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 feedstock stream is brought into countercurrent contact with a selective solvent for aromatics. The solvent affects the volatility of the different components of the feedstock 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 separated from the aliphatic components of the feedstock mixture by extractive distillation, with the latter being collected as the overhead product. In a second step, the aromatics are stripped from the solvent as the overhead product. Subsequently, the aromatic product stream can be further separated into individual aromatic fractions.The solvent, now depleted of aromatics, is recycled and reused in the extractive distillation process. 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 higher boiling points (relative to the solvent) from the solvent circuit. Impurities that are co-boilers (e.g., pyrolytic impurities) are not suitable for this purpose. co-boiler) Those substances that 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] US 3,476,680 A describes an extraction process for separating hydrocarbon mixtures into a raffinate product with reduced aromaticity and an extract product with increased aromaticity by contact with the solvent N-methyl-2-pyrrolidone in an extractor. The extract phase withdrawn from the extractor is subjected to a liquid-liquid countercurrent washing tower in contact with water to obtain a solvent-free extract oil product. Water containing dissolved NMP solvent and oil is transferred to another extractor, where it is subjected to countercurrent contact with light hydrocarbons to extract the oil. Water and NMP solvent are separated in a distillation tower and recycled for reuse.

[0010] WO 99 / 11740 A1 describes a separation process for aromatics using a hybrid extraction / extractive distillation system. A portion of a mixed hydrocarbon feedstock is fed to a separate extractive distillation column (EDC), which operates in parallel with the main extractor, extractive stripper, and water washing stages of the process. The use of an EDC enables the recovery and purification of aromatic compounds in a single operation. In the described process, steam is used as the stripping medium, and water is optionally used as a secondary solvent.

[0011] A method and an apparatus according to the preambles of claims 1 and 8 are known from EP 3 747 854 A1. EP 3 747 854 A1 describes a method for separating aromatic hydrocarbons by extractive distillation. In the described method, the raffinate from the extractive distillation still contains 5-40 wt% benzene and is fed to the bottom of an extraction column, to which solvent is added as the extraction agent in the upper part. After liquid-liquid extraction, a stream of raffinate free of aromatic hydrocarbons is drawn off at the top of the extraction column, and the solvent loaded with benzene is fed into the upper middle section of the extractive distillation column. The raffinate stream is washed with water in a washing column, the wash water being used as a stripping medium for separating the aromatic hydrocarbons from the solvent after removal of traces of non-aromatic hydrocarbons. 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 aliphatic compounds and / or compounds with aliphatic residues 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, a liquid-liquid extraction is carried out between the partial stream and an extraction agent for aliphatics for purification, wherein the raffinate of the liquid-liquid extraction is returned to the solvent circuit.

[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] In liquid-liquid extraction with an aliphatic extraction solvent, the aliphatic impurities are transferred from the solvent to the solvent. The aliphatic extraction solvent can also be suitable for extracting other impurities, such as naphthalene. The liquid-liquid extract therefore comprises the aliphatic impurities in addition to the solvent and is saturated with solvent. The raffinate of the liquid-liquid extraction is a purified solvent stream saturated with the extraction solvent and can be reused for extractive distillation. The mass ratio of aliphatic extraction solvent to solvent is preferably 1 / 20 to 10 / 1, more preferably 1 / 10 to 5 / 1, and particularly preferably 1 / 5 to 2 / 1.

[0018] By using liquid-liquid extraction to remove the aliphatic impurities with an aliphatic extraction solvent, the impurities are removed from the solvent as a solvate. In contrast, in known purification processes involving the addition of water, the solvent itself passes into the water as a solvate, while the impurities form an aliphatic, water-insoluble phase. According to the invention, the solvent can thus be purified without the addition of water to the partial stream to be purified. 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, as subsequent energy-intensive water removal can be avoided.

