KR830000970B1 - Separation of conjugated diolefins from C_4- or C_5-hydrocarbon mixtures - Google Patents

Abstract

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Description

Separation of conjugated diolefins from C4- or C5- hydrocarbon mixtures

The present invention relates to a process for separating conjugated diolefins from a C ₄ or C ₅ hydrocarbon mixture by extractive distillation with the aid of an optional solvent.

Extractive distillation is a well-known method for separating mixtures that cannot be easily separated by conventional fractional distillation, for example if the components to be separated form an azeotropic mixture or the difference in relative volatility is small. In extractive distillation, a relatively low volatility solvent is introduced into the distillation column in such an amount that the difference in the relative volatility of the components to be separated is increased to enable separation by distillation. Typical application examples for extractive distillation are described, for example, in C.S. Robinson et al., "Elements of Fractional Distillation", 4th edition McGraw-Hill Press, New York, (1959), 291.

For example, German application DOS 2,742,148, published German application DAS 1,568,902, German patent 1,163,795 or The Soviet Chemical Industry, No. 11, November 1971, pages 719-723, it is known that conjugated diolefins can be separated from C ₄ or C ₅ hydrocarbon mixtures by extractive distillation using an optional solvent.

Optional solvents can be used in the anhydrous state. In this process, however, the selectivity of C ₄ -or C ₅ -hydrocarbons is generally insufficient, especially when used in the case of solvents sensitive to hydrolysis.

Therefore, water has been added to the selective solvents to increase the selectivity and lower the boiling point. However, this addition of water to the selective solvent has the disadvantage of reducing the solubility of C ₄ or C ₅ hydrocarbons in the optional solvent, thereby increasing the amount of the optional solvent circulated in the extractor. Moreover, the addition of water can have an adverse effect on the viscosity and thus on the tray efficiency of the optional solvent.

It is an object of the present invention to provide a process for the separation of conjugated diolefins from C ₄ -or C ₅ hydrocarbon mixtures containing diolefins by single or multistage extraction species using an optional solvent, wherein The amount of optional solvent circulated is kept at a low level.

According to the present invention, by the method of separating the conjugated diolefin from the C ₄ -or C ₅ hydrocarbon mixture containing the diolefin by single or multiple stage extractive distillation using an optional solvent, the object of the present invention and other Objects and advantages are achieved and the solvent used here is

a) 50-99% by weight of optional solvent boiling between 140 ° -260C,

b) 1-50% by weight of organic solvent boiling between 45 ° -125 ° C

Solvent mixtures.

The solubility of C ₄ or C ₅ hydrocarbons in a solvent mixture used as an optional solvent according to the invention is substantially increased compared to conventional methods, while the selectivity of C ₄ or C ₅ hydrocarbons is similar and thus The amount of optional solvent circulated in the extractor for separating the conjugated diolefin can be greatly reduced. In particular, this fact greatly reduces the investment required for the extractor and the consumption of steam and electrical energy. Furthermore, the solvent mixtures used according to the invention have a lower viscosity, lower heat of evaporation and lower specific heat than conventional selective solvents having comparable C ₄ or C ₅ hydrocarbon selectivity.

The low viscosity of the solvent mixtures used according to the invention results in high tray efficiency in the extractive distillation column, while energy can be concomitantly saved as a result of low heat of evaporation and low specific heat.

Another advantage of using a mixture of one of the relatively high boiling optional solvents according to (a) above and one of the relatively low boiling organic solvents according to (b) is, for example, degassing zone or The solvent recovery zone of the extractor for separating conjugated diolefins operated as solvent stripping zones can be operated at a higher pressure than for the given tower bottom temperature than with the solvent according to (a) according to conventional processes. This has the advantage that, for example, because of the high pressure, the degassed hydrocarbons obtained from the solvent recovery zone can be introduced into the down stream running under high pressure in a simple manner without intervening the compressor or blower.

