to the cooling medium can be influenced in a targeted manner.

[0032] Whether it is a tubular reactor or a tube bundle reactor, the cooling of the tubes of the reactor can be carried out by a cooling medium (such as cooling water or an endothermic process fluid for heat integration) through the jacket space of the reactor or a heat exchanger in an external circulation system. Especially when a liquid heating medium is used, the construction of the jacket side should be such that there is a temperature gradient as uniform as possible at all tubes. The technical measures required for this purpose are known to those skilled in the art and are described in the literature (installing a deflection plate, an annular baffle structure, a heat carrier feed / discharge, etc. at various positions of the reactor). Preferably, the reaction medium and the heat carrier are conducted through the reactor tube or the reactor jacket in a co-current manner, more preferably from top to bottom. For example, a preferred embodiment is described in DE102006040433 A1.

[0033] The isomerization of 2,4,4-trimethylpent-2-ene to 2,4,4-trimethylpent-1-ene takes place exothermically, ie with the release of energy, which leads to an increase in the temperature of the reaction mixture. In order to limit the temperature increase, the feed stream can be diluted, for example by product recycle.

[0034] The one or more reactors used for the isomerization can be operated adiabatically, polytropically or virtually isothermally. Virtually isothermally means that the temperature at any point in the reactor is at most 10° C. higher than the temperature at the reactor inlet. In the case of adiabatic operation of the reactors, it is generally advantageous to connect a plurality of reactors in series and to provide cooling between the reactors. Suitable reactors for polytropic or virtually isothermal operation are, for example, the already mentioned tube bundle reactors as well as stirred tank reactors and loop reactors.

[0035] The process can be carried out at a fairly mild temperature. The isomerization is preferably carried out at a temperature of 25 to 90°C, preferably 30 to 80°C, more preferably 35 to 70°C. In addition, the isomerization of the present invention can be carried out at a pressure equal to or greater than the vapor pressure of the input stream mixture and / or the reaction mixture at the respective reaction temperatures, preferably at a pressure greater than 0 bar but less than 40 bar. Further preferably, the isomerization is carried out in the liquid phase. It should be clear that in this case, the pressure and temperature must be selected so that the input stream is present or can be present in the liquid phase.

[0036] In the one or more reactors, various catalysts based on zeolites or ion exchange resins can also be used for isomerization. For example, a mixture of ion exchange resins of different reactivity can be used. Similarly, the reactor can contain catalysts of different activities, which are arranged in layers, for example. If multiple reactors are used, each reactor can be filled with the same or different one or more catalysts based on zeolites or ion exchange resins.

[0037] As heterogeneous catalysts, catalysts based on zeolites or ion exchange resins can be used for the isomerization. The corresponding zeolites and ion exchange resins are widely available on the market. It has been found that catalysts based on zeolites preferably have a Si:Al ratio of 40:1 to 200:1. It has also been found that styrene-divinylbenzene types, preferably in H form and in partially neutralized form, are very suitable as catalysts based on ion exchange resins.

[0038] When the catalyst is a zeolite, some zeolites have proven to be particularly advantageous, such as beta zeolite and gamma zeolite. Therefore, the zeolite is preferably selected from Z-β-H-25, Z-β-H-38, Z-β-H-360, Z-Mor-H-20, ZYH-60, ZYH-80, Z-β-H, Z-CFG-1, Z-β-ammonium-38, Z-CBV 760CY (1.6), Z-CBV 780CY (1.6), CP 814E CY (1.6), CBV 500CY (1.6), H-CZB-150 and mixtures thereof.

