Methods for isoprene separation and recovery, and isoprene separation and recovery devices.

Abstract

Provided is an isolation and recovery method for isoprene. The method makes it possible to reduce the amount of polymers of isoprene generated when isoprene is isolated and recovered from a mixed fluid that includes isoprene. According to this isolation and recovery method for isoprene, isoprene is isolated and recovered from a mixed fluid that includes isoprene. The method includes: an extraction distillation step for extraction distilling the mixed fluid to obtain a fraction that includes impurities that are less soluble than isoprene in the extraction solvent used in the extraction distillation and a fraction that includes crude isoprene; and a fractional distillation step for fractionally distilling the fraction that includes the crude isoprene to obtain a fraction that includes impurities that have a higher boiling point than isoprene, a fraction that includes impurities that have a lower boiling point than isoprene, and a fraction that includes high-purity isoprene.

Description

Method and apparatus for separating and recovering isoprene

[0001] The present invention relates to a method and an apparatus for separating and recovering isoprene, and more particularly to a method and an apparatus for separating and recovering isoprene, which can reduce the amount of isoprene polymer generated when separating and recovering isoprene from a mixed fluid containing isoprene.

[0002] Conventionally, as a method for separating and recovering high-purity isoprene from a mixed fluid such as a C5 fraction by-produced when producing ethylene by steam cracking of hydrocarbons or other high-temperature treatments, a method using extractive distillation is known.

[0003] Specifically, as a method for separating and recovering isoprene from a mixed fluid such as a C5 fraction using extractive distillation, for example, a method is used in which impurities having a boiling point close to that of isoprene, such as pentane and pentene, are separated from a mixed fluid containing isoprene, and high-purity isoprene is separated and recovered (see, for example, Patent Document 1).

[0004] Here, in the above method for separating and recovering isoprene using extractive distillation, impurities having a lower boiling point than isoprene, such as 1,4-pentadiene and 2-butyne, which are inhibitory components of polymerization reactions such as isoprene synthetic rubber, and impurities having a higher boiling point than isoprene, such as piperylene, can be separated and removed.

[0005] Japanese Patent Application Laid-Open No. 47-41323

[0006] However, in the above method for separating and recovering isoprene using extractive distillation, it has been impossible to suppress the generation of isoprene polymers, which can also cause equipment fouling.

[0007] Therefore, an object of the present invention is to provide a method and an apparatus for separating and recovering isoprene, which can reduce the amount of isoprene polymer generated when separating and recovering isoprene from a mixed fluid containing isoprene.

[0008] The present invention aims to advantageously solve the above problems, and the isoprene separation and recovery method of the present invention is an isoprene separation and recovery method for separating and recovering isoprene from a mixed fluid containing isoprene, characterized by comprising: an extraction distillation step of extractively distilling the mixed fluid to obtain a fraction containing impurities whose solubility in the extraction solvent used for the extraction distillation is lower than that of isoprene, and a fraction containing crude isoprene; and a split distillation step of split distilling the fraction containing crude isoprene to obtain a fraction containing impurities with a higher boiling point than isoprene, a fraction containing impurities with a lower boiling point than isoprene, and a fraction containing high-purity isoprene. In this way, by split distilling the fraction containing crude isoprene, the heat load can be reduced, and the amount of isoprene polymer generated when isoprene is separated and recovered from a mixed fluid containing isoprene can be reduced. Accordingly, the frequency of polymer cleaning, which needs to be performed by stopping the operation of the isoprene separation and recovery apparatus, can be reduced. In this invention, "high-purity isoprene" means "isoprene with a higher concentration than the isoprene concentration in crude isoprene." Here, "isoprene concentration" can be measured using gas chromatography. Furthermore, in this invention, "split distillation" refers to dividing the material to be distilled into three or more (preferably three) fractions in a single distillation operation, and can be carried out using, for example, a vertical split distillation column.

[0009] In the isoprene separation and recovery method of the present invention, the extraction solvent in the extraction distillation step is preferably an amide compound, and more preferably dimethylformamide. By using an amide compound, particularly dimethylformamide, as the extraction solvent, extraction distillation can be performed efficiently.

[0010] Furthermore, the isoprene separation and recovery method of the present invention preferably further includes a second extraction distillation step in which the fraction containing the high-purity isoprene is further extracted and distilled to obtain a fraction containing impurities whose solubility in the extraction solvent used in the extraction distillation is higher than that of isoprene, and a fraction containing even higher purity isoprene. By further extracting and distilling the fraction containing the high-purity isoprene (second extraction distillation), easily soluble substances (impurities whose solubility in the extraction solvent is higher than that of isoprene) can be separated, and even higher purity isoprene can be obtained. In addition, by further extracting and distilling after partial distillation (second extraction distillation), the easily soluble substance cyclopentadiene is separated in advance by partial distillation, so even higher purity isoprene can be obtained efficiently.

