Methods for preventing three-phase separation 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 butenes as well as butanes 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 that contains butanes as well as butenes by extractive distillation using a suitable solvent. The process according to the invention is characterized by heat integration, in which the heat of the solvent is utilized for heating a different stream. [Background technology]

[0002] The separation of butane-butene mixtures by extractive distillation is known per se. For this, aprotic solvents (for example N-methyl-2-pyrrolidone (NMP) or acetonitrile (ACN)) are used to increase the relative volatility of the alkanes. In a single extractive distillation column, the absorber, the butenes are preferably dissolved in the solvent and the butanes are separated as overhead product. The loaded solvent is then stripped of the butenes at high temperature in a stripping column, the desorber, which are obtained in concentrated form as overhead product. The butene-depleted solvent is then recycled to the extractive distillation.

[0003] Due to the high solvent to feed ratio, heat integration is very important for the economics of the process. Hot solvent is obtained at the bottom of the desorber and its energy content can be utilized in various ways. US 2014 / 0124358 A1 presents a process for 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 for heating a side stream from the desorber, for heating the bottom product of the absorber that is sent to the desorber, for heating one or more side streams of the absorber, and for preheating the feed stream.

[0004] In the separation of butene-butane mixtures, both energy recovery and prevention of a three-phase system in the absorber are important functions. A butane-rich stream passes overhead through the absorber. To prevent a portion of the solvent from passing overhead, it is necessary to backwash the solvent. To achieve this purpose, a certain amount of reflux, which may contain a high percentage of n-butane, is sent to the backwash area at the top of the absorber. However, a high n-butane content is likely to cause a second liquid phase in the absorber, which not only hinders the separation work of the absorber but also may cause foaming problems (loss-type foaming). By integrating the butene-butane separation in an integrated chemical system, it must also be taken into account that a higher n-butane content may be present in the feed stream to the butane-butene separation. However, a high n-butane content in the feed stream shifts the equilibrium position of n-butane in the solvent, which results in a higher probability of a second liquid phase occurring. [Prior art documents] [Patent documents]

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

[0006] It is therefore an object of the present invention to provide a method that can reduce the occurrence of a second liquid phase and thus the possibility of foam formation. A further object of the present invention is to achieve increased separation efficiency and optimal energy utilization in butane-butene separation. [Means for solving the problem]

[0007] This object is achieved by the embodiment of the method proposed in claim 1. Preferred embodiments are given 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 vaporizing a liquid C4 hydrocarbon stream in a feed vaporizer, feeding a gaseous C4 hydrocarbon stream to an absorber, and feeding a liquid solvent to the absorber through a liquid distributor above the C4 hydrocarbon stream; the absorber has more than two random packed beds, and in the absorber, the C4 hydrocarbon stream and the solvent are contacted with each other to transfer primarily butenes from the C4 hydrocarbon stream to the solvent; The loaded solvent is collected in a liquid recovery device of the absorber, passed through an absorption evaporator, and then sent to the bottom of the absorber below the liquid recovery device, whereby mainly butane is degassed from the loaded solvent; The laden solvent is then sent as a bottom stream to a desorber; obtaining, at the top of the absorber, a stream rich in butanes compared to the C4-hydrocarbon stream used, which is at least partially condensed and a part of the condensate is returned as reflux to the top of the absorber; (b) the contained solvent, preferably NMP, is fed to the desorption apparatus; the desorber is at a higher temperature and preferably at a lower pressure than the absorber, in which butenes are separated from the solvent, preferably NMP, to obtain a butene-rich stream at the top of the desorber and an at least partially butene-free solvent, preferably NMP, at the bottom of the desorber, the at least partially butene-free solvent, preferably NMP, is collected in the liquid recovery device in the desorber, passed through a desorber and then sent to the bottom of the desorber below the liquid recovery device to degas any butenes remaining in the solvent; thereafter, the solvent, preferably NMP, is recycled to the absorber as a bottom stream. Including, The heat of the solvent recovered as the bottom stream of the desorber is utilized for heat integration by utilizing the heat of the solvent in at least one respective heat exchanger for preheating the loaded solvent sent to the desorber, for evaporation in the absorber-evaporator, and for evaporation of the liquid C4 hydrocarbon stream; wherein at least a portion of the liquid phase is recovered in the liquid distributor above the first or second random packed bed, separated into a heavy liquid phase and a light liquid phase in a decanter, and the heavy liquid phase is returned to the absorber, and / or reflux in the absorber is recovered from the absorber via a drain cup and mixed with the liquid solvent in a static mixer and then fed together with the liquid solvent to the liquid distributor above the first random packed bed.

