JPH0354718B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an improved process for the separation of ethylenically unsaturated hydrocarbons from hydrocarbon mixtures containing them.

Various hydrocarbon mixtures have been obtained from the pyrolysis of petroleum products such as naphtha, gas oil, kerosene, crude oil, etc. A typical hydrocarbon mixture from a cracking operation is pyrolysis gasoline containing aromatic and cycloparaffinic compounds, generally having 5 to 10 carbon atoms. Typical hydrocarbon mixtures obtained after removal of hydrocarbons containing 5 carbon atoms are shown in Table A.
It was shown to.

Table A Compound Weight % Non-aromatic 16-18 Benzene 33-37 Toluene 16-20 Etherbenzene 1-2 p/m xylene 5-7 o-xylene 2-3 Styrene 6-8 Dimethylcyclopentadiene <1 C ₉ aromatic ~1 α-methylstyrene <1 Vinyltoluene 2.5-3 Indene 2.5-3 Methylindene <1 Naphthalene <1 Phenylacetylene 0.1 or less The above hydrocarbon mixtures were used to illustrate typical hydrocarbon mixtures. It is to be understood that this is not intended to define such mixtures, as hydrocarbon mixture compositions can vary widely.

One of the more industrially valuable components found in the above products is styrene. Economic means of separating this preferred component have long been sought. Separating styrene from these mixtures by fractional distillation is impractical due to the presence of other components, particularly o-xylene, which have boiling points very close to that of styrene. Table B shows the boiling points of styrene and other hydrocarbons.

Table B Compound Boiling Point °C α-Methylstyrene 163.4 n-Propylbenzene 159.2 Cumene 152.4 Cyclooctane 148.5 Styrene 145.2 O- Xylene 144.4 3-Methyloctane 143−144 Cyclooctene 138−143 Phenylacetylene 142.4 4-Methyloctane 141− 142m -Xylene 139.1 p-xylene 138.4 Ethylbenzene 136.2 Toluene 110.6 One of the more widely used processes to utilize this styrene is to hydrogenate it to ethylbenzene, which is then separated from the xylene by precision fractional distillation. . After this distillation,
The ethylbenzene is then hydrogenated to styrene and purified by distillation again. This method is extremely complex and expensive. The disadvantages of the aforementioned methods have prompted research into the direct separation of styrene from hydrocarbon mixtures without first converting the styrene to ethylbenzene.

British Patent No. 1038606 proposes a method for extracting styrene from a hydrocarbon mixture using an aqueous solution of a silver salt such as AgNO ₃ and then treating with a mixture of clay to prevent slime formation. This method has the disadvantage of being expensive due to the use of silver salts.

Also, US Pat. No. 3,328,267 proposes a process consisting of extractive distillation for the separation of styrene using a di-lower-alkylformamide such as dimethylformamide as the extractive distillation solvent. This method uses quinone or hydroquinone or preferably p
Polymerization inhibitors such as -tert-butylpyrocatechol are also utilized. However, the styrene produced by this method has the undesirable property of being pale yellow in color. Furthermore, the temperature of the polymerization inhibitor needs to be low.

U.S. Pat. No. 3,580,839 (Fuerst) is entitled "Recovery of Aromatic Hydrocarbons from Hydrocarbon Mixtures by Selective Extraction Using Substituted Piperazine Solvents" and includes piperazine derivatives having the general formula: (where X is formyl or acetyl and R is lower alkyl). It is proposed to be used as an extractant. Therefore, this method separates a hydrocarbon mixture into two fractions; one containing mainly aromatic hydrocarbons such as benzene, toluene, xylene, ethylbenzene and styrene, and the other mainly containing paraffins, olefins and cycloparaffins. We propose separation into other fractions containing Piperazine derivatives can be used in pure form or mixed with other extractants such as tetramethylsulfone, diethylene glycol or triethylene glycol. N-formyl-N'-methylpiperazine is the preferred extractant. This process aims at general separation of the products.