[0019] Preferably, an extraction solvent for aliphatics is used, which is carried out of the solvent cycle via the aliphatic fraction during extractive distillation. Examples of such extraction solvents include alkanes, alkane-aliphatic mixtures, or oxygenates. MTBE or ETBE, Consideration is given to the extraction solvent. Preferably, the extraction solvent for aliphatics consists of C5-C9 hydrocarbons, primarily paraffins or their isomers. The addition of aromatics and cyclic non-aromatics (naphthenes) to the extraction solvent is also conceivable. In particular, the extraction solvent can be obtained by diverting a second partial stream from the aliphatic product stream.

[0020] Alternatively, the use of an extraction agent for aliphatics is conceivable, the enrichment of which in the solvent cycle up to the saturation limit only impairs the selectivity and capacity of the solvent to a tolerable extent.

[0021] According to the invention, the following further steps are carried out to recover solvent from the extract of the liquid-liquid extraction: Mixing the liquid-liquid extract with water to form an aqueous, solvent-containing phase and a hydrophobic phase, separating the aqueous phase from the hydrophobic phase and distilling the aqueous phase to remove the water, with the bottom product of the distillation being returned to the solvent cycle. The mass ratio of extract to water is preferably 1 / 20 to 40 / 1, more preferably 1 / 10 to 30 / 1, and particularly preferably 1 / 5 to 20 / 1. The addition of water and the separation of the aqueous phase are preferably carried out at a temperature in the range of 0°C to 80°C and a pressure of 0 bar to 40 bar overpressure.

[0022] Recovering the solvent from the solvent-saturated extract of the liquid-liquid extraction process leads to lower solvent consumption and facilitates further processing or disposal of the extract. Thus, recovering the solvent from the extract represents a particularly cost-effective and environmentally friendly variant of the process according to the invention.

[0023] If, for solvent recovery, only the extract from the liquid-liquid extraction, and not the entire partial stream to be purified, is treated with water, the amount of water required is significantly reduced, since the extract 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.

[0024] The distilled water is recycled in a water cycle and added back to the liquid-liquid extraction extract. This reuse of the water in a closed loop 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 prior to liquid-liquid extraction, and that the distillation is carried out using the heat energy generated in the heat exchanger. For the liquid-liquid extraction, a temperature of the partial stream in the range of 0°C to 80°C is advantageous, and a pressure of 0 to 40 bar gauge is preferred. Extraction at a lower temperature compared to the stripping temperature (approx. 160°C–240°C) is preferred, as this reduces the solubility of the impurities and the extraction solvent for aliphatics in the solvent. Temperatures that are too low should be avoided, particularly to prevent the solvent from solidifying. 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.Excess heat energy can be used to heat the solvent being returned to the solvent cycle. Alternatively or additionally, heat energy can be extracted from the main flow 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 100 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 liquid-liquid extract is mixed with water and the aqueous phase is separated, a hydrophobic phase remains, containing the extraction solvent and impurities. In preferred embodiments of the process, the impurities are separated from the hydrophobic phase. Separating the impurities is desirable if they are detrimental to subsequent processes or product purity.

[0028] Separating the impurities is particularly advantageous when the hydrophobic phase is recycled as an extraction solvent for aliphatics in a closed-loop extraction process. However, depending on the product requirements, separating the impurities may also be desirable when the hydrophobic phase is added to the aliphatic product stream.

[0029] Both liquid-liquid extraction for the extraction of aliphatics from the solvent and distillative separation of water and solvent can be carried out continuously or in batches.

[0030] 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.

[0031] 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.

[0032] 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 comprising aliphatic compounds and / or compounds with aliphatic residues from the partial stream.

[0033] According to the invention, the purification device includes a feed for an aliphatic extraction agent and at least one mixing chamber and a separation chamber for liquid-liquid extraction between the partial stream and an aliphatic extraction agent. Furthermore, the purification device has a return path for a raffinate from the liquid-liquid extraction into the solvent circuit.

[0034] The purification device has a discharge for an extract from the liquid-liquid extraction, which 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 further includes 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 from the distillation column, through which the bottoms product can be recycled back into the solvent cycle.

[0035] The distillation column also has a top discharge for the distilled water, which is connected to the mixing device for the addition of water, forming a water cycle.

[0036] 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.

[0037] 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 100 mbar (a) in a head region of the distillation column.

