Energy-efficient process for separating butene from C4 hydrocarbon streams

Abstract

The subject of the invention is a process for separating butenes from C4 hydrocarbon streams containing butenes and butanes by extractive distillation with suitable solvents. The method according to the invention is characterized by a heat integration by means of which different streams are heated and / or at least partially evaporated using the heat of the solvent, and electrification of the process is provided using a heat pump.

Description

[0001] The present invention relates to a process for separating butenes from a C4 hydrocarbon stream containing butenes and butanes by extractive distillation with a suitable solvent. The process according to the invention is characterized by heat integration, by means of which the heat of the solvent is used to heat and / or at least partially evaporate different streams, and by the use of a heat pump to provide electrification for the process.

[0002] The separation of butane-butene mixtures by extractive distillation is known per se. The process uses an aprotic solvent (e.g. N-methyl-2-pyrrolidone (NMP) or acetonitrile (ACN)) to increase the relative volatility of the alkanes with respect to the olefins. In the extractive distillation column (absorber), the butenes are preferably dissolved in the solvent and the butane is separated as the top product. Subsequently, in the stripping column (desorber), the butenes are removed from the loaded solvent at elevated temperature and / or reduced pressure and obtained as the top product in an enriched form. The solvent after removal of the butenes is then recycled to the extractive distillation.

[0003] Due to the high solvent-to-feed ratio, heat integration is crucial for the economics of the process. The hot solvent obtained at the bottom of the desorber has an energy content that can be utilized in various ways. There is also an increasing social and political demand for CO2 reduction. This also has an increasingly significant impact on the economics of the process. US2014 / 0124358 A1 proposes a process for the selective extraction of olefins, which allegedly solves the heat integration problem. It is proposed therein to utilize the energy content of the hot solvent to heat a side stream of the desorber, to heat the absorber bottom product fed to the desorber, to heat one or more side streams of the absorber and to preheat the feed stream.

[0004] However, the solutions proposed in the prior art can only incompletely or only by relatively complex structures solve the problem of recovering as completely as possible the energy streams present in the system. In addition, the solutions proposed therein, if any, only make a small contribution to reducing CO2 emissions.

[0005] The problem to be solved by the present invention is therefore to provide a process in which improved, preferably maximized, energy recovery is achieved and the complexity of the plant engineering is low. In addition, CO2 emissions should be reduced as much as possible, preferably with a CO2-free process operation in the case where green electricity is available.

[0006] This technical problem is solved by the process embodiment proposed in claim 1. Preferred embodiments are given in the dependent claims. The process according to the invention is a process for separating butenes from a C4 hydrocarbon stream containing at least butenes and butanes by extractive distillation with a solvent, wherein the process comprises the following steps:

[0007] a. At least partially evaporate a liquid C4 hydrocarbon stream in a feed evaporator, supply a gaseous C4 hydrocarbon stream and a liquid solvent located above the C4 hydrocarbon stream to an absorber, and let the C4 hydrocarbon stream and the solvent come into contact with each other in the absorber, whereby mainly butene is transferred from the C4 hydrocarbon stream to the solvent. The loaded solvent is collected in a liquid collector of the absorber, led through an absorber evaporator, and then introduced into the bottom of the absorber below the liquid collector, whereby mainly butane is degassed from the loaded solvent, and whereby the loaded solvent is subsequently conveyed as a bottom stream to a desorber;

[0008] b. Supply the loaded solvent to a desorber, the bottom of the desorber being at an elevated temperature and preferably a lower pressure relative to the bottom of the absorber, and butene being separated from the solvent therein, whereby a butene-rich stream is obtained at the top of the desorber. At least part of the solvent substantially free of butene is collected in a liquid collector of the desorber and led through a desorber evaporator, and then introduced into the bottom of the desorber below the liquid collector, whereby the butene still present in the solvent is degassed, and whereby the solvent as a bottom stream of the desorber is subsequently recycled as a heat source of a multi-stage high-temperature heat pump to the absorber;

[0009] It is characterized in that at least part of the heat of the solvent taken out as a bottom stream of the desorber is used for heat integration, in which the heat of the solvent in respective at least one heat exchanger is used for heat transfer in the heat pump, for evaporation in the absorber evaporator, and for evaporating the liquid C4 hydrocarbon stream; and

[0010] The heat for evaporation in the desorber evaporator is introduced by steam generated by a multi-stage high-temperature heat pump, wherein the high-temperature heat pump at least comprises: a first container containing a first heat exchanger; a second container containing a second heat exchanger; and at least one compressor, wherein

[0011] The first container contains a first working medium, and the heat from the solvent generated as a bottom stream of the desorber is transferred to the first working medium in the first heat exchanger,

[0012] The second container contains a second working medium, and the heat from the first working medium is transferred to the second working medium in the second heat exchanger.

