Olefin oligomerization process with control of oligomer content in a hydrocarbon stream to be oligomerized

Abstract

The present invention relates to a process for the oligomerization of olefins with a control of the oligomer content in the hydrocarbon stream to be oligomerized. The subject of the invention is a process for the oligomerization of C3- to C5-olefins using a catalyst, wherein the oligomerization is carried out in at least one reaction stage comprising at least one reactor and at least one distillation column, and wherein, after separation of the oligomers in the at least one distillation column, the oligomer content in the feed stream to the at least one reaction stage is less than 0.4% by weight.

Description

Technical Field

[0001] The present invention relates to a process for the oligomerization of C3- to C5-olefins using a catalyst, wherein the oligomerization is carried out in at least one reaction stage comprising at least one reactor and at least one distillation column, and wherein, after separation of the oligomers in the at least one distillation column, the content of oligomers in the feed stream to the at least one reaction stage is less than 0.4% by weight. Background Art

[0002] Oligomerization is generally understood to mean the reaction of an unsaturated hydrocarbon with itself, resulting in the formation of longer-chain hydrocarbons, so-called oligomers. Thus, for example, an olefin with six carbon atoms (hexene) can be formed by oligomerizing two olefins with three carbon atoms (propylene). The oligomerization of two molecules with one another is also known as dimerization.

[0003] The oligomers obtained are intermediates for example for the preparation of aldehydes, carboxylic acids and alcohols.The oligomerization of olefins is carried out on a large scale homogeneously over dissolved catalysts or heterogeneously over solid catalysts or using two-phase catalyst systems.

[0004] Oligomerization processes for olefins are well known in the prior art and are used on a large scale. Production in Germany alone amounts to several thousand tons per year. The source of the olefins used in the oligomerization process is usually an olefin-containing fraction from a cracking process (e.g., a steam cracker or a fluidized catalytic cracker), which, in addition to the olefins, also contains the corresponding alkanes.

[0005] After the production of olefin oligomers in one or more reactors connected in series, the oligomers must be separated from the oligomerization reaction mixture (the oligomerization discharge), which also contains unreacted olefins and / or alkanes fed. This separation is usually carried out in at least one distillation column, with the unreacted olefins and / or alkanes being distilled off overhead and at least partially recycled into the reactor or reactors.

[0006] The purpose of separating oligomer from oligomerization reaction mixture is normally to produce the pure oligomerization reaction mixture that does not have the starting material composition and the pure stream of unreacted alkene and / or alkane that feeds intake, then correspondingly further use them.Yet the problem is, along with the raising of the purity of mentioned logistics, the cost and / or energy cost that is used for one or more knockout units, for example owing to the tower reflux that needs to improve, is obviously higher.In order to reduce costs, therefore usually do not isolate oligomer with pure form, but in separated oligomer stream, keep a small amount of starting material.This applies equally to the logistics of unreacted alkene and / or alkane that feeds intake, and they also comprise a certain amount of oligomer after separation.

[0007] If these feed olefins and / or paraffins and oligomer streams are recycled to the reactor, it is worth noting that the oligomer yield decreases on the one hand and the reaction rate in the oligomerization decreases on the other hand, the higher the proportion of recycled oligomers. Therefore, a certain degree of suppression of oligomerization must be considered. Summary of the Invention

[0008] It was therefore an object of the present invention to provide a process for the oligomerization of C3 to C5 olefins in which no significant reduction in the reaction rate, ie no significant inhibition, is observed and in which a cost-effective separation is nevertheless achieved.

[0009] It has been found that the described disadvantages (reduction in oligomer yield and reaction rate) occur precisely when oligomers are not sufficiently separated from the stream of unreacted feed olefins and / or alkanes. Therefore, according to the invention, the underlying object can be achieved in that the oligomer content of the feed stream to the reactor(s) of the at least one reaction stage(s) is less than 0.4% by weight, based on the total composition of the feed to the reactor(s) of the at least one reaction stage(s). The feed consists of recycled residual oligomerization reaction mixture, which has been separated from the oligomers formed by distillation, and a fresh feed of the feed mixture. This is reproduced in claim 1. Preferred embodiments of the process are given in the dependent claims.

