METHOD FOR PURIFICATION OF ISOBUTEN FROM A C4 STREAM AND PROCESS ENGINEERING APPARATUS FOR THIS PROCESS

Description

[0001] The invention relates to a method and a process engineering plant for the purification of isobutene from a C4 stream comprising at least 1-butene, 2-butene, isobutane and isobutene.

[0002] The purity requirements for isobutene as a starting material for various products are constantly increasing. For example, particularly high purity is required when isobutene is used as a feedstock for the production of isobutene-containing plastics. These manufacturing processes generally specify purity requirements for the starting material, such as a minimum isobutene content and a maximum content of 1-butene and other components like butane, C3 and C5 hydrocarbons. A particular challenge in the production of isobutene-enriched products from a C4 stream containing various hydrocarbons with four carbon atoms per molecule, such as 1-butene, 2-butene, isobutane, and isobutene, is the separation of isobutene and 1-butene. This is because the boiling points of isobutene and 1-butene are very close, making separation by distillation possible only with a relatively high energy input.In contrast, the separation of isobutene and 2-butene is simpler due to the greater difference in the boiling points of these two butene compounds. Therefore, prior art methods are known that essentially rely on isomerizing the 1-butene in the C4 stream to 2-butene in order to facilitate the separation of isobutene from the C4 stream.

[0003] GB 570,692 discloses a process for separating isobutene in which, essentially, a C4 stream containing isobutene and 1-butene is contacted at a sufficiently high space velocity with a catalyst that accelerates the isomerization of 1-butene to 2-butene, such that 1-butene is converted to 2-butene, but not isobutene, and isobutene is obtained by fractionation. To increase the purity of the isobutene in the product stream of the process, the catalytic isomerization in a reactor and the fractionation in a rectification column can be repeated, although this significantly increases the energy consumption of the production process.Furthermore, a disadvantage is that the purity of the isobutene produced by this process is too low for numerous applications, since the mass fraction of 1-butene after isomerization is too high to achieve the necessary purity of the isobutene in the subsequent fractionation, as the 1-butene is enriched in the isobutene-containing product stream.

[0004] EP 0922 018 B1 discloses a process for producing isobutene from a C4 stream containing isobutene and 1-butene. The C4 stream is treated in a distillation column, and a portion of the liquid flowing through the column is withdrawn and fed to a reactor for the isomerization of 1-butene to 2-butene. In the reactor, the isomerization of 1-butene to 2-butene is favored over the isomerization of isobutene using a catalyst. However, a disadvantage is that the purity of the isobutene in the product stream is too low for certain subsequent uses of the product stream.

[0005] Other procedures are known from US 6,215,036 B1, US 5,536,887 A, DE 198 01 089 A1 and EP 1 200 378 B1, among others.

[0006] The object of the present invention is to alleviate or eliminate at least some of the disadvantages of known methods for purifying isobutene from a C4 stream. In particular, the invention aims to provide a method and a process plant for the efficient purification of isobutene from a C4 mixture and / or to achieve the highest possible isobutene purity levels.

[0007] The present invention provides a method for purifying isobutene from a C4 stream comprising at least 1-butene, 2-butene, isobutane and isobutene, in which at least the following steps are carried out: Feeding a mass stream enriched with isobutane and isobutene, derived from the C4 stream, and a hydrogen stream into an isomerization reactor, wherein the isomerization reactor comprises a catalyst having at least one hydrogenating metal on a support, preferably an aluminum oxide support; contacting the mass stream enriched with isobutane and isobutene and the hydrogen stream with the catalyst in the isomerization reactor, whereby 1-butene present in the mass stream enriched with isobutane and isobutene is isomerized to 2-butene; feeding a product stream from the isomerization reactor, which contains proportionally less 1-butene than the mass stream enriched with isobutane and isobutene, into a rectification column;and providing a mass stream enriched with isobutene by separating this mass stream ▪ via a side draw of the rectification column or ▪ via a side draw and as bottoms product of the rectification column or ▪ as bottoms product of the rectification column, wherein a mass stream enriched with isobutane is further separated as the overhead product of the rectification column, or o by feeding an isobutane-enriched overhead product of the rectification column, which contains isobutene in addition to the isobutane, to a second rectification column in order to separate the isobutane from the isobutene and to obtain the mass stream enriched with isobutene in the bottoms product of the second rectification column, ; wherein the C4 stream, from which the mass stream enriched with isobutane and isobutene is obtained, is subjected to a further rectification column, a further catalyst, comprising at least one hydrogenation-active metal on a support, preferably an aluminum oxide support, is supplied, wherein the C4 stream is separated by distillation in the further rectification column and a further hydrogen stream and a 1-butene-containing product stream of the further rectification column are brought into contact with the further catalyst, whereby 1-butene present in said product stream is isomerized to 2-butene, wherein the reaction product stream of the further catalyst is separated by distillation in the further rectification column and a 2-butene-enriched mass stream is separated as bottoms product of the further rectification column and the mass stream enriched with isobutane and isobutene is separated as overhead product of the further rectification column and is supplied to the isomerization reactor,where this material stream contains proportionally less 1-butene and 2-butene than the C4 stream.

