METHOD AND DEVICE FOR SEPARATION OF A HYDROGEN-CONTAINING SUBSTANCE FEED STREAM BY EXTRACTIVE DISTILLATION

Description

State of the art

[0001] The invention relates to a method for separating a hydrocarbon-containing feedstock stream by extractive distillation according to the preamble of claim 1 and a device according to the preamble of claim 8.

[0002] Aromatics, especially the simplest aromatic compounds benzene, toluene, and xylene, are of major industrial importance as intermediates for the chemical industry. Various technical processes are known for the production of aromatics. One method that achieves a particularly high purity of the aromatic product stream at comparatively low cost is extraction by extractive distillation from a hydrocarbon-containing feedstock stream. Suitable feedstock streams include, for example, naphtha, pyrolysis gasoline, reformate gasoline, or coke oven light oil. Heavier components are preferably removed from the feedstock stream prior to aromatic extraction, for example, by separating the C8+ fraction.

[0003] In the extraction of aromatics by extractive distillation, the feed stream is brought into contact with a selective solvent for aromatics in a countercurrent process. The solvent affects the volatility of the different components of the feed stream to varying degrees. The volatility of the aromatic components is reduced by dilution, while that of the aliphatic components is significantly increased. This enables a distillative separation into aromatics and non-aromatics / aliphatics. In a first step, the aromatics dissolved in the solvent are then separated from the aliphatic components of the feed mixture by extractive distillation according to a thermal separation step. The aliphatic components are collected as the overhead product of the distillation. In a second step, the aromatics are stripped from the solvent as the overhead product.The aromatic product stream can then be further separated into individual aromatic fractions. The solvent, now depleted of aromatics, is recycled back into the extractive distillation process and reused. In this way, individual aromatics can be obtained in pure form in a continuous process.

[0004] Solvents known for extractive distillation include sulfolane, methylsulfolane, N-methylpyrrolidone, N-formylmorpholine, ethylene glycol and mixtures thereof, as well as mixtures of these solvents with water. The solvents or solvent mixtures used are water-soluble.

[0005] Due to the continuous reuse of the same solvent in a solvent cycle, impurities that do not leave the process as overhead products of the distillation separation of aliphatics or as overhead products of the stripping of aromatics accumulate in the solvent. Driven by operators' efforts to optimize plant energy efficiency and conserve resources, such impurities are increasingly appearing in the feed stream of plants solely dedicated to the production of benzene and toluene. Particularly in plants that simultaneously produce xylene, an accumulation of such impurities is virtually unavoidable in the long term, as the feed stream in this case must contain a higher proportion of higher-boiling components.Furthermore, upstream processes such as clay treatment can introduce heavier components into the extractive distillation process, which then accumulate in the solvent. Additionally, incorrect operation or malfunctions in upstream equipment components, such as those used to remove higher-boiling components, can lead to increased contamination of the solvent circulating in the extractive distillation process with heavier-boiling impurities.

[0006] Over time, impurities cause the solvent to lose its extraction power and require replacement. To reduce the costs associated with solvent replacement, the possibility of purifying the solvent within the solvent cycle is desirable, as this removes the impurities. This can significantly extend the cycle time before the solvent needs to be replaced.

[0007] For example, US 2010 / 0228072 A1 discloses a method for purifying the solvent by subjecting a partial stream of the solvent circuit to distillation. The purified solvent exits the distillation as the overhead product, and impurities remaining as distillation residue are removed from the system. A disadvantage of this method is that it can only remove impurities with a higher boiling point than the solvent from the solvent circuit. Impurities that boil more easily than the solvent, or co-boilers, cannot be removed. co-boiler ) are close to the solvent, i.e., have a closely adjacent boiling point, remain in the solvent.

[0008] From DE 10 2012 111 292 A1, it is known to mix a partial stream of the extraction solvent drawn from the bottom of the stripper column with water and feed it into a distillation column. In the distillation column, the extraction solvent is separated from the added water and from hydrocarbons dissolved in the extraction solvent. The water and hydrocarbons are discharged over the top of the distillation column. This type of purification is based on the fact that the extraction solvent dissolves in the water, displacing the water-insoluble hydrocarbons from the solution in the extraction solvent and forming a more volatile phase that can be separated by distillation along with the water. A disadvantage, however, is that a large quantity of water must be used to treat the entire extraction solvent.Subsequently, all the water used must be distilled off again, at least in the case of extractive distillation with a largely anhydrous solvent. The known method for purifying the solvent is therefore associated with high energy and cost expenditure.

