Process for hydroformylation of diisobutylene with pre-distillation

Abstract

The present invention relates to a process for the hydroformylation of diisobutylene with pre-distillation. The subject of the invention is a process for the hydroformylation of diisobutylene, in which the diisobutylene stream used is distilled prior to the hydroformylation in such a way that the stream to be hydroformylated is enriched in 2, 4, 4-trimethylpent-1-ene. The hydroformylation is carried out with synthesis gas in the presence of a homogeneous catalyst system comprising at least Co or Rh and optionally a phosphorus-containing ligand.

Description

Technical Field

[0001] The invention relates to a process for the hydroformylation of diisobutene, wherein the diisobutene stream used is distilled before the hydroformylation so that the stream to be hydroformylated is enriched in 2,4,4-trimethylpent-1-ene. The hydroformylation is carried out with synthesis gas in the presence of a homogeneous catalyst system comprising at least Co or Rh and optionally a phosphorus-containing ligand. Background Art

[0002] 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

[0003] The object of the present invention is therefore a process for subjecting a stream to hydroformylation which does not have the abovementioned problems. In particular, the hydroformylation should be carried out using a diisobutene stream having a high proportion of 2,4,4-trimethylpent-1-ene.

[0004] 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.

[0005] The present invention describes a process for the hydroformylation of diisobutylene, wherein the process comprises at least the following steps:

[0006] 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;

[0007] b. supplying the top stream to hydroformylation, whereby 2,4,4-trimethylpent-2-ene and 2,4,4-trimethylpent-1-ene react in a reaction zone with synthesis gas in the presence of a homogeneous catalyst system comprising at least Co or Rh and optionally a phosphorus-containing ligand to obtain a liquid product mixture, wherein the liquid product mixture comprises at least aldehydes formed by hydroformylation, the homogeneous catalyst system and unreacted 2,4,4-trimethylpent-2-ene and 2,4,4-trimethylpent-1-ene;

[0008] c. separating the homogeneous catalyst system from the liquid product mixture to obtain a crude product mixture comprising at least the aldehyde formed by hydroformylation and unreacted 2,4,4-trimethylpent-2-ene and 2,4,4-trimethylpent-1-ene;

[0009] d. subjecting the crude product mixture to a distillative work-up in at least one distillation column to separate unreacted 2,4,4-trimethylpent-2-ene and unreacted 2,4,4-trimethylpent-1-ene, wherein unreacted 2,4,4-trimethylpent-2-ene and 2,4,4-trimethylpent-1-ene are separated and recycled to the hydroformylation in step b.

[0010] An advantage of the process is the distillation of the diisobutene stream before the hydroformylation, since this makes it possible to increase the proportion of 2,4,4-trimethylpent-1-ene in the top stream of the at least one distillation column compared to the stream used. Thus, it is possible to achieve 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, which is advantageous for the downstream hydroformylation for the reasons stated (2,4,4-trimethylpent-1-ene has a higher reactivity).

[0011] 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.

[0012] 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 may 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.

[0013] 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.

[0014] 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.

[0015] 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.

[0016] 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.

[0017] 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.

[0018] 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.

[0019] 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.

[0020] 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.

[0021] 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.

[0022] As is well known, distillation columns are heated at the bottom to be able to perform the separation task. Energy can be provided here by heating steam, which is usually provided at the chemical production site. For this purpose, part of the bottoms is conducted through a heat exchanger (bottom evaporator), heated there, and then returned to the bottoms of the distillation column. In order to reduce energy demand and / or CO2 emissions, heat integration can be designed in the distillation in step a. Heat integration means that the energy formed or present in the method is used in other locations. 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 present invention, heat integration is carried out in step a. so that at least a part of the condensation energy at the top is used to heat the bottom.

[0023] 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.

[0024] 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.

[0025] The top stream obtained from the distillation in step a is supplied to the subsequent hydroformylation 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. The isomerization can thus 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.

[0026] 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.

[0027] 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.

[0028] 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.

[0029] 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.

[0030] 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.

[0031] 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.

[0032] 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.

[0033] 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.

[0034] 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.

[0035] 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.

[0036] 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.

[0037] 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.

[0038] 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.

[0039] 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.

[0040] 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.

[0041] 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.

[0042] 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.

[0043] As described above, the top stream obtained by the distillation in step a is supplied to the subsequent hydroformylation step b, and reacted therein.

[0044] In step b, diisobutylene, i.e., 2,4,4-trimethylpent-2-ene and 2,4,4-trimethylpent-1-ene, reacts with synthesis gas (a mixture of carbon monoxide (CO) and hydrogen (H2)) to form aldehydes. The number of carbon atoms in the aldehyde increases by 1 carbon atom compared to the diisobutylene used. Thus, an aldehyde having 9 carbon atoms, i.e., trimethylhexanal, is produced from diisobutylene (8 carbon atoms).