In U.S. Pat. No. 3,684,665, Abe et al. disclose a process for the separation of styrene from hydrocarbons, including xylenes, by concentrating the styrene in a solvent, from which the styrene can then be recovered by extractive distillation using a suitable solvent. We propose a method consisting of Suitable solvents include dialkyl sulfoxides, alkylene carbonates, lactones, lactams, phenols, alkylphenols, salicylic acid, alkyl esters, aniline, alkylanilines,
Includes dialkylacetamides such as dimethylacetamide along with phthalic acid alkyl esters, tetraalkylureas, N,N'-dialkylcarbamate esters and glycol monoalkyl esters such as diethylene glycol monoalkyl ether and N-methylpyrrolidone. It will be done. The use of polymerization inhibitors such as hydroquinone, tert-butylcatechol, phenothiazine, sulfur or mixtures thereof acts to prevent styrene polymerization. This process, however, suffers from polymerization losses at temperatures above 100° C., producing styrene that is undesirably yellow in color.

In U.S. Pat. No. 3,736,015, Morimoto et al. show another extractive distillation process using a polar organic solvent in the coexistence of a nitrile polymerization inhibitor. Following extractive distillation, the styrene-containing solvent is treated with nitric acid and then distilled again to remove impurities and separate the styrene from the solvent. Suitable solvents for this process are indicated as diethylacetamide, β-methylpropionitrile, butyllactone, N-methylpyrrolidone, dimethylformamide and dimethylsulfoxide. Preferred polymerization inhibitors are sodium nitrite or potassium nitrite, used in combination with a compound having at least one nitro, nitroso, quinoid, phenolic or hydroxyl group in the molecule. Preferred additives are p-tert-butyl-catechol, hydroquinone, p-benzoquinone, p-dinitrosobenzene, alpha-nitro-beta-naphthol, o-nitrosonaphthol and alpha-naphthoquinone. This process produces a yellow styrene product that requires further treatment with nitric acid to remove colored impurities. Another problem is a decrease in yield due to polymerization.

In view of the above-mentioned shortcomings of the prior art, monovinylidene aromatics or other ethylenically unsaturated hydrocarbons,
It would be highly desirable to provide an effective separation method from hydrocarbon mixtures containing the same that simultaneously prevents polymerization and produces substantially pure, colorless products.

The present invention uses N-(aminoalkyl) as an extractive distillation solvent when extractively distilling a hydrocarbon mixture containing ethylenically unsaturated hydrocarbons to separate ethylenically unsaturated hydrocarbons from the hydrocarbon mixture.
A method for separating ethylenically unsaturated hydrocarbons from a hydrocarbon mixture is provided, the method comprising using piperazine.

The unsaturated hydrocarbons can then be separated off from the amine fraction, or the next process can be carried out without separation.

Surprisingly, in the extractive distillation process using amines as described above, ethylenically unsaturated hydrocarbons are extracted from hydrocarbon mixtures containing them as described in US Pat.
Effective separation can be achieved without the addition of other solvents and/or polymerization inhibitors as described in 3763015 and 3684665. Using the method, aliphatic unsaturated hydrocarbons such as butadiene or acetylene or monovinylidene aromatics such as styrene or vinyltoluene with unexpectedly high purity and/or desirable color can be produced without significant losses due to polymerization. You can get it without any problems. In a preferred embodiment of the invention, the amine is N-(aminoethyl)piperazine (AEP)
It is. In a particularly preferred embodiment, AEP is used as an amine solvent or as an extractant in an extractive distillation process for the separation of styrene from styrene-containing hydrocarbon mixtures. Due to the removal of colored substances by AEP, styrene with the desired color on the market can often be recovered with purity exceeding 99%.

An understanding of the invention will be facilitated by reference to the accompanying drawings. Figure 1 shows vinyltoluene and other _C9
FIG. 2 is a schematic diagram illustrating an embodiment of the invention particularly useful for the separation of vinyltoluene from aromatics or acetylene from mixtures containing butadiene and butenes; FIG. 2 illustrates another, more preferred embodiment of the invention; In the schematic diagram shown, the embodiment is particularly useful for separating styrene from hydrocarbon mixtures consisting primarily of hydrocarbons having 6 to 10 carbon atoms.

The method of the invention is best illustrated through a basic discussion of extractive distillation. Extractive distillation refers to a process in which high-boiling substances, often referred to as extractive distillation solvents, are added to alter the specific volatility of the hydrocarbon mixture to be subsequently separated using the extractive distillation process.

Generally, there are two main reasons for adding such solvents. The first reason is to change the specific volatility of one or more components in the feed stream. In particular, one or more components that have similar vapor pressures and distill together as long as they do not change the non-volatility of the components. For example, solvents change the non-volatility of unsaturated compounds and also change the specific volatility of materials with acetylenic unsaturation compared to materials with ethylenic unsaturation.