[0011] In the isoprene separation and recovery method of the present invention, the extraction solvent in the second extraction distillation step is preferably an amide compound, and more preferably dimethylformamide. By using an amide compound, particularly dimethylformamide, as the extraction solvent, extraction distillation can be performed efficiently.

[0012] Furthermore, in the isoprene separation and recovery method of the present invention, it is preferable that the isoprene concentration of the fraction (mixed fluid) containing impurities with a lower boiling point than isoprene is 5% by mass or more and 90% by mass or less. If the isoprene concentration of the mixed fluid is 5% by mass or more and 90% by mass or less, high-purity isoprene can be efficiently separated and recovered from the mixed fluid.

[0013] Furthermore, in the isoprene separation and recovery method of the present invention, it is preferable to perform the fractional distillation step in the presence of a polymerization inhibitor in an amount of 1 ppm by mass or more and 100 ppm by mass or less relative to the crude isoprene. Performing fractional distillation in the presence of the above-mentioned amount of polymerization inhibitor suppresses the polymerization reaction during fractional distillation, thereby preventing fouling and clogging in the fractional distillation column.

[0014] Furthermore, in the isoprene separation and recovery method of the present invention, it is preferable to perform the divided distillation in the divided distillation step in a divided distillation column and supply the polymerization inhibitor from the vertical upper part of the divided distillation column. By supplying the polymerization inhibitor from the vertical upper part of the divided distillation column, the polymerization inhibitor can be distributed throughout the entire divided distillation column. In this invention, "vertical upper part of the divided distillation column" means "the upper part of the divided distillation column that is 70% or more and 100% or less of the vertical height of the divided distillation column."

[0015] Furthermore, in the isoprene separation and recovery method of the present invention, it is preferable that the fraction containing the high-purity isoprene is in gaseous form. If the fraction containing the high-purity isoprene is in gaseous form, it is possible to prevent polymerization inhibitors from being included in the high-purity isoprene. Therefore, the high-purity isoprene can be advantageously used in polymerization to obtain polyisoprene and the like.

[0016] Furthermore, the isoprene separation and recovery method of the present invention preferably further includes a step of removing a polymerization inhibitor from the fraction containing the high-purity isoprene. By removing the polymerization inhibitor from the fraction containing the high-purity isoprene, the high-purity isoprene can be advantageously used for polymerization to obtain polyisoprene or the like.

[0017] Furthermore, this invention aims to advantageously solve the above problems, and the isoprene separation and recovery apparatus of the present invention is characterized by comprising: an extraction distillation section having a supply port for supplying a mixed fluid containing isoprene, and extracting and distilling the mixed fluid to obtain a fraction containing impurities whose solubility in the extraction solvent used for the extraction distillation is lower than that of isoprene, and a fraction containing crude isoprene; and a split distillation section having a supply port for supplying the fraction containing crude isoprene, and split distilling the fraction containing crude isoprene to obtain a fraction containing impurities with a higher boiling point than isoprene, a fraction containing impurities with a lower boiling point than isoprene, and a fraction containing high-purity isoprene. By split distilling the fraction containing crude isoprene, the heat load can be reduced, and the amount of isoprene polymer generated when isoprene is separated and recovered from a mixed fluid containing isoprene can be reduced.Therefore, the frequency of polymer cleaning, which needs to be performed by stopping the operation of the isoprene separation and recovery apparatus, can be reduced.

[0018] Here, the isoprene separation and recovery apparatus of the present invention preferably further comprises a supply port for supplying a fraction containing the high-purity isoprene, and a second extraction distillation section which further extracts and distills the fraction containing the high-purity isoprene to obtain a fraction containing impurities whose solubility in the extraction solvent used in the extraction distillation is higher than that of isoprene, and a fraction containing even higher purity isoprene. By further extracting and distilling the fraction containing high-purity isoprene, easily soluble substances (impurities whose solubility in the extraction solvent is higher than that of isoprene) can be efficiently separated, and even higher purity isoprene can be produced.

[0019] According to the present invention, the amount of isoprene polymer generated when isoprene is separated and recovered from a mixed fluid containing isoprene can be reduced.

[0020] This figure shows a schematic configuration of an example of an isoprene separation and recovery apparatus according to the present invention. This figure shows a schematic configuration of an example of a conventional isoprene separation and recovery apparatus.

