Energy-efficient process for separating butenes from c4-hydrocarbon streams

Abstract

The invention relates to a process for separating butenes from C4-hydrocarbon streams containing butanes as well as butenes by means of extractive distillation with a suitable solvent. The process according to the invention is characterized by heat integration which makes it possible to use the heat of the solvent for heating and / or at least partly evaporating various streams, and by the use of a heat pump for the electrification of the process.

Description

[0001] Energy-efficient process for the separation of butenes from C4 hydrocarbon streams

[0002] The present invention relates to a process for the separation of butenes from C4 hydrocarbon streams containing butanes in addition to butenes, by extractive distillation with a suitable solvent. The process according to the invention is characterized by heat integration, with which the heat of the solvent is used to heat and / or at least partially evaporate various streams, and the use of a heat pump to electrify the process.

[0003] The separation of butane-butene mixtures by extractive distillation is well known. An aprotic solvent (e.g., N-methyl-2-pyrrolidone (NMP) or acetonitrile (ACN)) is used to increase the relative volatility of the alkanes compared to the alkenes. In an extractive distillation column, the absorber, the butenes are preferentially dissolved in the solvent, and the butanes are separated as the overhead product. The laden solvent is then freed of the butenes in a stripping column, the desorber, at elevated temperature and / or reduced pressure, which are recovered in an enriched form as the overhead product. The butene-free solvent is then recycled to the extractive distillation.

[0004] Due to the high solvent-to-feed ratio, heat integration is of great importance for the economic viability of the process. Hot solvent is produced in the desorber bottoms, the energy content of which can be utilized in a variety of ways. Furthermore, the question of CO2 reduction is becoming increasingly important both socially and politically. This, too, is having an increasingly significant impact on the economic viability of the process. US 2014 / 0124358 A1 presents a process for the selective extraction of olefins that is intended to solve the problem of heat integration. It proposes using the energy content of the hot solvent to heat a side stream from the desorber, to heat the absorber bottoms product, which is fed to the desorber, to heat one or more absorber side streams, and to preheat the feed stream.

[0005] However, the solution proposed in the prior art cannot fully achieve the goal of recovering the energy flows present in the system, or can only do so through relatively complex structures. Furthermore, the solution proposed there can only make a minor, if any, contribution to reducing CG2 emissions.

[0006] The objective of the present invention was therefore to provide a process that achieves improved, ideally maximum, energy recovery and is less complex in terms of plant technology. Furthermore, the greatest possible reduction in CO2 emissions should be achieved and, ideally, with the availability of green electricity, a CO2-emission-free process should be enabled.

[0007] This object is achieved by the embodiment of the process proposed in claim 1. Preferred embodiments are specified in the subclaims. 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, the process comprising the following steps: a. At least partially evaporating the liquid C4 hydrocarbon stream in a feed evaporator, feeding the gaseous C4 hydrocarbon stream, and feeding the liquid solvent above the C4 hydrocarbon stream to an absorber in which the C4 hydrocarbon stream and the solvent are brought into contact with one another, whereby predominantly butenes from the C4 hydrocarbon stream pass into the solvent,wherein the thus-laden solvent is collected in a liquid collector of the absorber and passed through an absorber evaporator and then passed below the liquid collector into the bottom of the absorber, whereby predominantly butanes are outgassed from the laden solvent, and wherein the laden solvent is subsequently passed as a bottom stream to a desorber; b. feeding the laden solvent to the desorber, in the bottom of which there is an elevated temperature and preferably a lower pressure compared to the bottom of the absorber and in which the butenes are separated from the solvent, whereby a butene-enriched stream is obtained at the top of the desorber, wherein a solvent at least partially freed of butenes is collected in a liquid collector of the desorber and passed through a desorber evaporator and then passed below the liquid collector into the bottom of the desorber, whereby butenes still present in the solvent are outgassed,and wherein the solvent is subsequently returned to the absorber as a bottom stream of the desorber as a heat source for a multi-stage high-temperature heat pump; characterized in that the heat of the solvent removed as a bottom stream of the desorber is at least partially used for heat integration, in which the heat of the solvent is used in at least one heat exchanger for heat transfer in the heat pump, for evaporation in the absorber evaporator and for evaporation of the liquid C4 hydrocarbon stream; and that the heat for evaporation in the desorber evaporator is introduced by steam generated in the multi-stage high-temperature heat pump, wherein the high-temperature heat pump has at least one first container with a first,

[0008] Heat exchanger, a second container with a second heat exchanger and at least one compressor, wherein the first container contains a first working medium to which heat is transferred from the solvent obtained as a bottom stream of the desorber in the first heat exchanger, the second container contains a second working medium to which heat is transferred from the first working medium in the second heat exchanger.

