Energy-efficient method for oligomerizing olefins

Abstract

The present invention relates to a method for oligomerizing C2 to C8 olefins in at least two reaction stages, each comprising at least one reactor and at least one distillation column, and a subsequent separation stage comprising at least one distillation column, wherein reaction heat and / or the condensation energy is utilized with the aid of a heat transfer medium.

Description

[0001] Energy-efficient process for the oligomerization of olefins

[0002] The invention relates to a process for the oligomerization of C2 to C8 olefins in at least two reaction stages, each comprising at least one reactor and at least one distillation column, and a subsequent separation stage comprising at least one distillation column, wherein reaction heat and / or the condensation energy is utilized by means of a heat transfer medium.

[0003] Generally speaking, oligomerization is the reaction of unsaturated hydrocarbons with themselves, resulting in longer-chain hydrocarbons, known as oligomers. For example, the oligomerization of two olefins with three carbon atoms (propene) can produce an olefin with six carbon atoms (hexene). The oligomerization of two molecules with each other is also called dimerization.

[0004] The resulting oligomers are intermediates used, for example, in the production of aldehydes, carboxylic acids, and alcohols. The oligomerization of olefins is carried out on an industrial scale either in the homogeneous phase over a dissolved catalyst, heterogeneously over a solid catalyst, or with a two-phase catalyst system.

[0005] Processes for the oligomerization of olefins are well known in the art and are used on a large industrial scale. Production volumes in Germany alone amount to several thousand kilotons per year. To enable the highest possible conversion rates and the most continuous operation of oligomerization processes, industrial plants usually have not just one but several reaction stages connected in series, each comprising at least one reactor. This allows the oligomerization process to continue operating even if one reaction stage fails.

[0006] A reaction stage further comprises at least one distillation column to separate the oligomers formed from the olefins used. The feed olefin-containing stream is taken overhead as distillate, and the oligomer depleted in feed olefins is discharged via the bottoms. In industrial plants, the separation of the resulting oligomers after the reaction requires large amounts of energy, for example, in the form of heating steam to heat the distillation columns. Aside from the high costs of providing the heating steam, this process results in high CO2 emissions. Furthermore, problems can arise if the reaction conversion is to be increased. To increase conversion and ensure sustainable utilization of the feed stream, the oligomer-depleted stream, which is taken off at the top of the distillation column, can be at least partially recycled to the first reaction stage.However, this stream must be reprocessed in the column after conversion, resulting in additional energy consumption in the form of heating steam. The object of the present invention was to provide a process for the oligomerization of olefins that eliminates the aforementioned problems. The process should be able to be operated more cost-effectively and economically, and also be more resource-efficient when possible measures to increase conversion are implemented.

[0007] This object was achieved by the process according to the invention for the oligomerization of C2 to C8 olefins according to claim 1. Preferred embodiments are specified in the subclaims.

[0008] The process according to the invention is a process for the oligomerization of C2 to C8 olefins in at least two reaction stages R1 and RL, each comprising at least one reactor and at least one distillation column, and a separation stage A1 following RL, which comprises at least one distillation column DKA1, wherein a feed mixture containing at least the C2 to C8 olefins as reactants is subjected to oligomerization in the at least one reactor of the first reaction stage R1 using a heterogeneous catalyst and the reaction mixture obtained from the at least one reactor is distilled in the at least one distillation column DKR1 of the first reaction stage R1, whereby a residual stream RS1 containing at least unreacted reactants and an oligomerizate O1 containing at least the oligomers formed are obtained,

[0009] RS1 is at least partially fed to a reactor of a subsequent reaction stage; a residual stream from a previous reaction stage is subjected to oligomerization in the at least one reactor of the last reaction stage RL using a heterogeneous catalyst, and the reaction mixture obtained from the at least one reactor is distilled in the at least one distillation column DKRL of the last reaction stage RL, whereby a residual stream RSL containing at least unreacted reactant derivatives and an oligomerizate OL containing at least the oligomers formed are obtained;

[0010] OL is at least partially passed to the distillation column DKA1 of the subsequent separation stage A1 and distilled there, whereby a dimer stream D1, which consists of at least 90 wt.% of dimers of the reactants used, and a bottom stream S1, which contains at least trimers and higher oligomers of the reactants used, are obtained; the dimer stream D1 is obtained at the top of the DKA1, is condensed and then partly recycled as reflux to the DKA1 and partly discharged from the process, the energy generated during the condensation of the dimer stream D1 and the heat energy generated in the at least one reactor of the first reaction stage R1 are at least partly transferred to a liquid or gaseous heat transfer medium W1, whereby a heated heat transfer medium W1.1 is formed; and

[0011] Energy is transferred from the heated heat carrier W1.1 to another liquid or gaseous heat carrier W2, whereby a heated heat carrier W2.1 is created, which is first compressed and / or heated and via which a steam stream is then generated by means of a single- or multi-stage compression, with which at least the distillation columns DKA1 and DKR1 are heated.

[0012] For the purposes of the present invention, the term "reaction stage" refers to a plant section comprising at least one reactor and at least one distillation column. A reaction stage can therefore comprise one or more reactors and one or more distillation columns following the reactor(s). In a preferred embodiment, only one distillation column is present per reaction stage, following the reactor(s). It is further preferred that at least two reactors, particularly preferably exactly two reactors, are arranged in a reaction stage. The reactors can be connected in parallel or in series.

[0013] In the distillation columns of the respective reaction stages, the oligomers produced are separated from the remaining reactor output stream, which includes, for example, alkanes and unreacted olefins. The oligomers have a higher boiling point than the unreacted olefins and other substances present in the reactor output stream and are therefore concentrated in the bottom of the distillation column, while the lower boiling unreacted olefins and any analogous alkanes present in the feed stream pass overhead from the distillation column and are concentrated in the distillate.

[0014] The advantage of the process according to the invention is that the use of the heat transfer media according to claim 1 or according to the preferred embodiments allows for significant savings in externally supplied energy, primarily in the form of heating steam. This allows the process to be operated more cost-effectively and with lower CO2 emissions.

[0015] The feed mixture for the process according to the invention contains at least the C2 to C8 olefins, preferably C3 to C6 olefins, furthermore preferably C3 to C5 olefins, particularly preferably C4 olefins and their analogous alkanes. Suitable olefins include α-olefins, n-olefins, and cycloalkenes, preferably n-olefins. In a preferred embodiment, the olefin is n-butene.

[0016] The olefins are typically not used in pure form as reactants, but rather in industrially available mixtures. The term "feed mixture" additionally used in this invention is therefore to be understood as referring to any type of mixture containing the corresponding olefins to be oligomerized in an amount that allows the oligomerization to be carried out economically. The feed mixtures used according to the invention preferably contain virtually no other unsaturated compounds and polyunsaturated compounds such as dienes or acetylene derivatives. Preference is given to using feed mixtures containing less than 5% by weight, in particular less than 2% by weight, of branched olefins, based on the olefin content.

[0017] Propylene is produced on an industrial scale by cracking naphtha and is a readily available commodity chemical. C5 olefins are present in light gasoline fractions from refineries or crackers. Technical mixtures containing linear C4 olefins are light gasoline fractions from refineries, C4 fractions from FC or steam cracker fields, mixtures from Fischer-Tropsch syntheses, mixtures from the dehydrogenation of butanes, and mixtures formed by metathesis or other technical processes. For example, mixtures of linear butenes suitable for the process according to the invention can be obtained from the C4 fraction of a steam cracker. In the first step, butadiene is removed. This occurs either by extraction (distillation) of the butadiene or its selective hydrogenation. In both cases, a virtually butadiene-free C4 cut is obtained, the so-called raffinate I. In the second step, isobutene is removed from the C4 stream, e.g.by producing MTBE by reaction with methanol. The now isobutene- and butadiene-free C4 fraction, known as raffinate II, contains the linear butenes and, if present, butanes. If at least some of the 1-butene contained in it is also separated, raffinate III is obtained.

[0018] In a preferred embodiment, C4-olefin-containing streams are fed as feed mixtures in the process according to the invention. Suitable C4-olefin mixtures are, in particular, raffinate I, raffinate II, and raffinate III.