[0038] In further preferred embodiments, a separation device is provided for separating the impurities from the hydrophobic phase. The separation device can, for example, be a further distillation device, such as a distillation column. Preferably, the separation device is connected to the feed of the purification device, forming an extraction agent circuit.

[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 process according to the invention according to a first embodiment, in which a second partial stream is diverted from the aliphatic product stream as an extraction agent for aliphatics and the hydrophobic phase is fed to the aliphatic product stream. Fig. 2 schematically shows a flow diagram of the process according to the invention according to a second embodiment, in which the impurities are separated from the extraction agent for aliphatics and the extraction agent is circulated in an extraction agent cycle. Fig. 3 schematically shows a first embodiment of the device according to the invention, which is suitable for extracting the in Fig. 1 To carry out the methods shown, Fig. 4 schematically shows a second embodiment of the device according to the invention, which is suitable for carrying out the in Fig. 2 To carry out the method shown, Fig. 5 schematically shows a method relating to the section X in Fig. 3 and 4An alternative apparatus setup for carrying out extractive distillation in a single column for extractive distillation is shown schematically in Fig. 6, which corresponds to section X in the figure. Fig. 3 and 4 alternative 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 130 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 lower pressure compared to the distillation 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, aliphatic compounds and / or compounds with aliphatic residues accumulate as impurities in the solvent circuit 7. Therefore, in step 150, purification of at least a partial stream 8 of the aromatic-depleted solvent 4 is provided to remove the impurities. For purification 150, a liquid-liquid extraction is carried out between the partial stream 8 and an aliphatic extraction agent 9, with the raffinate 10 of the liquid-liquid extraction being recycled back into the solvent circuit 7. Preferably, the partial stream 8 and the aliphatic extraction agent 9 are fed countercurrently to each other for the liquid-liquid extraction.

[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] In the embodiment according to Fig. 1Furthermore, the recovery of solvent from the extract 11 of the liquid-liquid extraction is provided. For this purpose, the following additional steps are carried out: In step 160, the extract 11 of the liquid-liquid extraction is mixed with water 14, forming an aqueous, solvent-containing phase 12 and a hydrophobic phase 13. 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, and the bottoms product 15 of distillation 180 is returned to the solvent cycle 7.

[0048] 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 100 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.

[0049] Furthermore, it is provided that the distilled water 14 is recycled in a water cycle 16 and added again to the extract 11 of the liquid-liquid extraction. The hydrophobic phase 13 can be, as in Fig. 1 The hydrophobic phase 13 is shown to be fed into the aliphatic product stream 2. In some embodiments, the impurities can be separated from the hydrophobic phase before being fed into the aliphatic product stream 2. Alternatively, the hydrophobic phase 13 can also be discharged as a separate stream to the system boundary (not shown).

[0050] Preferably, to save energy, the partial stream 8 can be cooled in a heat exchanger before the liquid-liquid extraction and the distillation can be carried out using the heat energy generated in the heat exchanger.

[0051] 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.

[0052] 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.

[0053] In Fig. 2 A flowchart of the inventive method according to a second embodiment is shown. The flowchart differs from Fig. 1only by the passage of the extraction agent 9. In the second embodiment, the hydrophobic phase 13 is recycled as extraction agent 9 for aliphatics in an extraction agent circuit 17 into the liquid-liquid extraction. The extraction agent is thus reused. To enable continuous reuse of the extraction agent without replacement, the second embodiment further provides for the separation 190 of the impurities from the hydrophobic phase 13 before recycling it into the liquid-liquid extraction. The separated impurities 18 can be removed and disposed of separately or added to a stream whose specifications are not violated by the added impurities.

[0054] The extraction solvent 9 can be obtained, for example, by being drawn off from the aliphatic product stream 2. Alternatively, other aliphatics, such as alkanes, but also oxygenates like MTBE and ETBE, can be used as the extraction solvent 9, which are supplied separately from the aliphatic product stream 2. Since a certain portion of the extraction solvent is always discharged from the extraction solvent circuit 17 via the raffinate 12 and the bottoms product 15, the extraction solvent 9 is replenished from time to time.