[0008] This solves the aforementioned task.

[0009] Accordingly, the invention also provides a process plant for the purification of isobutene from a C4 stream containing at least 1-butene, 2-butene, isobutane, and isobutene. This plant comprises at least: an isomerization reactor comprising a catalyst having at least one hydrogenation-active metal on a support, preferably an aluminum oxide support; and a rectification column downstream of the isomerization reactor, wherein the process plant comprises a further rectification column to which a further catalyst is assigned, which has at least one hydrogenation-active metal on a support, preferably an aluminum oxide support, wherein the isomerization reactor is downstream of the head of the further rectification column. This also solves the aforementioned problem.

[0010] Surprisingly, purified isobutene with a mass fraction of isobutene of at least 95%, preferably at least 98%, and particularly preferably at least 99% can be produced using the process according to the invention.

[0011] A mass stream derived from the C4 stream and enriched with isobutane and isobutene, along with a hydrogen stream, is fed into an isomerization reactor, preferably designed as disclosed in EP 2 170 494 B1, to catalytically isomerize the 1-butene present in the mass stream enriched with isobutane and isobutene to 2-butene in the presence of hydrogen. For the purpose of accelerated isomerization, the isomerization reactor includes a catalyst comprising at least one hydrogenation-active metal on a support. The 1-butene from the mass stream enriched with isobutane and isobutene is isomerized with hydrogen from the hydrogen stream in the presence of the catalyst in the isomerization reactor to form 2-butene, in order to further reduce the proportion of 1-butene in the product stream of the isomerization reactor. This product stream is fed to a rectification column, whereby a stream enriched with isobutane is separated by distillation as the overhead product.An isobutene-enriched stream can be obtained from the rectification column via four different methods. In the first, second, and third methods, an isobutene-enriched stream is obtained via a side outlet, a side outlet, and as the bottoms product of the rectification column, respectively. In the fourth method, a stream containing isobutane and isobutene is fed as the overhead product of the first rectification column to a second rectification column to separate the isobutane from the isobutene and obtain an isobutane-enriched stream as the overhead product and an isobutene-enriched stream as the bottoms product of the second rectification column.

[0012] The C4 stream, from which the mass stream enriched with isobutane and isobutene is obtained, is fed to a further rectification column equipped with another catalyst comprising at least one hydrogenating metal on a support, preferably an aluminum oxide support. In this further rectification column, the C4 stream is separated by distillation, yielding a 1-butene-containing product stream. The 1-butene contained in this product stream is isomerized to 2-butene by contact of this product stream with another hydrogen stream in the presence of the further catalyst. The hydrogenating metal of the further catalyst accelerates the reaction of 1-butene to 2-butene. The product of this catalytic reaction, the reaction product stream, is separated by distillation in the further rectification column.At least some of the product streams generated during this rectification (countercurrent distillation) are re-contacted with the hydrogen from the subsequent hydrogen stream in the presence of the further catalyst to isomerize the 1-butene present in these product streams to 2-butene. The reaction product stream generated by this catalytic reaction is then separated again by distillation in the subsequent rectification column. This at least one repetition of the countercurrent distillation and catalytic reaction process steps ensures a low concentration of 1-butene in the subsequent process steps. A stream enriched with 2-butene from the C4 stream and from the catalytic isomerization of 1-butene is separated from the bottom of the subsequent rectification column.The isobutane- and isobutene-enriched stream is separated as the overhead product of the subsequent rectification column, so that the overhead of the subsequent rectification column is connected to the isomerization reactor. The isobutane- and isobutene-enriched stream contains proportionally less 1-butene and 2-butene than the C4 stream that is fed into the subsequent rectification column.