[0010] The process according to the invention is therefore a process for the oligomerization of C3- to C5-olefins, preferably C4-olefins, wherein in at least one reaction stage, a feed mixture comprising C3- to C5-olefins, preferably C4-olefins, is oligomerized using a heterogeneous oligomerization catalyst comprising a nickel compound and a support material comprising aluminum oxide, silicon dioxide or an aluminosilicate, wherein each reaction stage consists of at least one reactor, in which the oligomerization is carried out to form an oligomerization reaction mixture, and at least one distillation column, in which the oligomers formed during the oligomerization are at least partly separated from the remaining oligomerization reaction mixture, wherein at least a portion of the remaining oligomerization reaction mixture, from which the oligomers have been separated, is recycled to the reactor(s) of the at least one reaction stage, and the oligomer content of the feed to the reactor(s) of the at least one reaction stage, based on the total composition of the feed, is less than 0.4% by weight, preferably ≤0.2% by weight, the feed to the reactor(s) of the at least one reaction stage consisting of the recycled remaining oligomerization reaction mixture and a fresh feed of the feed mixture.

[0011] The oligomer content can also be monitored, for example, by gas chromatography during continuous operation. To achieve a sufficient separation between oligomers and residual oligomerization mixture and thus achieve an oligomer content in the feed of less than 0.4% by weight, preferably ≤ 0.2% by weight, various measures can be taken, individually or in combination, such as using one or more larger distillation columns, better packing in one or more distillation columns, reduced loading on one or more distillation columns, or increased distillate reflux in one or more distillation columns. Furthermore, the oligomer content according to the present invention can also be achieved by adjusting the ratio of recycled residual oligomerization mixture to fresh feed (recycled residual oligomerization mixture / fresh feed). In principle, an oligomer content of less than 0.4% by weight, preferably ≤ 0.2% by weight, can also be achieved by recycling only a small amount of residual oligomerization mixture. In a preferred embodiment, the ratio of recycled residual oligomerization reaction mixture (in t / h) to fresh feed (in t / h) is from 0.001 to 30, preferably from 0.005 to 20, particularly preferably from 0.01 to 15.

[0012] For the purposes of the present invention, the term "reaction stage" refers to a plant section comprising one or more reactors and one or more distillation columns following the reactors. In a preferred embodiment, each reaction stage comprises only one distillation column. In this distillation column, the oligomers formed are separated from the oligomerization reaction mixture (corresponding to the output stream from the reactor), which contains, in addition to the oligomers, alkanes and unreacted olefins. Conventional process technology equipment that can be installed in these reaction stages, such as preheaters for the feed, heat exchangers, etc., are not listed separately here but are familiar to those skilled in the art.

[0013] The process according to the invention comprises at least one reaction stage. However, the process may also comprise at least two reaction stages, with preferably no more than five reaction stages being present. In a preferred embodiment, the oligomerization process thus comprises two, three, four, or five reaction stages. Each of these reaction stages independently comprises one or more reactors and one or more subsequent distillation columns to separate the formed oligomers from the remaining output stream from the reactors. However, it is also conceivable that one of the reaction stages comprises multiple reactors, while the preceding or subsequent reaction stage comprises only one reactor.

[0014] In a one-stage process with only one reaction stage, the oligomers formed in the reactor or reactors of the first reaction stage are separated from the remaining oligomerization mixture in the distillation column of the first reaction stage such that, when the remaining oligomerization mixture is at least partially mixed with fresh feed and fed to the reactor or reactors of this reaction stage, the oligomer content in the total feed to the reactor or reactors is less than 0.4% by weight, preferably ≤ 0.2% by weight. In a process with two or more reaction stages, the oligomer content in the feed streams to all reactors of all reaction stages is less than 0.4% by weight, preferably ≤ 0.2% by weight. In a process based on two or more reaction stages, the remaining oligomerization mixture from which the oligomers have been separated in the distillation column can be fed partially to the reactor or reactors of the same reaction stage and partially to the next reaction stage. In the final reaction stage, it is naturally not practical to at least partially feed the remaining oligomerization mixture to the next reaction stage. Besides recycling to the reactor of the same reaction stage and conducting it further to the next reaction stage, a portion of the remaining oligomerization reaction mixture can also be withdrawn, for example in order to prevent an accumulation of inert alkanes in the system.

