JP2003128595A - Method for separating and refining unsaturated hydrocarbon - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for separating and refining an unsaturated hydrocarbon such as conjugated dienes, by which production of a rubber-like polymer or a pop corn polymer can be suppressed in the inside of a refining apparatus. SOLUTION: In this method for separating and refining the unsaturated hydrocarbon containing the a sulfur-containing compound by distilling, the unsaturated hydrocarbon contains the sulfur-containing compound in an amount of >=0.5 wt.ppm and <=30 wt.ppm expressed in terms of sulfur atom.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a method for separating and purifying a target unsaturated hydrocarbon from a raw material containing an unsaturated hydrocarbon such as a conjugated diene.

[0002]

BACKGROUND OF THE INVENTION Conjugated dienes such as 1,3-butadiene, isoprene, chloroprene and the like as unsaturated hydrocarbons generally crack naphtha and separate C ₂ and C ₃ hydrocarbons such as ethylene and propylene. It is separated and purified from the C ₄ fraction or C ₅ fraction as the raw material obtained by extraction distillation using an extraction solvent (Japanese Patent Publication No. 45-17405 and Japanese Patent Publication No. 45-17411).
JP-B, JP-B-47-41323, JP-A-56-
83421 publication).

Extractive distillation is usually divided into an extractive distillation column and a stripping column.
It is performed by using a device. C_Four Fraction or C₅Stay
Conjugated dienes, which are relatively easily dissolved in the solvent in the
Withdrawn from the bottom of the distillation column as a mixture with a solvent,
It is sent to the stripping tower and separated into conjugated dienes and solvent,
The solvent is returned to the extractive distillation column.

By the way, a conjugated diene as an unsaturated hydrocarbon tends to accidentally form a porous insoluble polymer, so-called popcorn polymer, in both the liquid phase and the gas phase. In particular, in industrial distillation, various conditions such as proper operating temperature, high monomer purity, coexistence of gas phase and liquid phase, mixing of water and the presence of iron rust are apt to cause popcorn polymerization.

Once formed, this popcorn polymer exponentially proliferates by using it as a nucleus, and the inside of the refining device is rapidly blocked. The popcorn polymer is a tough polymer that is insoluble in all known solvents and does not melt even when heated. Therefore, in order to remove the generated popcorn polymer, there is no good method other than cleaning by mechanical means, and for this cleaning, the purifier must be temporarily stopped, which is an economical disadvantage. Is inevitable. Moreover, the mechanical cleaning cannot completely remove the popcorn polymer, so when the operation of the refining device is restarted, the growth of the popcorn polymer starts again with the trace amount of the polymer that could not be removed as the nucleus. become.

On the other hand, it is known that sulfur-containing compounds such as hydrogen sulfide and mercaptans are effective in suppressing the popcorn polymer which is accidentally generated in industrial distillation. U.S. Pat. No. 4,404,413 includes
It is mentioned that hydrogen sulfide and ethanethiol, propanethiol and hexanethiol are known to suppress the formation of popcorn polymers. And
Japanese Patent Publication No. 5-509356 proposes a method of suppressing the formation of a popcorn polymer by adding a sulfur-containing compound of this kind to a raw material containing an unsaturated hydrocarbon such as a conjugated diene. ing.

[0007]

However, when the conventional technique for preventing the popcorn polymer is applied to the separation and purification apparatus for unsaturated hydrocarbons, it is different from the popcorn polymer in the high temperature part of the distillation column during the separation and purification. A rubbery polymer is formed. Like the popcorn polymer, this rubber-like polymer has no good method for removing it except that it is cleaned by mechanical means, and for this cleaning, the purifier must be temporarily stopped. No, it suffers from the same economic disadvantages as in popcorn polymers.

The object of the present invention is to suppress the formation of popcorn polymer inside the refining apparatus when separating and refining the target unsaturated hydrocarbon from a raw material containing unsaturated hydrocarbons such as conjugated dienes. Another object of the present invention is to provide a method for separating and purifying unsaturated hydrocarbons capable of suppressing the production of rubbery polymers.

[0009]

Means for Solving the Problems As a result of intensive studies to achieve the above object, the present inventors have surprisingly found that a sulfur-containing compound is not added to a raw material such as a conjugated diene to be purified. No, rather, by reducing the amount of the sulfur-containing compound contained as an impurity in the raw material, while suppressing the production of popcorn polymer, and found that it is also possible to prevent the formation of a rubber-like polymer, to this finding Based on this, the present invention has been completed.

