An energy efficient method for the recovery of butenes from C4-hydrocarbon streams.

Abstract

The present invention relates to a process for the separation of butenes from a C4-hydrocarbon stream containing butanes as well as butenes by extractive distillation using a suitable solvent.

Description

[Technical field]

[0001] The present invention relates to a process for the separation of butenes from a C4-hydrocarbon stream containing butanes as well as butenes by extractive distillation with a suitable solvent. The process according to the invention is characterized by heat integration, in which the heat of the solvent is utilized for the heating and / or at least partial evaporation of various streams. [Background technology]

[0002] The separation of butane-butene mixtures by extractive distillation is known per se. It uses aprotic solvents (for example N-methyl-2-pyrrolidone (NMP) or acetonitrile (ACN)) to increase the relative volatility of alkanes compared to alkenes. In one extractive distillation column, an adsorption unit, the butenes are preferably dissolved in the solvent and the butanes are separated as overhead product. The butenes are then released from the packing solvent in a stripping column, a desorption unit, at high temperature and / or reduced pressure, to obtain said butenes in concentrated form as overhead product. The solvent from which the butenes have been released is then recycled to the extractive distillation. Heat integration is very important for the economics of the process due to the high solvent to feed ratio. Hot solvent is obtained at the bottom of the desorber and its energy content can be utilized in various ways. US 2014 / 0124358 presents a method for the selective extraction of olefins that is said to solve the heat integration problem. This document proposes to utilize the energy content of the hot solvent to heat a side stream from the desorber, to heat the bottom product of the adsorber sent to the desorber, to heat one or more side streams of the adsorber, and to preheat the feed stream. However, the solutions proposed in the prior art only solve the problem of ideally complete recovery of the energy flows present in the system incompletely, or via relatively complex structures. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] US Patent No. 2014 / 0124358 Summary of the Invention [Problem to be solved by the invention]

[0004] It is therefore an object of the present invention to provide a method whereby an improved, ideally the maximum possible energy recovery is achieved and this is done with reduced plant engineering complexity. [Means for solving the problem]

[0005] This object can be achieved by the embodiment of the method proposed in claim 1. Preferred embodiments are described in the dependent claims. The method according to the invention is a method for separating butenes from a C4-hydrocarbon stream comprising at least butenes and butanes by extractive distillation using a solvent, the method comprising the steps of: a. at least partially evaporating a liquid C4-hydrocarbon stream in a feed evaporator to provide a gaseous C4-hydrocarbon stream and providing a liquid solvent, preferably NMP, on the C4-hydrocarbon stream to an adsorption device where the C4-hydrocarbon stream and the solvent contact each other to transfer mainly butenes from the C4-hydrocarbon stream to the solvent, the thus loaded solvent, preferably NMP, is collected in a liquid collector of the adsorption device, passes through an adsorption evaporator and then sent to the bottom of the adsorption device below the liquid collector to degas mainly butanes from the loaded solvent, preferably NMP, which is then sent to a desorber as bottom stream; b. feeding the charged solvent, preferably NMP, to a desorber, the bottom of which is at a higher temperature and preferably at a lower pressure compared to the bottom of the adsorber, and in which butenes are separated from the solvent, preferably NMP, to obtain a butenes-enriched stream at the top of the desorber, the solvent, preferably NMP, at least partially depleted of butenes, being collected in a liquid collector of the desorber, passing through a desorption evaporator and then being sent to the bottom of the desorber below the liquid collector to degas any butenes remaining in the solvent, after which the solvent, preferably NMP, is recycled to the adsorber as a bottom stream, The heat of the solvent, preferably NMP, recovered as the desorber bottom stream is at least partially used for preheating the charged solvent, preferably NMP, sent to the desorber, for evaporation in the adsorption evaporator, and for heat integration by utilizing the heat of the solvent, preferably NMP, in at least one of the respective heat exchangers for evaporation of the liquid C4-hydrocarbon stream.

[0006] One advantage of the method is the heat integration, which allows efficient energy recovery despite a relatively simple configuration. The simplest embodiment of the invention furthermore does not require an additional side evaporator, which entails additional plant engineering complexity and therefore higher costs.

