Energy-efficient process for separating butene from C4-hydrocarbon streams

Abstract

The subject of the invention is a process for separating butenes from C4-hydrocarbon streams containing both butenes and butane by extractive distillation with a suitable solvent. The method according to the invention is characterized in that the specific surface area of the random packing present in the inlet region of at least one random packing bed of the absorber is lower than the rest of the random packing bed.

Description

[0001] The present invention relates to a method for separating butenes from a C4-hydrocarbon stream containing not only butenes but also butanes by extractive distillation with a suitable solvent. The method according to the invention is characterized in that the specific surface area of the random packing present in the inlet zone of at least one random packing bed of the absorber is lower than that of the remainder of the random packing bed.

[0002] The separation of butane-butene mixtures by extractive distillation is known per se. This uses an aprotic solvent (such as N-methyl-2-pyrrolidone (NMP) or acetonitrile (ACN)) to increase the relative volatility of the alkanes with respect to the olefins. In an extractive distillation column, i.e., an absorber, butenes are preferably dissolved in the solvent and butane is separated as the top product. The loaded solvent is then stripped of butenes in a stripping column, i.e., a desorber, at elevated temperature and / or reduced pressure, and the butenes are obtained as the top product in an enriched form. The solvent free of butenes is then recycled to the extractive distillation. A typical method for separating butane-butene mixtures by extractive distillation is described, for example, in WO 2022 / 161869A1.

[0003] In all method variants, butenes are washed out of the butane-butene mixture, i.e., the C4-hydrocarbon stream used, with a solvent that is initially liquid in the absorption column. If the method is carried out as described in the prior art, it must be noted that in the inlet zone of the random packing bed of the absorber, due to temperature gradients and / or concentration gradients, a miscibility gap may occur or the condensation of droplets may be caused. This may lead to the accumulation of the liquid phase in the inlet zone of the random packing bed of the absorber, thereby causing premature blockage of the absorption column. This reduces the separation efficiency in these areas.

[0004] The methods described in the prior art may thus have the problem of reduced separation efficiency in the inlet zone. Overall, this leads to a reduction in the production capacity of the equipment and to the need to use a larger amount of solvent.

[0005] The problem solved by the present invention is thus to provide a method for achieving improved separation efficiency of the absorber in the simplest possible way. Another problem solved is to reduce the amount of solvent used.

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

[0007] a. A gaseous C4 - hydrocarbon stream and a liquid solvent, preferably NMP, are supplied to an absorber comprising at least three randomly packed beds arranged one below the other, and wherein the C4 - hydrocarbon stream and the solvent are brought into contact with each other to transfer mainly butene from the C4 - hydrocarbon stream into the solvent to form a loaded solvent, where the thus - loaded solvent is collected in a liquid collector of the absorber and conveyed through an absorber evaporator and then fed into the absorber bottom below the liquid collector to discharge mainly butane as a gas from the loaded solvent, and wherein subsequently the loaded solvent is sent as a bottoms stream to a desorber;

[0008] b. The loaded solvent is supplied to a desorber, the bottom of which is at an elevated temperature and preferably a lower pressure relative to the bottom of the absorber, and wherein butene is separated from the solvent to obtain an enriched - butene stream at the top of the desorber, where at least a portion of the butene - depleted solvent is collected in a liquid collector of the desorber and conveyed through a desorber evaporator and then fed into the desorber bottom below the liquid collector to discharge butene still present in the solvent as a gas, and wherein subsequently the solvent is recycled as a bottoms stream to the absorber;

[0009] It is characterized in that at least one randomly packed bed of the absorber contains different randomly packed materials, wherein the randomly packed material in the upper region of the randomly packed bed has a specific surface area y and the randomly packed material in the lower region of the randomly packed bed has a specific surface area x, where the specific surface area x is greater than the specific surface area y.