[0021] Embodiments of the present invention will be described in detail below. Herein, the isoprene separation and recovery method of the present invention can be used when separating and recovering isoprene from a mixed fluid raw material containing isoprene, such as a C5 fraction. Furthermore, the isoprene separation and recovery apparatus of the present invention can be suitably used, for example, when separating and recovering isoprene using the isoprene separation and recovery method of the present invention.

[0022] (Method for separating and recovering isoprene) The present invention provides a method for separating and recovering isoprene from a mixed fluid containing isoprene. Furthermore, the isoprene separation and recovery method of the present invention includes the steps of: extracting and distilling a mixed fluid containing isoprene to obtain a fraction containing impurities whose solubility in the extraction solvent used in the extracting and distillation is lower than that of isoprene, and a fraction containing crude isoprene (extracting and distillation step); optionally, dividing and distilling the fraction containing crude isoprene in the presence of a polymerization inhibitor to obtain a fraction containing impurities with a higher boiling point than isoprene, a fraction containing impurities with a lower boiling point than isoprene, and a fraction containing high-purity isoprene (dividing and distillation step); optionally, further extracting and distilling the fraction containing high-purity isoprene to obtain a fraction containing impurities whose solubility in the extraction solvent used in the extracting and distillation is higher than that of isoprene, and a fraction containing even higher-purity isoprene (second extracting and distillation step); and further removing the polymerization inhibitor used in the dividing and distillation from the fraction containing high-purity isoprene (removal step).

[0023] Furthermore, in the isoprene separation and recovery method of the present invention, by performing partial distillation of the fraction containing crude isoprene, the heat load can be reduced, thereby reducing the amount of isoprene polymer generated when isoprene is separated and recovered from the mixed fluid containing isoprene. Consequently, the frequency of polymer cleaning, which requires stopping the operation of the isoprene separation and recovery apparatus, can be reduced.

[0024] Furthermore, in the fractional distillation step of the isoprene separation and recovery method of the present invention, polymerization reactions during fractional distillation can be suppressed by performing fractional distillation in the presence of a polymerization inhibitor. Generally, the operating pressure and temperature when performing fractional distillation are relatively high compared to normal distillation, so polymerization reactions are likely to occur during fractional distillation. However, by performing fractional distillation in the presence of a polymerization inhibitor, polymerization reactions during fractional distillation can be suppressed, and fouling and clogging of equipment such as fractional distillation columns can be prevented.

[0025] Furthermore, in the isoprene separation and recovery method of the present invention, the polymerization inhibitor used in the fractional distillation is removed from the fraction containing high-purity isoprene, thereby preventing the polymerization inhibitor from being present in the high-purity isoprene. Specifically, if a polymerization inhibitor is present in high-purity isoprene, polymerization will be inhibited even when attempting to polymerize the high-purity isoprene. However, by removing the polymerization inhibitor used in the fractional distillation, it is possible to prevent the polymerization from being inhibited when attempting to polymerize high-purity isoprene.

[0026] Furthermore, in the isoprene separation and recovery method of the present invention, by extracting the fraction containing high-purity isoprene as a gas during the divided distillation process, it is possible to prevent the high-purity isoprene from containing polymerization inhibitors. Specifically, if high-purity isoprene contains polymerization inhibitors, polymerization will be inhibited even if an attempt is made to polymerize the high-purity isoprene. However, by extracting the fraction containing high-purity isoprene as a gas, it is possible to prevent the high-purity isoprene from containing polymerization inhibitors, thereby preventing the polymerization from being inhibited when attempting to polymerize high-purity isoprene.

[0027] <Mixed fluid containing isoprene> The mixed fluid preferably contains 1% by mass or more of isoprene. By having an isoprene content of 1% by mass or more in the mixed fluid, isoprene can be efficiently separated and recovered from the mixed fluid. Typically, the isoprene content in the mixed fluid is 5% by mass or more and 30% by mass or less. In addition to isoprene, the mixed fluid may contain n-pentane, 1,4-pentadiene, 2-butyne, piperylene, cyclopentadiene, etc.

[0028] <Extraction and Distillation Process> In the extraction and distillation process of the method for separating and recovering a mixed fluid according to the present invention, impurities whose solubility in the extraction solvent used for the extraction and distillation differs from that of isoprene are separated from the mixed fluid by extraction and distillation of the mixed fluid containing the mixed fluid, thereby obtaining a fraction containing crude isoprene.