[0007] Heat integration extracts heat from the solvent, not only to use it to heat other streams or columns, but also primarily to cool the solvent for adsorption. The adsorption of butenes (here, step a) is usually carried out at a lower temperature than the desorption (here, step b). If sufficient heat is recovered from the solvent during the heat integration, i.e. it has a suitable temperature, the solvent can be sent directly to the adsorber. However, it is also conceivable that, despite the presence of heat integration, the solvent still does not have a suitable temperature. In such cases, the solvent may be cooled to a suitable temperature after the heat integration by passing through a residue cooler before entering the adsorber.

[0008] Heat is a process parameter. Heat supplied or extracted corresponds to the change in internal energy minus the work done. The terms heat, heat transport and heat integration used in this invention are based in all cases on this definition.

[0009] The process relates to the separation of butenes from butene-containing C4-hydrocarbon streams. These streams typically contain butenes, but also alkanes (n-butane, isobutane). In the context of the present invention, unless otherwise stated, the term butane should be understood to mean both n-butane and isobutane. The process according to the invention can therefore use any C4-hydrocarbon stream containing at least butenes and butanes, as long as the amount of butenes and / or butanes present allows the economic performance of the process. In a preferred embodiment of the present invention, the C4-hydrocarbon stream used consists essentially of butanes and butenes, i.e. to an extent of more than 98% by weight, preferably to an extent of more than 99% by weight. The corresponding streams may also contain small amounts of impurities or other hydrocarbons, such as 1,3-butadiene or C5-hydrocarbons.

[0010] In the extraction process according to the invention, a liquid solvent is used which mainly dissolves the butenes of the gaseous C4-hydrocarbon stream used. Suitable solvents are aprotic solvents, for example N-methyl-2-pyrrolidone (NMP). The process according to the invention is preferably carried out with NMP as solvent. In a further preferred embodiment of the invention, the solvent contains water, in particular in the range of 1% to 10% by weight, preferably 4% to 9% by weight, in each case based on the total amount of solvent.

[0011] Adsorption devices that can be used include, in particular, random packed columns comprising at least two random packed beds. Such columns are known in principle to the skilled person. Preferably, above the first random packed bed, a backwash zone is arranged with a number of theoretical trays for arresting the solvent drawn into the gas phase. Above the backwash zone is the top of the adsorber, where a butane-enriched stream is obtained compared to the C4-hydrocarbon stream used. A liquid collector according to the invention is arranged below the last random packed bed, and the bottom of the adsorber is arranged below said collector. The exact structure of the adsorber depends on various parameters and is variable in the particular embodiment.

[0012] The liquid solvent is fed to the adsorption device spatially above the inlet of the C4-hydrocarbon stream. In a preferred embodiment, the solvent is fed to the adsorption device above the first random packed bed, and the C4-hydrocarbon stream is added to the adsorption device in one or more random packed beds below the first random packed bed. In the adsorption device, the liquid solvent drips down and contacts the (ascending) vaporous C4-hydrocarbon stream to transfer a portion of the C4-hydrocarbon stream, which mainly contains butenes, to the solvent to form the packed solvent. In step a, the C4-hydrocarbon stream and the solvent are contacted with each other, in particular in countercurrent flow. In a preferred embodiment of the present invention, the portion of the C4-hydrocarbon stream transferred to the solvent contains at least 70% by weight, particularly preferably at least 80% by weight of butenes, based on the composition of the portion of the C4-hydrocarbon stream transferred to the solvent. This results in particular in that at least 80% of the butenes present in the C4-hydrocarbon stream used, particularly preferably at least 90%, are transferred to the solvent.

[0013] The charged solvent flows downwards in the adsorber and is collected in a suitable liquid collector, in particular a chimney tray. The temperature of the charged solvent obtained in the liquid collector is preferably between 40 ° C and 90 ° C, particularly preferably between 45 ° C and 65 ° C. The charged solvent is withdrawn from the liquid collector, passes through an adsorptive evaporator and then sent to the bottom of the adsorber below the liquid collector to degas the charged solvent, mainly of butane. The adsorptive evaporator is preferably a once-through evaporator, in which the charged solvent passes through the evaporator only once. This allows the lowest possible temperatures to be achieved and thus fouling to be prevented. The operating temperature difference is further increased and thus allows an even more efficient energy utilization of the NMP stream. The adsorptive evaporator may also be configured as a multi-stage apparatus, i.e. there may be several heat exchangers or several evaporators belonging to the adsorptive evaporator.