[0019] With C4-olefin mixtures as feed stream, the following particularly preferred process results: Process for the oligomerization of butenes in at least two reaction stages R1 and RL, each comprising at least one reactor and at least one distillation column, and a separation stage A1 following RL, which comprises at least one distillation column DKA1, wherein a feed mixture which contains at least butenes as reactant olefins is subjected to oligomerization in the at least one reactor of the first reaction stage R1 using a heterogeneous catalyst and the reaction mixture obtained from the at least one reactor is distilled in the at least one distillation column of the first reaction stage R1, whereby a residual stream RS1 which contains at least unreacted butenes and an oligomerizate O1 which contains at least the oligomers formed are obtained,

[0020] RS1 is at least partially fed to a reactor of a subsequent reaction stage; a residual stream from a previous reaction stage is subjected to oligomerization in the at least one reactor of the last reaction stage RL using a heterogeneous catalyst, and the reaction mixture obtained from the at least one reactor is distilled in the at least one distillation column of the last reaction stage RL, whereby a residual stream RSL containing at least unreacted butenes and an oligomerizate OL containing at least the oligomers formed are obtained;

[0021] OL is at least partially passed to the distillation column DKA1 of the subsequent separation stage A1 and distilled there, whereby a dimer stream D1 , which consists of at least 90 wt. % of C8 oligomers, and a bottom stream S1 , which contains at least C12 oligomers and higher oligomers of the butenes used, are obtained; the dimer stream D1 is obtained at the top of the DKA1, is condensed and then partly recycled as reflux to the DKA1 and partly discharged from the process, the energy generated during the condensation of the dimer stream D1 and the thermal energy generated in the at least one reactor of the first reaction stage R1 are at least partly transferred to a heat transfer medium W1, whereby a heated heat transfer medium W1 .1 is formed; and

[0022] Energy is transferred from the heated heat carrier W1.1 to another heat carrier W2, whereby a heated heat carrier W2.1 is created, which is first compressed and / or heated and via which a steam stream is then generated by means of a single- or multi-stage compression, with which at least the distillation columns DKA1 and DKR1 are heated.

[0023] The process according to the invention comprises at least two reaction stages R1 and RL. The reaction stage R1 is the first reaction stage and RL means the last reaction stage. In a preferred embodiment of the present invention, at least one further reaction stage, which likewise comprises at least one reactor and at least one distillation column, is present between the reaction stage R1 and the reaction stage RL. In a further preferred embodiment of the present invention, at least two further reaction stages, each comprising at least one reactor and at least one distillation column, are present between the reaction stage R1 and the reaction stage RL. In a particularly preferred embodiment, the process for oligomerization comprises a maximum of five reaction stages, ieBetween reaction stage R1 and reaction stage RL, there are at least three further reaction stages, each comprising at least one reactor and at least one distillation column. In all cases, it is possible for one of the reaction stages to comprise several reactors, while in a preceding or subsequent reaction stage only one reactor is present. Accordingly, the process according to the invention can be carried out in at least one further reaction stage R2, wherein reaction stage R2 comprises at least one reactor and at least one distillation column DKR2. It is preferred if the vapor stream used to heat distillation columns DKA1 and DKR1 is also used to heat distillation column DKR2. This would make it possible to avoid the need to use an additional externally sourced energy source.

[0024] In the aforementioned case, a residual stream RS2 containing at least the unreacted reactants and an oligomerizate O2 containing at least the oligomers formed would be obtained at the DKR2. RS2 can then be recycled at least partially to the subsequent reaction stage and optionally at least partially to the at least one reactor of the at least one reaction stage R2. The oligomerizate O2 can be passed to the distillation column DKRL of the last reaction stage RL and / or to the distillation column DKA1 of the subsequent separation stage A1; preferably, the oligomerizate is passed to the distillation column DKRL of the last reaction stage RL.

[0025] In addition to reaction stage R2, a further reaction stage R3 may also be present. In this case, the process according to the invention is carried out in at least one further reaction stage R3, wherein reaction stage R3 comprises at least one reactor and at least one distillation column DKR3. It is preferred if the vapor stream used to heat distillation columns DKA1, DKR1, and DKR2 is also used to heat distillation column DKR3. This would make it possible to avoid the need for an additional external energy source.

[0026] In the aforementioned case, a residual stream RS3 containing at least the unreacted reactants and an oligomerizate O3 containing at least the oligomers formed would be obtained at DKR3. RS3 can then be at least partially recycled to the subsequent reaction stage and optionally to at least one reactor of the at least one reaction stage R3. Oligomerizate O3 can be passed to distillation column DKRL of the last reaction stage RL and / or to distillation column DKA1 of the subsequent separation stage A1.

[0027] The oligomerization of olefins is an exothermic reaction, i.e., a reaction that releases heat. The heat released during the oligomerization of butenes arises primarily from the isomerization of 1-butene to cis- or trans-2-butene. The reactor(s) in the respective reaction stages of the process according to the invention can be operated isothermally or adiabatically, preferably isothermally. In a preferred embodiment, only the reactor(s) of the last reaction stage is / are operated adiabatically, while all other reactors of the previous reaction stage(s) are operated isothermally, in particular are actively cooled. A cooling medium known to those skilled in the art, for example cooling water, can be used. In the context of the present invention, "isothermal" means that the temperature rise in the reactor does not exceed 10 K despite cooling. This corresponds to isothermal operation of the reactors.Based on a cooling capacity of 100% for the reactor(s) in the first reaction stage, the cooling capacity in the reactor(s) of the subsequent reaction stages is less than 100%, but not 0%, except in the last reaction stage.

[0028] According to the invention, the feed mixture, which contains at least the olefins used, is subjected to oligomerization in the at least one reactor of the first reaction stage R1 using a heterogeneous catalyst.

[0029] As the at least one reactor in the first reaction stage R1, all reactors known to the person skilled in the art that are suitable for oligomerization can be used, for example tubular reactors, fixed-bed reactors, tube-bundle reactors, settler-riser reactors or slurry reactors. Preference is given to tubular reactors and / or tube-bundle reactors. If the reaction stage has multiple reactors, the reactors may be the same or different from one another. The reactors in a reaction stage may also vary in their structure or design. The first reactor in a reaction stage may, for example, have a larger volume than the subsequent reactor in the same reaction stage. It is also possible for the reactors in the individual reaction stages to be the same or different from one another. It is also possible for the reactors in the individual reaction stages to differ in their structure or design.For example, the reactor in the first reaction stage may have a larger volume than one or all of the reactors in the subsequent reaction stages.

[0030] According to the invention, it is preferred that reaction stage R1 comprises at least one further reactor, which is connected in parallel or in series with the first reactor, preferably in series. The output from the first reactor preferably passes into the second reactor without prior separation of the oligomers. It is therefore preferred that the reactants are not fully converted in the first reactor. The reaction heat generated in the second reactor during oligomerization is preferably also transferred to the heat transfer medium W1.

[0031] One or more reactors in reaction stage R1 each contain a heterogeneous catalyst for carrying out the oligomerization. In principle, any catalyst suitable for oligomerization can be used. Suitable catalysts are known to those skilled in the art from the literature. The catalyst used is in particular in the form of granules, extrudates, or tablets.

[0032] The heterogeneous catalyst in the at least one reactor R1 preferably comprises a nickel compound, preferably nickel oxide, on an aluminosilicate support material. However, the heterogeneous catalyst preferably contains, based on the total composition of the oligomerization catalyst, less than 0.5% by weight, even more preferably less than 0.1% by weight, particularly preferably less than 0.01% by weight of titanium dioxide and / or zirconium dioxide. The support material can be an amorphous, mesoporous aluminosilicate, a crystalline, microporous aluminosilicate, or an aluminosilicate having amorphous and crystalline phases. "Amorphous" in the context of the present invention refers to the property of a solid which results from the fact that, unlike crystalline solids, the solid has no crystal structure, i.e., no long-range order.

[0033] The heterogeneous catalyst preferably has a composition of 15 to 40 wt.%, preferably 15 to 30 wt.% NiO, 5 to 30 wt.% Al2O3, 55 to 80 wt.% SiO2, and 0.01 to 2.5 wt.%, preferably 0.05 to 2 wt.% of an alkali metal oxide, preferably sodium oxide. The data relate to a total composition of 100 wt.%. The oligomerization catalyst is preferably substantially free of titanium dioxide and zirconium dioxide; in particular, the oligomerization catalyst contains less than 0.5 wt.%, preferably less than 0.1 wt.%, particularly preferably less than 0.01 wt.% of titanium dioxide and zirconium dioxide in its total composition.