[0029] [Extractive Distillation] Figure 1 is a schematic diagram of an example of an isoprene separation and recovery apparatus capable of carrying out the isoprene separation and recovery method according to the present invention. In Figure 1, the extractive distillation section 10 includes, for example, a first extractive distillation column 12 that extractive distills a mixed fluid raw material containing isoprene, such as a C5 fraction, to separate it into a fraction (C) and an extract (D), and a decontamination column 13 that removes a solvent from the extract (D).

[0030] Then, in the first extraction distillation column 12, the solvent is supplied to the upper stage (upper vertical direction) from the feed stage of the mixed fluid raw material containing isoprene such as the C5 fraction, and extraction distillation is performed to distill off a fraction (C) containing n-pentane (boiling point: 36.1°C), which is less soluble than isoprene in the solvent, from the top of the column, and an extract (D) containing isoprene, 1,4-pentadiene, 2-butyne, piperylene, cyclopentadiene, etc. is discharged from the bottom of the column.

[0031] Furthermore, known solvents used in the extraction distillation of C5 fractions, such as the solvent described in International Publication No. 99 / 051552, can be used as the solvent supplied to the first extraction distillation column 12. Among these, amide compounds are preferred, and dimethylformamide is more preferred. By using an amide compound, particularly dimethylformamide, as the extraction solvent, extraction distillation can be carried out efficiently.

[0032] Furthermore, in the evaporation column 13, the solvent is discharged from the bottom of the column, and a fraction (X) containing isoprene, 1,4-pentadiene, 2-butyne, piperylene, cyclopentadiene, etc. (a fraction containing crude isoprene) is distilled from the top of the column. The solvent recovered in the evaporation column 13 can be reused as needed in the first extraction distillation column 12 or the second extraction distillation column 15, which will be described later.

[0033] <Partial Distillation Process> In the partial distillation process of the isoprene separation and recovery method of the present invention, impurities with higher boiling points than isoprene and impurities with lower boiling points than isoprene are separated from the fraction containing crude isoprene by partial distillation, thereby obtaining a fraction containing high-purity isoprene. By performing partial distillation of the fraction containing crude isoprene in this way, the heat load can be reduced compared to the case in which the removal of high-boiling point components and the removal of low-boiling point components by distillation are carried out in two stages, and consequently, the amount of isoprene polymer generated when isoprene is separated and recovered from the mixed fluid containing isoprene can be reduced. Therefore, the frequency of polymer cleaning, which requires stopping the operation of the isoprene separation and recovery apparatus, can be reduced.

[0034] [Divided Distillation] Here, divided distillation, as described in Japanese Patent Publication No. 2016-524522, for example, uses a divided distillation column to discharge high-boiling-point components (fractions containing impurities with higher boiling points than isoprene) from the bottom of the column, medium-boiling-point components from the central region of the column, and low-boiling-point components (fractions containing impurities with lower boiling points than isoprene) from the top of the column, thereby obtaining a fraction containing impurities with higher boiling points than isoprene, a fraction containing impurities with lower boiling points than isoprene, and a fraction containing high-purity isoprene. The isoprene concentration in the fraction containing impurities with lower boiling points than isoprene, that is, the isoprene concentration at the top of the divided distillation column 21, is preferably 5% by mass or more and 90% by mass or less, and more preferably 10% by mass or more and 70% by mass or less. Thus, if the isoprene concentration in a fraction containing impurities with a lower boiling point than isoprene is between 5% by mass and 90% by mass, it is possible to prevent high-boiling-point components (impurities with a higher boiling point than isoprene) and low-boiling-point components (impurities with a lower boiling point than isoprene) from mixing with the medium-boiling-point components, thereby efficiently separating the high-boiling-point and low-boiling-point components. Typically, the isoprene concentration in a fraction containing impurities with a lower boiling point than isoprene is between 15% by mass and 25% by mass. Furthermore, it is preferable that the fraction containing impurities with a higher boiling point than isoprene contains 3% by mass or more of piperylene, which is a useful component.

[0035] - Split Distillation Column - Examples of split distillation columns include, for example, a vertical split column having split walls arranged in the longitudinal direction, as described in Japanese Patent Publication No. 2016-524522. The split wall divides the inside of the column into, for example, a feed section (left side of the split wall), a removal section (right side of the split wall), an upper-bound column section (rectification section), and a lower-bound column section (stripping section). The feed port (feed inlet) for supplying the fraction containing crude isoprene to be subjected to split distillation is generally located in the central region of the feed section (i.e., between the upper and lower regions of the feed section). One or more additional feed ports (feed inlets) may be provided in the central region of the feed section. Also, generally, one or more side flow outlets are located in the central region of the removal section (i.e., between the upper and lower regions of the removal section). One or more additional side flow outlets may be provided in the central region of the removal section. By using the split distillation column described above, it is possible to reduce costs by approximately 30% and shorten the residence time of the treated substance compared to the case of direct connection of a conventional high-boiling and low-boiling distillation column (for example, the case shown in Figure 2 later). In addition, it is possible to perform split distillation of the mixed fluid with a low heat load (separating and removing high-boiling and low-boiling components from the fraction containing crude isoprene).

