Process for the oligomerization of isobutene

Abstract

To provide an improved process for oligomerization of isobutene with a higher selectivity for 2,4,4-trimethylpent-1-ene in the diisobutene formed.SOLUTION: There is provided a process for producing diisobutene, comprising: performing an oligomerization of isobutene over an acid catalyst in at least one reaction stage which in each case contains at least one reactor and at least one distillation column, wherein at the top of the distillation column a residual hydrocarbon stream from the diisobutene formed based on the obtained product mixture is withdrawn and at least partially recirculated to the at least one reactor as recycle, wherein a ratio of recycle to feed is at least 4.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a process for oligomerizing isobutene by acid-catalyzed conversion of an isobutene-containing hydrocarbon stream in at least one reaction stage, wherein a specific ratio of recycle to feed is employed. [Background technology]

[0002] Isobutene oligomerization is a well-known large-scale industrial process for producing diisobutene, the technical name for a mixture of 2,4,4-trimethylpent-1-ene and 2,4,4-trimethylpent-2-ene, which is used in synthesis, e.g., hydroformylation to aldehydes, or as a fuel component after hydrogenation. Known technical improvements to this process are described, for example, in US Pat. No. 5,629,491. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] European Patent Application Publication No. 1 388 528 Summary of the Invention [Problem to be solved by the invention]

[0004] Despite the known methods, there is a continuous need for process improvements, particularly with regard to the selectivity to 2,4,4-trimethylpent-1-ene. In fact, in the hydroformylation of diisobutene, it is advantageous if 2,4,4-trimethylpent-1-ene is predominantly present in the diisobutene. Surprisingly, it has been found that the selectivity to 2,4,4-trimethylpent-1-ene can be improved depending on the ratio of recycle to feed. [Means for solving the problem]

[0005] The underlying problem of the present invention has been solved by the method according to the claims, which provides an improved process for the oligomerization of isobutene, in which the diisobutene formed has a higher selectivity for 2,4,4-trimethylpentene-1. Preferred embodiments of the process are described in the dependent claims.

[0006] The process according to the invention therefore comprises a process for producing diisobutene by acid-catalyzed oligomerization of isobutene in at least one reaction stage, each comprising at least one reactor and at least one distillation column, wherein: In the at least one reactor in the at least one reaction stage, an isobutene-containing feed stream comprising an isobutene-containing hydrocarbon stream as a feed and a recycle stream as a recycle is reacted to obtain a product mixture comprising diisobutene formed with a 2,4,4-trimethylpent-1-ene content of at least 75 mol % or more, preferably at least 76.5 mol % or more, more preferably at least 78 mol % or more, and unreacted isobutene, and the resulting product mixture is fed to at least one distillation column; At the top of the distillation column, a residual hydrocarbon stream is recovered from the diisobutene formed on the basis of the resulting product mixture and is at least partially recycled to at least one reactor, with a recycle to feed ratio of at least 4.

[0007] It has been surprisingly found that the selectivity of the oligomerization reaction to 2,4,4-trimethylpent-1-ene can be increased by providing an isobutene-containing feed stream with a recycle / feed ratio of at least 4. Preferably, the recycle to feed ratio is at least 5, and more preferably at least 6. This further improves the selectivity to 2,4,4-trimethylpent-1-ene.

[0008] In the production of diisobutene by the oligomerization of isobutene according to the invention, the isobutene-containing feed stream used in the first reactor and, if present, in each reactor of each reaction stage connected in parallel to the first reactor, comprises both an isobutene-containing hydrocarbon stream as feed (fresh feed) and a recycled stream from the distillation after oligomerization. Preferably, this isobutene-containing feed stream consists of an isobutene-containing hydrocarbon stream as feed (fresh feed), a recycled stream as recycled, and optionally a diluted stream of inert alkanes. In the process according to the invention, if one or more reactors are connected in series to the first reactor of each reaction stage present, these reactors are only fed with the effluent from the previous reactor and are not further fed with recycled materials.