[0009] One advantage of the present process is the relatively simple design of the heat integration, which nevertheless enables efficient energy recovery. The use of a heat pump also has the advantage that the process can be operated more independently; for example, no heating medium needs to be purchased in the desorber evaporator. Such a heating medium must first be available in sufficient quantities at the location where the process is carried out. Furthermore, energy recovery is optimized by the use of the heat pump. The waste heat from the solvent is raised to a certain temperature level by the heat pump so that it can be used directly in the desorber. The design according to the invention also enables considerable quantities of heating medium to be saved. This, in turn, saves several kilotons of CO2 per year. When using green electricity, even CO2-free separation of n- and iso-butane can be carried out.Furthermore, the separation of butanes results in significant energy savings and efficiency improvements in a network of multiple production plants, because the inert butanes do not have to be entrained through the production plants. This is especially true when the butane-butene separation according to the invention is used in the front part of the network.

[0010] The additional heat integration removes heat from the solvent originating from the desorber. The reason for this is not only to heat other streams or columns, but primarily to cool the solvent for absorption. The absorption of the butenes (here: step a) usually takes place at a lower temperature than desorption (here: step b). If sufficient heat is removed from the solvent during heat integration, i.e., if it has a suitable temperature, the solvent can be fed directly into the absorber. However, it is also conceivable that the solvent is not yet at the correct temperature despite the heat integration. In such a case, the solvent can be passed through a residual cooler after heat integration and before entering the absorber to be cooled to a suitable temperature.

[0011] Heat is a process variable. The heat added or removed corresponds to the change in internal energy minus the work performed. The terms heat, heat transport, and heat integration used in this document are always based on this definition.

[0012] The present process relates to the separation of butenes from butene-containing C4 hydrocarbon streams. These streams typically also contain alkanes (n-butane, isobutane) in addition to the butenes. The term butanes is understood in the context of the present invention to mean both n-butane and isobutane, unless otherwise stated. Therefore, all C4 hydrocarbon streams which contain at least butenes and butanes can be used in the process according to the invention, provided that the amounts in which the butenes and / or butanes are present permit economic implementation of the process. In a preferred embodiment of the present invention, the C4 hydrocarbon stream used consists essentially, i.e., to an extent of more than 98% by weight, preferably to an extent of more than 99% by weight, of butanes and butenes.The corresponding streams may also contain impurities or other hydrocarbons, such as 1,3-butadiene or C5 hydrocarbons, in small amounts.

[0013] The extraction process according to the invention uses a liquid solvent in which the butenes of the gaseous C4 hydrocarbon stream used primarily dissolve. Suitable solvents are aprotic solvents, for example N-methyl-2-pyrrolidone (NMP). The process according to the invention is preferably carried out using NMP as the solvent. In a further preferred embodiment of the present invention, the solvent contains water, in particular in the range from 1 to 10 wt. %, preferably from 4 to 9 wt. %, based in each case on the total amount of solvent.

[0014] Packed columns having at least two packed beds can be used as absorbers, in particular. Such columns are generally known to those skilled in the art. Above the first packed bed, there is preferably a backwash zone with several theoretical plates to retain the solvent entrained into the gas phase. Above the backwash zone is the top of the absorber, where a stream enriched in butanes compared to the C4 hydrocarbon stream used is obtained. The liquid collector according to the invention would be arranged below the last packed bed, below which would be the bottom of the absorber. The exact design of the absorber depends on various parameters and is variable to a certain extent.

[0015] The liquid solvent is added to the absorber spatially above the inlet for the C4 hydrocarbon stream. In a preferred embodiment, the solvent is added to the absorber above the first packed bed and the C4 hydrocarbon stream is added to one or more packed beds below the first packed bed. The liquid solvent will trickle downwards in the absorber and come into contact with the (ascending) vaporous C4 hydrocarbon stream, as a result of which a portion of the C4 hydrocarbon stream, which predominantly contains butenes, passes into the solvent, thereby forming a loaded solvent. The C4 hydrocarbon stream and the solvent are brought into contact with one another in step a, in particular in countercurrent. In a preferred embodiment of the present invention, the portion of the C4 hydrocarbon stream which passes into the solvent comprises at least 70% by weight, particularly preferably at least 80% by weight.-% butenes, based on the composition of the portion of the C4 hydrocarbon stream that has passed into the solvent. This means, in particular, that at least 80%, particularly preferably at least 90%, of the butenes present in the C4 hydrocarbon stream used pass into the solvent.

