Process for recovering 1,3-butadiene from a c4-fraction by extractive distillation using a selective solvent

Abstract

A process for recovering 1,3-butadiene from a C4-fraction by extractive distillation comprises: a) supplying a lean selective solvent to an upper section of an extractive distillation column and bringing the gaseous C4- fraction into contact with the lean selective solvent, to obtain an overhead fraction comprising butanes and butenes, and a bottom fraction comprising 1,3-butadiene dissolved in the selective solvent, b) desorbing 1,3- butadiene from the bottom fraction, to obtain at least a desorbed 1,3-butadiene stream and the lean selective solvent and recirculating the lean selective solvent to the extractive distillation column, c) withdrawing from the extractive distillation column at least a portion of a liquid phase underneath the supply of the lean selective solvent and phase-separating the withdrawn liquid phase into a heavy liquid phase comprising selective solvent saturated with dissolved butanes and butenes, and a light liquid phase comprising butanes and butenes, d) returning the heavy liquid phase to the extractive distillation column underneath a position from which the liquid phase is withdrawn, thermally separating the light liquid phase into a volatile fraction and a less volatile fraction, both the volatile fraction and the less volatile fraction comprising selective solvent, butanes and butenes, wherein the mass fraction of selective solvent in the volatile fraction is lower than the mass fraction of selective solvent in the less volatile fraction, and e) returning the less volatile fraction underneath the position from which the liquid phase is withdrawn, and returning the volatile fraction above the supply of the lean selective solvent and / or into a condenser circuit of the extractive distillation column. In the process, the accidental formation of a second liquid phase in the extractive distillation column is reduced or even avoided.

Description

[0001] 240966W001 1

[0002] Process for Recovering 1 ,3-Butadiene from a C4-Fraction by Extractive Distillation Using a Selective Solvent

[0003] The present invention relates to a process for recovering 1 ,3-butadiene from a effraction comprising butanes, butenes, and 1 ,3-butadiene, by extractive distillation using a selective solvent.

[0004] 1 ,3-Butadiene is generally obtained industrially from effractions, i.e. mixtures of hydrocarbons in which the Cf hydrocarbons, in particular 1-butene, isobutene and 1 ,3-butadiene, predominate. Typical Cffractions contain, depending on the previous process step(s) and feedstock used, different C4 molecules like 1 ,3-butadiene, 1,2-butadiene, n-butane, isobutane, 1-butene, isobutene, cis-2-butene, trans-2-butene, vinylacetylene, 1 -butyne and traces of shorter and longer hydrocarbons.

[0005] C4-fractions are obtained, for example, in the preparation of ethylene and propylene by thermal cracking, usually in steam crackers, in particular naphtha or gas crackers. Furthermore, 1,3-butadiene-comprising C4-fractions are obtained in the catalytic dehydrogenation of n-butane and / or n-butene. The 1,3-butadiene-comprising C4-fractions will subsequently be referred to as C4-fractions or crude C4-fractions. They comprise not only small amounts of C3- and Cs-hydrocarbons but generally also acetylene(s) (methylacetylene, ethylacetylene and vinylacetylene).

[0006] It is generally known that pure 1 ,3-butadiene can be isolated from crude C4-fractions by means of a sequence of particular process steps in which a crude 1 ,3-butadiene is firstly obtained from the crude C4-fraction and the crude 1,3-butadiene is then purified further in order to isolate the pure 1 ,3-butadiene therefrom. Crude 1 ,3-butadiene is a mixture comprising from about 90 to 99.5 wt.-% of 1,3-butadiene, in particular from 97 to 99 wt.-% of 1,3-butadiene. The required specifications for pure 1,3-butadiene frequently provide for a minimum content of 1,3-butadiene of 99.6 wt.-% and a maximum permissible content of acetylenes and of 1,2-butadiene of 20 ppm in each case, based on the mass of the pure 1,3-butadiene.

[0007] The isolation of 1,3-butadiene from C4-fractions is a complex separation task because of the small differences in the relative volatilities of the components. An extractive distillation, i.e. a distillation with addition of a selective solvent, for example N-methyl-2-pyrrolidone (NMP), dimethylformamide (DMF) or acetonitrile (ACN), which has a boiling point higher than the mixture to be fractionated and increases the differences in the relative volatilities of the components to be separated, is therefore carried out. The crude 1,3-butadiene obtained in this way is, in order to meet required specifications, purified by distillation to give pure 1,3-butadiene. Besides 1,3-butadiene, this process yields a further economically interesting fraction, namely the so called raffinate 1, containing butanes and butenes.

[0008] For example, according to WO 2011 / 110562 A1, a crude C4-fraction is selectively hydrogenated, high-boiling constituents are subsequently separated off from the selectively hydrogenated C4-fraction and the remaining240966W001 2

[0009] extraction is then worked up further by extractive distillation in order to obtain crude 1 ,3-butadiene. The crude 1 ,3-butadiene is purified further to give pure 1 ,3-butadiene.

[0010] In extractive distillation processes of extractions using selective solvents, the selective solvent enters an extractive distillation column above the gaseous Cffraction. The selective solvent becomes loaded with the components of the Cffraction to which it has a greater affinity by countercurrent conducting of the Cffraction to be fractionated in vapor form with the liquid selective solvent under suitable thermodynamic conditions, generally at low temperatures, usually in the range from 20 to 80 °C, e.g. 40 to 60 °C, and at moderate pressures, frequently from about 1.5 to 10 bara, e.g. 4 to 6 bara, while the components with which the selective solvent has a lower affinity remain in the vapor phase and are taken off as overhead stream. The more soluble Cfcomponents dissolve in the selective solvent and leave the extractive distillation column at the bottom (for further processing in downstream columns), while the less soluble Cfcomponents, mainly the butanes and butenes leave the extractive distillation column at the top.

[0011] To ensure the purity of raffinate 1 and increase the yield of 1,3-butadiene, the composition at the top of the extractive distillation column consists mainly of the butanes and butenes together with other less soluble contaminants such as propanes and propenes. As the solubility of those molecules is low in the selective solvent, the formation of a second liquid phase can occur in the extractive distillation column, typically directly below the selective solvent supply into the extractive distillation column. For example, such a second liquid phase occurs if the C4 feed has a high concentration of butanes. The second phase gradually dissolves into the main liquid phase as both phases move towards the bottom of the column. However, the occurrence of a second liquid phase has major drawbacks as it leads to foaming and a reduction in separation efficiency. Ross type foaming due to surface tension gradients close to the solubility gap could lead to additional foaming problems in the extractive distillation column. By adding anti-foam products, the foaming can be suppressed. However, this disadvantageously results in increased anti-foam product consumption, an increase of unwanted side effects of the anti-foam product due to its increased consumption, and the necessity of separation of the antifoam product from the (crude) product streams.