[0010] The solution according to the invention thus consists in using two randomly packed materials with different specific surface areas in at least one randomly packed bed of the absorber. Randomly packed beds are generally filled with stacked randomly packed materials. First, the randomly packed bed is filled with the randomly packed material having the higher specific surface area x, and subsequently with the randomly packed material having the lower specific surface area. The randomly packed material having the specific surface area y forming the upper region is thus arranged on the randomly packed material having the specific surface area x forming the lower region. The difference in the specific surface area of the randomly packed materials for the extractive distillation column according to the invention is, for example, based on the size of the randomly packed materials. Larger randomly packed materials are known to have a smaller specific surface area based on the filled volume of the randomly packed materials.

[0011] Regarding the specific surface areas x and y of the randomly packed materials, it is not possible to restrict to exact numerical values or limits. The surface areas to be used depend on the spatial configuration of the extractive distillation system or the composition of the hydrocarbon stream used. However, the specific surface area x of the randomly packed material in the lower region of the at least one randomly packed bed is preferably at least 10% higher than the specific surface area y of the randomly packed material in the upper region of the at least one randomly packed bed.

[0012] The inlet zone of a random packing bed, especially the inlet zone of the uppermost bed, is characterized by significant temperature and concentration profiles. Here, cold unloaded solvent is added to a hot gas stream, thereby causing condensation in the gas phase. There is also a high risk of forming a second liquid phase here. The formation of droplets through the concentration or temperature profile ensures that the droplets are kept suspended by the gas stream and do not flow away immediately. Therefore, the liquid load in the inlet zone of the random packing bed is higher than that in the rest of the random packing bed, and liquid accumulation, i.e., so-called flooding, occurs. Flooding in the inlet zone results in a hydraulic bottleneck and also a loss of separation efficiency. It has been found that using two different random packings in one random packing bed in the upper part of an absorber brings gains in capacity and separation efficiency.

[0013] The exact spatial configuration of a random packing bed containing different random packings according to the invention depends on the configuration of the absorber. Thus, apart from the fact that the random packing with a lower specific surface area y is arranged above the random packing with a larger specific surface area x, the exact implementation can vary and can be adapted to the conditions present in each case. However, in principle, the situation is that preferably a larger part of the volume of the random packing bed should be filled with the random packing with specific surface area x, i.e., the random packing with a larger surface area. In this regard, it is preferred that a maximum of 20% of the volume of the random packing bed is filled with the random packing with specific surface area y. The remaining 80% of the volume is then allocated to the random packing with specific surface area x. When installing the random packing, it may be preferred to observe the filling height of the random packing in the random packing bed. In this regard, it is preferred that the random packing with specific surface area y occupies 20% of the filling height of the random packing bed. The remaining 80% of the filling height is then allocated to the random packing with specific surface area x.

[0014] The absorber according to the method of the invention comprises at least three random packing beds. According to the invention, it is preferred that the at least one random packing bed with different random packings is the uppermost random packing bed among the at least three random packing beds of the absorber. However, it is also possible that two or three of the at least three random packing beds of the absorber contain different random packings according to the configuration of the invention. A particularly preferred embodiment consists in that all the random packing beds in the absorber are equipped with different random packings according to the configuration of the invention.

[0015] The absorber may also contain more than three dumped packing beds. If the absorber contains more than three dumped packing beds, preferably, the at least one dumped packing bed having different dumped packings is the uppermost dumped packing bed among the at least three dumped packing beds of the absorber. However, it is also possible that two or three of the at least three dumped packing beds of the absorber contain different dumped packings configured according to the present invention. In a preferred embodiment of the present invention, the two or three dumped packing beds containing different dumped packings configured according to the present invention are the uppermost two or uppermost three dumped packing beds of the absorber. A particularly preferred embodiment is that all the dumped packing beds in the absorber are equipped with different dumped packings configured according to the present invention.