That is, the method for separating and purifying an unsaturated hydrocarbon according to the present invention is a method for separating and purifying a target unsaturated hydrocarbon by distilling a raw material containing an unsaturated hydrocarbon and a sulfur-containing compound, The raw material is characterized in that the amount of the sulfur-containing compound is 0.5 wtppm or more and 30 wtppm or less in terms of sulfur atom.

In the present invention, the amount of the sulfur-containing compound contained in the raw material at the time of carrying out the distillation may be adjusted within the above range. That is, a raw material in which the amount of the sulfur-containing compound is adjusted within the above range from the beginning may be used. However, in addition to unsaturated hydrocarbons, this type of raw material usually contains 30 wt.
Since a sulfur-containing compound exceeding about ppm (as converted to sulfur atoms) is contained as an impurity, a raw material in which the amount of the sulfur-containing compound is reduced within the above range is often used.

The raw material (petroleum fraction) that can be used in the present invention is
Although not particularly limited, it is usually a light fraction called naphtha having a boiling range of about 30 to 170 ° C. that is cracked and separated. As such a raw material, a C ₂ fraction mainly containing a hydrocarbon of 2 carbons, a C ₃ fraction mainly containing a hydrocarbon of 3 carbons, a C ₄ fraction mainly containing a hydrocarbon of 4 carbons are used. And a C ₅ fraction containing mainly 5 hydrocarbons. Among these, those in which the concentration of unsaturated hydrocarbons is increased by extractive distillation or the like are preferable, those containing a large amount of conjugated dienes as unsaturated hydrocarbons are preferable, and particularly, a C ₄ fraction containing a large amount of butadiene, C ₅ cuts which are rich in isoprene are preferred.

The "sulfur-containing compound" in the present invention means, for example, elemental sulfur existing in the form of an inorganic or organic compound such as free sulfur, elemental sulfur, hydrogen sulfide, mercaptans, disulfides and thiophene. . In the present invention, a raw material in which the amount of the sulfur-containing compound is adjusted within a predetermined range is used, but it is particularly preferable to use a raw material in which the amount of mercaptans (preferably methyl mercaptan) is adjusted within a predetermined range. Among the sulfur-containing compounds,
Particularly, by adjusting (preferably decreasing) the amount of mercaptans, it is suitable for suppressing the production of the rubber-like polymer.

The "mercaptans" referred to in the present invention are hydrocarbons having one or more --SH groups and include both aliphatic and aromatic ones, and these are substituents. It may or may not have. Aromatic mercaptans have only one benzene ring,
Including those having two or more benzene rings (for example, naphthalene). Examples of aromatic mercaptans include thiophenols (eg thiophenol itself), thiocresols (eg m-thiocresol and p-thiocresol), benzyl mercaptans (eg benzyl mercaptan, 2-chlorobenzyl mercaptan and 4- Chlorobenzyl mercaptan), naphthalene thiols (for example, 1-naphthalene thiol and 2-naphthalene thiol), and the like. Examples of the aliphatic mercaptan having one —SH group include methyl mercaptan and ethyl mercaptan. As the aliphatic mercaptan having two or more —SH groups,
Examples thereof include 1,2-ethanedithiol, 2,3-butanedithiol, 1,4-butanedithiol and 1,3-propanedithiol.

In the present invention, the amount of the sulfur-containing compound contained in the raw material means the weight concentration of sulfur atoms in the raw material (wtp.
pm). The weight concentration of this sulfur atom is, for example,
Gas chromatography with a sulfur chemiluminescence detector (SCD) used to measure trace amounts of sulfur (G
It can be measured using C). This SCD-GC
In the analysis method, all the sulfur contained in the raw material that is vaporized under the GC analysis conditions is converted into SO by burning under hydrogen in the SCD, and further converted into excited SO ₂ by the ozone treatment of SO. It The weight concentration of the sulfur atom can be measured by detecting the luminescence generated when the excited state SO ₂ is changed to the ground state SO ₂ .

A method for reducing the amount of the sulfur-containing compound contained in the raw material is not particularly limited, and for example, washing with an alkaline aqueous solution such as NaOH, removal by addition of monoethanolamine or the like, removal by an adsorbent such as silica-alumina or the like. Etc. can be used.

For the alkaline cleaning, an aqueous solution of caustic soda is usually used, and the amount of addition depends on the composition and properties of the fraction to be treated, but usually a concentration of about 2 to 10 wt% is used. After washing with an alkali, washing with water is generally performed, but soft water is usually used as washing water. As the alkaline cleaning tank, one whose inner surface is lined with lead is used, which has an oiling pipe, a chemical supply pipe at the top, and a waste liquid pipe at the bottom, and a continuous method using a continuous cleaning device is also used.