[0012] A further disadvantage of the occurrence of a second liquid phase in the extractive distillation column is the reduction of separation efficiency. This is due to blanketing of the selective solvent by the second liquid phase due to its lower surface tension and density. A reduction of the separation efficiency in the extractive distillation column will result in a higher heat demand to reach comparable product purities.

[0013] The formation of a second liquid phase can be avoided by increasing the selective solvent to feed ratio, by reducing the raffinate 1 reflux to the extractive distillation column or by increasing the temperature of the selective solvent. However, these measures also result in an increased heat demand to reach comparable product purities.240966W001 3

[0014] US 2024 / 034704 A1 describes a process for separating butenes from a C4-hydrocarbon stream which contains at least butenes and butanes by extractive distillation with a solvent in an absorber. In said process, a portion of a liquid phase is withdrawn at the liquid distributor above a first or second random-packing bed and separated into a heavy liquid phase and a light liquid phase in a decanter, of which the heavy liquid phase is returned to the absorber and the light liquid phase is returned to downstream process steps, e.g. to the desorber.

[0015] It is therefore an object of the present invention to provide a process for recovering 1 ,3-butadiene from a C4-fraction with a high separation efficiency, in particular a process which allows for obtaining high yields of valuable products, especially of 1 ,3-butadiene, at an energy input as low as possible.

[0016] This object is solved by a process for recovering 1 ,3-butadiene from a C4-fraction comprising butanes, butenes, and 1 ,3-butadiene, by extractive distillation using a selective solvent. The process comprises:

[0017] a) supplying a lean selective solvent to an upper section of an extractive distillation column and bringing the gaseous C4-fraction into contact with the lean selective solvent in the extractive distillation column, to obtain an overhead fraction comprising butanes and butenes, and a bottom fraction comprising 1 ,3-butadiene dissolved in the selective solvent,

[0018] b) desorbing 1,3-butadiene, and, optionally, co-absorbed constituents, from the bottom fraction, to obtain at least a desorbed 1,3-butadiene stream and the lean selective solvent and recirculating the lean selective solvent to the extractive distillation column,

[0019] c) withdrawing from the extractive distillation column at least a portion of a liquid phase underneath the supply of the lean selective solvent and phase-separating the withdrawn liquid phase into a heavy liquid phase comprising selective solvent saturated with dissolved butanes and butenes, and a light liquid phase comprising butanes and butenes,

[0020] d) returning the heavy liquid phase to the extractive distillation column underneath a position from which the liquid phase is withdrawn, thermally separating the light liquid phase into a volatile fraction and a less volatile fraction, both the volatile fraction and the less volatile fraction comprising selective solvent, butanes and butenes, wherein the mass fraction of selective solvent in the volatile fraction is lower than the mass fraction of selective solvent in the less volatile fraction, and

[0021] e) returning the less volatile fraction underneath the position from which the liquid phase is withdrawn, and returning the volatile fraction above the supply of the lean selective solvent and / or into a condenser circuit of the extractive distillation column.

[0022] In the inventive process for recovering 1,3-butadiene from a C4-fraction, the accidental formation of a second liquid phase in the extractive distillation column is reduced or even avoided. This advantageously allows for both obtaining high yields of valuable products, especially of 1,3-butadiene, and for providing a process having a high separation efficiency at an energy input as low as possible.240966W001 4

[0023] Step a)

[0024] The effraction comprises at least butanes, butenes, and 1,3-butadiene. The Cffraction typically additionally comprises C4-acetylene(s). In many cases, the Cffraction comprises 1,3-butadiene, butanes, butenes, C4-acetylene(s), Ca-hydrocarbons and C5+-hydrocarbons.

[0025] The C4-fraction is, for example, a C4-fraction from a naphtha cracker.

[0026] A typical C4-fraction from a naphtha cracker has the following composition in wt.-%:

[0027] 15 to 85 wt.-% of 1,3-butadiene,

[0028] 4 to 30 wt.-% of butanes,

[0029] 24 to 64 wt.-% of butenes,

[0030] 0.2 to 2 wt.-% of C4-acetylenes,

[0031] 0.01 to 2.0 wt.-% of Ca-hydrocarbons, and

[0032] 0.01 to 0.5 wt.-% of C5+-hydrocarbons.

[0033] C4-Fractions from naphtha crackers thus comprise predominantly butanes, butenes and 1,3-butadiene. In addition, small amounts of other hydrocarbons are comprised. C4-acetylenes are frequently comprised in a proportion of up to 2 wt.-% or even up to 0.1 wt.-%.

[0034] Herein, the designator "Cx” refers to a hydrocarbon including x carbon atoms; "Cx+” refers to a hydrocarbon or mixture of hydrocarbons including x or greater carbon atoms.

[0035] Step a) involves supplying a lean selective solvent to an upper section of an extractive distillation column and bringing the gaseous C4-fraction into contact with the lean selective solvent in the extractive distillation column. An overhead fraction comprising butanes and butenes, and a bottom fraction comprising 1,3-butadiene dissolved in the selective solvent is obtained. Depending on its composition or origin, the C4-fraction typically further comprises constituents for which the selective solvent has a similar or higher affinity than for 1,3-butadiene, such as C4-acetylenes, 1,2-butadiene, propyne etc., which may be co-absorbed in the selective solvent. Butanes and butenes, although having a lower absorption coefficient, are also co-absorbed in the selective solvent to a certain extent.

[0036] This step allows for dissolving the valuable product 1,3-butadiene contained in the C4-fraction in the bottom fraction. Besides 1,3-butadiene, the bottom fraction may also contain co-absorbed constituents as detailed above. Preferably, the overhead fraction comprises only very low amounts of the valuable product 1,3-butadiene, especially, the overhead fraction is essentially free of 1,3-butadiene.240966W001 5

[0037] The gaseous effraction is typically brought into contact with the selective solvent by conveying the gaseous extraction in countercurrent to the selective solvent in at least one section of the extractive distillation column.

[0038] Pressure and temperature are set in the extractive distillation column in such a way that those components of the extraction for which the selective solvent has a lower affinity than for 1 ,3-butadiene, in particular the butanes and the butenes, remain mostly in the gas phase while 1 ,3-butadiene is essentially completely absorbed by the selective solvent. The extractive distillation column can, for example, be operated at a temperature of from 20 to 80 °C, preferably 40 to 60 °C, and at a pressure of from 1.5 to 10 bara, preferably 4 to 6 bara. In this way, the overhead fraction comprising butanes and butenes and the bottom fraction comprising 1 ,3-butadiene, and, optionally, co-absorbed constituents, dissolved in the selective solvent, are obtained.