[0016] The method of the present invention relates to the separation of butenes from a C4-hydrocarbon stream containing butenes. In addition to butenes, these streams generally also contain alkanes (n-butane, isobutane). In the present invention, unless otherwise described, the term butane should be understood to mean n-butane and isobutane. The method according to the present invention can thus use all C4-hydrocarbon streams containing at least butenes and butanes, provided that the amounts of butenes and / or butanes present are such that the method can be carried out economically. In a preferred embodiment of the present invention, the C4-hydrocarbon stream used consists essentially, i.e., to an extent greater than 98% by weight, preferably to an extent greater than 99% by weight, of butanes and butenes. The corresponding streams may also contain small amounts of impurities or other hydrocarbons, such as 1,3-butadiene or C5-hydrocarbons.

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

[0018] In the present invention, the absorber used is a dumped packing column comprising at least three dumped packing beds arranged one below the other. Such columns are known in principle to those skilled in the art. Preferably, a stripping section containing a plurality of theoretical plates is arranged above the first dumped packing column to retain the solvent entrained in the gas phase. Above the stripping section is the top of the absorber, where a stream enriched in butane with respect to the C4-hydrocarbon stream used is obtained. A liquid collector according to the present invention is arranged below the last dumped packing bed, and the bottom of the absorber is arranged below the liquid collector. The exact construction of the absorber depends on various parameters and is variable in some respects.

[0019] The liquid solvent is preferably supplied to the absorber spatially above the inlet of the C4-hydrocarbon stream. In a preferred embodiment, the solvent is supplied to the absorber above the first random packing bed, and the C4-hydrocarbon stream is supplied to the absorber in one or more random packing beds below the first random packing bed. In the absorber, the liquid solvent trickles down and contacts the (upward flowing) gaseous C4-hydrocarbon stream to transfer a part of the C4-hydrocarbon stream mainly containing butene into the solvent to form a loaded solvent. In step a, the C4-hydrocarbon stream and the solvent are thus brought into contact with each other, especially in a countercurrent manner. In a preferred embodiment of the present invention, the part of the C4-hydrocarbon stream transferred into the solvent contains at least 70% by weight, particularly preferably at least 80% by weight of butene based on the composition of the part of the C4-hydrocarbon stream transferred into the solvent. This has the particular result that at least 80%, particularly preferably at least 90% of the butene contained in the C4-hydrocarbon stream used is transferred into the solvent.

[0020] The loaded solvent flows downward in the absorber and is collected in a suitable liquid collector, especially a chimney tray (Kaminboden). The temperature of the loaded solvent produced in the liquid collector is preferably between 40 and 90 °C, particularly preferably between 45 and 65 °C. The loaded solvent is taken out of the liquid collector, conveyed through the absorber evaporator, and then fed into the bottom of the absorber below the liquid collector to mainly discharge butane as a gas from the loaded solvent. The absorber evaporator is preferably a single-pass evaporator, in which the loaded solvent is only passed through the evaporator once. This enables the achievement of as low a temperature as possible, thereby preventing fouling. Additionally, the driving temperature difference is increased, thereby enabling more efficient energy utilization of the NMP stream. The absorber evaporator can also be configured as a multi-stage device, i.e., there can be multiple heat exchangers or multiple evaporators belonging to the absorber evaporator.

[0021] The solvent mainly loaded with butene then remains at the bottom, from where it is taken out and sent as a bottom stream to the desorber. The temperature in the absorber bottom stream sent to the desorber is preferably between 70 °C and 130 °C, particularly preferably between 85 °C and 120 °C.

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

[0023] Depending on the requirements for the resulting butane-containing product stream, it may be necessary to dry the butane-containing product stream after condensation, preferably in a drying column, to separate the still contained water. The butane-containing product stream preferably contains a maximum water content of 50 weight ppm, preferably 25 weight ppm, after drying. The water obtained during the drying process can be recycled to the absorber for condensation.