[0009] The isobutene-containing feed stream used as the feed for the process according to the invention can in principle be any isobutene-containing hydrocarbon mixture containing an amount of isobutene that allows the process to be run economically. Preferably, a mixture of isobutene with other C4 hydrocarbons, i.e., a C4 hydrocarbon stream, is used. In the context of the present invention, the effluent from a previous oligomerization reactor is also considered to be an isobutene-containing feed stream. Examples of technical mixtures containing isobutene include light gasoline fractions from refineries, C4 fractions from crackers (steam crackers, hydrocrackers, cattle crackers, etc.), mixtures from Fischer-Tropsch synthesis, mixtures from butane dehydrogenation, mixtures from skeletal isomerization of normal butenes, and mixtures formed by olefin metathesis.

[0010] In a particularly preferred embodiment of the present invention, a pure isobutene stream is used as the isobutene-containing hydrocarbon stream, i.e., as the feed. In this context, the term "pure" is understood to mean that the pure isobutene stream contains at least 98% by mass of isobutene, based on the total mass of the stream. The isobutene concentration at the inlet of the first reaction stage or at the first reactor of the first reaction stage, i.e., the isobutene concentration in the isobutene-containing feed stream used, is preferably 90% or less, more preferably 87% or less, and particularly preferably 85% or less.

[0011] To limit the isobutene concentration and thereby the temperature rise in the reactor, a certain amount of solvent or diluent can be added to the isobutene-containing hydrocarbon stream. Suitable solvents or diluents include inert materials such as alkanes, preferably isobutane.

[0012] The total feed rate of the isobutene-containing feed stream to the first reaction stage or the first reactor of the first reaction stage can vary within a wide range. It depends on the actual configuration (e.g., one or more reactors) and the size of the reactors and distillation column. In a preferred embodiment of the present invention, the first reaction stage or the first reactor of the first reaction stage, or all reactors connected in series in the first reaction stage, are operated so that the total feed rate of the isobutene-containing feed stream is at least 2.5 tons per ton of catalyst and time (hour) (units ton / (ton x hour)), preferably at least 3 tons / (ton x hour), and more preferably at least 3.5 tons / (ton x hour). The total feed rate refers to the feed rate related to the mass of catalyst present per unit time (hour). It always relates to the total catalyst mass of the reactors connected in series. If there is only one reactor, the catalyst mass is the mass of catalyst of one reactor. If there are two or more reactors connected in series, the catalyst mass is the sum of the catalyst masses of the two or more reactors connected in series.

[0013] The oligomerization of isobutene according to the invention is carried out in at least one reaction stage. Although it may be advantageous to use two or more reaction stages, the oligomerization of isobutene according to the invention preferably involves only one reaction stage. This is easier to implement from the standpoint of plant engineering and may also result in cost savings.

[0014] In the context of the present invention, a reaction stage comprises at least one reactor and at least one distillation column. There may also be multiple reactors and multiple distillation columns. In the case of multiple reaction stages, the number of reactors and / or distillation columns may be the same or different for all reaction stages. Preferably, a reaction stage comprises at least two reactors connected in series or parallel. When two reactors are connected in parallel, fresh feed and recycle are fed to each reactor in the ratio according to the present invention. When reactors are connected in series, the product mixture from the first reactor is fed to the second reactor.

[0015] According to the present invention, the oligomerization of isobutene can be carried out batchwise or, preferably, continuously. Suitable reactors for continuous processes include fixed-bed reactors, tube bundle reactors, continuous stirred-tank reactors, flow reactors such as loop reactors, or combinations thereof. Stirred-tank reactors are suitable for batch processes. The reactors used in the present process can be operated adiabatically, polytropically, or substantially isothermally, i.e., using a coolant to cool the reactor. Substantially isothermal means that the temperature at any point in the reactor is at most 15 K higher than the temperature at the reactor inlet.

[0016] The oligomerization of isobutene is carried out by contacting an isobutene-containing feed stream with an acid catalyst at a temperature of preferably 5 to 160°C, more preferably 30 to 110°C, and most preferably 40 to 90°C.