Another advantage of using a mixture of one of the relatively high boiling solvents according to (a) and one of the lower boiling solvents according to (b) is, for example, as degassing or solvent stripping. The solvent recovery table of the extraction apparatus being operated can be operated at a low top temperature when using the same pressure as in the conventional process, whereby contamination of the extraction unit by polymer formation can be more easily prevented.

Solvent mixtures used in accordance with the invention, for example mixtures of N-methylpyrrolidone and acetonitrile, have good hydrocarbon selectivity as good as, for example, the mixture of N-methylpyrrolidone and water used in the prior art. It was surprising to show that if acetonitrile is used as the optional solvent for separating the conjugated olefins, the solvent after addition of water only shows the appropriate hydrocarbon selectivity. (See, eg, US Pat. No. 3,317,627)

In the method according to the invention,

(a) 50-99 wt% selective solvation boiling at 140-260 ° C., preferably 150-210 ° C. under atmospheric pressure,

(b) A solvent mixture consisting of 1-50% by weight of organic solvent boiling at 45-125 ° C., preferably 50-115 ° C., especially 55-105 ° C., under atmospheric pressure is employed.

In practice for suitable optional solvents according to (a) above, butyrolactone, furfuraldehyde, methoxy propionitrile, and preferably N-alkyl-substituted lower fatty acid amides, for example dimethylform Amide, diethylformamide, dimethylacetamide, diethylacetamide and formylmorpholine, and N-alkyl-substituted aliphatic cyclic amides (lactams) having five rings, for example alkyl having 1-3 Carbon, especially N-alkylpyrrolidone, such as N-methylpyrrolidone, etc. are mentioned. Particularly advantageous is the use of dimethylformamide and in particular N-methylpyrrolidone as solvent (a).

Examples of suitable container solvents according to (b) above include natrils, aliphatic or aliphatic ring ethers, lower fatty carboxylic acid esters and carbonate esters, amines, alcohols, aliphatic ketones, ether-amines Aliphatic hydrocarbons and aromatic hydrocarbons boiling at 45 ° -125 ° C. Examples of suitable natrils include butyronitrile, propionitrile and preferably acetonitrile.

Examples of suitable amines are, for example, 4 or 5 carbon sources such as n-butylamine, secondary-butylamine, isobutylamine, n-amylamine, isoamylamine, tetra-amylamine and secondary-n-amylamine Primary aliphatic amines containing an aliphatic hydrocarbon group having a valence, for example, secondary fatty amines containing aliphatic hydrocarbon groups having a total of 4-6 carbon atoms such as diethylamine, dipropylamine, diisopropylamine and piperidine Tertiary aliphatic amines containing, for example, N, N-dimethylisobutylamine and triethylamine and aliphatic hydrocarbon groups having a total of 5 or 6 carbon atoms. Examples of suitable alcohols include, for example, alcohols having 1-5 carbon atoms, such as methanol, ethanol, propanol, isopropanol, butanol, isobutanol and terrestrial-amyl alcohol, with isopropanol being preferred. Examples of suitable ketones include aliphatic ketones having a total of 3-5 carbon atoms such as, for example, acetone, methylethyl ketone, diethyl ketone and methylpropyl ketone. Examples of suitable ether-amines include, for example, alkoxy alkylamines having a total of three or four carbon atoms, such as 2-methoxyethylamine, 2-ethoxy ethylamine and 3-methoxypropyl amine. Good aliphatic hydrocarbons are hydrocarbons having 6-8 carbon atoms, for example hexane, heptane and octane.

Examples of suitable aliphatic ring hydrocarbons include, for example, hydrocarbons having 6-8, preferably 6 or 7 carbon atoms, such as cyclohexane and methylcyclohexane. Examples of suitable aromatic hydrocarbons include benzene and toluene. Of the solvents according to (b) above, it is particularly advantageous to use esters, preferably nitriles, and in particular aliphatic or aliphatic ring ethers.