[0034] The preparation of an oligomerization catalyst can be carried out by the known methods of impregnation, in which the support material is treated with a solution of a transition metal compound, especially a nickel compound, and then calcined, or by coprecipitation, in which the entire catalyst composition is precipitated from a single, usually aqueous solution. The oligomerization catalyst can also be prepared by other methods familiar to the person skilled in the art. A hydrothermal treatment can also be used during preparation, in which the still-moist catalyst is kept at elevated temperature before being subjected to drying.

[0035] The oligomerization can be carried out in one or all reactors of the final reaction stage RL at a temperature in the range from 50 to 200°C, preferably 60 to 180°C, more preferably in the range from 60 to 130°C. The pressure in each of the reaction stages present can be from 10 to 70 bar, preferably from 20 to 55 bar. In a preferred embodiment of the present invention, the oligomerization is carried out in the liquid phase in each reaction stage. If the oligomerization is to take place in the liquid phase, the pressure and temperature parameters must be selected such that the feed mixture (the olefins or olefin mixtures used) is in the liquid phase.

[0036] During the oligomerization in the at least one reactor of reaction stage R1, a reaction mixture is formed which is withdrawn from the at least one reactor. The reaction mixture obtained from the at least one reactor is distilled in the at least one distillation column DKR1 of the first reaction stage R1, resulting in a residual stream RS1 which contains at least unreacted olefins, and an oligomerizate O1 which contains at least the oligomers formed. Consequently, the distillation separates at least a portion of the oligomers formed from the unreacted olefins. The energy required for the separation of the reaction mixture is introduced in particular by at least one bottom evaporator.

[0037] According to the invention, bottom evaporators are evaporators that heat the bottom of the distillation column. Such a bottom evaporator is usually located outside the respective distillation column. Since energy, in particular heat, is transferred from one stream to another in bottom evaporators, they act as heat exchangers. The stream to be evaporated is withdrawn via an outlet at the bottom of the distillation column and fed to the bottom evaporator. The evaporated stream, optionally with a residual liquid portion, is returned to the respective distillation column in the bottom region via at least one inlet.

[0038] Suitable evaporators that can be used as bottom evaporators include natural circulation evaporators, forced circulation evaporators, forced circulation evaporators with expansion, kettle evaporators, falling-film evaporators, or thin-film evaporators. A tube bundle or plate apparatus is typically used as the heat exchanger for the evaporator in natural circulation evaporators and forced circulation evaporators. In addition to the above, any other evaporator design known to those skilled in the art that is suitable for use in a distillation column can also be used.

[0039] According to the invention, it is preferred that the reaction mixture be preheated before being introduced into the distillation column DKR1. This has the advantage that not all of the energy needs to be introduced via the at least one bottom evaporator. Furthermore, preheating enables an increase in capacity because the hydraulic load in the distillation column is reduced.

[0040] The reaction mixture is preferably preheated in a heat exchanger. Preheating can be carried out using heat exchangers known to those skilled in the art. Suitable evaporators that can be used as heat exchangers include, for example, natural circulation evaporators, forced circulation evaporators, forced circulation evaporators with expansion, kettle evaporators, falling-film evaporators, or thin-film evaporators. In addition to the aforementioned evaporators, any other evaporator design known to those skilled in the art that is suitable for the desired preheating can also be used.

[0041] Any distillation column known to the person skilled in the art can be used as the at least one distillation column DKR1 for distilling the reaction mixture. Preferably, the distillation column of the first reaction stage R1 contains internals. Suitable internals include, for example, trays, unstructured packings (random packing), or structured packings. Trays typically used are bubble-cap trays, sieve trays, valve trays with fixed or movable valves, tunnel trays, or slotted trays. Unstructured packings are generally random packings. Raschig rings, Pall rings, Berl saddles, SuperRings / SuperRings Plus, or Intalox® saddles are typically used as packings. Structured packings are marketed, for example, under the trade name Mellapak® by Sulzer. In addition to the internals mentioned, other suitable internals are known to the person skilled in the art and can also be used.

[0042] Preferred internals exhibit a low specific pressure drop per theoretical plate. Structured packings and random packings, for example, have a significantly lower pressure drop per theoretical plate than trays. This has the advantage of keeping the pressure drop in the distillation column of the first reaction stage R1 as low as possible.

[0043] In a particularly preferred embodiment of the present invention, the distillation column of the first reaction stage R1 comprises a plurality of trays, preferably between 5 and 100 trays, further preferably between 10 and 50 trays.

[0044] The distillation conditions, such as temperature and pressure, are usually determined by the structure (column height, number of trays, type of trays or packing, spacing, etc.). During operation, the separation properties of the distillation can still be controlled via the temperature distribution and / or the heat input in the column and the reflux in the distillate. Likewise, the separation properties can be adjusted within certain limits by changing the pressure. The exact settings cannot therefore be defined overridingly and independently of the structure of the distillation column. This is known to those skilled in the art. In a preferred embodiment, the pressure during distillation is in the range from 1 to 6 bar absolute, more preferably in the range from 2 to 5 bar absolute. The temperature at the top of the distillation column is furthermore preferably in the range from 15 to 60 °C, more preferably in the range from 25 to 50 °C.

[0045] Distillation of the reaction mixture produces a residual stream RS1, which contains at least unreacted olefins, and an oligomerizate 01, which contains at least the oligomers formed. The residual stream RS1 is generally obtained at the top of the distillation column DKR1. The oligomerizate 01 then occurs at the bottom of the distillation column DKR1.

[0046] The residual stream RS1 is at least partially fed to a reactor of a subsequent reaction stage. The subsequent reaction stage can be reaction stage RL. In this case, there are only two reaction stages in total. However, the subsequent reaction stage can also be a reaction stage present between reaction stage R1 and reaction stage RL. In this case, there are at least three reaction stages. Embodiments are also possible in which more than two reaction stages are present between reaction stage R1 and reaction stage RL. According to the invention, it is preferred that at least one further reaction stage, which comprises at least one reactor and at least one distillation column, is present between reaction stage R1 and reaction stage RL.

[0047] It is further preferred that the residual stream RS1 be at least partially recycled to the at least one reactor of reaction stage R1. This recycling to the residual stream allows the feed mixture to be diluted.

[0048] In a preferred embodiment of the present invention, the residual stream RS1 is separated into at least two substreams RS1a and RS1b. The substream RS1b can then be recycled to the reactor of the first reaction stage R1. It is further preferred that the substream RS1a is compressed, thereby producing a stream VR1 that is more compressed than the residual stream RS1, and that energy from the compressed stream VR1 is used to preheat the reaction mixture upstream of the DKR1 and / or to preheat the feed mixture upstream of the oligomerization. Preheating can therefore also be achieved by means of heat-integrating measures, in this case vapor recompression, which eliminates the need for external energy in the form of heating steam. Here, only electrical energy needs to be used for compression.

[0049] The compression of the partial stream RS1a can be carried out in any desired manner known to those skilled in the art. For example, compression can be carried out mechanically and in a single-stage or multi-stage process. In this context, "single-stage" means that compression takes place from one pressure level to another. "Multi-stage" means that compression occurs first to a pressure level X and then from X to pressure level Y. With multi-stage compression, several compressors of the same design or compressors of different designs can be used. Multi-stage compression can be carried out with one or more compressor machines. The use of single-stage compression or multi-stage compression depends on the compression ratio and thus on the pressure to which the partial stream RS1a is to be compressed.

[0050] Any compressor known to the person skilled in the art, preferably a mechanical compressor with which gas streams can also be compressed, is suitable as a compressor in the process according to the invention, particularly for compressing partial stream RS1a. Suitable compressors include single- or multi-stage geared turbocompressors, piston compressors, screw compressors, centrifugal compressors, or axial compressors.