[0015] The process according to the invention can generally be carried out as follows: Starting with a feed mixture containing C3- to C5-olefins, preferably C4-olefins. The feed mixture is first oligomerized in at least one reactor of a first reaction stage, and the resulting oligomerization mixture is passed to a distillation column, where the oligomers formed (preferably C6- to C24-olefins, particularly preferably C8- to C24-olefins) are separated as a bottom product from the remaining oligomerization mixture, which contains at least unreacted olefins and alkanes from the feed mixture and is obtained as a top product. Depending on the reaction stage, the remaining oligomerization mixture is then at least partially passed as a feed stream to the respective next reaction stage and partially recycled to the reactors of the same reaction stage, having previously been combined with a fresh feed consisting of a fresh feed mixture or with an oligomerization mixture from a previous stage depleted of oligomers. In the final reaction stage, after the oligomers have been separated, the remaining oligomerization mixture can be partially recycled to one of the reactors and at least partially discharged from the process. If the remaining oligomerization reaction mixture from the last reaction stage is discharged from the process described here, it can be used as a synthesis raw material for other processes (e.g. hydroformylation, C source for arc in acetylene production), as a combustion gas or, after complete hydrogenation to alkanes, as a propulsion gas / fuel gas (Treibgas), as a cooking gas, etc.

[0016] As olefins used in the process according to the invention, C3- to C5-olefins, preferably C4-olefins, or olefin mixtures based thereon, which may also contain proportions of similar alkanes, are used. Suitable olefins are, in particular, α-olefins, n-olefins, and cycloolefins, preferably n-olefins. In a preferred embodiment, the C4-olefin is n-butene.

[0017] The olefins are not used as starting materials in pure form usually, but are used in the form of industrially available mixtures. Therefore, the term feed mixture used in the present invention is understood to mean that it relates to any type of mixture containing the corresponding olefins for oligomerization in an amount that allows oligomerization to be carried out economically. Preferably, the feed mixture used according to the present invention does not actually comprise other unsaturated compounds and polyunsaturated compounds, such as diolefins or acetylene derivatives. Preferably, the feed mixture comprises a feed mixture that is less than 5 % by weight, especially less than 2 % by weight, of branched olefins based on the olefin ratio.

[0018] Propylene is produced on a large scale by cracking naphtha and is a readily available basic chemical. C5 olefins are contained in the light petroleum fractions from refineries or crackers. Industrial mixtures containing linear C4 olefins include light petroleum fractions from refineries, C4 fractions from FC or steam crackers, mixtures from Fischer-Tropsch synthesis, mixtures from butane dehydrogenation, and mixtures formed by metathesis or other industrial processes. For example, a mixture of linear butenes suitable for the process according to the present invention can be obtained from the C4 fraction of a steam cracker. In this process, butadiene is removed in a first step. This is achieved by extraction (extractive distillation) of butadiene or its selective hydrogenation. In both cases, a virtually butadiene-free C4 fraction, the so-called raffinate I, is obtained. In a second step, isobutene is removed from the C4 stream, for example by reacting it with methanol to produce MTBE. The C4 fraction, now free of isobutene and butadiene, the so-called raffinate 11, contains linear butenes and optionally butanes. If at least a portion of the 1-butene contained therein is also separated therefrom, the so-called raffinate III is obtained.

[0019] In a preferred embodiment, in the process according to the invention, a C4-olefin-containing substance stream is fed as feed mixture. Suitable C4-olefin-containing substance streams are, in particular, raffinate I, raffinate II and raffinate III.