The solvent mixture used according to the invention comprises one to 50% by weight, preferably 2 to 25% by weight, in particular 3 to 20% by weight, of one of the organic solvents according to (b) above. Thus, such solvent mixtures generally comprise 5-99% by weight, preferably 75-98% by weight, in particular 80-97% by weight, of one of the solvents according to (a) above. It is particularly advantageous to use a solvent mixture according to the invention containing 6-15% by weight of one of the organic solvents according to (b) above.

The solvent mixture used according to the invention may comprise a small amount of water, for example up to 10% by weight. However, advantageously the water content is limited to a content of at most 5% by weight, preferably at most 3% by weight, based on the solvent mixture. However, it may be advantageous to adopt an anhydrous solvent mixture comprising substantially up to 1% by weight, preferably up to 0.5% by weight, based on the solvent mixture. If an organic solvent according to (b) is used, which forms an azeotropic mixture with water, for example as in the case of acetonitrile, it is usually based on the azeotropic ratio of water to organic solvent, based on the organic solvent contained in the solvent mixture. It may be more advantageous to adopt a solvent mixture according to the invention with a corresponding water content. If water is added to the solvent mixture according to the invention in which acetonitrile is used as the organic solvent (b), the weight ratio of water to acetonitrile in the solvent mixture is advantageously from 1: 3 to 1: 9, preferably Is from 1: 4 to 1: 8.

The process of separating the conjugated diolefin from a C ₄ or C ₅ hydrocarbon mixture containing it using a solvent mixture adopted as the optional solvent according to the invention is carried out in one or multiple stages, advantageously in one or two stages of extractive distillation. By conventional methods (see, eg, German Patent Nos. 1,184,334 and German Applications DAS 1,568,876 and 1,568,902). For example, conjugated diolefins such as 1,3-butadiene, isoprene, and 1,3-pentadiene are both C ₄ containing both higher solubility hydrocarbons and lower solubility hydrocarbons than conjugated diolefins. or C ₅ hydrocarbon mixture to extractive distillation with a solvent mixture to be used according to the present invention is separated from the C ₄ or C ₅ hydrocarbon mixture, on the other by the same distillation process, the distilled water solubility include lower hydrocarbons, conjugated An extract is obtained comprising a diolefin, high solubility hydrocarbons, and an optional solvent. The conjugated diolefin can be separated from the extract in the form of a crude product with a purity suitable for certain embodiments, but it may also be subjected to an additional purification process such as, for example, fractional distillation, but advantageously The conjugated diolefins are separated through two successive extraction distillation steps using a solvent mixture employed in accordance with the present invention.

By using this latter method, in the first stage of extraction distillation, for example, as described above, distillates containing low solubility hydrocarbons, conjugated diolefins and high solubility hydrocarbons, and optional solvents are contained. An extract is produced. The selective solvent in this extract is liberated to obtain a mixture of conjugated diolefins and highly soluble hydrocarbons. This mixture uses a selective solvent to produce a conjugated diolefin as a second extraction distillate, and also an extract containing highly soluble hydrocarbons and an optional solvent. The selective solvent is subsequently liberated in the extract thus obtained to obtain a hydrocarbon stream containing highly soluble hydrocarbons.

Hydrocarbon mixtures containing conjugated diolefins, which are used as starting materials for the process of the present invention, are butadiene obtained by petroleum fractions (e.g. LPG, naphtha, etc.) or by dehydrogenation of n-butane or n-butene. It was obtained by the thermal decomposition of a fraction containing or a fraction containing isoprene obtained by dehydrogenation of isopentane or isoamylene. Generally, C ₄ -hydrocarbon mixtures contain 1,3-butadiene as conjugated diolefins and at the same time butane, n-butene, isobutene, vinylacetylene, ethylacetylene and 1,2-butadiene, with a small amount of C _With or without ₃ or C ₅ hydrocarbons. The C ₅ hydrocarbon mixture contains isoprene, trans- and cis-1,3-pentadiene, and cyclopentadiene as conjugated diolefins with pentane, n-pentene, isoamylene, cyclopentene and high density acetylene.