[0051] It has already been mentioned that, in a preferred embodiment, the process comprises at least one second reaction stage R2, wherein a reaction mixture is obtained in the at least one reactor and is separated in the distillation column DKR2. It is particularly preferred that energy from the compressed stream VR1 is also used to preheat the reaction mixture upstream of the DKR2. After preheating, the partial stream RS1a can be at least partially condensed and then at least partially passed as a feed mixture to the at least one reactor of the second reaction stage R2.

[0052] Oligomerizate 01 contains the formed oligomers. In a preferred embodiment, oligomerizate 01 is passed at least partially, preferably completely, to the distillation column of the final reaction stage RL. All oligomerizates can be collected there and then passed together to the separation stage A1. In addition, any remaining unreacted olefins can be separated there.

[0053] Regardless of how many reaction stages are present, the residual stream from the previous reaction stage is fed to the last reaction stage RL. This can be at least a portion of the residual stream RS1 from the first reaction stage R1, but could also be a different residual stream if there is at least one further reaction stage between R1 and RL. In this respect, a residual stream from a previous reaction stage is fed to at least one reactor of the last reaction stage RL. This residual stream can be the residual stream RS1 if there is no further reaction stage between the two reaction stages R1 and RL. If there is at least one reaction stage between the reaction stage R1 and the reaction stage RL, the residual stream from one of these reaction stages, the penultimate reaction stage, is fed to the last reaction stage RL.

[0054] According to the invention, the supplied residual stream is subjected to oligomerization in the at least one reactor of the last reaction stage RL using a heterogeneous catalyst.

[0055] As the at least one reactor in the first reaction stage RL, all reactors known to the person skilled in the art that are suitable for oligomerization can be used, for example tubular reactors, fixed-bed reactors, tube bundle reactors, settler-riser reactors or slurry reactors. Preference is given to tubular reactors and / or tube bundle reactors. If the reaction stage has multiple reactors, the reactors may be the same or different from one another. The reactors in a reaction stage may also vary in their structure or design. The first reactor in a reaction stage may, for example, have a larger volume than the subsequent reactor in the same reaction stage. It is also possible for the reactors in the individual reaction stages to be the same or different from one another. It is also possible for the reactors in the individual reaction stages to differ in their structure or design.For example, the reactor in the first reaction stage may have a larger volume than one or all of the reactors in the subsequent reaction stages.

[0056] According to the invention, it is preferred that reaction stage R1 comprises at least one further reactor, which is connected in parallel or in series with the first reactor, preferably in series. The output from the first reactor preferably passes into the second reactor without prior separation of the oligomers. It is therefore preferred that the reactants are not fully converted in the first reactor. The reaction heat generated in this further reactor can also be integrated via a heat transfer medium, as already described for the first reactor.

[0057] One or more reactors of reaction stage RL each contain a heterogeneous catalyst for carrying out the oligomerization. In principle, any catalyst suitable for oligomerization can be used. Suitable catalysts are known to those skilled in the art from the literature. The catalyst used is in particular in the form of granules, extrudates, or tablets.

[0058] The heterogeneous catalyst in the at least one reactor of reaction stage RL preferably comprises a nickel compound, preferably nickel oxide, on an aluminosilicate support material. However, the heterogeneous catalyst preferably contains, based on the total composition of the oligomerization catalyst, less than 0.5% by weight, even more preferably less than 0.1% by weight, particularly preferably less than 0.01% by weight of titanium dioxide and / or zirconium dioxide. The support material can be an amorphous, mesoporous aluminosilicate, a crystalline, microporous aluminosilicate, or an aluminosilicate having amorphous and crystalline phases. "Amorphous" in the context of the present invention refers to the property of a solid which results from the fact that, unlike crystalline solids, the solid has no crystal structure, i.e., no long-range order.

[0059] The heterogeneous catalyst in the at least one reactor of reaction stage RL preferably has a composition of 15 to 40 wt.%, preferably 15 to 30 wt.% NiO, 5 to 30 wt.% Al2O3, 55 to 80 wt.% SiO2, and 0.01 to 2.5 wt.%, preferably 0.05 to 2 wt.% of an alkali metal oxide, preferably sodium oxide. The data relate to a total composition of 100 wt.%. The oligomerization catalyst is preferably substantially free of titanium dioxide and zirconium dioxide; in particular, the oligomerization catalyst contains less than 0.5 wt.%, preferably less than 0.1 wt.%, particularly preferably less than 0.01 wt.% titanium dioxide and zirconium dioxide in its total composition.

[0060] The preparation of an oligomerization catalyst can be carried out by the known methods of impregnation, in which the support material is treated with a solution of a transition metal compound, in particular a nickel compound, and then calcined, or coprecipitation, in which the entire catalyst composition is precipitated from a single, usually aqueous solution. The oligomerization catalyst can also be prepared by other methods familiar to the person skilled in the art. A hydrothermal treatment can also be carried out during preparation, in which the still-moist catalyst is kept at elevated temperature before the catalyst is subjected to drying. The oligomerization is carried out in the reactor(s) of the final reaction stage preferably at a temperature in the range of 50 to 200°C, preferably 60 to 180°C, more preferably in the range of 60 to 130°C.The pressure can range from 10 to 70 bar, preferably from 20 to 55 bar. In a preferred embodiment of the present invention, the oligomerization is carried out in the liquid phase in each reaction stage. If the oligomerization is to take place in the liquid phase, the pressure and temperature parameters must be selected such that the feed mixture (the olefins or olefin mixtures used) is in the liquid phase.

[0061] During the oligomerization in the at least one reactor of the reaction stage RL, a reaction mixture is formed which is removed from the at least one reactor. The reaction mixture obtained from the at least one reactor is distilled in the at least one distillation column DKRL of the last reaction stage RL, whereby a residual stream RSL, which contains at least unreacted olefins, and an oligomerizate OL, which contains at least the oligomers formed, are obtained. By means of the distillation, at least a portion of the oligomers formed is separated from the unreacted olefins. In addition to the reaction mixture, the oligomerizates from the previous reaction stages, for example the oligomerizate 01, can also be worked up in the distillation column DKRL. The energy required for the separation of the reaction mixture is introduced in particular by at least one bottom evaporator.

[0062] According to the invention, bottom evaporators are evaporators that heat the bottom of the distillation column. Such a bottom evaporator is usually located outside the respective distillation column. Since energy, in particular heat, is transferred from one stream to another in bottom evaporators, they act as heat exchangers. The stream to be evaporated is withdrawn via an outlet at the bottom of the distillation column and fed to the bottom evaporator. The evaporated stream, optionally with a residual liquid portion, is returned to the respective distillation column in the bottom region via at least one inlet.

[0063] Suitable evaporators that can be used as bottom evaporators include natural circulation evaporators, forced circulation evaporators, forced circulation evaporators with expansion, kettle evaporators, falling-film evaporators, or thin-film evaporators. A tube bundle or plate apparatus is typically used as the heat exchanger for the evaporator in natural circulation evaporators and forced circulation evaporators. In addition to the above, any other evaporator design known to those skilled in the art that is suitable for use in a distillation column can also be used.

[0064] According to the invention, it is preferred that the reaction mixture is preheated before being introduced into the distillation column DKRL. This has the advantage that not all of the energy needs to be introduced via the at least one bottom evaporator. Furthermore, preheating enables an increase in capacity because the hydraulic load in the distillation column is reduced. The reaction mixture is preferably preheated in a heat exchanger. Preheating can be carried out using heat exchangers known to those skilled in the art. Suitable evaporators that can be used as heat exchangers include, for example, natural circulation evaporators, forced circulation evaporators, forced circulation evaporators with expansion, kettle evaporators, falling-film evaporators, or thin-film evaporators. In addition to those mentioned, any other evaporator design known to those skilled in the art that is suitable for use for the desired preheating can also be used.

[0065] Any distillation column known to the person skilled in the art can be used as the at least one distillation column DKRL for distilling the reaction mixture from the reactor of the last reaction stage RL. The distillation column DKRL of the last reaction stage RL preferably contains internals. Suitable internals include, for example, trays, unstructured packings (random packing), or structured packings. Trays typically used are bubble-cap trays, sieve trays, valve trays with fixed or movable valves, tunnel trays, or slotted trays. Unstructured packings are generally random packings. Raschig rings, Pall rings, Berl saddles, SuperRings / SuperRings Plus, or Intalox® saddles are typically used as packings. Structured packings are marketed, for example, under the trade name Mellapak® by Sulzer. In addition to the internals mentioned, other suitable internals are known to the person skilled in the art and can also be used.