[0009] FR 2 259 891 A1 describes a process for separating aromatic hydrocarbons. In addition to a solvent, the process adds water to both the extractor and the stripper. This results in a significant water content already present in the solvent cycle. According to FR 2 259 891 A, the solvent is purified by a solvent regenerator. First, additional water is added to the solvent to be purified. The mixture is then separated from low- and high-boiling impurities by steam distillation under vacuum. The solvent is recovered and returned to the extractor. The water and impurities are discarded.

[0010] US 3,476,680 A discloses a purely extractive separation process for aromatic hydrocarbons by liquid-liquid extraction in an extractor with a solvent. Subsequently, the solvent is extracted by adding water in a water wash, and the remaining aromatics are removed. The solvent is then recovered by distillation of the water-solvent mixture.

[0011] US 3,451,925 A and CA 610,414 A describe processes similar to US 3,476,680 A, based on a double liquid-liquid extraction with solvent and water, in which the water must subsequently be separated from the solvent by distillation. WO 99 / 11740 A1 shows a parallel combination of an extraction process with an expectorant distillation, in which steam is used to strip the aromatics from the solvent. Disclosure of the invention

[0012] The object of the invention is therefore to provide a method and a device for separating a hydrocarbon-containing feedstock stream by extractive distillation, in which the selectivity and capacity of the solvent used is ensured over a long period of time by a resource-saving process.

[0013] This problem is solved by a method for separating a hydrocarbon-containing feedstock stream by extractive distillation having the features of claim 1 and a device having the features of claim 8.

[0014] This creates a process for separating a hydrocarbon-containing feedstock stream by extractive distillation into at least one aliphatic product stream and one aromatic product stream, which comprises the following steps: Contacting the feedstock stream with a water-soluble solvent for aromatics in countercurrent flow, separating an aliphatic fraction from the resulting mixture by distillation while retaining the aromatic-enriched solvent and removing the aliphatic fraction in the aliphatic product stream, stripping the aromatics from the aromatic-enriched solvent and removing the aromatics in the aromatic product stream, recycling the aromatic-depleted solvent in a solvent cycle for the extraction of further aromatics from the feedstock stream, whereby compounds with a lower boiling point compared to the solvent accumulate as impurities in the solvent cycle, and purifying at least a partial stream of the aromatic-depleted solvent to remove the impurities.

[0015] According to the invention, the partial stream is subjected to a thermal separation process for purification, in which the impurities are at least partially removed in a head product and the remaining purified solvent is returned to the solvent cycle.

[0016] The partial stream according to the invention can comprise any proportion of the total solvent circuit. In particular, the partial stream can also be the entire solvent stream in the solvent circuit. Preferably, a partial stream in the purification stage corresponds to a proportion of 1 wt% to 20 wt% of the total solvent stream in the solvent circuit.

[0017] The thermal separation process separates the more volatile impurities from the solvent and removes them as a separate overhead product.

[0018] The separation point of the thermal separation process is preferably selected such that the purified solvent obtained as bottoms product contains no more than 5 wt%, and particularly preferably no more than 1 wt%, of low-boiling impurities. To achieve a sufficient purity of the purified solvent in this sense, co-boilers with the solvent and a portion of the solvent itself are preferably also removed in the overhead product during the thermal separation process.

[0019] For the purposes of this disclosure, a component is considered to have a low boiling point relative to the solvent if its boiling point (at the operating pressure of the thermal separation process) is at least 10 K lower than the boiling point of the solvent, or if the component forms a low-boiling azeotrope with the solvent in this sense. Components or azeotropes whose boiling point lies within ±10 K of the boiling point of the solvent are considered to have a boiling point relative to the solvent. For the purposes of this disclosure, the boiling point of a substance, without further specification of the ambient conditions, is understood to be the standard boiling point of the substance. If a mixture of several components is used as the solvent, the term "boiling point of the solvent" for the purposes of this disclosure refers to the boiling point of the most low-boiling component of the solvent mixture.

