An energy-efficient process for the separation of butenes from C4 hydrocarbon streams

Abstract

The present invention relates to a process for separating butenes from a C4 hydrocarbon stream containing butenes and butanes by extractive distillation using a suitable solvent. The process according to the invention is characterized by heat integration, using the heat of the solvent to heat and / or at least partially vaporize various streams, and by the use of a heat pump to electrify the process.

Description

[Technical Field]

[0001] The present invention relates to a process for separating butenes from a C4 hydrocarbon stream containing butenes and butanes by extractive distillation using a suitable solvent. The process according to the invention is characterized by heat integration, using the heat of the solvent to heat and / or at least partially vaporize various streams, and by the use of a heat pump to electrify the process. [Background technology]

[0002] The separation of butane-butene mixtures by extractive distillation is known per se. It uses aprotic solvents (e.g., N-methyl-2-pyrrolidone (NMP) or acetonitrile (ACN)) to increase the relative volatility of alkanes compared to alkenes. In one extractive distiller, the absorber, the butenes are preferentially dissolved in the solvent, and the butanes are separated as an overhead product. Then, in one absorber, the desorber, the butenes are removed from the butene-containing solvent at elevated temperature and / or reduced pressure and recovered in concentrated form as an overhead product. The butene-depleted solvent is recycled to the extractive distillation.

[0003] Heat integration is crucial to the economic efficiency of the process due to the high solvent-to-feed ratio. A hot solvent is produced in the bottom of the desorber, and its energy can be utilized in various ways. Furthermore, social and political demands for CO2 reduction are increasing, which is having an increasingly large impact on the economic efficiency of the process. Patent Document 1 presents a process for the selective extraction of olefins, which aims to solve the heat integration problem. Patent Document 1 proposes utilizing the energy of the hot solvent to heat a side stream from the desorber, to heat the bottom product of the absorber that is 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 either do not solve the problem of recovering as much of the energy flow present in the system as possible, or only do so with relatively complex structures, and moreover, they make little contribution to reducing CO2 emissions. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] US Patent Application Publication No. 2014 / 0124358 Summary of the Invention [Problem to be solved by the invention]

[0006] The problem addressed by the present invention is therefore to provide a process that is as uncomplicated in terms of plant engineering as possible while improving energy recovery as much as possible, and that also reduces CO2 emissions as much as possible and, if green electricity is available, allows for at best CO2-emission-free process management. [Means for solving the problem]

[0007] This problem is solved by the design of the process proposed in claim 1. Preferred embodiments are set out 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 using a solvent, comprising: (a) at least partially evaporating liquid C4 hydrocarbons in a feed evaporator to provide a gaseous C4 hydrocarbon stream, and feeding a liquid solvent above the C4 hydrocarbon stream to an absorber, where the C4 hydrocarbon stream and the solvent are brought into contact with each other to transfer mainly the butenes from the C4 hydrocarbon stream to the solvent, and recovering the solvent containing the butenes in a liquid collector of the absorber, passing it through an absorption evaporator, and feeding it to the bottom of the absorber from below the liquid collector, and degassing and releasing mainly the butanes from the solvent containing the butenes, and then feeding the solvent containing the butenes as a bottom stream to a desorber; b) feeding the solvent containing the butenes to the desorber, wherein the bottom of the desorber is at a higher temperature and preferably a lower pressure than the bottom of the absorber, separating the butenes from the solvent to produce a butene-rich stream at the top of the desorber, recovering the solvent from which the butenes have been at least partially removed in the liquid collector of the desorber, passing it through a desorption evaporator, and feeding it from below the liquid collector to the bottom of the desorber to degas the butanes remaining in the solvent, and then recycling the solvent to the absorber as the bottom stream of the desorber as a heat source for a multi-stage high-temperature heat pump; where: The heat of the solvent removed as the bottom stream of the desorber is at least partially used for heat integration by utilizing it in at least one heat exchanger for heat transfer in the multi-stage high temperature heat pump, for evaporation in the absorption evaporator, and for evaporation of a liquid C4 hydrocarbon stream, wherein: Heat for evaporation in the desorber-evaporator is introduced via vapor generated by the multi-stage high-temperature heat pump, wherein the multi-stage high-temperature heat pump comprises at least a first vessel including a first heat exchanger, a second vessel including a second heat exchanger, and at least one compressor, wherein the first vessel contains a first working medium, and heat from the solvent obtained as a bottom stream of the desorber is transferred to the first heat exchanger; and The second vessel contains a second working medium to which heat is transferred from the first working medium in the second heat exchanger.