[0039] To promote heat and mass transfer between the rising extraction vapors and the trickling selective solvent, the extractive distillation column may be filled with column internals. The column internals may be selected from trays, structured packings and unstructured packings. Useful internals include all commonly used internals, such as packings, for example structured packings and / or random packings. The packings provide a large area contact between the rising extraction vapors and the trickling selective solvent.

[0040] The overhead vapors are suitably condensed, e.g. in a condenser circuit of the extractive distillation column. Means for condensing streams are known by the skilled person. At least a part of the condensed overhead vapors may be returned to the extractive distillation column as a reflux, preferably at a position above the inlet of the selective solvent.

[0041] Said reflux provides a suitable downflowing liquid for scrubbing. Scrubbing may occur in a scrubbing section of the extractive distillation column. The scrubbing section may comprise internals. Said internals may be any suitable internals for columns, e.g. trays, structured packings and unstructured packings, as described above. This advantageously allows for avoiding selective solvent entrainment into the overhead stream.

[0042] The remainder of the condensed overhead vapors is the overhead fraction comprising butanes and butenes. It constitutes a valuable stream of the process of the invention and may suitably be withdrawn from the process. It may suitably be directed to further processes or stored. The overhead fraction is usually referred as raffinate 1.

[0043] Possible selective solvents are substances or mixtures which in general have a boiling point higher than that of the mixture to be fractionated and also a greater affinity for conjugated double bonds and triple bonds than for single double bonds and single bonds. Preferred selective solvents are dipolar solvents, particularly preferably dipolar aprotic solvents. For engineering reasons, preference is given to substances which are not corrosive or have little corrosivity. Suitable selective solvents for the process of the invention are, for example, nitriles such as acetonitrile (ACN), propionitrile, methoxypropionitrile, ketones such as acetone, furfural, N-alky l-substi tuted lower aliphatic acid amides such as dimethylformamide, diethylformamide (DMF), dimethylacetamide,240966W001 6

[0044] diethylacetamide, N-formylmorpholine, N-alkyl-substituted cyclic acid amides (lactams) such as N-alkyl pyrrolidones, in particular N-methylpyrrolidone (NMP). In general, N-alkyl-substituted lower aliphatic acid amides or N-alkyl-substituted cyclic acid amides are used. Dimethylformamide, acetonitrile, furfural and in particular N-methylpyrrolidone are particularly advantageous.

[0045] However, it is also possible to use mixtures of these solvents with one another, for example of N-methylpyrrolidone with acetonitrile, mixtures of these solvents with cosolvents such as water, alcohols, in particular those having 5 or fewer carbon atoms, e.g. methyl alcohol, ethyl alcohol, n-propyl alcohol, isopropyl alcohol, n-butyl alcohol, isobutyl alcohol, sec-butyl alcohol, tert-butyl alcohol, n-pentyl alcohol, or alicyclic alcohols such as cyclopentanol, diols, such as ethylene glycol and / or tert-butyl ethers, for example methyl tertbutyl ether, ethyl tert-butyl ether, propyl tert-butyl ether, n-butyl or isobutyl tert-butyl ether.

[0046] In a preferred embodiment of the process of the invention, the (lean) selective solvent comprises at least 80 wt.-% of N-methylpyrrolidone (NMP). The selective solvent preferably comprises from 85 to 95 wt.-% of NMP and from 5 to 15 wt.-% of water. N-methylpyrrolidone, preferably in aqueous solution, in particular with from 7 to 9 wt.-% of water, particularly preferably with 8.3 wt.-% of water, is particularly suitable.

[0047] In addition, the selective solvent can further comprise, in particular, auxiliaries, inhibitors, anti-foam products, organic secondary components and the like as impurity.

[0048] Step b)

[0049] Step b) involves desorbing 1 ,3-butadiene, and, co-absorbed constituents, from the bottom fraction, to obtain at least a desorbed 1 ,3-butadiene stream and the lean selective solvent and recirculating the lean selective solvent to the extractive distillation column.

[0050] Step b) allows for obtaining a stream comprising 1 ,3-butadiene, i.e. the valuable product of the process of the invention. Depending on the desired purity of the product, the crude 1 ,3-butadiene may be subjected to further purification steps, e.g. to one or more further distillative purification step(s), as described in detail below.

[0051] The bottom fraction comprises not only 1 ,3-butadiene dissolved in the selective solvent but generally also, as outlined above, co-absorbed constituents such as butanes and butenes, C4-acetylenes, 1 ,2-butadiene, propyne etc.

[0052] For this reason, a fractional desorption in which the hydrocarbons absorbed in the selective solvent are desorbed in the reverse order of their affinity for the selective solvent is normally carried out.240966W001 7

[0053] Typically, a stream comprising butanes and butenes may be desorbed first. Thus, in an embodiment, the process comprises desorbing co-absorbed butanes and butenes from the bottom fraction to obtain a stream comprising desorbed butanes and butenes. The stream comprising desorbed butanes and butenes can be directed to the extractive distillation column.

[0054] Preferably also a gas comprising C4-acetylenes, in particular vinylacetylene, is desorbed from the bottom fraction as a separate fraction as described in further detail below.

[0055] Step b) may be carried out in one column which may be referred to as desorber column or degasser column. Step b) may also be carried out in a setup of more than one column. Preferably, step b) is carried out in a setup of two columns which are referred to as rectifier and degasser, respectively, in the following.

[0056] The rectifier column can, for example, be operated at a temperature at the top of from 40 to 100 °C, preferably 40 to 70 °C, and at a pressure of from 1.6 to 10.1 bara, preferably 4.2 to 6.2 bara.

[0057] The degasser column can, for example, be operated at a temperature at the top of from 80 to 150 °C, preferably 90 to 110 °C, and at a pressure of from 1.1 to 6 bara, preferably 1.2 to 1.8 bara.

[0058] The step of desorbing co-absorbed butanes and butenes may be carried out in the rectifier, preferably in an upper part of a rectifier. In this case, the upper section of the rectifier column acts as stripping section in which the co-absorbed butanes and butenes and also other low boilers can be driven off and taken off at the top. For carrying out this step, the process preferably comprises bringing at least a portion of the desorbed 1 ,3-butadiene stream into countercurrent contact with the bottom fraction. Suitably, the bottom fraction is introduced at the top of the rectifier, and the desorbed 1 ,3-butadiene stream obtained from the desorbing step, e.g. obtained at the top of the degasser as described below, is introduced at the bottom of the rectifier. Before introducing the desorbed 1 ,3-butadiene stream at the bottom of the rectifier, the desorbed 1 ,3-butadiene stream may be compressed.