[0020] Applying a thermal separation process to the partial stream of the solvent cycle has the advantage that it eliminates the need to add an additional extraction solvent—such as water or an aliphatic extraction solvent—to the partial stream, which would then have to be separated from the solvent. According to the invention, no additives need to be introduced into the solvent cycle for the actual purification of the solvent. This is particularly advantageous in processes for the direct, anhydrous synthesis of aromatics, where the water content in the solvent cycle must be kept sufficiently low. By eliminating the need for an additional extraction solvent, the process according to the invention can also be easily integrated as a retrofit solution into existing systems for the extractive distillation of aromatics.

[0021] According to the invention, in addition to purifying the solvent, solvent is recovered from the overhead product. The following further steps are provided for this purpose: The overhead product is mixed with water to form an aqueous, solvent-containing phase and a hydrophobic phase, the aqueous phase is separated from the hydrophobic phase, and the aqueous phase is distilled to remove the water, with the bottom product of the distillation being returned to the solvent cycle.

[0022] Recovering the solvent from the overhead product leads to lower solvent consumption and facilitates further processing or disposal of the overhead product. Solvent recovery from the overhead product thus represents a particularly cost-effective and environmentally friendly aspect of the process according to the invention.

[0023] If, for solvent recovery, only the overhead product of the thermal separation process, and not the entire partial stream of the solvent cycle requiring purification, is treated with water, the amount of water required is significantly reduced, since the overhead product has a solvent content that is orders of magnitude lower. The energy required for distilling the aqueous phase is therefore considerably reduced compared to known solvent purification processes based solely on water washing. Preferably, water is added to the overhead product in a mass ratio ranging from 10:1 to 1:1.

[0024] Preferably, the distilled water is recycled in a water cycle and added back to the liquid-liquid extract. Reusing the water in a water cycle reduces the amount of wastewater requiring treatment and ensures resource-efficient operation.

[0025] Furthermore, it is preferred that the partial stream is cooled in a heat exchanger before the thermal separation process is carried out, and that the distillation is performed using the heat energy generated in the heat exchanger. A temperature of the partial stream in the range of 140°C to 200°C is advantageous for carrying out the thermal separation process. Thermal separation at a lower temperature compared to the stripping temperature (approx. 160°C–240°C) reduces the thermal stress on the solvent and simultaneously allows the use of heat energy for solvent recovery. The amount of energy generated during the cooling of the partial stream in the heat exchanger is generally more than sufficient for carrying out the distillation. Alternatively or additionally, heat energy can be taken from the main stream of the solvent cycle to operate the distillation column.

[0026] Preferably, the distillation is carried out with a top pressure of less than 1 bar (a), particularly preferably less than 500 mbar (a), and especially preferably less than 200 mbar (a). When the distillation is carried out under vacuum, the boiling point of water is lowered, thus reducing the temperature in the distillation sump. This reduces the amount of energy required for the distillation and avoids undesirable side reactions in the distillation sump. Preferably, the vacuum is adjusted so that the sump temperature is in a range up to a maximum of 230°C, particularly preferably between 150°C and 200°C.

[0027] After the overhead product is mixed with water and the aqueous phase is separated, a hydrophobic phase remains, which contains a predominant proportion of the impurities to be removed. In preferred embodiments of the process, a partial stream of the hydrophobic phase is removed, and another partial stream of the hydrophobic phase is used as reflux in the thermal separation process. A reflux ratio between the reflux to be returned and the reflux to be removed in the range of 4:1 to 8:1 is particularly preferred.

[0028] Both the thermal separation process and the distillative separation of water and solvent can be operated continuously or in batches.

[0029] The process according to the invention is particularly advantageous for the direct production of anhydrous aromatics. Anhydrous, as used in this disclosure, means that the water content of the aromatic fraction after extractive distillation directly meets the requirements for the pure product, and no subsequent drying steps are necessary. In particular, it is then unnecessary to separate a separate aqueous phase from the condensed aromatic fraction. In such processes, the solvent in the solvent cycle (bottom of the stripper column) typically has a water content of less than 1 wt%, preferably less than 0.5 wt%, and most preferably less than 1000 ppm. Furthermore, in this variant, no steam is added to the stripper column, as this would lead to an increased water content in the aromatic fraction.

[0030] Suitable solvents for extractive distillation include sulfolane, methylsulfolanes, N-methylpyrrolidone, N-formylmorpholine, ethylene glycol, and mixtures thereof, as well as mixtures of these solvents with water. The solvent preferably contains N-formylmorpholine, which is particularly suitable for the direct synthesis of anhydrous aromatics.