When the removal with an adsorbent is used, the removal is preferably carried out by contacting with silica-alumina having a specific composition ratio. Specifically, the composition ratio of silica is 4
It is preferable to use a method of bringing the raw material into contact with silica-alumina in the range of 0 to 85% by weight. The composition ratio of silica to silica-alumina is more preferably in the range of 45 to 80% by weight. The silica-alumina may be obtained and used as an industrially produced product.

The shape, pore size, and specific surface area of silica-alumina are not particularly limited, but usually those having a specific surface area per gram of 50 m ² or more, preferably 100 m ² or more, more preferably 200 m ² or more are used.

The method of contacting the raw material with silica-alumina is not particularly limited. For example, a batch treatment method in which a raw material and silica-alumina are charged into a container selected appropriately and brought into contact with stirring, and a continuous treatment in which silica-alumina is filled in a packed tower in advance and the raw material is circulated and brought into contact therewith There is a law. The raw material may be directly contacted with silica-alumina without being diluted with a solvent, or may be diluted with a solvent and contacted.

The diluent solvent for the raw material is not particularly limited,
For example, aliphatic hydrocarbons such as n-pentane, cyclopentane, n-hexane, cyclohexane and n-heptane, aromatic hydrocarbons such as benzene, toluene and xylene, halogenated hydrocarbons such as dichloromethane and chloroform, diethyl. Ethers such as ether, tetrahydrofuran, dioxane and the like can be mentioned. Among these,
Aliphatic or aromatic hydrocarbons are preferred, and aromatic hydrocarbons are more preferred.

In the present invention, the raw material is distilled by the extractive distillation method when the unsaturated hydrocarbon content (concentration) is low, and by the ordinary distillation method when the unsaturated hydrocarbon content is high.

The solvent (extraction solvent) used when the raw materials are distilled by the extractive distillation method is a solvent capable of dissolving and extracting unsaturated hydrocarbons such as conjugated dienes such as butadiene and isoprene. If it is not particularly limited as long as it is, specifically, acetone, methyl ethyl ketone, dioxane, isoprene cyclic sulfone, acetonitrile, alcohol, glycol, N-methyl rolldamine, N-ethyl succinimide, N-methyl pyrrolidone, N- Methyl-2-pyrrolidone, hydroxylethylpyrrolidone, N-methyl-5-methylpyrrolidone, furfural, 2-heptenone, dimethylformamide (D
MF), dimethylacetamide, N, N-dimethylacetone acetic acid amide, morpholine, N-formylmorpholine, N-methylmorpholine-3-one, sulfolane, methylcarbitol, tetrahydrofuran, aniline, N.
-Methyloxazolidone, N-methylimidazole,
N, N'-dimethylimidazolin-2-one, 1-oxo-1-methylphosphorin, methyl cyanoacetate, ethyl acetoacetate, ethyl acetate, malonic acid dimethyl ester, propylene carbonate, methyl carbitol, triethyl phosphate, diethylene glycol monomethyl Examples thereof include ether, dimethyl sulfoxide, γ-butyrolactone and the like. Among these, amide compounds, particularly dimethylformamide (DMF), are preferable. Further, a polymerization inhibitor, an antioxidant, an antifoaming agent or the like which prevents the polymerization of diolefins and acetylenes can be used together.

In the extractive distillation column, the extractive solvent is usually supplied to the extractive distillation column from an extractive solvent supply stage provided at a position higher than the stage for supplying the raw materials (petroleum fraction supply stage). preferable.

In the method for separating and refining unsaturated hydrocarbons according to the present invention, the concentration of unsaturated hydrocarbons in the petroleum fraction is usually 90%.
% Or more, preferably 95% or more (specifically, a petroleum fraction is subjected to extractive distillation to increase the concentration of unsaturated hydrocarbons), and it is effective when applied. .

[0026]

The operation and effect of the present invention: The present inventors are effective in preventing the formation of popcorn polymer in the portion of the distillation column where the temperature tends to be low when the amount of the sulfur-containing compound contained in the raw material during distillation is large. However, on the other hand, it was confirmed that a rubber-like polymer different from the popcorn polymer was likely to be generated in a portion of the distillation column where the temperature was high, and this rubber-like polymer caused the same problem as the popcorn polymer. Although the mechanism is not necessarily clear, the sulfur-containing compound in the unsaturated hydrocarbon separation and purification device is a part of the distillation column that tends to reach high temperatures (for example, the bottom of the first extractive distillation column and the second extractive distillation column). At the bottom of the column), it is thought that they act as a polymerization initiator rather than as a chain transfer agent. Is likely to be generated. On the other hand, the sulfur-containing compound in the separation and purification device is a portion of the distillation column where the temperature tends to be low (for example, the top of the second extractive distillation column, the bottom of the low boiling point removal column, and the top of the high boiling point removal column. ), It is believed that the compound acts as a chain transfer agent, and therefore, if the amount of the sulfur-containing compound contained in the raw material is small, a popcorn polymer may be produced in the low temperature part of the distillation column.