[0016] The loaded solvent flows downward in the absorber and is collected in a suitable liquid collector, in particular a chimney tray. The temperature of the loaded solvent accumulating in the liquid collector is preferably between 40 and 90°C, particularly preferably between 45 and 65°C. The loaded solvent is removed from the liquid collector, passed through an absorber evaporator, and then passed below the liquid collector into the absorber sump, where predominantly butanes are outgassed from the loaded solvent. The absorber evaporator is preferably a once-through evaporator, in which the loaded solvent is passed through the evaporator only once. This allows the lowest possible temperatures to be achieved, thus preventing fouling. In addition, the driving temperature difference is increased, enabling even more efficient energy utilization of the NMP stream.The absorber evaporator can also be designed in several stages, i.e. there can be several heat exchangers or several evaporators belonging to the absorber evaporator.

[0017] The solvent, predominantly loaded with butenes, then remains in the bottoms, which are removed from there and fed to the desorber as a bottoms stream. The temperature in the bottoms stream of the absorber, which is fed to the desorber, is preferably between 70 and 130 °C, particularly preferably between 85 and 120 °C.

[0018] At the top of the absorber, a stream enriched in butanes, in particular, compared to the C4 hydrocarbon stream used, is obtained. The top pressure in the absorber can be between 3 and 7 bar absolute, preferably between 4 and 6.5 bar absolute. The butane-enriched stream can additionally contain water originating from the solvent. This water can be separated in a subsequent step. The butane-enriched stream is withdrawn at the top of the absorber and subjected to a single- or multi-stage condensation, whereby a water-containing stream and a butane-containing product stream are condensed out. These two streams can be separated from one another in a suitable device, for example a condenser. The water-containing stream separated from the butane-containing product stream can, depending on its composition, be used to

[0019] absorber or desorber and / or partially removed from the process.

[0020] The butane-containing product stream thus obtained from the condensation may still contain small amounts of water, in particular in an amount of up to 1500 ppm by weight, based on the total composition of the butane-containing product stream. Furthermore, the butane-containing product stream obtained from the condensation may still contain residual butenes, with the streams typically containing less than 20% by weight, preferably less than 15% by weight, particularly preferably less than 5% by weight of butenes, based on the total composition of the butane-containing product stream.

[0021] Depending on the requirements for the resulting butane-containing product stream, it may be necessary to subject the butane-containing product stream to drying after condensation, preferably in a drying column, to remove any remaining water. Preferably, the butane-containing product stream after drying has a maximum water content of 50 ppm by weight, preferably 25 ppm by weight. The water obtained during drying can be recycled for condensation on the absorber.

[0022] The solvent removed from the bottom of the absorber and predominantly laden with butenes is fed to the desorber. For this purpose, the laden solvent can be fed to the desorber, for example, by means of a pump. In the bottom of the desorber, the temperature is higher and preferably the pressure is lower than in the bottom of the absorber. The temperature in the bottom of the desorber is preferably between 120 and 200 °C, more preferably between 130 and 195 °C. The top pressure in the desorber can be between 1 and 6 bar absolute, preferably between 2 and 5 bar absolute. Due to the higher temperature and the preferably lower pressure compared to the absorber, the butenes and any butanes still present are at least partially removed from the solvent. In a preferred embodiment, the solvent from which at least some of the butenes have been freed contains up to 5000 ppm by weight of butenes, particularly preferably 100 to 900 ppm by weight of butenes.The solvent, at least partially freed of butenes, flows downwards in the desorber and is collected in a liquid collector of the desorber. From there, the solvent, at least partially freed of butenes, is passed through a desorber evaporator and then directed below the liquid collector, in particular a chimney tray, into the desorber sump, whereby any butenes still present in the solvent are outgassed. The desorber evaporator is preferably a once-through evaporator, in which the solvent, at least partially freed of butenes, is passed through the evaporator only once. This allows the lowest possible temperatures to be achieved, which can prevent fouling. The desorber evaporator can also be designed in several stages, i.e., there can be several heat exchangers belonging to the desorber evaporator.The solvent freed from butenes then remains in the bottom, which is removed from there, led as a bottom stream to the absorber and used there again as a solvent for the absorption of butenes.