[0031] The problem is solved by means of a device for separating a hydrocarbon-containing feedstock stream into at least one aliphatic product stream and one aromatic product stream by extractive distillation, comprising: A device for contacting the feedstock stream with a water-soluble solvent for aromatics in countercurrent flow; a device for the distillative separation of an aliphatic fraction from the resulting mixture, retaining the aromatic-enriched solvent and providing a discharge for the aliphatic fraction as an aliphatic product stream; a device for stripping the aromatics from the aromatic-enriched solvent and providing a discharge for the aromatics as an aromatic product stream; a return of the aromatic-depleted solvent in a solvent circuit to the device for contacting the feedstock stream with the solvent; and a purification device for the solvent, which is arranged in the solvent circuit and, during operation, is at least temporarily traversed by at least a partial stream of the aromatic-depleted solvent.for the removal of impurities, including compounds with a lower boiling point than the solvent, from the partial stream.

[0032] According to the invention, the purification device comprises a thermal separation unit with a discharge for the thermal separation and removal of impurities in a head product of the thermal separation unit. Furthermore, the purification device includes a return path for the remaining purified solvent to the solvent circuit.

[0033] According to the invention, the discharge of the purification device for the overhead product is connected to a solvent recovery unit. The solvent recovery unit includes at least one mixing device for adding water to form an aqueous phase and a hydrophobic phase, and at least one separating device for separating the aqueous phase from the hydrophobic phase. The solvent recovery unit also has a discharge for the aqueous phase, which is connected to a distillation column for distilling off the water. The distillation column has a discharge for a bottoms product of the distillation column, through which the bottoms product can be recycled to the solvent cycle.

[0034] Preferably, the distillation column has a top discharge for the distilled water, which is connected to the mixing device for the addition of water, forming a water circuit.

[0035] Furthermore, preferably at least one heat exchanger is arranged upstream of the purification device for cooling the partial stream, which is connected to the distillation column for transferring the heat energy generated in the heat exchanger.

[0036] In preferred embodiments, the distillation column is connected to a vacuum generation device which is configured to generate a negative pressure of less than 1 bar (a), preferably less than 500 mbar (a) and particularly preferably less than 200 mbar (a) in a head region of the distillation column.

[0037] In further preferred embodiments, a branch is provided for the discharge of a partial flow of the hydrophobic phase, and a further partial flow of the hydrophobic phase can be fed to the purification device as a return flow via a feeder.

[0038] Furthermore, a second heat exchanger for cooling the overhead product is preferably arranged between the thermal separation device and the solvent recovery unit. Particularly preferably, the overhead product is generated at a temperature greater than 120°C, cooled in a heat exchanger, and enters the solvent recovery unit at a temperature in the range of 0°C to 60°C. Recovery at a lower temperature compared to the temperature of the thermal separation is preferred because this reduces the solubility of impurities in the solvent. Temperatures that are too low must be avoided to prevent the solvent from solidifying.

[0039] Further advantageous embodiments can be found in the following description and the dependent claims.

[0040] The invention is explained in more detail below with reference to the exemplary embodiments shown in the accompanying figures. Brief description of the drawings

[0041] Fig. 1 schematically shows a flow diagram of the inventive method according to a first embodiment, in which a partial stream of the solvent circuit is purified by a thermal separation process. Fig. 2 schematically shows a first embodiment of the inventive device, which is suitable for separating the solvent in Fig. 1 To carry out the methods shown, Fig. 3 schematically shows one relating to the section X in Fig. 2 An alternative apparatus setup for carrying out extractive distillation in a single column for extractive distillation is shown schematically in Fig. 4, which corresponds to section X in the figure. Fig. 2alternative apparatus setup for carrying out extractive distillation in three separate columns. Embodiments of the invention

[0042] In the various figures, identical parts are always marked with the same reference symbols and are therefore usually only named or mentioned once.

[0043] In Fig. 1 Figure 100 shows a flowchart of the process according to a first embodiment of the invention. In process 100, a hydrocarbon-containing feedstock stream 1 is separated by extractive distillation into at least one aliphatic product stream 2 and one aromatic product stream 3.

