Method for separating a c4 hydrocarbon mixture

Description

The subject of the invention is a process of a four-carbon hydrocarbon mixture (C4 hydrocarbon mixture) containing 1,3-butadiene, butenes, butanes and other four-carbon hydrocarbons with N-methyl-2-pyrrolidinone or an aqueous solution of N-methyl-2-pyrrolidinone (NMP), with extractive distillation for at least four fractions a) from fraction (a) 1,3-butadiene, b) fraction (b) from butenes, c) fraction (c) from butanes, and d) for the separation of one or more fractions (d) consisting of 1,3-butadiene and other four-carbon hydrocarbons, in which process 1. the gaseous C4 hydrocarbon mixture is first brought into contact with NMP in the extraction zone (El), where the mass ratio of the NMP / C4 hydrocarbon mixture is between 5:1 and 20:1, and 1,3-butadiene and other four-carbon hydrocarbons it is completely absorbed by NMP, while butanes and butanes remain in the gas phase; 2. the non-absorbed butenes and butanes [(Gbc) gas stream] and the extraction solution formed in step 1 [(Ead) extraction solution] are removed separately from the (El) extraction zone; 3. the extraction solution (Ead) is transferred to the desorption zone (Dl) with a pressure of 2-6 bar compared to the extraction zone (El) and / or a temperature 20-25 °C higher than the extraction zone (El), and in this ( Ead) 1,3-butadiene is desorbed from the extraction solution, while most of the other four-carbon hydrocarbons remain in the liquid phase; 4. the extraction solution obtained in step 3 [(Ed) extraction solution] and the desorbed 1,3-butadiene [(Fa) fraction] are separately removed from the (Dl) desorption zone, and if applicable, a part of the (Fa) fraction is (El) we lead back to the extraction zone; 5. the extraction solution (Ed) is transferred to the second desorption zone (Dll) with reduced pressure and / or higher temperature compared to the desorption zone (Dl) with a pressure and / or temperature gradient, and in this extraction solution (Ed) there is still 1, 3-butadiene and other four-carbon hydrocarbons are desorbed by fractionation as at least two separate (Fd) fractions, while in at least one of the fractions [(Fd) fractions] the proportion of other four-carbon hydrocarbons, based on the proportion of all four-carbon hydrocarbons, is at least ten times higher, as in the (Ed) extraction solution, and in at least one of the fractions [(FdR) fractions] the proportion of other four-carbon hydrocarbons, based on the proportion of total four-carbon hydrocarbons, is correspondingly lower than in the (Fd) fractions; 6. the NMP obtained in the (Dll) desorption zone, which is essentially free of four-carbon hydrocarbons, and the (Fd) and (FdR) fractions are removed separately from the (Dll) desorption zone, and one or more (FdR) fractions are removed from the (Dl) ) we return to the desorption zone; 7. the (Gbc) gas stream was first obtained in step 6 It is brought into contact with NMP in an extraction zone (Eli), where the butenes are completely absorbed by the NMP and the butanes remain in the gas phase; 8. the non-absorbed butanes [fraction (Fc)] and the extraction solution obtained in step 1 [extraction solution (Eb)] are removed from the extraction zone (Eli); 9. the extraction solution (Eb) is transferred to the desorption zone (Dili) with reduced pressure and / or higher temperature compared to the extraction zone (Eli), and in this the butenes are desorbed from the extraction solution (Eb); 10. the NMP formed in step 9, which is free of four-carbon hydrocarbons, and the desorbed butenes [(Fb) fraction] are removed from the (Dili) desorption zone; 11. the NMP formed in step 9 is returned to one of the extraction zones (El) and (Eli); 12. a part of the 1,3-butadiene fraction (a) removed from the desorption zone (Dl) is returned to the extraction zone (El) [(Fal) fraction], and the other part [(Fa2) fraction] in an (EliI) extraction zone It is brought back into contact with the NMP recovered in step 6, where the NMP / (Fa2) crude butadiene fraction mass ratio is between 1:3 and 1:7, and a part of the (Fa2) fraction and the majority of the other four-carbon hydrocarbons, which are still They are present as impurities in fraction (Fa2), absorbed by NMP [(Eax) extraction solution]; and 13. the unabsorbed part of the fraction (Fa2) [fraction (Fa3)] leaves the extraction zone, and the extraction solution (Eax) is returned to the extraction zone (El). The procedure is schematically illustrated in Figure 1. A process for separating 1,3-butadiene from a C4 hydrocarbon mixture is known, for example, from DE-A-2,724,365. In this process, it is briefly described that from a C4 hydrocarbon mixture, which contains butanes, butenes, It contains 1,3-butadiene and other four-carbon hydrocarbons, by means of extractive distillation, using NMP as an absorption agent, through various absorption and desorption steps, a butane-butene mixture fraction, a 1,3-butadiene fraction and a fraction containing four consists of a conventional mixture of hydrocarbons with carbon atoms. The required amount of NMP goes through a closed circuit within the framework of the entire procedure. The NMP, which no longer contains four-carbon hydrocarbons (uncharged NMP), is then loaded with the C4 hydrocarbon mixture at the beginning of a cycle, run through various absorption and desorption steps until, by the end of a cycle, uncharged NMP is obtained, from which the four carbon hydrocarbons were completely desorbed. The method is distinguished by the fact that the individual steps are particularly advantageously connected to indirect heat exchange processes. 