[0013] One advantage of this method is that the heat integration structure is relatively simple, yet it can efficiently recover energy. Another advantage of using a heat pump is that the method can operate more independently. For example, it does not require the purchase of a heating medium in the desorber evaporator. First, there must be a sufficient amount of this heating medium at the site where the method is carried out. In addition, by using a heat pump, the energy recovery is optimized. The waste heat of the solvent is heated to a specific temperature level by the heat pump so that it can be directly used in the desorber. The configuration of the present invention can also save a large amount of heating medium. This in turn reduces thousands of tons of CO2 per year. Therefore, in the case of using green electricity, n-butane and isobutane can even be separated without CO2. In addition, since the inert butane does not need to be entrained by the production equipment, high energy savings and efficiency improvements are also achieved in the separation of butane in an integrated system composed of multiple production equipment. This is especially true if the butane-butene separation of the present invention is employed at the front of the integrated system.

[0014] Through additional heat integration, heat is extracted from the solvent originating from the desorber. The reason for this is not only to use it to heat other streams or columns, but mainly to cool the solvent used for absorption. The absorption of butene (here: step a) is usually carried out at a lower temperature than the desorption (here: step b). If sufficient heat is extracted from the solvent during the heat integration process, i.e., the solvent has a suitable temperature, the solvent can be directly fed into the absorber. However, it is also conceivable that, despite this heat integration, the solvent does not have the correct temperature. In this case, the solvent can be passed through a residual cooler after the heat integration and before entering the absorber to be cooled to a suitable temperature.

[0015] Heat is a process parameter. The heat supplied or removed is equal to the change in internal energy minus the work done. The terms "heat", "heat transfer", and "heat integration" used in the present invention are all based on this definition.

[0016] This method relates to the separation of butene from a C4 hydrocarbon stream containing butene. These hydrocarbon streams usually contain alkanes (n-butane, isobutane) in addition to butene. In the present invention, unless otherwise specified, the term "butane" should be understood to refer to n-butane and isobutane. Therefore, all C4 hydrocarbon streams containing at least butene and butane can be used in the method of the present invention as long as the amounts of butene and / or butane present allow for the economic implementation of the method. In a preferred embodiment of the present invention, the C4 hydrocarbon stream used consists essentially, i.e., more than 98% by weight, preferably more than 99% by weight, of butane and butene. The corresponding stream may also contain small amounts of impurities or other hydrocarbons, such as 1,3-butadiene or C5 hydrocarbons.

[0017] In the extraction process of the present invention, a liquid solvent is used, which mainly dissolves butene in the gaseous C4 hydrocarbon stream used. Suitable solvents are aprotic solvents, such as N-methyl-2-pyrrolidone (NMP). The process of the present invention is preferably carried out using NMP as the solvent. In another preferred embodiment of the present invention, the solvent contains water, especially in an amount of 1 to 10% by weight, preferably 4 to 9% by weight, each based on the total amount of the solvent.

[0018] Absorbers that can be used especially include packed towers containing at least two packed beds. Such towers are in principle well known to those skilled in the art. Preferably, a backwash zone is provided above the first packed bed, and this backwash zone contains a plurality of theoretical plates to intercept the solvent entrained in the gas phase. Above the backwash zone is the top of the absorber, where a butane-rich stream is obtained relative to the C4 hydrocarbon stream used. According to the present invention, a liquid collector is provided below the last packed bed, and the bottom of the absorber is provided below this liquid collector. The specific structure of the absorber depends on various parameters and is variable in some aspects.

[0019] Spatially, the liquid solvent is supplied to the absorber above the inlet of the C4 hydrocarbon stream. In a preferred embodiment, the solvent is supplied to the absorber above the first packed bed, and the C4 hydrocarbon stream in one or more packed beds is supplied to the absorber below the first packed bed. In the absorber, the liquid solvent trickles down and contacts the (rising) vaporous C4 hydrocarbon stream, thereby transferring a part of the C4 hydrocarbon stream mainly containing butene to the solvent, and thus forming a loaded solvent. In step a, the C4 hydrocarbon stream and the solvent contact each other especially in a countercurrent manner. In a preferred embodiment of the present invention, the part of the C4 hydrocarbon stream transferred to the solvent contains at least 70% by weight of butene, particularly preferably at least 80% by weight of butene, based on the composition of the part of the C4 hydrocarbon stream transferred to the solvent. As a result, in particular, at least 80%, particularly preferably at least 90% of the butene contained in the C4 hydrocarbon stream used is transferred to the solvent.