[0036] The following will explain, with reference to the drawings, the case in which partial distillation is performed in a partial distillation section consisting of a partial distillation column. In Figure 1, the partial distillation section 20 includes, for example, a partial distillation column 21 that performs partial distillation of a fraction (X) containing crude isoprene distilled from the top of the decontamination column 13. The partial distillation column 21 distills off a fraction (E) containing low-boiling-point impurities such as 1,4-pentadiene (boiling point: 26°C) and 2-butyne (boiling point: 27°C) contained in the fraction (X) obtained in the extraction distillation section 10 from the top of the column, a fraction (F) containing high-boiling-point impurities such as piperylene (boiling point: 42°C) from the bottom of the column, and high-purity isoprene (boiling point: 34.1°C) is distilled off from the central region of the column as a fraction (G) enriched with isoprene (boiling point: 34.1°C).

[0037] In addition, when performing divided distillation, the operating pressure and temperature are generally relatively high compared to normal distillation, making polymerization reactions more likely to occur during divided distillation. Therefore, polymerization reactions are likely to occur in the divided distillation column 21, but by performing divided distillation in the presence of a polymerization inhibitor, polymerization reactions during divided distillation can be suppressed, preventing fouling and clogging in the divided distillation column 21.

[0038] -Polymerization inhibitor- There are no particular restrictions on specific examples of polymerization inhibitors; for example, 4-tertiary butylcatechol (TBC), diethylhydroxyamine (DEHA), etc., can be used.

[0039] There are no particular restrictions on the amount of polymerization inhibitor to be present during fractional distillation, but from the viewpoint of suppressing polymerization reactions during fractional distillation, it is preferable that the amount be 1 ppm by mass or more relative to crude isoprene, and from the viewpoint of reducing the amount of polymerization inhibitor in high-purity isoprene, it is preferable that the amount be 100 ppm by mass or less relative to the mass of crude isoprene.

[0040] The location of supplying the polymerization inhibitor is not particularly limited, as long as the polymerization inhibitor is present during the split distillation. The polymerization inhibitor may be supplied directly to the split distillation column 21, or it may be supplied to the piping immediately preceding the split distillation column 21. By supplying the polymerization inhibitor in the vertically upper part of the split distillation column 21 above the supply stage for the fraction (X) containing crude isoprene, the polymerization inhibitor can be distributed throughout the entire split distillation column 21.

[0041] Furthermore, in the divided distillation section 20, the fraction containing high-purity isoprene is extracted as a gas from the divided distillation column 21, thereby preventing the high-purity isoprene from containing polymerization inhibitors. Specifically, if high-purity isoprene contains polymerization inhibitors, polymerization will be inhibited even when attempting to polymerize the high-purity isoprene. However, by extracting the fraction containing high-purity isoprene as a gas from the divided distillation column 21, it is possible to prevent the high-purity isoprene from containing polymerization inhibitors, thereby preventing the polymerization from being inhibited when attempting to polymerize the high-purity isoprene.

[0042] <Second Extractive Distillation Step> In the method for separating and recovering isoprene of the present invention, it is preferable to further subject the fraction containing high-purity isoprene to extractive distillation (second extractive distillation). By thus further subjecting the fraction containing high-purity isoprene to extractive distillation (second extractive distillation), a fraction containing even higher-purity isoprene can be obtained. Here, regarding cyclopentadiene, which is a substance highly soluble in the extraction solvent, by previously reducing the cyclopentadiene concentration of the fraction containing high-purity isoprene in the split distillation section, even higher-purity isoprene can be efficiently produced in the second extractive distillation.

[0043] [Second Extractive Distillation] In FIG. 1, the second extractive distillation section 30 includes a second extractive distillation column 15 that further subjects the fraction (G) containing high-purity isoprene to extractive distillation (second extractive distillation) and separates it into a fraction (A) and an extract (B), and a stripping column 16 that removes the solvent from the extract.