[0023] The solvent freed from butenes can be partially or completely regenerated before being fed to the absorber, whereby impurities, for example the aforementioned by-products present in the C4 hydrocarbon stream used and / or formed from the butenes at the temperatures in the desorber, such as oligomers or polymeric compounds, are removed from the solvent, preferably the NMP. Regeneration is preferably carried out by conveying the solvent freed from butenes into a vessel and evaporating it at a pressure of less than 500 mbar absolute, more preferably less than 200 mbar absolute, and a temperature between 100 and 150°C. A column can be connected to the vessel. Regeneration removes, in particular, high boilers.If only a portion of the butene-free solvent is subjected to regeneration, the regenerated portion of the solvent is subsequently combined with the non-regenerated solvent and returned to the absorber.

[0024] At the top of the desorber, a stream enriched in butenes compared to the C4 hydrocarbon stream used then arises. This butene-enriched stream may also contain water originating from the solvent. This water can be separated in a subsequent step. The butene-enriched stream is withdrawn at the top of the desorber and subjected to a single- or multi-stage condensation, during which a water-containing stream, which may also contain residual organic matter in addition to water, and a butene-containing product stream are condensed out. These two streams can be separated from one another in a suitable device, e.g., a condenser. The water-containing stream separated from the butene-containing product stream can then be returned to the desorber. It is also possible to discharge all or part of the water-containing stream in order to remove the organic matter.

[0025] In a preferred embodiment of the present invention, the condensation of the butene-enriched stream removed at the top of the desorber is carried out in two stages. In a first stage, a water-containing stream is condensed out, which is then recycled to the desorber, and in the second stage, the butene-containing product stream is condensed out. However, any water still present may also be condensed out in the second stage. This residual water can be separated from the butene-containing product stream using a suitable device, for example, a separator.

[0026] The butene-containing product stream obtained from the condensation preferably contains less than 20 wt. %, more preferably less than 16 wt. % of butanes, based on the total composition of the butene-containing product stream. Instead, the butene-containing product stream obtained from the condensation preferably has a butene content of at least 70

[0027] % by weight, further preferably at least 75 % by weight, particularly preferably at least 86 % by weight, based on the total composition of the butene-containing product stream.

[0028] A characteristic feature of the present invention is the heat integration using the heat of the solvent on the way from the desorber to the absorber and the hot condensate produced in the desorber evaporator. The heat of the solvent removed as the bottom stream from the desorber, preferably the NMP, is used according to the invention for heat integration by using the heat of the solvent in at least one heat exchanger for heat transfer in the heat pump, for evaporation in the absorber evaporator, and for evaporation of the liquid C4 hydrocarbon stream.

[0029] According to the invention, the solvent, preferably NMP, which has been at least partially freed of butenes, is collected in a liquid collector of the desorber and passed through a desorber evaporator, whereby any butenes still present in the solvent can be degassed. The heat for evaporation in the desorber evaporator can be introduced into a heat exchanger by heat transfer from a suitable heat transfer medium. The heat transfer medium is steam produced by a heat pump integrated into the process and a heat integration system and can, for example, be in the pressure range from 5 to 30 bar, preferably in the range from 13 to 17 bar absolute. The condensation temperatures between 150°C and 270°C result from the specified pressures.

[0030] Within the scope of the present invention, the steam is generated in the multi-stage high-temperature heat pump. In principle, a single-stage high-temperature heat pump can also be designed and used. The multi-stage high-temperature heat pump comprises at least a first tank with a first heat exchanger, a second tank with a second heat exchanger, and at least one compressor. It is possible to use only a single multi-stage compressor capable of compressing different gases independently of one another. However, it is also preferably possible for the multi-stage high-temperature heat pump to comprise at least two compressors, at least one per stage.

[0031] The first vessel contains a first working medium, to which heat is transferred in the first heat exchanger from the solvent emerging as the bottom stream of the desorber. The first working medium can, in principle, be any 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 the group consisting of water, n-hexane, n-pentane, methanol, and mixtures thereof. The first vessel can also be a kettle evaporator comprising a heat exchanger integrated into a vessel.