[0008] One advantage of the process of the invention is the relatively simple equipment setup, which makes it possible to prevent the occurrence of a second liquid phase and / or the risk of foam formation. This increases the separation efficiency of the process and achieves energetic optimization of the process. The process according to the invention is further characterized by an efficient energy recovery by heat integration with a hot solvent.

[0009] With heat integration, heat is removed from the solvent. The reason for this is not only that other streams or columns are heated together, but rather that the solvent is primarily cooled for absorption. The absorption of butenes (step a) is usually carried out at a lower temperature than the desorption (step b). If enough heat is removed from the solvent during the heat integration, i.e. the solvent is at the right temperature, it can be sent directly to the absorber. However, it is also possible that, despite the heat integration, the solvent is not yet at the right temperature. 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 the right temperature.

[0010] The present process relates to the separation of butenes from butene-containing C4-hydrocarbon streams. These streams usually contain butenes as well as alkanes (n-butane, isobutane). In the present context, 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 is such that the process can be carried out economically. In a preferred embodiment of the present invention, the C4-hydrocarbon stream used essentially contains butanes and butenes, i.e. to an extent of more than 98% by weight, preferably more than 99% by weight. The corresponding streams may contain small amounts of impurities or other hydrocarbons such as 1,3-butadiene or C5-hydrocarbons.

[0011] 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 comprises water, in particular in the range of 1% to 10% by weight, preferably 4% to 9% by weight, in each case relative to the total amount of solvent.

[0012] Absorbers that can be used include, in particular, random packed beds consisting of 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 preventing the mixing of the solvent into the gas phase. Above the backwash zone is the top of the absorber, where a stream rich in butanes compared to the C4-hydrocarbon stream used is obtained. Above each random packed bed, a liquid distributor is arranged, by which the liquid is distributed. A liquid recovery device according to the invention is arranged below the last random packed bed, and the bottom of the absorber is arranged below said recovery device. The exact structure of the absorber depends on various parameters and varies in a specific manner.

[0013] The liquid solvent is fed to the liquid distributor and fed into the absorber spatially above the inlet of the C4-hydrocarbon stream. In a preferred embodiment, the solvent is fed to the liquid distributor above the first or second random packed bed, and the C4-hydrocarbon stream is added to the absorber in one or more random packed beds below the first or second random packed bed. In the absorber, the liquid solvent drips downwards and contacts the (ascending) vaporous C4-hydrocarbon stream, transferring a portion of the C4-hydrocarbon stream, mainly containing butenes, to the solvent. In a further 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, relative to the composition of the portion of the C4-hydrocarbon stream transferred to the solvent. This results in that in particular at least 80%, particularly preferably at least 90% of the butenes present in the C4-hydrocarbon stream used are transferred to the solvent.

[0014] In step (a), the C4-hydrocarbon stream and the solvent are brought into contact with each other, in particular in countercurrent. The temperature at the bottom of the absorber is preferably between 40° C. and 70° C., particularly preferably between 45° C. and 65° C. The head pressure in the absorber can be between 3 and 7 bar absolute, preferably between 4 and 6.5 bar absolute.