[0059] A partial stream of the desorbed 1,3-butadiene stream is taken off as side offtake stream from the rectifier column. The stream may comprise 1,3-butadiene together with the co-absorbed constituents for which the selective solvent has a similar or higher affinity than for 1,3-butadiene, such as C4-acetylenes, 1 ,2-butadiene, propyne.

[0060] Preferably, the process further comprises scrubbing at least a portion of the desorbed 1,3-butadiene stream with lean selective solvent to remove C4-acetylenes therefrom to obtain crude 1,3-butadiene. This step may be carried out in a scrubbing extractive distillation column. Suitably, this step comprises introducing the desorbed 1,3-butadiene stream, e.g. withdrawn from the rectifier as described above, preferably withdrawn via a sidedraw from the rectifier, into the bottom of the scrubbing extractive distillation column, and bringing the desorbed 1,3-240966W001 8

[0061] butadiene stream into countercurrent with the lean selective solvent, which is preferably introduced at the top of the scrubbing extractive distillation column. Crude 1 ,3-butadiene is obtained at the top of the scrubbing extractive distillation column. A liquid stream comprising C4-acetylenes dissolved in the selective solvent is obtained at the bottom of the scrubbing extractive distillation column. The scrubbing extractive distillation column is suitably operated at a temperature at the top of from 20 to 80 °C, preferably 40 to 60 °C, and at a pressure of from 1.5 to 10 bara, preferably 4 to 6 bara.

[0062] The scrubbing extractive distillation column can be formed by a separate column, e.g. a side column assigned to the rectifier column. Alternatively, the scrubbing extractive distillation column may be formed by an upper section of the rectifier column separated off by a dividing wall which runs essentially in the longitudinal direction of the column. In an upper region of the rectifier column, a dividing wall is then arranged in the longitudinal direction of the column to form a first upper section serving for extraction, a second upper section forming the scrubbing extractive distillation column and a third section which adjoins the dividing wall at the bottom. The dividing wall is preferably arranged non-centrally in such a way that the cross-sectional area of the scrubbing extractive distillation column is smaller than the cross-sectional area of the extraction zone.

[0063] The liquid stream comprising C4-acetylenes is preferably directed back to the rectifier or else conveyed into the degasser.

[0064] The prestripped selective solvent obtained in the bottoms from the rectifier column stream is directed into the degasser column. In the degasser 1,3-butadiene, 1,2 butadiene, C4-acetylenes such as methylacetylene and C5+-hydrocarbons are desorbed.

[0065] Preferably, the process further comprises taking off the gas comprising mostly C4-acetylenes as a sidedraw from the degasser column. For example, the gas comprising mostly C4-acetylenes which is taken off as sidedraw stream from the degasser column can be scrubbed with water in an acetylene scrubber (hereinafter also referred to as "acetylene washer”) in order to recover the selective solvent. The acetylene scrubber can be configured as side column of the degasser column. The scrubbing water can be recycled to the selective solvent circuit, e.g. into the degasser column and / or the rectifier column. Water vapor which is entrained by the scrubbed gas comprising C4-acetylenes can be condensed out and recirculated in its entirety or partly to the acetylene scrubber. The obtained C4-acetylenes may, e.g., be hydrated or recirculated to a cracker.

[0066] Step c)

[0067] Step c) involves withdrawing from the extractive distillation column at least a portion of a liquid phase underneath the supply of the lean selective solvent and phase-separating the withdrawn liquid phase into a heavy liquid phase comprising selective solvent saturated with dissolved butanes and butenes, and a light liquid phase comprising butanes and butenes.240966W001 9

[0068] The liquid phase is withdrawn from the extractive distillation column underneath the supply of the lean selective solvent. In this context, the term "underneath” denotes a position close below the supply of the lean selective solvent. For example, the liquid phase is collected via a collecting tray below the supply of the lean selective solvent. The liquid may be directed from the collecting tray to a collecting channel or receiver (downcomer) that may be formed integrally with the collecting tray. From the collecting channel or receiver, the liquid can conveniently be withdrawn, e.g. by means of a pump.

[0069] In order to fully exploit contact area between rising vapors and trickling solvent provided by column internals, the liquid phase is suitably withdrawn above such column internals such as packings.

[0070] By withdrawing liquid phase to be phase-separated underneath the supply of the lean selective solvent, it is ensured that the second liquid phase, if present in the extractive distillation column, is removed from the extractive distillation column and directed to phase-separation, e.g. in a decanter.

[0071] The withdrawn liquid phase is phase-separated. The term "phase separation” refers to a process during which an unstable liquid system separates into separate and distinct phases, e.g., the migration of a light liquid phase to the top under the influence of buoyancy. Phase separation is accomplished by a non-mechanical process or a mechanical process. A non-mechanical phase separation refers to a passive physical process in which the phases separate via specific density separation due to the force of gravity. A mechanical phase separation refers to a process in which phases separate due to additionally or alternatively using a man-made force such, as a centripetal force, caused by a centrifuge. Preferably, phase separation is accomplished by settling in a decanter. For this purpose, the withdrawn liquid phase is suitably directed and introduced into a decanter.

[0072] Step d)

[0073] Step d) involves returning the heavy liquid phase to the extractive distillation column underneath a position from which the liquid phase is withdrawn, thermally separating the light liquid phase into a volatile fraction and a less volatile fraction both the volatile fraction and the less volatile fraction comprising selective solvent, butanes and butenes, wherein the mass fraction of selective solvent in the volatile fraction is lower than the mass fraction of selective solvent in the less volatile fraction.

[0074] The heavy liquid phase mostly contains selective solvent saturated with dissolved butanes and butenes. The heavy liquid phase is a valuable stream and should therefore be reintroduced into the extractive distillation column in order to avoid loss of both butanes and butenes, and selective solvent.

[0075] The heavy liquid phase is returned to the extractive distillation column underneath the position from which the liquid phase is withdrawn. In this context, the term "underneath” denotes a position close below the position240966W001 10

[0076] from which the liquid phase is withdrawn. Preferably, the heavy liquid phase is returned directly below the position from which the liquid phase is withdrawn, e.g., onto the subsequent tray or a liquid distributor or packing of the extractive distillation column below the position, e.g. from the tray, from which the liquid phase is withdrawn.

[0077] The light liquid phase typically comprises butanes and butenes, and traces of the selective solvent. The light liquid phase is a valuable stream and should therefore be reintroduced to the process in order to avoid loss of both valuable product (butenes) and the selective solvent. However, it is not advisable to direct the light liquid phase to downstream process steps to avoid unwanted contamination of the butadiene product. Furthermore, directly returning the light liquid phase back to the extractive distillation column would disadvantageously result in the formation of a second liquid phase in the extractive distillation column which is to be avoided as described above.