A second reason for using a solvent is to prevent azeotrope formation of the raw mixture components. Generally, the added solvent has a higher boiling point than the components in the raw mixture, thus preventing the formation of azeotropes.

With particular reference to the accompanying drawings: FIG. 1 schematically illustrates one embodiment of the present invention for separating ethylenically unsaturated hydrocarbons, such as vinyltoluene, from hydrocarbon mixtures containing them using an extractive distillation column. Illustrated. In the illustrated embodiment, a hydrocarbon mixture containing unsaturated hydrocarbons is fed to extractive distillation column 101 by line 10. Amine solvent, N-(aminoalkyl)
Piperazine is added to column 101 via line 11. Because it is generally desirable to maintain high concentrations of amines throughout the extractive distillation column, and because amines are generally less volatile than the components of the hydrocarbon feed, amines are preferably used to transport the hydrocarbon feed into the extractive distillation column. Add to the column at a point above the feed point. It is also preferred to add the solvent at a point sufficient below the top of the distillation column to make the amine concentration in the rising vapors negligible before passing the overhead product out. Steam exiting from the top of column 101 is led to overhead condenser 12 to condense the steam. A portion of the condensed vapor is returned to column 101 as a liquid overflow. Line 13 is 1,2,4 containing vinyltoluene and α-methylstyrene-dicyclopentadiene or generally α-methylstyrene and/or dicyclopentadiene.
- or carry away the distillate which is distilled off in the separation of vinyltoluene from a hydrocarbon mixture containing 1,2,3-trimethylbenzene. The extractables, ie ethylenically unsaturated hydrocarbons such as vinyltoluene, and high boiling components (bottoms) of the hydrocarbon feedstock are removed from the bottom of column 101 via line 14. Because amines have relatively high boiling points, the bottoms removed by line 14 generally contains a high concentration of amine. The materials removed through line 14 typically pass through reboiler 15 to return some of their components to column 101 as reboiler steam.

Most of the bottoms material is not returned to column 101 and enters stripping column 202. As illustrated in the embodiment shown in FIG. 1, additional amine is introduced into stripping column 202 via line 21 above the bottoms material inlet to the stripping column. Further addition of amines is not necessary for the process of the invention, but is preferred, especially when the bottoms leaving column 101 contain high boiling substances other than phenylacetylene or amines. Unsaturated hydrocarbons are transferred from column 202 as vapor to condenser 22
to condense gaseous substances. A portion of the condensed material is returned to column 202 and the remainder is withdrawn via line 23. The material in line 23 is essentially pure, ie, at least 98% pure, preferably at least 99% pure, and of excellent color.

The amine along with any impurities it may contain leaves the bottom of the stripping column and a portion of this material passes through the reboiler 24. The remaining portion generally contains impurities such as some high boilers and polymeric materials or the like, so the amine is effectively purified prior to reuse. As such a purification method, a method of subsequent distillation is generally effective. In FIG. 1, this purification is carried out by directing the amine to purification column 303, distilling off the more volatile impurities via line 30, and returning the amine to both the extractive distillation column and the stripping column via line 11. . Heavier or less volatile impurities can be removed via line 31.

FIG. 2 illustrates a preferred embodiment of the invention that is particularly useful for recovering styrene from hydrocarbon products obtained from the cracking of petroleum products such as naphtha, gas oil, kerosene or crude oil and the like. The preferred embodiment shown in Figure 2 includes (a) a first extractive distillation column 111 for separating styrene from liquids with close boiling points such as xylenes, especially o-xylene, and ethylbenzene; (b) amines; (c) a second extractive distillation column 333 for removing high-boiling substances and impurities from styrene; (c) a second extractive distillation column 333 for removing high-boiling substances and impurities from styrene; d) a solvent recovery column 444 for removing high boilers and impurities such as phenylacetylene from the amine; and (e) a solvent purification column 555 for removing heavy impurities such as polymers from the amine. including.

The recovery of styrene from hydrocarbon mixtures obtained from cracking operations typically requires a pre-distillation column (not shown) for the removal of light hydrocarbons, such as those having 5 or fewer carbon atoms, and generally 11 or more columns. A predistillation column (not shown) for the removal of heavy hydrocarbons, such as those containing carbon atoms, is often advantageously used prior to introducing hydrocarbons into column 111. In such a case, the removal of light and heavy hydrocarbons is carried out at normal pressure between 120°C and 160°C, preferably between 125°C and 155°C.
This process is effectively carried out under conditions that produce a hydrocarbon fraction having a boiling point of .degree.