[0015] The loaded solvent flows downwards in the absorber and is collected in a suitable liquid recovery device, in particular in a chimney tray. The temperature of the content solvent obtained in the liquid recovery device is preferably between 40°C and 90°C, particularly preferably between 45°C and 65°C. The content solvent is recovered from the liquid recovery device, passes through an absorption evaporator and then passes to the bottom of the absorption device below the liquid recovery device, where mainly butane is degassed from the content solvent. The absorption evaporator is preferably a one-through evaporator in which the content solvent passes through the evaporator only once. This makes it possible to achieve the lowest possible temperatures and to prevent contamination. Due to the even greater operating temperature difference, the energy utilization of the NMP stream can be made even more efficient. The absorption evaporator may also be configured as a multi-stage device, i.e. there may be several heat exchangers / several evaporators belonging to the absorption evaporator.

[0016] The loaded solvent, mainly containing butenes, then remains at the bottom, from where it is recovered and sent as bottom stream to the desorber. The temperature of the absorber bottom stream fed to the desorber is preferably 70°C to 130°C, particularly preferably 85°C to 120°C.

[0017] In particular, a stream rich in butanes compared to the C4 hydrocarbon stream used is obtained at the top of the absorber. This stream is at least partially, preferably completely, condensed in a suitable device, for example a condenser, to obtain a condensate. At least a portion of the condensate is then sent as reflux to the absorber. The reflux is preferably fed above the backwash zone of the absorber, from where it is sent to a liquid distributor above the first random packed bed (below the backwash zone). The liquid solvent can be continuously fed to the liquid distributor above the first random packed bed. At this point, or at the random packed bed located below it, the proportion of butane in the reflux can lead to the formation of a second liquid phase, which leads to the formation of undesirable bubbles.

[0018] The invention starts from this point. The liquid phase, consisting of the liquid solvent and the liquid returning from the reflux / backwash area to the absorber, is collected in a liquid distributor above the first random packed bed and sent to a decanter. There, separation takes place into a heavy liquid phase consisting mainly of NMP and a light liquid phase consisting mainly of butane from the reflux. The heavy liquid phase is then returned to the absorber, in particular to the liquid distributor in the absorber. The light liquid phase can be discharged from the process and sent to a desorber or subjected to further separation. This optional one or more stages of separation are carried out before entering the desorber. One option is to heat the light liquid phase and send it to a flash vessel, where a liquid phase containing the liquid solvent and a gas phase containing butane are obtained. Only the liquid phase is then sent to the desorber. The gas phase can be collected from the flash vessel, condensed and then discharged from the process, for example together with a butane-containing product stream.

[0019] Another option is to collect the liquid phase in a liquid distributor above the second random packing bed and send it to a decanter. The first random packing bed is "sacrificed", i.e. a third phase is allowed to develop in or above the first random packing bed. Only afterwards is this prevented by suitable means, i.e. by passing through a decanter. The liquid phase collected above the second random packing bed contains the mixture originating from the first random packing bed.

[0020] The formation of a second liquid phase and the associated foam formation can also be reduced or prevented in another way according to the invention. According to the invention, the reflux to the absorber can be withdrawn, preferably completely, from the absorber via the drain cup. The reflux does not come into contact with the liquid solvent in the liquid distributor. Instead, the reflux is mixed with the liquid solvent in a static mixer and then sent together with the liquid solvent to the absorber, in particular to the liquid distributor above the first random packed bed of the absorber. The use of such a static mixer reduces the tendency for foam formation, in particular due to the small concentration difference between the reflux and the NMP in the absorber. A further advantage is that all foam formation occurs outside the absorber, allowing the absorber to be better handled. The static mixer can be placed both upstream and downstream of the residue cooler for the recirculated NMP.

[0021] The above two methods, mixing with a solvent and passing through a decanter, may be combined with each other.

[0022] The butane-rich stream may further comprise water originating from the solvent. This water may be separated in a subsequent step. The butane-rich stream is recovered at the top of the absorber and subjected to a single- or multi-stage condensation, resulting in a water-containing stream which also contains butane and a butane-containing product stream. These two streams may be separated from each other in a suitable device, for example a spider. Depending on its composition, the water-containing stream separated from the butane-containing product stream may be sent to an absorber or a desorber and / or may be partially discharged from the process. Thus, in the context of this specification, reflux to the absorber should be understood to mean a portion of the butane-containing product stream.