[0008] One advantage of this process is its efficient energy recovery despite a relatively simple heat integration design. The use of a heat pump also allows for more independent operation of the process, eliminating the need to purchase a heating medium for the desorber / evaporator. Such a heating medium must first be available in sufficient quantities locally. Furthermore, energy recovery is optimized by using a heat pump. The waste heat from the solvent can be heated to a certain temperature level by the heat pump, allowing it to be directly used in the desorber. The design of the present invention also saves a significant amount of heating medium, resulting in several tons of CO2 reduction per year. When using green electricity, n-butane and isobutane can be separated without CO2 emissions. Furthermore, because butane separation does not require the transport of inert butane through production plants, significant energy savings and improved energy efficiency can be achieved in networks of multiple production plants. This is especially true when the butane-butene separation of the present invention is used in an early stage of the system.

[0009] Further heat integration removes heat from the solvent coming from the desorber. This is primarily for cooling the solvent for absorption, as well as for heating other streams or columns. The absorption of butenes ((a) above) is usually carried out at a lower temperature than its desorption ((b) above). If sufficient heat is extracted from the solvent during heat integration, i.e., if the solvent is at the appropriate temperature, it can be fed directly to the absorber. However, it is possible that, despite heat integration, the solvent is not yet at the appropriate temperature. In such cases, the solvent can be passed through a residue cooler to cool it to the appropriate temperature after heat integration and before being fed to the absorber.

[0010] Heat is the process variable. Heat supplied or removed corresponds to the change in internal energy minus the work done. The terms "heat," "heat transport," and "heat integration" used in this invention will always be based on this definition.

[0011] The present process relates to the separation of butenes from a butene-containing C4 hydrocarbon stream. This stream typically contains butenes and alkanes (n-butane, isobutane). In the context of the present invention, the term "butane" is understood to mean both n-butane and isobutane, unless otherwise specified. This means that all C4 hydrocarbon streams containing at least butenes and butanes can be used in the process according to the invention, as long as the amount of butenes and / or butanes present makes the process economically viable. In a preferred embodiment of the present invention, the C4 hydrocarbon stream used consists essentially of butanes and butenes, i.e., 98% by mass or more, preferably 99% by mass or more. The corresponding stream may contain small amounts of impurities or other hydrocarbons, such as 1,3-butadiene or C5 hydrocarbons.

[0012] The extraction process according to the invention uses a liquid solvent that primarily dissolves the butenes of the gaseous C4 hydrocarbon stream used. Suitable solvents are, for example, aprotic solvents such as N-methyl-2-pyrrolidone (NMP). The process according to the invention is preferably carried out using NMP as solvent. In a further preferred embodiment of the invention, the solvent contains, in particular, water in the range of 1% to 10% by weight, preferably 4% to 9% by weight, based in any case on the total amount of solvent.

[0013] In particular, a packed column with at least two packed beds may be used as the absorber. Such columns are generally known to those skilled in the art. A backwash zone with several theoretical trays is preferably located above the first packed bed to retain the solvent entrained in the gas phase. Above the backwash zone is the top of the absorber, where a stream richer in butanes than the C4 hydrocarbon stream used is produced.

[0014] The liquid collector of the present invention is located below the last packed bed, below which is located the bottom of the absorber. The exact configuration of the absorber depends on various parameters and is variable in some embodiments.

[0015] The liquid solvent is fed to the absorber above the inlet of the C4 hydrocarbon stream. In a preferred embodiment, the solvent is fed above the first packed bed, and the C4 hydrocarbon stream is fed to the absorber via one or more packed beds below the first packed bed. The liquid solvent is dropped into the absorber and contacted with the (rising) gaseous C4 hydrocarbon stream, so that the portion of the C4 hydrocarbon stream containing mainly butenes passes through the solvent, thereby loading the solvent with butenes. The C4 hydrocarbon stream and the solvent contact each other, particularly in countercurrent flow, in (a) above. In a preferred embodiment of the present invention, the portion of the C4 hydrocarbon stream that has passed through the solvent contains at least 70% by mass, particularly preferably at least 80% by mass, of butenes relative to the composition of the portion of the C4 hydrocarbon stream that has passed through the solvent. This results in at least 80%, particularly preferably at least 90%, of the butenes contained in the C4 hydrocarbon stream used being transferred to the solvent.