[0039] Ion exchange resins which can be used are those which are prepared, for example, by sulfonation of phenol / aldehyde condensates or by sulfonation of copolymers of aromatic vinyl compounds. Examples of aromatic vinyl compounds for preparing copolymers are: styrene, vinyltoluene, vinylnaphthalene, vinylethylbenzene, methylstyrene, vinylchlorobenzene, vinylxylene and divinylbenzene. For isomerization, it is particularly preferred to use ion exchange resins which are prepared by sulfonation of copolymers formed by the reaction of styrene with divinylbenzene. Ion exchange resins can be prepared in a gel-like, macroporous or spongy form. It is well known that the properties of these resins, in particular the specific surface area, porosity, stability, expansion or contraction and exchange capacity can be varied by the preparation process.

[0040] Preferred ion exchange resins of the styrene-divinylbenzene type are sold, inter alia, under the following trade names: CT 151 and CT 275 from Purolite, 15. 35. IR-120, 200, Dowex M-31 from Dow, Lanxess K 2621, K-2431.

[0041] The pore volume of the ion exchange resins which can be used as catalysts, in particular the preferred ion exchange resins of the styrene-divinylbenzene type, is preferably 0.3 to 0.9 ml / g, more preferably 0.5 to 0.9 ml / g. The pore volume can be determined, for example, by adsorption techniques. The particle size of the ion exchange resin is preferably 0.3 mm to 1.5 mm, more preferably 0.5 mm to 1.0 mm. Narrower or wider particle size distributions can be selected. Thus, for example, ion exchange resins with very uniform particle sizes (monodisperse resins) can be used.

[0042] The ion exchange resins which can be used as isomerization catalysts can be present as partially neutralized ion exchange resins. To this end, the ion exchange resins can be treated with acids or bases, as described in EP 1360160B1.

[0043] An isomerized stream is obtained from the optional isomerization, wherein the proportion of 2,4,4-trimethylpent-2-ene in the isomerized stream is lower than that in the residual stream used, and the proportion of 2,4,4-trimethylpent-1-ene in the isomerized stream is higher than that in the residual stream used. The isomerized stream may be at least partially supplied to the distillation in step a, and preferably the isomerized stream is completely supplied to the distillation in step a.

[0044] The process may also comprise the supply of an input stream to feed the process. The input stream comprising 2,4,4-trimethylpent-2-ene and 2,4,4-trimethylpent-1-ene to feed the process may be supplied to the distillation unit in step a together with the isomerization stream and / or supplied to the isomerization together with the residual stream.

[0045] A flexible supply of the input stream is advantageous here. This makes it possible to adapt the process to the respective conditions, for example depending on the input stream used. If the ratio of 2,4,4-trimethylpent-2-ene to 2,4,4-trimethylpent-1-ene in the input stream is close to the equilibrium distribution, this stream can be supplied directly to the distillation. If the ratio of 2,4,4-trimethylpent-2-ene to 2,4,4-trimethylpent-1-ene in the input stream deviates from the equilibrium distribution, this stream can first be supplied to the isomerization. It can thus be integrated into existing production plants in a simple manner depending on the composition of the input stream.

[0046] As described above, the top stream obtained by the distillation in step a is supplied to the subsequent alkoxycarbonylation step b, and reacted therein.

[0047] In step b, diisobutylene, i.e., 2,4,4-trimethylpent-2-ene and 2,4,4-trimethylpent-1-ene, reacts with carbon monoxide (CO) and an alcohol to form an ester. Compared to the diisobutylene used, the number of carbon atoms in the ester is increased by 1 carbon atom from carbon monoxide and by the number of carbon atoms from the alcohol used. Thus, an ester having 9 carbon atoms in the acid portion of the ester and in addition the carbon atoms of the alcohol in the alcohol portion of the ester is produced from diisobutylene (8 carbon atoms).

[0048] In step b, the carbon monoxide can be provided directly in the form of a feed mixture or by adding a carbon monoxide-containing gas selected from synthesis gas, water gas, producer gas and other carbon monoxide-containing gases. Carbon monoxide can also be provided by first separating the carbon monoxide-containing gas into its components in a manner known to those skilled in the art and passing the carbon monoxide into the reaction zone. Here, the carbon monoxide may still contain a certain proportion of hydrogen or other gases, because complete separation cannot be achieved.

