Extractive distillation column system and the use thereof in the separation of butenes from c4-hydrocarbon streams

Abstract

To provide an extractive distillation column system which comprises a combination column and a side rectification column.SOLUTION: The present invention relates to a process for separation of butenes from C4-hydrocarbon streams using an extractive distillation column system.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to an extractive distillation column system comprising a combination column (1) and a side rectification column (2). The present invention further relates to a method for separating butenes from a C4 hydrocarbon stream using the extractive distillation column system. [Background technology]

[0002] Methods for separating butenes from C4 hydrocarbon streams containing butanes in addition to butenes are known. For this purpose, extractive distillation is usually employed using aprotic solvents (e.g., N-methyl-2-pyrrolidone (NMP) or acetonitrile (ACN)) to increase the relative volatility of alkanes compared to alkenes. Plants for such extractive distillation usually consist of two separate columns. In one absorption column, butenes are dissolved in a solvent and butanes are separated as an overhead product. In the desorption column, butenes are removed from the solvent loaded with butenes at elevated temperature and / or reduced pressure, and the butenes are obtained in concentrated form at the top of the desorption column. The solvent liberated from the butenes is then recycled to the absorption column. Summary of the Invention [Problem to be solved by the invention]

[0003] In known plants where the absorption and desorption columns are spatially separated, a liquid stream is conducted from the absorption column to the desorption column. This is usually done by a pump. Such pumps are expensive to purchase and ultimately result in significant operating and maintenance costs. The corresponding plants require sufficient space for each column and other assemblies. However, sufficient space is not always available. Therefore, there is a need to build and operate plants for the more cost-effective and space-saving separation of butenes from C4 hydrocarbon streams.

[0004] Therefore, an object of the present invention is to provide an extractive distillation column system that requires less space and has low operating costs, and a further object is to provide a space-saving and low-cost process for separating butenes. [Means for solving the problem]

[0005] These problems can be solved by the embodiment of the extractive distillation column system proposed in claim 1 and the method specified in claim 7. Preferred embodiments are specified in the dependent claims.

[0006] The extractive distillation column system according to the present invention is an extractive distillation column system for separating butenes from a C4 hydrocarbon stream containing at least butenes and butanes using a solvent, the extractive distillation column system comprising a combination column (1) and a side rectification column (2), The combination column includes, from top to bottom, at least the following: the combination column (1) comprises an upper section in which a stream enriched in butanes is obtained compared to the C4 hydrocarbon stream used; a packed section comprising at least two packed beds; a recovery section comprising at least two liquid collectors, preferably a chimney bottom; a regeneration section comprising at least one packed bed; and a lower section in which a solvent is obtained; wherein at least two side evaporation systems (5, 6) are arranged on the combination column (1), and in each of said systems, a liquid phase is at least partially evaporated from one of the liquid collectors of the recovery section and then recycled to the recovery section via respective inlets (5a, 6a), wherein the inlet (5a) is arranged such that at least one of the liquid collectors is spatially arranged above the inlet (6a); The side rectification column (2) has at least two separating trays or one packed or packed bed and is fed with the gas phase obtained from the stripping section of the combination column below the inlet (5a) and above or at the same level as the inlet (6a). In a preferred embodiment of the invention, the upper section comprises trays or packing.

[0007] It should be noted that the liquid phases taken from one of the liquid collectors of the recovery section and passing through the side evaporation systems (5, 6) are each mainly in liquid form. However, since a gas phase is also present in the combination column, a portion of the gas phase may be entrained in the liquid phase to a (very) small extent, for example in the form of bubbles. The term "liquid phase" is not intended to explicitly exclude this possibility.

[0008] According to the present invention, the combination column (1) with its associated sections combines the absorption column and desorption column of a known extractive distillation column. Spatially, the upper part of the combination column, i.e., the upper section, packing section, and stripping section, correspond to the absorption column, in which butenes from the C4 hydrocarbon stream pass through the solvent. Spatially, the lower part of the combination column, i.e., the stripping section, regeneration section, and lower section, correspond to the desorption column, in which butenes are removed from the solvent (spatially, the lower part of the desorption column). The side rectification column (2), in which butenes are separated from the solvent, is obtained at its upper part, and therefore corresponds to the upper part of the desorption column. Since the butenes accumulate at the upper part, the side rectification column (2) can be designed as an independent column (see FIGS. 1 and 2) or can be integrated into the combination column (1) (see FIGS. 3 and 4), i.e., it can be arranged in a common column shell together with the combination column (1).