[0017] The oligomerization according to the present invention can be carried out at a pressure equal to or greater than the vapor pressure of the feed stream at the respective reaction temperature, preferably at a pressure of 40 bar or less. It is desirable that the isobutene-containing feed stream is entirely or partially in a liquid phase during the oligomerization. In a preferred embodiment, the oligomerization is carried out in the liquid phase. Adjustment of pressure and temperature to obtain a liquid phase reaction is well known to those skilled in the art and can be set based on the above ranges.

[0018] The catalyst used for the oligomerization of isobutene is an acid catalyst. Typical acid catalysts for oligomerizing isobutene to diisobutene are known to those skilled in the art. In a preferred embodiment, the acid catalyst used is an acid ion exchange resin in which some of the acidic protons are replaced by metal ions.

[0019] In the oligomerization according to the present invention, more preferably, a solid sulfonated ion exchange resin is used, in which particularly 0.1 to 70%, preferably 30 to 65%, of the acidic protons of the sulfonic acid groups are replaced with metal ions. Metal ions suitable for replacing the protons include alkali metals, alkaline earth metals, chromium, manganese, iron, cobalt, nickel, zinc, aluminum, and ions of the lanthanoid group (rare earths). For this purpose, alkali metal ions, particularly sodium ions, are preferably used. Alternatively, replacement with two or more different metal ions may be used.

[0020] Suitable ion exchange resins are prepared, for example, by sulfonating a cooligomer of a phenol / aldehyde condensate and an aromatic vinyl compound. Examples of aromatic vinyl compounds from which the cooligomers are prepared include styrene, vinyltoluene, vinylnaphthalene, vinylethylbenzene, methylstyrene, vinylchlorobenzene, vinylxylene, and divinylbenzene. In particular, the cooligomer produced by reacting styrene with divinylbenzene is used as a precursor for preparing the preferred sulfonated ion exchange resins herein. The properties of these resins, particularly the specific surface area, porosity, stability, swelling / shrinkage, and exchange capacity, can be varied depending on the preparation method. The resins can be prepared in a gel, macroporous, or sponge form.

[0021] The particle size of the ion exchange resin used as the acid catalyst according to the present invention is preferably 500 μm to 1500 μm, more preferably 600 μm to 1000 μm. The particle size can be measured by laser light diffraction according to ISO 13320:2020-01. The particle size distribution may be narrow or broad. For example, ion exchange resins with extremely uniform particle sizes (monodisperse resins) can be used. However, ion exchange resins in the shape of cylinders, rings, spheres, etc. may also be used. When multiple reactors are used in the method according to the present invention, the reactors can be filled with ion exchange resins of the same or different particle sizes, or with ion exchange resins of the same or different particle size distributions, or in the form of different molded bodies.

[0022] Preferred ion exchange resins according to the present invention can be prepared by various methods known to those skilled in the art. When the ion exchange resin is in the H form, protons may be replaced by metal ions. When the resin is a metal salt, protons can be replaced by acid. This ion exchange can, in principle, be carried out in either an organic or aqueous suspension. A convenient procedure involves slurrying the H+ form of the ion exchange resin with sufficient liquid (approximately 1 to 10 times the specific volume of the ion exchange resin) to form a stirrable suspension. A solution containing the desired ions is then added to this suspension. The ion exchange is preferably carried out at a temperature in the range of 10 to 100°C, particularly preferably 20 to 40°C. After completion of the ion exchange, the ion exchange resin is washed and dried. Drying can be carried out in vacuum or in an inert gas stream, such as a nitrogen stream. The drying temperature is typically 10 to 120°C.

[0023] A preferred method for preparing the catalyst used in the process of the present invention is to exchange the protons with metal ions in an aqueous phase, wash the partially exchanged ion exchange resin with water, and then dry it.

[0024] The ions to be attached to the resin may be in the form of a hydroxide solution or a salt of an organic or inorganic acid. In the case of a salt of a polybasic acid, an acid salt may be used. Compounds containing other organic residues, such as alcohol acid salts and acetylacetonates, may also be used. Metal hydroxides and inorganic acid salts are preferably used as sources of metal ions. In particular, alkali metal hydroxides, such as sodium hydroxide, alkali metal halides, such as sodium chloride, alkali metal sulfates, such as sodium sulfate, alkali metal nitrates, such as sodium nitrate, alkaline earth metal hydroxides, and alkaline earth metal nitrates are preferably used.