[0023] The butane-containing product stream thus obtained from the condensation may still contain small amounts of water, in particular up to 1500 ppmw, based on the total composition of the butane-containing product stream. In addition, the butane-containing product stream obtained from the condensation may further contain residual butenes, which stream usually contains less than 20% by weight, preferably less than 15% by weight, particularly preferably less than 5% by weight, based on the total composition of the butane-containing product stream.

[0024] Depending on the requirements of the butane-containing product stream obtained, it may be necessary to dry the butane-containing product stream after condensation, preferably in a drying column, to separate the water still present. The butane-containing product stream preferably contains a maximum of 50 ppmw, preferably 25 ppmw, of water after drying. The water obtained during drying can be reused for condensation in the absorber.

[0025] The solvent recovered at the bottom of the absorber and mainly containing butenes is fed to the desorber. For this purpose, the containing solvent can be sent to the desorber, for example using a pump. Compared to the bottom of the absorber, the bottom of the desorber is preferably at a higher temperature and 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 in the desorber can be between 1 and 6 bar absolute, preferably between 2 and 5 bar absolute. The higher temperature and preferably lower pressure compared to the absorber results in that the butenes and possibly all butanes still present are at least partially removed from the solvent. In a preferred embodiment, the at least partially butene-free solvent contains at most 5000 ppmw butenes, particularly preferably between 100 and 900 ppmw butenes. The at least partially butene-free solvent flows downwards in the desorber and is collected in the liquid recovery device of the desorber. From there, the at least partially butene-free solvent is passed to a desorption evaporator and then to the bottom of the desorption device below the liquid recovery device, specifically a chimney tray, in order to degas the butenes remaining in the solvent. The desorption evaporator is preferably a one-through evaporator, in which the at least partially butene-free solvent is passed only once through the evaporator. This makes it possible to achieve the lowest possible temperatures and to prevent fouling. The desorption evaporator can be configured as a multi-stage device, i.e. there can be several heat exchangers belonging to the desorption evaporator. The butene-free solvent then remains at the bottom, from where it is recovered and sent as a bottom stream to an absorber, where it is reused as solvent for butene absorption.

[0026] Before being sent to the absorber, the butene-free 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 formed from butenes at the temperature in the desorber, such as oligomeric or polymeric compounds, from the solvent, preferably NMP. This regeneration is preferably carried out by transferring the butene-free solvent to a vessel and evaporating it at a pressure of less than 500 mbar absolute, more preferably less than 200 mbar absolute, at a temperature of 100° C. to 150° C. The vessel may have a column leading to it. In particular, the heavy boiler is separated by regeneration. If only a portion of the butene-free solvent is subjected to regeneration, the regenerated portion of the solvent is then mixed with the unregenerated solvent and recycled to the absorber.

[0027] A stream that is particularly rich in butenes compared to the C4-hydrocarbon stream used is then obtained at the top of the desorber. This butene-rich stream may further comprise water originating from the solvent. This water may be separated in a subsequent step. The butene-rich stream is recovered at the top of the desorber and subjected to a single- or multi-stage condensation to condense an aqueous stream that may contain not only water but also organic residues and a butene-containing product stream. These two streams may be separated from each other in a suitable device, for example a spider. The aqueous stream separated from the butene-containing product stream may then be recycled to the desorber. It is also possible to discharge all or part of the aqueous stream in order to remove the organics.

[0028] In a preferred embodiment of the invention, the condensation of the butene-rich stream recovered at the top of the desorber is configured as a two-stage condensation, in a first stage the water is condensed and recycled to the desorber, and in a second stage the butene-containing product stream is condensed, although it may also be the case that residual water is condensed in the second stage. This residual water can be separated from the butene-containing product stream via a suitable device, for example a spider.

[0029] The butene-containing product stream obtained from the condensation 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 condensation preferably has a butene content of at least 70 wt.-%, more preferably at least 75 wt.-%, particularly preferably at least 86 wt.-%, based on the total composition of the butene-containing product stream.