[0016] The butene-containing solvent (from which butenes have been removed) flows downward through the absorber and is collected in a suitable liquid collector, particularly a chimney base. The temperature of the butene-containing solvent accumulated in the liquid collector is preferably 40°C to 90°C, particularly preferably 45°C to 65°C. The butene-containing solvent is collected from the liquid collector, passes through an absorption evaporator, and then is fed to the bottom of the absorber from below the liquid collector, where it is degassed and discharged, primarily to remove butanes from the butene-containing solvent. The absorption evaporator is preferably a once-through evaporator, through which the butene-containing solvent passes only once. This allows the temperature to be kept as low as possible, thereby preventing fouling. Furthermore, the driving temperature difference is increased, resulting in even more efficient energy utilization of the NMP stream. The absorption evaporator may be of a multi-stage design, i.e., equipped with multiple heat exchangers or multiple evaporators.

[0017] The solvent, mainly comprising butenes, then remains at the bottom, where it is stripped and fed as a bottom stream to the desorber. The temperature of the absorber bottom stream fed to the desorber is preferably between 70°C and 130°C, particularly preferably between 85°C and 120°C.

[0018] In this case, a butane-rich stream is obtained, particularly at the top of the absorber, compared to the C4 hydrocarbon stream used. The absorber top pressure may be 3 to 7 bar (absolute), preferably 4 to 6.5 bar (absolute). The butane-rich stream may further contain water originating from the solvent. This water may be separated in a subsequent step. The butane-rich stream is removed at the top of the absorber and fed to a single- or multi-stage condensation process, in which a water-containing stream and a butane-containing product stream are condensed. These two streams can be separated from each other in a suitable device, for example a spider. Depending on its composition, the water-containing stream separated from the butane-containing product stream can be fed to an absorber or a desorber and / or partially discharged from the process.

[0019] The butane-containing product streams obtained from the condensation in this way may still contain small amounts of water, in particular in an amount of up to 1500 ppm by mass, based on the total composition of the butane-containing product stream. Furthermore, the butane-containing product streams obtained from the condensation may still contain residual butenes, in which case these streams may typically contain less than 20% by mass, preferably less than 15% by mass, and particularly preferably less than 5% by mass, of butenes, based on the total composition of the butane-containing product stream.

[0020] Depending on the requirements of the resulting butane-containing product stream, it may be necessary to dry the butane-containing product stream after condensation, preferably in a dryer, to separate any water present. Preferably, the butane-containing product stream contains a maximum amount of water of 50 ppm by weight, preferably 25 ppm by weight, after drying. Water formed during drying can be returned to the absorber and condensed.

[0021] The solvent removed at the bottom of the absorber and mainly comprising butenes is fed to the desorber. The solvent comprising butenes may be fed to the desorber, for example, using a pump. The bottom of the desorber is at a higher temperature and preferably at a lower pressure than the bottom of the absorber. The temperature at the bottom of the desorber is preferably 120°C to 200°C, more preferably 130°C to 195°C. The overhead pressure in the desorber may be 1 to 6 bar (absolute), preferably 2 to 5 bar (absolute). At a higher temperature and preferably lower pressure than in the absorber, butenes and possibly still present butanes are at least partially removed from the solvent. In a preferred embodiment, the solvent from which at least butenes have been removed contains up to 5000 mass ppm butenes, particularly preferably 100 to 900 mass ppm butenes. The solvent from which at least butenes have been removed flows downward in the desorber and is recovered in the liquid collector of the desorber. From there, the solvent from which the butenes have been at least partially removed passes through a desorption-evaporator and is then fed to a liquid collector, in particular the bottom of the desorber below the chimney base, to degas the remaining butanes in the solvent. The desorption-evaporator is preferably a once-through evaporator, through which the solvent from which the butenes have been at least partially removed passes only once. This allows the temperature to be kept as low as possible, thereby preventing fouling. The desorption-evaporator may be of a multi-stage design, i.e., comprise multiple heat exchangers. The butene-depleted solvent remains at the bottom, where the solvent is removed and fed as a bottom stream to an absorber for reuse as a solvent for butene absorption.