[0009] The advantages of the extractive distillation column system according to the invention are clear: in any embodiment, no pump is required between the combination column (1) and the side rectification column (2). This avoids acquisition and operational costs. Furthermore, the side rectification column (2) of the invention can be much smaller than the second column (desorber) of known plants. Therefore, the column system according to the invention requires less space. If the side rectification column (2) is integrated into the combination column (1), even less space is required. Furthermore, no piping is required to the side rectification column (2).

[0010] The present invention relates to the separation of butenes from a C4 hydrocarbon stream using an extractive distillation column system according to the present invention. C4 hydrocarbon streams typically include butenes and alkanes (n-butane, isobutane). In the context of the present invention, the term "butane" is understood to mean both n-butane and isobutane, unless otherwise specified. Therefore, the process according to the present invention can be used with any C4 hydrocarbon stream containing at least butenes and butanes, provided that the amount of butenes and / or butanes present allows the process to be carried out economically. In a preferred embodiment of the present invention, the C4 hydrocarbon stream used consists essentially of butanes and butenes, i.e., 98% by mass or more, preferably 99% by mass or more. The corresponding stream may also contain small amounts of impurities or other hydrocarbons, such as 1,3-butadiene, C3 or C5 hydrocarbons.

[0011] The solvent used is a liquid solvent that dissolves mainly the butenes of the gaseous C4 hydrocarbon stream used. Suitable solvents are aprotic solvents, such as N-methyl-2-pyrrolidone (NMP). Preferably, NMP is used as the solvent. In a further preferred embodiment of the present invention, the solvent contains water, in particular in an amount ranging from 1 to 10% by weight, preferably from 4 to 9% by weight, relative to the total amount of solvent. The combination column (1) of the extractive distillation column system according to the present invention has, in particular, a suitable inlet for the solvent, which inlet is preferably located above the first packed bed in the packed section or above the second packed bed in the packed section.

[0012] The combination column (1) of the extractive distillation column system according to the present invention has a suitable inlet for the C4 hydrocarbon stream from which butenes are to be separated. A liquid solvent is fed into the combination column (1) spatially above the inlet for the C4 hydrocarbon stream, i.e., the inlet for the solvent is located above the inlet for the C4 hydrocarbon stream. In a preferred embodiment, the inlet for the C4 hydrocarbon stream is arranged such that at least one packed bed is located below the inlet for the solvent when viewed from above. The liquid solvent is allowed to drip through the combination column (1) and contact the (ascending) vaporous C4 hydrocarbon stream, transferring the portion of the C4 hydrocarbon stream that mainly contains butenes to the solvent.

[0013] Before the C4 hydrocarbon stream enters the combination column (1) via the inlet, the stream is preferably at least partially vaporized. To this end, the extraction column system may include a feed vaporizer (4) through which the C4 hydrocarbon stream from the inlet is at least partially vaporized before entering the combination column (1). Advantageously, the vaporization does not have to take place entirely within the combination column (1).

[0014] The extractive distillation column system according to the present invention has two side evaporation systems (5, 6). The two side evaporation systems (5, 6) are arranged one below the other, so that the at least partially evaporated streams therein are recycled to the stripping section of the combination column (1) via one of the inlets (5a, 6a). The inlet (5a) belongs to the side evaporation system (5), and the inlet (6a) belongs to the side evaporation system (6). The side evaporation system (5) of the present invention preferably has a single evaporator or two evaporators arranged in parallel or in series. When the side evaporation system (5) has two evaporators arranged in parallel or in series, an additional inlet to the stripping section of the combination column (1) may be present. This additional inlet is located spatially above or at the same height as the inlet (5a). The side evaporation system (6) of the present invention preferably has a single evaporator or two evaporators arranged in parallel or in series. If the side evaporation system (6) has two evaporators arranged in parallel or in series, there may be an additional inlet into the stripping section of the combination column (1), which is spatially located below or at the same height as the inlet (6a).

[0015] If the side evaporation system (5) and / or the side evaporation system (6) have two evaporators arranged in parallel or in series, the recovery section of the combination column (1) may require two or more liquid recovery vessels fed and / or withdrawn with the recirculated stream from each evaporator.