[0030] A characteristic feature of the present invention is the heat integration using the heat of the solvent on its way from the desorber to the absorber and the hot condensate obtained in the desorber-evaporator. According to the present invention, the heat of the solvent, preferably NMP, recovered as the bottom stream of the desorber is utilized for preheating the loaded solvent sent to the desorber, for evaporation in the absorber-evaporator, and for heat integration for evaporation of the liquid C4-hydrocarbon stream by utilizing the heat of the solvent in at least one respective heat exchanger.

[0031] In a preferred embodiment of the invention, the pre-heating of the containing solvent sent to the desorption device is carried out in two stages. The first heat transfer to the containing solvent sent to the desorption device is carried out in a heat exchanger, preferably a tube bundle heat exchanger, and the second heat transfer to the containing solvent sent to the desorption device is carried out in a kettle evaporator. Such an embodiment has the advantage that in the above-mentioned preferred embodiment, the heat transferred to the containing solvent in both stages, i.e. in the heat exchanger and in the kettle evaporator, originates from the solvent recovered as the bottom stream of the desorption device as the heat transfer medium. The use of a kettle evaporator also has the advantage that the supply pressure in the conduit to the desorption device can be low. Usually, a high supply pressure is necessary to prevent evaporation in the pipe conduit, which can cause problems such as bursting of the pipe conduit. A further advantage is that the heat load is limited, ensuring that the temperature difference is or remains large enough for heat transfer.

[0032] According to the invention, the at least partially butene-free solvent, preferably NMP, is recovered in the liquid recovery unit of the desorption unit and passed to the desorption / evaporation unit, where all butenes remaining in the solvent are degassed. The heat for evaporation in the desorption / evaporation unit can be introduced into the heat exchanger by heat transfer from a suitable heat transfer medium. The heat transfer medium can in particular be heating steam, which is used in the form of medium- or high-pressure steam. Preferred heating steam is medium-pressure steam at a temperature of 150° C. to 270° C., preferably 160° C. to 250° C. Medium-pressure steam preferably has a pressure of 15 to 30 bar absolute, particularly preferably 17 to 25 bar absolute. Steam with an absolute pressure of more than 30 bar can also be used as heating steam. Such heating steam can also be called high-pressure steam.

[0033] The heating steam used for evaporation may undergo at least partial condensation in the heat exchanger, resulting in the production of a hot condensate with a pressure of 10-20 bar absolute, preferably 12-17 bar absolute, and a temperature of 150°C-200°C, preferably 160°C-200°C. Preferably, downstream of the heat exchanger, a condensate container is arranged in which the hot condensate can be separated from the steam. The pressure in the condensate container is preferably lower than the pressure in the heat exchanger. The lower pressure leads to the evaporation of part of the hot condensate, so that a mixed steam, i.e. the non-condensed part of the heating steam and the hot condensate evaporated in the condensate container by the reduced pressure, is obtained as low-pressure steam in the condensate container. In this case, the low-pressure steam preferably has an absolute pressure of more than 0 bar and less than 10 bar. The temperature of the low-pressure steam is preferably 100°C-180°C.

[0034] The resulting low-pressure steam still contains energy, which is not utilized in any known method. However, this is not advantageous from an energetic or economic point of view. However, this energy can be utilized in a preferred embodiment of the invention. To this end, the heating steam used for the evaporation in the desorption-evaporation device can be provided preferably using a controllable steam discharge device (thermocompressor). The thermocompressor is then fed with both the heating steam to be used, particularly the medium-pressure steam to be used, e.g. originating from a suitable steam network, and the low-pressure steam from the condensate container, so that a mixed steam is formed, which is the heat transfer medium for the desorption-evaporation device. Thus, in this embodiment, the mixed steam is the heating steam. Such a steam discharge device is configured so that it can run on motive steam and draw in the aspirated steam from the container by means of a negative pressure (back pressure in the steam discharge device) and then form the mixed steam to be used as the heat transfer medium. In this case, the motive steam is the heating steam / medium-pressure steam, and the low-pressure steam is drawn in as aspirated steam from the condensate container and mixed with the motive steam.