1,3-butadiene and 2-butenes and 1,3-butadiene and acetylenes separately from C4 hydrocarbon mixtures2 HU 225 347 The separation of Β1 into stationary fractions is described by V. A. Gorshkov et al. in "The Soviet Chemical Industry", No. 11, November 1971. The subject of patent document No. EP-A-141,356 is also a process for separating a 1,3-butadiene fraction from a C4 hydrocarbon mixture by means of extractive distillation using NMP. The process is made particularly economical by the use of columns in which the absorption and desorption zones are integrated into a single column. A process for separating a 1,3-butadiene and a butyne fraction from a C4 hydrocarbon mixture by extractive distillation using NMP is known from patent document No. EP-A-5788. The subject of patent document No. EP-A-9630 is a process for the batch separation of styrene and 1,3-butadiene from a mixture that otherwise contains four-carbon hydrocarbons, where styrene is separated from the mixture by distillation, and 1,3-butadiene from the remaining mixture it is separated by extractive distillation. US-5,242,550 describes the separation of a butene-butane mixture by extractive distillation using MNP as an absorption material. The task of the invention was to develop a process with which the separation of a C4 hydrocarbon mixture into the fraction of butanes, butenes and 1,3-butadiene, as well as into a fraction containing other four-carbon hydrocarbons, is particularly efficient and economically possible. In this process, the energy used and the investment costs are particularly low. Accordingly, we found the procedure described in the introduction. The method is applicable to C4 hydrocarbon mixtures containing 1,3-butadiene, butenes, butanes and other C4 hydrocarbons, as well as minor C3 and C5 hydrocarbon impurities. Such C4 hydrocarbon mixtures are, for example, obtained as C4 fractions during the production of ethylene and / or propylene by thermal decomposition of a petroleum fraction, such as liquefied petroleum gas (LPG), light gasoline (naphtha), diesel or the like. Furthermore, such C4 fractions are obtained in the catalytic dehydrogenation of butane and / or butene. The C4 fractions usually contain butanes, butene, isobutene, 1,3-butadiene, vinyl acetylene, ethyl acetylene, 1,2-butadiene and optionally small amounts of C5 hydrocarbons where the 1,3-butadiene content is generally 10-80% by weight, preferably 20-70% by weight, especially 30-60% by weight, while the vinyl-acetylene-, ethyl-acetylene- and 1,2-butadiene content of the C4 fractions (in the following text "other hydrocarbons”) generally does not exceed about 5% by weight in the aggregate. The method according to the invention can be advantageously applied in particular to C4 hydrocarbon mixtures which - 10-80% by weight 1,3-butadiene, - 10-60 wt% butenes, - 5-40 wt% butanes, - 0.1-5% by weight of other four-carbon hydrocarbons, and - They contain three- and five-carbon hydrocarbons in amounts ranging from 0 to a maximum of 5% by weight. In the case of N-methyl-2-pyrrolidinone used as a selective solvent, as well as its aqueous solution (N-methyl-2-pyrrolidinone and its aqueous solution hereinafter abbreviated as "NMP"), it is usually a standard technical product, up to 15% by weight may contain water. The extraction zones are preferably formed in the form of columns, through which the gas streams are led in countercurrent to the NMP. In the first step, the C4 hydrocarbon mixture to be separated is fed into an extraction zone (El) in gaseous state with the NMP and brought into contact with each other, where the 1,3-butadiene and other four-carbon hydrocarbons are essentially completely absorbed in the NMP, however, buffets and butanes remain essentially in the gas phase. In the case of the fed NMP and C4 hydrocarbon mixture, the mass ratio of the NMP:C4 hydrocarbon mixture ranges from 5:1 to 20:1 in the extraction zone (El). Generally known extraction procedures can be used for this extraction step. From the extraction zone (El), a gas flow is usually led to the head of the column, which primarily contains unabsorbed butanes and butenes, and if the C4 mixture contains three- and five-carbon hydrocarbons as impurities, propane, propene and propadiene, as well as traces of five-carbon hydrocarbons [(Gbc ) gas stream] and an extraction solution [(Ead) extraction solution] at the bottom of the column. The extraction solution (Ead) usually contains only 0-2% by weight of butenes and butanes and, if present, propyne and / or almost the entire amount of five-carbon hydrocarbons. In addition to butenes and butanes, the (Gbc) gas stream usually contains only 0-1% by weight of the 1,3-butadiene and other four-carbon hydrocarbons originally present in the C4 hydrocarbon mixture. The extraction zone (El) is usually designed in the form of a washing tower, fitted with plates, packing bodies or structured packings. These preferably represent 40-80 theoretical plates. The tower pressure depends on the temperature of the coolant (well water, river water, sea water, coolant such as liquid propylene, liquid ammonia or salts). This is between 2-6 bar, preferably 4.5 bar. The temperature profile in the extraction zone is provided by the temperature of the NMP. It is advantageous to reduce the temperature profile by partially condensing the (Gbc) fraction, as the separation performance will be better at a lower temperature. A typical value for condensation is 20%. This results in a temperature of 40-60 °C at the column head. HU 225 347 Β1 In order to desorb 1,3-butadiene from the extraction solution (Ead), the solution is transferred to the desorption zone (Dl) with reduced pressure and / or increased temperature compared to the extraction zone (El), and in this 1,3-butadiene from the extraction solution (Ead) butadiene [(Fa) 1,3-butadiene fraction] are desorbed, while most of the other four-carbon hydrocarbons, propyne and five-carbon hydrocarbons, remain in the liquid phase. Preferably, the pressure in the desorption zone (Dl) is the same as in the extraction zone (El) and the temperature is 20-25 °C higher than in the extraction zone (El). The 1,3-butadiene fraction (Fa) removed from the desorption zone (Dl) is usually 95-99% pure by weight. The extraction solution (Ed) produced by the desorption of 1,3-butadiene in the desorption zone (Dl) is then removed from the desorption zone (Dl) and a second one (Dll) with reduced pressure and / or increased temperature compared to the desorption zone (Dl) transferred to the desorption zone. During the transfer of the extraction solution (Ed) from the desorption zone (Dl) to the desorption zone (Dll), it preferably passes through a heat exchange zone, in which a part of the hydrocarbons in the extraction solution (Ed) evaporates, where this gas stream is directly recirculated to the ( Dl) is fed into the bottom of the desorption zone. The pressure and temperature are chosen here in such a way that practically all four-carbon hydrocarbons still remaining in the NMP are desorbed, they usually correspond to 1.5 bar and 150 °C. In the desorption zone (Dll), the remaining 1,3-butadiene and other four-carbon hydrocarbons and the five-carbon hydrocarbons still present in the extraction solution (Ed) are desorbed by fractionation into at least two separated fractions (Fd), where the fractions are at least in one [fraction (Fd)] the proportion of other