[0044] Process 100 comprises the following steps: In step 110, the feedstock stream 1 is brought into countercurrent contact with a water-soluble solvent 4 for aromatics, resulting in a mixture 5. Subsequently, in step 120, an aliphatic fraction is separated from the resulting mixture 5 by distillation, leaving behind the aromatic-enriched solvent 6, and the aliphatic fraction is removed in the aliphatic product stream 2. Following this, in step 130, the aromatics are stripped from the aromatic-enriched solvent 6 and removed in the aromatic product stream 3. Stripping is preferably carried out at a higher temperature and / or pressure compared to the distillation-based separation of the aliphatic fraction. In step 140, the aromatic-depleted solvent 4 is recycled in a solvent cycle 7 for the extraction of further aromatics from the feedstock stream 1.

[0045] During process 100, compounds with a lower boiling point than solvent 4 accumulate as impurities in the solvent circuit 7. These impurities are also so high-boiling that they cannot leave the solvent circuit 7 via distillation 120 or aromatic stripping 130. Therefore, step 150 involves purifying at least a partial stream 8 of the aromatic-depleted solvent 4 to remove the impurities. For purification 150, the partial stream 8 is subjected to a thermal separation process in which the impurities are at least partially removed in an overhead product 11, and the remaining purified solvent 10 is recycled back into the solvent circuit 7.

[0046] It can be provided that the purification of solvent 4 is only carried out temporarily during the execution of the process. For this purpose, the partial stream 8 can, for example, be controlled via a control valve. The volumetric flow rate of the partial stream 8 is preferably regulated such that the impurities in the solvent are adjusted to a target value or target range. The target value or target range of the impurities in the solvent is preferably in the range of 0.1–20 wt%, more preferably 0.1–10 wt%, and particularly preferably 1–5 wt%. In this way, the consumption of resources required to ensure excellent selectivity and capacity of the solvent can be reduced.

[0047] Distillation or rectification is the preferred thermal separation method. The thermal separation process can be single- or multi-stage. For example, single- or multi-stage distillation or single- or multi-stage flash distillation are conceivable.

[0048] In the embodiment according to Fig. 1Furthermore, the recovery of solvent from the overhead product 11 of the thermal separation process is provided. For this purpose, the following additional steps are carried out: In step 160, the overhead product 11 of the thermal separation process is mixed with water 14, forming an aqueous, solvent-containing phase 12 and a hydrophobic phase 13. Preferably, water is added to the overhead product in a mass ratio in the range of 30:1 to 1:3, particularly 20:1 to 1:2, and most preferably 10:1 to 1:1. Subsequently, in step 170, the aqueous phase 12 is separated from the hydrophobic phase 13. Finally, in step 180, the aqueous phase 12 is distilled to remove the water, with the bottom product 15 of the distillation 180 being returned to the solvent cycle 7.

[0049] Distillation 180 is preferably carried out with a top pressure of less than 1 bar (a), more preferably less than 500 mbar (a), and particularly preferably less than 200 mbar (a). The bottom temperatures of distillation 180 are preferably set in the range of less than 230°C, more preferably in the range of 150–200°C.

[0050] It is also preferably provided that the distilled water 14 is recycled in a water circuit 16 and added again to the overhead product 11 of the thermal separation process.

[0051] A partial stream 18 of the hydrophobic phase 13 can be discharged. For example, the partial stream 18 can be, as in Fig. 1As shown, it is discharged as a separate stream to the plant boundary. Provided the specifications of the aliphatic product stream 2 permit, this partial stream 18 can also be mixed with the aliphatic product stream 2 (not shown). A further partial stream 9 of the hydrophobic phase is preferably used as a return effluent in the thermal separation process.

[0052] Preferably, to save energy, the partial stream 8 is cooled in a heat exchanger before the thermal separation process is carried out, and the distillation is performed using the heat energy generated in the heat exchanger. Furthermore, it is preferable to cool the overhead product 11 before recovering the solvent from it.

[0053] The solvent 4 in the solvent cycle 7 preferably has a water content of less than 3 wt%, more preferably less than 1 wt% and particularly preferably less than 1000 ppm.

[0054] In preferred process variants, the solvent 4, 6 contains N-formylmorpholine. Particularly preferably, the solvent 4 contains a mass fraction of at least 50% N-formylmorpholine.

[0055] In Fig. 2Figure 1 shows an embodiment of the device 200 according to the invention for separating a hydrocarbon-containing feedstock stream 1 by extractive distillation into at least one aliphatic product stream 2 and one aromatic product stream 3. The device comprises a device 210 for contacting the feedstock stream with a water-soluble solvent 4 for aromatics in countercurrent flow, a device for distillatively separating an aliphatic fraction 220 from the resulting mixture 5 while retaining the aromatics-enriched solvent 6 with a discharge 221 for the aliphatic fraction as aliphatic product stream 2, and a device 230 for stripping the aromatics from the aromatics-enriched solvent 6 with a discharge for the aromatics as aromatic product stream.