[0016] A bottom evaporator (7) is preferably arranged in the lower section of the combination column (1) of the extractive distillation column system. This bottom evaporator at least partially evaporates the liquid accumulating at the bottom, removing any remaining butenes from the solvent. The recovered hot solvent, i.e., the solvent from which the butenes have been removed, accumulates at the bottom. The solvent obtained at the bottom is preferably recycled to the solvent inlet. In a preferred embodiment, the heat of the solvent recycled to the inlet of the combination column (1) is used for heat integration, i.e., the heat of the solvent is preferably used for evaporation in the feed evaporator (4) and in the side evaporation systems (5, 6). The feed evaporator (4) and the side evaporation systems (5, 6) are preferably equipped with heat exchangers that enable this heat transfer.

[0017] Heat integration removes heat from the solvent, both to heat other streams and columns and primarily to cool the solvent. If sufficient heat is extracted from the solvent during heat integration, i.e., if it is at the correct temperature, it can be transferred directly to the packed section of the combination column (1). However, it is possible that the solvent is not yet at the correct temperature despite the heat integration. In this case, after heat integration and before entering the combination column (1), the solvent can be fed to a residual cooler to cool it to the correct temperature.

[0018] Heat is a process parameter. Heat supplied or removed corresponds to the change in internal energy minus the amount of work. The terms "heat", "heat transfer" and "heat integration" used in this invention are always based on this definition.

[0019] An embodiment of the side rectification column (2) is characterized by the presence of at least two separating trays or one packed bed. The side rectification column is fed with the gas phase discharged from the stripping section of the combination column (1) below the inlet (5a) and above or at the same level as the inlet (6a). The gas phase contains, in particular, mainly butenes, but may also contain solvent residues, for example in the form of entrained droplets. According to the invention, the solvent residues are preferably separated and recycled to the combination column, for example via a suitable conduit. For this purpose, an inlet for the recycled solvent residues is installed in the stripping section of the combination column (1). A stream enriched in butenes compared to the C4 hydrocarbon stream used can then be recovered at the top of the side rectification column (2).

[0020] The present invention further provides a method for separating butenes from a C4 hydrocarbon stream by extractive distillation using the extractive distillation column system according to the present invention described above. The separation of butenes comprises at least the following steps: a C4 hydrocarbon stream at least partially vaporized in a feed vaporizer (4) is fed to a packed section of a combination column, and a liquid solvent is fed to at least one packed bed above said C4 hydrocarbon stream, thereby bringing said C4 hydrocarbon stream and said liquid solvent into contact with each other and transferring primarily butenes from the C4 hydrocarbon stream to said liquid solvent, thereby obtaining a butenes-loaded solvent; wherein the butene-laden solvent is collected in a liquid collector of the collection section, passes through a first side evaporation system (5) where it is at least partially evaporated, and then is recycled to the collection section via an inlet (5a); wherein the liquid phase obtained in the further liquid collector of said recovery section passes through a second side evaporation system (6) where it is at least partially evaporated and then recycled via an inlet (6a) to said recovery section, from where said liquid phase enters the regeneration section; wherein the liquid phase obtained below the last packed bed of the regeneration section, comprising the solvent and residues of butenes and / or butanes, passes through a bottom evaporator (7) and is then fed to a lower section, whereby the butenes and / or butanes still present in the solvent are at least partially discharged, and the solvent obtained is recovered as a bottom stream and recycled to the packed section; and a gas stream comprising at least butenes and residual solvent is fed from the stripping section of the combination column below the inlet (5a) and above or at the same height as the inlet (6a), and the gas stream is fed to a side rectification column (2), thereby obtaining a butene-enriched stream at the top of the side rectification column, The heat extracted as the bottom stream is transferred to the first side evaporative system (5), the second side evaporative system (6) and the feed evaporator (4) and is at least partially used for heat integration; This is done by:

[0021] The present process relates to the separation of butenes from a C4 hydrocarbon stream containing butenes. C4 hydrocarbon streams typically include butenes and alkanes (n-butane, isobutane). In the context of the present invention, the term "butane" is understood to mean both n-butane and isobutane, unless otherwise specified. The process according to the present invention can therefore be used with any C4 hydrocarbon stream containing at least butenes and butanes, provided that the amount of butenes and / or butanes present allows the process to be carried out economically. In a preferred embodiment of the present invention, the C4 hydrocarbon stream used consists essentially of butanes and butenes, i.e., at least 98% by mass, preferably at least 99% by mass. The corresponding stream may also contain small amounts of impurities or other hydrocarbons, such as 1,3-butadiene, C3 or C5 hydrocarbons.