four-carbon hydrocarbons relative to the proportion of all four-carbon hydrocarbons is at least ten times, usually 10-100 times, preferably 20-80 times higher than in the extraction solution (Ed), and the fractions are at least in one of them [(FdR) fraction], relative to the proportion of all four-carbon hydrocarbons, the proportion of other four-carbon hydrocarbons is lower than in the (Fd) fraction. Preferably, in the desorption zone (Dll), the hydrocarbons of the extraction solution (Ed) are separated into a fraction (Fd) and a fraction (FdR), where the fraction (Fd) is preferably substantially at least 20% by weight, particularly preferably 20-40% by weight % consist of other four-carbon hydrocarbons and otherwise butadiene, and the (FdR) fraction essentially consists of more than 80% by weight, particularly preferably 85-95% by weight of butadiene and otherwise other four-carbon hydrocarbons. The NMP obtained in the (Dll) desorption zone, which is substantially free of hydrocarbons, and the (Fd) and (FdR) fractions are separated from the (Dll) desorption zone and one or more (FdR) fractions are recycled to the (Dl) desorption zone , for example in the bottom of the washing tower. Preferably, the pressure drop is achieved here via a compressor. Fraction (Fd) is usually treated with water (condensate) in countercurrent to absorb most of the NMP in it. Generally, the mass ratio of fractions returned to the desorption zone (Dl) compared to those introduced into the system ranges from 20:1 to 80:1. The desorption zone (Dll) usually consists of a main tower with a side tower. Both are designed as washing towers. The main tower usually contains stuffing body charges, because here their low pressure loss is particularly advantageously used. The main tower should fit 10-15 theoretical plates. The side tower usually corresponds to 10 practice plates. The pressure is usually 1.5-1.6 bar; the temperature at the bottom of the main tower is 140-150 °C and at the top 80-100 °C. While the (Fd) fractions are preferably removed as a side stream at 130-140 °C, the (FdR) fractions are usually removed at the head. If a particularly high-purity 1,3-butadlene fraction is desired, it is preferable to proceed as follows: -The 1,3-butadiene fraction (Fa), which is removed from the desorption zone (Dl), is divided into two subflow fractions (Fal) and (Fa2), where the fraction (Fal) is returned to the extraction zone (El) [preferably the ( El) is led to the bottom of the extraction column] and the fraction (Fa2) is contacted once again in an extraction zone (Elll) with NMP, which was recovered from the desorption zone (Dll) or (Dili), where a part of the fraction (Fa2) and the excess of the other four-carbon hydrocarbons, which are still present as impurities in the (Fa2) fraction, is absorbed with NMP [(Eax) extraction solution]. - The unabsorbed amount of fraction (Fa2) [fraction (Fa3)] is separated from the extraction zone and removed, and the extraction solution (Eax) is returned to the extraction zone (El). This solution is illustrated in Figure 2. The mass ratio of NMP / (Fa) 1,3-butadiene fraction is usually 1:3-1:7 depending on the composition of the incoming C4 mixture and the specification of the (Fa3) fraction. The ratio of the material flow of the (Fal) and (Fa2) fractions is usually 1:1-4:1. The 1,3-butadiene fraction (Fa3) primarily contains three- and five-carbon hydrocarbons as impurities, such as 1,2-butadiene. These impurities are usually separated afterwards in two traditional distillation towers. Regarding the construction of the extraction column and the pressure and temperature parameters, the same applies to the (Elll) extraction zone as to the (El) extraction zone. The mass ratio of the fed NMP and (Fa2) raw butadiene fraction is 1:3-1:7. The unabsorbed 1,3-butadiene and the 1,3-butadiene discharged from the extraction zone (Elll) are usually purer than 98% by weight. HU 225 347 Β1 The (Gbc) gas stream, optionally supplemented with the external supplemental stream [(Zbc) gas stream], is subsequently brought into contact with the NMP recovered in the desorption zone (Dl I) in an extraction zone (Eli), where the butenes from the NMP are essentially completely absorbed , but butanes essentially remain in the gas phase. The extraction zone (Eli) is usually designed as a scrubber, fitted with plates, packing bodies or structured packings. For satisfactory separation efficiency, these should correspond to 30-70 theoretical plates. The pressure in the extraction zone (Eli) is chosen so that the gas flow (Gbc) can pass from the extraction zone (El) to the extraction zone (Eli) without any additional technical aids. The pressure also depends on the refrigerant available to condense the (Fc) fraction. Typical value for the pressure is 4.0 bar assuming water cooling. Preferably, the washing tower is provided with a backwashing zone in the column head, which corresponds to, for example, 4 theoretical plates. This backwash zone is used to recover the NMP contained in the gas phase by recirculating the liquid hydrocarbon onto which fraction (c) was previously condensed. At the same time, the temperature profile in the extraction zone (Elll) can be influenced. As mentioned for the (El) extraction zone, low pressure increases the separation efficiency here as well. The typical temperature at the head of the column is between 35-45 °C. Depending on the specification of the fractions (Fb) and (Fc) and the composition of the incoming C4 mixture and the additional stream (Zbc), the mass ratio of the NMP / (Gbc) gas stream, including the (Zbc) gas stream where appropriate, is the extraction zone (Eli) at the entrance 10:1-20:1. An extraction solution (Eb) containing a gaseous butane fraction [fraction (c)] and a butene fraction [fraction (b)] is formed in the extraction zone (Eli). If the extractive distillation is carried out as above, a fraction (b) is obtained which is contaminated with butanes up to 5% by weight, and a fraction (c) which is contaminated with butenes up to 15% by weight. The extraction solution (Eb) is transferred to the desorption zone (Dili) with reduced pressure and / or higher temperature compared to the extraction zone (Eli), and in this the butenes are desorbed from the extraction solution (Eb). The desorption of butenes and other four-carbon hydrocarbons present as impurity in this case can basically be done analogously to the desorption of other four-carbon hydrocarbons (Dil) in the desorption zone. The (Dili) desorption