[0032] The heat is transferred from the solvent removed as the bottom stream from the desorber to the first working medium in the first heat exchanger. The first heat exchanger can be connected to the bottom of the first vessel and the first working medium can be fed back to the first vessel via the first heat exchanger. In the first heat exchanger, the first working medium is heated and at least partially evaporated. This also increases the pressure in the first vessel. The evaporated first working medium can then be removed at the vessel lid. The first working medium is raised to a first temperature level by the heat transfer. The temperature of the first working medium is preferably between 80 and 140 °C. The pressure is preferably in the range from 2 to 8 bar absolute. The evaporated first working medium is fed via the at least one compressor or via the first compressor to the second heat exchanger and from there back to the first vessel.During the return from the second heat exchanger, the first working medium can be passed through a further heat exchanger, with which the evaporated, first working medium is further heated before passing through the at least one compressor or the first compressor.

[0033] The second vessel contains a second working medium to which heat is transferred from the first 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). Preferably, the second working medium should not be supercritical even at temperatures > 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 can also be a kettle evaporator comprising a heat exchanger integrated into a vessel.

[0034] The heat is transferred from the first working medium to the second working medium 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 fed back to the second container via the second heat exchanger. In the second heat exchanger, the first working medium is heated and at least partially evaporated. This also increases the pressure in the second container. The evaporated first working medium can then be removed from the container lid. The first working medium is raised to a second temperature level by the heat transfer, whereby the second temperature level is higher than the first temperature level. The temperature of the first working medium is preferably between 80 and 140 °C. The pressure is preferably in the range of 2 to 8 bar absolute.The evaporated second working medium is fed via the at least one compressor or via the second compressor as vapor according to the invention to the desorber evaporator and from there back to the second vessel. Before the evaporated working medium reaches the desorber evaporator, fresh condensate can be injected to bring the temperature and pressure to the desired level, preferably to slightly cool the vapor. During the return from the desorber evaporator, the second working medium can be passed through another heat exchanger, which further heats the evaporated second working medium before passing through the at least one compressor or the second compressor.

[0035] The advantage of such a design is obvious. The steam is provided intrinsically by the heat pump and does not need to be purchased. Furthermore, the utilization of the heat generated in the process is significantly greater than in other known processes. This represents significantly improved heat integration. Furthermore, a significant amount of steam can be saved because the hot condensate is more effectively utilized in this case.

[0036] In a preferred embodiment of the present invention, the absorber in the sump has a dividing plate, whereby the sump is divided into two segments, and the two-stage evaporation is carried out in such a way that the laden solvent collected in the liquid collector is passed through a first evaporator, preferably a once-through evaporator, and guided to the first segment, and that the laden solvent from the first segment is passed through a second evaporator, preferably a forced circulation evaporator, and flashed into the second segment, from which the bottom stream is then withdrawn to the desorber. One advantage of this is that the design in the sump of the absorber, i.e. the presence of a dividing plate and two-stage evaporation, allows the height of the absorber to be reduced while increasing separation efficiency.

[0037] A further preferred embodiment can also be provided if the desorber has a side evaporator. In such a case, the heat transfer medium used for the side evaporator can be the mixed steam from the steam jet, while medium-pressure steam is used as heating steam in the desorber evaporator. The hot condensate from the desorber evaporator and the side evaporator is then passed to a condensate tank as described above. The low-pressure steam produced there is then used in the steam jet, whose mixed steam is used in the side evaporator. The advantage of this variant is that the resulting hot condensate can be further expanded in order to provide a larger amount of low-pressure steam. The process described here can be used in chemical complexes, which in particular comprise oligomerization and optionally hydroformylation.It is possible for the separation of butenes according to the process of the invention to be carried out at various points within the complex. It is also possible for the separation of butenes according to the invention to be present at several points within a chemical complex.

[0038] It is possible, for example, for the process described here to be used at the beginning of such a network. The C4 hydrocarbon stream used can then be, in particular, a cracked C4, a raffinate 1, a raffinate 2 or a mixture thereof. If cracked C4 and / or raffinate 2 are used, a cracked C4 hydrogenation, in which butadiene is selectively hydrogenated, or a butadiene separation, in which butadiene is removed extractively with a solvent such as NMP or nitriles, can take place before the separation process according to the invention in order to reduce the butadiene content. After an extractive butadiene separation and before the separation according to the invention, a hydroisomerization can be arranged in order to facilitate the separation task in the process according to the invention, since 1-butene is converted into 2-butene, which is generally better absorbed by the solvent.The advantage of separating butanes is that the residence time in all reaction stages is longer because less inert butane needs to be sent through each stage. From an energy perspective, integration is particularly desirable after butadiene separation and before MTBE synthesis. This allows the inert i-butane and n-butane to be separated early from the process and does not require all subsequent distillation steps.