[0020] As the reactor for each reaction stage, all reactors suitable for oligomerization known to those skilled in the art can be used, such as tubular reactors, tube bundle reactors, settler-riser reactors, and slurry reactors. Tubular reactors and / or tube bundle reactors are preferred. If a reaction stage has multiple reactors, these reactors may be identical or different from each other. The multiple reactors in a reaction stage may also vary in their structure or configuration. For example, the first reactor in a reaction stage may have a larger volume than the subsequent reactors in the same reaction stage. Similarly, if there are multiple reaction stages, the reactors in each reaction stage may be identical or different from each other. Here, the reactors in each reaction stage may also differ in their structure or configuration. 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.

[0021] The one or more reactors of each reaction stage each contain an oligomerization catalyst, in particular a heterogeneous oligomerization catalyst, for carrying out the oligomerization. In this case, the oligomerization catalyst is in particular in the form of granules, extrudates or tablets.

[0022] The (heterogeneous) oligomerization catalysts in the individual reactors of the reaction stage can each be independently selected from transition metal-containing oligomerization catalysts. The transition metal or the corresponding transition metal compound used is preferably disposed on a support material containing aluminum oxide, silicon dioxide, or an aluminosilicate, preferably an aluminosilicate support material. Particularly suitable transition metal compounds for the oligomerization catalyst according to the invention are compounds of nickel, cobalt, chromium, titanium, and tantalum. Nickel compounds and cobalt compounds are preferred, with nickel compounds being particularly preferred.

[0023] According to the present invention, the oligomerization catalyst comprises a nickel compound, preferably nickel oxide, and may use a support material comprising or consisting of aluminum oxide, silicon dioxide, or an aluminosilicate, preferably an aluminosilicate. The support material is preferably an amorphous mesoporous aluminosilicate, a crystalline microporous aluminosilicate, or an aluminosilicate having both amorphous and crystalline phases. "Amorphous" in the sense of the present invention refers to the property of a solid resulting from the lack of a crystalline structure, i.e., the absence of long-range order. However, within the meaning of the present invention, amorphous aluminosilicates having small crystalline domains are not excluded.

[0024] According to the present invention, it is further preferred that the oligomerization catalyst has a composition of 15 to 40% by weight, preferably 15 to 30% by weight, NiO, 5 to 30% by weight, Al2O3, 55 to 80% by weight, SiO2, and 0.01 to 2.5% by weight, preferably 0.05 to 2% by weight, of an alkali metal oxide, preferably sodium oxide. These figures are based on a total composition of 100% by weight. In a particularly preferred embodiment of the present invention, the oligomerization catalyst is substantially free of titanium dioxide and / or zirconium dioxide, in particular comprising less than 0.5% by weight, preferably less than 0.1% by weight, and particularly preferably less than 0.01% by weight of titanium dioxide and / or zirconium dioxide in its total composition.

[0025] The specific surface area of ​​the oligomerization catalyst (calculated according to BET) is preferably 150 to 700 m² / g, more preferably 190 to 600 m² / g, particularly preferably 220 to 550 m² / g. The BET surface area is measured by nitrogen physical adsorption in accordance with DIN-ISO 9277 (2014-01 edition).

[0026] If multiple reactors are present in a single reaction stage or in multiple reaction stages, multiple oligomerization catalysts are naturally also present. The oligomerization catalysts present in the individual reactors of a reaction stage can each be independently selected from the above-mentioned substances. The individual oligomerization catalysts in the reactors are not always identical, but rather differ in composition, possibly only to a minor extent. This is because, even if each reactor contains exactly the same catalyst composition upon initial startup of the process according to the invention, this composition may change over time during operation due to various factors over the years.

[0027] The preparation of the oligomerization catalyst can be carried out by known impregnation methods, in which the support material is loaded with a solution of a transition metal compound, in particular a solution of a nickel compound, and then calcined, or by coprecipitation, whereby the entire catalyst composition is precipitated from a single, generally aqueous solution. The oligomerization catalyst can also be prepared by other methods well known to those skilled in the art.