[0044] In the second extractive distillation column 15, the solvent is supplied to a stage above (vertically above) the supply stage of the fraction (G) containing high-purity isoprene distilled from the split distillation column 21, and the fraction (G) containing high-purity isoprene is further subjected to extractive distillation (second extractive distillation). As a result, a fraction (A) containing even higher-purity isoprene is distilled from the top of the column, and an extract (B) containing a substance (e.g., cyclopentadiene) more soluble in the solvent than isoprene is withdrawn from the bottom of the column. In the stripping column 16, the solvent is withdrawn from the bottom of the column, and a substance more soluble in the solvent than isoprene is distilled from the top of the column. The solvent recovered in the stripping column 16 can be arbitrarily reused in the first extractive distillation column 12, the second extractive distillation column 15, etc.

[0045] As the solvent to be supplied to the second extractive distillation column 15, for example, known solvents used in the extractive distillation of C5 fractions, such as the solvents described in International Publication No. 99 / 051552, can be used. Among these, amide compounds are preferable, and dimethylformamide is more preferable. By using an amide compound, particularly dimethylformamide, as the extraction solvent, other extractive distillations can be efficiently performed.

[0046] <Removal Step> Also, in the method for separating and recovering isoprene of the present invention, the polymerization inhibitor used in the fractional distillation in the fractional distillation column 21 is removed from the fraction containing high-purity isoprene. By removing the polymerization inhibitor used in the fractional distillation in the fractional distillation column 21 from the fraction containing high-purity isoprene in this way, it is possible to prevent the high-purity isoprene from containing the polymerization inhibitor. Specifically, if the high-purity isoprene contains a polymerization inhibitor, the polymerization will be inhibited even when attempting to polymerize the high-purity isoprene. However, if the polymerization inhibitor used in the fractional distillation in the fractional distillation column 21 is removed from the fraction containing high-purity isoprene, it is possible to prevent the polymerization from being inhibited when attempting to polymerize the high-purity isoprene. As a method for removing the polymerization inhibitor, there is no particular limitation, and for example, a method of washing the fraction containing high-purity isoprene with water, a method of separating by distillation, etc. can be used.

[0047] (Isoprene Separation and Recovery Apparatus) Also, the isoprene separation and recovery apparatus of the present invention can be suitably used when separating and recovering isoprene using the above-described isoprene separation and recovery method. And an example of the isoprene separation and recovery apparatus of the present invention has a configuration as shown in FIG. 1, for example.

[0048] Here, the separation and recovery apparatus 100 shown in FIG. 1 includes an extractive distillation unit 10 that performs extractive distillation on a mixed fluid as a raw material to obtain a fraction (X) containing crude isoprene, and a fractional distillation unit 20 that performs fractional distillation on the fraction (X) obtained in the extractive distillation unit 10 to obtain a fraction (E) containing impurities with a lower boiling point than isoprene, a fraction (F) containing impurities with a higher boiling point than isoprene, and high-purity isoprene as a fraction (G) enriched with high-purity isoprene. The separation and recovery apparatus 100 further includes a second extractive distillation unit 30 that performs extractive distillation on the fraction (G) enriched with isoprene to obtain a fraction containing even higher-purity isoprene. In the separation and recovery apparatus 100, as the mixed fluid, a C5 fraction or the like that is by-produced when producing ethylene by hydrocarbon steam cracking or other high-temperature treatments can be used.

[0049] <Extraction and Distillation Section> In Figure 1, the extraction and distillation section 10 includes a supply port for supplying a mixed fluid raw material containing isoprene, such as a C5 fraction, and a first extraction and distillation column 12 that extracts and distills (first extraction and distillation) the mixed fluid raw material supplied through the supply port to separate it into a fraction (C) and an extract (D).

[0050] Then, in the first extraction distillation column 12, the solvent is supplied to the upper stage (upper vertical direction) from the mixed fluid supply stage, and the mixed fluid is subjected to extraction distillation (first extraction distillation), causing a fraction (C) containing pentane, pentene, etc., which are less soluble in the solvent than isoprene, to be distilled from the top of the column, while an extract (D) containing isoprene, 1,4-pentadiene, 2-butyne, piperylene, cyclopentadiene, etc., to be discharged from the bottom of the column.

[0051] Furthermore, known solvents used in the extraction distillation of C5 fractions, such as the solvent described in International Publication No. 99 / 051552, can be used as the solvent supplied to the first extraction distillation column 12. Among these, amide compounds are preferred, and dimethylformamide is more preferred. By using an amide compound, particularly dimethylformamide, as the extraction solvent, extraction distillation can be carried out efficiently.