[0055] Furthermore, the above statements regarding the one in Fig. 1 shown embodiment for Fig. 2 accordingly.

[0056] In Fig. 3Figure 1 shows a first embodiment of the device 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 aromatic-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 aromatic-enriched solvent 6 with a discharge for the aromatics as aromatic product stream.

[0057] 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 aliphatic compounds and / or compounds with aliphatic residues from the partial stream 8.

[0058] The purification unit 250 has a feed 251 for an extraction solvent 9 for aliphatics and at least one mixing chamber 252 and a separation chamber 253 for liquid-liquid extraction between the partial stream 8 and an extraction solvent 9 for aliphatics. The purification unit 250 also has a return 254 for a raffinate 10 from the liquid-liquid extraction into the solvent circuit 7. The raffinate 10 can be fed into the solvent circuit 7, for example, via a pump 223.

[0059] At the in Fig. 3In the illustrated embodiment, the purification device 250 is equipped with a two-stage liquid-liquid extraction system comprising two mixing chambers 252 and two separation chambers 253. In principle, a single-stage or even a multi-stage liquid-liquid extraction system can also be used. In multi-stage liquid-liquid extractions, the solvent is mixed with the extraction agent in a mixing chamber 252 of the respective stage in each stage and separated from it again in a separation chamber 253 of the respective stage. Preferably, the solvent and extraction agent are circulated countercurrently in the individual stages. Particularly preferably, the extract from the subsequent stage serves as the extraction agent for one stage. In such a multi-stage extraction, the extract 11 of the liquid-liquid extraction is formed by the extract from the first stage in the direction of flow of the solvent 8.In a multi-stage liquid-liquid extraction process, both cross-flow and counter-flow processes can be selected.

[0060] As in Fig. 3 As shown, the mixing chamber 252 and the separation chamber 253 can be configured within the same vessel, for example as a mixer-settler unit or as a single- or multi-stage extraction column. The terms mixing chamber 252 and separation chamber 253 then refer to different sections of the same cavity, each fulfilling its respective function during operation.

[0061] The purification device 250 further comprises a discharge 255 for the extract 11 of the liquid-liquid extraction, 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.

[0062] The solvent recovery device 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 extract 11 stream.

[0063] Preferably, extract 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.

[0064] 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.

[0065] 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.

[0066] 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 100 mbar (a) in a head region 273 of the distillation column 270.

[0067] 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.

[0068] The cooling of the partial stream 8 before entering the purification device 250 preferably takes place to a temperature range of 0 °C to 60 °C. For this purpose, further heat exchangers 281, 282 can be provided, which are preferably arranged downstream of the heat exchanger 280 in the partial stream 8. The additional heat energy 286 generated in these heat exchangers 281, 282 can, for example, be used to heat the solvent stream consisting of raffinate 10 and bottoms product 15 before it is returned to the solvent circuit 7. Alternatively or additionally, the heat energy can also be used at other points in the extractive distillation process.

[0069] After exiting the solvent recovery unit 260, the hydrophobic phase 13 can be discharged into the aliphatic product stream 2. A separation device for removing impurities (not shown) from the hydrophobic phase 13 can be provided in the discharge. This separation device can, for example, be a further distillation column. Alternatively, the impurities leave the device 200 via the aliphatic product stream 2.

[0070] At the in Fig. 3 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.

[0071] Fig. 4shows a second embodiment of the device according to the invention. The second embodiment differs from the one in Fig. 3 The first embodiment shown is distinguished by the provision of a separation device 290 for separating the impurities from the hydrophobic phase 13. The separation device 290 is connected to the feed 251 of the purification device 250, forming an extraction agent circuit 17. The separated impurities 18 can be discharged and disposed of separately or added to a stream whose specifications are not violated by the added impurities.

[0072] Furthermore, the statements regarding the first point apply. Fig. 3 shown embodiment for Fig. 4 accordingly.

[0073] Fig. 5 shows an alternative apparatus setup for the section X in the devices according to Fig. 3 and 4 . In the Fig. 5The 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 reduced equipment complexity and a smaller footprint for the apparatus 200.