[0078] Therefore, according to the invention, the light liquid phase is thermally separated into a volatile fraction and a less volatile fraction. The term "thermally separating” (also referred to as "thermal separation”) denotes any process step which allows for a separation of the light liquid phase by exploiting the different volatilities or boiling points of its components. For example, thermal separation may involve evaporation such as flash evaporation (also referred to as "flashing” hereinafter) and / or distillation.

[0079] The step of thermal separation aims at providing a volatile fraction having a mass fraction of selective solvent which is lower than the mass fraction of selective solvent in the less volatile fraction, preferably a volatile fraction which is essentially free of the selective solvent, i.e. which essentially comprises butanes and butenes. Such a volatile fraction can then be returned to the extractive distillation column at an appropriate position. The less volatile fraction contains, besides the selective solvent, butanes and butenes, and can also be returned to the extractive distillation column at an appropriate position.

[0080] In an embodiment, thermally separating comprises heating the light liquid phase and flashing the heated light liquid phase into a vessel.

[0081] Heating the light liquid phase may comprise heat-exchanging the light liquid phase with hot lean selective solvent. This advantageously allows for providing the heat input needed for heating the light liquid phase by the (hot) selective solvent and makes this process step devoid of supplying any external heat input. Supplying external heat input would disadvantageously deteriorate the process economy.

[0082] The heated light liquid phase may have a temperature in the range of from 20 to 230 °C, preferably 50 to 180 °C, and a pressure in the range of from 1.6 to 100 bara, preferably 4.1 to 15 bara.240966W001 11

[0083] The thus heated light liquid phase is introduced into a vessel and flashed, i.e. at least partially evaporated. Suitable vessels for carrying out an evaporation step are known by the skilled person.

[0084] The heated light liquid phase may be flashed to a pressure in the range of from 1.6 to 99 bara, preferably 4.1 to 6.1 bara, at a temperature in the range of from 20 to 220 °C, preferably 30 to 80 °C.

[0085] In another embodiment, thermally separating comprises distilling the light liquid phase in a distillation column. Distilling the light liquid phase allows to even further reduce the concentration of selective solvent in the volatile fraction, compared to the step of heating and flashing.

[0086] The volatile fraction is obtained as an overhead of the distillation column, and the less volatile fraction is obtained at the bottom of the distillation column.

[0087] Distillation may be carried out at a temperature in the range of from 20 to 220 °C, preferably 30 to 80 °C, and a pressure in the range of from 1.6 to 99 bara, preferably 4.1 to 6.1 bara.

[0088] While the thermal energy supplied to the distillation column may be from any suitable source, it may be advantageous to exploit intrinsic energy sources of the process. In an embodiment, the process further comprises heat-exchanging the bottoms of the distillation column with hot lean selective solvent. This allows for providing thermal energy to the distillation column via a bottoms circuit. Means for carrying out such a heatexchange step such as heat-exchangers are well known by the skilled person.

[0089] Another part of the less volatile fraction, e.g. the remainder of the less volatile fraction not introduced into the bottoms circuit, may be returned to the extractive distillation column, as described in detail in step e) below.

[0090] Besides the distillation column, a cascade of heat-exchangers and vessels can be used to further reduce the concentration of selective solvent in the volatile fraction.

[0091] Step e)

[0092] Step e) involves returning the less volatile fraction to the extractive distillation column underneath the position from which the liquid phase is withdrawn, and returning the volatile fraction above the supply of the lean selective solvent and / or into a condenser circuit of the extractive distillation column.

[0093] The less volatile fraction is returned to the extractive distillation column underneath the position from which the liquid phase is withdrawn. In this context, the term "underneath” denotes a position close below the position from which the liquid phase is withdrawn. Preferably, the less volatile fraction is returned directly below the position from which the liquid phase is withdrawn, e.g., onto the subsequent tray or packing of the extractive240966W001 12

[0094] distillation column below the position, e.g. from the tray, from which the liquid phase is withdrawn. For example, the less volatile fraction is returned to the extractive distillation column onto the same tray or packing as the heavy liquid phase.

[0095] The volatile fraction may be returned above the supply of the lean selective solvent. Preferably, the volatile fraction is returned directly above the supply of the selective solvent, e.g., onto the subsequent tray or packing of the extractive distillation column above the supply of the selective solvent. The lower the concentration of selective solvent in the volatile fraction, the higher the position may be at which the volatile fraction can be returned into the extractive distillation column.

[0096] Suitably, if thermal separation involves heating the light liquid phase and flashing the heated light liquid phase into a vessel, the volatile fraction is returned above the supply of the lean selective solvent.

[0097] Additionally or alternatively, the volatile fraction may be returned into a condenser circuit of the extractive distillation column.

[0098] Suitably, if thermal separation involves distillation of the light liquid phase, the volatile fraction is returned into the condenser circuit of the extractive distillation column.

[0099] In an embodiment, the process further comprises at least partially condensing the volatile fraction and returning the condensed fraction at least partially as a reflux to the distillation column. This may involve at least partially condensing the volatile fraction in a condenser circuit of the distillation column.

[0100] The extractive distillation column and the distillation column may utilize a common condenser circuit. In this case, a part of the volatile fraction may be at least partially condensed, e.g. in a condenser. A part of the condensed stream may be returned to an upper section of the distillation column as a reflux. Another part of the condensed stream, e.g. the remainder of the condensed stream, may be recycled to the extractive distillation column. In other words, in this embodiment, the overhead vapors are returned as a reflux to the distillation column and / or extractive distillation column.

[0101] Downstream process

[0102] For obtaining pure 1 ,3-butadiene that meets specific specifications from the crude 1 ,3-butadiene stream, further process steps may be necessary.

[0103] At least part of the crude 1 ,3-butadiene is fed to one or more distillative purification steps. Purification by distillation of the crude 1 ,3-butadiene may be carried out in one distillative purification column or preferably by240966W001 13

[0104] a sequence of distillative purification columns, preferably in a low boiler removal distillation column, followed by a high boiler removal distillation column.

[0105] Thus, in an embodiment, the process further comprises subjecting the crude 1 ,3-butadiene to low boiler removal to obtain a propyne-containing stream and a low boiler-depleted stream. The step of low boiler removal is suitably carried out in a low boiler removal distillation column. Typically, the propyne-containing stream is obtained at the low boiler removal distillation column top, and the low boiler-depleted stream is obtained at the low boiler removal distillation column bottom.