[0056] The device further comprises a return 240 for the aromatic-depleted solvent 4 in a solvent circuit 7 to the device 210 for contacting the feedstock stream 1 with solvent 4 in countercurrent flow, as well as a purification device 250 for the solvent 4 which is arranged in the solvent circuit 7 and is traversed during operation by at least a partial stream 8 of the aromatic-depleted solvent 4, for removing impurities comprising compounds with a lower boiling point compared to the solvent from the partial stream 8.

[0057] The purification device 250 comprises a thermal separation device 252 with a discharge 255 for the thermal separation and removal of the impurities in a head product 11, and a return 254 for the remaining purified solvent 10 to the solvent circuit 7. The purified solvent 10 can be supplied to the solvent circuit 7, for example, via a pump 223.

[0058] The thermal separation device 252 can be used as described in Fig. 2 This can be represented, for example, by a distillation column, which may preferably be equipped with an evaporator 253 in the bottom section. Alternatively or additionally, multi-stage distillations and / or a single- or multi-stage flash distillation unit can also be used as a thermal separation device 252.

[0059] The purification device 250 further comprises a discharge 255 for the overhead product 11 of the thermal separation process, which is connected to a solvent recovery device 260. The solvent recovery device 260 includes at least one mixing device 261 for the addition of water 14 to form an aqueous phase 12 and a hydrophobic phase 13, and at least one separating device 262 for separating the aqueous phase 12 from the hydrophobic phase 13.

[0060] The solvent recovery unit 260 can be configured as a single-stage or multi-stage unit. The mixing device 261 can be configured together with the separating device 262 in a single vessel, for example, a mixer-settler unit or as a single-stage or multi-stage extraction column. Alternatively, the mixing device 261 can simply consist of a pipe branch through which water can be fed into the stream of the overhead product 11.

[0061] Preferably, the overhead product 11 and water 14 are passed countercurrently in the solvent recovery unit 260. Particularly preferably, in multi-stage recovery units 260, the addition of water 14 is achieved by adding the aqueous phase 12 of the subsequent stage. In this way, the solvent concentration in the aqueous phase increases across the stages in the opposite direction to the concentration of the solvent in the hydrophobic phase 13. This reduces the need for fresh or treated water.

[0062] The solvent recovery unit 260 has a discharge 263 for the aqueous phase 12, which is connected to a distillation column 270 for the distillation of the water 14. The distillation column 270 has a discharge 271 for a bottoms product 15 of the distillation column 270, via which the bottoms product 15 can be returned to the solvent cycle 7.

[0063] The distillation column 270 also has a head discharge 272 for the distilled water 14, which is connected to the mixing device 261 for the addition of water 14, forming a water circuit 16.

[0064] The distillation column 270 is preferably connected to a vacuum generating device 274, which is configured to generate a negative pressure of less than 1 bar (a), preferably less than 500 mbar (a) and particularly preferably less than 200 mbar (a) in a head region 273 of the distillation column 270.

[0065] Preferably, heat integration of the distillation column 270 is provided. For this purpose, at least one heat exchanger 280 for cooling the partial stream 8 can be arranged upstream of the purification device 250, which is connected to the distillation column 270 for transferring the heat energy 285 generated in the heat exchanger 280. Particularly preferably, the entire energy requirement of the distillation column 270 is covered by the transferred heat energy 285.

[0066] Before entering the solvent recovery unit 260, the overhead product 11 can be cooled in a second heat exchanger 281. Preferably, the cooling in the heat exchanger 281 takes place to a temperature range of 0 °C to 60 °C. The additional heat energy generated in this heat exchanger 281 can, for example, be used to heat the aqueous phase 12 before it enters the distillation column 270.

[0067] After exiting the solvent recovery unit 260, the hydrophobic phase 13 can have a branch 290 for the discharge of a partial stream 18 of the hydrophobic phase 13. A further partial stream 9 of the hydrophobic phase 13 can be fed to the purification unit 250 via a feeder 251 as a return flow. The partial stream 18 can be discharged as a separate stream to the system boundary or, for example, mixed with the aliphatic product stream 2.