[0022] The butene-free solvent can be partially or completely regenerated before being fed to the absorber, thereby removing impurities, such as by-products present in the C4 hydrocarbon stream used and / or by-products formed from butenes at the temperature in the desorber, such as oligomeric or polymeric compounds, from the solvent, preferably NMP. Regeneration is preferably carried out by feeding the butene-free solvent to a vessel and evaporating it at a pressure of less than 500 mbar (absolute), more preferably less than 200 mbar (absolute), and at a temperature of 100°C to 150°C. A column can also be connected to the vessel. Regeneration processes are particularly used in the separation of high-boiling boilers. If only the butene-free solvent portion is regenerated, the regenerated solvent portion is recycled to the absorber in combination with unregenerated solvent.

[0023] At the top of the desorber, a stream is produced that is richer in butenes than the C4 hydrocarbon stream used. This butene-rich stream may further contain water originating from the solvent. This water may be separated in a subsequent step. The butene-rich stream is removed at the top of the desorber and fed to a single-stage or multi-stage condensation process to condense a water-containing stream, which may also contain water and organic residues, and a butene-containing product stream. These two streams can be separated from each other in a suitable device, for example a spider. The water-containing stream, which may also contain water and organic residues, separated from the butene-containing product stream can then be recycled to the desorber. All or part of the water-containing stream, which may also contain water and organic residues, may be discharged to remove the organics.

[0024] In a preferred embodiment of the invention, the condensation of the butene-rich stream removed at the top of the desorber is configured as a two-stage condensation, in which in the first stage a water-containing stream is condensed and then recycled to the desorber, and in the second stage a butene-containing product stream is condensed. However, residual water may also be condensed in the second stage. This residual water may be separated from the butene-containing product stream via a suitable device, for example a spider.

[0025] The butene-containing product stream obtained from the condensation preferably comprises less than 20% by weight, more preferably less than 16% by weight, of butanes, based on the total composition of the butene-containing product stream, whereas the butene content of the butene-containing product stream obtained from the condensation is preferably 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.

[0026] A feature of the present invention is the heat integration using the heat of the solvent in the process from the desorber to the absorber and the heat of the hot condensate obtained in the desorption evaporator. According to the present invention, the heat of the solvent, preferably NMP, removed as the bottom stream of the desorber is used for heat integration by utilizing it in at least one heat exchanger for heat transfer by a heat pump, for evaporation in the absorption evaporator, and for evaporation of the liquid C4 hydrocarbon stream.

[0027] According to the present invention, the solvent, preferably NMP, from which at least part of the butenes have been removed is recovered in the liquid collector of the desorber and passed through a desorption-evaporator to degas the remaining butenes in the solvent. The heat for evaporation in the desorption-evaporator can be introduced into the heat exchanger by heat transfer from a suitable heat transfer medium. The heat transfer medium can be steam generated by a heat pump integrated into the process and heat integration, for example, at a pressure in the range of 5 to 30 bar, preferably 13 to 17 bar (absolute). A condensation temperature of 150°C to 270°C results from the specified pressure.

[0028] In the context of the present invention, steam is generated by a multi-stage high-temperature heat pump. In principle, a single-stage high-temperature heat pump may be envisaged and used. A multi-stage high-temperature heat pump comprises at least a first vessel containing a first heat exchanger, a second vessel containing a second heat exchanger, and at least one compressor. Only a single multi-stage compressor capable of compressing different gases independently of each other may be used. However, preferably, a multi-stage high-temperature heat pump may comprise at least two compressors, at least one for each stage.

[0029] The first vessel contains a first working medium, and heat from the solvent obtained as the bottom stream of the desorber is transferred to the first heat exchanger. The first working medium can be basically any known heat transfer medium. However, it is desirable that the first working medium is not in a supercritical state in the high temperature range (i.e., temperatures above 120°C). In a preferred embodiment, the first working medium is selected from the group consisting of water, n-hexane, n-pentane, methanol, and mixtures thereof. The first vessel can be a kettle evaporator with a heat exchanger integrated into the vessel.

[0030] Heat transfer from the solvent removed as the bottom stream of the desorber to the first working medium occurs in a first heat exchanger. The first heat exchanger can be connected to the bottom of the first vessel, and the first working medium can be recycled to the first vessel via the first heat exchanger. The first working medium is heated in the first heat exchanger and at least partially vaporizes. This also increases the pressure in the first vessel. The vaporized first working medium is removed through the vessel lid. The first working medium is raised to a first temperature level by heat transfer. The temperature of the first working medium is preferably 80°C to 140°C. The pressure is preferably in the range of 2 to 8 bar (absolute). The vaporized first working medium is fed via at least one compressor or via the first compressor to a second heat exchanger, from which it is recycled to the first vessel. During recirculation from the second heat exchanger, the first working medium may pass through a further heat exchanger, whereby the evaporated first working medium is further heated before passing through the at least one compressor or the first compressor.