[0020] The loaded solvent flows downward in the absorber and is collected in a suitable liquid collector, especially a chimney tray (Kaminboden). The temperature of the loaded solvent generated in the liquid collector is preferably 40°C to 90°C, particularly preferably 45°C to 65°C. The loaded solvent is taken out from the liquid collector, led through the absorber evaporator, and then introduced into the bottom of the absorber below the liquid collector, thereby mainly degassing butane from the loaded solvent. The absorber evaporator is preferably a direct-flow evaporator, where the loaded solvent is led through the evaporator only once. This can achieve as low a temperature as possible, thereby preventing fouling. The driving temperature difference is also increased, which can more efficiently utilize the energy of the NMP stream. The absorber evaporator can also be configured in multiple stages, that is, there can be multiple heat exchangers or multiple evaporators belonging to the absorber evaporator.

[0021] The solvent mainly loaded with butene remains at the bottom and is withdrawn therefrom and sent as a bottom stream to a desorber. The temperature of the absorber bottom stream sent to the desorber is preferably from 70 °C to 130 °C, particularly preferably from 85 °C to 120 °C.

[0022] Then, a stream rich in butane is particularly obtained at the top of the absorber as compared to the C4 hydrocarbon stream used. The top pressure of the absorber can be from 3 to 7 bar absolute pressure, preferably from 4 to 6.5 bar absolute pressure. The butane-rich stream may also contain water derived from the solvent. These waters can be separated out in a subsequent step. The butane-rich stream is withdrawn from the top of the absorber and is subjected to single-stage or multi-stage condensation to condense out a water-containing stream and a butane-containing product stream. These two streams can be separated from each other in a suitable device, such as a spider collector (Euter). The water-containing stream separated from the butane-containing product stream can be fed to the absorber or the desorber according to its composition, and / or partially discharged from the process.

[0023] The butane-containing product stream obtained by this condensation may still contain a small amount of water, especially up to 1500 weight ppm based on the total composition of the butane-containing product stream. In addition, the butane-containing product stream obtained by condensation may also contain residual butene, wherein based on the total composition of the butane-containing product stream, the stream usually contains less than 20% by weight, preferably less than 15% by weight, particularly preferably less than 5% by weight of butene.

[0024] Depending on the requirements for the resulting butane-containing product stream, it may be necessary to dry the condensed butane-containing product stream. Preferably in a drying column to separate out the still contained water. After drying, the butane-containing product stream preferably has a maximum amount of water of 50 weight ppm, more preferably 25 weight ppm. The water generated during drying can be recycled to the absorber for condensation.

[0025] The solvent mainly loaded with butene taken from the bottom of the absorber is transported to the desorber. For this purpose, a pump can be used, for example, to transport the loaded solvent to the desorber. The bottom stream of the desorber has a high temperature and preferably a lower pressure relative to the bottom stream of the absorber. The temperature of the bottom stream of the desorber is preferably 120 °C to 200 °C, more preferably 130 °C to 195 °C. The top pressure of the desorber can be 1 to 6 bar absolute pressure, preferably 2 to 5 bar absolute pressure. Due to the increased temperature and preferably lower pressure relative to the absorber, butene and optionally still contained butane are at least partially removed from the solvent. In a preferred embodiment, the solvent at least partially free of butene contains at most 5000 weight ppm of butene, particularly preferably 100 to 900 weight ppm of butene. The solvent at least partially free of butene flows downward in the desorber and is collected in the liquid collector of the desorber. From there, the solvent at least partially free of butene is led through the desorber evaporator and then introduced into the bottom of the desorber below the liquid collector (especially a chimney tray), thereby degassing the butene still present in the solvent. The desorber evaporator is preferably a once-through evaporator, where the solvent at least partially free of butene is led through the evaporator only once. This enables the lowest possible temperature, thus preventing fouling. The desorber evaporator can also be configured in multiple stages, i.e., there can be multiple heat exchangers belonging to the desorber evaporator. Then, the solvent free of butene remains at the bottom, from where it is taken out, transported as a bottom stream to the absorber, and reused there as a solvent for absorbing butene.