For example, by extractive distillation of a C ₄ -fraction, firstly, a distillate containing butane and butene and an extract containing 1,3-butadiene, ethylacetylene, vinylacetylene and 1,2-butadiene are obtained. This extract, when further extracted and distilled, produces 1,3-butadiene as distillate while the extract contains ethylacetylene, vinylacetylene and 1,2-butadiene.

Ethylacetylene, vinylacetylene and 1,2-butadiene are separated in the degas unit from the extract containing these hydrocarbons and the degassed solvent is recycled to the extractive distillation unit. The 1,3-butadiene obtained as a distillate can be fractionally distilled continuously to remove trace amounts of C ₃ -or C ₅ -hydrocarbons that may still be present.

The following examples are intended to illustrate the invention.

Example 1

The C ₄ hydrocarbon mixture (C ₄ fraction from ethylene unit) with the composition shown in Table 1 is separated in a butadiene recovery unit with two extractive distillation units connected in series, ie distillate containing butane and butene 1 Extracts containing, 3-butadiene, ethylacetylene, vinylacetylene and 1,2-butadiene are obtained in the first extraction distillation stage. The extract is subjected to a second extractive distillation to yield 1,3-butadiene as distillate, while the extract contains ethylacetylene, vinylacetylene and 1,2-butadiene. In order to remove the hydrocarbons by degassing, the extract is introduced into the degas unit where the degassed optional solvent is obtained as the bottom product and the hydrocarbon stream containing vinylacetylene, ethylacetylene and 1,2-butadiene is Obtained as a government product, which enters the power plant as a waste stream and is burned there.

TABLE 1

An optional solvent used is a mixture of 88% by weight N-methylpyrrolidone (NMP), 10% by weight acetonitrile (ACN) and 2% by weight of water, which mixture constitutes a solvent according to the invention. Where the content of ACN and water corresponds to the content of azeotropic ACN / water mixtures under 1 bar pressure.

In the comparative test, instead of the solvent according to the present invention, a mixture (comparative solvent) of 91.7% by weight of NMP and 8.3% by weight of water of the prior art is used.

The hydrocarbon selectivity (1,3-butadiene selectivity of 1) found for the solvents and the comparative solvents according to the invention is shown in Table 2.

TABLE 2

The selectivity of the key component (cis-but-2-ene) of the first extractive distillation and the reference component (ethylacetylene) of the second extractive distillation is determined within the limits of the measurement error and the solvent according to the invention. Is the same for. (Selectivity is the ratio of Bunsen absorption coefficient of 1,3-butadiene and hydrocarbons separated and removed)

Under a pressure of 4.5 bar, the solvent according to the invention shows solubility in a C ₄ -hydrocarbon mixture which is 60% greater than the solubility of the comparative solvent. Therefore, when using a solvent according to the present invention instead of a comparative solvent, the amount of the optional solvent supplied for the first and second extractive distillation can result in a 60% reduction in liquid. This fact reduces the column diameter of the extraction distillation column by 30%.

With the use of the solvent according to the invention, the tray efficiency is increased (described below), so that the height of the extraction distillation column can be further reduced by about 25%, so that the cost of the apparatus required for the extraction distillation column is increased. Can be reduced by more than 50%.

At the same time, the consumption of steam can be reduced by 10% as the amount of the optional solvent fed to the extractive distillation is reduced when using the solvent according to the invention.

Using the solvent according to the invention, the tray of the extractive distillation column has a 27% higher efficiency than when using a comparative solvent. Thus, the same degree of separation can be achieved when using a solvent according to the present invention using an extractive distillation column whose height is reduced by about 25% compared to the extractive distillation column adopted with the comparative solvent.

At temperatures in the range 130-160 ° C., which are important temperature ranges for the degassing process, the vapor pressures of the solvent and the comparative solvent according to the invention are essentially the same. For example, at 150 ° C., degassing the extract obtained after the second extractive distillation produces a pressure of about 1.7 bar in the degasifier, which is an exhaust containing C ₄ -acetylenes (vinylacetylene and ethylacetylene). The pressure is high enough to allow the gas mixture to be fed directly to a power plant or waste gas flare operating at atmospheric pressure without the role of a compressor or blower relay. Therefore, if the gas is combusted in flares, there is no need to adopt a special low pressure flare.