[0014] The solvent, mainly loaded with butenes, then remains at the bottom, from where it is recovered and sent as bottom stream to the desorber. The temperature in the adsorber bottom stream sent to the desorber is preferably between 70°C and 130°C, particularly preferably between 85°C and 120°C.

[0015] A stream enriched in butanes, in particular compared to the C4-hydrocarbon stream used, is then obtained at the top of the adsorber. The head pressure of the adsorber can be between 3 and 7 bar absolute, preferably between 4 and 6.5 bar absolute. The butane-enriched stream may further comprise water originating from the solvent. This water can be separated in a subsequent step. The butane-enriched stream is recovered at the top of the adsorber and subjected to a single-stage or multi-stage concentration to concentrate a water-containing stream and a butane-containing product stream. These two streams can be separated from each other in a suitable device, for example a spider. The water-containing stream separated from the butane-containing product stream may, depending on its composition, be sent to an adsorber or a desorber and / or may be partially discharged from the process.

[0016] The butane-containing product stream thus obtained from the concentration may still contain small amounts of water, in particular in amounts of up to 1500 ppmw, based on the total composition of the butane-containing product stream. Furthermore, the butane-containing product stream obtained from the concentration may further contain residual butenes, which typically contains less than 20 wt.%, preferably less than 15 wt.%, particularly preferably less than 5 wt.% butenes, based on the total composition of the butane-containing product stream.

[0017] Depending on the requirements of the butane-containing product stream obtained, it may be necessary to subject the butane-containing product stream after concentration to drying, preferably in a drying tower, to separate the water still present. The butane-containing product stream preferably contains a maximum amount of water of 50 ppmw, preferably 25 ppmw, after drying. The water obtained during drying can be recycled to the concentration in the adsorption device.

[0018] The solvent recovered at the bottom of the adsorber and loaded mainly with butenes is fed to the desorber. For this purpose, for example, a pump can be used to send the loaded solvent to the desorber. Compared to the bottom of the adsorber, the bottom of the desorber is at a higher temperature and preferably at a lower pressure. The temperature at the bottom of the desorber is preferably between 120°C and 200°C, more preferably between 130°C and 195°C. The head pressure of the desorber can be between 1 and 6 bar absolute, preferably between 2 and 5 bar absolute. The higher temperature and preferably the lower pressure compared to the adsorber results in that the butenes and possibly any butanes still present are at least partially removed from the solvent. In a preferred embodiment, the solvent at least partially depleted of butenes contains up to 5000 ppmw of butenes, particularly preferably between 100 and 900 ppmw of butenes. The solvent at least partially depleted of butenes flows downwards in the desorber and is collected in a liquid collector of the desorber. From there, the solvent at least partially depleted of butenes passes through a desorption evaporator and then is sent to a liquid collector, in particular to the bottom of the desorption device below the chimney tray, to degas all butenes remaining in the solvent. The desorption evaporator is preferably a once-through evaporator, in which the solvent at least partially depleted of butenes passes through the evaporator only once. This allows the lowest possible temperatures to be achieved and therefore fouling to be prevented. The desorption evaporator may also be configured as a multi-stage device, i.e. there may be several heat exchangers belonging to the desorption evaporator. The butene-depleted solvent then remains at the bottom, from where it is recovered and sent as an underflow to the adsorption device, where it is reused as solvent for the adsorption of butenes.

[0019] Before being sent to the adsorber, the butene-releasing solvent can be subjected to partial or complete regeneration in order to remove impurities, such as the above-mentioned by-products present in the C4-hydrocarbon stream used and / or the above-mentioned by-products formed from butenes at the temperature in the desorber, such as oligomeric or polymeric compounds, from the solvent, preferably NMP. The regeneration is preferably carried out such that the butene-releasing solvent is sent to a vessel and evaporated at an absolute pressure of less than 500 mbar, more preferably less than 200 mbar, and at a temperature of 100°C to 150°C. The vessel can have a column connected to it. In particular large boilers are separated by regeneration. If only a portion of the butene-releasing solvent is subjected to regeneration, the regenerated portion of the solvent is then combined with the non-regenerated solvent and recycled to the adsorber.