[0026] Before being transported to the absorber, the solvent free of butene can be partially or fully regenerated to remove impurities in the solvent (preferably NMP), such as the impurities present in the used C4 hydrocarbon stream mentioned above and / or by-products formed from butene at the temperature of the desorber, such as oligomers or polymeric compounds. The regeneration is preferably carried out as follows: The solvent free of butene is transported to a container and evaporated at an absolute pressure below 500 mbar, more preferably below 200 mbar, and a temperature of 100 °C to 150 °C. This container can be connected to a column. In particular, high-boiling substances can be separated out by regeneration. If only a part of the solvent free of butene is regenerated, the regenerated part of the solvent is subsequently combined with the non-regenerated solvent and recycled to the absorber.

[0027] Then, a butene-rich stream is obtained particularly at the top of the desorber, compared to the C4 hydrocarbon stream used. This butene-rich stream may also contain water from the solvent. This water can be separated out in subsequent steps. The butene-rich stream is taken from the top of the desorber and undergoes single-stage or multi-stage condensation to condense out a water-containing stream (which may contain not only water but also organic residues) and a butene-containing product stream. These two streams can be separated from each other in a suitable device (such as a spider collector). Then, the water-containing stream separated from the butene-containing product stream can be recycled back to the desorber. All or part of the water-containing stream can also be discharged to remove organic substances.

[0028] In a preferred embodiment of the present invention, the condensation of the butene-rich stream taken from the top of the desorber is carried out in a two-stage condensation manner, where in the first stage, the water-containing stream is condensed out and recycled to the desorber; in the second stage, the butene-containing product stream is condensed out. However, it is also possible that in the second stage, any remaining water is also condensed out. These residual waters can be separated from the butene-containing product stream by a suitable device (such as a spider collector).

[0029] The butene-containing product stream obtained by condensation preferably contains less than 20% by weight, more preferably less than 16% by weight of butane, based on the total composition of the butene-containing product stream. In contrast, the butene-containing product stream obtained by condensation preferably has a butene content of at least 70% by weight, more preferably at least 75% by weight, and particularly preferably at least 86% by weight, based on the total composition of the butene-containing product stream.

[0030] A remarkable feature of the present invention is the use of heat integration by utilizing the heat of the solvent from the desorber to the absorber and the heat of the hot condensate obtained in the desorber evaporator. According to the present invention, the heat of the solvent (preferably NMP) taken as the bottom stream of the desorber is used for heat integration, where the heat of the solvent in at least one respective heat exchanger is used for heat transfer in a heat pump, for evaporation in the absorber evaporator, and for evaporating the liquid C4 hydrocarbon stream.

[0031] According to the present invention, at least part of the butene-free solvent (preferably NMP) is collected in the liquid collector of the desorber and led through the desorber evaporator, whereby the butene still present in the solvent can be degassed. The heat for evaporation in the desorber evaporator can be introduced in a heat exchanger by heat transfer of a suitable heat transfer medium. The heat transfer medium is steam generated by a heat pump integrated in the process and heat integration, and is, for example, in a pressure range of 5 to 30 bar, preferably 13 to 17 bar absolute pressure. The condensation temperature of 150 °C to 270 °C is obtained from the indicated pressure.

[0032] In the present invention, steam is generated in a multi-stage high-temperature heat pump. In principle, a single-stage high-temperature heat pump can also be envisaged and used. The multi-stage high-temperature heat pump includes at least one first container containing a first heat exchanger, a second container containing a second heat exchanger, and at least one compressor. It is also possible to use only a multi-stage compressor capable of independently compressing different gases from each other. However, the multi-stage high-temperature heat pump preferably also includes at least two compressors, with at least one for each stage.

[0033] The first container contains a first working medium, and the heat from the solvent generated as the bottom stream of the desorber is transferred to the first working medium in the first heat exchanger. The first working medium can in principle be a known heat transfer medium. However, it should be a medium that is not supercritical in the high-temperature range (i.e., at temperatures > 120 °C). In a preferred embodiment, the first working medium is selected from water, n-hexane, n-pentane, methanol, and mixtures thereof. The first container can also be a kettle evaporator that contains a heat exchanger integrated in the container.

[0034] The heat transfer from the solvent generated as the bottom stream of the desorber to the first working medium takes place in the first heat exchanger. The first heat exchanger can be connected to the bottom of the first container, and the first working medium can be circulated through the first heat exchanger back to the first container. The first working medium is heated and at least partially evaporated in the first heat exchanger. This also increases the pressure inside the first container. The evaporated first working medium can then be taken out from the container lid. Through heat transfer, the first working medium is raised to a first temperature level. The temperature of the first working medium is preferably 80 °C to 140 °C. The pressure is preferably 2 to 8 bar absolute pressure. The evaporated first working medium is conveyed to the second heat exchanger via the at least one compressor or via the first compressor and circulated back to the first container from there. During the circulation from the second heat exchanger, the first working medium can be passed through another heat exchanger, and the evaporated first working medium is further heated by this heat exchanger before passing through the at least one compressor or the first compressor.