[0022] The solvent used is a liquid solvent that dissolves primarily the butenes of the gaseous C4 hydrocarbon stream used. Suitable solvents are aprotic solvents, such as N-methyl-2-pyrrolidone (NMP). Preferably, NMP is used as the solvent. In a further preferred embodiment of the present invention, the solvent contains water, in particular in an amount ranging from 1 to 10% by weight, preferably from 4 to 9% by weight, relative to the total amount of solvent.

[0023] A liquid solvent is fed into the combination column (1) spatially above the inlet for the C4 hydrocarbon stream. The liquid solvent is dropped through the combination column (1) and contacted with the (ascending) vaporous C4 hydrocarbon stream, transferring a portion of the C4 hydrocarbon stream containing mainly butenes to the solvent, forming a packed solvent. The C4 hydrocarbon stream and the solvent are contacted with each other, particularly in countercurrent flow. In a preferred embodiment of the present invention, the portion of the C4 hydrocarbon stream that passes through the solvent contains at least 70% by mass, more preferably at least 80% by mass, of butenes relative to the composition of the portion of the C4 hydrocarbon stream that passes through the solvent. This results in, in particular, at least 80%, particularly preferably at least 90%, of the butenes contained in the C4 hydrocarbon stream used being transferred to the solvent.

[0024] The solvent loaded with butenes flows downward within the combination column (1) and is collected in a suitable liquid collector, particularly the chimney bottom, in the recovery section. The loaded solvent is collected from the liquid collector, passes through a first side evaporation system (5), and then recycled to the recovery section via an inlet (5a) below the liquid collector. The side evaporation system (5) of the present invention preferably includes or consists of a through-flow evaporator, where the loaded solvent passes through the evaporator only once. This allows the lowest possible temperature to be achieved and prevents fouling. The side evaporation system (5) of the present invention is preferably a single evaporator or two evaporators arranged in parallel or series. When the side evaporation system (5) includes two evaporators arranged in parallel or series, an additional inlet into the recovery section of the combination column (1) may be present. This additional inlet is spatially located above or at the same height as the inlet (5a).

[0025] The liquid phase accumulates in the recovery section's additional liquid collector, where it is recovered and passed through a second side evaporation system (6) before being recycled to the recovery section via an inlet (6a) below this liquid collector. The remaining (unevaporated) liquid phase then enters the regeneration section. The inventive side evaporation system (6) preferably includes or consists of a through-flow evaporator, where the loaded solvent passes through the evaporator only once. This allows the lowest possible temperature to be achieved and prevents fouling. The inventive side evaporation system (6) preferably has a single evaporator or two evaporators arranged in parallel or in series. If the inventive side evaporation system (6) has two evaporators arranged in parallel or in series, an additional inlet into the recovery section of the combination column (1) may be located spatially below or at the same height as the inlet (6a).

[0026] The liquid collectors from which the loaded solvent or liquid phase is collected and passed to the side evaporation systems (5, 6) are spatially arranged below one another, and the liquid collector from which the loaded solvent passes to the side evaporation system (5) is arranged above the liquid collector from which the liquid phase reaches the side evaporation system (6). The streams at least partially evaporated in the side evaporation systems (5, 6) are each recycled to the recovery section of the combination column (1) via one of the inlets (5a, 6a). The vapor portion of each of these recycled streams rises upward, while the liquid portion of each of these streams descends within the combination column.

[0027] The liquid phase flows further downward from the recovery section through a regeneration section containing at least one packed bed. Below the last packed bed in the regeneration section, the liquid phase is preferably recovered in a suitable recovery vessel. The liquid phase that arrives below the last packed bed, or is optionally collected in the recovery vessel, contains the solvent and residual butenes and / or butanes, and is fed to the lower section after passing through a bottom evaporator (7), whereby the butenes and / or butanes present in the solvent are at least partially discharged. A temperature rise occurs at the bottom of the combination column (1). The temperature at the bottom of the combination column (1) is preferably 120°C to 200°C, more preferably 130°C to 195°C.