[0020] A butene-enriched stream, in particular compared to the C4-hydrocarbon stream used, is then obtained at the top of the desorber. This butene-enriched stream may further comprise water originating from the solvent. This water can be separated in a subsequent step. The butene-enriched stream is recovered at the top of the desorber and subjected to a single-stage or multi-stage concentration to concentrate a water-containing stream, which may contain not only water but also organic residues, as well as 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 separated from the butene-containing product stream can then be recycled to the desorber. It is also possible to discharge the water-containing stream in whole or in part to remove the organic matter.

[0021] In a preferred embodiment of the invention, the concentration of the butene-enriched stream recovered at the top of the desorber is configured as a two-stage concentration, in a first stage a water-containing stream is concentrated and then recycled to the desorber, and in a second stage a butene-containing product stream is concentrated. However, it is also possible to concentrate the residual water in a second stage. This residual water can be separated from the butene-containing product stream by a suitable device, for example a spider.

[0022] The butene-containing product stream obtained from the concentration preferably contains less than 20 wt.%, more preferably less than 16 wt.% butanes, based on the total composition of the butene-containing product stream. In contrast, the butene-containing product stream obtained from the concentration preferably has a butene content of at least 70 wt.%, more preferably at least 75 wt.%, and particularly preferably at least 86 wt.%, based on the total composition of the butene-containing product stream.

[0023] The defining feature of the present invention is the heat integration using the heat of the solvent on its way from the desorber to the adsorber and the heat of the hot concentrate obtained in the desorption evaporator. The heat of the solvent, preferably NMP, recovered as the desorber bottom stream is used in accordance with the present invention for heat integration by utilizing the heat of the solvent in at least one of the respective heat exchangers for preheating the charge solvent sent to the desorber, for evaporation in the adsorber evaporator and for evaporation of the liquid C4-hydrocarbon stream.

[0024] In a preferred embodiment of the invention, the pre-heating of the loading solvent sent to the desorber is performed in two stages, the first heat transfer to the loading solvent sent to the desorber is performed in a heat exchanger, preferably a tube bundle heat exchanger, and the second heat transfer to the loading solvent sent to the desorber is performed in a kettle evaporator. Such an embodiment has the advantage that in the above preferred embodiment, the heat transferred to the loading solvent in both stages, i.e. the heat exchanger and the kettle evaporator, originates from the solvent recovered as the desorber bottom stream as the heat transfer medium. The use of a kettle evaporator also has the advantage that the feed pressure to the desorber in the conduits can be reduced. A high feed pressure is usually necessary to prevent evaporation in the pipe conduits, which can lead to problems including the bursting of the pipe conduits. A further advantage is that it ensures that the heat load is limited and thus a temperature difference large enough to transfer heat is maintained.

[0025] According to the invention, the solvent, preferably NMP, at least partially depleted of butenes, is collected in a liquid collector of the desorber and passes through a desorption evaporator to allow degassing of all butenes remaining 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 may in particular be heating steam, which is utilized in the form of medium- or high-pressure steam. Preferred heating steam is medium-pressure steam having a temperature of 150°C to 270°C, preferably 160°C to 250°C. Medium-pressure steam preferably has an absolute pressure of 15 to 30 bar, particularly preferably 17 to 25 bar. Steam with an absolute pressure of more than 30 bar can also be used as heating steam. Such heating steam may also be called high-pressure steam.

[0026] The heating steam used for evaporation can be at least partially condensed in the heat exchanger, thus producing a hot concentrate at an absolute pressure of 10-20 bar, preferably 12-17 bar, and a temperature of 150 ° C to 210 ° C, preferably 160 ° C to 200 ° C. Preferably, downstream of the heat exchanger a concentrate vessel is arranged in which the hot concentrate can be separated from the steam. The pressure in the concentrate vessel is preferably lower than in the heat exchanger on the heating steam side. The lower pressure allows a part of the hot concentrate to be evaporated, so that a combined steam, i.e. a non-condensed part of the heating steam and the hot concentrate evaporated in the concentrate vessel by the reduced pressure, is obtained as low-pressure steam in the concentrate vessel. In this case, the low-pressure steam preferably has an absolute pressure above 0 bar and below 10 bar. The temperature above the low pressure is preferably between 100 ° C and 180 ° C.