[0106] The process may further comprise subjecting the low boiler-depleted stream to high boiler removal to obtain 1 ,3-butadiene and a 1 ,2-butadiene-rich stream. The step of high boiler removal is suitably carried out in a high boiler removal distillation column. Typically, the 1 ,3-butadiene is obtained at the high boiler removal distillation column top, and the 1 ,2-butadiene-rich stream is obtained at the high boiler removal distillation column bottom.

[0107] The distillative purification column(s), i.e. the low boiler removal distillation column and / or the high boiler removal distillation column, can, for example, be operated at a temperature at the bottom of from 20 to 80 °C, preferably 40 to 60 °C, and at a pressure from 1.5 to 10 bara, preferably 4 to 6 bara.

[0108] The invention is further illustrated by the accompanying drawings and the following example.

[0109] Fig. 1 depicts an extractive distillation process for recovering 1 ,3-butadiene from a effraction known from the prior art.

[0110] Figs. 2 and 3 depict an extractive distillation process for recovering 1 ,3-butadiene from a Cffraction according to the invention.

[0111] Fig. 4 depicts an overall process for recovering 1 ,3-butadiene from a effraction, not including steps c) to e).

[0112] Fig. 1 depicts a known process for recovering 1 ,3-butadiene from a Cffraction comprising butanes, butenes, and 1 ,3-butadiene, by extractive distillation using a selective solvent. For this purpose, a lean selective solvent 1 is supplied to an upper section of an extractive distillation column 101 above a packing 107 and below a packing 108. The gaseous Cffraction 2 is supplied to a lower section of the extractive distillation column 101 below the packing 107. The gaseous Cffraction 2 is brought into contact with the lean selective solvent 1 in the extractive distillation column 101 in countercurrent. Overhead vapors 3 are passed through condenser circuit 104 and may at least partially be condensed using condenser 110. A condensed overhead fraction 3 comprising butanes and butenes (known as raffinate 1) is thus obtained. The remainder of the condensed overhead vapors may partly be recycled to the extractive distillation column 101 above the packing 108 as a reflux. A bottom fraction 4 is obtained at the bottom of the extractive distillation column 101. The bottom fraction 4 essentially240966W001 14

[0113] consists of the selective solvent in which the remainder of the effraction (I . e. , the constituents of the effraction not recovered in the overhead fraction 3) is dissolved.

[0114] 1 ,3-Butadiene and the co-absorbed constituents are desorbed from the bottom fraction 4 in at least one stripping column (not shown). The lean selective solvent 1 obtained is recirculated to the extractive distillation column 101. The temperature of the lean selective solvent 1 is adjusted using cooler 109. A gaseous downstream C4-fraction 11 from downstream processes, e.g. a stream comprising desorbed butanes and butenes, is recycled to the lower section of the extractive distillation column 101 below the packing 107.

[0115] Fig. 2 depicts an inventive process for recovering 1 ,3-butadiene from a Cffraction comprising butanes, butenes, and 1 ,3-butadiene, by extractive distillation using a selective solvent. For this purpose, a lean selective solvent 1 is supplied via supply 102 to an upper section of an extractive distillation column 101 on a tray 111. The tray 111 is located above a packing 107 and below a packing 108 of the extractive distillation column 101. The gaseous Cffraction 2 is supplied to a lower section of the extractive distillation column 101 below the packing 107. The gaseous Cffraction 2 is brought into contact with the lean selective solvent 1 in the extractive distillation column 101 in countercurrent.

[0116] Overhead vapors 3 are passed through condenser circuit 104 and may at least partially be condensed using condenser 110. A condensed overhead fraction 3 comprising butanes and butenes (known as raffinate 1) is thus obtained. The remainder of the condensed overhead vapors may partly be recycled to the extractive distillation column 101 above the packing 108 as a reflux. A bottom fraction 4 is obtained at the bottom of the extractive distillation column 101. The bottom fraction 4 essentially consists of 1,3-butadiene, besides the remainder of the Cffraction (I ,e. , the constituents of the Cffraction not recovered in the overhead fraction 3) is dissolved in the selective solvent.

[0117] 1 ,3-Butadiene and the co-absorbed constituents are desorbed from the bottom fraction 4 in at least one stripping column (not shown). The lean selective solvent 1 obtained is recirculated to the extractive distillation column 101. A gaseous downstream effraction 11 from downstream processes, e.g. a stream comprising desorbed butanes and butenes, is recycled to the lower section of the extractive distillation column 101 below the packing 107.

[0118] A portion of a liquid phase 5 is withdrawn from the extractive distillation column 101 at position 103. Position 103 is located at the tray 111 and underneath the supply 102 of the lean selective solvent 1. The withdrawn liquid phase 5 is phase-separated into a heavy liquid phase 6 and a light liquid phase 7 in a decanter 112. The heavy liquid phase 6 comprises selective solvent saturated with dissolved butanes and butenes. The light liquid phase 7 comprises butanes and butenes.240966W001 15

[0119] The heavy liquid phase 6 is returned to the extractive distillation column 101 underneath the position 103 from which the liquid phase 5 is withdrawn.

[0120] The light liquid phase 7 is thermally separated. Thermally separating comprises heating the light liquid phase 7 by heat-exchanging with the lean selective solvent 1 using reboiler 113 to obtain the heated light liquid phase 7H. The temperature of the lean selective solvent 1 after the heat-exchange can be further adjusted using cooler 109.

[0121] Thermally separating further comprises flashing the heated light liquid phase 7H into a vessel 105 to obtain a volatile fraction 8 and a less volatile fraction 9. Both the volatile fraction 8 and the less volatile fraction 9 comprise selective solvent, butanes and butenes. The mass fraction of selective solvent in the volatile fraction 8 is lower than the mass fraction of selective solvent in the less volatile fraction 9.

[0122] The less volatile fraction 9 is returned to the extractive distillation column 101 underneath the position 103 from which the liquid phase 5 is withdrawn, above the packing 107. The volatile fraction 8 is returned above the supply 102 of the lean selective solvent 1 at the packing 108.

[0123] Fig. 3 depicts an inventive process similar to the process shown in Fig. 2, with the following differences:

[0124] Thermally separating the light liquid phase 7 comprises distilling it in a distillation column 106.

[0125] Thermal energy is provided to the distillation column 106 via a bottoms circuit of a least a part of the less volatile fraction 9 in the reboiler 113, which is heated by the hot lean selective solvent 1. Another part of the less volatile fraction 9 is returned to the extractive distillation column 101 as described above (see Fig. 2).