zone can be formed, for example, in the form of a washing tower, which has 5-15, preferably 8-10 theoretical plates and a backwashing zone, for example 4 theoretical plates. This backwash zone is used to recover NMP in the gas phase by liquid hydrocarbon recirculation, onto which fraction (b) is previously condensed. Preferably, the use of built-in filling body dressings is recommended. The column head pressure is usually between 1.5 bar and 1.6 bar. The temperature at the bottom of the tower is usually 130-150 °C. The NMP recovered in the desorption zone (Dili) is returned to the extraction zone (El), (Eli) and / or (Elll). An additional advantage arises when the NMP recovered in the (Dili) desorption zone is only returned to the (El) and (Eli) extraction zones, and the NMP recovered from the (Dil) desorption zone is essentially returned to the (Elll) extraction zone. The advantage is related to the fact that the separation of butenes / butanes from a C4 hydrocarbon mixture with NMP takes place more easily than the separation of a butene-butane mixture into two high-purity butene and butane fractions. Here it remains in a single solvent cycle. Unlike extraction zone (Elll) which requires high purity degassed NMP, the quality of NMP for extraction zones (El) and (Eli) does not need to be as good. This is an economic gain from the point of view that the degree of degassing of the NMP and thus the use of external steam for the desorption of hydrocarbons in the (Dili) desorption zone does not have to be very high. Unlike the NMP from the (Dil) desorption zone, where we aim for 0-10 ppm by weight of four-carbon hydrocarbons, the NMP from the (Dili) desorption zone can show values ​​of 1000 ppm by weight and more. This does not interfere with the product purity of fractions (b) and (c). On the other hand, hydrocarbon content lowers the boiling point of LM. Since the heat content of the NMP is used from the (Dili) desorption zone for economic reasons, the boiling point reduction cannot be increased at will by increasing the residual content of hydrocarbons. For these reasons, the previously stated bottom temperatures of 130-150 °C follow. A bottom temperature of 138 °C results in a residual hydrocarbon content of approximately 800 ppm by mass. The process according to the invention can be carried out particularly economically when the heat of the NMP obtained by boiling the extraction solutions (Eb) and (Ed) by indirect heat exchange in a heat exchange zone, which is the desorption zone (Dl), (Dil) and / or (Dili) leads to and promotes desorption in these desorption zones because the temperature of the desorption zone (Dl) compared to the extraction zone (El) and the temperature of the desorption zone (Dil) compared to the desorption zone (Dl) and (Eli) compared to the extraction zone, the temperature of the desorption zone (Dili) is increased. Fraction (a) (butadiene) is preferably separated from the C4 hydrocarbon mixture as described in DE-A-2,724,365. Particularly preferably, this part of the process is carried out as shown in Figure 3. According to this version of the procedure, we proceed as follows. Extractive distillation is carried out in more than one column, usually two columns, which together correspond to more than 100 practice plates. Ideally, when using two columns, the absorption step above the point at which the C4 hydrocarbon mixture is introduced into the extractive distillation zone is the first column5 HU 225 347 Β1 ba, the hydrocarbon mixture feed! and the enrichment step below is emptied into the second column, i.e. the hydrocarbon mixture feed! point is at the top of the second column, or preferably at the bottom of the first column. Preferably, we do not connect a compression step between the absorption step and the enrichment step, but rather maintain such pressure conditions in the extractive distillation zone that, in the absence of compression and / or pressure reduction steps in the extractive distillation zone, are automatically adjusted in the extractive distillation zone in such a way that they correspond to the normal pressure loss in the columns pressure in the lower part of the extractive distillation zone corresponds to at least the pressure measured at the head of the extractive distillation zone. As a rule, the pressure difference between the top and bottom of the extractive distillation zone is 0.1-3 bar, preferably 0.2-2 bar. In general, a pressure of 1-9 bar, preferably 2-8 bar, especially 3-7 bar is used in the extractive distillation zone. The pressures in the lower third of the extractive distillation zone, i.e. in the range that represents the lower plates of the extractive distillation zone, which correspond to approximately one third of the plate number of the extractive distillation zone, are usually 1.5 to 9 bar, preferably 2.5 to 8 bar, in particular They have a value of 3.5-7 bar. The extract led from the extractive distillation zones is first brought to a higher pressure than the pressure in the extractive distillation zone. This can be done, for example, with a liquid pump. In general, this increase in pressure occurs essentially isothermally, i.e. only such temperature changes occur, for example a temperature increase of up to 1 °C, which requires an operation leading to an increase in pressure, such as the use of a pump. In general, the extract is pressurized, which is 1-20 bar, preferably 2-18 bar, especially 3-15 bar above the pressure of the extractive distillation zone, especially above the lower third of the extractive distillation zone. The pressurized extract is then heated by indirect heat exchange in a heat exchange zone with a selective solvent obtained as a bottoms product from the solvent recovery zone. After the heat exchange, the selective solvent is returned to the extractive distillation zone. By heat exchange with a selective solvent, the temperature of the extract generally rises by 5-80 °C, preferably by 10-70 °C, especially by 15-60 °C. Said extract is then expanded by expansion distillation (equilibrium evaporation) to a pressure that is at least equal to the pressure of the extractive distillation zone, preferably the pressure of the lower third of the extractive distillation zone, and higher than the pressure of the downstream solvent recovery zone. In addition to the pressure drop, the amount of steam formed during the expansion distillation of the extract is returned to the distillation zone without a compression step. Accordingly, in the expanding distillation, we