[0013] The process plant includes a further rectification column to which a further catalyst is assigned, which has at least one hydrogenation-active metal on a support, preferably an aluminum oxide support, wherein the isomerization reactor is downstream of the head of the further rectification column.

[0014] In a preferred embodiment, the additional catalyst is located at least partially outside the further rectification column in a reactor, the reactor being connected to the further rectification column by a feed line and a return line. A 1-butene-containing product stream, generated during the distillation in the further rectification column, is separated from the further rectification column via a side draw and fed to the reactor via the feed line. Additionally, the further hydrogen stream is fed to the reactor to provide the hydrogen required for isomerization. The reaction product stream generated during isomerization at the additional catalyst is fed to the further rectification column via the return line and separated there by distillation.

[0015] In another preferred embodiment, the additional catalyst is provided in at least one separation stage of the further rectification column. The C4 stream and the additional hydrogen stream are fed into the further rectification column, and a 1-butene-containing product stream, which arises during the distillative separation in the further rectification column, is fed to the additional catalyst within the further rectification column. The 1-butene of this product stream is isomerized to 2-butene in the presence of hydrogen. The reaction product stream generated during this catalytic isomerization within the further rectification column is separated by distillation in the further rectification column.

[0016] To achieve a high purity of the isobutene obtained, it is advantageous if the mass fraction of isobutene in the C4 stream, which is fed to the further rectification column, is at least 10%, preferably at least 15%, and in particular at least 20%.

[0017] Furthermore, for a high purity of the isobutene obtained, it is advantageous if the mass fraction of 1-butene in the C4 stream, which is fed to the further rectification column, is a maximum of 40%, preferably a maximum of 30%, and in particular a maximum of 25%.

[0018] Furthermore, for a high purity of the isobutene obtained, it is advantageous if the mass fraction of 2-butene in the C4 stream, which is fed to the further rectification column, is a maximum of 60%, preferably a maximum of 50%, and in particular a maximum of 40%.

[0019] To make the isomerization of 1-butene to 2-butene particularly preferable to the isomerization of isobutene, it is advantageous if the temperature in the isomerization reactor is between 20 °C and 130 °C, preferably between 30 °C and 80 °C, and especially between 40 °C and 70 °C.

[0020] According to a preferred embodiment, the pressure in the isomerization reactor is between 3 bar and 30 bar, preferably between 5 bar and 20 bar, and in particular between 7 bar and 16 bar, in order to particularly favor isomerization of 1-butene to 2-butene in relation to isomerization of isobutene.

[0021] According to a further preferred embodiment, the mass stream enriched with isobutane and isobutene is at least partially liquefied in a condenser of the subsequent rectification column to obtain a liquid phase or a mixed phase of this mass stream. Furthermore, it is advantageous if the isomerization reactor includes a mixing and distribution device. Particularly preferably, the mass stream enriched with isobutane and isobutene from the subsequent rectification column, as a liquid phase or a mixed phase, and the hydrogen stream, as a gaseous phase, are brought into uniform contact with the catalyst of the isomerization reactor via this mixing and distribution device to ensure the highest possible mixing of the mass stream enriched with isobutane and isobutene with the hydrogen stream. Such mixing and distribution devices are well known in the prior art, so further descriptions are unnecessary.

[0022] To achieve a high isomerization rate, it is advantageous if the hydrogen flow rate per t / h of the isobutane- and isobutene-enriched mass stream is between 0.02 Nm³ / h and 200 Nm³ / h, preferably between 0.1 Nm³ / h and 50 Nm³ / h, and particularly between 0.5 Nm³ / h and 5 Nm³ / h, when fed into the isomerization reactor. This ratio ensures that 1-butene is isomerized to 2-butene at a high isomerization rate and that the reaction rate of the side reaction of isobutene with hydrogen to form isobutane is minimized.

[0023] According to a preferred embodiment, the rectification column has between 100 and 220 stages, preferably between 120 and 200 stages, and particularly between 130 and 180 stages. Furthermore, it is advantageous if the reflux-to-distillate ratio of the rectification column is at least 10:1, preferably at least 15:1, and particularly at least 20:1.

[0024] To increase the yield of purified isobutene while maintaining the same input of C4 feedstock, it is advantageous to feed at least part of the bottoms product from the rectification column into the C4 stream as a recycled stream. For this purpose, the bottoms of the rectification column are connected to the line intended for carrying the C4 stream, which is fed into the subsequent rectification column.