[0068] At the in Fig. 2 In the illustrated embodiment, the main process of extractive distillation is shown in section X. The countercurrent contact device 210 and the distillative separation device 220 are combined in a single extractive distillation column 225, and a separate stripper column 226 is provided for the stripping device 230.

[0069] Fig. 3shows an alternative apparatus setup for the section X in the device according to Fig. 2 . In the Fig. 3 The illustrated setup combines the countercurrent contact device 210, the distillative separation device 220, and the stripping device 230 in a single column for extractive distillation 229 with integrated stripping. Advantages of this setup include, for example, reduced equipment complexity and a smaller footprint for the apparatus 200.

[0070] Fig. 4 shows another alternative apparatus setup for the section X in the device according to Fig. 2 . In the Fig. 4The illustrated setup includes a column 227 for extractive distillation for the countercurrent contact unit 210 and a separate column 228 for raffinate purification for the distillative separation unit 220. The stripping unit 230 is located in a separate stripper column 226. The advantages of this setup lie in the lower height of the extractive distillation column 227. Therefore, this setup can be preferred when practical or regulatory restrictions on the plant's height apply. Reference symbol list

[0071] 1 Feed stream 2 Aliphatic product stream 3 Aromatic product stream 4 Solvent for aromatics 5 Mixture of feed and solvent 6 Solvent enriched with aromatics 7 Solvent cycle 8 Partial stream of the solvent cycle 9 Partial stream of the hydrophobic phase 10 Purified solvent 11 Overhead product of the thermal separation process 12 Aqueous phase 13 Hydrophobic phase 14 Water 15 Bottom product of distillation 16 Water cycle 18 Partial stream of the hydrophobic phase 100 Process for separating a hydrocarbon-containing feedstock stream 110 Contacting the feedstock stream with the solvent in countercurrent flow 120 Distillative separation of an aliphatic fraction 130 Stripping the aromatics from the solvent 140 Recycling the solvent 150 Purifying the partial stream of the aromatic-depleted solvent 160 Adding water 170 Separating the aqueous phase from the hydrophobic phase 180 Distilling the aqueous phase 200 Device for separating a hydrocarbon-containing feed stream 210 Countercurrent contact device 220 Device for distillative separation 221 Discharge 222 Branch 223 Pump 225, 227 Extractive distillation column 226 Stripper column 228 Refined product purification column 229 Extractive distillation column with integrated stripping 230 Stripping device 240 Solvent recirculation 250 Purification device 251 Purification device feed 252 Thermal separation device 253 Evaporator 254 Purified solvent recirculation 255 Overhead product discharge 260 Solvent recovery device 261 Mixing device 262 Separation device 263 Aqueous phase discharge 270 Distillation column 271 Discharge for the bottom product 272 Head discharge 273 Head area 274 Vacuum generating unit 280 to 282 Heat exchanger 285 Thermal energy 290 Branch

Claims

1. Process for separating a hydrocarbon-containing feed stream (1) by extractive distillation into at least one aliphatic product stream (2) and one aromatic product stream (3), comprising the following steps: • Bringing the feed stream (1) into contact (110) with a water-soluble solvent (4) for aromatics in countercurrent, • Distillative separation (120) of an aliphatic fraction from the mixture obtained (5), leaving the solvent enriched with aromatics (6), and removal of the aliphatic fraction in the aliphatic product stream (2) • Stripping the aromatics (130) from the solvent enriched with aromatics (6) and discharging the aromatics in the aromatics product stream (3) • Returning (140) the solvent (4) depleted of aromatics in a solvent circuit (7) for the extraction of further aromatics from the feed stream (1), whereby compounds with a lower boiling point than the solvent (4) accumulate as impurities in the solvent circuit (7), and • Purifying (150) at least one partial stream (8) of the solvent (4) depleted of aromatics to remove the impurities, characterized in that the partial stream (8) is subjected to a thermal separation process for purification (150), in which the impurities are at least partially removed in a head product (11) and the remaining purified solvent (10) is returned to the solvent circuit (7), wherein the following further steps are carried out to recover solvent from the head product (11) of the thermal separation process: • mixing (160) the head product (11) of the thermal separation process with water (14) to form an aqueous, solvent-containing phase (12) and a hydrophobic phase (13), • separating (170) the aqueous phase (12) from the hydrophobic phase (13), and • distilling (180) the aqueous phase (12) to distill off water, wherein the bottom product (15) of the distillation (180) is returned to the solvent circuit (7).