[0049] The alcohol used in the reaction of step b is preferably a monohydric alcohol having 1 to 4 carbon atoms, in particular methanol, ethanol, propanol or butanol. In this case, esters having a chain length corresponding to the alcohol used are obtained. For example, when methanol is used, methyl esters are formed.

[0050] The alcohol used in step b, preferably a monohydric alcohol having 1 to 4 carbon atoms, in particular methanol, ethanol, propanol or butanol, is used in a molar ratio to the total amount of all diisobutene, i.e. alcohol:diisobutene of 10:1 to 1:1, preferably 8:1 to 1.5:1, more preferably 7:1 to 2:1. The alcohol is therefore added in at least the same molar amount as the diisobutene used, but preferably in a molar excess.

[0051] The reaction in step b of the present invention 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 (PSE) or a compound thereof, a phosphorus-containing ligand and an acid as a promoter. The content of the metal of Groups 8 to 10 of the Periodic Table of Elements, especially palladium, in the alkoxycarbonylation reaction solution in step b is preferably 100 to 500 ppm, more preferably 150 to 450 ppm, particularly preferably 180 to 350 ppm.

[0052] The metal of PSE Group 8 to 10 is preferably palladium. Palladium is preferably used in the form of a precursor compound as a palladium compound coordinated with a phosphorus-containing ligand. An example of a palladium compound that can be used as a precursor compound is palladium chloride [PdCl 2 ]、Acetylacetonate palladium(II)[Pd(acac) 2 ]、palladium(II) acetate[Pd(OAc) 2 ]、Dichloro(1,5-cyclooctadiene)palladium(II)[Pd(cod) 2Cl 2 ]、Bis(dibenzylideneacetone)palladium(0)[Pd(dba) 2 ], tris(dibenzylideneacetone)dipalladium(0)[Pd 2 (dba) 3 ], bis(acetonitrile)dichloropalladium(II)[Pd(CH 3 CN) 2 Cl 2 ]、(Cinnamyl)palladium dichloride [Pd(cinnamyl)Cl 2 ]. Preferably, the compound [Pd(acac) 2 ] or [Pd(OAc) 2 ]. The palladium metal concentration in step b is preferably from 0.01 to 0.6 mol %, preferably from 0.03 to 0.3 mol %, more preferably from 0.04 to 0.2 mol %, based on the molar amount of hydrocarbon used.

[0053] Suitable phosphorus-containing ligands of the catalyst system of the present invention preferably have a bidentate structure. Preferred phosphorus-containing ligands of the catalyst system of the present invention are diphosphine compounds based on benzene, for example disclosed in EP 3121184A2. The ligand can be combined with palladium in a pre-reaction, thereby supplying the palladium-ligand complex to the reaction zone, or added in situ to the reaction and combined with palladium there. The molar ratio of ligand: metal in the reaction described in step b can be 1: 1 to 10: 1, preferably 2: 1 to 6: 1, more preferably 3: 1 to 5: 1.

[0054] 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. Of 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.

[0055] Suitable Bronsted acids preferably have an acid strength of pKa ≤ 5, more preferably an acid strength of pKa ≤ 3. The acid strength pKa refers to the pKa value determined under standard conditions (25° C., 1.01325 bar). For polyprotic acids, in the context of the present invention, the acid strength pKa refers to the pKa value of the first proton migration step. The Bronsted acid is preferably added in a molar ratio of Bronsted acid: ligand of 1:1 to 15:1, preferably 2:1 to 10:1, more preferably 3:1 to 5:1.

[0056] The Bronsted acids 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.

[0057] The alkoxycarbonylation in step b is preferably carried out at a temperature of 60 to 120° C., further preferably 65 to 110° C., particularly preferably 70 to 100° C. The alkoxycarbonylation in step b is further preferably carried out at a carbon monoxide pressure of 10 to 35 bar, preferably 12.5 to 30 bar, more preferably 15 to 25 bar.