[0031] The second vessel contains a second working medium, to which heat is transferred from the first working medium in a second heat exchanger. The second working medium may be any known heat transfer medium. However, it is desirable that the second working medium is not in a supercritical state in the high temperature range (i.e., temperatures above 120°C). In a preferred embodiment, the second working medium should preferably not be in a supercritical state even at temperatures above 150°C. In a preferred embodiment, the second working medium is selected from the group consisting of water, n-hexane, n-pentane, methanol, and mixtures thereof. The second vessel may be a kettle evaporator including a heat exchanger integrated into the vessel.

[0032] Heat transfer from the first working medium to the second working medium occurs in a second heat exchanger. The second heat exchanger can be connected to the bottom of the second vessel, and the second working medium can be recycled to the second vessel via the second heat exchanger. The first working medium is heated in the second heat exchanger and at least partially vaporizes. This also increases the pressure in the second vessel. The evaporated first working medium can be removed through the vessel lid. The first working medium is raised to a second temperature level by heat transfer, which 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 in the range of 2 to 8 bar (absolute). According to the present invention, the evaporated second working medium is supplied as vapor via at least one compressor or via a second compressor to a desorption-evaporator, from which it is recycled to the second vessel. Before the evaporated working medium reaches the desorption evaporator, fresh condensate can be injected to bring the temperature and pressure to the desired level and preferably to cool the vapor somewhat. During recirculation from the desorption evaporator, the second working medium may pass through a further heat exchanger, whereby the evaporated second working medium is further heated before passing through the at least one compressor or second compressor.

[0033] The advantages of such an embodiment are clear: steam does not need to be purchased, since it is provided by the heat pump. Furthermore, the utilization efficiency of the heat generated in this process is significantly higher than in other known methods. Heat integration is therefore significantly improved. Furthermore, in this case, a considerable amount of steam can be saved, since the hot condensate is better utilized.

[0034] In a preferred embodiment of the present invention, the absorber is provided with a dividing wall at the bottom, thereby dividing the bottom into two segments, and the two-stage evaporation is carried out by passing the butene-containing solvent collected in the liquid collector through a first evaporator, preferably a once-through evaporator, to supply it to the first segment, and passing the butene-containing solvent from the first segment through a second evaporator, preferably a forced circulation evaporator, to flash it into the second segment, and then withdrawing the bottom stream to the desorber. One of the advantages of this method is that the design of the bottom of the absorber, i.e., the presence of a dividing wall and a two-stage evaporation device, can increase the separation efficiency while reducing the height of the absorber.

[0035] In a further preferred embodiment, the desorber includes a secondary evaporator. In such a case, the heat transfer medium for the secondary evaporator can use the mixed steam from the steam jet, while the desorption evaporator uses medium-pressure steam as heating steam. The hot condensate from the desorption evaporator and secondary evaporator is then fed to a condensate vessel as described above. The resulting low-pressure steam is then used in the steam jet, and the mixed steam is used in the secondary evaporator. The advantage of this variant is that the resulting hot condensate can be further expanded to provide a larger amount of low-pressure steam.