[0024] The solvent mainly loaded with butene taken from the bottom of the absorber is supplied to the desorber. For this purpose, the loaded solvent can be pumped to the desorber, for example. The bottom of the desorber is at an elevated temperature and preferably a lower pressure relative to the bottom of the absorber. 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 top pressure of the desorber can be between 1 and 6 bar absolute pressure, preferably between 2 and 5 bar absolute pressure. The elevated temperature and preferably lower pressure relative to the absorber cause at least partial removal of butene and optionally still contained butane from the solvent. In a preferred embodiment, the solvent from which at least part of the butene has been removed contains at most 5000 weight ppm of butene, particularly preferably 100 to 900 weight ppm of butene. The solvent from which at least part of the butene has been removed flows downward in the desorber and is collected in the liquid collector of the desorber. From here, the solvent from which at least part of the butene has been removed is passed through the desorber evaporator and then fed into the liquid collector, in particular the bottom of the desorber below the chimney tray, to discharge as a gas the butene still present in the solvent. The desorber evaporator is preferably a single-pass evaporator, in which the solvent from which at least part of the butene has been removed is only passed through the evaporator once. This enables the achievement of as low a temperature as possible, thereby preventing fouling. The desorber evaporator can also be configured as a multi-stage device, i.e., there can be multiple heat exchangers belonging to the desorber evaporator. The solvent from which butene has been removed is then retained at the bottom, from where it is taken out as a bottom stream and sent to the absorber, where it is used again as a solvent for absorbing butene.

[0025] Before being sent to the absorber, the solvent from which butene has been removed can be partially or completely regenerated to remove impurities from the solvent, preferably NMP, such as the above-mentioned by-products formed from the butene in the C4-hydrocarbon stream used and / or at the temperature in the desorber, such as oligomeric or polymeric compounds. The regeneration is preferably carried out by feeding the solvent from which butene has been removed into a vessel and evaporating it at a temperature between 100 °C and 150 °C at an absolute pressure of less than 500 mbar, more preferably less than 200 mbar absolute pressure. A column can be connected to this vessel. High boilers are particularly separated by the regeneration. If only a part of the solvent from which butene has been removed is regenerated, the regenerated part of the solvent is subsequently combined with the non-regenerated solvent and recycled to the absorber.

[0026] The method according to the invention may preferably furthermore be characterized by thermal integration, by means of which the heat of the solvent is used for heating and / or at least partial evaporation of different streams. The heat of the solvent removed as the bottoms stream of the desorber, preferably the heat of NMP, is at least partly used for thermal integration - wherein in at least one respective heat exchanger the heat of the solvent, preferably NMP, is used for preheating the loaded solvent fed to the desorber, preferably NMP, for evaporation in the absorber evaporator and for evaporation of the liquid C4-hydrocarbon stream in the feed evaporator.

[0027] An advantage is the simple construction of the thermal integration, but still enabling efficient energy recovery. The simplest embodiment of the invention furthermore does not require a mandatory additional side evaporator, which would entail additional plant engineering complexity and thus higher costs.

[0028] Thermal integration removes heat from the solvent. The reason is not only that other streams or columns are to be heated, but mainly that the solvent is cooled for absorption. The absorption of butene (here: step a) is usually carried out at a lower temperature than the desorption (here: step b). If sufficient heat is removed from the solvent during thermal integration, i.e. it has a suitable temperature, the solvent can be fed directly into the absorber. However, it is also conceivable that, despite the thermal integration, the solvent still does not have the correct temperature. In this case, the solvent can be passed through a residual cooler after thermal integration and before entering the absorber to be cooled to a suitable temperature.

[0029] Heat is a process parameter. The heat supplied or removed corresponds to the change in internal energy minus the work done. The terms heat, heat transfer and thermal integration used in the present invention are always based on this definition.

[0030] In a preferred embodiment of the invention, the preheating of the loaded solvent fed to the desorber is carried out in two stages, wherein the first heat transfer to the loaded solvent fed to the desorber is carried out in a heat exchanger, for example a tube bundle heat exchanger, and the second heat transfer to the loaded solvent fed to the desorber is carried out in a kettle evaporator. Such an embodiment has the advantage that, in the above preferred embodiment, in two stages, i.e. in the heat exchanger and in the kettle evaporator, the heat transferred to the loaded solvent is derived from the solvent removed as the bottoms stream of the desorber as the heat transfer medium. The advantage of using a kettle evaporator is also that it allows a lower pre-pressure to exist in the conduit leading to the desorber. Usually a high pre-pressure is required to prevent evaporation in the pipeline, which can lead to problems including pipeline bursting. A further advantage is that the heat load is limited, thereby ensuring that the temperature difference is large enough or remains large enough for heat transfer.