[0058] The alkoxycarbonylation in step b is carried out 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 be selected in particular from a stirred tank reactor, a loop reactor, a jet loop reactor, a bubble column reactor or a combination thereof. If there are a plurality of reactors, the reactors may be identical or different from one another.

[0059] The alkoxycarbonylation in step b above yields a liquid product mixture, which contains at least the ester formed by the alkoxycarbonylation, the homogeneous catalyst system, unreacted diisobutylene 2,4,4-trimethylpent-2-ene and 2,4,4-trimethylpent-1-ene, and unreacted alcohol. In addition, the liquid product mixture may contain low-boiling side components such as dimethyl ether or formic acid and / or high-boiling components such as ligand decomposition products.

[0060] The product mixture thus obtained is supplied to subsequent step c, to separate the homogeneous catalyst system from the liquid product mixture. Before the supply product mixture, low boiling components, such as a part of unreacted alcohol and / or low boiling by-products can be separated. Alcohol can be recycled to step b, i.e. alkoxycarbonylation. Low boiling by-products can be discharged from the method as a purge, so that they are not enriched in the method thus. A crude product mixture is obtained by the separation of the homogeneous catalyst system, which crude product mixture comprises at least an ester, unreacted diisobutylene and at least a part of unreacted alcohol formed by alkoxycarbonylation.

[0061] In step c, the homogeneous catalyst system can be separated by various separation methods, for example by thermal separation and / or by membrane separation to obtain a crude product mixture. Those skilled in the art are familiar with the corresponding methods. Preferably, in the context of the present invention, in step c, the homogeneous catalyst system is preferably separated by membrane separation. It is well known that retentate and permeate are produced in membrane separation. The homogeneous catalyst system is enriched in the retentate. At this point, the permeate constitutes the aforementioned crude product mixture and is directed to the subsequent distillation post-treatment step d.

[0062] According to the present invention, the retentate is preferably recycled to the alkoxycarbonylation in step b or to the reaction zone for carrying out the alkoxycarbonylation. Thus the catalyst system can be reused. In the method for the preferred continuous protection, a catalyst loop is thus formed, wherein only a small amount of catalyst loss (if any) related to the process needs to be compensated. When the diisobutylene stream, alcohol and homogeneous catalyst system are mixed in a suitable mixing vessel before the alkoxycarbonylation in step b according to a preferred embodiment, the retentate is supplied 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) can be taken out in addition to avoid accumulation in the one or more reaction zones.

[0063] Various suitable membrane materials can be used for membrane separation. In the membrane separation in step c of the process according to the invention, OSN membrane materials (OSN=organic solvent nanofiltration) are preferably used. Such membrane materials preferably consist of at least a separation active layer (also referred to as: active separation layer) and a substructure in which the separation active layer is located. The membrane material according to the invention preferably consists of at least a separation active layer and a substructure.

[0064] The membrane material consisting of at least the separation active layer and the substructure should have acid stability so that the membrane material is not damaged by the acid present in the liquid product mixture. The term "acid stability" in the context of the present invention means that the membrane material remains stable in the presence of the acid of the catalyst system for at least 300 hours and maintains separation performance.

[0065] The substructure preferably has a porous structure that is permeable to permeates that have passed through the separation active layer. The substructure has a stabilizing function and serves as a carrier for the separation active layer. The substructure can in principle be composed of various suitable porous materials. The corresponding materials are familiar to those skilled in the art. However, a prerequisite is that the material has acid and alkali stability. The substructure can also be composed of the same material as the separation active layer. The preferred material of the substructure is a plastic, such as polypropylene or a PAEK polymer (PAEK means polyaryletherketone). PAEK polymers are particularly PEEK (polyetheretherketone), more preferably a PEEK polymer with a sulfonation degree of less than 20%, more preferably a sulfonation degree of less than 10%.