[0126] The volatile fraction 8 taken off from the top of the distillation column 106 is guided into the condenser circuit 104 of the extractive distillation column 101. In the process of Fig. 2, the extractive distillation column 101 and the distillation column 106 have a common condenser circuit 104. A part of the volatile fraction 8 is partially condensed in condenser 110. A part of the condensed stream (condensed fraction 10) is returned to an upper section of the distillation column 106 as a reflux. Another part of the condensed stream (condensed overhead vapors 3) is recycled to the extractive distillation column 101 above the packing 108 as a reflux as described above (see Fig. 2).

[0127] Fig. 4 depicts an overall process for recovering 1,3-butadiene from a effraction. A process according to the invention is obtained by implementing the features of Fig. 2 or Fig. 3 into the process of Fig. 4.

[0128] A lean selective solvent 1 is supplied to an upper section of an extractive distillation column 101. A gaseous C4-fraction 2 is supplied to a lower section of the extractive distillation column 101 and brought into contact with240966W001 16

[0129] the lean selective solvent 1. An overhead fraction 3 comprising butanes and butenes is obtained at the top of the extractive distillation column 101. A bottom fraction 4 comprising 1,3-butadiene dissolved in the selective solvent is obtained at the bottom of the extractive distillation column 101.

[0130] Co-absorbed butanes and butenes are desorbed from the bottom fraction 4 in a rectifier 201. A stream comprising desorbed butanes and butenes 11 is obtained at the top of the rectifier and directed to the lower section the extractive distillation column 101. A partially desorbed bottom fraction 23a still comprising 1,3-butadiene and C4-acetylenes leaves the rectifier at the bottom.

[0131] In a degasser 202, 1,3-butadiene, and co-absorbed constituents such as C4-acetylenes, are desorbed from the partially desorbed bottom fraction 23a. A desorbed 1,3-butadiene stream 21a at least comprising 1,3-butadiene and C4-acetylenes is obtained at the top of the degasser 202. The lean selective solvent 1 is obtained at the bottom of the degasser and recirculated to the extractive distillation column 101.

[0132] The desorbed 1,3-butadiene stream 21a taken off at the top of the degasser 202 is introduced into the lower section of the rectifier 201 and brought into countercurrent contact with the bottom fraction 4 in the lower section of the rectifier 201. A desorbed 1,3-butadiene stream 21b is withdrawn via a sidedraw of the rectifier 201 and introduced into a lower section of a scrubbing extractive distillation column 204. Lean selective solvent 1 is supplied to the upper section of the scrubbing extractive distillation column 204. The desorbed 1,3-butadiene stream 21b is scrubbed with the lean selective solvent 1. C4-acetylenes are removed from the desorbed 1,3-butadiene stream 21b in the scrubbing extractive distillation column 204. Crude 1,3-butadiene 22 is obtained at the top of the scrubbing extractive distillation column 204. A stream 23b comprising C4-acetylenes (and 1,3-butadiene) dissolved in selective solvent is obtained at the bottom of the scrubbing extractive distillation column 204.

[0133] The stream 23b comprising C4-acetylenes (and 1,3-butadiene) is introduced into the rectifier 201.

[0134] A C4-acetylene-rich stream is obtained at the top of an acetylene washer 203.

[0135] The crude 1,3-butadiene 22 is subjected to low boiler removal in a low boiler removal distillation column 205. A propyne-containing stream 25 is obtained at the top of the low boiler removal distillation column 205. A low boiler-depleted stream 26 is obtained at the bottom of the low boiler removal distillation column 205.

[0136] The low boiler-depleted stream 26 is subjected to high boiler removal in a high boiler removal distillation column 206. Valuable product 1,3-butadiene is obtained as stream 27 at the top of the high boiler removal distillation column 206. A 1,2-butadiene-rich stream 28 is obtained at the bottom of the high boiler removal distillation column 206.240966W001 17

[0137] Examples

[0138] For simulation calculations, BASF in-house software Chemasim was used; comparable results were obtained using commercially available software such as Aspen Plus (manufacturer: AspenTech, Burlington / Massachusetts, USA) or PRO II (Fullerton, USA). The set of parameters was based on comprehensive measurements, studies on laboratory set-ups and operating data from various plants.

[0139] All pressures indicated herein are absolute pressures, unless noted otherwise.

[0140] Four comparative and inventive processes for recovering 1 ,3-butadiene from a Cffraction by extractive distillation using a selective solvent were simulated. The composition of the Cffraction used in the simulations is shown in Table 1.

[0141] Table 1: Composition of the effraction.

[0142]

[0143] For simulations 1 to 4, the following assumptions were made:

[0144] - top pressure of the extractive distillation column: 4.8 bara.

[0145] - concentration of 1 ,3-butadiene in overhead fraction 3 (raffinate 1): 0.2 wt.-%

[0146] - purity of 1 ,3-butadiene in the butadiene product: 99.7 wt.-%

[0147] - selective solvent: aqueous NMP (91.7 wt.-% NMP)240966W001 18

[0148] - steam demand referred to in Table 2 = steam having a temperature of 198.6 °C and a pressure of 13.6 bara supplied to the reboiler of the degasser.

[0149] Simulations 1 to 4 as described in detail below were carried out, wherein the following operational parameters were altered as described in detail below:

[0150] - mass flow ratio of lean selective solvent to effraction (to the extractive distillation column)

[0151] - reflux ratio of the extractive distillation column

[0152] - temperature of the lean selective solvent entering the extractive distillation column

[0153] Simulation 1 (comparative) refers to the overall process for recovering 1,3-butadiene from a Cffraction by extractive distillation using a selective solvent as shown in Fig. 4 with the setup as shown in Fig. 1. In simulation 1, the operational parameters were adjusted such that the maximum butanes and butenes concentration in the extractive distillation column was 95% of the critical concentration that would lead to a liquid-liquid separation in the extractive distillation. Thus, in simulation 1, no liquid-liquid separation occurs in the extractive distillation column, i.e. a second liquid phase is not formed in the extractive distillation column.

[0154] Simulation 2 (comparative) refers to the overall process for recovering 1,3-butadiene from a Cffraction by extractive distillation using a selective solvent as shown in Fig. 4. In simulation 2, the operational parameters were adjusted such that the separation efficiency in the extractive distillation column is reduced by 95% due to liquid-liquid separation occurring in the extractive distillation column. In other words, in simulation 2, liquid-liquid separation occurs in the extractive distillation column, i.e. a second liquid phase is formed in the extractive distillation column.

[0155] Simulation 3 (inventive) refers to the overall process for recovering 1,3-butadiene from a Cffraction by extractive distillation using a selective solvent as shown in Fig. 4 having implemented the setup as shown in Fig. 2.