[0025] According to a further preferred embodiment, the isobutene-enriched stream obtained from the rectification column is fed to an additional rectification column to obtain a further purified isobutene stream containing a lower ratio of 1-butene to 2-butene than the isobutene-enriched stream. Particularly preferred is the mass fraction of isobutene in the further purified isobutene stream of the additional rectification column being at least 95%, preferably at least 98%, and most preferably at least 99%, and most particularly at least 99.5%.

[0026] To minimize the use of C4 stream, it is advantageous to feed at least part of the bottom product from the additional rectification column into the C4 stream as a recycled stream, thereby increasing the yield of purified isobutene while maintaining the same C4 input. For this purpose, the bottom of the additional rectification column is connected to the line intended for carrying the C4 stream, which is fed into the subsequent rectification column.

[0027] According to a further preferred embodiment, the isobutene-enriched stream is separated from the rectification column via a side draw-off, wherein between 8% and 25%, preferably between 10% and 20%, and particularly between 12% and 15% of the total separation stages of the rectification column are located below the separation stage containing the side draw-off. Particularly preferably, the mass fraction of isobutene in this isobutene-enriched stream is at least 95%, more preferably at least 98%, and more preferably at least 99%, and particularly at least 99.5%.

[0028] To reduce energy consumption, it is advantageous if the subsequent rectification column has a higher temperature than the rectification column and a heat exchanger is connected to the rectification column and the subsequent rectification column for heat transfer between the rectification column and the subsequent rectification column, in order to supply the rectification column with heat from the subsequent rectification column.

[0029] According to another preferred embodiment, the further catalyst is a PdO catalyst supported with Al2O3.

[0030] According to a further preferred embodiment, the hydrogenation-active metal of the catalyst of the isomerization reactor is from group 8, 9, or 10 of the periodic table of elements, in particular palladium or platinum. Particularly preferred is the hydrogenation-active metal of this catalyst palladium with a mass fraction between 0.01% and 5%, preferably between 0.1% and 0.7%, and particularly between 0.2% and 0.5%.

[0031] According to a particularly preferred embodiment, the aluminium oxide support of the catalyst of the isomerization reactor has spherical shaped bodies.

[0032] According to another preferred embodiment, the aluminium oxide support of the catalyst of the isomerization reactor comprises extrudates or tablets.

[0033] The invention is further explained below with reference to the non-limiting embodiments shown in the drawings. Fig. 1 shows a process flow diagram of a process engineering plant according to the invention, in which isobutene is purified from a C4 stream. Fig. 2 shows a process flow diagram of another embodiment of the process plant. Fig. 3 shows a process flow diagram of a third embodiment of the process plant. Fig. 4 shows a process flow diagram of a fourth embodiment of the process plant.

[0034] In Fig. 1 Figure 1 shows a process flow diagram of a plant 1 according to the invention, comprising an isomerization reactor 5, a rectification column 6, a further rectification column 2a, and a reactor 3 containing a further catalyst 4a. The further catalyst 4a in reactor 3 and the further rectification column 2a serve for the repeated isomerization and distillative separation of 1-butene in a C4 stream, wherein reactor 3, which includes the further catalyst 4a for the isomerization of the 1-butene, is located outside the further rectification column 2a. Processes for the repeated isomerization and distillative separation of 1-butene in a C4 stream with a rectification column and a catalyst located at least partially outside the rectification column are known, for example, from EP 0922 018 B1.

[0035] In the embodiment shown according to Fig. 1 A C4 stream 7, whose mass fractions can be 10 to 40% isobutane, 10 to 20% isobutene, 4 to 10% 1-butene, and 30 to 60% 2-butene, is continuously fed into the further rectification column 2a. In the further rectification column 2a, the C4 stream 7 is separated by distillation, and a 1-butene-containing product stream 8 formed in the further rectification column 2a is removed from the further rectification column 2a via at least one side outlet. This product stream 8 is continuously fed to a reactor 3 via a line together with another hydrogen stream 9a, the reactor 8 being located outside the further rectification column 2a and containing the further catalyst 4a. The product stream 8 is fed into the reactor 3 separately from the further hydrogen stream 9a, whereby this product stream 8 can also be mixed with the further hydrogen stream 9a before being fed into the reactor 3.In reactor 3, the 1-butene contained in product stream 8 reacts with the hydrogen from the further hydrogen stream 9a in the presence of the further catalyst 4a, which is a PdO catalyst supported with Al₂O₃, to form 2-butene. The resulting reaction product stream 10, which contains less 1-butene and more 2-butene than product stream 8, is fed back to the further rectification column 2a via a return line. As in [reference]... Fig. 1 As shown, the feed of the recirculated reaction product stream 10 into the same separation stage of the further rectification column 2a as the withdrawal of the product stream 8 takes place. The bottoms product of the further rectification column 2a is a 2-butene-enriched stream 11, and the overhead product is a stream 12 enriched with isobutane and isobutene, wherein this stream 12 contains less 1-butene and 2-butene compared to the C4 stream 7 fed into the further rectification column 2a. The mass fractions of the isobutane- and isobutene-enriched stream 12 can be, for example, approximately 48% isobutane, approximately 50% isobutene, 600 to 1000 ppm 1-butene, and 200 to 400 ppm 2-butene.