[0036] The process according to the invention can be used in an integrated chemical system, in particular in oligomerization and, in some cases, hydroformylation. The butene separation according to the process according to the invention can be used in various parts of the integrated plant. The butene separation according to the invention can be used in multiple parts of an integrated chemical plant. The process described herein may be used at the beginning of such an integrated system. The C4 hydrocarbon stream used may be, in particular, cracked C4, raffinate 1, raffinate 2, or a mixture thereof. When cracked C4 and / or raffinate 2 are used, the separation method of the present invention may be preceded by cracked C4 hydrogenation, which selectively hydrogenates butadiene, or by butadiene separation, which extractively removes butadiene with a solvent such as NMP or nitrile. To facilitate the separation process in the process of the present invention, hydroisomerization, which converts 1-butene to 2-butene, which is more easily absorbed by the solvent, may be performed after extractive butadiene separation and before the separation of the present invention. The advantage of separating butane is that less inert butane passes through each stage, thereby increasing the residence time in all reaction stages. From an energy perspective, integration is desirable, particularly after butadiene separation and before MTBE synthesis. As a result, inert i- / n-butane can be separated from the compounds at an early stage, eliminating the need to pass through all subsequent distillation steps. If the separation method is used in the first stage of an integrated system, the resulting product stream can be fed to MTBE synthesis, followed preferably by 1-butene separation, oligomerization, and one or more hydroformylations of the purified oligomers in succession. Hydroformylation can be carried out on both product streams from the oligomerization, for example, to produce INA (isononanol) from di-n-butene or ITDA (isotridecanal) from tributene after subsequent hydrogenation, and 2-PH (2-propylheptanol) can be produced from unreacted butenes in the oligomerization after subsequent aldol condensation and subsequent hydrogenation. Unreacted butenes in the oligomerization can optionally be used for further oligomerization instead of hydroformylation. The conditions for the individual process steps are well known to those skilled in the art. The individual process steps can include additional steps, such as product separation or treatment of the resulting streams, which are not explicitly mentioned herein. However, the separation method according to the present invention can be incorporated into any other part of such an integrated system.

[0037] In one embodiment of the present invention, the C4 hydrocarbon stream used in the separation process according to the invention is removed from the MTBE synthesis after separation of MTBE, and the butene-containing product stream is then fed to 1-butene separation followed by oligomerization and one or more hydroformylations in succession to produce 2-PH, ITDA and / or INA. The individual process steps can include further steps, such as product separation or treatment of the resulting streams, which are not explicitly mentioned herein.

[0038] In a further embodiment of the invention, the C4 hydrocarbon stream used in the separation process according to the invention is removed from the 1-butene separation, and the butene-containing product stream is then fed to oligomerization followed by one or more hydroformylations to produce 2-PH, ITDA and / or INA. The individual process steps can include further steps, such as product separation or treatment of the resulting streams, which are not explicitly mentioned herein.

[0039] In a further embodiment of the invention, the C4 hydrocarbon stream used in the separation process according to the invention is removed from oligomerization and the butene-containing product stream is then fed to hydroformylation to produce 2-PH. The individual process steps may include further steps, such as product separation or treatment of the resulting stream, which are not explicitly mentioned herein.

[0040] In a further embodiment of the present invention, the separation method according to the present invention is used at the end of an integrated system. In this case, the C4 hydrocarbon stream used is removed from the 2-PH production process after hydroformylation. The butene-containing product stream obtained from the separation method according to the present invention can be recycled, for example, and used for 1-butene separation, oligomerization, or one or more hydroformylations in another suitable part of the integrated system. This can increase the efficiency of the overall integrated system, since at most 20% by weight of butenes can be present in the fruit bunches even after the last process step of the integrated system has been performed.

[0041] The butane-containing product stream can be fed, for example, to adiabatic oligomerization, hydrogenation of any butenes still present, or n / iso butane splitting, regardless of the location of the integrated system in which the separation process according to the invention is located. The n / iso splitting can be carried out after the adiabatic oligomerization. As mentioned above, in the combination of MTBE synthesis, 1-butene separation, oligomerization, and hydroformylation, the butane-containing product stream can also be incorporated before oligomerization.

[0042] In a particularly preferred embodiment of the invention, the energy required for the n / iso splitting can be provided, at least in part, by heat integration with the first stage of a two-stage condensation at the top of the desorber, which has the advantage that the energy gained in the condensation is utilized and not simply released into the environment as in the prior art. The present invention will now be described with reference to the drawings, which are for illustrative purposes and are not to be understood in a limiting sense. [Brief explanation of the drawings]