2. Method according to claim 1, characterized in that the distilled water (14) is returned in a water circuit (16) and added again to the head product (11) of the thermal separation process.

3. Method according to claim 1 or 2, characterized in that the partial stream (8) is cooled in a heat exchanger (280) before the thermal separation process is carried out, and the distillation (180) is carried out using the heat energy (285) generated in the heat exchanger (280).

4. Method according to one of claims 1 to 3, characterized in that the distillation (180) is carried out at a head pressure of less than 1 bar (a), preferably less than 500 mbar (a) and particularly preferably less than 200 mbar (a).

5. Method according to one of claims 1 to 4, characterized in that a partial stream (18) of the hydrophobic phase (13) is discharged and a further partial stream (9) of the hydrophobic phase (13) is used as a return flow in the thermal separation process.

6. Method according to one of claims 1 to 5, characterized in that the solvent (4) in the solvent circuit (7) has a water content of less than 3% by mass, preferably less than 1% by mass, and particularly preferably less than 1000 ppm.

7. Method according to one of claims 1 to 6, characterized in that the solvent (4, 6) contains N-formylmorpholine.

8. Device for separating a hydrocarbon-containing feed stream (1) by extractive distillation into at least one aliphatic product stream (2) and one aromatic product stream (3), comprising: • a device for bringing the feed stream into countercurrent contact (210) with a water-soluble solvent (4) for aromatics, • a device for distillatively separating an aliphatic fraction (220) from the mixture obtained (5), leaving the solvent enriched with aromatics (6) with a discharge (221) for the aliphatic fraction as an aliphatic product stream (2), • a device for stripping (230) the aromatics from the solvent (6) enriched with aromatics, with a discharge for the aromatics as an aromatics product stream (3), • a recirculation line (240) for the solvent depleted of aromatics (4) in a solvent circuit (7) to the device for bringing the feed stream (1) into countercurrent contact (210) with solvent (4), and • a purification device (250) for the solvent (4), which is arranged in the solvent circuit (7) and, during operation, is at least temporarily traversed by at least a partial stream (8) of the solvent (4) depleted of aromatics, for removing impurities comprising compounds with a lower boiling point than the solvent (4) from the partial stream (8), wherein the purification device (250) comprises a thermal separation device (252) with a discharge (255) for the thermal separation and discharge of the impurities in a head product (11), and the purification device (250) has a return line (254) for the remaining purified solvent (10) into the solvent circuit (7), characterized in that the discharge line (255) for the head product (11) of the thermal separation device (252) is connected to a solvent recovery device (260) in which at least one mixing device (261) for the addition of water (14) to form an aqueous phase (12) and a hydrophobic phase (13) and at least one separating device (262) for separating the aqueous phase (12) from the hydrophobic phase (13) are arranged, wherein the solvent recovery device (260) has a discharge (263) for the aqueous phase (12), which is connected to a distillation column (270) for distilling off the water (14), and the distillation column (270) has an outlet (271) for a bottom product (15) of the distillation column (270), via which the bottom product (15) can be returned to the solvent circuit (7).

9. Device according to claim 8, characterized in that the distillation column (270) has a head outlet (272) for the distilled water (14), which is connected to the mixing device (261) for adding water (14), forming a water circuit (16).

10. Device according to claim 8 or 9, characterized in that upstream of the purification device (250) at least one first heat exchanger (280) is arranged for cooling the partial stream (8), which is connected to the distillation column (270) for transferring the heat energy (285) generated in the first heat exchanger (280).

11. Device according to one of claims 8 to 10, characterized in that the distillation column (270) is connected to a vacuum generating device (274) which is designed to generate a negative pressure of less than 1 bar (a), preferably less than 500 mbar (a) and particularly preferably less than 200 mbar (a) in a head region (273) of the distillation column (270).

12. Device according to one of claims 8 to 11, characterized in that a branch (290) is provided for discharging a partial stream (18) of the hydrophobic phase (13), and a further partial stream (9) of the hydrophobic phase (13) can be fed to the purification device (250) via a feed (251) as a return flow.

13. Device according to any one of claims 8 to 12, characterized in that a second heat exchanger (281) for cooling the head product (11) is arranged between the thermal separation device (252) and the solvent recovery device (260).