[0052] Furthermore, in the evaporation column 13, the solvent is discharged from the bottom of the column, and a fraction (X) containing isoprene, 1,4-pentadiene, 2-butyne, piperylene, cyclopentadiene, etc. (a fraction containing crude isoprene) is distilled from the top of the column. The solvent recovered in the evaporation column 13 can be reused in the first extraction distillation column 12 or the second extraction distillation column 15, if desired.

[0053] <Divided Distillation Section> In Figure 1, the divided distillation section 20 has a supply port for supplying a fraction (X) (a fraction containing crude isoprene) obtained by removing the solvent from the extract (D), and is equipped with a divided distillation column 21 that performs divided distillation (divided distillation) on the fraction (X) supplied through the supply port. The divided distillation column 21 distills off a fraction (E) containing low-boiling point impurities such as 1,4-pentadiene and 2-butyne from the top of the column, a fraction (F) containing high-boiling point impurities such as piperylene from the bottom of the column, and a fraction (G) containing high-purity isoprene from the central region of the column.

[0054] <Second Extraction Distillation Section> In Figure 1, the second extraction distillation section 30 includes a second extraction distillation column 15 that further extracts and distills (second extraction distillation) a fraction (G) containing high-purity isoprene to separate it into a fraction (A) (a fraction containing even higher-purity isoprene) and an extract (B), and a decontamination column 16 that removes the solvent from the extract.

[0055] In the second extraction distillation column 15, solvent is supplied to the upper stage (vertically upward) above the feed stage of the fraction (G) containing high-purity isoprene distilled from the split distillation column 21, and the fraction (G) containing high-purity isoprene is further extracted and distilled (second extraction distillation). This causes a fraction (A) containing even higher purity isoprene to distill from the top of the column, and an extract (B) containing a substance more readily soluble in the solvent than isoprene (e.g., cyclopentadiene) to be discharged from the bottom of the column. In the decontamination column 16, the solvent is discharged from the bottom of the column, and a substance more readily soluble than isoprene is distilled from the top of the column. The solvent recovered in the decontamination column 16 can be reused in the first extraction distillation column 12 or the second extraction distillation column 15 as desired.

[0056] Furthermore, as the solvent supplied to the second extraction distillation column 15, known solvents used for the extraction distillation of C5 fractions, such as the solvent described in International Publication No. 99 / 051552, can be used. Among these, amide compounds are preferred, and dimethylformamide is more preferred. By using an amide compound, particularly dimethylformamide, as the extraction solvent, other extraction distillations can be carried out efficiently.

[0057] The isoprene separation and recovery apparatus of the present invention has been described above using one example, but the isoprene separation and recovery apparatus of the present invention is not limited to the above example. Furthermore, the configuration of the extraction distillation section 10, the split distillation section 20, and the other extraction distillation sections 30 is not limited to the above configuration, and can be changed to any configuration that enables the separation and recovery of isoprene.

[0058] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples.

[0059] (Example 1) Isoprene was separated and recovered using the separation and recovery apparatus 100 shown in Figure 1. Specifically, isoprene was separated and recovered from a mixed fluid consisting of the C5 fraction, which is a by-product when ethylene is produced by steam cracking or other high-temperature processing of hydrocarbons. The amount of isoprene in the mixed fluid consisting of the C5 fraction was 20% by mass. The compositions of the mixed fluid (C5 fraction), fraction (C), fraction (E), fraction (F), and fraction (G) were measured using a gas chromatograph (Agilent Technologies, 7890A) under the following conditions. The results are shown in Table 1. • Gas chromatograph: Agilent® 7890A (manufactured by Agilent Corporation) • Column: Agilent 19091P-S33, 30.0 m × 250 μm × 5.00 μm • Column temperature: 35°C × 2.5 min ⇒ increase at 5°C / min ⇒ 100°C ⇒ increase at 10°C / min ⇒ 180°C × 10 min • Injection temperature: 200°C • Detector temperature: 200°C • Carrier gas: Helium • Split ratio: 200 / 1 • Detector: FID

[0060]

[0061] (Comparative Example 1) Isoprene was separated and recovered in the same manner as in Example 1, except that the separation and recovery apparatus 200 shown in Figure 2 was used instead of the separation and recovery apparatus 100 shown in Figure 1. The separation and recovery apparatus 200 is the same as in Figure 1, except that the divided distillation section 20 is replaced by an impurity removal section 40.

[0062] <Impurity Removal Section> The impurity removal section 40 includes a low-boiling-point removal column 41 that removes impurities with a lower boiling point than isoprene contained in the fraction (X), and a high-boiling-point removal column 42 that removes impurities with a higher boiling point than isoprene.