[0039] If the separation process is used at the beginning of the network, the resulting product stream can be fed to an MTBE synthesis, followed preferably by successive 1-butene separation, oligomerization, and one or more hydroformylation steps on the purified oligomers. Hydroformylation can be carried out either with the product stream from the oligomerization, whereby, for example, INA (isononanol) can be produced from di-n-butenes after subsequent hydrogenation, or ITDA (isotridecanal) from tributenes, or with the unreacted butenes from the oligomerization, whereby, after subsequent aldol condensation and subsequent hydrogenation, 2-PH (2-propylheptanol) can be produced. With the unreacted butenes from the oligomerization, a further oligomerization could also be carried out instead of hydroformylation. The conditions of the individual process steps are familiar to the person skilled in the art.The individual process steps may include further steps such as, for example, the separation of the products or the workup of the resulting streams, but are not explicitly mentioned here. However, the separation process according to the invention can also be inserted at any other point in such a network. In one embodiment of the present invention, the C4 hydrocarbon stream used in the separation process according to the invention is taken from an MTBE synthesis after the separation of MTBE, and the butene-containing product stream is subsequently fed to a 1-butene separation, after which an oligomerization and one or more hydroformylation steps are successively carried out to subsequently prepare 2-PH, ITDA and / or INA. The individual process steps may include further steps such as, for example, the separation of the products or the workup of the resulting streams, but are not explicitly mentioned here.

[0040] In a further embodiment of the present invention, the C4 hydrocarbon stream used in the separation process according to the invention is withdrawn from a 1-butene separation, and the butene-containing product stream is subsequently fed to an oligomerization, followed by one or more hydroformylation steps for the subsequent preparation of 2-PH, ITDA, and / or INA. The individual process steps may include further steps, such as the separation of the products or the workup of the resulting streams, but these are not explicitly mentioned here.

[0041] In a further embodiment of the present invention, the C4 hydrocarbon stream used in the separation process according to the invention is withdrawn from an oligomerization, and the butene-containing product stream is then fed to a hydroformylation for the subsequent production of 2-PH. The individual process steps may include further steps, such as the separation of the products or the workup of the resulting streams, but are not explicitly mentioned here.

[0042] In a further embodiment of the present invention, the separation process according to the invention is used at the end of the combined process. In this case, the C4 hydrocarbon stream used is taken from a 2-PH production process following the hydroformylation. The butene-containing product stream then obtained from the separation process according to the invention can in this case be recycled and used at a suitable point in the combined process, for example for 1-butene removal, for oligomerization, or for one or more hydroformylation(s). This can increase the efficiency of the entire combined process, since up to 20 wt. % butenes can still be present in the combined process even after the last process step.

[0043] Regardless of the location in the network where the separation process according to the invention is located, the butane-containing product stream can be fed, for example, to an adiabatic oligomerization, a hydrogenation of the remaining butenes, or an n-iso splitting of the butanes, in which n-butane and isobutane are separated from each other. The n-iso splitting can also be carried out after an adiabatic oligomerization. It would also be possible to incorporate the butane-containing product stream before oligomerization into a network described above comprising MTBE synthesis, 1-butene separation, oligomerization, and hydroformylation.

[0044] In a particularly preferred embodiment of the present invention, the energy required for n / iso splitting can be provided at least partially by heat integration with the first stage of a two-stage condensation at the top of the desorber. This has the advantage that the energy generated during the condensation is utilized and not simply released into the environment as in the prior art.

[0045] The present invention is explained below with reference to figures. The figures are for illustrative purposes only and are not to be construed as limiting.