[0028] The bottom evaporator (7) is preferably a through-type evaporator, in which the liquid phase passes through it only once. This allows the lowest possible temperature to be achieved, preventing fouling. It also allows for a small average temperature difference, simplifying heat transfer. The bottom evaporator (7) may also be a multi-stage device, i.e., there are several heat exchangers or several evaporators in the bottom evaporator (7). The solvent then accumulates in the lower section of the combination column and is recycled to the packed section of the combination column (1), in particular to the corresponding inlet.

[0029] An important feature of the present invention is the heat integration using the heat of the solvent on its way from the bottom to the packed section of the combination column (1) and, in some cases, the high-temperature condensed water generated in the bottom evaporator (7). According to the present invention, the heat of the solvent, preferably NMP, recovered at the bottom of the combination column (1) is used for heat integration by transferring the heat of the solvent in the first side evaporation system (5), the second side evaporation system (6), and the feed evaporator (4).

[0030] Heat in the bottom evaporator (7) can be supplied to the heat exchanger by heat transfer from a suitable heat transfer medium. Heat transfer mediums include, in particular, heating steam, which is used as medium-pressure steam or high-pressure steam. Medium-pressure steam is preferred as the heating steam, and its temperature is 150°C to 270°C, preferably 160°C to 250°C. The pressure of the medium-pressure steam is preferably 15 to 30 bar, particularly preferably 17 to 25 bar. Steam with an absolute pressure of 30 bar or more can be used as heating steam. Such heating steam is also called high-pressure steam.

[0031] The heating steam used for evaporation in the bottom evaporator (7) is at least partially condensed in the heat exchanger to produce a hot condensate at an absolute pressure of 10 to 20 bar, preferably 12 to 17 bar, and a temperature of 150 to 210°C, preferably 160 to 200°C. A condensate container is preferably arranged downstream of the heat exchanger, allowing the hot condensate to be separated from the steam. The pressure in the condensate container is preferably lower than the pressure in the heat exchanger on the heating steam side. Due to the lower pressure, a portion of the hot condensate evaporates, and the entire steam, i.e., the non-condensable portion of the heating steam and the hot condensate evaporated in the condensate container due to the pressure release, accumulates in the condensate container as low-pressure steam. In the present invention, the absolute pressure of the low-pressure steam is preferably 0 bar to less than 10 bar. The temperature of the low-pressure steam is preferably 100 to 180°C.

[0032] The low-pressure steam generated there still contains usable energy. However, this is not energetically or economically advantageous. However, this energy can be utilized in a preferred embodiment of the present invention. For this purpose, the heating steam used for evaporation in the bottom evaporator (7) can be supplied, preferably by means of a controllable steam ejector (thermocompressor). The thermocompressor is then supplied with heating steam, particularly preferably medium-pressure steam, supplied, for example, from a corresponding steam network, and low-pressure steam from a condensate container, thereby generating a mixed steam serving as the heat transfer medium for the bottom evaporator (7). In this embodiment, this mixed steam is the heating steam. Such a steam ejector is designed to operate with motive steam and, after drawing suction steam from the container by means of negative pressure (the dynamic pressure of the steam ejector), generate a mixed steam serving as the heat transfer medium. In this embodiment, the motive steam is drawn from the condensate container as heating steam or low-pressure steam, which is mixed with the motive steam to produce medium-pressure steam.

[0033] The advantages of such an embodiment are clear: the energy of the low-pressure steam obtained in the condensate vessel can be utilized, thereby realizing energy and cost savings. Such a method can also be advantageous for other reasons: the steam ejector used can be controlled so that the amount of medium- or high-pressure and low-pressure steam can be adjusted, for example, depending on specific process parameters. The amount of suction steam is adjusted via the amount of motive steam. The amounts of low-pressure and medium-pressure steam can be adjusted, for example, depending on the temperature of the combination column (1).

[0034] At the top of the combination column (1), a stream is produced that is particularly enriched in butanes compared to the C4 hydrocarbon stream used. The absolute pressure at the top of the combination column (1) can be 1 to 7 bar, preferably 2 to 6.5 bar. The butane-enriched stream may also contain water originating from the solvent. This water can be separated in a subsequent step. In this process, a butane-rich stream is recovered at the top of the combination column and subjected to a single-stage or multi-stage condensation to condense a water-containing stream and a butane-containing product stream. These two streams can 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 can be sent to the combination column (1) or to a side rectification column (2) and / or partially discharged from the process.