[0045] The synthesis gas used in the process according to the invention can be used in different mixing ratios of carbon monoxide and hydrogen. The molar ratio between the synthesis gas and the hydrocarbon stream used, which contains the olefins to be hydroformylated, 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 further solvents known to those skilled in the art, but preferably no further solvents are used, but rather the olefins used serve as solvent in the hydroformylation.

[0046] The homogeneous catalyst system that can be used for hydroformylation can comprise Co or Rh, preferably Rh, and optional phosphorus-containing ligand. The corresponding catalyst system is familiar to those skilled in the art. Preferably, phosphorus-containing ligand is used. In a particularly preferred embodiment, the homogeneous catalyst system comprises Rh and phosphorus-containing ligand or is composed of Rh and phosphorus-containing ligand. Suitable ligands for catalyst system of the present invention are known to those skilled in the art. The phosphorus-containing ligand for catalyst system of the present invention is preferably phosphine (for example TPP (triphenylphosphine), monophosphite (for example Alkanox 240 (tris (2,4-di-tert-butylphenyl) phosphite)) or diphosphite (for example Biphephos). For example, a mixture of ligands can also be used.

[0047] The temperature during the homogeneously catalyzed hydroformylation is preferably 80 to 250° C., further preferably 90 to 225° C. and particularly preferably 100 to 210° C. The pressure in the homogeneously catalyzed hydroformylation is preferably 100 to 350 bar, more preferably 175 to 325 bar and particularly preferably 200 to 300 bar.

[0048] The pressure during the hydroformylation generally corresponds to the total gas pressure. In the context of the present invention, the total gas pressure is the sum of the existing pressures of all gaseous substances present, i.e. the pressure of the (entire) gas phase. In the present process, this corresponds in particular to the sum of the partial pressures of CO and H2, i.e. the total gas pressure is now the synthesis gas pressure.

[0049] Homogeneous catalytic hydroformylation can be operated as a liquid discharge process ("liquid recycle") or as a gas discharge process ("gas recycle"). Both process variants are known to those skilled in the art and are described in many textbooks. In the context of the present invention, it is not necessary to specifically select such a method, because the method can be carried out in two ways in principle. The most important thing in homogeneous catalysis is the separation of the catalyst system from the reaction discharge. In the case of liquid discharge, this can be carried out, for example, by flash evaporation or membrane separation. In the case of gaseous discharge, this is carried out, for example, by condensation and / or washing. This is also known to those skilled in the art and does not need to be explained in detail. The further post-treatment of the reaction discharge, in particular the separation of the reaction products, is also familiar to those skilled in the art and can be carried out, for example, by thermal separation methods such as distillation. Thermal separation or thermal separation method in the sense of the present invention refers to a separation method in which separation is carried out by means of boiling point.

[0050] By the hydroformylation described in step b, a liquid product mixture is obtained, which contains at least the aldehyde formed by the hydroformylation, the homogeneous catalyst system and unreacted diisobutylene, namely 2,4,4-trimethylpent-2-ene and 2,4,4-trimethylpent-1-ene.

[0051] The product mixture thus obtained is supplied to the subsequent step c, to separate the homogeneous catalyst system from the liquid product mixture. Before supplying the product mixture, low-boiling components, such as low-boiling by-products, can be separated, for example, by thermal separation (flash, distillation, etc.), for which reason it may be necessary to reduce the pressure of the product mixture under high pressure.

[0052] In a preferred embodiment of the present invention, the product mixture is further cooled to a temperature of 40 to 100° C., preferably 50 to 95° C., particularly preferably 60 to 90° C., before the membrane separation in step c. Suitable cooling devices are required for this purpose. In particular, cooling is carried out using an effluent cooler. For example, tube bundle heat exchangers have proven useful, in which the reaction mixture is preferably conducted through the tubes and the cooling medium is preferably conducted through the jacket of the heat exchanger.

[0053] The cooling of the product mixture ensures a reduction in the catalyst metal utilization factor. The problem is that during the hydroformylation and the subsequent separation, a small amount of metal, especially rhodium, is always lost in various ways. Due to the high price of the metals used, especially the metal, this increases the process costs, because the losses must be compensated by re-dosing. However, the cooling according to the invention now has the effect of reducing the utilization factor, i.e. less catalyst metal, especially rhodium, is lost, and therefore less re-dosing is required. In this way, the process costs can be significantly reduced.

[0054] Separating the homogeneous catalyst system in step c to obtain a crude product mixture can be carried out by various separation methods, such as by thermal separation and / or by membrane separation. The corresponding method is familiar to those skilled in the art. Preferably, thermal separation is first carried out, such as evaporation, and then membrane separation is carried out. During evaporation, the main product aldehyde (trimethylhexanal) and unreacted diisobutylene overflow through the top as a crude product mixture. A high-boiling phase is formed at the bottom, which contains a homogeneous catalyst, trimethylhexanal and a high-boiling substance that may be formed. Then the high-boiling phase can be subjected to membrane separation to discharge possible high-boiling substances. It is well known that retentate and permeate are produced during membrane separation. The permeate can be supplied to further post-processing.