[0036] In the embodiment shown according to Fig. 1 The overhead product of the further rectification column 2a, the mass stream 12 enriched with isobutane and isobutene, is at least partially liquefied in a condenser 13 of the further rectification column 2a and fed continuously to an isomerization reactor 5, which is located downstream of the overhead of the further rectification column 2a and is operationally connected to it. In this context, "operationally connected" means that the isomerization reactor 5 and the further rectification column 2a are connected to each other during the operation of the process plant comprising these components in such a way that a mass and / or energy exchange can take place between the isomerization reactor 5 and the further rectification column 2a. Additionally, a hydrogen stream 14 is supplied to the isomerization reactor 5.The mass stream 12 enriched with isobutane and isobutene is fed separately from the hydrogen stream 14 into the isomerization reactor 5. This mass stream 12 can also be mixed with the hydrogen stream 14 before being fed into the isomerization reactor 5. Between 0.5 Nm³ / h and 5 Nm³ / h of hydrogen per t / h of the isobutane and isobutene-enriched mass stream 12 is fed into the isomerization reactor 5 via the hydrogen stream 14. Through this three-phase reaction of the mass stream 12 enriched with isobutane and isobutene as liquid phase, the hydrogen stream 14 as gaseous phase and the catalyst of the isomerization reactor 5 as solid phase, a mixing and distribution device, such as that known from EP 2 170 494 B1, is provided in the isomerization reactor 5 in order to achieve the highest possible mixing of the reactants.The mixing and distribution device comprises a trough distributor with trough-shaped channels and drain tubes in the trough-shaped channels for the liquid phase, and a distributor base located below the trough distributor with vertical nozzles. Furthermore, the isomerization reactor 5 comprises a catalyst with a horizontally arranged catalyst bed containing spherical particles, the catalyst comprising at least one hydrogenation-active metal on an aluminum oxide support. The hydrogenation-active metal of this catalyst is palladium with a mass fraction between 0.2% and 0.5%.The liquid phase of the mass stream 12, enriched with isobutane and isobutene, and the gaseous phase of the hydrogen stream 14 are passed from top to bottom in a co-current flow process through the isomerization reactor 5 via the mixing and distribution device over the fixed bed of the catalyst. The 1-butene present in the mass stream 12 enriched with isobutane and isobutene is catalytically isomerized to 2-butene using hydrogen. During this isomerization in the isomerization reactor 5, the temperature is between 40 °C and 70 °C and the pressure is between 7 bar and 16 bar.

[0037] In the embodiment shown according to Fig. 1 The product stream 15 from isomerization in isomerization reactor 5 is fed to a rectification column 6, which is downstream of isomerization reactor 5 and operationally connected to it. Rectification column 6 has between 130 and 180 stages, and the reflux-to-distillate ratio is 20:1. In rectification column 6, product stream 15, which consists of approximately 48% isobutane, approximately 50% isobutene, 100 to 200 ppm 1-butene, and 700 to 1200 ppm 2-butene, is separated by distillation. An isobutane-enriched stream is separated from rectification column 6 as the overhead product 16, with an isobutane mass fraction of 80 to 95% and an isobutene mass fraction of 5 to 20%. The rectification column 6 has a side draw-off 17, wherein between 12% and 15% of the total separation stages of the rectification column 6 are below the separation stage in which the side draw-off 17 is located.A stream 18 enriched with isobutene is separated via this side outlet 17, the mass fractions of which are 99.7% isobutene, 0.2% isobutane, 200 ppm 1-butene, and 400 ppm 2-butene. In the bottoms product 19 of the rectification column 6, the mass fraction of isobutene is approximately 98% and the mass fraction of 2-butene is approximately 2%. In the embodiment shown according to... Fig. 1 A portion of the bottom product 19 is fed into the C4 stream 7 as recycling stream 20. The bottom of the rectification column 6 and the line intended for feeding the C4 stream 7 into the further rectification column 2a are operationally connected by a line for carrying the recycling stream 20.