[0028] The oligomerization can be carried out in each of the existing reaction stages at a temperature of 50 to 200° C., preferably 60 to 180° C., particularly preferably 60 to 130° C. The pressure in each of the existing reaction stages can be 10 to 70 bar, preferably 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 be carried out in the liquid phase, the parameters pressure and temperature must be selected so that the starting material stream (the olefin or olefin mixture used) is present in the liquid phase.

[0029] The weight-based space velocity (weight hourly space velocity (WHSV)) is the mass of reactants per unit time per unit catalyst mass and the mass of reactants per unit time per hour (i.e., 1 h -1 ) to 190 hours -1 , preferably 2 h -1 Up to 35 hours -1 , particularly preferably 3 h -1 Up to 25 hours -1 .

[0030] In particular, when using a catalyst comprising a nickel compound, preferably nickel oxide, on a support material, the degree of dimerization after oligomerization (also referred to as "percent selectivity based on dimerization") is at least 60%, further preferably at least 75%, particularly preferably at least 80%, based on the reacted starting materials.

[0031] The linearity of the oligomerization products or resulting dimers is described by the ISO index, which represents the average number of methyl branches in the dimer. Thus, for example, n-octene (for butene as the starting material) contributes 0 to the ISO index of the C8 fraction, methylpentene 1, and dimethylhexene 2. The lower the ISO index, the more linear the molecules formed in the respective fraction. The ISO index is calculated according to the following general formula, where the proportions of the individual dimer fractions are based on the entire dimer fraction:

[0032]

[0033] Thus, a dimer mixture with an ISO index of 1.0 has, on average, exactly one methyl branch per dimer molecule.

[0034] The ISO index of the product obtained from the oligomerization process according to the invention is preferably from 0.8 to 1.2, particularly preferably from 0.8 to 1.15.

[0035] The oligomers prepared by the method according to the invention are particularly useful for preparing aldehydes, alcohols and carboxylic acids. Thus, for example, a dimer derived from linear butenes can be hydroformylated to give a nonanal mixture. This provides the corresponding carboxylic acids by oxidation or a C9-alcohol mixture by hydrogenation. The C9-acid mixture can be used to prepare lubricants or driers. The C9-alcohol mixture is a precursor for preparing plasticizers, in particular dinonyl phthalate or DINCH. DETAILED DESCRIPTION Example

[0036] Example 1 (according to the present invention):

[0037] The oligomerization was carried out in a largely isothermally operated tubular reactor with the following dimensions: length 2.0 m, inner diameter 6 mm. The reactor was suspended in a thermostat for constant temperature control. Marlotherm, a product of Sasol, was used as a heat carrier. The catalyst used was 12.6 g of a substance prepared according to Example 1 of WO 2011 / 000697 A1 and worked up according to Example 4 of the same publication.

[0038] The reaction was carried out in the liquid phase at an absolute pressure of 30 bar and a temperature of 80° C. As fresh feed to the reactor, 1 kg / h of a C4-hydrocarbon mixture was used, which comprised the following components:

[0039] 1-Butene 22.7 wt%

[0040] 2-Butene 58.4 wt%

[0041] Isobutylene 0.7 wt%

[0042] Butane 18.1 wt%

[0043] C8-olefins 0.1 wt%

[0044] A conversion of the C4-olefins of 43.9% was achieved, with the following oligomer distribution being obtained in the reactor discharge (oligomer distribution in the oligomerization reaction mixture):

[0045] C8-olefins 83.9%

[0046] C12-olefins 12.5%

[0047] C16+-olefins 3.7%

[0048] This corresponds to a production amount of 34.4 g / h of C8-olefins.