[0027] The low-pressure steam obtained there still contains energy, which is not utilized in the known method. However, this is not beneficial from an energetic or economic point of view. However, this energy can be utilized in a preferred embodiment of the invention. For this purpose, the heating steam used for the evaporation in the desorption evaporator can be preferably supplied using a controllable steam ejector (heat compressor). The heat compressor is then supplied with both the heating steam used, e.g. here in particular the medium-pressure steam used preferably, and the low-pressure steam from the concentrate container, originating from a suitable steam network, thus forming a mixed steam, which is the heat transfer medium for the desorption evaporator. In this embodiment, the mixed steam is therefore the heating steam. Such a steam ejector is configured to operate with motive steam and to be able to suck the suction steam from the container by negative pressure (back pressure in the steam ejector) to form a mixed steam, which is then used as the heat transfer medium. The motive steam is in this case the heating steam / medium-pressure steam, whereby the low-pressure steam is sucked as suction steam from the concentrate container and mixed with the motive steam.

[0028] The advantages of such an embodiment are clear: the energy of the low-pressure steam obtained in the concentrate vessel can be utilized, which allows energy and cost savings. Such a procedure can also be advantageous for other reasons: the steam ejector used may be controllable so that the amount of medium- or high- and low-pressure steam can be adjusted, for example according to certain process parameters. The amount of suction steam is adjusted via the amount of motive steam. The amount of low- and medium-pressure steam can be adjusted, for example according to the temperature in the desorber.

[0029] In a further preferred embodiment, the desorption device comprises a side evaporator. In such a case, the desorption evaporator uses medium pressure steam as heating steam, while the heat transfer medium used for the side evaporator may be the mixed steam from the steam ejector. The hot condensate from the desorption evaporator and the side evaporator is then sent to the condensate container according to the above embodiment. The low pressure steam obtained there is then used in the steam ejector, and the mixed steam is used in the side evaporator. The advantage of this variant is that the hot condensate obtained can be further depressurized to provide more low pressure steam.

[0030] The method described herein may be used in an integrated chemical system, in particular including oligomerization and optionally hydroformylation. The separation of butenes by the method according to the invention may be used at various points in an integrated plant. The separation of butenes by the method according to the invention may also be at various points in an integrated chemical plant. For example, the method described herein may be used at the start of such an integrated system. The C4-hydrocarbon stream used may then be in particular crack C4, raffinate 1, raffinate 2 or a mixture thereof. If crack C4 and / or raffinate 2 are used, the separation method according to the invention may be arranged upstream of it with a C4 hydrogenation, where butadiene is selectively hydrogenated, or arranged with a butadiene separation, where butadiene is extractively removed with a solvent such as NMP or nitrile to reduce the butadiene content. It is possible to arrange a hydroisomerization downstream of the extractive butadiene separation and upstream of the separation according to the invention to facilitate the separation operation in the method according to the invention, since it converts 1-butene into 2-butene, which is more easily absorbed by the solvent.

[0031] If the separation method is used at the start of the integrated system, the resulting product stream can be fed to the MTBE synthesis, preferably followed by 1-butene separation, oligomerization and one or more hydroformylations of the purified oligomers. The hydroformylation can be carried out not only with the product stream from the oligomerization, which allows for example the production of INA (isononanol) from di-n-butene or ITDA (isotridecanal) from tributenes after subsequent hydrogenation, but also with the unconverted butenes of the oligomerization, which allows the production of 2-PH (2-propylheptanol) after subsequent aldol condensation and subsequent hydrogenation. The unconverted butenes from the oligomerization can also be used, if necessary, to operate a further oligomerization instead of the hydroformylation. The conditions of the individual process steps are well known to the person skilled in the art. The individual process steps can include further steps, such as separation of the products or workup of the resulting streams, which are not mentioned explicitly here. However, the separation method according to the invention can also be introduced at any other point in such an integrated system.

[0032] In one embodiment of the present invention, the C4-hydrocarbon stream used in the separation process according to the invention is recovered from an MTBE synthesis after separation of MTBE, and the butene-containing product stream is subsequently fed to a 1-butene separation, followed by oligomerization and then one or more hydroformylations in succession to produce 2-PH, ITDA and / or INA. The individual process steps may comprise further steps, such as separation of the products or work-up of the resulting streams, which are not mentioned explicitly here. In a further embodiment of the invention, the C4-hydrocarbon stream used in the separation process according to the invention is recovered from a 1-butene separation and the butene-containing product stream is subsequently fed to an oligomerization followed by one or more subsequent hydroformylations to produce 2-PH, ITDA and / or INA. The individual process steps may comprise further steps, such as separation of the products or work-up of the resulting streams, which are not mentioned explicitly here.