[0046] Fig. 1 shows the basic design of the present invention. The liquid C4 hydrocarbon stream is evaporated via a heat exchanger (4) and passed into the absorber (1). The solvent is brought to the desired temperature via a residual cooler (3) - if necessary - and also passed into the absorber, with the inlet being spatially above the inlet for the C4 hydrocarbon stream, in this case above the first packed bed. At the top of the absorber (1), the butane-enriched stream is obtained and removed. A possible condensation is not shown here; only the recirculation of a possible partial stream is indicated. The laden solvent is collected in the bottom of the absorber (1), which is indicated in the figure by the chimney tray. There, at least a portion of the laden solvent is removed and passed via an absorber evaporator (5) to the bottom of the absorber (1).The laden solvent is removed from the bottom of the absorber (1) and conveyed by a pump (9) to the desorber (2), where the butenes present in the solvent are separated from the solvent. At the top of the desorber, the butene-enriched stream is obtained. This stream can be subjected to single- or multi-stage condensation, which is not shown in the figure. Only a possible recycle stream is indicated. In the bottom of the desorber (2), the solvent that has been at least partially freed of butenes is collected, which is indicated in the figure by the chimney tray. There, at least a portion of the laden solvent is removed and conveyed via a desorber evaporator (7) to the bottom of the desorber.The solvent freed from butenes is then removed from the bottom of the desorber (2) and returned to the absorber by means of a pump (8) via the first vessel with the first heat exchanger (20), the absorber evaporator (5), the heat exchanger (4) for evaporating the C4 hydrocarbon stream, and the residual cooler (3). In the first vessel with the first heat exchanger (20), at least a portion of the first working medium is evaporated and passed via the further heat exchanger (21), where further heating takes place, and the first compressor (22) to the second vessel with the second heat exchanger (23). In the second vessel with the second heat exchanger (23), at least a portion of the second working medium is evaporated and passed via the second compressor (24) to the desorber evaporator (7).

[0047] Fig. 2 shows a preferred embodiment of the present invention in which a separating plate is present in the sump of the absorber (1). In this embodiment, a portion of the laden solvent is removed from the chimney plate of the absorber (1) and passed via an absorber evaporator (5) to the first segment in the sump of the absorber (1), in which a separating plate is present. The laden solvent is removed from the first segment and passed by a pump (13) via a second evaporator (14) to the second segment in the sump of the absorber. The laden solvent is removed from the second segment in the sump of the absorber (1) and passed by a pump (9) via the heat exchanger (6) to preheat the laden solvent and to the desorber (2), where the butenes present in the solvent are separated from the solvent. During the recirculation of the solvent, which has been at least partially freed of butenes, heat is transferred in the heat exchanger in this preferred embodiment.

[0048] Fig. 3 shows a preferred embodiment of the present invention, in which a flash tank (26) for intermediate expansion (26) and an additional compressor (25) are present. The first working medium is guided to the second heat exchanger (23) by means of the two compressors (22, 25) and is thereby at least partially condensed. The first working medium then reaches the flash tank (26) and is separated there. A portion passes via the additional heat exchanger (21) to the first tank with the first heat exchanger (20). The other portion is guided between the two compressors (22 and 25), thereby relieving the load on the first compressor (22). The entire working medium no longer needs to be compressed from the low pressure level to the high pressure level, but only a certain portion, which brings further energetic advantages.

[0049] Fig. 4 shows an embodiment of the present invention in which, according to Fig. 2, a separating plate is present in the absorber and in which the first working medium is subjected to an intermediate expansion in the flash container (26) according to Fig. 3.

[0050] The invention is explained below using a simulation. This embodiment represents only a preferred embodiment and is not to be understood as limiting.

[0051] Example

[0052] The butane-butene separation shown in Fig. 1 was simulated using Aspen Plus V10. A modified NRTL parameter set was used to describe the interactions between the components. In the simulation, 27 t / h of a hydrocarbon-containing feed was fed into a 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% transbutene, and 5 wt% cisbutene.

[0053] A total of 10 t / h of butane-containing overhead product is removed from the absorber. The butane-containing overhead product of the absorber consists of 70 wt.% n-butane, 27 wt.% iso-butane, 1 wt.% 1-butene, and 2 wt.% iso-butene. The solvent laden with the butene-containing product stream is removed in the bottom. The butene-containing product stream contains 14 wt.% n-butane, 15 wt.% 1-butene, 47 wt.% iso-butene, 8 wt.% cis-butene, and 16 wt.% trans-butene. With the set solvent / feed ratio of 13, a 98% butene yield can be achieved. The large excess solvent is then also used for heat integration and as a heat source for the heat pump.