In the present invention, sulfur-containing compounds (preferably mercaptans, more preferably methyl mercaptan)
The raw material whose amount is 30 wtppm or less in terms of sulfur atom is distilled. Since a raw material of this kind usually contains a sulfur-containing compound in excess of about 30 wtppm (sulfur atom conversion), the amount of the sulfur-containing compound is 30 w in terms of sulfur atom conversion.
Distill after reducing to below tppm. This allows
Distillation column for separation and purification, for example, 120 ° C or higher 160
It is possible to effectively suppress the formation of a rubber-like polymer different from the popcorn polymer in the portion where the temperature tends to be high, such as about ℃ or less. On the other hand, if the amount of the sulfur-containing compound in the raw material is too small, or if the amount of the sulfur-containing compound is excessively reduced, the popcorn polymer is easily generated in the portion of the distillation column that tends to be at a low temperature during separation and purification. Tends to become. Therefore, in the present invention, the lower limit of the amount of the sulfur-containing compound in the raw material is set to 0.5 wtppm in terms of sulfur atom. Thereby, it is possible to effectively suppress the production of the popcorn polymer in a portion of the distillation column during separation and purification, which is likely to have a low temperature of, for example, 40 ° C. or higher and 60 ° C. or lower.

That is, according to the method for separating and purifying unsaturated hydrocarbons according to the present invention, a purifying device is used for separating and purifying a target unsaturated hydrocarbon from a raw material containing unsaturated hydrocarbons such as conjugated dienes. It is possible to suppress the generation of the rubber-like polymer while suppressing the generation of the popcorn polymer inside, and to prevent the inside of the device from being soiled. As a result, long-term continuous operation of the device can be stably performed.

[0029]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention will be described below based on the embodiments shown in the drawings. FIG. 1 is a schematic diagram showing the overall configuration of the separation and purification apparatus used in this embodiment.

In this embodiment, as an apparatus used in the separation and purification method of the present invention, the separation and purification apparatus 1 shown in FIG. 1 is exemplified, and this apparatus 1 is used to contain conjugated dienes as unsaturated hydrocarbons. From C ₄ fraction as a raw material, C
A method for separating _four compounds and purifying butadiene will be specifically described.

In this embodiment, first, the amount of the sulfur-containing compound (particularly mercaptans) contained in the raw material (C ₄ component in naphtha) BBF containing butadiene is adjusted to 0.5 wtppm or more and 30 wtppm or less in terms of sulfur atom. Reduce. Preferably 0.8 wtppm or more and 25 wtpp
m or less, more preferably 1 wtppm or more and 18 wtpp
m or less. This effectively suppresses the formation of the rubber-like polymer and the popcorn polymer as described later. In order to reduce the amount of the sulfur-containing compound contained in the raw material, for example, the raw material is washed with an aqueous NaOH solution of about 5 wt%, or silica alumina having a silica composition ratio of 40 to 85 wt% is added to the raw material. It may be carried out by contacting.

After that, as shown in FIG. 1, the raw material BBF in which the content of the sulfur-containing compound is reduced to a predetermined range is supplied to the evaporation tower 2 to gasify the raw material BBF. In the evaporation tower 2,
In order to gasify BBF, the temperature in the column is preferably 2
It is maintained at 0 to 80 ° C., more preferably 40 to 80 ° C., and the column internal pressure is absolute pressure, preferably 2 to 8 atm,
More preferably, the pressure is maintained at 4-6 atm.

Raw material BBF gasified in this evaporation tower 2
Is then fed to the first extractive distillation column 4. The first extractive distillation column 4 is a column for performing the first stage extractive distillation of the gasified raw material BBF to take out the first distillate and the first bottoms. This first extractive distillation column 4 generally stores a column body, a condenser for cooling and liquefying the vapor discharged from the top of the column body, and a fraction liquefied by the condenser. A reflux drum, a reflux line for re-supplying a part of the fraction stored in the reflux drum to the vicinity of the top of the tower body, and a reboiler arranged at the bottom of the tower body (reboiler). However, these are omitted in the present embodiment. As the form of the distillation column, for example, the column body is divided by many horizontal plates so that the contact between the liquid and the vapor is carried out stepwise, or in order to efficiently perform mass transfer between different phases. It may be in any form such as a packed tower in which packing is packed in the tower. When using a tray tower, the number of trays is usually 100 to 300, preferably 150 to 200.
It is a step. The accuracy of distillation (the ability to separate those having a close boiling point) is superior as the number of trays is large, but the cost is increased when the number of trays is too large, and therefore the balance between capacity and cost is selected.