usually expand to pressures that are 0.05-2.0 bar, preferably 0.1-1 bar higher than the amount of the extract in the form of steam being fed into the extractive distillation zone! pressure measured at Expanding distillation is carried out, for example, on an adiabatic still equipped with a pressure reducing valve, to which a phase separation vessel is attached for better separation, if necessary, which is used to separate the vapor and liquid phases formed during the expanding distillation. The combination of the heat exchange zone for the heat exchange between the extract of the extractive distillation zone and the selective solvent returned from the solvent recovery zone formed by the downstream expansion distillation can be used in one step. However, it is also possible to use more than one, for example 2-4, preferably 2-3, combinations of this kind, preferably connected one after the other. The use of more than one such heat exchange / expanding vaporization step and the recirculation of the resulting sub-streams to distinct inflow points of the extractive distillation zone reduce the desired separation performance of the extractive distillation zone and the size of the extractive distillation column. It is also possible to insert an additional heat exchange zone between the last expansion distillation zone and the solvent recovery zone. The portion of the extract in the form of steam formed in the expanding distillation zone or zones, which usually contains 20-80% by weight, preferably 40-70% by weight of hydrocarbons, is returned to the extractive distillation zone. Generally, the recovered vapor phase is introduced into the lower third of the extractive distillation zone, preferably at the bottom of the extractive distillation zone, for example at a point approximately at the height of the lowest column plate. Step by step! in expansion distillation, the fractions in the form of steam obtained in each step can be separated or, after being combined, returned to the extractive distillation zone. The liquid phase of the extract remaining after the expansion distillation is led from the extractive distillation zone to a solvent recovery zone, which is operated at a lower pressure than the pressure of the expansion distillation zone. The expansion of the remaining liquid extract phase to a lower pressure takes place in the solvent recovery zone with an expediently inserted pressure reducing valve. In general, the pressure in the solvent recovery zone is 0.1 to 8 bar, preferably 0.5 to 7 bar, especially 1 to 6 bar lower than the pressure in the expansion distillation zone or zones. For example, the solvent recovery zone can act as a degasser or solvent separator. Heat is usually supplied to the solvent recovery zone, for example with a water vapor indirect heat exchanger (boiler). The hydrocarbon-free NMP obtained as a bottom product of the solvent recovery zone is returned to the heat exchange zone, in which the heat exchange takes place with the extract from the extractive distillation zone, to the extraction steps (El) and (Elll). The product containing hydrocarbons obtained from the solvent recovery zone, which is usually removed as an overhead stream or overhead and side streams, is first partially or, if applicable, fully ke6 HU 225 347 Β1 passes through a compression step and after compression is led to the extractive distillation zone. In the compression zone, the hydrocarbon stream is compressed to a pressure that is at least equal to the pressure of the extractive distillation zone. In general, the hydrocarbon stream is compressed to a pressure 0.05-2 bar, preferably 0.1-1 bar, higher than the pressure measured at the introduction of the vapor fraction of the extract into the extractive distillation zone. Figure 3 shows a schematic diagram of one embodiment of the preferred version. In this embodiment, two extractive distillation zones are connected one after the other. The first extractive distillation zone consists of column (1) and the updated upper column part (2), while the second extractive distillation zone consists of column (4) and the lower column part (3). NMP is added to the top of column (1) through line (5) and to the top of column (4) through line (6). Through line (7), a C4 hydrocarbon mixture is led to the bottom of column (1). Also, columns (2 / 3) and (4) are directly connected. From the column (2), a gaseous partial flow is removed and washed in countercurrent with LM using line (6). At the head of the column (1) a raffinate, which essentially consists of butenes and butanes, is sucked through the line (8). Essentially pure 1,3-butadiene is aspirated at the head of column (4) through line (9). Through the side extractor of the column (10), through the line (11), a gas stream containing essentially other hydrocarbons and other impurities is removed. The pressure in column section (3) is approximately 5 bar. The extract extracted through the line (12) is brought to a pressure of 15 bar through the liquid pump (13), and then in the heat exchanger (14) from 70 °C to 125 °C, extracted from the degasser (10) through the line (24), heated with NMP essentially free of four-carbon hydrocarbons. The heated extract is then passed through the pressure reducing valve (15) and brought to a pressure slightly higher than 5 bar. As soon as the gaseous phase formed in the phase separation tank (16) is immediately returned to the column (3) through the lines (22) and (23), the liquid phase obtained after the expansion distillation of the extract is led through the line (17) through an additional pressure reducing valve (18) , where the pressure drop to the pressure level of column (10) occurs, which is usually 1.5 bar. At the head of the column (10) we draw off a hydrocarbon stream through the line (19), which, after compression in the compressor (20), is also introduced into the bottom of the column (3) through the line (23). For safety reasons, it is important to cool the gas stream (19) before entering the compressor (20) by means of heat exchange (not shown in Figure 3) so that the temperature of the gas stream does not exceed 110 °C after leaving the compressor. The gas stream is usually cooled to 45 °C. The NMP, which is drawn off through line (24) and cooled in heat exchanger (14), almost free of four-carbon hydrocarbons, is led to heat exchanger (2) through line (25). An additional heat exchange (not shown in Figure 3) then takes place in which the temperature of the LM is adjusted to 38 °C. Then, the