[0049] Example 2 (not according to the invention):

[0050] The oligomerization was carried out in a largely isothermally operated tubular reactor with the following dimensions: length 2.0 m, inner diameter 6 mm. The reactor was suspended in a thermostat for constant temperature control. Marlotherm, a product of Sasol, was used as a heat carrier. The catalyst used was 12.6 g of a substance prepared according to Example 1 of WO 2011 / 000697 A1 and worked up according to Example 4 of the same publication.

[0051] The reaction was carried out in the liquid phase at an absolute pressure of 30 bar and a temperature of 80° C. As fresh feed to the reactor, 1 kg / h of a C4-hydrocarbon mixture was used, which comprised the following components:

[0052] 1-Butene 22.2 wt%

[0053] 2-Butene 57.9 wt%

[0054] Isobutylene 0.6 wt%

[0055] Butane 18.2 wt%

[0056] C8-olefins 1.1 wt%

[0057] A conversion of the C4-olefins of 41.1% was achieved, with the following oligomer distribution being obtained in the reactor discharge (oligomer distribution in the oligomerization reaction mixture):

[0058] C8-olefins 83.9%

[0059] C12-olefins 12.4%

[0060] C16+-olefins 3.8%

[0061] This corresponds to a production amount of 32.0 g / h of C8-olefins.

[0062] It could be shown that an increase in the C8-olefin content in the feed to the reactor leads to a decrease in the conversion by 2.8 percentage points and to a 7% decrease in the amount of C8-oligomers produced.

[0063] Example 3 (according to the present invention):

[0064] The oligomerization was carried out in a largely adiabatically operated tubular reactor without thermostatting having the following dimensions: length 2.0 m, inner diameter 20.5 mm. 300 g of a substance prepared according to Example 1 of WO 2011 / 000697 A1 and worked up according to Example 4 of the same publication were used as catalyst.

[0065] The reaction was carried out in the liquid phase at an absolute pressure of 30 bar and a reactor feed temperature of 90° C. As fresh feed to the reactor, 1.75 kg / h of a C4-hydrocarbon mixture comprising the following components was used:

[0066] 1-Butene 35.8 wt%

[0067] 2-Butene 42.4 wt%

[0068] Isobutylene 0.9 wt%

[0069] Butane 20.9 wt%

[0070] C8-olefins 0.0 wt%

[0071] A conversion of 31.7% of the C4-olefins was achieved, with the following oligomer distribution being obtained in the reactor discharge (oligomer distribution in the oligomerization reaction mixture):

[0072] C8-olefins 85.1%

[0073] C12-olefins 12.6%

[0074] C16+-olefins 2.3%

[0075] Example 4 (according to the present invention):

[0076] The conditions and the reactor corresponded to those of Example 3. A C4 mixture was used which had the following composition:

[0077] 1-Butene 36.0 wt%

[0078] 2-Butene 43.8 wt%

[0079] Isobutylene 0.7 wt%

[0080] Butane 19.3 wt%

[0081] C8-olefins 0.2 wt% (equivalent to 3.5 g / h)

[0082] A conversion of 31.7% of the C4-olefins was achieved, with the following oligomer distribution being obtained in the reactor discharge (oligomer distribution in the oligomerization reaction mixture):

[0083] C8-olefins 85.0%

[0084] C12-olefins 12.6%

[0085] C16+-olefins 2.4%

[0086] Compared with Example 3, no decrease in conversion rate was observed.

[0087] Example 5 (not according to the invention):

[0088] The conditions and the reactor corresponded to those of Example 3. A C4 mixture was used which had the following composition:

[0089] 1-Butene 36.1 wt%

[0090] 2-Butene 44.1 wt%

[0091] Isobutylene 1.2 wt%

[0092] Butane 18.0 wt%

[0093] C8-olefins 0.4 wt% (equivalent to 7 g / h)

[0094] A conversion of the C4-olefins of 30.1% was achieved, with the following oligomer distribution being obtained in the reactor discharge (oligomer distribution in the oligomerization reaction mixture):

[0095] C8-olefins 85.0%

[0096] C12-olefins 12.6%

[0097] C16+-olefins 2.4%

[0098] Relative to Example 3, a slight decrease in conversion was observed.