[0035] The second container contains a second working medium, and the heat of the first working medium is transferred to the second working medium in the second heat exchanger. The second working medium can in principle be a known heat transfer medium. However, it should be a medium that is not supercritical in the high-temperature range (i.e., at temperatures > 120 °C). Even at temperatures > 150 °C, the second working medium is preferably not supercritical. In a preferred embodiment, the second working medium is selected from water, n-hexane, n-pentane, methanol, and mixtures thereof. The second container can also be a kettle evaporator that contains a heat exchanger integrated in the container.

[0036] Heat transfer from the first working medium to the second working medium takes place in the second heat exchanger. The second heat exchanger can be connected to the bottom of the second container, and the second working medium can be circulated to the second container through the second heat exchanger. The first working medium is heated and at least partially evaporated in the second heat exchanger. This also increases the pressure inside the second container. The evaporated first working medium can then be taken out at the container lid. The first working medium is raised to a second temperature level by heat transfer, where the second temperature level is higher than the first temperature level. The temperature of the first working medium is preferably 80 °C to 140 °C. The pressure is preferably 2 to 8 bar absolute pressure. The evaporated second working medium is conveyed in the form of steam according to the invention via the at least one compressor or via the second compressor to the desorber evaporator and circulated from there to the second container. Fresh condensate can be injected before the evaporated working medium reaches the desorber evaporator to bring the temperature and pressure to the required level, preferably to slightly cool the steam. During the circulation from the desorber evaporator, the second working medium can be passed through another heat exchanger through which the evaporated second working medium is further heated before passing through the at least one compressor or the second compressor.

[0037] The advantages of this embodiment are obvious. The steam is inherently provided by the heat pump without the need for additional purchase. In addition, the heat utilization rate in this method is significantly higher than other known methods. This is a significantly improved heat integration. In addition, due to the higher utilization rate of the heat condensate in this case, a large amount of steam can also be saved.

[0038] In a preferred embodiment of the present invention, a separation plate is provided at the bottom of the absorber, whereby the bottom is divided into two sections and two-stage evaporation is carried out so that the loaded solvent collected in the liquid collector passes through the first evaporator (preferably a once-through evaporator) and enters the first section; the loaded solvent from the first section passes through the second evaporator (preferably a forced-circulation evaporator) and flashes into the second section, and then the bottom stream is taken out from the second section to the desorber. One advantage of this structure is that the embodiment of the bottom of the absorber (i.e., through the presence of the separation plate and two-stage evaporation) can reduce the height of the absorber while improving the separation efficiency.

[0039] In another preferred embodiment, it is also possible that the desorber includes a side evaporator. In this case, the heat transfer medium used in the side evaporator can be the mixed steam from the steam ejector, while the medium-pressure steam is used as the heating steam for the desorber evaporator. The hot condensate from the desorber evaporator and the side evaporator is then conveyed to the condensate container as described above. The low-pressure steam obtained there is then used for the steam ejector, and its mixed steam is used for the side evaporator. The advantage of this solution is that the obtained hot condensate can be further depressurized, so that a larger amount of low-pressure steam can be provided.

[0040] The method according to the present invention can be used in a chemical integration system, which particularly includes oligomerization and optionally hydroformylation. The butene separation of the method according to the present invention can be used at different positions in the integration system. The butene separation of the present invention can also be used at multiple positions within the chemical integration system.

[0041] For example, the method described herein can be used at the starting stage of the integration system. The C4 hydrocarbon stream used can be in particular cracked C4, raffinate 1, raffinate 2, or a mixture thereof. If cracked C4 and / or raffinate 2 are used, cracked C4 hydrogenation can be carried out before the separation method of the present invention, in which butadiene is selectively hydrogenated, or butadiene separation can be carried out, in which butadiene is removed by extraction with a solvent such as NMP or nitrile to reduce the butadiene content. Hydroisomerization can also be provided after the extraction butadiene separation and before the separation of the present invention to simplify the separation task in the method of the present invention, since 1-butene is converted into 2-butene, which is generally more easily absorbed by the solvent. The advantage of butane separation is that the residence time of all reaction stages is longer because less inert butane needs to be transported to each stage. From an energy perspective, integration is desirable, especially after butadiene separation and before MTBE synthesis. Thus, inert isobutane / n-butane can be separated from the integration system as early as possible without going through all subsequent distillation steps.