[0035] The butane-containing product stream obtained from the condensation in this way can contain small amounts of water, in particular in an amount of up to 1500 ppmw, based on the total composition of the butane-containing product stream. Furthermore, the butane-containing product stream obtained from the condensation can still contain residual butenes, with the stream usually containing less than 20% by weight, preferably less than 15% by weight, particularly preferably less than 5% by weight, of butenes, based on the total composition of the butane-containing product stream.

[0036] 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 any water still present. Preferably, the butane-containing product stream after drying contains a maximum of preferably 50 ppmw, preferably 25 ppmw, of water. The water obtained during drying or the vapor stream from the drying can be recycled to the combination column (1) and reused for condensation.

[0037] A gas stream is obtained in the stripping section of the combination column (1) below the inlet (5a) and above or at the same level as the inlet (6a) and is fed to a side rectification column. The gas phase mainly contains butenes, but may also contain, in particular, butane residues and solvent, for example in the form of droplets. This side rectification column (2), as described above, has at least two separating trays or one packed bed and is used, in particular, for separating the solvent. The maximum pressure of the side rectification column may be between 1 and 7 bar absolute, preferably between 2 and 6.5 bar absolute. Preferably, the pressures in the combination column (1) and the side rectification column (2) are coupled.

[0038] At the top of the side rectification column (2), a stream enriched in butenes is produced compared to the C4 hydrocarbon stream used. This butene-enriched stream may further contain water originating from the solvent. This water can be separated in a subsequent step. In this process, the butene-enriched stream is recovered at the top of the side rectification column (2) and condensed in one or more stages to produce a water-containing stream containing residual organic matter and a butene-containing product stream. These two streams can be separated from each other using a suitable device, for example a spider. The water-containing stream separated from the butene-containing product stream can then be recycled to the side rectification column (2) or the combination column. It is also possible to retain the organic matter present by discharging the water-containing stream in whole or in part.

[0039] In a preferred embodiment of the invention, the butene-enriched stream recovered at the top of the side rectification column (2) is condensed in two stages: in the first stage, a water-containing stream is condensed and then recycled to the side rectification column (2), and in the second stage, the butene-containing product stream is condensed. However, the remaining water may also be condensed in the second stage. This remaining water can be separated from the butene-containing product stream via a suitable device, for example a spider.

[0040] The butene-containing product stream obtained from the condensation preferably contains less than 20% by mass, more preferably less than 16% by mass, of butanes relative to 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% by mass, more preferably at least 75% by mass, and particularly preferably at least 86% by mass, relative to the total composition of the butene-containing product stream.

[0041] At the bottom of the side rectification column (2) or at the base of the side rectification column (2), a liquid bottoms stream can be produced which essentially comprises the solvent supplied from the combination column (1). This stream is only obtained in embodiments in which the side rectification column (2) is configured as an independent column (see FIGS. 1 and 2). This liquid bottoms stream can be (re)circulated from the side rectification column (2) to the combination column (1). The recycled stream is fed to the combination column (1) at a suitable point which is advantageous, for example from the viewpoint of concentration. [Brief explanation of the drawings]

[0042] [Figure 1] 1 is a diagram showing a basic configuration of the present invention. [Figure 2] FIG. 1 shows a further preferred embodiment of the invention in which the steam ejector (12) is present in the bottom evaporator (7). [Figure 3] FIG. 2 is a diagram showing a schematic configuration of a steam ejector (12). [Figure 4] FIG. 1 illustrates a further subject of the present invention. [Figure 5] FIG. 1 shows a further preferred embodiment of the invention in which the steam ejector (12) is present in the bottom evaporator (7). DETAILED DESCRIPTION OF THE INVENTION

[0043] The invention will now be described with reference to the drawings, which are for purposes of illustration and are not to be construed as limiting.