[0033] In a further embodiment of the invention, the C4-hydrocarbon stream used in the separation process according to the invention is recovered from the oligomerization, and the butene-containing product stream is subsequently fed to a hydroformylation for subsequent production of 2-PH. The individual process steps may comprise further steps, such as separation of the products or work-up of the resulting streams, which are not explicitly mentioned here.

[0034] 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 that case, the C4-hydrocarbon stream used is recovered from the 2-PH production downstream of hydroformylation. The butene-containing product stream obtained from the separation method according to the present invention can then be recycled and used at a suitable point in the integrated system, for example for 1-butene separation, oligomerization or one or more hydroformylations. This makes it possible to increase the efficiency of the overall integrated system, since even after passing through the last process step in the integrated system, up to 20% by weight of butenes may still be present.

[0035] Regardless of the point in the integrated system in which the separation method according to the invention is located, the butane-containing product stream can be fed, for example, to an adiabatic oligomerization, to hydrogenation of the butenes still present, or to an n / iso splitting of butane, in which n-butane and isobutane are separated from each other. The n / iso splitting can also be carried out after the adiabatic oligomerization. Another possibility would be to include the butane-containing product stream upstream of the oligomerization in the above-mentioned integrated system consisting of MTBE synthesis, 1-butene separation, oligomerization and hydroformylation.

[0036] 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 involving the first stage of a two-stage enrichment at the top of the desorber, which has the advantage that the energy gained in the enrichment is utilized and not simply released to the environment as in the prior art. The invention will now be described with reference to the drawings, which are intended as illustrative and are not to be understood as limiting. [Brief description of the drawings]

[0037] [Figure 1] The basic configuration of the invention is shown. The liquid C4-hydrocarbon stream is evaporated through a heat exchanger (4) and sent to the adsorber (1). The solvent is, if necessary, brought to the desired temperature through a residue cooler (3) and is also sent to the adsorber (with its inlet spatially above the inlet of the C4-hydrocarbon stream, in this case above the first random packed bed). At the top of the adsorber (1), a stream enriched in the butanes to be recovered is obtained. Possible enrichments are not shown here, only possible substream recycles are shown. The loading solvent is collected at the bottom of the adsorber (1), as indicated by the chimney tray in the figure. There, at least a portion of the loading solvent is recovered and sent to the bottom of the adsorber (1) through an adsorption evaporator (5). The loading solvent is recovered from the bottom of the adsorber (1) and sent to the desorber (2) through a heat exchanger (6) for preheating of the loading solvent using a pump (9), where the butenes present in the solvent are separated from the solvent. A butene-enriched stream is obtained at the top of the desorber. This stream may be subjected to single-stage or multi-stage enrichment, not shown. Only possible recycle streams are shown. The solvent, at least partially depleted of butenes, is collected at the bottom of the desorber (2), as indicated by a chimney tray in the figure. There, at least a part of the charge solvent is recovered and sent to the bottom of the desorber via a desorption evaporator (7). The butene-depleted solvent is then recovered from the bottom of the desorber (2) and recycled to the adsorber, using a pump (8), via a heat exchanger (6) for preheating the charge solvent, the adsorption evaporator (5), the heat exchanger (4) for evaporating the C4-hydrocarbon stream, and the residue cooler (3). [Diagram 2]A preferred embodiment of the invention is shown in which the pre-heating of the charge solvent sent to the desorber (2) is performed in two stages. The first heat transfer takes place in a heat exchanger (6) and then the second heat transfer takes place in a kettle evaporator (10). The mode of operation of the kettle evaporator will be clarified in the description of FIG. 5. Everything else corresponds to that specified above in connection with FIG. 1. [Diagram 3] A further preferred embodiment of the invention is shown, in which a steam ejector (12) is present in the desorption evaporator (7). This steam ejector is supplied with normal heating steam, i.e., for example, with medium-pressure steam from the steam network and with low-pressure steam obtained in the concentrate vessel (11), thus forming a mixed steam, which is then used as heating steam for the desorption evaporator (7). The operating mode of the steam ejector is clarified in the description of FIG. 6. Everything else corresponds to what was specified above in connection with FIG. 1. [Figure 4] A combination of the two embodiments of Figures 2 and 3 is shown in which the charge solvent further passes through a kettle evaporator (10) and the desorption evaporator is supplied with mixed steam via a steam ejector (12) which is supplied with low pressure steam from, inter alia, a concentrate vessel (11). [Diagram 5] The schematic of the kettle evaporator (10) is shown. The liquid feed is sent to the evaporator via the shell-side feed port (101). The liquid feed is partially evaporated in the kettle evaporator and sent to the desorber via the shell-side gas port (103). The portion of the feed that is not evaporated passes over a weir and enters the desorber (2) as liquid product via the shell-side product port (102). On the tube side, the hot bottom product of the desorber (2) is used as a heating medium passing through the tubes via the inlet port (104) and exiting again through the outlet port (105). [Figure 6]A schematic diagram of the steam ejector (12) is shown. Here, the motive steam (121) is the heating steam, in particular the medium pressure steam from the steam network. The suction steam (123) is the low pressure steam from the concentrate vessel. These two are mixed via the control unit (124) and sent as mixed steam (122) via an outlet to the desorption evaporator (7). The amount of motive steam and suction steam can be adjusted via the control unit, so that the pressure and temperature of the mixed steam and therefore the possible heating power can be influenced. EXAMPLES