In such an operation, a styrene-containing hydrocarbon mixture is introduced through line 2 into the first extractive distillation column. A hydrocarbon mixture is introduced into column 111. At a point above where the hydrocarbon mixture is introduced into column 111, the amine is introduced into the first extractive distillation column. In order to reduce the amine concentration in the overhead product, this amine inlet is located several trays (which may be the number of effective or theoretical plates) below the top of the column 111.
The exhaust vapor from the top of column 111 is conducted to an overhead condenser to condense the vapor and return a portion of it to the column. Line 4 withdraws the distillate for further processing and/or subsequent use. Generally speaking, the distillate consists primarily of xylene and ethylbenzene. The material discharged from the bottom of column 111 generally consists of separated styrene, amines, phenylacetylene and impurities such as higher boiling hydrocarbons and polymeric materials and is passed through line 5 to solvent stripping column 222. sent to. The remaining portion of this material is passed through a reboiler and the material is returned to column 111.

The amine is separated from the styrene in a solvent stripper column 222. The separated amine is sent to column 222.
It is extracted from the bottom of the column and introduced near the top of the extractive distillation column. The separated styrene, generally containing phenylacetylene and other impurities, exits the top of column 222, is condensed and passes a portion of the condensate through line 7 to column 333 at a point below the point of introduction of the amine.
lead to. In this second extractive distillation column 333, styrene is separated from phenylacetylene and high boiling materials, and styrene exits the top of column 333 relatively pure, preferably at least 99% pure. The relatively pure material is condensed and sent to line 8 for further use.
will be moved. The amine containing phenylacetylene and/or high boilers exits column 333 and a portion thereof is sent via line 9 to solvent recovery column 444. In the solvent recovery column 444, the amine and phenylacetylene are separated. The phenylacetylene exiting from the top of column 444 is condensed and sent to line 41.
A part of it is moved for next use.
The amine containing impurities, such as polymeric materials, is now removed from column 444 via line 42. A portion of this material is passed through a reboiler and returned to column 444. A second, relatively large portion of this material is returned via line 43 to line 3 for reuse in the first extractive distillation column. The remaining amine and high boiling impurities are introduced via line 42 to solvent purification column 555. In column 555, the amine is separated from high boiling impurities. The relatively pure separated amine exits the top of column 555 and passes through column 111.
It is returned to line 3 for continued reuse inside. Heavy impurities are withdrawn from the bottom of column 555 via line 44.

For those skilled in the art, it is possible to modify, remove, or add certain process features according to specific process parameters selected;
And it will be clear that such selection will depend on various practical considerations, such as economy, convenience, and energy conservation.

For example, although it is preferred that there be a high concentration of ethylenically unsaturated hydrocarbons to be separated in the hydrocarbon feedstock, lower concentrations are also suitable and within the scope of the present invention. However, in order to obtain a hydrocarbon feedstock containing higher concentrations of unsaturated hydrocarbons and thus improving the overall efficiency of the separation process,
Pre-distillation can be carried out efficiently. Additionally, components exhibiting volatility similar to the amine can reduce the practical performance of the amine and should preferably be removed. From the above description, it is clear that multiple separation columns are used at various points in the overall process, such as hydrocarbon feed introduction, amine recovery, etc., and/or purification of various streams. It must be. Additionally, the extractive distillation portion of the process in which the amine is used as a solvent may be carried out in one or more columns, with amine solvent recovery operations interposed between the columns.