[0042] If the separation method is used at the starting stage of the integration system, the resulting product stream can be fed to MTBE synthesis, preferably followed successively by 1-butene separation, oligomerization, and one or more hydroformylations of the purified oligomer. Hydroformylation can be carried out not only with the product stream of oligomerization, so that for example INA (isononanol) can be prepared from di-n-butene or ITDA (isotridecanal) can be prepared from tri-butene by subsequent hydrogenation; it can also be carried out with the unreacted butenes in the oligomerization, so that 2-PH (2-propylheptanol) can be prepared by subsequent aldol condensation and subsequent hydrogenation. With the unreacted butenes in the oligomerization, further oligomerization can also be optionally carried out instead of hydroformylation. Those skilled in the art are familiar with the conditions of each method step. Each method step may include other steps, such as product separation or post-treatment of the resulting stream, but these are not explicitly mentioned herein. However, the separation method of the present invention can also be introduced at various other positions in the integration system.

[0043] In one embodiment of the present invention, the C4 hydrocarbon stream used in the separation method of the present invention is taken out from MTBE synthesis after MTBE is separated, and then the butene-containing product stream is sent to 1-butene separation, followed successively by oligomerization and one or more hydroformylations to subsequently prepare 2-PH, ITDA, and / or INA. Each method step may include other steps, such as separation of the product or post-treatment of the resulting stream, but these are not explicitly mentioned herein.

[0044] In another embodiment of the present invention, the C4 hydrocarbon stream used in the separation method of the present invention is taken from the 1-butene separation, and then the butene-containing product stream is sent to oligomerization, followed by one or more hydroformylations to subsequently prepare 2-PH, ITDA, and / or INA. Each method step may include other steps, such as the separation of the product or the post-treatment of the resulting stream, but these are not explicitly mentioned herein.

[0045] In another embodiment of the present invention, the C4 hydrocarbon stream used in the separation method of the present invention is taken from oligomerization, and then the butene-containing product stream is fed into hydroformylation to subsequently prepare 2-PH. Each method step may include other steps, such as the separation of the product or the post-treatment of the resulting stream, but these are not explicitly mentioned herein.

[0046] In another embodiment of the present invention, the separation method of the present invention is used at the end of an integrated system. In this case, the C4 hydrocarbon stream used is taken from the preparation of 2-PH after hydroformylation. The butene-containing product stream thus obtained by the separation method of the present invention can be recycled in this case and used at a suitable location in the integrated system, for example, for 1-butene separation, for oligomerization, or for one or more hydroformylations. This can improve the efficiency of the entire integrated system because up to 20 wt% of butene may still be present even after the last method step in the integrated system.

[0047] Regardless of the position of the separation method of the present invention in the integrated system, the butane-containing product stream can be transported to, for example, adiabatic oligomerization, hydrogenation of the remaining butene, or normal / iso separation of butane (where n-butane and isobutane are separated from each other). The normal / iso separation can also be carried out after adiabatic oligomerization. Another possibility is to integrate the butane-containing product stream into the integrated system consisting of MTBE synthesis, 1-butene separation, oligomerization, and hydroformylation before oligomerization.

[0048] In a particularly preferred embodiment of the present invention, the energy required for normal / iso separation can be achieved at least in part by thermal integration with the first stage of the two-stage condensation at the top of the desorber. The advantage of this is that the energy generated during the condensation process is utilized, rather than simply being discharged into the environment as in the prior art.

[0049] The present invention will be described in detail below with reference to the accompanying drawings. The drawings are for illustrative purposes only and should not be construed as limiting the present invention.