[0063] Then, in the low-boiling-point substance removal column 41, a fraction (E) containing impurities with a lower boiling point than isoprene is distilled off from the top of the column, and a bottom-effect liquid enriched with isoprene is discharged from the bottom of the column.

[0064] Furthermore, in the high-boiling-point substance removal column 42, a fraction (G) further enriched with isoprene is distilled from the top of the column, while a fraction (F) containing impurities with higher boiling points than isoprene is discharged from the bottom of the column.

[0065] In Example 1 and Comparative Example 1, after one year of continuous operation, the distillation columns were stopped and visually inspected. The amount of isoprene polymer produced in Example 1 was less than in Comparative Example 1.

[0066] According to the isoprene separation and recovery method and apparatus of the present invention, by performing segmented distillation, the heat load can be reduced, thereby reducing the amount of isoprene polymer produced, and consequently, the frequency of polymer cleaning, which requires stopping the operation of the isoprene separation and recovery apparatus, can be reduced.

[0067] 10 Extraction distillation section 12 First extraction distillation column 13 Deposition column 15 Second extraction distillation column 16 Deposition column 20 Split distillation section 21 Split distillation column 30 Second extraction distillation section 40 Impurity removal section 41 Low boiling point substance removal column 42 High boiling point substance removal column 100 Separation and recovery device 200 Separation and recovery device

Claims

DEPCT631. Method for the separation and recovery of isoprene from a fluid mixture containing isoprene, which includes a distillation step to extract the fluid mixture to obtain fractions containing impurities with lower solubility than isoprene in the distillation extraction medium and fractions containing crude isoprene, and a partition wall distillation step to distill the partition wall of the crude isoprene fractions to obtain fractions containing impurities with boiling points higher than isoprene, fractions containing impurities with boiling points lower than isoprene, and high-purity isoprene fractions.

2. Method for the separation and recovery of isoprene according to Patent 1, where the extraction medium used in the distillation step is an amide compound.

3. Method for the separation and recovery of isoprene according to Patent 2, where the amide compound is dimethylformamide. 4.The method of separation and recovery of isoprene under one of the claims 1 to 3, which includes an additional distillation step for further extraction of the fraction containing high-purity isoprene to obtain a fraction containing contaminants with higher solubility than isoprene in the extraction medium used in the distillation, and a fraction containing even higher purity isoprene.

5. The method of separation and recovery of isoprene under claim 4, where the extraction medium used in the second distillation step is an amide compound.

6. The method of separation and recovery of isoprene under claim 5, where the amide compound is dimethylformamide.

7. The method of separation and recovery of isoprene under one of the claims 1 to 6, where the fraction containing contaminants with boiling points lower than isoprene has an isoprene concentration of not less than 5% by mass and not more than 90% by mass. 8.

9. One of the methods for isoprene separation and recovery under Reimbursements 1 to 7, where partition wall distillation in the partition wall distillation step is performed with not less than 1 ppm by mass and not more than 100 ppm by mass of polymerization inhibitor relative to crude isopburement.

10. One of the methods for isoprene separation and recovery under Reimbursements 1 to 8, where partition wall distillation in the partition wall distillation step is performed in the partition wall column and the polymerization inhibitor is fed from the top section in the vertical direction of the partition wall column.

11. One of the methods for isoprene separation and recovery under Reimbursements 1 to 9, where the fraction containing high-purity isopburement is a gas.

12. One of the methods for isopburrene separation and recovery under Reimbursements 1 to 9, which includes an additional step for separating the polymerization inhibitor from the fraction containing high-purity isopburement.The isoprene separation and recovery equipment comprises a distillation section, which includes a feed section for feeding the mixed fluid containing isoprene and where the distillation of the mixed fluid is extracted to obtain fractions containing contaminants with lower solubility than isoprene in the extraction medium and fractions containing crude isoprene; and a partition wall distillation section, which includes a feed section for feeding the fractions containing crude isoprene and where the partition wall of the fractions containing crude isoprene is distilled to obtain fractions containing contaminants with boiling points higher than isoprene, fractions containing contaminants with boiling points lower than isoprene, and high-purity fractions containing isoprene.13.The isoprene separation and recovery apparatus under claim12 incorporates a secondary distillation section which includes a feed section for feeding fractions containing high-purity isoprene and which performs further distillation of the high-purity isoprene fractions to obtain fractions with higher solubility impurities than isoprene in the distillation extraction medium and higher-purity isoprene fractions.