The supply position of the gasified raw material BBF to the first extractive distillation column 4 is not particularly limited, and is usually supplied to an approximately intermediate stage.

An extraction solvent (solvent) is supplied to the first extractive distillation column 4 together with the gasified raw material BBF. The amount of solvent supplied to the first extractive distillation column 4 is generally
It is preferably 100 to 100 parts by weight of the raw material BBF.
The amount is 1000 parts by weight, more preferably 200 to 800 parts by weight. The lower the temperature of the solvent is, the higher the solubility is, which is preferable, but the solvent temperature affects the internal temperature of the first extractive distillation column 4 and the increase / decrease of the reflux amount, and therefore is preferably 10-100.
C., more preferably 20 to 60.degree.

The extraction solvent is used in the first extractive distillation column 4
The gasified raw material BBF is supplied to the first extractive distillation column 4 from an extraction solvent supply stage provided at a position higher than the stage (petroleum fraction supply stage) for supplying the gasified raw material BBF.

The first extraction distillation column 4 may be supplied with the first polymerization inhibitor together with the gasified raw material BBF. In the present embodiment, since the amount of sulfur contained in the raw material BBF before distillation is reduced to a predetermined range, a portion (column bottom 4b) where the temperature of the first extractive distillation column 4 tends to become high (about 120 to 160 ° C). In addition, although the production of the rubbery polymer is suppressed, the production of the rubbery polymer at the bottom of the first extractive distillation column 4 can be more effectively suppressed by supplying the first polymerization inhibitor. . Such a first polymerization inhibitor contains, for example, one or both of nitrite and di-lower alkylhydroxylamine, and may further contain a phosphorus-containing compound. Examples of the nitrite include sodium nitrite and potassium nitrite. Examples of di-lower alkylhydroxylamine include diethylhydroxylamine, dimethylhydroxylamine, methylethylhydroxylamine, dipropylhydroxylamine, dibutylhydroxylamine, dipentylhydroxylamine and the like. As the phosphorus-containing compound, for example, a phosphoric acid compound selected from phosphoric acid, phosphonic acid, phosphinic acid, diphosphonic acid, diphosphoric acid, tripolyphosphoric acid, and metaphosphoric acid; dihydrogen alkyl ester phosphate; dialkyl hydrogen phosphate ester; Trialkyl phosphate; triphenyl phosphate; tris (nonylphenyl) phosphite, dimethyl phosphonate, diethyl phosphonate, triisopropyl phosphonate, triphenyl phosphonate, metaphosphoric acid ester; phosphoric acid ester-based surfactant and phosphorus Esters of acid compounds; phosphoric acid first salt; phosphoric acid second salt; phosphoric acid tertiary salt; polymetaphosphate salts; sodium tripolyphosphate, potassium pyrophosphate, sodium pyrophosphate, potassium tripolyphosphate; dialkyl phosphates; mono Alkyl phosphate second And a phosphine compound; and the like. Among them, a phosphoric acid ester-based surfactant (usually used as a rust preventive), a phosphoric acid compound and an alkali metal salt of a phosphoric acid compound are preferable, and phosphorus is more preferable. It is an alkali metal dihydrogen acid salt. The use ratio of one or both of nitrite and di-lower alkylhydroxylamine to the phosphorus-containing compound is usually 1:10 to 100: 1 by weight.
Is. The total amount of one or both of nitrite and di-lower alkylhydroxylamine and the phosphorus-containing compound is usually 0.1 to 2000 p, based on the weight of the raw material.
pm.

Gasified raw material BBF, extraction solvent and first
Along with the supply of the polymerization inhibitor, the first extractive distillation column 4 is heated by a reboiler (not shown) arranged at the bottom of the column to perform the first stage extractive distillation. The bottom pressure of the first extractive distillation column 4 is an absolute pressure, preferably 1 to 10 atm, more preferably 5 atm.
The column bottom temperature is controlled to preferably 100 ° C. or higher, more preferably 110 ° C. or higher, still more preferably 120 ° C. or higher, preferably 160 ° C. or lower, more preferably 130 ° C. or lower.

At the top of the first extractive distillation column 4, the raw material BBF was added.
The residual gas BBR obtained by separating the butadiene content from the butadiene, that is, a fraction containing a large amount of butane or butene having a volatility (solubility) higher than that of butadiene is taken out, and this fraction is condensed by a condenser (not shown). A part is refluxed and returned to the top of the column, and the rest is taken out as a first distillate. On the other hand, from the bottom of the first extractive distillation column 4, a high-concentration butadiene extract containing a large amount of higher acetylene and allene hydrocarbons is taken out as a first bottom product and sent to the stripping column 8.