[0050] Figure 1Shows a basic embodiment of the present invention. The liquid C4 hydrocarbon stream is evaporated through a heat exchanger (4) and fed into an absorber (1). If necessary, the solvent is heated to the required temperature through a residual cooler (3) and also fed into the absorber, where the inlet is spatially above the C4 hydrocarbon stream inlet, and in this case above the first packing bed. A butane-rich stream is produced at the top of the absorber (1) and is withdrawn. Possible condensation is not shown in the figure, only the circulation of possible sub-streams is shown. The loaded solvent is collected at the bottom of the absorber (1), as shown by the chimney tray in the figure. There, at least part of the loaded solvent is withdrawn and sent to the bottom of the absorber (1) through an absorber evaporator (5). The loaded solvent is withdrawn from the bottom of the absorber (1) and sent to a desorber (2) through a pump (9), where the butene present in the solvent is separated from the solvent. A butene-rich stream is produced at the top of the desorber. This stream can be condensed in one or multiple stages, which is not shown in the figure. Only the possible circulating streams are shown. At least part of the butene-free solvent is collected at the bottom of the desorber (2), as shown by the chimney tray in the figure. There, at least part of the loaded solvent is withdrawn and sent to the bottom of the desorber through a desorber evaporator (7). The butene-free solvent is then withdrawn from the bottom of the desorber (2) and circulated to the absorber using a pump (8) via a first container containing a first heat exchanger (20), an absorption evaporator (5), a heat exchanger (4) for evaporating the C4 hydrocarbon stream, and a residual cooler (3). In the first container containing the first heat exchanger (20), at least part of the first working medium is evaporated and sent to a second container containing a second heat exchanger (23) via another heat exchanger (21) for further heating and a first compressor (22). In the second container containing the second heat exchanger (23), at least part of the second working medium is evaporated and sent to the desorber evaporator (7) via a second compressor (24).

[0051] Figure 2 Shows a preferred embodiment of the present invention, where a separation plate is provided at the bottom of the absorber (1). In this embodiment, a part of the loaded solvent is withdrawn from the chimney tray of the absorber (1) and sent to the first section at the bottom of the absorber (1) with the separation plate through an absorber evaporator (5). The loaded solvent is withdrawn from the first section and sent to the second section at the bottom of the absorber through a pump (13) via a second evaporator (14). The loaded solvent is withdrawn from the second section at the bottom of the absorber (1) and sent to the desorber (2) through a pump (9) via a heat exchanger (6) for preheating the loaded solvent, where the butene present in the solvent is separated from the solvent. During the circulation of at least part of the butene-free solvent, heat is transferred in the heat exchanger in this preferred embodiment.

[0052] Figure 3Shows a preferred embodiment of the present invention, in which there is a flash tank (26) for intermediate pressure reduction (26) and an additional compressor (25). Through these two compressors (22, 25), the first working medium is delivered to the second heat exchanger (23) and thus at least partially condensed. Then, the first working medium enters the flash tank (26) and separates therein. A part is delivered via another heat exchanger (21) to the first container containing the first heat exchanger (20). Another part is delivered between the two compressors (22 and 25), thus reducing the load on the first compressor (22). Therefore, it is no longer necessary to compress all the working medium from a low pressure level to a high pressure level, but only a certain proportion thereof, which brings further energy advantages.

[0053] Figure 4 Shows an embodiment of the present invention, in which according to Figure 2 There is a separating plate in the absorber, and according to Figure 3 , the first working medium undergoes intermediate pressure reduction in the flash vessel (26).

[0054] The present invention will now be illustrated in conjunction with simulations. This embodiment is only a preferred embodiment and should not be construed as limiting. Example

[0055] Figure 1 The shown butane-butene separation was simulated using Aspen Plus V10. An improved NRTL parameter set was used to describe the interactions between the components. In the simulation, a hydrocarbon feed of 27 tons per hour was fed into the butane / butene separation. This feed contains a total of 45 wt% butane (35 wt% n-butane and 10 wt% isobutane), 30 wt% isobutene, 10 wt% 1-butene, 10 wt% trans-butene, and 5 wt% cis-butene.

[0056] A total of 10 tons per hour of butane-containing top product was taken out from the absorber. The butane-containing top product of the absorber consists of 70 wt% n-butane, 27 wt% isobutane, 1 wt% 1-butene, and 2 wt% isobutene. The solvent loaded with the butene-containing product stream was extracted from the bottom. The butene-containing product stream contains 14 wt% n-butane, 15 wt% 1-butene, 47 wt% isobutene, 8 wt% cis-butene, and 16 wt% trans-butene. With a set solvent / feed ratio of 13, a butene yield of 98% can thus be achieved. A large excess of solvent is also used for heat integration and as a heat source for the heat pump.

[0057] The solvent stream (here NMP) is fed from the bottom of the desorber (2) to a heat exchanger, namely a kettle evaporator (20), where n-hexane evaporates at an absolute pressure of 3.6 bar. The NMP is cooled from about 180 °C to 190 °C to about 120 °C to 125 °C and transfers 13.4 MW. This forms a n-hexane recycle stream of slightly more than 240 t / h, which is superheated by 42 K at the gas superheater (21). Subsequently, the n-hexane stream is compressed to a pressure level of 14.1 bar absolute pressure by a multi-stage compressor (22). In another heat exchanger, namely a kettle evaporator (23), the working medium n-hexane condenses inside the tubes. Water evaporates on the shell side at an absolute pressure of 7 bar. This steam is compressed to 13.1 bar absolute pressure by another compressor (24). This forms about 35 t / h of steam, which is used for evaporation in the desorber evaporator. Both working media are circulated.