[0066] The separation active layer of the present invention is preferably composed of a PAEK polymer (polyaryletherketone). PAEK is characterized in that, within the repeating unit, the aromatic groups are alternately connected via ether functional groups and ketone functional groups. The preferred separation active layer of the present invention is composed 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 polymer and its preparation are described in WO 2015 / 110843 A1.

[0067] The membrane separation in step c is preferably carried out at a temperature of 25° C. to 100° C., further preferably at 30° C. to 80° C., particularly preferably at 40° C. to 70° C. In order to bring the product mixture to a temperature at which membrane separation preferably occurs, the product mixture can be cooled. In addition to active cooling using a cooling medium, cooling can also be achieved by means of a heat exchanger, thereby heating another stream within the process of the invention.

[0068] The transmembrane pressure (TMP) in the membrane separation in step c is preferably 10 to 60 bar, further preferably 15 to 55 bar, particularly preferably 20 to 50 bar. The permeate side pressure can be higher than atmospheric pressure, preferably up to 15 bar, preferably 3 to 7 bar. The difference between TMP and the permeate side pressure produces the retentate side pressure. In a preferred embodiment, in the case of the pressure ratio and especially the permeate side pressure, care should be taken to adjust the pressure according to the hydrocarbon used, the alcohol used and the temperature present, so as to avoid evaporation after passing through the membrane. Evaporation may lead to unstable operation.

[0069] In the subsequent step d, the crude product mixture or permeate from the membrane separation is worked up by distillation in at least one distillation column to separate unreacted alcohol and unreacted diisobutylene. An ester product comprising the formed ester is obtained. The ester product comprises the ester formed from diisobutylene, i.e., 3,5,5-trimethylhexanoic acid alkyl ester, wherein the alkyl group contains 1 to 4 carbon atoms, depending on the alcohol used.

[0070] In the distillative workup of the crude product mixture or the permeate in step d, unreacted alcohol and unreacted diisobutylene are obtained at the top of the at least one distillation column. Thus, the ester product is produced at the bottom of the at least one distillation column. The top stream containing the unreacted alcohol and unreacted diisobutylene separated in the at least one distillation column is recycled to the alkoxycarbonylation in step b. If the components used are mixed before the alkoxycarbonylation, the top stream is of course supplied to the mixing. This makes it possible to operate the process of the invention continuously at the highest possible yield. A purge can be taken from the recycled top stream in order to remove low-boiling by-products from the process.

[0071] The distillative work-up in step d for separating unreacted alcohol and unreacted diisobutylene can be carried out in one distillation column. It is conceivable that the distillative work-up in step d for separating unreacted alcohol and unreacted diisobutylene is carried out in multiple distillation columns. However, this means that the equipment expenditure will be significantly higher. Therefore, the distillative work-up in step d is preferably carried out in a single distillation column.

[0072] The pressure in the distillation column during the distillation work-up in step d is preferably 0.3 to 2 bar, further preferably 0.4 to 1 bar, and particularly preferably 0.5 to 0.7 bar. The bottom temperature of the distillation column during the distillation work-up in step d is preferably 80° C. to 160° C. The top temperature of the distillation column during the distillation work-up in step d is preferably 30 to 80° C. In addition, the reflux ratio in the distillation column is preferably 1 to 2. The distillation column used for separation in step d preferably comprises 10 to 30 theoretical plates. The distillation column may contain a high-performance structured packing here. Corresponding high-performance structured packings are known to those skilled in the art.

[0073] The ester produced in step b and separated and optionally purified in step d is then hydrogenated in step e. The ester groups are cleaved by the hydrogen used in the process, thereby forming the target alcohol, and the alcohol incorporated in the ester formation in step b can be recovered. Thus, an alcohol mixture containing at least the target alcohol, the eliminated alcohol and the unreacted ester is produced during the hydrogenation.