With respect to the materials used in the practice of this invention, the hydrocarbon mixture from which the ethylenically unsaturated hydrocarbon is separated is at least two or more ethylenically unsaturated hydrocarbons, one of which is subsequently separated. It is a mixture of hydrocarbons. Ethylenically unsaturated hydrocarbons are ethylenically unsaturated (bonds) between two carbon atoms that are not part of an aromatic ring.
These include alkadienes such as butadiene, acetylene, monovinylidene aromatics such as styrene, alkyl-substituted styrenes such as vinyltoluene, and ethylvinylbenzene and vinylnaphthalene. Other hydrocarbon components may contain ethylenic unsaturation, such as vinyltoluene, which is often present in the separation of styrene from pyrolyzed petroleum products, but generally the other components are primarily aliphatic and This includes cycloaliphatic and aromatic hydrocarbons. Additionally, the hydrocarbon mixture may optionally include one or more inorganic components or substituent-bearing hydrocarbon components. The process of the invention is particularly effective for the separation of monovinylidene aromatics, especially styrene or vinyltoluene, from hydrocarbon mixtures containing one or more aromatic components other than styrene and/or vinyltoluene. Such other aromatic components generally include:
Benzene, toluene, ethylbenzene, o-, p
- and m-xylene and/or indene.
More particularly, the process of the present invention provides the separation of styrene from pyrolysis gasoline and the separation of vinyltoluene and α-
It is preferably utilized for the separation of vinyltoluene from mixtures of methylstyrene, dicyclopentadiene, or 1,2,4- or 1,2,3-trimethylbenzene.

The amines of the invention allow selective separation of unsaturated hydrocarbons from hydrocarbon mixtures and less than 1, preferably less than 0.5% by weight of unsaturated hydrocarbons can be separated by the process of the invention. It is so effective that it does not polymerize during the process.

A particularly preferably used amine as the N-(aminoalkyl)piperazine used in the present invention is an N-(aminoalkyl)piperazine having 1 to 4 carbon atoms, and the most preferred amine is N-(aminoalkyl)piperazine.
-(aminoethyl)piperazine.

The conditions under which separation of unsaturated hydrocarbons is most conveniently carried out will depend on a number of factors, including the particular amine used and the composition of the hydrocarbon mixture and the unsaturated hydrocarbons separated therefrom. As a particular embodiment, in a preferred embodiment in which an extractive distillation column is used to separate styrene from a hydrocarbon mixture containing o-xylene, the extractive distillation column or columns advantageously have a number of theoretical plates from 90 to 130; Preferably, the number of theoretical plates is 115 to 125. This number of stages has been effectively achieved by packing the column with packing such as regular sheet packing or dumped packing. The extractive distillation process is carried out at a combination of pressure and temperature conditions that are sufficiently effective for separation but do not promote undesirable polymerization.
Generally, this means that bottom temperatures of 120°C to 140°C are utilized to advantage, with temperatures of 120°C to 135°C being preferred.

Higher temperatures often promote undesirable reactions and reduce the economic efficiency of the process.
To help save energy costs and reduce undesirable reactions, the process is generally carried out under reduced pressure. Conveniently the bottom pressure is 70 to 125 mmHg.
The temperature is preferably maintained within the range of 110 to 120 mmHg. Similar considerations of efficiency and suppression of undesirable reactions are applied here. The temperature at the top of the column conveniently ranges from 45°C to 70°C, preferably from 45°C to 55°C. Conveniently the overhead pressure is approximately 30
The range is from 35 to 45 mmHg, preferably from 35 to 45 mmHg. The amine/styrene ratio of the hydrocarbon feedstock conveniently ranges from about 5 to 9, with a ratio of about 8 being preferred.

In another preferred embodiment of separating styrene from phenylacetylene by extractive distillation, the extractive distillation column or columns advantageously has a number of theoretical plates of 70 to 80, preferably 70 to 75. Columns used for separation typically have bubble cap, sheep or bulb trays. The number of stages can also be obtained by packed columns using packing such as sheets or dumped packing. Also,
The extractive distillation process is carried out at a combination of pressure and temperature conditions that are sufficiently effective for separation but do not promote undesired polymerization. Generally speaking,
This means that bottom temperatures of 140°C to 160°C are effectively used, with temperatures of 145°C to 150°C being preferred. Higher temperatures often promote undesired reactions, while lower temperatures result in a reduction in the economic efficiency of the process. The process generally operates at reduced pressure, saving energy costs and preventing undesired reactions. 100 in favor
Bottom pressures of between 120 mmHg and 100 mmHg are used.
A pressure of g is preferred. Similar considerations of efficiency and suppression of undesirable reactions apply here as well. The column top temperature is conveniently between 45°C and 70°C.
, preferably from 45°C to 55°C. The overhead pressure conveniently ranges from 30 to 45 mm Hg, with a pressure of 35 to 40 mm Hg being preferred. The amine/styrene ratio in the hydrocarbon feedstock advantageously ranges from 7 to 9, preferably about 8.