[0038] Example 1 - embodiment according to FIG. The butane-butene separation shown in Figure 1 was simulated using AspenPlus v10. A modified NRTL parameter set is used to account for the interactions between the components. In the simulation, 19 t / h of hydrocarbon-containing feed was subjected to butane / butene separation (according to Figure 1). It contains a total of 45 wt% butane, 30 wt% isobutene and 25 wt% n-butene.

[0039] A total of 7 t / h of butane-containing overhead product is recovered in the adsorber. The butane-containing overhead product from the adsorber consists of 70 wt.% n-butane, 27 wt.% isobutane and 3 wt.% butenes. The solvent charged with the butene-containing product stream is recovered at the bottom. The butene-containing product stream contains 14 wt.% n-butane, 47 wt.% isobutene and 39 wt.% n-butenes. The established solvent / feed ratio of 13 thus makes it possible to achieve a butene yield of 98%. A large surplus of solvent is then also used for heat integration.

[0040] Only in the desorber (2) is energy introduced from outside the plant, i.e. by heating steam for the desorption evaporator (7). 6.9 MW is transferred to the desorption evaporator (7). Otherwise, heat integration with the solvent takes place throughout this example, so no further external energy is required. The hot bottom product from the desorber (2) is sent via a heat exchanger to the preheating of the desorber (6). Here 8.4 MW is transferred. After preheating the desorber (6), the solvent is sent to the bottom of the adsorber (1), where 7.8 MW is transferred via the heat exchanger (5) present therein. For the evaporation of the C4 feed stream, a further 1.8 MW is transferred from the solvent to the feed via the heat exchanger (4) for the feed evaporation. In the residue cooler (3), the solvent is brought to the optimum extraction temperature with cooling water. In this example, a temperature of 40 ° C was assumed. Therefore, to reach this temperature, another 2.5 MW must be recovered from the solvent. This setup allows reducing the external heat input and optimally utilizing the internal heat. For example, if at least one of the heat exchangers (4), (5) and (6) were not present, the untransmitted energy would have to be recovered and thus eliminated in the residue cooler (3). Furthermore, the untransmitted energy in that case would have to be supplied from an external source. This process mode requires only 6.9 MW of external energy in total (see Table 1).

[0041] Example 2 - Embodiment according to FIG. 2 / Kettle Evaporator Calculations and simulations were carried out similarly to example 1, with the additional presence of a kettle evaporator (10). In order to transfer 12 MW of thermal energy in the heat exchanger (6), the charge solvent must be in liquid form. For this purpose, the sump pump (9) of the adsorber (1) must generate a corresponding power. However, if the preheater is a multi-stage preheater and the second stage is the kettle evaporator (10), the pump (9) only needs to generate a low pressure, thus saving pump power. If the amount of thermal energy of 8.4 MW is divided equally over both stages, i.e. the heat exchanger (6) and the kettle evaporator (10) transfer 4.2 MW each, the power generated by the pump can be reduced by 33%. This process mode requires only 5.6 MW of external energy in total (see Table 1).