[0031] Then, a butene-enriched stream is obtained especially at the top of the desorber, compared to the C4-hydrocarbon stream used. This butene-rich stream may additionally contain water originating from the solvent. This water can be separated in subsequent steps. The butene-enriched stream is taken out at the top of the desorber and subjected to single-stage or multi-stage condensation to condense an aqueous stream containing not only water but also possibly residual organic matter and a product stream containing butene. These two streams can be separated from each other in a suitable device, such as a spider collector. The aqueous stream separated from the product stream containing butene can then be recycled to the desorber. It is also possible to discharge all or part of the aqueous stream to remove organic matter.

[0032] The product stream containing butene obtained by condensation preferably contains less than 20% by weight, more preferably less than 16% by weight of butane, based on the total composition of the product stream containing butene. In contrast, the product stream containing butene obtained by condensation preferably has a butene content of at least 70% by weight, more preferably at least 75% by weight, particularly preferably at least 86% by weight, based on the total composition of the product stream containing butene.

[0033] According to the present invention, at least part of the solvent from which butene has been removed, preferably NMP, is collected in the liquid collector of the desorber and conveyed through the desorber evaporator to discharge as a gas the butene still present in the solvent. The heat for evaporation in the desorber evaporator can be introduced in a heat exchanger by heat transfer from a suitable heat transfer medium. The heat transfer medium can be especially heating steam used in the form of medium-pressure steam or high-pressure steam. The preferred heating steam is medium-pressure steam having a temperature of 150°C to 270°C, preferably 160°C to 250°C. The medium-pressure steam preferably has a pressure of 15 to 30 bar absolute, particularly preferably 17 to 25 bar absolute. Steam having a pressure of >30 bar absolute can also be used as the heating steam. Such heating steam can also be referred to as high-pressure steam.

[0034] The heating steam for evaporation can undergo at least partial condensation in the heat exchanger, thereby generating hot condensate at a pressure of 10 to 20 bar absolute, preferably 12 to 17 bar absolute, and a temperature of 150°C to 210°C, preferably 160°C to 200°C. A condensate container is preferably provided downstream of the heat exchanger, in which the hot condensate can be separated from the steam. The pressure in the condensate container is preferably lower than the pressure on the heating steam side in the heat exchanger. The lower pressure can cause a part of the hot condensate to evaporate, so that combined steam, i.e., the uncondensed part of the heating steam and the hot condensate evaporated by pressure reduction in the condensate container, is obtained as low-pressure steam in the condensate container. In this case, the low-pressure steam preferably has a pressure greater than 0 bar and less than 10 bar absolute. The temperature of the low-pressure steam is preferably 100°C to 180°C.

[0035] The low-pressure steam obtained here still contains energy, but this is not utilized in any known method. However, this is disadvantageous from an energy and economic perspective. However, this energy can be utilized in a preferred embodiment of the present invention. For this purpose, the heating steam for evaporation in the desorber evaporator can be provided using a preferably controllable steam ejector (thermal compressor). Then, both the heating steam used (derived from, for example, a suitable steam network, in particular preferably used medium-pressure steam here) and the low-pressure steam from the condensate vessel are supplied to the thermal compressor, thereby forming a mixed steam, which is accordingly the heat transfer medium for the desorber evaporator. In this embodiment, the mixed steam is accordingly the heating steam. Such a steam ejector is configured to operate with motive steam and can suck in the suction steam from the vessel by means of a negative pressure (back pressure in the steam ejector) to form the mixed steam used as the heat transfer medium. The motive steam in this case is the heating steam or medium-pressure steam, by means of which the low-pressure steam is sucked in from the condensate vessel as the suction steam and mixed with the motive steam.