[0025] By following the above procedure, catalysts with different activity and selectivity can be prepared depending on the degree of exchange, type of ion, and resin.

[0026] The reactors in the process of the present invention may contain a mixture of resins with different reactivities. Similarly, the reactors may be layered with catalysts of different activities. When multiple reactors are used, the individual reactors may be filled with catalysts of the same or different activities.

[0027] In the oligomerization according to the invention, a product mixture is obtained in at least one reactor, which contains diisobutene formed in an amount of at least 75 mol %, preferably at least 76.5 mol %, particularly preferably at least 78 mol % of 2,4,4-trimethylpent-1-ene, and unreacted isobutene, and may also contain isobutane.

[0028] The product mixture is then fed to at least one distillation column in the reaction stage, and the product is separated from the light-end boiler. The distillation is carried out so that at least the lower boilers, i.e., unreacted isobutene and, if present, isobutane, are recovered as a residual hydrocarbon stream at the top of the at least one distillation column. This residual hydrocarbon stream is partially or completely recycled to the at least one reactor. By completely recycling the residual hydrocarbon stream from the at least one distillation column, 100% conversion of isobutene can be achieved. Thus, only the isobutene of the isobutene-containing hydrocarbon stream, the mass of which is equal to the mass of the product produced at the bottom of the at least one distillation column, is fed to the at least one reactor.

[0029] The distillation in at least one distillation column is preferably carried out at a pressure of 2 to 9 bar (g) (bar gauge pressure), preferably 3 to 8 bar g, in particular 4 to 7 bar g. The temperature at the bottom of the column during distillation is preferably 100 to 220°C, more preferably 120 to 210°C, and particularly preferably 150 to 200°C. In a particularly preferred embodiment of the present invention, the distillation in at least one distillation column is operated with reflux (i.e., a portion of the total distillation stream (vapor) is returned to the top of the column). The reflux ratio (ratio of vapor to reflux) is preferably 0.001 to 2, more preferably 0.005 to 1.5, and even more preferably 0.01 to 1.

[0030] The resulting mixture of oligomers is produced at the bottom of the distillation column, the mixture produced at the bottom preferably comprising at least 80% by weight of diisobutene, more preferably at least 86% by weight of diisobutene, most preferably at least 92% by weight of diisobutene. A portion of the mixture may be triisobutene or higher oligomers, but in particular triisobutene.

[0031] In a particularly preferred embodiment, the reaction stage of the process according to the invention comprises at least two distillation columns, preferably connected in series. In a preferred series connection, the second distillation column is fed from the bottom of the first distillation column. The second distillation column can be used to separate the mixture of oligomers obtained in the first distillation, diisobutene from any higher oligomers that may be present, such as triisobutene.

[0032] For this reason, the pressure in the second distillation column is set to 0.1 to 5 bar(a) (absolute pressure), more preferably 0.2 to 3 bar(a), and particularly preferably 0.3 to 1.5 bar(a). The temperature at the bottom of the second distillation column is preferably 30 to 180°C, more preferably 45 to 170°C, and particularly preferably 60 to 160°C. The reflux ratio in the second distillation column is preferably 0 to 2, more preferably 0.01 to 1.8, and particularly preferably 0.05 to 1.5.