[0054] The solvent stream, here NMP, was led from the bottom of the desorber (2) to a heat exchanger, a kettle evaporator (20), in which n-hexane is evaporated at 3.6 bar abs. The NMP is cooled from around 180 to 190 °C to around 120 to 125 °C and 13.4 MW are transferred. This creates an n-hexane cycle stream of just over 240 t / h, which is superheated by 42 K in a gas superheater (21). The n-hexane stream is then brought to a pressure level of 14.1 bar abs. using a multi-stage compressor (22). In another heat exchanger, another kettle evaporator (23), the working medium n-hexane is condensed in the tubes. Water is added on the shell side at 7 bar abs. evaporated. The steam is brought to a pressure level of 13.1 bar abs by another compressor (24). This produces approximately 35 t / h of steam, which is used for evaporation in the desorber evaporator. Both working fluids are operated in a closed loop.

[0055] Compared to conventional butane-butene separation processes, where the heating media must be purchased or provided, the inventive design provides significant savings potential of up to 35 t / h of steam. This amount is now produced internally by the heat pump.

Claims

Patent claims 1. A process for separating butenes from a C4 hydrocarbon stream containing at least butenes and butanes by extractive distillation with a solvent, the process comprising the following steps: a. At least partially evaporating the liquid C4 hydrocarbon stream in a feed evaporator, feeding the gaseous C4 hydrocarbon stream and feeding the liquid solvent above the C4 hydrocarbon stream to an absorber in which the C4 hydrocarbon stream and the solvent are brought into contact with one another, whereby predominantly butenes from the C4 hydrocarbon stream pass into the solvent, wherein the thus-laden solvent is collected in a liquid collector of the absorber and passed through an absorber evaporator and then passed below the liquid collector into the bottom of the absorber, whereby predominantly butanes are outgassed from the laden solvent,and wherein the loaded solvent is subsequently fed to a desorber as a bottom stream; b. feeding the loaded solvent to the desorber, in the bottom of which there is an elevated temperature and preferably a lower pressure compared to the bottom of the absorber, and in which the butenes are separated from the solvent, whereby a butene-enriched stream is obtained at the top of the desorber, wherein a solvent at least partially freed from butenes is collected in a liquid collector of the desorber and passed through a desorber evaporator and then passed below the liquid collector into the bottom of the desorber, whereby butenes still present in the solvent are outgassed, and wherein the solvent is subsequently returned to the absorber as a bottom stream of the desorber as a heat source for a multi-stage high-temperature heat pump; characterized inthat the heat of the solvent removed as the bottom stream of the desorber is used at least partially for heat integration, in which the heat of the solvent is used in at least one heat exchanger for heat transfer in the heat pump, for evaporation in the absorber evaporator and for evaporation of the liquid C4 hydrocarbon stream; and that the heat for evaporation in the desorber evaporator is introduced by steam generated in the multi-stage high-temperature heat pump, wherein the high-temperature heat pump has at least one first container with a first, Heat exchanger, a second container with a second heat exchanger and at least one compressor, wherein the first container contains a first working medium to which heat is transferred from the solvent obtained as the bottom stream of the desorber in the first heat exchanger, the second container contains a second working medium to which heat is transferred from the first working medium in the second heat exchanger. Process according to claim 1, wherein the heat pump comprises at least two compressors. Process according to 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. Process according to 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. Process according to one of claims 1 to 4, wherein the first working medium and the second working medium are not identical.Method according to one of claims 1 to 5, wherein the first working medium is at least partially evaporated by the heat introduced during the heat transfer. Method according to claim 6, wherein the evaporated working medium is passed via the at least one compressor to the second heat exchanger and from there back to the first container, preferably via a further third heat exchanger, with which the evaporated, first working medium is further heated before passing through the at least one compressor. Method according to claim 7, wherein the second working medium is at least partially evaporated by the heat introduced during the heat transfer. Method according to claim 8, wherein the second working medium is passed via the at least one compressor to the desorber evaporator and from there, at least partially condensed, back to the second container, preferably via a further fourth. Heat exchanger with which the second working medium is further heated before passing through the second compressor.

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

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

12. Process according to one of the preceding claims, wherein a stream enriched in butanes compared to the C4 hydrocarbon stream used is obtained at the top of the absorber.

13. Process according to one of the preceding claims, wherein the temperature in the bottom stream of the absorber which is fed to the desorber is between 70 and 130 °C, preferably between 85 and 120 °C.

14. Process according to one of the preceding claims, wherein the temperature in the bottom of the desorber is between 120 and 200 °C, preferably 130 and 195 °C.

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