amount of solvent, as it arrives through line (26), is divided into two sub-streams: line (6) leads to column (4), while line (27) ends in the additional butene-butane distribution (Elll) extractive distillation zone . From there, the LM comes back again via wire (5). For the sake of simplification in the drawing, all previously mentioned backwashing zones with liquid hydrocarbon refluxes were omitted in the case of columns (1) and (4). The side column mentioned above located at the main column (10) in Figure 3 is also missing. Example In contrast to Fig. 3, the process diagram of the example (Fig. 4) is essentially more voluminous, even if we omitted the representation of all pumps here. That's why we have listed all heat exchangers next to the columns, as they greatly contribute to the economy of the process. Likewise, all phase separators are indicated in the drawing. The numbering system is a It can be adopted in a similar way in Figure 4. The extraction zone (El) and the desorption zone (Dl) are located after column (120) (Figure 4A). The extraction zone (Elll) is column (130). The desorption zone (Dll) is formed by columns (140) and (150) (Figure 4A and Figure 4B). The extraction zone (Eli) is column (100) and the desorption zone (Dili) is column 110. Finally, the entire process includes the two final distillation columns (160) and (170), in which the raw butadiene is converted to the final quality. The procedure has three entry streams: (10) stream: supplementary stream containing butenes and butanes (Zbc), (40) stream: C4 fraction feed, (69) stream: condensate addition to reduce NMP loss. Composition (mass%) and quantitative data (kg / hour) of stream (10): Butane 26.0 Isobutane 9.5 Butene 42.0 trans-2-Butene 13.0 cis-2-Butene 9.5 Quantity=4200. (40) stream composition (mass%) and quantitative i (kg / hour): Propane 0.1 Propene 0.1 Propadiene 0.05 Propyne 0.15 Butane 7.3 Isobutane 4.0 Butene 14.0 Isobutene 24.6 HU 225 347 Β1 trans-2-Butene 4.5 cis-2-Butene 3.5 1,3-Butadiene 40.0 1,2-Butadiene 0.45 Ethyl-acetylene 0.2 Vinyl-acetylene 0.75 Isopentane 0.1 3- Methyl-2-butene 0.1 2-Methyl-2-butene 0.1 Quantitative 5,000. Quantity data for current (69) (kg / hour): Quantitative 100. Solvent requirement (kg / hour) for the three extraction zones and their composition (mass %): (SZH=hydrocarbons) (El) extraction zone, (42) current with 65,000 NMP with water SZH total 91.63 8.29 0.08 (Elll) extraction zone, (46) current=35,000 with NMP 91.7 with water 8.3 SZH total 1 mass ppm ( Eli) extraction zone, (12) current with OO 000 NMP 91.63 with water 8.29 SZH total 0.08 (57) current with 65 000 NMP 91.7 with water 8.3 SZH total 1 mass ppm Temperature: usually 38 °C. For the following data, when describing the columns, the plate number is usually counted from the bottom of the column. Operating conditions for column (100): Number of theoretical plates = 4+50 (including SZH return plate for the backwashing zone) = 1 LM feed plate = 5 SZH feed plate = 42 (Zbc) auxiliary flow plate = 42 Pressure on the 1st plate = 4.0 bar Temperature On plate 1 = 38.5 °C SZH recirculation amount = 5000 kg / hour. Operating conditions for column (110): Number of theoretical plates =4+9 (including SZH recirculation plate backwashing zone) =1 Extract feed plate =5 Pressure on plate 1 =1.526 bar Temperature on plate 1 =6.7 °C Amount of SZH recirculation = 5000 kg / hour Energy consumption = 10,361 kW. Operating conditions for column (120): Number of theoretical plates =25+23+7 SZH return plate (in two columns) =1 LM feed plate SZH suction plate =1 =49 [for the (Eli) extraction zone] SZH feed plate =26 Pressure on plate 1 =4.5 bar Temperature on plate 1 =41.5 °C SZH return quantity = 2094 kg / hour. Operating conditions for column (130): Number of theoretical plates =4+30 (including backwash zone) SZH return plate =1 LM feed plate =5 Pressure on plate 1 =5.0 bar Temperature on plate 1 =45 .3 °C amount of SZH recirculation = 2120 kg / hour. Operating conditions for column (140): Number of theoretical plates = 10 Extract feed plate = 1 SZH extraction plate = 6 [for column (150)] Pressure on plate 1 = 1.52 bar Temperature on plate 1 = 104.6 ° C Temperature on the 10th plate = 146.1 °C Amount of SZH recirculation = 2120 kg / hour Energy consumption = 6773 kW. Operating conditions for column (150): Number of theoretical plates = 2 Water supply plate = 1 Pressure on plate 1 = 1.52 bar Temperature on plate 1 = 108 °C. Operating conditions for column (160): Number of theoretical plates = 46 SZH return plate = 1 Extract feed plate = 16 Pressure on plate 1 = 7.0 bar Temperature on plate 1 = 46.6 °C Amount of SZH return = 6130 kg / hour Energy requirement = 7 61 kW. Operating conditions for column (170): Number of theoretical plates = 45 SZH return plate = 1 Extract feed plate = 23 Pressure on plate 1 = 4.2 bar Temperature on plate 1 = 39.3 °C Amount of SZH return = 11 197 kg / hour Energy requirement = 1671 kW. The individual procedural steps are as follows: The usually liquid C4 hydrocarbon mixture [stream (40)] is vaporized in the heat exchanger (240) and enters the extraction zone (El) in a vapor state approximately in the middle of the column (120). The LM is conducted countercurrently with the rising gases via stream (42). HU 225 347 Β1 This results in two new streams: a gaseous product [(43) stream], essentially mainly propane, propene, propadiene, butanes and butenes, and an extract [(53) stream] with hydrocarbons consisting of 1,3-butadiene dissolved in LM and with other hydrocarbons, including five-carbon hydrocarbons. The 1,3-butadiene content, an essential specification value for the separation requirement of the extraction zone (El), is below 100 ppm by weight. In order to reduce the temperature profile in the column (120), 20% by weight of the gas flow (43) is condensed in the heat exchanger (230). A side stream leaves column (120) through stream (51), which is counter-washed with LM [stream (46)] in the extraction zone (Eli), which is column (130). To reduce the temperature profile and simultaneously reduce the loss of NMP, the column is equipped with liquid hydrocarbon recirculation [(50) stream]. The LM amount [(46) stream] is adjusted to meet the specifications for ethyl and vinyl acetylene for subsequent pure 1,3-butadiene. The decanter (320) built into the head circle is used for partial water separation from the raw butadiene. The extract from the extraction zone (El), this stream (53), passes through a heat exchanger (255) and is then partially desorbed