[0038] In the embodiment shown according to Fig. 1 A mass stream 21, which is a portion of the mass stream drawn off the top of the further rectification column 2a, is fed to the heat exchanger 22, which is the evaporator of rectification column 6, in order to transfer heat to the mixture to be evaporated in the bottom of rectification column 6 via the heat exchanger 22. To supply heat to the evaporator of rectification column 6, the further rectification column 2a is operated at a higher temperature and pressure than rectification column 6. A line for conveying the mass stream 21 connects the top of the further rectification column 2a to the heat exchanger 22 of rectification column 6.After heat transfer, a mass stream 23, which has a lower energy content than mass stream 21, is fed from the heat exchanger 22 into the condenser 13 of the further rectification column 2a in order to return the mass stream taken from the head of the further rectification column 2a for heat transfer to the head of the further rectification column 2a. Accordingly, the heat exchanger 22 of rectification column 6 and the condenser 13 of the further rectification column 2a are connected by a line for conveying the mass stream 23.

[0039] In Fig. 2 A process flow diagram of a further plant 1b according to the invention is shown, comprising a further rectification column 2b, a further catalyst 4b, the isomerization reactor 5, and the rectification column 6. The further catalyst 4b and the further rectification column 2b serve for the repeated isomerization and distillative separation of 1-butene in a C4 stream, wherein the further catalyst 4b is located in a separation stage within the further rectification column 2b for the isomerization of the 1-butene. Processes for the repeated isomerization and distillative separation of 1-butene in a C4 stream with a rectification column and a catalyst located in the rectification column are known, for example, from EP 1 200 378 B1.

[0040] In the embodiment shown according to Fig. 2 Before being fed into the further rectification column 2b, the C4 stream 7 is mixed with another hydrogen stream 9b and then fed into the further rectification column 2b. In addition to mixing the C4 stream 7 with the other hydrogen stream 9b, it is also possible to feed these two streams separately into the further rectification column 2b. In the further rectification column 2b, the C4 stream 7 is separated by distillation, and the 1-butene-containing product stream 8 formed in the further rectification column 2b, together with the hydrogen from the other hydrogen stream 9b, is fed to a further catalyst 4b, the further catalyst 4b being located in a separation stage within the further rectification column 2b. Fig. 2 Product stream 8 is not shown because it corresponds to a mass stream in the further rectification column 2b, which is located in the same separation stage as the further catalyst 4b and is brought into contact with it. In the presence of the further catalyst 4b, which is an Al₂O₃-supported PdO catalyst, the 1-butene contained in product stream 8 reacts with the hydrogen from the further hydrogen stream 9b in the further rectification column 2b to form 2-butene. The resulting reaction product stream 10, which contains less 1-butene and more 2-butene than product stream 8, is also located in the same separation stage as the further catalyst 4b and is separated by distillation in the further rectification column 2b. For this reason, reaction product stream 10 is also shown. Fig. 2 Not shown. The bottoms product of the further rectification column 2b is a 2-butene-enriched stream 11, and the overhead product is an isobutane- and isobutene-enriched stream 12, wherein this stream 12 contains less 1-butene and 2-butene than the C4 stream 7 fed to the further rectification column 2b before this C4 stream 7 is mixed with the further hydrogen stream 9b. The further process steps downstream of the further rectification column 2b in the illustrated embodiment according to Fig. 2 The process steps for obtaining a mass stream enriched with isobutene are the same as those following the further rectification column 2a in the embodiment according to Fig. 1 .

[0041] In Fig. 3 A process flow diagram of a further plant 1c according to the invention is shown, which includes the further rectification column 2b, the further catalyst 4b, the isomerization reactor 5 and the rectification column 6 according to the embodiment shown in the figure. Fig. 2 features. In contrast to the version according to Fig. 2 The rectification column 6 in the embodiment shown according to Fig. 3 No side outlet 17 is used to separate an isobutene-enriched material stream 18. The overhead product 16 of the rectification column 6 is fed to a second rectification column 24, which is located downstream of the overhead of rectification column 6. For this reason, the overhead of rectification column 6 and the second rectification column 24 are operationally connected.