[0099] Example 6 (not according to the invention):

[0100] The conditions and the reactor corresponded to those of Example 3. A C4 mixture was used which had the following composition:

[0101] 1-Butene 34.3 wt%

[0102] 2-Butene 44.1 wt%

[0103] Isobutylene 1.1 wt%

[0104] Butane 19.9 wt%

[0105] C8-olefins 0.7 wt% (equivalent to 12 g / h)

[0106] A conversion of 28.8% of the C4-olefins was achieved, with the following oligomer distribution being obtained in the reactor discharge (oligomer distribution in the oligomerization reaction mixture):

[0107] C8-olefins 85.1%

[0108] C12-olefins 12.6%

[0109] C16+-olefins 2.3%

Claims

1. A process for the oligomerization of C3- to C5-olefins, wherein in at least one reaction stage, a feed mixture comprising C3- to C5-olefins is oligomerized using a heterogeneous oligomerization catalyst comprising a nickel compound and a support material comprising aluminum oxide, silicon dioxide or an aluminosilicate, wherein each reaction stage consists of at least one reactor, in which the oligomerization is carried out to form an oligomerization reaction mixture, and at least one distillation column, in which the oligomers formed during the oligomerization are at least partially separated from the remaining oligomerization reaction mixture. It is characterized by: at least a portion of the remaining oligomerization mixture from which the oligomers have been separated is recycled to the one or more reactors of the at least one reaction stage, and the oligomer content of the feed to the one or more reactors of the at least one reaction stage is ≤ 0.2% by weight, based on the total composition of the feed, the feed to the one or more reactors of the at least one reaction stage consisting of the recycled remaining oligomerization mixture and a fresh feed of the feed mixture, The oligomer content was monitored during continuous operation.

2. The process according to claim 1 , wherein the process for oligomerization is carried out in at least two reaction stages, wherein the oligomers formed in the reactor(s) of the first reaction stage are separated from the remaining oligomerization mixture in a distillation column of the first reaction stage, and wherein the remaining oligomerization mixture is conveyed partly to the reactor(s) of the same reaction stage and partly to the reactor(s) of the next reaction stage.

3. The process of claim 1 or 2, wherein the support material of the oligomerization catalyst comprises an aluminosilicate.

4. The process according to claim 3, wherein the support material of the oligomerization catalyst consists of an aluminosilicate.

5. The process according to claim 3, wherein the heterogeneous oligomerization catalyst has a composition of 15 to 40 wt% NiO, 5 to 30 wt% Al2O3, 55 to 80 wt% SiO2 and 0.01 to 2.5 wt% alkali metal oxide.

6. The process according to claim 1 or 2, wherein the oligomerization catalyst has a molecular weight of 150 to 700 m 2 / g is the specific surface area calculated according to BET.

7. The process according to claim 1 or 2, wherein the oligomerization is carried out at a temperature of 50 to 200°C in each of the reaction stages present.

8. The process according to claim 1 or 2, wherein the oligomerization is carried out at a temperature of 60 to 180°C in each of the reaction stages present.

9. The process according to claim 1 or 2, wherein the oligomerization is carried out at a temperature of 60 to 130°C in each of the reaction stages present.

10. The process according to claim 1 or 2, wherein the pressure during the oligomerization in each of the reaction stages present is from 10 to 70 bar.

11. The process according to claim 1 or 2, wherein the pressure during the oligomerization in each of the reaction stages present is from 20 to 55 bar.

12. The process according to claim 1 or 2, wherein the process is a process for the oligomerization of C4-olefins.

13. The process according to claim 1 or 2, wherein the oligomerization is carried out in the liquid phase in each of the at least one reaction stage.

14. The process according to claim 1 or 2, wherein the degree of dimerization after the oligomerization is at least 60%, based on the reacted starting materials.

15. The process according to claim 1 or 2, wherein the weight hourly space velocity during oligomerization is 1h -1 Until 190h -1 .