[0066] Preferred internals exhibit a low specific pressure drop per theoretical plate. Structured packings and random packings, for example, have a significantly lower pressure drop per theoretical plate than trays. This has the advantage of keeping the pressure drop in the distillation column of the first reaction stage (RL) as low as possible.

[0067] In a particularly preferred embodiment of the present invention, the distillation column DKRL comprises a plurality of trays, preferably between 5 and 100 trays, further preferably between 10 and 50 trays.

[0068] The distillation conditions, such as temperature and pressure, are usually determined by the structure (column height, number of trays, type of trays or packing, spacing, etc.). During operation, the separation properties of the distillation can still be controlled via the temperature distribution and / or the heat input in the column and the reflux in the distillate. Likewise, the separation properties can be adjusted within certain limits by changing the pressure. The exact settings cannot therefore be defined at a higher level and independently of the structure of the distillation column. This is known to those skilled in the art. The pressure during distillation is preferably in the range of 1 to 6 bar absolute, more preferably in the range of 2 to 5 bar absolute.The distillation of the reaction mixture and any oligomers present from previous stages produces a residual stream (RSL), which contains at least unreacted olefins, and an oligomer (OL), which contains at least the oligomers formed. The residual stream (RSL) is generally obtained at the top of the distillation column (DKRL). The oligomer (OL) is then obtained at the bottom of the distillation column (DKRL).

[0069] The residual stream RL can be at least partially recycled to one or more reactors of the same reaction stage or the previous reaction stage(s). At least a partial stream can also be removed as purge to prevent the accumulation of inert alkanes or impurities. If at least a partial stream is removed as purge and thus removed from the process, this partial stream can be used as a synthesis raw material for further processes (e.g., hydroformylation, C source for arc in acetylene production), as combustion gas, or after full hydrogenation to the alkanes, as propellant gas, as cooking gas, or similar.

[0070] The oligomer OL contains the formed oligomers. The formed oligomers generally include at least dimers, trimers, and tetramers. However, higher oligomers may also be present in the oligomer in very small amounts. The resulting oligomer is therefore subjected to further processing in separation stage A1 to separate the dimers, trimers, and tetramers.

[0071] The oligomer OL is thus at least partially passed to the distillation column DKA1 of the separation stage A1 and distilled there, producing a dimer stream D1 which, based on the total weight of the dimer stream D1, consists of at least 90% by weight, preferably at least 95% by weight, particularly preferably at least 99% by weight, of dimers of the olefins used, and a bottom stream S1 which contains at least trimers and higher oligomers of the olefins used. Preferably, the oligomer OL is passed completely to the distillation column DKA1 of the separation stage A1.

[0072] The bottom stream S1, which contains at least trimers and higher oligomers of the reactants used, can be broken down into further oligomers in one or more subsequent distillation steps, which are then converted into valuable products such as aldehydes or alcohols. The oligomers from the dimer stream D1 can then each be subjected to further processing, for example, hydroformylation, alkoxycarbonylation, or hydrogenation. The dimers of butenes, C8 olefins, can be converted into an isononanal mixture by hydroformylation. This isononanal mixture yields either the corresponding carboxylic acids by oxidation or a C9 alcohol mixture by hydrogenation. The C9 carboxylic acids can be used to produce lubricants or siccatives.The C9 alcohol mixture is a precursor for the production of plasticizers, in particular di-isononyl phthalates (DINP), DINCH (1,2-di-isononylcyclohexanedicarboxylic acid ester) or DINCD (1,4-di-isononylcyclohexanedicarboxylic acid ester). The energy required for the separation of the oligomer OL in the distillation column DKA1 is introduced in particular by at least one bottom evaporator. According to the invention, bottom evaporators are referred to as evaporators that heat the bottom of the distillation column. Such a bottom evaporator is usually arranged outside the respective distillation column. Since energy, in particular heat, is transferred from one stream to another in bottom evaporators, they are heat exchangers. The stream to be evaporated is withdrawn via an outlet at the bottom of the distillation column and fed to the bottom evaporator.The evaporated stream is returned to the respective distillation column in the bottom region via at least one inlet, possibly with a residual portion of liquid.

[0073] Suitable evaporators that can be used as bottom evaporators include natural circulation evaporators, forced circulation evaporators, forced circulation evaporators with expansion, kettle evaporators, falling-film evaporators, or thin-film evaporators. A tube bundle or plate apparatus is typically used as the heat exchanger for the evaporator in natural circulation evaporators and forced circulation evaporators. In addition to the above, any other evaporator design known to those skilled in the art that is suitable for use in a distillation column can also be used.

[0074] Any distillation column known to the person skilled in the art can be used as the at least one distillation column DKA1 for the distillation of the oligomer OL. Distillation column DKA1 of separation stage A1 preferably contains internals. Suitable internals include, for example, trays, unstructured packings (random packings), or structured packings. Trays typically used are bubble-cap trays, sieve trays, valve trays with fixed or movable valves, tunnel trays, or slotted trays. Unstructured packings are generally random packings. Raschig rings, Pall rings, Berl saddles, SuperRings / SuperRings Plus, or Intalox® saddles are typically used as packings. Structured packings are marketed, for example, under the trade name Mellapak® by Sulzer. In addition to the internals mentioned, other suitable internals are known to the person skilled in the art and can also be used.

[0075] Preferred internals exhibit a low specific pressure drop per theoretical plate. Structured packings and random packings, for example, have a significantly lower pressure drop per theoretical plate than trays. This has the advantage of keeping the pressure drop in the distillation column of the first reaction stage (RL) as low as possible.

[0076] In a particularly preferred embodiment of the present invention, the distillation column DKA1 comprises a plurality of trays, preferably between 5 and 100 trays, more preferably between 10 and 50 trays. The distillation conditions, for example temperature and pressure, are usually determined by the structure (column height, number of trays, type of trays or packing, spacing, etc.). During operation, the separation properties of the distillation can also be controlled via the temperature distribution and / or the heat input in the column and the reflux in the distillate. Likewise, the separation properties can be adjusted within certain limits by changing the pressure. The precise settings cannot therefore be defined overridingly and independently of the structure of the distillation column. This is known to the person skilled in the art.

[0077] The dimer stream D1, which arises at the top of the DKA1, is condensed and then partially recycled to the DKA1 as reflux and partially discharged from the process. The energy generated during the condensation of the dimer stream D1 and the thermal energy generated in at least one reactor of the first reaction stage R1 are at least partially transferred to a heat transfer medium W1, thereby producing a heated heat transfer medium W1.1.

[0078] The condensation of the dimer stream D1 can take place in any condenser known to those skilled in the art, which is designed as a heat exchanger to transfer the condensation heat energy to the liquid or gaseous heat transfer medium W1. Possible heat exchangers that can be used include, for example, natural circulation evaporators, forced circulation evaporators, forced circulation evaporators with expansion, kettle evaporators, falling-film evaporators, or thin-film evaporators. In a preferred embodiment, a kettle evaporator is used as the heat exchanger, in whose tubes the dimer stream D1 condenses and in whose shell the heat transfer medium is heated.

[0079] Any working medium familiar to the person skilled in the art can be used as heat transfer medium W1 in the process according to the invention. The heat transfer medium W1 is preferably selected from the group consisting of water; alcohols; alcohol-water mixtures; salt-water solutions; ammonia; mineral oils, such as diesel oils; thermal oils, such as silicone oils; biological oils, such as limonene; and aromatic or aliphatic hydrocarbons, such as dibenzyltoluene. Preference is given to using water, methanol, ethanol, propanol, n-pentane, n-butane, n-hexane, n-propane, or ammonia as heat transfer medium W1. Water is particularly preferably used as heat transfer medium W1.

[0080] If the heat transfer medium W1 is used in the liquid phase, i.e., a liquid heat transfer medium W1, and energy, preferably heat, is supplied to it, the heat transfer medium W1 is at least partially evaporated, thereby producing an at least partially gaseous heat transfer medium W1.1. If the heat transfer medium W1 is used in the gaseous phase, i.e., a gaseous heat transfer medium W1, and energy, preferably heat, is supplied to it, a gaseous heat transfer medium W1.1 is also obtained.