[0033] The present invention will be described below with reference to Figures 1 to 4. It should be noted that these figures show specific embodiments and are useful for explaining the subject matter of the present invention, but are not limiting. [Brief explanation of the drawings]

[0034] [Figure 1] FIG. 1 shows an embodiment of the process of the invention comprising a reactor (2) in a reaction stage with two distillation columns (4, 5). [Figure 2] The embodiment shown in Figure 2 comprises two reactors (2, 11) connected in series. [Figure 3]The embodiment shown in Figure 3 comprises two reactors (2, 12), which are connected in parallel. [Figure 4] FIG. 4 illustrates one embodiment of the present invention having three reactors (2, 11, 12), in each case one reactor connected in parallel and one reactor connected in series to the first reactor. DETAILED DESCRIPTION OF THE INVENTION

[0035] FIG. 1 shows an embodiment of the process according to the invention, which comprises a reactor (2) in the reaction stage with two distillation columns (4, 5). In this process, an isobutene-containing hydrocarbon stream (feed) (1) composed of an isobutene-containing hydrocarbon stream and a recycle stream (recycle) (8) from the first distillation column (4) is fed to the reactor (2), where the isobutene contained therein is oligomerized. In the present invention, the recycle to feed ratio of the isobutene-containing feed stream is at least 4, preferably at least 5, and particularly preferably at least 6. The discharge (3) from the reactor (2), which is a mixture of at least unreacted isobutene and isobutene oligomers, is released from the light-end boiler (isobutene, optionally isobutane) in the first distillation column (4), which is recovered at the top of the distillation column (4) and recycled to the reactor (2). The bottom of the distillation column (4) essentially consists mainly of diisobutene and higher oligomers, which are separated from each other in the subsequent distillation column (5). Diisobutene (6) is sent to the top of the column, while higher oligomers (7) accumulate at the bottom. The diagram shows two optional embodiments: the addition of an inert alkane (9) and the discharge of part of the light boiler (10).

[0036] In contrast to FIG. 1, the embodiment shown in FIG. 2 comprises two reactors (2, 11) connected in series. An isobutene-containing feed stream, composed of an isobutene-containing hydrocarbon stream (feed) (1) and a recycle stream (recycle) (8) from the first distillation column (4), is fed to the first reactor (2) to oligomerize the isobutene contained therein. In the present invention, the recycle to feed ratio of the isobutene-containing feed stream is at least 4, preferably at least 5, particularly preferably at least 6. The effluent (3) from the first reactor (2), which is a mixture of at least unreacted isobutene and isobutene oligomers, is then sent to the second reactor (11), where the remaining isobutene is oligomerized. The effluent from the second reactor is then released from the light ends boiler (isobutene, optionally isobutane) in the first distillation column (4), which is recovered at the top of the distillation column (4) and recycled to the first reactor (2). The bottom of the distillation column (4) essentially consists mainly of diisobutene and higher oligomers, which are separated from each other in the subsequent distillation column (5). Diisobutene (6) is sent to the top of the column, while the higher oligomers (7) collect at the bottom. Two optional embodiments are shown in the figure: an additional supply of inert alkanes (9) and a partial discharge of the light boiler (10).

[0037] The embodiment according to FIG. 3 also contains two reactors (2, 12), but they are connected in parallel. An isobutene-containing feed stream, consisting of an isobutene-containing hydrocarbon stream (feed) (1) and a recycle stream (recycle) (8) from the first distillation column (4), is fed to the first reactor (2) and the second reactor (12) to oligomerize the isobutene contained therein. In the present invention, the recycle to feed ratio of the isobutene-containing feed stream is at least 4, preferably at least 5, particularly preferably at least 6. The discharge (3) from the first reactor (2) and the effluent (12), which are a mixture of at least unreacted isobutene and isobutene oligomers, are then released from the light boiler (isobutene, optionally isobutane) in the first distillation column (4) and are recovered at the top of the distillation column (4) and recycled to the first and second reactors (2, 12). The bottom of the distillation column (4) essentially consists mainly of diisobutene and higher oligomers, which are separated from each other in the subsequent distillation column (5). Diisobutene (6) is sent to the top of the column, while the higher oligomers (7) collect at the bottom. Two optional embodiments are shown in the figure: an additional supply of inert alkanes (9) and a partial discharge of the light boiler (10).