[0055] The retentate comprises the homogeneous catalyst system. According to the invention, the retentate is preferably recycled to the hydroformylation in step b or to the reaction zone in which the hydroformylation is carried out. The catalyst system can thus be reused. In the preferred continuous process of the claimed method, a catalyst loop is thus formed, wherein only a small amount of catalyst losses (if any) related to the process need to be compensated. When the diisobutylene stream and the homogeneous catalyst system are mixed according to a preferred embodiment before the hydroformylation in step b, in particular in a suitable mixing vessel, the retentate is supplied to the mixing vessel.

[0056] Any suitable membrane material can be used for the membrane separation. In the membrane separation after evaporation in the process according to the invention, preference is given to using OSN membrane materials (OSN=organic solvent nanofiltration). 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.

[0057] The membrane separation after evaporation is preferably carried out at a temperature of 25° C. to 100° C., more 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 preferably present for membrane separation, 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 according to the invention.

[0058] 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 40 to 50 bar. The permeate side pressure can be higher than atmospheric pressure, preferably up to 15 bar, preferably 2 to 7 bar. The difference between TMP and the permeate side pressure produces the retentate side pressure. In a preferred embodiment, the pressure ratio and especially the permeate side pressure should be carefully adjusted to avoid evaporation after passing through the membrane. Evaporation may lead to unstable operation.

[0059] In the subsequent step d, the crude product mixture is worked up by distillation in at least one distillation column to separate unreacted diisobutylene. An aldehyde product comprising the aldehyde formed is obtained. The aldehyde product comprises the aldehyde formed from diisobutylene, namely trimethylhexanal.

[0060] In the distillative workup of the crude product mixture in step d, unreacted diisobutene is obtained at the top of the at least one distillation column. Thus, the aldehyde product is produced at the bottom of the at least one distillation column. The top stream containing the unreacted diisobutene separated in the at least one distillation column is recycled to the hydroformylation in step b. If the components used are mixed before the hydroformylation, 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.

[0061] The distillative work-up for separating off unreacted diisobutene in step d can be carried out in one distillation column. It is conceivable that the distillative work-up for separating off unreacted diisobutene in step d is carried out in a plurality of distillation columns. However, this means that the equipment expenditure would be significantly greater. Therefore, the distillative work-up in step d is preferably carried out in a single distillation column.

[0062] 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. DETAILED DESCRIPTION

[0063] 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.

[0064] 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 a hydroformylation (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 2,4,4-trimethylpent-2-ene and 2,4,4-trimethylpent-1-ene as stream (10), which is recycled to the hydroformylation (5).

[0065] Figure 2 Another 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 process for the hydroformylation of diisobutylene, wherein the process 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, 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 a residue stream being depleted in 2,4,4-trimethylpent-1-ene compared to the diisobutylene stream used; b. supplying the overhead stream to hydroformylation, whereby 2,4,4-trimethylpent-2-ene and 2,4,4-trimethylpent-1-ene react in a reaction zone with synthesis gas in the presence of a homogeneous catalyst system comprising at least Co or Rh and optionally a phosphorus-containing ligand to obtain a liquid product mixture, wherein the liquid product mixture comprises at least aldehyde formed by hydroformylation, the homogeneous catalyst system and unreacted 2,4,4-trimethylpent-2-ene and 2,4,4-trimethylpent-1-ene; c. separating the homogeneous catalyst system from the liquid product mixture to obtain a crude product mixture comprising at least the aldehyde formed by hydroformylation and unreacted 2,4,4-trimethylpent-2-ene and 2,4,4-trimethylpent-1-ene; d. Subjecting the crude product mixture to a distillative work-up in at least one distillation column to separate unreacted 2,4,4-trimethylpent-2-ene and unreacted 2,4,4-trimethylpent-1-ene, wherein unreacted 2,4,4-trimethylpent-2-ene and 2,4,4-trimethylpent-1-ene are separated and recycled to the hydroformylation in step b.

2. The process according to claim 1, wherein the residual stream in step a) is withdrawn as a bottom stream or a side stream of the at least one distillation column.

3. The process according to claim 1 , 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 in the residual stream, while the proportion of 2,4,4-trimethylpent-1-ene is higher than that in the residual stream.

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

6. The process according to claim 3 , wherein the input stream comprising 2,4,4-trimethylpent-2-ene and 2,4,4-trimethylpent-1-ene, which feeds the process, is supplied to the distillation unit in step a together with the isomerization stream and / or 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 produced by sulfonation of phenol / aldehyde condensates or by sulfonation of copolymers of aromatic vinyl compounds.

11. The process according to claim 1, wherein the hydroformylation in step b is carried out at a temperature of 90 to 250°C, preferably 120 to 200°C, particularly preferably 120 to 170°C.

12. The process according to any one of the preceding claims, wherein the hydroformylation in step b is carried out at a pressure of 100 to 350 bar, preferably 175 to 325 bar, more preferably 200 to 300 bar.

13. 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 thermal separation and / or membrane separation.

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

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