[0081] In a preferred embodiment of the present invention, the separation stage A1 comprises at least one further distillation column DKA2 for distilling the bottom stream S1, with which trimers are separated from the higher oligomers. The trimers would be discharged as a stream at the top of the

[0082] Distillation column DKA2. The higher oligomers are therefore produced in the bottom of the DKA2.

[0083] Any distillation column known to the person skilled in the art can be used as the at least one distillation column DKA2 for distilling the bottom stream S1. Preferably, the distillation column DKA2 of the separation stage A1 contains internals. Suitable internals include, for example, trays, unstructured packings (random packings), or structured packings. Trays typically used are bubble-cap trays, sieve trays, valve trays with fixed or movable valves, tunnel trays, or slotted trays. Unstructured packings are generally random packings. Raschig rings, Pall rings, Berl saddles, SuperRings / SuperRings Plus, or Intalox® saddles are typically used as packings. Structured packings are marketed, for example, under the trade name Mellapak® by Sulzer. In addition to the internals mentioned, other suitable internals are known to the person skilled in the art and can also be used.

[0084] Preferred internals exhibit a low specific pressure drop per theoretical plate. Structured packings and random packings, for example, have a significantly lower pressure drop per theoretical plate than trays. This has the advantage of keeping the pressure drop in the distillation column of the first reaction stage (RL) as low as possible.

[0085] In a particularly preferred embodiment of the present invention, the distillation column DKA2 comprises a plurality of internals, preferably between 5 and 80 separation stages, further preferably between 10 and 40 separation stages.

[0086] The distillation conditions, such as temperature and pressure, are usually determined by the structure (column height, number of trays, type of trays or packing, spacing, etc.). During operation, the separation properties of the distillation can still be controlled via the temperature distribution and / or the heat input in the column and the reflux in the distillate. Likewise, the separation properties can be adjusted within certain limits by changing the pressure. The precise settings cannot therefore be defined at a higher level and independently of the structure of the distillation column. This is known to those skilled in the art. The pressure during distillation is preferably in a vacuum, more preferably in the range from 100 to 800 mbar, more preferably in the range from 200 to 700 mbar, particularly preferably 300 to 500 mbar.

[0087] The overhead stream arising from DKA2 is preferably condensed and then preferably partially recycled to DKA2 as reflux and partially discharged from the process. The energy generated during the condensation of the overhead stream from DKA2 is particularly preferably additionally transferred at least partially to a heat transfer medium W1. The energy from the heated heat transfer medium W1.1 is then transferred to another heat transfer medium W2, creating a heated heat transfer medium W2.1, which is initially compressed and / or heated and then, by means of single- or multi-stage compression, generates a vapor stream with which at least the distillation columns DKA1 and DKR1 are heated.

[0088] First, energy, in particular thermal energy, is transferred from the heat transfer medium W1.1 to the heat exchanger W2. Any working medium familiar to the person skilled in the art can be used as the heat transfer medium W2 in the process according to the invention. The heat transfer medium W2 is preferably selected from the group consisting of water; alcohols; alcohol-water mixtures; salt-water solutions; ammonia; mineral oils, such as diesel oils; thermal oils, such as silicone oils; biological oils, such as limonene; and aromatic or aliphatic hydrocarbons, such as dibenzyltoluene. Preference is given to using water, methanol, ethanol, propanol, n-pentane, n-butane, n-hexane, n-propane or ammonia as the heat transfer medium W2. Particular preference is given to using water and / or methanol as the heat transfer medium W2.

[0089] If the heat transfer medium W2 is used in the liquid phase, i.e., a liquid heat transfer medium W2, and energy, preferably heat, is supplied to it, the heat transfer medium W2 is at least partially evaporated, thereby producing an at least partially gaseous heat transfer medium W2.1. If the heat transfer medium W2 is used in the gaseous phase, i.e., a gaseous heat transfer medium W2, and energy, preferably heat, is supplied to it, a gaseous heat transfer medium W2.1 is also obtained.

[0090] The transfer of energy from W1.1 to W2 can be carried out using methods known to those skilled in the art or using heat exchangers known to those skilled in the art, for example, the evaporators already mentioned. Suitable evaporators that can be used as heat exchangers include natural circulation evaporators, forced circulation evaporators, forced circulation evaporators with expansion, boiler evaporators, falling-film evaporators, or thin-film evaporators. In addition to the aforementioned methods, any other evaporator design known to those skilled in the art can also be used, provided that it ensures the desired energy transfer.

[0091] The heat transfer media W1 and W2 can, in principle, be the same or different from each other. This means that it is fundamentally possible for the heat exchanger W1 and the heat exchanger to be the same liquid or gas. It is equally possible for the two heat transfer media W1 and W2 to be different. Both process variants are described below.

[0092] According to the invention, the heated heat transfer medium W2.1 is first compressed and / or heated in order to then generate a vapor stream by means of single- or multi-stage compression. Heating can be carried out, for example, by means of the evaporators already described. Compression can be carried out in any desired manner known to those skilled in the art, as already described above. In a particularly preferred embodiment of the present invention, methanol is used as the heat transfer medium W2. By transferring energy from the heated heat transfer medium W1.1, the methanol is brought to a higher pressure and / or a higher temperature (and referred to as W2.1) and then compressed in one or more stages, preferably in several stages. The subsequent compression produces the compressed heat transfer medium W2.2, here methanol.

[0093] The compression of methanol as W2.1, for example, can be carried out mechanically and in a single-stage or multi-stage process. Single-stage in this context means that compression occurs from one pressure level to another. Multi-stage means that compression occurs first to a pressure level X and then from X to pressure level Y. With multi-stage compression, several compressors of the same type or compressors of different types can be used. Multi-stage compression can be carried out with one or more compressor machines. The use of single-stage compression or multi-stage compression depends on the compression ratio and thus on the pressure to which the heat transfer medium W2.1 is to be compressed.

[0094] In the present case, the methanol as W2.1 is brought to a pressure in the range of 3 to 30 bar, preferably 5 to 20 bar, preferably 7 to 15 bar, by single- or multi-stage compression to W2.2.

[0095] Any compressor known to the person skilled in the art, preferably a mechanical compressor, with which gas streams can be compressed is suitable as a compressor in the process according to the invention, in particular for compressing methanol as the heat transfer medium W2.1. Suitable compressors include, for example, single- or multi-stage geared turbocompressors, piston compressors, screw compressors, centrifugal compressors, or axial compressors.

[0096] In an equally particularly preferred embodiment of the present invention, water is used as the heat transfer medium W2, which is present in a slight vacuum in the range between 300 and 800 mbar. Due to the energy transfer from the heated heat transfer medium W1.1, the water is at least partially evaporated (and referred to as W2.1). The partially evaporated water as W2.1 is preferably brought to a higher pressure via a single- or multi-stage, preferably multi-stage, blower, i.e. compressed, and is obtained as sludge steam. The compression described produces the compressed heat transfer medium W2.2, here sludge steam. The resulting sludge steam is preferably used to heat or preheat the feed streams to the distillation columns.

[0097] Regardless of which heat transfer medium is used as heat transfer medium W2, a heated heat transfer medium W2.1 will always be produced, which is compressed and produced as compressed heat transfer medium W2.2. In a further preferred embodiment of the present invention, energy is then transferred from the compressed heat transfer medium W2.2 to a further heat transfer medium W3, preferably water, thereby producing a heated heat transfer medium W3.1 which is compressed in one or more stages, preferably in more stages, and is then used as a vapor stream to heat at least the distillation columns DKA1 and DKR1, preferably all of the distillation columns present in the reaction stages and all of the separation stage. Furthermore, the vapor stream generated by the heat integration described according to the invention can also be used additionally to heat the distillation column DKA2, provided that this distillation column is present.

[0098] The heat transfer medium W3, preferably water, is compressed in one or more stages, preferably in multiple stages. Through this single- or multi-stage compression, the heat transfer medium W3 is brought to a pressure in the range of 5 to 40 bar, preferably 10 to 30 bar, preferably 12 to 25 bar, and in this range it exists as vapor. If multi-stage compression is used, water condensate is preferably injected between the compressor stages to prevent overheating during compression.