[0035] The advantages of such an embodiment are clear: the energy of the low-pressure steam available in the condensate container can be utilized, which allows energy and cost savings. Such a procedure can also be advantageous for other reasons: the steam discharge device used can be controllable so that the amount of medium- and low-pressure steam can be adjusted, for example according to certain process parameters. The amount of suction steam is adjusted by 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.

[0036] In a further preferred embodiment, the desorption device comprises a side evaporator. In such a case, the heat transfer medium used in the side evaporator is the mixed steam from the steam discharge device, and the desorption evaporator uses the medium pressure steam as heating steam. The hot condensate from the desorption evaporator and the side evaporator is then sent to the condensate container according to the above embodiment. The resulting low pressure steam is then used in the steam discharge device, and the mixed steam is used in the side evaporator. The advantage of this variant is that the resulting hot condensate can be further depressurized to provide a larger amount of low pressure steam.

[0037] The presently described process can be used in an integrated chemical system, in particular including oligomerization and optionally hydroformylation. The butene separation by the method according to the invention can be used at various points in an integrated plant. It is also possible for the butene separation according to the invention to take place at various points in an integrated chemical plant. For example, the process described herein can be used at the beginning of such an integrated system. The C4-hydrocarbon stream used can in particular be crack C4, raffinate 1, raffinate 2 or a mixture thereof. When crack C4 and / or raffinate 2 are used, the separation method according to the invention can be arranged upstream of the hydrogenation of crack C4, in which butadiene is selectively hydrogenated, or the separation of butadiene, in which butadiene is extractively removed with a solvent such as NMP or nitrile, resulting in a reduced butadiene content. In order to facilitate the separation operation in the method according to the invention, it is possible to arrange a hydroisomerization downstream of the extractive butadiene separation and upstream of the separation according to the invention, since this converts 1-butene into 2-butene, which is more easily absorbed by the solvent.

[0038] If this separation method is used at the beginning of an integrated system, the resulting product stream can be fed to the MTBE synthesis, followed preferably by 1-butene separation, oligomerization, and one or more hydroformylations of the purified oligomers in succession. Hydroformylation can be carried out with the product stream from the oligomerization, which makes it possible to produce INA (isononanol) from di-n-butene after subsequent hydrogenation, or ITDA (isotridecanal) from tributenes. Similarly, hydroformylation can be carried out with the unconverted butenes of the oligomerization, which makes it possible to produce 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 further oligomerization instead of hydroformylation. The conditions of the individual steps are well known to those skilled in the art. The individual steps can include further steps, such as, for example, product separation or treatment of the resulting stream, which are not explicitly mentioned here. However, the separation method according to the invention may be implemented at any other point in such an integrated system.

[0039] In one embodiment of the present invention, the C4-hydrocarbon stream used in the separation process according to the invention is recovered from MTBE synthesis after separation of MTBE, and then the butene-containing product stream is fed to 1-butene separation, followed by oligomerization and then one or more hydroformylations for the production of 2-PH and / or INA in succession. The individual steps may include further steps, such as, for example, separation of the products or treatment of the resulting streams, which are not mentioned explicitly herein.

[0040] 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 then the butene-containing product stream is fed to a 1-butene separation, followed by oligomerization and then one or more hydroformylations for the production of 2-PH, ITDA and / or INA in succession. The individual steps may include further steps, such as, for example, separation of the products or treatment of the resulting streams, which are not mentioned explicitly herein.

[0041] 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, after which the butene-containing product stream is fed to an oligomerization, after which one or more hydroformylations for the subsequent production of 2-PH, ITDA and / or INA are carried out. The individual steps may include further steps, such as, for example, product separation or treatment of the resulting streams, which are not explicitly mentioned herein.

[0042] 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 product downstream of hydroformylation. In that case, the butene-containing product stream obtained from the separation method according to the present invention is recycled and used at a suitable point in the integrated system, for example for the separation of 1-butene, 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 final step of the integrated system, up to 20% by weight of butenes may still be present.