[0036] The advantages of such an embodiment are obvious. The energy of the low-pressure steam obtained in the condensate vessel can be utilized, thereby saving energy and costs. For another reason, such a procedure is also advantageous. The steam ejector used can be controllable so that, for example, the amounts of medium-pressure steam or high-pressure steam and low-pressure steam can be adjusted according to specific process parameters. The amount of suction steam is adjusted by the amount of motive steam. The amounts of low-pressure steam and medium-pressure steam can be adjusted, for example, according to the temperature in the desorber.

[0037] In a further preferred embodiment, the desorber can also contain a side evaporator. In such a case, the heat transfer medium for the side evaporator can be the mixed steam from the steam ejector, while medium-pressure steam is used as the heating steam in the desorber evaporator. The hot condensate from the desorber evaporator and the side evaporator is then sent to the condensate vessel as described above. The low-pressure steam obtained therein is then used for the steam ejector, and its mixed steam is used for the side evaporator. The advantage of this variant is that the resulting hot condensate can be further depressurized to be able to provide a larger amount of low-pressure steam.

[0038] The methods described herein can be used in chemical integration systems, which particularly include oligomerization and optionally hydroformylation. The separation of butenes by the method according to the invention is potentially useful at various points in such an integration system. The separation of butenes according to the invention can also be present at various points within a chemical integration system. For example, the methods described herein can be used at the start of such an integration system. The C4-hydrocarbon feedstock used can subsequently be, in particular, cracked C4, raffinate 1, raffinate 2, or a mixture thereof. If cracked C4 and / or raffinate 2 are used, upstream of the separation method according to the invention, a cracked C4 hydrogenation can be provided, in which butadiene is selectively hydrogenated, or a butadiene separation can be provided, in which butadiene is removed by extraction with a solvent such as NMP or a nitrile, to reduce the butadiene content. A hydroisomerization can be provided downstream of the butadiene extraction separation and upstream of the separation according to the invention to facilitate the separation task in the method according to the invention, since this converts 1-butene into 2-butene, which is generally more readily absorbed by the solvent.

[0039] If the separation method is used at the start of the integration system, the resulting product stream can be supplied to MTBE synthesis, and then 1-butene separation, oligomerization, and one or more hydroformylations of the purified oligomer can preferably be carried out successively. The hydroformylation can be carried out not only with the product stream from the oligomerization, whereby it is possible, for example, to produce INA (isononanol) from di-n-butene after subsequent hydrogenation or ITDA (isotridecanal) from tri-butene, but also with the unreacted butenes from the oligomerization, whereby it is possible to produce 2-PH (2-propylheptanol) after subsequent aldol condensation and subsequent hydrogenation. The unreacted butenes from the oligomerization can also optionally be used for further oligomerization instead of hydroformylation. The conditions of the individual method steps are familiar to those skilled in the art. The individual method steps can include further steps, such as the separation of products or the work-up of the resulting streams, but these are not explicitly mentioned herein. However, the separation method according to the invention can also be introduced at various other points in such an integration system.

[0040] In one embodiment of the invention, the C4-hydrocarbon feedstock used in the separation method according to the invention is withdrawn from the MTBE synthesis after MTBE separation, and then the butene-containing product stream is supplied to 1-butene separation, and then oligomerization and one or more hydroformylations are carried out successively to subsequently produce 2-PH, ITDA, and / or INA. The individual method steps can include further steps, such as the separation of products or the work-up of the resulting streams, but these are not explicitly mentioned herein.

[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 the 1-butene separation, and subsequently the butene-containing product stream is supplied to oligomerization, after which one or more hydroformylations are carried out to subsequently produce 2-PH, ITDA, and / or INA. Each process step may include further steps, such as separation of the product or work-up of the resulting stream, but these are not explicitly mentioned here.

[0042] In a further embodiment of the present invention, the C4-hydrocarbon stream used in the separation process according to the invention is withdrawn from the oligomerization, and subsequently the butene-containing product stream is supplied to hydroformylation to subsequently produce 2-PH. Each process step may include further steps, such as separation of the product or work-up of the resulting stream, but these are not explicitly mentioned here.