[0099] Heat transfer media W1, W2, and W3 are all used to transfer energy, particularly energy in the form of heat. The respective energy transfer will reduce the temperature and / or pressure, resulting in at least partial condensation. Heat transfer media W1, W2, and W3 preferably form their own circuit, meaning the heat transfer media are returned after the energy transfer so that energy can be collected again.

[0100] When returning the heat transfer fluids, these heat transfer fluids can be used to heat the heat transfer fluid in the circuit before compression. For example, heat transfer fluid W2.2 could transfer additional energy to W2.1 before compression after the energy transfer. Known heat exchangers can be used for this purpose.

[0101] The present invention is described with reference to the drawings described below. The drawings merely represent examples of suitable embodiments and do not limit the subject matter of the invention.

[0102] Fig. 1 shows a non-inventive circuit for oligomerization with subsequent separation of the oligomers. The feed mixture is first fed to the first reaction stage (R1), where oligomerization takes place in reactor (1) and the subsequent separation of the reaction mixture in the distillation column DKR1 (2) takes place. The residual stream obtained at the top of the distillation column DKR1 (2) is at least partially condensed in a condenser (3) and then partly fed back to the reactor (1) and to the next reaction stage (RX). RX in this example would be RL in the sense of the present invention. The oligomerizate 01 is fed to the distillation column DKRX (6). The energy for the separation in the distillation column DKR1 (2) is introduced via a bottom evaporator (4). The residual stream fed to the next reaction stage RX is converted in the reactor (5). The resulting reaction mixture is separated in the distillation column DKRX (6).In this example, DKRX would correspond to DKRL. The residual stream obtained at the top of the distillation column DKRX (6) is at least partially condensed in a condenser (7) and then at least partially returned to the reactor (5). The energy for the separation in the distillation column DKRX (6) is introduced via a bottom evaporator (8). The oligomer OL obtained in the bottom is passed to separation stage A1, where the oligomers are separated in the distillation column DKA1 (9). The dimer stream D1 is obtained at the top and is at least partially condensed in a heat exchanger (10). The energy for the separation in the distillation column DKA1 (9) is introduced via a bottom evaporator (11).

[0103] Fig. 2 also shows a non-inventive oligomerization circuit. In addition to the process shown in Fig. 1, there is an additional vapor compression step, in which the residual stream accumulating at the top of the distillation column DKR1 (2) is compressed in a compressor (13) and subsequently used to heat the reaction mixture in a preheater (14). During recirculation from the preheater (14), the stream is preheated upstream of the compressor (13) in a further preheater (12).

[0104] Fig. 3 also shows a non-inventive oligomerization circuit. In addition to the process shown in Fig. 2, the residual stream compressed in the compressor (13) is used to heat the reaction mixture of reaction stage RX in a preheater (15).

[0105] Fig. 4 shows an inventive circuit for oligomerization. In addition to the process shown in Fig. 1, heat integration takes place according to the present invention. The heat of condensation at the distillation column DKA1 (9) is removed via the heat exchanger (10) and the heat of reaction from the reactor (1) is removed via the heat exchanger (16) by means of a heat transfer medium A. Using the heat transfer medium A thus heated, another heat transfer medium B is heated in an evaporator (17) and subjected to multi-stage compression in a compressor (19). The compressed heat transfer medium B is then used to heat another heat transfer medium C, for example water, in an evaporator (20). When the heat transfer medium B is returned, a flash tank (23) can be interposed, in which the gas phase arising there is conveyed between the compression stages of the compressor (19).The liquid discharge from the flash tank (23) can be used in a heat exchanger (18) to preheat the heat transfer medium B prior to compression. The heat transfer medium C is also compressed in several stages in a compressor (21) and then used to heat the bottom evaporators (4 and 11). When returning the heat transfer medium C to the bottom evaporators, a flash tank (22) can be interposed, in which the gas phase arising there is conveyed between the compression stages of the compressor (21). The liquid discharge from the flash tank (22) is returned to the evaporator (20).

[0106] Fig. 5 also shows an inventive oligomerization circuit. In contrast to the process shown in Fig. 4, there are only two heat transfer media. Heat transfer media B is heated in the evaporator (17) and then compressed in the compressor (19), which is preferably a blower here. The compressed heat transfer media is fed to a flash tank (24). The gas phase obtained there is fed to a further compressor (21), compressed in several stages, and then used to heat the bottom evaporators (4 and 11). The liquid phase from the flash tank is at least partially returned to the evaporator (17) by means of a pump (25), but can also be fed between the compression stages of the compressor (17) or downstream of the compressor (21).

[0107] Fig. 6 also shows an inventive oligomerization circuit. In addition to the process shown in Fig. 5, there are two additional preheaters (26 and 27). These preheaters (26, 27) are operated directly with the gas phase from the flash vessel (24) as the energy source.

[0108] The following examples are intended to illustrate the invention without limiting its scope of application, which is apparent from the description and the claims.

[0109] Examples

[0110] All examples listed were simulated with Aspen Plus V.10. The kinetic model and material data were validated using operating data. All examples were simulated under the same boundary conditions. A butene content of 70 wt% was considered in the 40 t / h feed (25 wt% 1-butene, 30 wt% trans butene, and 15 wt% cis butene). The n / i-butane content was considered at 30 wt%, assuming 3% isobutane in the feed. The feed temperatures to the reaction stages were kept constant at 95°C in all cases.

[0111] Example 1 (not according to the invention)

[0112] A configuration as shown in Fig. 1 was used for the simulation. The fresh feed is mixed with a recyclate stream of 19 t / h and brought to a feed temperature of 95°C using a heat exchanger. The feed is passed through a reaction stage R1 (tubular reactor (1) with catalyst) at 25 bar abs. The reactor (1) is cooled to remove the reaction heat. A total of 4.2 MW must be removed. After the first reaction stage, the reaction mixture is subjected to distillative separation. The distillation column (2) is operated at a head pressure of 4.3 bar abs. The distillation column (2) preferably has a separation efficiency of less than 1 percent high boilers in the distillate so as not to inhibit the reaction too much. The resulting head temperature is 45°C. 13 trays are considered.To achieve purity, a return flow of 16 t / h and a heating capacity of 5.1 MW are required, which is provided by 20 bar steam (purchased externally). Condensation heat of 5.3 MW is generated, which is removed by an air cooler or a device operated with recooling water (3). Part of the liquid distillate is recycled to the first reaction stage (19 t / h), and the other part, 20 t / h (with a weight fraction of n / i-butane of 60%), to a further, final reaction stage RL. This stream is in turn mixed with a recyclate stream of 15 t / h and brought to a feed temperature of 95°C. A reactor (5) is used, which is identical to the reactor (1) of the first stage R1. Here, too, the reaction heat is removed via a process water circuit operated in cocurrent. 1 MW must be removed. The reaction mixture also undergoes a distillative separation here.The distillation column (6) has a total of 28 trays. A C8 content of less than 0.1 wt% is specified for the distillate from the second column. This requires a reflux of 2 t / h and a heating capacity of 2 MW, which is again supplied by external heating steam. 3 MW must be removed via the condenser (10). Column (9) is also operated at 4.3 abs., resulting in a head temperature of 44°C. The distillate stream is again divided. A portion (15 t / h) returns to the reaction stage, while the other portion (14.5 t / h) containing 82 wt% n / i-butane can be sent to another process unit or to a tank farm. A conversion of 90% can be achieved.

[0113] The C8 / C12 / C16+ oligomers are obtained in the bottom of the distillation column (6) and are subjected to further separation in the separation unit A1. In the distillation column (9), the C8 isomers (preferably 1-octene and 2-methylheptene) are separated from the longer-chain oligomers under vacuum at a head pressure of 350 mbar. To achieve a purity of preferably greater than 99%, a reflux rate of 14 t / h must be set. This results in a head temperature of 86°C. A total of 1.4 MW of heating capacity is required (external steam), and 3 MW of condensation heat must be removed.

[0114] A total of 11.3 MW of condensation heat and 5.2 MW of reaction heat are extracted from the system (16.5 MW in total). A total of 8.5 MW of heating power must be supplied to the system.