Example 2

Here, one extractive distillation of the C ₄ -hydrocarbon mixture is illustrated. A 0.716 kg / h C ₄ -hydrocarbon mixture with the following composition is fed to the bottom of a packed column having a 25 mm inner diameter and a 2.50 mm height operating under a pressure of 1 bar at 15 ° C.

At the top, 4.62 kg / h of circulating optional solvent containing 88% by weight of N-methylpyrrolidone, 10% by weight of acetonitrile and 2% by weight of water is introduced at 15 ° C. 0.374 kg / h of traffic containing 7.46% by weight of 1,3-butadiene and 5.61% by weight of cis-but-2-ene (reference component for separation) is discharged as gas from the tower. 1,2-butadiene and C ₄ -acetylene (ethylacetylene and vinylacetylene) are no longer detected in the residue. Extracts containing more readily soluble hydrocarbons are discharged from the bottom and then to the top of the downflow tower, which is operated at a tower bottom temperature of 130-140 ° C. with 10 bnbble-cap trays. By feeding the extract is degassed. An optional solvent, substantially free of hydrocarbons, flows out of the bottom of the tower, cools and then circulates to the top of the packed tower.

In the middle of the double cap tray tower is 0.342 kg / h of crude butadiene containing 79.80% by weight of 1,3-butadiene. Hydrocarbons exiting the top of the double-cap tray tower are circulated as gas to the tower tower.

Comparative experiment

In the comparative experiments, the method described in Example 2 above was carried out as is, except that the optional solvent used was a mixture of 91.7% by weight of N-methylpyrrolidone and 8.3% by weight of water, which in Example 2 A larger amount, i.e., 6.00 kg / h, was fed into the packed column and the C ₄ -hydrocarbon mixture was introduced from the bottom of the packed tower at a lower amount than 0.4, i.e. 0.471 kg / h, yielding 0.235 kg / h. The exception is that additional residue and crude butadiene of 0.236 kg / h are obtained.

Although in the comparative experiments the ratio of inlet to selective solvent (12.74) of the inlet to the C ₄ -hydrocarbon mixture is virtually twice that of the corresponding proportion in Example 2 (6.45), the ratio in Example 2 In the same comparative experiment as (0.374 / 0.342), an extract containing 14.77% by weight of 1,3-butadiene was obtained, while in Example 2, the residue contained only 7.46% by weight of 1,3-butadiene. Furthermore, cis-but-2-ene, the reference component, was added from the comparative experiment (4.41 wt% cis-but-2-ene) than the weight residue according to Example 2 (5.61 wt% cis-but-2-ene). -2-yen) to a lesser extent. While 1,2-butadiene, ethylacetylene and vinylacetylene are still present in the extracts from the comparative experiments in amounts that are clearly detected, the content of these components in the extracts according to Example 2 falls short of the detection limit. . Moreover, the crude butadiene obtained in the comparative experiment contains only 69.07% by weight of 1,3-butadiene while the crude butadiene according to Example 2 contains 79.80% by weight.

Example 3

The method as described in Example 2 was carried out as such, except that 0.858 kg / h of a C ₄ -hydrocarbon mixture was fed to the bottom of the packed tower and 90% by weight of N-methylpyrrolidone and 10% by weight of methyl The exception is that a 4.60 kg / h circulating optional solvent composed of tetra-butyl ether is fed to the tower top of the tower. 0.418 kg / h of weight residue containing 7.89% by weight of 1, 3-butadiene and 4.78% by weight of cis-but-2-ene is discharged as gas from the tower.