[0074] The alcohol recovered during the hydrogenation in step e can be separated off from the resulting alcohol mixture in a subsequent process step and recirculated to the first reaction zone.

[0075] Hydrogenation is a reaction known per se. Typical hydrogenation conditions are known to those skilled in the art and are disclosed, for example, in EP1042260 A1. The hydrogenation in step e 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, waste gas can be additionally taken out to remove low-boiling components such as impurities such as nitrogen or low-boiling by-products.

[0076] The hydrogenation in step e is carried out in the presence of a heterogeneous catalyst system. Typical catalyst systems are known, for example, from EP1338557 A1. The heterogeneous catalyst system preferably comprises a metal selected from a compound of copper, rhodium, ruthenium, rhenium or 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 oxide and / or aluminum oxide are suitable as support materials.

[0077] The hydrogen required for the hydrogenation can be provided directly as a feedstock. It is also possible to provide the hydrogen by previously separating the hydrogen-containing gas into its components in a manner known to those skilled in the art and then supplying the hydrogen to the hydrogenation zone. The hydrogen may still contain a certain proportion of carbon monoxide or other gases, since complete separation is not possible.

[0078] In the subsequent step f, 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 to separate the target alcohol formed in step e from the remaining alcohol mixture. The separation process is preferably distillation. The corresponding process conditions are known to those skilled in the art. Multi-stage distillation can also be carried out.

[0079] Furthermore, the alcohol separated off in the at least one separation process step used in the alkoxycarbonylation can be recycled to the reaction zone. In the recycling, a purge stream can be withdrawn, for example, to remove hydrogenation by-products, i.e. inert alkanes, aldehydes, acetals, ethers, ketones or carbon from the process. DETAILED DESCRIPTION

[0080] Refer to the attached pictures Figure 1 and Figure 2 The invention is explained in more detail.The drawings show specific embodiments and are not intended to limit the subject matter of the invention.

[0081] Figure 1 An embodiment is shown in which a diisobutylene stream (1) is supplied to a distillation column (2) in step a. The top stream (3) is enriched in 2,4,4-trimethylpent-1-ene compared to the diisobutylene stream used. The distillation also produces a residue stream (4) which is depleted in 2,4,4-trimethylpent-1-ene compared to the diisobutylene stream used. The top stream (3) is subsequently supplied to an alkoxycarbonylation (5) in step b, thereby producing a product mixture (6). This product mixture (6) is separated by a catalyst (7) in step c to produce a crude product mixture (8), which is distilled (9) in step d. In this distillation, a product (11) is obtained as well as unreacted alcohol and unreacted 2,4,4-trimethylpent-2-ene and 2,4,4-trimethylpent-1-ene as stream (10), which is recycled to the alkoxycarbonylation (5). The product, alkyl 3,5,5-trimethylhexanoate, is subsequently fed to the hydrogenation ( 14 ) and converted there into the target alcohol, which is separated off as stream ( 16 ) in the downstream distillative separation ( 15 ).

[0082] Figure 2Another embodiment is concerned in which an isomerization (12) is also present. The diisobutene stream (13) used can be supplied here to the isomerization and / or distillation (2). This is indicated by the dashed line. The isomerization stream (1) then becomes the inflow of the distillation (2). The isomerization is also fed with the residual stream (4) from the distillation in order to at least partially convert the 2,4,4-trimethylpent-2-ene into 2,4,4-trimethylpent-1-ene there.