EXAMPLE 1 A total mixture obtained by pyrolysis of a petroleum fraction such as naphtha is separated by one of the conventional methods, e.g. by distillation at normal or reduced pressure, and heated to a temperature of about 125°C to 155°C. A boiling point fraction between This fraction contains styrene, xylenes, ethylbenzene, paraffins, naphthalene, polyalkyl-substituted aromatics, phenylalkynes, and dienes with 4 to 9 carbon atoms, and typically contains 65
It had the APHA color of Representative examples of such mixtures are: Ingredients Weight % Light Hydrocarbons 0.6 Benzene and Toluene 6.0 Ethylbenzene 8.0 m- and p-xylene 32.0 o-xylene 14.0 Styrene 37.8 C-9 fraction 0.7 C-8 fraction and other aromatics 0.7 This mixture was reduced to approx. It was fed into a packed column about 50 m high with a theoretical plate number of 100 to about 125 and introduced at a point about 20 m below the top of the column. AEP was fed to the column at a point near the top, eg about 2 meters below the top, in a 3:1 weight ratio of AEP:hydrocarbon feed. The reflux ratio was 7.5. The top pressure and temperature were about 40 mm Hg and about 60°C, and the reboiler temperature was about 130°C. Even with this high temperature, losses due to polymerization were less than 0.2% based on the styrene present in the feed.
The top product of this column contained only about 1.0% styrene, and the bottom product contained almost all of the styrene originally present in the feed. The bottoms product containing styrene AEP and phenylacetylene was sent to a stripping column where the AEP was recovered substantially free of styrene, phenylacetylene and colorants. Styrene with hydrocarbon mixture/
Phenyl acetylene from the top of this tower about 70 to 80
It was sent to a second packed distillation column with a height of about 30 m and having a number of plates, and was introduced about 30 m below the top of the column.
The AEP recovered from the bottom of the stripping column acts as a solvent and is added to the second distillation column from the top of the column.
Point AEP:hydrocarbon feed was fed at a weight ratio of approximately 8:1 2.5 m below. The reflux ratio was approximately 4. The top pressure and temperature were about 35 mm Hg and about 50°C, respectively, and the reboiler temperature was about 55°C.

The top product of this second packed distillation column is approximately 99.6%
It contained pure styrene and was colorless. AEP acts as a very efficient inhibitor so that styrene polymerization was virtually zero in this second distillation column. Since the colored compounds present remained in the AEP, high purity, low colored styrene was obtained from the top of the second column. The styrene product from the second extractive distillation column had an APHA color of 5 or less. Note that the higher the reflux ratio of the extractive distillation column, the greater the dilution of the extractant by increasing the amount of non-extractant material in the liquid overflow, and the effect of this dilution is generally a reduction in specific volatility. I want to be The optimum reflux ratio is easily determined for a particular process set up by a skilled operator.

Example 2 Using the extractive distillation technique generally embodied in FIG. 1 and employing the technique employed in Example 1 for styrene separation, α-methylstyrene, 1,
2,4-trimethylbenzene and 1,2,3-
Vinyltoluene was removed in the presence of N-aminoethylpiperazine from a hydrocarbon mixture containing primarily aromatic hydrocarbons with 9 carbon atoms, including trimethylbenzene. The top product from the extractive distillation column contained less than about 2% vinyltoluene, while the bottom product contained vinyltoluene, indene, and aminoethylpiperazine. Vinyltoluene with excellent color was easily obtained from indene and/or aminoethylpiperazine using an additional extractive distillation column.

Example 3 A hydrocarbon stream containing primarily 4 carbon hydrocarbons including acetylene, butadiene, butene, isobutene and butane is fed to an extractive distillation column and then treated in the presence of N-aminoethylpiperazine. Distilled. The material exiting the top of the extractive distillation column contained most of the butadiene, butyne, isobutene, and butane contained in the hydrocarbon feed. The bottom of the column consisted essentially of AEP and acetylenes, with only minor amounts of other _C4 hydrocarbons present.