[0042] Example 3 - Embodiment according to FIG. 3 / steam ejector Calculations and simulations were carried out similarly to example 1, with the additional presence of a steam ejector (12). Only in the desorber is external energy introduced via heating steam. According to example 1, this amounts to a total of 6.9 MW. If a steam ejector is used, it is possible to save about 10%, i.e. 0.69 MW, which are then provided via the residual heat utilization of the steam ejector. This process mode requires only 4.8 MW of external energy in total (see table 1).

[0043] [Table 1]

Claims

1. 1. A method 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 a liquid C4-hydrocarbon stream in a feed evaporator to provide a gaseous C4-hydrocarbon stream, and feeding a liquid solvent on the C4-hydrocarbon stream to an adsorption unit where the C4-hydrocarbon stream and the solvent contact each other to transfer mainly butenes from the C4-hydrocarbon stream to the solvent, the solvent thus loaded is collected in a liquid collector of the adsorption unit, passes through an adsorptive evaporator, and then is sent to the bottom of the adsorption unit below the liquid collector to degas mainly butanes from the loaded solvent, and the loaded solvent is then sent to a desorber as a bottom stream; b) feeding the loaded solvent to a desorber, the bottom of which is at a higher temperature than the bottom of the adsorber, where the butenes are separated from the solvent to obtain a butene-enriched stream at the top of the desorber, the solvent at least partially depleted of butenes being collected in a liquid collector of the desorber, passed through a desorption evaporator and then sent to the bottom of the desorber below the liquid collector to degas any butenes remaining in the solvent, and the solvent then being recycled to the adsorber as an underflow; the heat of the solvent recovered as the bottom stream of the desorber is at least partially used for preheating the loaded solvent sent to the desorber, for evaporation in the adsorptive evaporator, and for heat integration by utilizing the heat of the solvent in at least one of the respective heat exchangers for evaporation of the liquid C4-hydrocarbon stream; The heating steam used is at least partially condensed in the heat exchanger, thus producing a hot condensate at an absolute pressure of 10-20 bar and a temperature of 150°C to 210°C, which is sent to a condensate vessel.

2. 2. The process according to claim 1, wherein the solvent used is NMP.

3. 2. The method of claim 1, wherein the solvent / NMP contains water, and the water content is between 1% and 10% by weight.

4. 2. The process according to claim 1, in which a stream enriched in butanes compared to the C4-hydrocarbon stream used is obtained at the top of the adsorber.

5. 2. The process of claim 1, wherein the butene-enriched stream obtained at the top of the desorber further comprises water derived from the solvent.

6. 6. The process of claim 5, wherein the butene-enriched stream is recovered at the top of the desorber and subjected to concentration, and a water-containing stream and a butene-containing product stream are concentrated and separated from each other.

7. 7. The process of claim 6, wherein the butene-containing product stream obtained from the concentration has a butene content of at least 70 wt.%, based on the total composition of the butene-containing product stream.

8. 2. The process of claim 1, wherein the temperature of the adsorber underflow sent to the desorber is from 70°C to 130°C.

9. The method of claim 1, wherein the temperature at the bottom of the desorber is between 120°C and 200°C.

10. The method of claim 1, wherein the head pressure in the desorber is between 1 and 6 bar absolute.

11. 2. The method of claim 1, wherein preheating of the charge solvent delivered to the desorber is accomplished in two stages, a first heat transfer to the solvent occurring in a heat exchanger and a second heat transfer to the solvent occurring in a kettle evaporator.

12. 2. The method of claim 1, wherein the heat for evaporation in the desorption evaporator is introduced into a heat exchanger by heat transfer through a suitable heat transfer medium.

13. 2. The method of claim 1, wherein the pressure in the concentrate vessel is lower than the heating vapor side of the heat exchanger, thus causing a portion of the heating concentrate to re-vaporize, resulting in a combined vapor being obtained as a low pressure vapor.

14. 2. The method of claim 1, wherein the heating steam for the desorption evaporator is provided using a steam ejector fed with high or medium pressure steam and the low pressure steam obtained in the concentrate vessel.

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