[0156] Simulation 4 (inventive) refers to the overall process for recovering 1,3-butadiene from a Cffraction by extractive distillation using a selective solvent as shown in Fig. 4 having implemented the setup as shown in Fig. 3.

[0157] The results of simulations 1 to 4 are shown in Table 2.240966W001 19

[0158] Table 2: Simulation results.

[0159]

[0160] [1] Simulation according to Fig. 4 without liquid-liquid separation in the extractive distillation column

[0161] [2] Simulation according to Fig. 4 with liquid-liquid separation in the extractive distillation column

[0162] [3] Simulation according to Fig. 4 + Fig. 2

[0163] [4] Simulation according to Fig. 4 + Fig. 3

[0164] ‘comparative example

[0165] It can be seen from the results shown in Table 2 that the yields of 1 ,3-butadiene and of butanes / butenes are identical in all simulations 1 to 4. The steam demand and thus, the costs for providing steam and potential carbon emissions are reduced for the inventive simulations 3 and 4 in contrast to comparative simulations 1 and 2 by about 4.5 to 5%. The steam demand presented in T able 2 is the only source of thermal energy provided to the process. Other heat exchangers are fully heat-integrated, i.e. heated by either the hot lean selective solvent heated up by said steam, or by a condensate thereof.

[0166] List of reference signs

[0167] 1 lean selective solvent

[0168] 2 gaseous effraction

[0169] 3 overhead fraction

[0170] 4 bottom fraction

[0171] 5 liquid phase

[0172] 6 heavy liquid phase

[0173] 7 light liquid phase

[0174] 7H heated light liquid phase

[0175] 8 volatile fraction

[0176] 9 less volatile fraction

[0177] 10 condensed fraction

[0178] 11 stream comprising desorbed butanes and butenes240966W001 20

[0179] 21 desorbed 1 ,3-butadiene stream

[0180] 22 crude 1 ,3-butadiene

[0181] 23 stream comprising 1 ,3-butadiene and C4-acetylenes

[0182] 24 C4-acetylene-rich stream

[0183] 25 propyne-containing stream

[0184] 26 low boiler-depleted stream

[0185] 27 1,3-butadiene

[0186] 28 1,2-butadiene-rich stream

[0187] 101 extractive distillation column

[0188] 102 supply (of the lean selective solvent)

[0189] 103 position (from which the liquid phase is withdrawn from the extractive distillation column) 104 condenser circuit

[0190] 105 vessel

[0191] 106 distillation column

[0192] 107 packing

[0193] 108 packing

[0194] 109 cooler

[0195] 110 condenser

[0196] 111 tray

[0197] 112 decanter

[0198] 113 reboiler

[0199] 201 rectifier

[0200] 202 degasser

[0201] 203 acetylene washer

[0202] 204 scrubbing extractive distillation column

[0203] 205 low boiler removal distillation column

[0204] 206 high boiler removal distillation column

Claims

240966W001 21Claims1. A process for recovering 1 ,3-butadiene from a effraction comprising butanes, butenes, and1 ,3-butadiene, by extractive distillation using a selective solvent, the process comprising:a) supplying a lean selective solvent (1) to an upper section of an extractive distillation column (101) and bringing the gaseous effraction (2) into contact with the lean selective solvent (1) in the extractive distillation column (101), to obtain an overhead fraction (3) comprising butanes and butenes, and a bottom fraction (4) comprising 1 ,3-butadiene dissolved in the selective solvent, b) desorbing 1 ,3-butadiene, and, optionally, co-absorbed constituents, from the bottom fraction (4), to obtain at least a desorbed 1 ,3-butadiene stream (20a, 20b) and the lean selective solvent (1) and recirculating the lean selective solvent (1) to the extractive distillation column (101),c) withdrawing from the extractive distillation column (101) at least a portion of a liquid phase (5) underneath the supply (102) of the lean selective solvent (1) and phase-separating the withdrawn liquid phase (5) into a heavy liquid phase (6) comprising selective solvent saturated with dissolved butanes and butenes, and a light liquid phase (7) comprising butanes and butenes,d) returning the heavy liquid phase (6) to the extractive distillation column (101) underneath a position (103) from which the liquid phase (5) is withdrawn, thermally separating the light liquid phase (7) into a volatile fraction (8) and a less volatile fraction (9), both the volatile fraction (8) and the less volatile fraction (9) comprising selective solvent, butanes and butenes, wherein the mass fraction of selective solvent in the volatile fraction (8) is lower than the mass fraction of selective solvent in the less volatile fraction (9), ande) returning the less volatile fraction (9) underneath the position (103) from which the liquid phase (5) is withdrawn, and returning the volatile fraction (8) above the supply (102) of the lean selective solvent (1) and / or into a condenser circuit (104) of the extractive distillation column (101).

2. The process according to claim 1, wherein thermally separating comprises heating the light liquid phase (7) and flashing the heated light liquid phase (7H) into a vessel (105).

3. The process according to claim 2, wherein heating the light liquid phase (7) comprises heat-exchanging the light liquid phase (7) with hot lean selective solvent (1).

4. The process according to claim 1, wherein thermally separating comprises distilling the light liquid phase (7) in a distillation column (106).

5. The process according to claim 4, comprising heat-exchanging the bottoms of the distillation column (106) with hot lean selective solvent (1).240966W001 226. The process according to claim 4 or 5, comprising at least partially condensing the volatile fraction (8) and returning the condensed fraction (10) at least partially as a reflux to the distillation column (106).

7. The process according to any one of the preceding claims, comprising, prior to step b), desorbing coabsorbed butanes and butenes from the bottom fraction (4) to obtain a stream comprising desorbed butanes and butenes (11), and directing the stream comprising desorbed butanes and butenes to the extractive distillation column (101).

8. The process according to any one of the preceding claims, comprising bringing at least a portion of the desorbed 1 ,3-butadiene stream (20a) into countercurrent contact with the bottom fraction (4).

9. The process according to any one of the preceding claims, comprising scrubbing at least a portion of the desorbed 1 ,3-butadiene stream (20b) with lean selective solvent (1) to remove C4-acetylenes therefrom to obtain crude 1 ,3-butadiene (22).

10. The process according to claim 9, comprising subjecting the crude 1 ,3-butadiene (22) to low boiler removal to obtain a propyne-containing stream (25) and a low boiler-depleted stream (26).

11. The process according to claim 10, comprising subjecting the low boiler-depleted stream (26) to high boiler removal to obtain 1 ,3-butadiene (27) and a 1,2-butadiene-rich stream (28).

12. The process according to any one of the preceding claims, wherein the lean selective solvent comprises at least 80 wt.-% of N-methylpyrrolidone.

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