The stripping tower 8 is a tower for distilling the sent first bottom product and taking out the second distillation product and the second bottom product. The diffusion tower 8 is generally composed of a tower body,
A condenser for cooling and liquefying the vapor discharged from the top of the tower body, a reflux drum for storing the fraction liquefied by the condenser, and a part of the fraction stored in the reflux drum. A reflux line re-supplied near the top of the tower body,
Although it has a reboiler arranged at the bottom of the column body, these are omitted in the present embodiment as in the case of the first extractive distillation column 4. The form of the stripping tower 8 may be a plate tower or a packed tower.

The supply position of the first bottom product to the stripping tower 8 is not particularly limited, and is usually supplied to the intermediate stage. Along with the supply of the first bottom product, distillation is performed by heating with a reboiler (not shown) arranged at the bottom of the stripping column 8. In the stripping tower 8, the tower bottom pressure is maintained at 1 to 3 atm in absolute pressure, the tower bottom temperature is maintained at 150 to 200 ° C., the solvent is separated from the extract, and the second bottom product is separated from the tower bottom. Discharge.
On the other hand, at the top of the stripping tower 8, the solvent is separated and a stripped gas containing a large amount of butadiene, higher acetylene and allene hydrocarbons is generated, and part of the stripped gas is condensed by a condenser (not shown). In that case, the condensed portion is returned to the top of the stripping tower 8 and refluxed. A part of the uncondensed portion is returned to the first extractive distillation column 4 via the compressor 10, and the rest is sent to the second extractive distillation column 12 as a second distillate. When the emitted gas is totally condensed by the condenser, a part of the condensate is returned to the top of the diffusion column 8 to be refluxed, and the rest is passed through the compressor 10 and a part to the first extractive distillation column 4. It is returned, and the rest is sent to the second extractive distillation column 12 as the second distillate. What is returned to the first extractive distillation column 4 is
In this way, it may be returned as a gas or a liquid.

The second extractive distillation column 12 receives the second
This is a column for performing the second stage extractive distillation of the distillate and taking out the third distillate and the third bottoms. In the present embodiment, a configuration similar to that of the first extractive distillation column 4 described above is used. Although adopted, it is not particularly limited in the present invention.

The feed position of the second distillate fraction to the second extractive distillation column 12 is not particularly limited, and is usually fed near the lower stage.

In addition, the second extractive distillation column 12 has a second
The same first polymerization inhibitor as in the first extractive distillation column 4 may be supplied together with the distillate. In this embodiment, since the amount of sulfur contained in the raw material BBF before distillation is reduced to a predetermined range, the high temperature of the second extractive distillation column 12 (1
20-160 ° C) (the bottom 12b)
In addition, the formation of a rubber-like polymer is suppressed.
By supplying the polymerization inhibitor, it is possible to more effectively suppress the production of the rubber-like polymer at the bottom of the second extractive distillation column 12.

In addition, the second extractive distillation column 12 has a second
The second polymerization inhibitor may be supplied together with the distillate. In the present embodiment, since the amount of sulfur contained in the raw material BBF before distillation is reduced to a predetermined range, the portion (the top 12 of the second extractive distillation column 12) which is likely to be at a low temperature (about 40 to 60 ° C.).
Generation of a popcorn polymer is suppressed in a), but the generation of the popcorn polymer at the top of the second extractive distillation column 12 can be suppressed more effectively by supplying the second polymerization inhibitor. . Examples of such a second polymerization inhibitor include, for example, 1,1-diphenyl-2-picrylhydrazyl and 1,3,5-triphenylfelder which inhibit or suppress the polymerization by trapping radicals by stable radicals. Zil, 2,6-di-t-butyl-α- (3,
5-di-t-butyl-4-oxo-2,5-cyclohexanediene-1-ylidene-p-tolyloxy, 2,2
6,6-Tetramethyl-4-piperidone-1-oxyl, N- (3-N-oxyanilino-1,3-dimethylbutylidene) -aniline oxide, 2- (2-cyanopropyl) -ferdazyl; chain transfer reaction Those which have an active NH bond, such as diphenylpicrylhydrazine, diphenylamine, diethylhydroxylamine, dimethylhydroxylamine, methylethylhydroxylamine, dipropylhydroxylamine, dibutylhydroxylamine, dipentylhydroxylamine, which inhibits or suppresses polymerization by Hydroquinone,
having a phenolic OH bond such as t-butylcatechol; dithiobenzoyl disulfide, p, p'-
Ditolyl trisulfide, p, p'-ditolyl tetrasulfide, dibenzyl tetrasulfide, tetraethyl thiuram disulfide; oxygen, sulfur, anthracene,
2-benzanthracene, tetracene; chloranil, p
-Benzoquinone, 2,6-dichlorobenzoquinone, 2,
Nitro compounds such as benzoquinone derivatives such as 5-dichlorobenzoquinone, furfuridene malononitrile, trinitrobenzene and m-dinitrobenzene; nitroso compounds such as nitrosobenzene and 2-methyl-2-nitrosopropane; and ferric chloride , And metal salts such as ferric bromide. Among these, those which inhibit or suppress the polymerization by chain transfer reaction, particularly di-lower alkylhydroxylamine, specifically diethylhydroxylamine are preferable. The amount of the second polymerization inhibitor here is usually 0.1 to 200 based on the weight of the raw material.
It is ppm.