[0058] Compared to conventional butane-butene separation that requires the purchase or provision of heating media, the embodiments of the present invention ensure a significant saving potential of up to 35 t / h. This amount is now produced internally by the heat pump.

Claims

1. A method for separating butene from a C4 hydrocarbon stream containing at least butene and butane by solvent extraction distillation, wherein the method comprises the following steps: a. At least partially evaporate the liquid C4 hydrocarbon stream in a feed evaporator, supply the gaseous C4 hydrocarbon stream and the liquid solvent located above the C4 hydrocarbon stream to an absorber, where the C4 hydrocarbon stream and the solvent come into contact with each other, thereby mainly transferring butene from the C4 hydrocarbon stream to the solvent. The loaded solvent is collected in the liquid collector of the absorber, passed through the absorber evaporator, and then introduced into the bottom of the absorber below the liquid collector, thereby mainly degassing butane from the loaded solvent. And subsequently, the loaded solvent is conveyed as a bottom stream to a desorber; b. Supply the loaded solvent to the desorber. The bottom of the desorber is at a higher temperature and preferably a lower pressure relative to the bottom of the absorber, and butene is separated from the solvent therein, thereby obtaining a butene-rich stream at the top of the desorber. At least part of the butene-free solvent is collected in the liquid collector of the desorber and passed through the desorber evaporator, and then introduced into the bottom of the desorber below the liquid collector, thereby degassing the butene still present in the solvent. And the solvent as the bottom stream of the desorber is subsequently recycled to the absorber as the heat source of a multi-stage high-temperature heat pump; It is characterized in that at least part of the heat of the solvent taken out as the bottom stream of the desorber is used for heat integration, in which the heat of the solvent in respective at least one heat exchanger is used for heat transfer in the heat pump, for evaporation in the absorber evaporator, and for evaporating the liquid C4 hydrocarbon stream; and The heat for evaporation in the desorber evaporator is introduced by steam generated by a multi-stage high-temperature heat pump, where the high-temperature heat pump at least includes: a first container containing a first heat exchanger; a second container containing a second heat exchanger; and at least one compressor, wherein The first container contains a first working medium, and the heat from the solvent generated as the bottom stream of the desorber is transferred to the first working medium in the first heat exchanger, The second container contains a second working medium, and the heat from the first working medium is transferred to the second working medium in the second heat exchanger.

2. The method according to claim 1, wherein the heat pump includes at least two compressors.

3. The method according to claim 1 or 2, wherein the first working medium is selected from water, n-hexane, n-pentane, methanol, and mixtures thereof.

4. The method according to any one of claims 1 to 3, wherein the second working medium is selected from water, n-hexane, n-pentane, methanol, and mixtures thereof.

5. The method according to any one of claims 1 to 4, wherein the first working medium and the second working medium are different.

6. The method according to any one of claims 1 to 5, wherein at least part of the first working medium is evaporated by the heat introduced during heat transfer.

7. The method according to claim 6, wherein the evaporated working medium is conveyed via the at least one compressor to a second heat exchanger and circulated from there to the first container, preferably via a further third heat exchanger, and the evaporated first working medium is further heated using the third heat exchanger before being passed through the at least one compressor.

8. The method according to claim 7, wherein the second working medium is at least partially evaporated by the heat introduced during heat transfer.

9. The method according to claim 8, wherein the second working medium is circulated via the at least one compressor to a desorber evaporator and circulated from there to the second container in at least partially condensed form, preferably via a further fourth heat exchanger, and the second working medium is further heated using the fourth heat exchanger before being passed through the second compressor.

10. The method according to any one of the preceding claims, wherein the solvent used is NMP.

11. The method according to claim 10, wherein the solvent or NMP contains water and the water content is from 1 wt% to 10 wt%, preferably from 4 wt% to 9 wt%.

12. The method according to any one of the preceding claims, wherein a butane-rich stream is obtained at the top of the absorber as compared to the C4 hydrocarbon stream used.

13. The method according to any one of the preceding claims, wherein the temperature of the absorber bottom stream conveyed to the desorber is from 70 °C to 130 °C, preferably from 85 °C to 120 °C.

14. The method according to any one of the preceding claims, wherein the temperature of the desorber bottom stream is from 120 °C to 200 °C, preferably from 130 °C to 195 °C.

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