[0044] FIG. 1 shows the basic design of the present invention. A liquid C4 hydrocarbon stream is evaporated via a feed evaporator (4) and fed to the packed section (1b) of the combination column (1). If necessary, the solvent can be brought to the desired temperature via a residue cooler (3) and is also fed to the packed section (1b) of the combination column (1). In this case, the inlet is located spatially above the first packed bed and above the inlet for the C4 hydrocarbon stream. In the upper section (1a) of the combination column (1), a butane-enriched stream is fed and recovered. The possibility of condensation is not shown here; only the possibility of partial stream recycling is indicated by arrows. In the recovery section (1c) of the combination column (1), the butene-laden solvent is recovered in a liquid recovery vessel, represented by a chimney bottom in the diagram. At least a portion of the butene-laden solvent is recovered there and recycled to the recovery section (1c) via the first side evaporation system (5) and the inlet (5a) via the inlet. The liquid phase is recovered in a further liquid recovery vessel and recycled from there via the inlet (6a) through a second side evaporation system (6) to the recovery section, from which the liquid phase is fed to the regeneration section (1d). Below the last packed bed, the resulting liquid phase is recovered and fed via a bottom evaporator (7) to the bottom (1e) of the combination column (1). The solvent depleted of butenes is then recovered from the bottom (1e) of the combination column (1) and recycled to the packed section of the combination column (1) via the side evaporation systems (5, 6) and the feed evaporator using pump (8). Between the inlet (5a) and the inlet (6a), a gas stream is recovered and fed to the side rectification column (2) to separate the residual solvent and water from the butenes. A butene-enriched stream is recovered at the top of the side rectification column (2). This stream can be condensed in one or more stages, not shown, and the arrows indicate only the recycle stream, where a liquid phase accumulates at the bottom of the side rectification column (2) and can be recycled to the recovery section of the combination column (1).

[0045] Figure 2 shows a further preferred embodiment of the invention, in which a steam ejector (12) is present in the bottom evaporator (7). This steam ejector is supplied with conventional heating steam, for example medium-pressure steam from the steam network, and low-pressure steam obtained in the condensate container (11), to form a mixed steam, which is used as heating steam for the bottom evaporator (7). The operation of the steam ejector is explained in Figure 3. The rest is the same as the explanation for Figure 1 above.

[0046] Figure 3 shows a schematic diagram of the steam ejector (12). Here, the power steam (121) is heating steam, in particular medium-pressure steam from the steam network. The suction steam (123) is low-pressure steam from the condensate container. The two are mixed via a control unit (124) and fed as mixed steam (122) to the bottom evaporator (7) via an outlet. By adjusting the amounts of power steam and suction steam via the control unit, the pressure and temperature of the mixed steam, and thus the heating output, can be influenced.

[0047] FIG. 4 illustrates a further object of the present invention. The operating method is similar to that shown in FIG. 1, differing only in its design. The combination column (1) and the side rectification column (2) are therefore separate units whose functions are relevant to the present invention. However, the side rectification column is spatially integrated with the combination column and is structurally designed as a single column shell. The side rectification column (2) is spatially open at the bottom and is filled with an ascending gas phase containing at least butenes, residual solvent, and water. A butene-enriched stream is obtained in the side rectification column (2). This stream can be condensed in one or more stages, not shown. Only the recycle stream is indicated by an arrow.

[0048] Figure 5 shows a further preferred embodiment of the invention, in which a steam ejector (12) is present in the bottom evaporator (7). This steam ejector is supplied with conventional heating steam, for example medium-pressure steam from the steam network, and low-pressure steam obtained in the condensate container (11), to form a steam mixture, which is used as heating steam for the bottom evaporator (7). The operation of the steam ejector is as explained in Figure 3. Otherwise, the explanation is the same as for Figure 1 above.

Claims

1. An extractive distillation column system for separating butenes from a C4 hydrocarbon stream containing at least butenes and butanes using a solvent, wherein the extractive distillation column system includes a combination column and a side rectification column, The combination column, when viewed from top to bottom, includes at least the following: An upper section where a stream enriched in butane compared to the C4 hydrocarbon stream used is obtained; a packed section including at least two packed beds; a recovery section including at least two liquid collectors or chimney bottoms; a regeneration section including at least one packed bed; and a lower section where a solvent is obtained; At least two side evaporation systems are arranged on the combination column. In each of the side evaporation systems, a liquid phase is at least partially evaporated from one of the liquid collectors in the recovery section and then recycled to the recovery section through each of the inlets (5a, 6a), where the inlet (5a) has at least one of the liquid collectors spatially arranged above the inlet (6a), The side rectification column has at least two separation trays, or one packed bed or packing bed, and supplies a vapor phase obtained from the recovery section of the combination column below the inlet (5a) and above or at the same height as the inlet (6a). Extractive distillation column system.