[0043] In a further embodiment of the present invention, the separation process according to the invention is used at the end of an integrated system. In this case, the C4-hydrocarbon stream used is taken from the 2-PH production downstream of the hydroformylation. Subsequently, the butene-containing product stream obtained by the separation process according to the invention can in this case be recycled and used at a suitable point in the integrated system, for example for 1-butene separation, for oligomerization, or for one or more hydroformylations. This makes it possible to enhance the efficiency of the entire integrated system, since even after the last process step in the integrated system, up to 20 wt% of butene may still be present.

[0044] Regardless of the point at which the separation process according to the invention is arranged in the integrated system, the butane-containing product stream can be supplied to, for example, adiabatic oligomerization, hydrogenation of the butene still present, or the n / i-splitting of butane in which n-butane and i-butane are separated from each other. The n / i-splitting can also be carried out after the adiabatic oligomerization. Another possibility is to incorporate 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.

[0045] In a particularly preferred embodiment of the present invention, the energy required for the n / i-splitting can be at least partially achieved by thermal integration with the first stage of the two-stage condensation at the top of the desorber. This has the advantage that the energy obtained in the condensation is utilized instead of simply being released to the environment as in the prior art.

[0046] The present invention is illustrated below with reference to the accompanying drawings. The drawings are used for illustrative purposes and should not be construed as limiting.

[0047] Figure 1Shows an embodiment according to the prior art (WO 2022 / 161869 A1). A liquid C4 - hydrocarbon stream is evaporated via a heat exchanger (4) and fed into an absorber (1). If necessary, the solvent is brought to the required temperature via a residual cooler (3) and likewise fed into the absorber, where the inlet is spatially above the inlet of the C4 - hydrocarbon stream, in this case above the first random packing bed. A butane - enriched stream is obtained at the top of the absorber (1) and withdrawn. Possible condensation is not shown here, only the recirculation of possible sub - streams is shown. The loaded solvent is collected at the bottom of the absorber (1), as shown by the chimney trays in the figure. Here, at least a part of the loaded solvent is withdrawn and sent to the bottom of the absorber (1) via an absorber evaporator (5). The loaded solvent is withdrawn from the bottom of the absorber (1) and sent to a desorber (2) using a pump (9) via a heat exchanger (6) for pre - heating the loaded solvent, where the butene present in the solvent is separated from the solvent. An butene - enriched stream is obtained at the top of the desorber. This stream can be subjected to single - stage or multi - stage condensation, which is not shown in the figure. Only possible recirculation streams are shown. At least part of the solvent with butene removed is collected at the bottom of the desorber (2), as shown by the chimney trays in the figure. Here, at least a part of the loaded solvent is withdrawn and sent to the bottom of the desorber via a desorber evaporator (7). Then the solvent with butene removed is withdrawn from the bottom of the desorber (2) and recycled to the absorber using a pump (8) via the heat exchanger (6) for pre - heating the loaded solvent, the absorber evaporator (5), the heat exchanger (4) for evaporating the C4 - hydrocarbon stream, and the residual cooler (3).

[0048] Figure 2 Shows a particularly preferred embodiment of the present invention, in which different random packings are contained in each random packing bed in the absorber (1). Further implementation is as Figure 1 described in. The random packing in the upper grey area of the random packing bed has a specific surface area y, and the random packing in the lower area of the random packing bed has a specific surface area x, where the specific surface area x is greater than the specific surface area y.

[0049] Figure 3 Shows Figure 2 a part of, in which the structure of the random packing bed (10) is shown in more detail. In this case, the random packing bed not only contains the support ring (12) of the liquid distributor, but also contains a compression grid (11), which is arranged on the random packing (13, 14) and holds the stacked random packing in the random packing bed. Random packing (13) with a lower specific surface area y is present in the upper region of the random packing bed. Random packing (14) with a larger specific surface area x is present in the lower part of the random packing bed.