[0043] [Figure 1]1 shows the basic configuration of the present invention. A liquid C4 hydrocarbon stream is evaporated via a heat exchanger (4) and fed to an absorber (1). The solvent is optionally brought to the desired temperature via a residual cooler and fed to the absorber. In this case, the inlet is located spatially above the inlet of the C4 hydrocarbon stream, in this case above the first packed bed. A butane-rich stream is collected at the top of the absorber (1). The possibility of condensation is not shown here, only the return of a partial stream. The butene-containing solvent is collected at the bottom of the absorber (1), as indicated by the chimney tray in the diagram. There, at least a portion of the butene-containing solvent is removed and fed to the bottom of the absorber (1) via an absorption evaporator (5). The butene-containing solvent is removed from the bottom of the absorber (1) and fed to a desorber (2) by a pump (9), where the butenes in the solvent are separated from the solvent. A butene-rich stream is obtained at the top of the desorber. This stream is condensed in one or more stages, which are not shown in the figure. Only a possible reflux is shown. The at least partially butene-free solvent is collected at the bottom of the desorber (2), as indicated by the chimney tray in the figure. There, at least a portion of the butene-containing solvent is removed and fed to the bottom of the desorber via a desorption evaporator (7). The butene-free solvent is then removed from the bottom of the desorber (2) and recycled by a pump (8) to the absorber via a first vessel with a first heat exchanger (20), an absorption evaporator (5), a heat exchanger (4) for evaporating the C4 hydrocarbon stream, and a residue cooler (3). In the first vessel with the first heat exchanger (20), at least a portion of the first working medium is evaporated and fed via a further heat exchanger (21), where further heating is performed, and a first compressor (22) to a second vessel with a second heat exchanger (23). In the second vessel, which comprises a second heat exchanger (23), at least a portion of the second working medium is evaporated and supplied to the desorption evaporator (7) via a second compressor (24). [Figure 2]1 shows a preferred embodiment of the present invention in which a dividing wall is present at the bottom of the absorber (1). In this embodiment, a portion of the butene-containing solvent is removed from the chimney tray of the absorber (1) and fed via an absorption evaporator (5) to the first segment at the bottom of the absorber (1), where the dividing wall is present. The butene-containing solvent is removed from the first segment and fed via a pump (13) to a second evaporator (14) to the second segment at the bottom of the absorber. The butene-containing solvent is removed from the second segment at the bottom of the absorber (1) and is removed at the bottom of the absorber (1) by a pump (9) and fed to a desorber (2) via a heat exchanger (6) for preheating the butene-containing solvent, where the butenes present in the solvent are separated from the solvent. In this preferred embodiment, heat is transferred in the heat exchanger during the recirculation of at least a portion of the butene-free solvent. [Figure 3] 1 shows a preferred embodiment of the present invention in which a flash vessel (26) and a further compressor (25) for intermediate expansion are present. The first working medium is fed by two compressors (22, 25) to a second heat exchanger (23) where it is at least partially condensed. The first working medium then enters the flash vessel (26) where it is separated. A portion of it passes through a further heat exchanger (21) and is sent to the first vessel comprising the first heat exchanger (20). The other portion is fed between the two compressors (22 and 25) and discharges the first compressor (22). This means that the entire working medium no longer needs to be compressed from a low pressure level to a high pressure level, but rather, there is an energetic advantage in that only a certain percentage is compressed. [Figure 4] FIG. 3 shows an embodiment of the invention in which a separator plate is present in the absorber as shown in FIG. 2 and the first working medium is subjected to intermediate pressure reduction in a flash vessel (26) as shown in FIG. DETAILED DESCRIPTION OF THE INVENTION

[0044] The present invention will be described below by way of simulations. The present embodiment is merely a preferred embodiment and should not be understood as being limiting. [Example]

[0045] The butane-butene separation shown in Figure 1 was simulated using Aspen Plus V10. A modified NRTL parameter set was used to describe the interactions between components. In the simulation, 27 t / h of hydrocarbon-containing feed was introduced into the butane / butene separation, containing a total of 45 mass% butane (35 mass% n-butane and 10 mass% isobutane), 30 mass% isobutene, 10 mass% 1-butene, 10 mass% trans-butene, and 5 mass% cis-butene. A total of 10 tons per hour of butane-containing overhead product is extracted from the absorber. The butane-containing overhead product of the absorber consists of 70% by mass of n-butane, 27% by mass of isobutane, 1% by mass of 1-butene, and 2% by mass of isobutene. A solvent-containing butene-containing product stream is removed from the bottom. The butene-containing product stream contains 14% by mass of n-butane, 15% by mass of 1-butene, 47% by mass of isobutene, 8% by mass of cis-butene, and 16% by mass of trans-butene. A butene yield of 98% can be achieved by setting a solvent / feed ratio of 13. The large amount of excess solvent is then also used for heat integration and as a heat source for the heat pump.