2. The extractive distillation column system according to claim 1, comprising a feed evaporator (4) for evaporating the C4 hydrocarbon stream at least partially before feeding the C4 hydrocarbon stream to the combination column.

3. The extractive distillation column system according to claim 2, wherein the solvent obtained at the bottom of the combination column is recycled to an inlet for the solvent.

4. The extractive distillation column system according to claim 3, wherein the solvent is used for heat integration by transferring the heat of the solvent in the first side evaporation system (5), the second side evaporation system (6) and the feed evaporator.

5. The extractive distillation column system according to claim 1, wherein a bottom evaporator is arranged in the lower section of the combination column, and the bottom evaporator at least partially evaporates the liquid obtained in the lower section to remove residual butenes from the solvent.

6. The extraction distillation column system according to claim 1, wherein the stream in which butane is concentrated is recovered at the upper part of the side rectification column.

7. A method for separating butenes from a C4 hydrocarbon stream containing at least butenes and butanes by extraction distillation using the extraction distillation column system according to claim 1, wherein the separation of the butenes is as follows: Supplying the C4 hydrocarbon stream at least partially vaporized in a feed evaporator to the packed section of the combination column, and supplying a liquid solvent to at least one packed bed above the C4 hydrocarbon stream, thereby bringing the C4 hydrocarbon stream into contact with the liquid solvent to transfer mainly butenes from the C4 hydrocarbon stream to the liquid solvent to obtain a solvent loaded with butenes, wherein the solvent loaded with butenes is recovered in the liquid recovery device of the recovery section, passes through a first side evaporation system (5), is at least partially evaporated therein, and then is recycled to the recovery section through the injection port (5a); wherein the liquid phase obtained in a further liquid recovery device of the recovery section passes through a second side evaporation system (6), is at least partially evaporated therein, and then is recycled to the recovery section through the injection port (6a), from where the liquid phase enters the regeneration section; wherein the liquid phase containing the solvent and residues of butene and / or butane obtained under the last packed bed of the regeneration section passes through a bottom evaporator (7), and then is supplied to the lower section, whereby at least part of the butene and / or butane still present in the solvent is discharged, and the obtained solvent is recovered as a bottom stream and recycled to the packed section; and supplying a gas stream containing at least the butenes and the residual solvent from the recovery section below the injection port (5a) and above or at the same height as the injection port (6a) to the side rectification column (2), thereby obtaining a stream in which the butenes are concentrated at the upper part of the side rectification column, the heat recovered as the bottom stream is transferred to the first side evaporation system (5), the second side evaporation system (6) and the feed evaporator and is at least partially used for heat integration; A method performed by.

8. The method according to claim 7, wherein the solvent used is NMP. Claim 9 The method according to claim 7, wherein heat for evaporation in the bottom evaporator is supplied to the heat exchanger by heat transfer with a suitable heat transfer medium, in particular with heating steam. Claim 10 The method according to claim 9, wherein the heating steam used is at least partially condensed in the heat exchanger, thereby producing a high-temperature condensate at an absolute pressure of 10 to 20 bar or 12 to 17 bar and at 150 to 210 °C or 160 to 200 °C and supplying it to a condensate container. Claim 11 The method according to claim 10, wherein the pressure in the condensate container is lower than the pressure in the heat exchanger on the heating steam side, and a portion of the high-temperature condensate is re-evaporated to obtain low-pressure steam. Claim 12 The method according to claim 11, wherein the heating steam for the bottom evaporator is supplied using a steam ejector supplied with high-pressure or medium-pressure steam and the low-pressure steam obtained in the condensate container. Claim 13. The method according to claim 7, wherein the side rectification column comprises a column bottom to which a liquid bottom stream supplied from the bottom to the combination column is supplied. Claim 14 The method according to claim 7, wherein the bottom evaporator is a through-flow evaporator. Claim 15 The method according to claim 7, wherein at least one or both of the two side evaporation systems comprise or consist of a through-flow evaporator.

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