[0038] FIG. 4 shows an embodiment of the present invention having three reactors (2, 11, 12), one reactor connected in parallel and one reactor connected in series with the first reactor. An isobutene-containing feed stream, consisting of an isobutene-containing hydrocarbon stream (feed) (1) and a recycle stream (recycle) (8) from the first distillation column (4), is fed to the first reactor (2) and the second reactor (12), connected in parallel, to oligomerize the isobutene contained therein. In this invention, the ratio of recycle to feed of the isobutene-containing feed stream is at least 4, preferably at least 5, and particularly preferably at least 6. The effluent (3) from the first reactor (2) is sent to the third reactor (11), connected in series, to oligomerize the remaining isobutene. The effluent from the third reactor (11) and the effluent from the second reactor (12), which are a mixture of at least unreacted isobutene and isobutene oligomers, are then released from the light-end boiler of the first distillation column (4) (isobutene, possibly isobutane), which are recovered at the top of the distillation column (4) and recycled to the first and second reactors (2, 12). The bottom of the distillation column (4) essentially consists mainly of diisobutene and higher oligomers, which are separated from each other in the subsequent distillation column (5). Diisobutene (6) is sent to the top of the column, while the higher oligomers (7) collect at the bottom. Two optional embodiments are shown in the figure: an additional supply of inert alkanes (9) and a partial discharge of the light-end boiler (10).

Claims

1. 1. A process for producing diisobutene by acid-catalyzed oligomerization of isobutene in at least one reaction stage, the at least one reaction stage comprising at least one reactor and at least one distillation column, wherein: reacting an isobutene-containing feed stream, including an isobutene-containing hydrocarbon stream as a feed and a recycle stream as a recycle, in the at least one reactor in the at least one reaction stage to obtain a product mixture containing diisobutene formed with a 2,4,4-trimethylpent-1-ene content of at least 75 mol % or more, 76.5 mol % or more, or 78 mol % or more, and unreacted isobutene, and feeding the resulting product mixture to the at least one distillation column; At the top of the distillation column, a residual hydrocarbon stream is recovered from the diisobutene formed based on the resulting product mixture and is at least partially recycled to the at least one reactor as recycle, wherein the recycle to feed ratio is at least 4. method.

2. 10. The method of claim 1, wherein the recycle to feed ratio is at least 5.

3. 3. The method of claim 1 or 2, wherein the recycle to feed ratio is at least 6.

4. 4. The process according to any one of claims 1 to 3, wherein the isobutene-containing hydrocarbon stream is a C4 hydrocarbon stream.

5. 4. The process according to claim 1, wherein the isobutene-containing hydrocarbon stream is a pure isobutene stream.

6. 6. The process according to any one of claims 1 to 5, wherein the residual hydrocarbon stream recovered at the top of the distillation column is fully recycled to the at least one reactor.

7. 7. The method according to any one of claims 1 to 6, wherein the reaction stage comprises at least two reactors connected to each other in series or in parallel.

8. The method according to any one of claims 1 to 7, wherein the oligomerization is carried out in the liquid phase.

9. The method according to any one of claims 1 to 8, wherein the acid catalyst is an acidic ion exchange resin in which some of the acidic protons are substituted with metal ions.

10. 10. The method of claim 9, wherein 0.1% to 70%, or 30% to 65% of the acidic protons are substituted with metal ions.

11. 11. The method according to claim 9 or 10, wherein the metal ions are ions of alkali metals, alkaline earth metals and / or rare earths.

12. The process according to any one of claims 1 to 11, wherein the reactor is a flow reactor, a fixed bed reactor, a tube bundle reactor, a continuous stirred tank reactor or a loop reactor.

13. 13. The method according to any one of claims 1 to 12, wherein the at least one reactor is operated adiabatically, polytropically or isothermally with a coolant.

14. The method of claim 1, wherein the oligomerization is carried out at a temperature of 5°C to 160°C, 30°C to 110°C, or 40°C to 90°C.

15. 15. The process of any one of claims 1 to 14, wherein the first reaction stage is conducted with a total feed of the isobutene-containing feed stream of at least 2.5 tonnes per tonne of catalyst and hour (hours) (units: tonnes / (tonnes x hr)), at least 3 tonnes / (tonnes x hr), or at least 3.5 tonnes / (tonnes x hr).

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