[0115] Example 2 (not according to the invention):

[0116] A circuit as shown in Fig. 2 was used for the simulation. The information from Example 1 also applies here. In addition, there is vapor recompression, in which the condensation heat is at least partially utilized via the compressor (13) and the heat exchangers (12, 14). In this example, the feed preheater (14) introduces 1.75 MW into the system. In order to bring the vapor stream to the required temperature level, an electrical power of 200 kW is required. Excessive energy input via the feed evaporator results in a shift in the temperature profile. High boilers are boiled to the top. More reflux is required. The total heating output increases to 5.75 MW. However, the external heating requirement is reduced to 4 MW at the first distillation column. Consequently, the total external heating output is reduced from 7.2 MW.

[0117] Example 3 (not according to the invention): A circuit as shown in Fig. 3 was used for the simulation. The information from Examples 1 and 2 also applies here. In addition to the feed preheater (14), the feed preheater (15) of the last stage is also operated via vapor compression. This adds a further 1.2 MW to the system. Overall, the heating output of the last stage increases to 2.4 MW, but the external heating output decreases to 1.2 MW. For this, an electrical output of 350 kW must be generated via the compressor. The total external heating output is 6.4 MW.

[0118] Example 4 (according to the invention):

[0119] A circuit as shown in Fig. 4 was used for the simulation. The information on the reaction stages and the separation stage from Example 1 also applies here. Here, the condensation heat of the vacuum distillation and the reaction heat of the first stage are at least partially transferred to a hot water circuit via heat exchangers (10, 16). The heat from the hot water circuit is then used to evaporate a heat transfer medium, in this case methanol, at 2.0 bar abs. in the evaporator (17). Methanol is subjected to multi-stage compression (19) to 10 bar abs. This requires an electrical output of 1.2 MW. The condensation of the methanol evaporates water at 3 bar abs. in the evaporator (20). The water vapor is subjected to multi-stage compression (21) to 20 bar abs. The compression to 20 bar abs. requires an electrical output of 1.6 MW. The steam is needed to heat the sump evaporators (4, 8, 11).A total of 8.5 MW of external heating capacity is replaced by 2.8 MW of electrical power. No external heating medium (steam) is required.

[0120] Example 5 (according to the invention):

[0121] A circuit as shown in Fig. 5 was used for the simulation. The information regarding the reaction stages and the separation stage from Example 1 and the further information from Example 4 also apply here. The circuit is identical to Example 4. Here, water is used as the heat transfer medium instead of methanol. Water is evaporated in a slight vacuum (550 mbar) and compressed to 3 bar abs in the compressor (19). This process requires more electrical power. A total of 3.1 MW of electrical power is required to replace 8.5 MW of external heating power (steam). Example 6 (according to the invention):

[0122] A configuration as shown in Fig. 5 was used for the simulation. The information regarding the reaction stages and the separation stage from Example 1, as well as the further information from Example 5, also applies here. It shows the optimization of Example 5. Here, the concept of the feed evaporators (26, 27) is used again (see Examples 2 and 3). In this example, the feed preheaters (26, 27) are operated with the generated 3 bar absolute steam, so that a smaller amount needs to be brought to the highest pressure level. The electrical power is reduced to 2.2 MW.

[0123] An overview of the results of examples 1 to 6 can be found in Table 1 :

[0124] Table 1 : Comparison of energy values ​​of all examples

Claims

Patent claims 1. A process for the oligomerization of C2 to C8 olefins in at least two reaction stages R1 and RL, each comprising at least one reactor and at least one distillation column, and a separation stage A1 following RL, which comprises at least one distillation column DKA1, wherein a feed mixture containing at least the C2 to C8 olefins as reactants is subjected to oligomerization in the at least one reactor of the first reaction stage R1 using a heterogeneous catalyst, and the reaction mixture obtained from the at least one reactor is distilled in the at least one distillation column DKR1 of the first reaction stage R1, whereby a residual stream RS1 containing at least unreacted reactants and an oligomerizate O1 containing at least the oligomers formed are obtained, RS1 is at least partially fed to a reactor of a subsequent reaction stage; a residual stream from a previous reaction stage is subjected to oligomerization in the at least one reactor of the last reaction stage RL using a heterogeneous catalyst, and the reaction mixture obtained from the at least one reactor is distilled in the at least one distillation column DKRL of the last reaction stage RL, whereby a residual stream RSL containing at least unreacted reactant derivatives and an oligomerizate OL containing at least the oligomers formed are obtained; OL is at least partially passed to the distillation column DKA1 of the subsequent separation stage A1 and distilled there, whereby a dimer stream D1 , which consists of at least 90 wt. % of dimers of the reactants used, and a bottom stream S1 , which contains at least trimers and higher oligomers of the reactants used, are obtained; the dimer stream D1 is obtained at the top of the DKA1, is condensed and then partly recycled as reflux to the DKA1 and partly discharged from the process, the energy generated during the condensation of the dimer stream D1 and the heat energy generated in the at least one reactor of the first reaction stage R1 are at least partly transferred to a liquid or gaseous heat transfer medium W1, whereby a heated heat transfer medium W1 .1 is formed; and Energy is transferred from the heated heat carrier W1 .1 to another liquid or gaseous heat carrier W2, creating a heated heat carrier W2.1, which is first compressed and / or heated and then, by means of a single- or multi-stage compression, a steam stream is generated with which at least the distillation columns DKA1 and DKR1 are heated.

2. Process according to claim 1, wherein RS1 is at least partially recycled to at least one reactor of reaction stage R1.

3. Process according to claim 1 or 2, wherein between the reaction stage R1 and the reaction stage RL there is at least one further reaction stage comprising at least one reactor and at least one distillation column.

4. Process according to one of the preceding claims, wherein the reaction stage R1 comprises at least one further reactor R1.2, which is connected in parallel or in series to the reactor R1.1, preferably connected in series.

5. The method according to claim 4, wherein the energy generated at the reactor 2.1 is also transferred at least partially to the heat transfer medium W1.

6. Process according to one of the preceding claims, wherein the process is carried out in at least one further reaction stage R2, wherein reaction stage R2 comprises at least one reactor R2.1 and at least one distillation column DKR2.

7. Process according to one of the preceding claims, wherein the vapor stream generated is also used to heat the distillation column DKR2.

8. The method according to any one of the preceding claims, wherein the heat transfer medium W1 is selected from the group consisting of water; alcohols, alcohol-water solutions; salt-water solutions; mineral oils, such as diesel oils; thermal oils, such as silicone oils; biological oils, such as limonene; and aromatic hydrocarbons, such as dibenzyltoluene.

9. The method according to any one of the preceding claims, wherein the heat transfer medium W2 is selected from the group consisting of water; alcohols, alcohol-water solutions; salt-water solutions; mineral oils, such as diesel oils; thermal oils, such as silicone oils; biological oils, such as limonene; and aromatic hydrocarbons, such as dibenzyltoluene.

10. Method according to one of the preceding claims, wherein the heated heat carrier W2.1 is compressed and is obtained as compressed heat carrier W2.

2.

11. Process according to claim 10, wherein energy is transferred from the compressed heat carrier W2.2 to a further heat carrier W3, whereby a heated heat carrier W3.1 is produced, which is compressed in one or more stages, preferably in several stages, and is then used as a vapor stream to heat all distillation columns present in the reaction stages and all in the separation stage.

12. The method according to claim 11, wherein the heat transfer medium W3.1 is brought to a pressure in the range of 5 to 40 bar, preferably 10 to 30 bar, preferably 12 to 25 bar by the single-stage or multi-stage compression.

13. Process according to one of the preceding claims, wherein the reaction mixture is preheated before being introduced into the distillation column DKR1.

14. A process for oligomerization according to any one of the preceding claims, wherein an oligomerization catalyst comprising a nickel compound on an aluminosilicate support material and preferably containing less than 0.5 wt.% of titanium dioxide and zirconium dioxide in its total composition is used in the reactors of the individual reaction stages.

15. A process for oligomerization according to any one of the preceding claims, wherein the process is a process for oligomerizing C3 to C6 olefins, preferably C3 to C5 olefins, particularly preferably C4 olefins.