Claims

1. A method for producing a target alcohol, wherein the method comprises at least the following steps: a. supplying a diisobutylene stream comprising 2,4,4-trimethylpent-2-ene and 2,4,4-trimethylpent-1-ene to at least one distillation column and separating the diisobutylene stream into at least one overhead stream and a residue stream, the overhead stream being enriched in 2,4,4-trimethylpent-1-ene compared to the diisobutylene stream used and containing more than 85% by weight of 2,4,4-trimethylpent-1-ene, and the residue stream being depleted in 2,4,4-trimethylpent-1-ene compared to the diisobutylene stream used; b. supplying the top stream to an alkoxycarbonylation, whereby 2,4,4-trimethylpent-2-ene and 2,4,4-trimethylpent-1-ene are reacted in a reaction zone with an 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 to obtain a liquid product mixture, wherein the liquid product mixture comprises at least an ester formed by the alkoxycarbonylation, the homogeneous catalyst system, unreacted 2,4,4-trimethylpent-2-ene and 2,4,4-trimethylpent-1-ene and unreacted alcohol; c. separating the homogeneous catalyst system from the liquid product mixture to obtain a crude product mixture comprising at least the ester formed by alkoxycarbonylation, unreacted 2,4,4-trimethylpent-2-ene and 2,4,4-trimethylpent-1-ene and unreacted alcohol; d. subjecting the crude product mixture to a distillative work-up in at least one distillation column to separate unreacted alcohol and unreacted 2,4,4-trimethylpent-2-ene and 2,4,4-trimethylpent-1-ene, wherein unreacted alcohol and unreacted 2,4,4-trimethylpent-2-ene and 2,4,4-trimethylpent-1-ene are separated and recycled to the alkoxycarbonylation in step b; e. hydrogenating the ester obtained in step d with hydrogen in the presence of a heterogeneous catalyst system in a hydrogenation zone to obtain an alcohol mixture comprising at least the target alcohol, the eliminated alcohol and the unreacted ester; and f. separating 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 residual stream in step a is taken off as a bottom stream or a side stream of the at least one distillation column.

3. The process according to any of the preceding claims, wherein the residual stream is supplied to an isomerization, wherein 2,4,4-trimethylpent-2-ene is at least partially isomerized to 2,4,4-trimethylpent-1-ene using a heterogeneous catalyst based on zeolites or ion exchange resins.

4. The process according to claim 3, wherein the isomerization results in an isomerized stream in which the proportion of 2,4,4-trimethylpent-2-ene is lower than that of the residual stream, and the proportion of 2,4,4-trimethylpent-1-ene is higher than that of the residual stream.

5. The process according to claim 3 or 4, wherein the isomerized stream is at least partly supplied to the distillation in step a.

6. The process according to any one of claims 3 to 5, wherein the input stream comprising 2,4,4-trimethylpent-2-ene and 2,4,4-trimethylpent-1-ene feeding the process is supplied to the distillation unit in step a together with the isomerization stream and / or is supplied to the isomerization together with the residual stream.

7. The process according to any one of claims 3 to 6, wherein the isomerization is carried out at a temperature of 25 to 90°C, preferably 30 to 80°C, more preferably 35 to 70°C.

8. The process according to any one of claims 3 to 7, wherein the zeolite has a Si:Al ratio of 40:1 to 200:

1.

9. The process according to any one of claims 3 to 8, wherein the zeolite is selected from the group consisting of β-zeolite and γ-zeolite.

10. The process according to claim 3, wherein the ion exchange resins used are those which are produced by sulfonation of phenol / aldehyde condensates or by sulfonation of copolymers of aromatic vinyl compounds.

11. The process according to any one of the preceding claims, 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.

12. The process according to any one of the preceding claims, wherein the alkoxycarbonylation in step b is carried out at a carbon monoxide pressure of 10 to 35 bar, preferably 12.5 to 30 bar, more preferably 15 to 25 bar.

13. The process according to any one of the preceding claims, wherein the alcohol is a monohydric alcohol having 1 to 4 carbon atoms, in particular methanol, ethanol, propanol or butanol.

14. The process according to any one of the preceding claims, wherein the separation of the homogeneous catalyst system in step c is carried out by membrane separation.

15. The process according to any one of the preceding claims, wherein the diisobutylene stream, the alcohol and the homogeneous catalyst system are first mixed in a mixing vessel before they are introduced into the reaction zone.

Images