While supplying the second distillate, the first polymerization inhibitor and the second polymerization inhibitor, the second distillate is heated in a reboiler (not shown) arranged at the bottom of the second extractive distillation column 12 to produce a second mixture. Perform the extractive distillation of the first stage. In this second extractive distillation column 12, impurities whose volatility (solubility) is equal to or lower than butadiene are separated from the column bottom, and at the column top, a gas containing a high concentration of butadiene (third distillate) is taken out. The bottom pressure is maintained at 3 to 6 atm in absolute pressure, and the tower bottom temperature is preferably 100 ° C. or higher, more preferably 110 ° C. or higher, even more preferably 120 ° C. or higher, preferably 160 ° C. or lower, more preferably Is 1
It is controlled at 30 ° C or lower. The column top temperature is preferably 40
The temperature is not lower than 60 ° C and not higher than 60 ° C.

The extract containing a large amount of impurities separated from the bottom of the second extractive distillation column 12 is introduced into the first stripping column 13 as a third bottom product.

The first stripping tower 13 is a tower for distilling the sent third bottom product and taking out the sixth distillate part and the sixth bottom product. In the first stripping tower 13, the tower bottom pressure is maintained at 1 to 3 atm in absolute pressure, and the tower bottom temperature is 120 to 1
The temperature is maintained at 80 ° C., butadiene is separated from the extract, and the stripped gas containing butadiene (sixth distillate) is returned to the condenser inlet of the stripping column 8. The bottom liquid of the first stripping tower 13 (the sixth bottom product) is sent to the second stripping tower 14.

In the second stripping tower 14, the tower bottom pressure is kept at 1 to 3 atm in absolute pressure and the tower bottom temperature is kept at 150 to 200 ° C., and the solvent is separated from the extract as the seventh bottom product, It is discharged from and reused. The stripped gas as the seventh distillate is discharged from the top of the tower.

The distillation gas containing a large amount of butadiene taken out from the top of the second extractive distillation column 12 is condensed in a condenser (not shown), and a part of it is refluxed to the second extractive distillation column 12
Is returned to the top of the column, and the rest is sent to the low boiling point removal column 16 as the third distillate.

The low-boiling-points removing tower 16 is a tower for distilling the sent distillation gas (third distillate) containing a large amount of butadiene to take out the fourth distillate and the fourth bottom distillate. Therefore, in this embodiment, a configuration similar to that of the first extractive distillation column 4 described above is adopted, but the present invention is not particularly limited. The position for supplying the third distillate to the low-boiling-points removing column 16 is not particularly limited, but it is usually supplied to the intermediate stage.

In addition to the third distillate, the low boiling point removal column 16 may be supplied with the same second polymerization inhibitor as in the case of the second extractive distillation column 12. In this embodiment,
Since the amount of sulfur contained in the raw material BBF before distillation is reduced to a predetermined range, the low boiling point removal column 16 is operated at a low temperature (40-
Although the production of popcorn polymer is suppressed in the part (column bottom 16b) where the temperature tends to be about 60 ° C., by supplying the second polymerization inhibitor, the popcorn at the bottom of the low boiling point substance removal column 16 is supplied. The generation of the polymer can be suppressed more effectively.

With the supply of the third distillate and the second polymerization inhibitor, heating is performed in a reboiler (not shown) arranged at the bottom of the low boiling point removal column 16 for distillation. This low boiling point removal tower 1
In 6, the tower bottom pressure was 3 to 7 atm and the tower bottom temperature was 40 to 60.
By setting the temperature to ℃, methylacetylene, which is an impurity with a boiling point lower than that of butadiene, is extracted from the top of the column, this fraction is condensed in a condenser (not shown), and part of it is refluxed to remove low-boiling substances. It is returned to the top of the tower 16 and the rest is taken out and removed as the fourth distillate. On the other hand, a distillation gas containing more butadiene, cis-2-butene, pentene, and the like is taken out from the bottom of the low-boiling-points removing tower 16 as a fourth bottom product, and is passed to the high-boiling-points removing tower 18. Sent.