Example 4 A hydrocarbon stream of the following composition was treated. Component weight % C ₄ hydrocarbons 2.2 Isopentane 12 1-pentene 4 Isoprene 18 n-pentane 23 Methyl-substituted butenes 8.4 Other pentenes 3.2 Cyclopentadiene 5.6 Pentadiene 10.5 Other C ₅ hydrocarbons 4.6 Other hydrocarbons Class 8.5 A hydrocarbon stream of the above composition is fed to a packed distillation column to separate the roller stream into a top product containing light components (e.g. C ₄ hydrocarbons) and a bottom product consisting of the remaining components of this stream. did. The separated hydrocarbon stream containing the heavy components is fed to a second distillation column which converts this stream into a bottoms product containing polybutadienes and other heavy components and other components, particularly isopentane, n-pentane and isoprene. The top product containing: The top product from this column was combined with N-(aminoethyl)piperazine and top product 1
A weight ratio of 3 parts per part of AEP was mixed and the resulting mixture was fed to a third distillation column. The specific volatility of the hydrocarbon component in this stream was now sufficiently different from that of isoprene to yield isoprene of greater than 98% purity. One method for obtaining isoprene is to remove the pure isoprene fraction from the side of the column. In another method, a side stream is used, and the bottoms product contains a mixture of isoprene, AEP, and cyclopentadiene. In this method, isoprene is easily separated from AEP and/or cyclopentadiene using an additional extractive distillation column.

Alternatively, when AEP is not used, isoprene can only be recovered as a mixture with significant amounts of isopentane, n-pentane, cyclopentadiene, and various other components.

By repeating the process described above using different weight ratios of AEP:isoprene-containing hydrocarbon streams, different purities of isoprene can be obtained. Specifically, as the relative concentration of AEP to the isoprene-containing hydrocarbon stream decreases, the recovered isoprene generally contains greater amounts of other components.

The above description and examples are intended to illustrate the invention and its advantages, and should not be construed as limiting the invention. Further variations of the invention will be apparent to those skilled in the art. All such variations are considered to be within the scope of the invention as defined by the claims.

[Brief explanation of drawings]

FIG. 1 is a schematic diagram illustrating aspects of the invention. 101...extractive distillation column, 202...stripping column, 303...purification column. FIG. 2 is a second schematic diagram illustrating aspects of the invention. 111...First extractive distillation column, 222...Solvent stripper column, 333...Second extractive distillation column, 44
4...Solvent recovery tower, 555...Solvent purification tower.

Claims (1)

[Claims] 1. N-(aminoalkyl)piperazine is used as an extractive distillation solvent when extractively distilling a hydrocarbon mixture containing ethylenically unsaturated hydrocarbons to separate ethylenically unsaturated hydrocarbons from the hydrocarbon mixture. A method for separating ethylenically unsaturated hydrocarbons from a hydrocarbon mixture, characterized by using. 2. The method according to claim 1, wherein the N-(aminoalkyl)piperazine has a lower alkyl group having 1 to 4 carbon atoms. 3. The method according to claim 1, wherein the N-(aminoalkyl)piperazine is N-(aminoethyl)piperazine. 4. The method according to claim 1, wherein the ethylenically unsaturated hydrocarbon is a monovinylidene aromatic hydrocarbon. 5. The method of claim 4, wherein the hydrocarbon mixture comprises o-xylene and the monovinylidene aromatic hydrocarbon is styrene. 6. The method according to claim 1, wherein the ethylenically unsaturated hydrocarbon is butadiene or substituted butadiene. 7. The method according to claim 6, wherein the ethylenically unsaturated hydrocarbon is isoprene. 8. The process of claim 1, wherein less than 1% of unsaturated hydrocarbons polymerize during the separation process. 9. The method of claim 8, wherein the hydrocarbon mixture contains o-xylene and the ethylenically unsaturated hydrocarbon is styrene. 10 The hydrocarbon mixture is α-methylstyrene,
1,2,4-trimethylbenzene, 1,2,3-
9. The method of claim 8, containing trimethylbenzene or a mixture thereof and wherein the ethylenically unsaturated hydrocarbon is vinyltoluene. 11. The process according to claim 8, wherein the hydrocarbon mixture contains n-pentane, cyclopentadiene and/or isopentane and the ethylenically unsaturated hydrocarbon is isoprene. 12. The method of claim 1, wherein the hydrocarbon mixture contains phenylacetylene and the ethylenically unsaturated hydrocarbon is styrene. 13 The N-(aminoalkyl)piperazine is N
-(aminoethyl)piperazine. The method according to claim 12. 14. The method of claim 12, wherein the separated styrene has a purity greater than 99.5% and an APHA color less than 5.