under pressure in the expansion tank (410), where two streams are generated: a gaseous part [(59) stream], which is immediately returned to column (120) via stream (67), and a liquid portion [stream (60)]. The temperature of stream (60), which is still under the increased vaporization pressure of expansion tank (410), is raised by 5°C in an additional heat exchanger (260) before it is expanded under reduced pressure into column (140). The four-carbon hydrocarbons are almost completely desorbed from the extract, stream (61), in column (140) with external added energy. The resulting gas, stream (62), is cooled in the heat exchanger (256) to the previously mentioned 45 °C, and in the expansion tank (420) into an insignificant amount of liquid phase [stream (66)] and a major part into gas phase [( 64) current] is distributed. The gas stream (64) is compressed in the compressor (500) and, after combining with the gas streams (59) and (66) as a stream (67), is returned to the lower part of the column (120). A gas stream (68) is withdrawn from approximately the middle of the column (140). It contains water in addition to hydrocarbons. This gas stream is washed countercurrently with the condensate in the column (150), the gaseous product [stream (70)] is cooled in the heat exchanger (270) and after a separation into a gas and liquid phase [streams (72) and (73)] as a product we'll take it. The NMP content in stream (70) is 160 ppm by mass, which corresponds to an NMP loss of 0.19 kg / h in this section. The almost completely desorbed LM from column (140) on heat exchanger (255) [heating the extract from column (120)], heat exchanger (250) [heat exchanger for column (170)], heat exchanger (240) [the C4 hydrocarbon mixture distillation] and passes through (235) heat exchanger [LM aftercooler to adjust the LM temperature] one after the other. This completely ran through the extraction zones (El) and (Elll) and the desorption zones (Dl) and (Dll). The overhead product of column (120) [stream (45)] and the additional stream (Zbc) [stream (11)] are fed into the lower third of the extraction zone (Eli), i.e. column (100). Together with the gas flow obtained after the heat exchange in the heat exchanger (215) and the subsequent rapid expansion in the expansion tank (400), the gases are led in countercurrent to the LM [flow (12) and flow (57)]. Here, a butane fraction of high purity containing only 0.43 wt% butene is obtained [stream (13)]. As with the overhead product of column (130), the gas stream (13) is also condensed [(200) heat exchanger] and then partially dehydrated in the settler (300), regardless of whether it is as a liquid hydrocarbon return [(16) stream] or (c) is given as the butene fraction, i.e. (17) current, product. The extract, which has already been heated by heat exchange, from the extraction zone (Eli), i.e. stream (20), is fed to the desorption zone (Dili) i.e. column (110) with another indirect heat exchange in the heat exchanger (220), after reducing the pressure. Here, by introducing external heat, the extract is largely freed from four-carbon hydrocarbons. The resulting butene fraction (b), stream (23), is also of high purity and contains only 1.85% by weight of butanes. After condensation in the heat exchanger (225) and partial dewatering in the settler (225), the butene fraction is re-introduced in liquid form into the column (110) [current (26)] and taken as a product [current (27)]. The heat exchanger (225) requires a refrigerant due to the low condensation temperature of the butene fraction. The pressure in column (110) cannot be increased. On the one hand, the bottom temperature of the (110) column would increase above the 150 °C limit, which would mean an inadmissible thermal load on the LM, and on the other hand, the desorption of hydrocarbons would become more difficult, which could only be compensated by additional external energy input. The LM desorbed in column (110) successively passes through heat exchanger (220) (extract pre-heating), heat exchanger (215) (increasing the temperature of the extract to reduce pressure), heat exchanger (210) [distillator of the secondary stream (10)] and (205) on a heat exchanger (end cooler to adjust the LM temperature). Due to the multifaceted tasks, certain temperature levels are specified, which means that the hydrocarbon content of stream (28) cannot be arbitrarily high. In our example, the concentration is 800 ppm by mass. With this, we completely ran through both the (III) absorption zone and the desorption zone. Only the part concerning the distillation columns (160) and (170) for the final quality adjustment of the (a) 1,3-butadiene fraction remained. The crude butadiene feed [stream (80)] occurs in the upper third of column (160). The gaseous overhead product [stream (81)] is condensed, and after partial water separation in the settler (330), it is fed back into the column (160) as a liquid hydrocarbon [stream (84)] and withdrawn as a product [stream (83)]. It should be noted that current (81)9 HU 225 347 Β1 must not exceed a given propyne concentration for safety reasons. This threshold concentration is pressure dependent. At a head pressure of 7 bar, this value is 50% by volume. The nearly water-free bottom product of column (160) is added to the approximate center of column (170). There, the mixture is separated into a high-purity 1,3-butadiene fraction [stream (89)] and a bottoms product [stream (91)], where stream (91) is mainly cis-2-butene, 1,3-butadiene, 1,2- It consists of a mixture of butadiene and hydrocarbons with 5 carbon atoms. The 1,3-butadiene yield can be advantageously influenced by the 1,3-butadiene concentration. In the following example, this means 25% by weight. The product specification of fraction (a), i.e. the composition of pure butadiene: 1,3-Butadiene =99.6 wt% 15 Butenes in total =0.4 wt% Propyne =10 wt ppm 1,2-Butadiene =50 wt ppm C4 and acetylene in total <5 wt ppm C5 and SZH in total <5 wt ppm 20 (C4 and C5 mean hydrocarbons with four and five carbon atoms, respectively) Finally, we list the amounts of energy exchanged by condensers and heat exchangers [kW]: 25 (200) heat exchanger: (205) heat exchanger: (210) heat exchanger: 785 8991 482 (215) heat exchanger: 3127 (220) heat exchanger: 4000 30 (225) heat exchanger: 1679 (230) heat exchanger: 230 (235) ) heat exchanger: 2945 (240) heat exchanger: 1772 (245) heat exchanger: 857 35 (250) heat exchanger: 1671 (255) heat exchanger: 7264 (260) heat exchanger: 744 (265) heat exchanger: 1729 (270) heat exchanger: 572 40 (275) ) heat exchanger: 693 (280) heat exchanger: 1757 PATENT CLAIMS 45