[0042] In the embodiment shown according to Fig. 3 compared to the version according to Fig. 2 The rectification column 6 is operated at a higher pressure and / or temperature, such that a stream enriched with isobutane and isobutene is separated from the rectification column 6 as overhead product 16. This overhead product 16 is fed to the second rectification column 24 to separate the isobutene from the isobutane and to obtain an isobutane-enriched stream in overhead product 25 and an isobutene-enriched stream 18 in bottom product 26 of the second rectification column 24. The mass fraction of isobutene in this isobutene-enriched stream 18 is at least 99%.

[0043] In Fig. 4 A process flow diagram of a further plant 1d according to the invention is shown, which includes the further rectification column 2a, the reactor 3, which includes the further catalyst 4a, the isomerization reactor 5 and the rectification column 6 according to the embodiment shown in the Fig. 1 features. In contrast to the version according to Fig. 1 The rectification column 6 in the embodiment shown according to Fig. 4 No side outlet 17 is used to separate an isobutene-enriched material stream 18. The bottoms product 19 of the rectification column 6 is fed to an additional rectification column 27, which is located downstream of the bottoms of the rectification column 6. For this reason, the bottoms of the rectification column 6 and the additional rectification column 27 are operationally connected.

[0044] In the embodiment shown according to Fig. 4The mass stream 18, enriched with isobutene as bottom product 19 of rectification column 6, is fed to the additional rectification column 27. In the additional rectification column 27, the isobutene is separated from the 2-butene of the isobutene-enriched mass stream 18, and a further purified isobutene mass stream 28 is obtained as the overhead product 29 of the additional rectification column 27. The mass fraction of isobutene in this further purified isobutene mass stream 28 is at least 99.7%. The bottom product 30 of the additional rectification column 27, which contains isobutene and 2-butene, is partially fed to the C4 stream 7 as recycling stream 31. The sump of the additional rectification column 27 and the line intended for feeding the C4 stream 7 into the further rectification column 2a are operationally connected by a line for carrying the recycling stream 31.

Claims

1. A process for the purification of isobutene from a C4 stream (7) which comprises at least 1-butene, 2-butene, isobutane and isobutene, comprising the following steps: - supplying a stream of material which is concentrated in isobutane and isobutene (12) obtained from the C4 stream (7) and a stream of hydrogen (14) to an isomerization reactor (5), wherein the isomerization reactor (5) comprises a catalyst which comprises at least one metal which is active in hydrogenation on a support, preferably an aluminium oxide support; - bringing the stream of material which is concentrated in isobutane and isobutene (12) and the stream of hydrogen (14) into contact with the catalyst in the isomerization reactor (5), whereupon 1-butene present in the stream of material which is concentrated in isobutane and isobutene (12) is isomerized to 2-butene; - supplying a product stream (15) which comprises less 1-butene in relation to the stream of material which is enriched with isobutane and isobutene (12) from the isomerization reactor (5) to a rectification column (6); and - providing a stream of material which is concentrated in isobutene (18): ∘ by separating this stream of material (18): ▪ via a side stream (17) from the rectification column (6), or ▪ via a side stream (17) and as the bottom product (19) from the rectification column (6), or ▪ as a bottom product (19) from the rectification column (6), wherein furthermore, a stream of material which is concentrated in isobutane is separated from the rectification column (6) as the overhead product (16), or ∘ in which an overhead product (16) from the rectification column (6) that is concentrated in isobutane, which contains isobutene in addition to the isobutane, is supplied to a second rectification column (24) in order to separate the isobutane from the isobutene and to obtain the stream of material which is concentrated in isobutene (18) in the bottom product (26) from the second rectification column (24), wherein the C4 stream (7) from which the stream of material which is concentrated in isobutane and isobutene (12) is obtained is supplied to a further rectification column (2a, 2b) which is associated with a further catalyst which comprises at least one metal which is active in hydrogenation on a support, preferably on an aluminium oxide support, wherein the C4 stream (7) is separated by distillation in the further rectification column (2a, 2b) and a further hydrogen stream (9a, 9b) and a product stream which contains 1-butene (8) from the further rectification column (2a, 2b) are brought into contact with the further catalyst (4a, 4b), whereupon 1-butene present in said product stream is isomerized to 2-butene, wherein the reaction product stream (10) from the further catalyst (4a, 4b) is separated by distillation in the further rectification column (2a, 2b) and a stream of material which is concentrated in 2-butene (11) is separated from the further rectification column (2a, 2b) as the bottom product and the stream of material (12) which is concentrated in isobutane and isobutene is separated from the further rectification column (2a, 2b) as the overhead product and supplied to the isomerization reactor (5), wherein this stream of material (12) contains less 1-butene and 2-butene compared with the C4 stream (7).