[0074] Fig. 6 shows another alternative apparatus setup for the section X in the devices according to Fig. 3 and 4 . In the Fig. 6The 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

[0075] 1 Feed stream 2 Aliphatic product stream 3 Aromatic product stream 4 Aromatic solvent 5 Mixture of feed and solvent 6 Aromatic-enriched solvent 7 Solvent cycle 8 Partial solvent cycle 9 Aliphatic extraction solvent 10 Liquid-liquid extraction refiner 11 Liquid-liquid extraction extract 12 Aqueous phase 13 Hydrophobic phase 14 Water 15 Distillation bottoms 16 Water cycle 17 Extraction solvent cycle 18 Separated impurities 100 Process for separating a hydrocarbon-containing feedstock stream 110 Countercurrent contact of feedstock stream with solvent 120 Distillative separation of an aliphatic fraction 130 Stripping of aromatics from the solvent 140 Recycling of the solvent 150 Purification of the partial stream of the aromatic-depleted solvent 160 Addition of water 170 Separation of the aqueous phase from the hydrophobic phase 180 Distillation of the aqueous phase 190 Separation of impurities from the hydrophobic 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 Mixing chamber 253 Separation chamber 254 Recirculation for raffinate 255 Extract discharge 260 Solvent recovery device 261 Mixing device 262 Separating device 263 Discharge for aqueous phase 270 Distillation column 271 Discharge for the bottom product 272 Head discharge 273 Head area 274 Vacuum generating unit 280 to 284 Heat exchanger 285, 286 Thermal energy 290 Separation unit

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 behind 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 depleted of aromatics (4) in a solvent circuit (7) for the extraction of further aromatics from the feed stream (1), whereby aliphatic compounds and / or compounds with aliphatic residues 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, wherein the purification (150) is carried out by means of a liquid-liquid extraction between the partial stream (8) and an extraction agent (9) for aliphatic compounds, the raffinate (10) of the liquid-liquid extraction being returned to the solvent circuit (7), and the following further steps being carried out to recover solvent from an extract (11) of the liquid-liquid extraction: • Mixing (160) the extract (11) from the liquid-liquid extraction 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), characterized in that the aqueous phase (12) is distilled (180) to remove water, the bottom product (15) of the distillation (180) is returned to the solvent circuit (7) and the distilled water (14) is returned in a water circuit (16) and added again to the extract (11) of the liquid-liquid extraction.

2. Method according to claim 1, characterized in that the partial stream (8) is cooled in a heat exchanger (280) prior to the liquid-liquid extraction, and the distillation (180) is carried out using the heat energy (285) generated in the heat exchanger (280).

3. Method according to one of claims 1 or 2, 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 100 mbar (a).

4. Method according to one of claims 1 to 3, characterized in that the separation (190) of the impurities from the hydrophobic phase (13) is carried out.

5. Method according to one of claims 1 to 4, characterized in that the hydrophobic phase (13) is fed to the aliphatic product stream (2) or is returned to the liquid-liquid extraction as an extraction agent (9) for aliphatics in an extraction agent circuit (17).

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, • a recirculation line (240) for the solvent (4) depleted in aromatics 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 aliphatic compounds and / or compounds with aliphatic residues from the partial stream (8), wherein the purification device (250) contains a feed (251) for an extraction agent (9) for aliphatic compounds and at least one mixing chamber (252) and one separation chamber (253) for liquid-liquid extraction between the partial stream (8) and the extraction agent (9) for aliphatic compounds, the purification device (250) has a return line (254) for a raffinate (10) from the liquid-liquid extraction into the solvent circuit (7), and the purification device (250) has a discharge line (255) for an extract (11) from the liquid-liquid extraction, which 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, characterized in that 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), wherein the distillation column (270) has a discharge (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), and a head outlet (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).

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

10. Device according to one of claims 8 or 9, 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 100 mbar (a) in a head region (273) of the distillation column (270).

11. Device according to one of claims 8 to 10, characterized in that a separating device (290) is provided for separating the impurities from the hydrophobic phase (13).

12. Device according to claim 11, characterized in that the separating device (290) is connected to the feed (251) of the purification device (250), forming an extraction agent circuit (17).