[0046] The solvent stream, here NMP, is sent from the bottom of the desorber (2) to a heat exchanger, a kettle evaporator (20), where n-hexane is evaporated at 3.6 bar (absolute). The NMP is cooled from about 180-190°C to about 120-125°C, transferring 13.4 MW. This generates an n-hexane recycle stream of just over 240 tons per hour, which is superheated at 42 K in a gas superheater (21). The n-hexane stream is pressurized in a multistage compressor (22) to a pressure level of 14.1 bar (absolute), and the working medium n-hexane is condensed in a further heat exchanger, another kettle evaporator (23). Water is evaporated on the shell side at 7 bar (absolute). This steam is raised to a pressure level of 13.1 bar (absolute) by a further compressor (24). This produces approximately 35 tons of steam per hour, which is used for evaporation in the desorption evaporator. Both working media are recycled. Compared to conventional butane-butene separations, which require purchasing or supplying a heating medium, embodiments according to the invention can save up to 35 t / h of steam, which is generated internally by a heat pump.

Claims

1. 1. A process for separating butenes from a C4 hydrocarbon stream containing at least butenes and butanes by extractive distillation using a solvent, the process comprising: (a) at least partially evaporating liquid C4 hydrocarbons in a feed evaporator to provide a gaseous C4 hydrocarbon stream, and feeding a liquid solvent above the C4 hydrocarbon stream to an absorber, where the C4 hydrocarbon stream and the solvent are brought into contact with each other to transfer mainly the butenes from the C4 hydrocarbon stream to the solvent, and the solvent containing the butenes is recovered in a liquid collector of the absorber, passed through an absorption evaporator, and then fed to the bottom of the absorber from below the liquid collector; and after degassing and releasing mainly the butanes from the solvent containing the butenes, the solvent containing the butenes is fed to a desorber as a bottom stream; (b) feeding the solvent containing the butenes to the desorber, the bottom of which is at a higher temperature and preferably a lower pressure than the bottom of the absorber, separating the butenes from the solvent to produce a butene-rich stream at the top of the desorber, recovering the solvent from which at least a portion of the butenes has been removed in the liquid collector of the desorber, passing it through a desorption-evaporator, and feeding it from below the liquid collector to the bottom of the desorber to degas the butanes remaining in the solvent, before recycling the solvent to the absorber as the desorber bottom stream to serve as a heat source for a multi-stage high-temperature heat pump; where: The heat of the solvent removed as the bottom stream of the desorber is at least partially used for heat integration by utilizing it in at least one heat exchanger for heat transfer by the multi-stage high temperature heat pump, for evaporation in the absorption evaporator, and for evaporation of a liquid C4 hydrocarbon stream, wherein: Heat for evaporation in the desorber-evaporator is introduced via vapor generated by the multi-stage high-temperature heat pump, wherein the multi-stage high-temperature heat pump comprises at least a first vessel including a first heat exchanger, a second vessel including a second heat exchanger, and at least one compressor, wherein the first vessel contains a first working medium, and heat from the solvent obtained as a bottom stream of the desorber is transferred to the first heat exchanger; and The process wherein the second vessel contains a second working medium and heat is transferred from the first working medium in the second heat exchanger.

2. The process of claim 1 , wherein the multi-stage high temperature heat pump comprises at least two compressors.

3. 3. The process of claim 1 or 2, wherein the first working medium is selected from the group consisting of water, n-hexane, n-pentane, methanol, and mixtures thereof.

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

5. The process of any one of claims 1 to 4, wherein the first and second working media are not the same.

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

7. 7. The process of claim 6, wherein the evaporated working medium is passed through at least one compressor to the second heat exchanger, from which it is recycled to the first vessel, preferably via a third heat exchanger, where the evaporated first working medium is further heated before being passed to the at least one compressor.

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

9. 9. The process of claim 8, wherein the second working medium is returned to the desorption evaporator via at least one compressor, from where it is recycled in an at least partially condensed state to the second vessel, preferably via a further fourth heat exchanger, where it is further heated before being fed to the second compressor.

10. 10. The process of any one of claims 1 to 9, wherein the solvent used is NMP.

11. 11. The process of claim 10, wherein the solvent or NMP contains water, and the water content is from 1% to 10% by weight, or from 4% to 9% by weight.

12. 12. The process according to any one of claims 1 to 11, wherein at the top of the absorber a butane-rich stream is obtained compared to the C4 hydrocarbon stream used.

13. 13. The process of any one of claims 1 to 12, wherein the temperature of the absorber bottoms stream fed to the desorber is from 70°C to 130°C, or from 85°C to 120°C.

14. The process of any one of claims 1 to 13, wherein the temperature at the bottom of the desorber is from 120°C to 200°C, or from 130°C to 195°C.

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