2. The process as claimed in claim 1, characterized in that at least a portion of the further catalyst (4a) is located outside the further rectification column (2a) in a reactor (3), the product stream (8) is separated from the further rectification column (2a) via a side stream, the product stream (8) and the further stream of hydrogen (9a) are supplied to the reactor (3) and the reaction product stream (10) from the further catalyst (4a) is supplied to the further rectification column (2a).

3. The process as claimed in claim 1, characterized in that the further catalyst (4b) in the further rectification column (2b) is provided in at least one separation stage of the further rectification column (2b), the C4 stream (7) and the further stream of hydrogen (9b) are supplied to the further rectification column (2b) and the reaction product stream (10) is produced inside the further rectification column (2b).

4. The process as claimed in one of claims 1 to 3, characterized in that the temperature in the isomerization reactor (5) is between 20°C and 100°C, preferably between 30°C and 80°C, in particular between 40°C and 70°C.

5. The process as claimed in one of claims 1 to 4, characterized in that the pressure in the isomerization reactor (5) is between 3 bar and 30 bar, preferably between 5 bar and 20 bar, in particular between 7 bar and 16 bar.

6. The process as claimed in one of claims 1 to 5, characterized in that when supplied to the isomerization reactor (5), the flow rate of hydrogen (14) per t / h of the stream of material which is concentrated in isobutane and isobutene (12) is between 0.02 Nm3 / h and 200 Nm3 / h, preferably between 0.1 Nm3 / h and 50 Nm3 / h, in particular between 0.5 Nm3 / h and 5 Nm3 / h.

7. The process as claimed in one of claims 1 to 6, characterized in that at least a portion of the bottom product (19) from the rectification column (6) is supplied to the C4 stream (7) as the recycle stream (20).

8. The process as claimed in one of claims 1 to 7, characterized in that the stream of material which is concentrated in isobutene (18) is separated from the rectification column (6) via a side stream (17), wherein between 8% and 25%, preferably between 10% and 20%, in particular between 12% and 15% of the total separation stages of the rectification column (6) are below the separation stage in which the side stream (17) is located.

9. The process as claimed in one of claims 2 to 9, characterized in that the further rectification column (2a, 2b) is at a higher temperature than the rectification column (6) and the rectification column (6) is supplied with heat.

10. The process as claimed in one of claims 1 to 9, characterized in that the metal which is active in hydrogenation of the catalyst of the isomerization reactor (5) is from group 8, 9 or 10 of the periodic table of the elements, in particular palladium or platinum.

11. A processing facility (1a, 1b, 1c, 1d) for the purification of isobutene from a C4 stream (7) which contains at least 1-butene, 2-butene, isobutane and isobutene, comprising the following equipment: - an isomerization reactor (5) which comprises a catalyst which comprises at least one metal which is active in hydrogenation on a support, preferably an aluminium oxide support; anda rectification column (6) which is connected downstream of the isomerization reactor (5), characterized in that the processing facility comprises a further rectification column, which is associated with a catalyst which comprises at least one metal which is active in hydrogenation on a support, preferably on an aluminium oxide support, wherein the isomerization reactor is downstream of the head of the further rectification column.

12. The processing facility (1a, 1b, 1c, 1d) as claimed in claim 11, characterized in that it comprises a heat exchanger (22) which is connected to the rectification column (6) and the further rectification column (2a, 2b) for heat transfer between the rectification column (6) and the further rectification column (2a, 2b).

13. The processing facility (1a, 1b, 1c, 1d) as claimed in claim 11 or 12, characterized in that the rectification column (6) comprises a side stream (17) for separating a stream of material containing isobutene.

14. The processing facility (1a, 1b, 1c, 1d) as claimed in one of claims 11 to 13, characterized in that the bottom of the rectification column (6) is connected to the line provided to convey the C4 stream (7) for at least partial recycling of the bottom product (19) from the rectification column (6).