Comparative experiment

In a comparative experiment, the method described in Example 3 above was carried out as it is, except that the optional solvent used was a mixture of 91.7% by weight of N-methylpyrrolidone and 8.3% by weight of water, which in Example 3 A larger amount, i.e., 6.00 kg / h, was fed to the packed tower, and the C ₄ -hydrocarbon mixture was introduced at the bottom of the packed tower at a lower amount, 0.471 kg / h, than in Example 3, yielding 0.235 kg / h The exception is that raffinate and crude butadiene of 0.236 kg / h are obtained. Although in the comparative experiments the ratio of selective solvent inflow to C ₄ -hydrocarbon mixture (12.74) was increased by 138% compared to the equivalent ratio (5.36) in Example 3, but the amount of crude residue and crude butadiene In a comparative experiment in which the ratio with the amount of (0.235 / 0.236) was substantially the same as the ratio in Example 3 (0.418 / 0.440), an extract containing 14.77% by weight of 1,3-butadiene was obtained, whereas in Example 3 The resulting extract contains only 7.89% by weight of 1,3-butadiene. Moreover, the reference component cis-but-2-ene was the weight residue from the comparative experiment (4.41 wt% cis-but-2-ene) than the weight residue according to Example 3 (4.78 wt% cis-but-2-ene). -2-yen) to a lesser extent. While 1,2-butadiene, ethylacetylene and vinyl acetylene are still present in the extracts from the comparative experiments in amounts that are clearly detected, the content of these components in the extracts according to Example 3 is below the detection limit. . Furthermore in the comparative experiments the crude butadiene contained only 69.07% by weight of 1,3-butadiene while the crude butadiene according to Example 3 contained 74.55% by weight.

Example 4

The method as described in Example 2 was carried out as it is, except that 0.700 kg / h of a C ₄ -hydrocarbon mixture was fed to the bottom of the packed tower and 90% by weight of N-methyl pyrrolidone and 10% by weight of toluene The exception is that a circulating optional solvent of 4.46 kg / h consisting of water is fed to the tower top of the tower. 0.350 kg / h of residue containing 8.53% by weight of 1,3-butadiene and 4.45% by weight of cis-but-ene is discharged as gas from the tower. 0.350 kg / h of crude butadiene containing 75.42% by weight of 1,3-butadiene is discharged in the middle of the bubble-cap tray tower.

[Comparison Experiment]

In the comparative experiments, the method described in Example 4 above was carried out as it is, except that the optional solvent used was a mixture of 91.7 wt% N-methyl pyrrolidone and 8.3 wt% water, which is Example 4 Is supplied to the packed column at a greater amount than, i.e., 6.00 kg / h, and the C ₄ -hydrocarbon mixture is introduced into the bottom of the packed tower at a lesser amount than Example 4, i.e. 0.471 kg / h and is 0.235 kg / h. The exception is that raffinate of h and crude butadiene of 0.236 kg / h are obtained. Although in the comparative experiments the ratio of selective solvent inflow to C ₄ -hydrocarbon mixture (12.74) increased by 89% compared to the corresponding proportion in Example 4 (6.73), the amount of crude residue and crude butadiene In a comparative experiment in which the ratio with the amount of (0.235 / 0.236) was substantially the same as the ratio in Example 4 (0.350 / 0.350), an extract containing 14.77% by weight of 1,3-butadiene was obtained, whereas in Example 4 The resulting extract contains only 8.53% by weight of 1,3 butadiene. While 1,2-butadiene, ethyl acetylene and vinylacetylene are still present in the extracts from the comparative experiments in amounts that are clearly detected, the content of these components in the extracts according to Example 4 is below the detection limit. . Moreover, the crude butadiene obtained in the comparative experiment contains only 69.07% by weight of 1,3-butadiene while the crude butadiene according to Example 4 contains 75.42% by weight.