Claims

1. A process for separating a mixture of four carbon hydrocarbons (C4-50 hydrocarbon mixture) containing 10-80 wt.% 1,3-butadiene, 10-60 wt.% butenes, 5-40 wt.% butanes and 0.1-5 wt.% other four carbon hydrocarbons into at least four fractions a)-d) - where a) fraction (a) is a 1,3-butadiene fraction, b) fraction (b) is a butene fraction, c) fraction (c) is a butane fraction, and 55 d) one or more fractions (d) consist of 1,3-butadiene and the other four carbon hydrocarbons by extractive distillation with N-methyl-2-pyrrolidinone or an aqueous solution of N-methyl-2-pyrrolidinone (NMP), characterized in that 60 1. the gaseous C4-hydrocarbon mixture is first is also contacted with NMP in the extraction zone (El), where the weight ratio of the NMP / C4-hydrocarbon mixture is between 5:1 and 20:1, and the 1,3-butadiene and other four-carbon hydrocarbons are completely absorbed by the NMP, while the butenes and butanes remain in the gas phase; 2. the unabsorbed butenes and butanes [gas stream (Gbc)] and the extraction solution formed in step 1 [extraction solution (Ead)] are separately removed from the extraction zone (El); 3. the extraction solution (Ead) is passed to the desorption zone (Dl) at a pressure of 2-6 bar compared to the extraction zone (El) and / or at a temperature 20-25 °C higher than the extraction zone (El), and 1,3-butadiene is desorbed from this extraction solution (Ead), while most of the other four-carbon hydrocarbons remain in the liquid phase; 4. the extraction solution obtained in step 3 [(Ed) extraction solution] and the desorbed 1,3-butadiene [(Fa) fraction] are separately removed from the desorption zone (Dl), and optionally a portion of the (Fa) fraction is recycled to the extraction zone (El); 5. the extraction solution (Ed) is passed through a pressure and / or temperature gradient to a second desorption zone (Dll) with a reduced pressure and / or higher temperature than the desorption zone (Dl), and the 1,3-butadiene and other four-carbon hydrocarbons remaining in this extraction solution (Ed) are fractionated and desorbed as at least two separated fractions (Fd), while in at least one of the fractions [(Fd) fractions] the proportion of other four-carbon hydrocarbons, relative to the proportion of all four-carbon hydrocarbons, is at least ten times higher than in the extraction solution (Ed), and in at least one of the fractions [(FdR) fractions] the proportion of other four-carbon hydrocarbons, relative to the proportion of all four-carbon hydrocarbons, is correspondingly lower than in the fractions (Fd); 6. removing the NMP obtained in the desorption zone (Dll) which is essentially free of hydrocarbons having four carbon atoms, and the fractions (Fd) and (FdR) separately from the desorption zone (Dll) and recycling one or more fractions (FdR) to the desorption zone (Dl); 7. the gas stream (Gbc) is first contacted with the NMP obtained in step 6 in an extraction zone (Eli), where the butenes are completely absorbed by the NMP and the butanes remain in the gas phase; 8. the unabsorbed butanes [fraction (Fc)] and the extraction solution obtained in step 1 [extraction solution (Eb)] are removed from the extraction zone (Eli); 9. the extraction solution (Eb) is passed to the desorption zone (Dili) at a reduced pressure and / or higher temperature compared to the extraction zone (Eli), and the butenes are desorbed from this extraction solution (Eb); HU 225 347 Β1 10. removing the NMP formed in step 9, which is free of four-carbon hydrocarbons, and the desorbed butenes [fraction (Fb)] from the desorption zone (Dili); 11. the NMP formed in step 9 is recycled to one of the extraction zones (El) and (Eli); 12. a portion of the 1,3-butadiene fraction (a) removed from the desorption zone (Dl) is recycled to the extraction zone (El) [fraction (Fal)], and the other portion [fraction (Fa2)] is re-contacted with the NMP recovered in step 6 in an extraction zone (EliI), where the weight ratio of NMP / (Fa2) crude butadiene fraction is between 1:3 and 1:7, and a portion of the (Fa2) fraction and the majority of other four-carbon hydrocarbons still present as impurities in the (Fa2) fraction are absorbed by the NMP (Eax); and 13. the unabsorbed part of the fraction (Fa2) [fraction (Fa3)] is removed from the extraction zone, and the extraction solution (Eax) is returned to the extraction zone (El).

2. The process according to claim 1, characterized in that the NMP and the C4-hydrocarbon mixture are fed into the extraction zone (El) in a weight ratio of 5:1 to 20:

1.

3. The process according to claim 1 or 2, characterized in that the extraction zone (El) is formed as two interconnected columns.

4. The process according to any one of claims 1-3, characterized in that the extraction zones (El), (Eli), (Elll) are formed in the form of columns, and the gas streams are passed through them in countercurrent to the NMP.

5. The process according to claims 1-4. The method according to any one of claims 1 to 3, characterized in that claim 1 comprises the steps 3 and 5.The desorption described in step (1) is carried out by increasing the temperature in the desorption zone (D1) relative to the extraction zone (E1) and the temperature in the desorption zone (D11) relative to the desorption zone (D1), in which process the heat of the NMP removed from the desorption zone (D11) according to step 11 of claim 1 is introduced to the desorption zone (D1) by indirect heat exchange in a heat exchange zone.

6. The process according to any one of claims 1-5, characterized in that a further hydrocarbon stream [(Zbc) make-up stream] is added to the gas stream formed in step 1, the latter consisting essentially of a mixture of butanes and butenes.

7. The process according to steps 1-6.

8. The process according to any one of claims 1-7, characterized in that the temperature increase in the desorption zones (Dll) and (Dili) is carried out by indirect heat exchange with steam for the complete desorption of NMP from the hydrocarbons.Process according to any one of claims 1 to 11, characterized in that the recycle gas required for the separation of fractions (b) and (c) is obtained by partial desorption of the extraction solution (Eb) in the extraction zone (Eli), where the necessary temperature increase is derived from N-methylpyrrolidinone free of four-carbon hydrocarbons obtained from the desorption zone (Dili) by indirect heat exchange.