Claims

1. A method for separating butene from a C4 - hydrocarbon feed stream containing at least butene and butane by extractive distillation with a solvent, wherein the method comprises the following steps: a. Supplying a gaseous C4 - hydrocarbon feed stream and a liquid solvent to an absorber comprising at least three randomly packed beds arranged one below the other, and wherein the C4 - hydrocarbon feed stream and the solvent are brought into contact with each other to mainly transfer butene from the C4 - hydrocarbon feed stream into the solvent and form a loaded solvent, wherein the thus - loaded solvent is collected in a liquid collector of the absorber and conveyed through an absorber evaporator and then fed into the absorber bottom below the liquid collector to mainly discharge butane as a gas from the loaded solvent, and wherein subsequently the loaded solvent is sent as a bottom stream to a desorber; b. Supplying the loaded solvent to a desorber, the bottom of which is at an elevated temperature and preferably a lower pressure relative to the bottom of the absorber, and wherein butene is separated from the solvent to obtain an butene - enriched stream at the top of the desorber, wherein at least a part of the solvent from which butene has been removed is collected in a liquid collector of the desorber and conveyed through a desorber evaporator and then fed into the desorber bottom below the liquid collector to discharge butene still present in the solvent as a gas, and wherein subsequently the solvent is recycled as a bottom stream to the absorber; It is characterized in that At least one of the randomly packed beds of the absorber contains different randomly packed materials, wherein the randomly packed material in the upper region of the randomly packed bed has a specific surface area y and the randomly packed material in the lower region of the randomly packed bed has a specific surface area x, wherein the specific surface area x is greater than the specific surface area y.

2. The method according to claim 1, wherein the at least one randomly packed bed having different randomly packed materials is the uppermost randomly packed bed of the absorber.

3. The method according to claim 1 or 2, wherein at least two or three of the randomly packed beds of the absorber contain different randomly packed materials.

4. The method according to claim 3, wherein the two or three randomly packed beds having different randomly packed materials are the uppermost two or the uppermost three randomly packed beds of the absorber.

5. The method according to any one of the preceding claims, wherein all of the randomly packed beds in the absorber contain different randomly packed materials.

6. The method according to any one of the preceding claims, wherein a maximum of 20% of the volume of the randomly packed bed is filled with randomly packed material having a specific surface area y.

7. The method according to claim 1, wherein the solvent used is NMP.

8. The method according to claim 1 or 2, wherein the solvent or NMP contains water, and the water content is between 1 wt% and 10 wt%, preferably between 4 wt% and 9 wt%.

9. The method according to any one of the preceding claims, wherein the temperature in the absorber bottom stream fed to the desorber is between 70°C and 130°C, preferably between 85°C and 120°C.

10. The method according to any one of the preceding claims, wherein the temperature at the desorber bottom is between 120°C and 200°C, preferably between 130°C and 195°C.

11. The method according to any one of the preceding claims, wherein the top pressure of the desorber is between 1 and 6 bar absolute pressure, preferably between 2 and 5 bar absolute pressure.

12. The method according to any one of the preceding claims, wherein the preheating of the loaded solvent fed to the desorber is carried out in two stages, wherein the first heat transfer to the solvent is carried out in a heat exchanger and the second heat transfer to the solvent is carried out in a kettle evaporator.

13. The method according to any one of the preceding claims, wherein the heat for evaporation in the desorber evaporator is introduced by heat transfer in a heat exchanger with a suitable heat transfer medium, in particular heating steam.

14. The method according to any one of the preceding claims, wherein at least partial condensation of the heating steam used occurs in the heat exchanger, whereby hot condensate is generated at a pressure of 10 to 20 bar absolute pressure, preferably 12 to 17 bar absolute pressure, and a temperature of 150 °C to 210 °C, preferably 160 °C to 200 °C, and is sent to a condensate vessel.

15. The method according to any one of the preceding claims, wherein the heating steam for the desorber evaporator is provided using a steam ejector, and high-pressure steam or medium-pressure steam and low-pressure steam obtained in the condensate vessel are supplied to the steam ejector.

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