Example 5

C ₄ - according to one extractive distillation of hydrocarbon mixtures, 0.768kg / h in the embodiment of the composition shown in Example 2 C ₄ - hydrocarbon mixture is packed column with, 25mm inner diameter and a height of 2.50m is operated under atmospheric pressure at 15 ℃ Inflow from the bottom of the tower. 4.50 kg / h of circulating selective solvent containing 90% by weight of dimethylformamide and 10% by weight of ethyl acetate is introduced at 15 ° C. in the tower. 0.379 kg / h of additional residues are discharged as gas from the tower. At the bottom, an extract containing more readily soluble hydrocarbons is obtained, which is degassed by feeding the extract to the top of the downflow tower, which has 10 bubble-cap trays and is operated at a tower bottom temperature of about 140 ° C. An optional solvent, substantially free of hydrocarbons, flows from the bottom of the tower, cools and circulates to the top of the packed tower. 0.389 kg / h of crude butadiene containing 80.61% by weight of 1,3-butadiene is discharged in the middle of the bubble-cap cray top. Hydrocarbons exiting the top of the bubble-cap tray tower are circulated as gas to the bottom of the packed column. The ratio of circulating solvent S (4.60 kg / h) to C ₄ -hydrocarbon mixture inlet M (0.768 kg / h) is 5.99.

[Comparison Experiment]

In the comparative experiments, the method described in Example 5 above was carried out as it is, provided that pure dimethylformamide was used as the optional solvent and that the C ₄ -hydrocarbon mixture had a smaller amount than in Example 5, i.e. 0.621 kg / h. Flows into the bottom of the packed column at a flow rate of; With the exception that 0.306 kg / h weight residue and 0.315 kg / h crude butadiene are obtained, the C ₄ -hydrocarbon mixture is actually divided into weight residue and crude butadiene in the same ratio as in Example 5. Cis-but-2-ene and 1, 3-butadiene as reference components have the same contents as in Example 5 in the extract and crude butadiene in the comparative experiment. The S / M ratio of the circulating solvent S (4.60 kg / h) to the inflow M (0.621 kg / h) of the C ₄ -hydrocarbon mixture is 7.41, i.e., the S / M ratio in the comparative experiments shows the same separation effect. To be achieved should be about 23% higher than in Example 5.

Example 6

The same procedure as described in Example 2 is carried out as is, except that in Example 6 the optional solvent is a mixture of 90% by weight of N-methylpyrrolidone and 10% by weight of tetrahydrofuran and circulated solvent S The S / M ratio of the inflow M of the C ₄ -hydrocarbon mixture is maintained at 6.50 while the S / M ratio of 12.74 in the comparative experiments involved in Example 6 is maintained to achieve the same degree of separation effect, ie The S / M ratio in the comparative experiment should be 96% higher than in the examples to achieve the same degree of separation effect.

Example 7

The method described in Example 5 and the corresponding comparative experiments are carried out as is, except that in Example 7, the temperature is 5 ° C. higher and the optional solvent is 90 wt% N-methylpyrrolidone and 10 wt% diethyl The S / M ratio of the inflow M of the solvent S to C ₄ -hydrocarbon mixture which is a mixture of carbonates and circulated is maintained at 6.60, whereas in the comparative experiments involving Example 7, the optional solvent is 91.7% by weight of N- The exception is that the S / M ratio of the mixture M of methyl-pyrrolidone and 8.3% by weight of water and the inflow M of the solvent S to C ₄ -hydrocarbon mixture circulated is maintained at 12.74. This fact means that in the comparative experiments involving Example 7, the S / M ratio should be 93% higher in order to achieve the same separation effect as Example 7 itself.

Claims (1)

Boiling point of 75-98% by weight based on solvent mixture in the process for separating conjugated diolefin from C ₄ -or C ₅ -hydrocarbon mixture containing diolefin by single or multi-stage extractive distillation using an optional solvent Dimethyl formamide, diethyl formamide, dimethyl acetamide, diethylacetamide and formylformoline, N-methylpyrrolepyrrolidone, butyrolactone, purpuraldehyde and methoxy propionitrile at 140 ° -260 ° C. Or a solvent mixture consisting of 2-25% by weight of acetonitrile and containing at most 5% by weight of water as an optional solvent.