[0043] Independently of the point in the integrated system where the separation process 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 a butane n / iso separation unit, in which n-butane and isobutane are separated from one another. An n / iso separation unit can also be carried out after the adiabatic oligomerization. Another possibility would be to include a butane-containing product stream upstream of the oligomerization in the above-mentioned integrated system consisting of MTBE synthesis, 1-butene separation, oligomerization and hydroformylation.

[0044] In a particularly preferred embodiment of the invention, the energy required for the n / iso separation unit can be at least partially influenced by heat integration with the first stage of a two-stage condensation at the top of the desorber, which has the advantage that the energy gained in the condensation is utilized instead of simply being released to the surroundings as in the prior art.

[0045] The invention will now be described with reference to the drawings, which are illustrative and should not be understood as limiting. [Brief description of the drawings]

[0046] [Figure 1] FIG. 1 shows the basic configuration of the present invention. [Diagram 2] FIG. 2 shows an embodiment nearly identical to that shown in FIG. [Diagram 3] FIG. 3 shows a preferred embodiment of the present invention. [Figure 4] FIG. 4 shows a further embodiment according to the invention. EXAMPLES

[0047] FIG. 1 shows the basic configuration of the invention. The liquid C4-hydrocarbon stream is evaporated via a heat exchanger (4) and sent to an absorber (1). The solvent is, if necessary, brought to the desired temperature via a residue cooling device (3) and is also sent to the absorber. Its inlet is spatially above the inlet of the C4-hydrocarbon stream, in this case above the first random packed bed leading to a liquid distributor (not shown). From there the liquid phase is recovered and sent to a decanter (31). The light liquid phase is returned (together with the loaded solvent) to the desorber and the heavy liquid phase is returned via a pump (32) to the absorber (1). At the top of the absorber (1) is obtained a butane-rich stream, which is recovered. Possible condensation is not shown, only reflux. The loaded solvent is recovered at the bottom of the absorber (1), as shown by the chimney tray in the drawing. At least a part of the loaded solvent is recovered and sent to the bottom of the absorber (1) via an absorption evaporator (5). The loaded solvent is withdrawn from the bottom of the absorber (1) and sent, using a pump (9), via a heat exchanger (6) to the desorber (2) for preheating the loaded solvent, where the butenes present in the solvent are separated from the solvent. A butene-rich stream is obtained at the top of the desorber. This stream can be subjected to a single-stage or multi-stage condensation, not shown. Only a possible reflux is shown. The at least partially butene-free solvent is recovered at the bottom of the desorber (2), as shown by a chimney tray in the drawing. At least a portion of the loaded solvent is recovered and sent to the bottom of the desorber (2) via a desorber-evaporator (7). The butene-free solvent is then withdrawn from the bottom of the desorber (2) and recycled, using a pump (8), via a heat exchanger (6) to the absorber for preheating the loaded solvent, to the absorber-evaporator (5) for evaporation of the C4-hydrocarbon stream, to the heat exchanger (4) and to the residue cooler (3).

[0048] Figure 2 shows an embodiment that is nearly identical to that shown in Figure 1. The difference is that the liquid phase is withdrawn from a liquid distributor (not shown) above the second random packed bed and sent to a decanter (31).

[0049] Figure 3 shows a preferred embodiment of the invention in which the light liquid phase is first heated in a suitable heating device (33) and then fed to a flash vessel (34). The gas phase is discharged, various equipment not shown. The liquid phase is sent from the flash vessel (34) together with the contained solvent to the desorber (2).

[0050] 4 shows a further embodiment according to the invention. The reflux is collected via the drain cup and sent via pump (35) to a static mixer (36) arranged downstream of the residue cooler (3). In the static mixer (36), the reflux is mixed with the liquid solvent and is then sent together with the liquid solvent to the absorber (1). Alternatively, the static mixer (36) may already be arranged upstream of the residue cooler (3), i.e. immediately downstream of the heat exchanger (4).

Claims

1. 1. 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: (a) at least partially vaporizing a liquid C4 hydrocarbon stream in a feed vaporizer, feeding a gaseous C4 hydrocarbon stream to an absorber, and feeding a liquid solvent to the absorber through a liquid distributor above the C4 hydrocarbon stream; the absorber has more than two random packed beds, and in the absorber, the C4 hydrocarbon stream and the solvent are contacted with each other to transfer primarily butenes from the C4 hydrocarbon stream to the solvent; The charge solvent is collected in a liquid recovery unit of the absorber, passed through an absorption evaporator, and then sent to the bottom of the absorber below the liquid recovery unit to degas the loaded solvent, primarily butane; The laden solvent is then sent as a bottom stream to a desorber; obtaining, at the top of the absorber, a stream rich in butanes compared to the C4-hydrocarbon stream used, which is at least partially condensed and a part of the condensate is returned as reflux to the top of the absorber; (b) the containing solvent is supplied to the desorption device; the desorber is at a higher temperature than the absorber, and in the desorber butenes are separated from the solvent, obtaining a butene-rich stream at the top of the desorber and an at least partially butene-free solvent at the bottom of the desorber; the at least partially butene-free solvent is collected in the liquid recovery device within the desorber, passed through a desorber and then sent to the bottom of the desorber below the liquid recovery device to degas any remaining butenes in the solvent; thereafter, recycling said solvent to said absorber as a bottoms stream. Including, The heat of the solvent recovered as the bottom stream of the desorber is utilized for heat integration by utilizing the heat of the solvent in at least one respective heat exchanger for preheating the loaded solvent sent to the desorber, for evaporation in the absorber-evaporator, and for evaporation of the liquid C4 hydrocarbon stream; wherein at least a portion of the liquid phase is recovered in the liquid distributor above the first or second random packed bed, separated into a heavy liquid phase and a light liquid phase in a decanter, and the heavy liquid phase is returned to the absorber, and / or reflux in the absorber is recovered from the absorber via a drain cup and mixed with the liquid solvent in a static mixer and then fed together with the liquid solvent to the liquid distributor above the first random packed bed.

2. 2. The method of claim 1, wherein the solvent used is NMP.

3. 2. The method of claim 1, wherein the solvent or the NMP comprises water and has a water content of 1% to 10% by weight.

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

5. 6. The process of claim 5, wherein the butene-rich stream is recovered at the top of the desorber, subjected to condensation, and condensed into water and a butene-containing product stream, which are separated from one another, and the water is recycled to the absorber.

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

7. 2. The method of claim 1, wherein the heavy liquid phase is transferred from the decanter to the absorber using a pump.

8. 2. The process of claim 1, wherein the light liquid phase obtained in the decanter is sent to the desorber.

9. 9. The process of claim 8, wherein the light liquid phase is first heated and sent to a flash vessel where a liquid phase and a vapor phase are obtained, and the liquid phase is sent to the desorber.

10. The method of claim 9, wherein the vapor phase from the flash vessel is condensed and discharged.

11. 2. The method of claim 1, wherein preheating of the loaded solvent sent to the desorber is performed in two stages, a first heat transfer to the solvent occurs in a heat exchanger and a second heat transfer to the solvent occurs in a kettle evaporator.

12. 2. The method according to claim 1, wherein the heat for evaporation in the desorption-evaporation device can be introduced into the heat exchanger by heat transfer using a suitable heat transfer medium.

13. 2. The method of claim 1, wherein the heating steam used is at least partially condensed in the heat exchanger, thereby producing a hot condensate at an absolute pressure of 10-20 bar and a temperature of 150° C.-200° C., which is sent to a condensate container.

14. 14. The method of claim 13, wherein the pressure in the condensate container is lower than the pressure in the heat exchanger, thereby causing a portion of the heated condensate to be re-evaporated, resulting in a mixed vapor as low pressure vapor.

15. 2. The method of claim 1, wherein the heating steam for the desorber is provided using a steam discharge system that supplies medium pressure steam and the low pressure steam obtained in the condensate vessel.

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