The high-boiling-points removing tower 18 is for carrying out distillation of the distillation gas (the fourth bottom product) containing a larger amount of butadiene and the like sent thereto, and taking out the fifth distillate fraction and the fifth bottom product. It is a tower and may be a tray tower or a packed tower as described above. The number of trays in the case of using the tray tower is the same as that in the low boiling point removal tower 16. The supply position of the fourth bottom product to the high boiling point removal tower 18 is
Although not particularly limited, it is supplied at a high level, approximately in the middle.

In addition to the fourth bottoms, the high boiling point removal tower 18 may be supplied with the same second polymerization inhibitor as in the second extractive distillation tower 12. In this embodiment,
Since the amount of sulfur contained in the raw material BBF before distillation is reduced to a predetermined range, the high boiling point removal tower 18 is cooled at a low temperature (40-
Although the production of popcorn polymer is suppressed in the portion (column top 18a) where the temperature tends to be about 60 ° C., by supplying the second polymerization inhibitor, the popcorn at the top of the high boiling point removal column 18 The generation of the polymer can be suppressed more effectively. In addition, the supply position of the second polymerization inhibitor to the high boiling point removal tower 18 is preferably at the upper stage. It is not preferable that the second polymerization inhibitor used here is mixed in highly purified butadiene which is a raw material of polybutadiene or the like. The higher the supply position of the second polymerization inhibitor, the more the effect of suppressing the formation of the popcorn polymer is improved, but the second polymerization inhibitor tends to be easily mixed in the high-purity butadiene, and the lower the supply position, the higher the It becomes difficult to mix in pure butadiene, but the effect of preventing polymerization of the popcorn polymer tends to decrease. Specifically, for example, the high boiling distillation column 16
When a plate column is used as the above, it is preferable to supply it to the position of the first plate from the top.

Along with the supply of the fourth bottom product and the second polymerization inhibitor, distillation is carried out by heating with a reboiler (not shown) arranged at the bottom of the high boiling point removal column 18.

In the high-boiling-points removing tower 18, the tower bottom pressure is set to 3 to 7 atmospheres and the tower bottom temperature is set to 40 to 70 ° C., so that impurities having a boiling point higher than that of butadiene, for example, cis- A fraction containing a large amount of 2-butene and penten is taken out and removed as a fifth bottom product. On the other hand, a highly concentrated fraction of butadiene is taken out from the top of the high-boiling-points removing column 18, this fraction is condensed by a condenser (not shown), and a part of it is reflux line. It is returned to the top of the high-boiling-point removing tower 18 through (not shown), and the rest is taken out as a fifth distillate. In the present embodiment, the concentration of butadiene in the finally obtained extraction liquid (fifth distillate fraction) is 99% or more, and is finally used as a raw material such as polybutadiene as high-purity butadiene.

As described above, in the method of separating the C ₄ compound from the raw material C ₄ fraction and purifying butadiene according to the present embodiment, the amount of the sulfur-containing compound contained as an impurity in the raw material C ₄ fraction is increased. Is reduced to a predetermined range and then distilled. For this reason, a rubber-like material different from the popcorn polymer is present in the parts such as the bottom parts 4b and 12b of the first extractive distillation column 4 and the second extractive distillation column 12, respectively, which are likely to reach a high temperature of 120 ° C. or higher and 160 ° C. or lower. It is possible to effectively suppress the formation of a polymer. Further, such as the top portion 12a of the second extractive distillation column 12, the bottom portion 16b of the low-boiling-point removing column 16, and the top portion 18a of the high-boiling-point removing column 18, for example, 40 ° C. or higher 6
It is possible to effectively suppress the formation of the popcorn polymer in the portion where the temperature tends to be as low as 0 ° C. or less.
That is, the inside of the device can be prevented from becoming dirty. as a result,
The long-term continuous operation of the device can be stably performed.

In this embodiment, the first extractive distillation column 4
Since a specific polymerization inhibitor is supplied to each of the second extractive distillation column 12, the low-boiling-point removing column 16 and the high-boiling-point removing column 18, the production of rubbery polymers and popcorn polymers can be suppressed. It can be performed more efficiently.

Therefore, according to the separation and purification method of the present embodiment, it is possible to separate and purify high-purity butadiene at a cost lower than conventional ones.

Although the embodiments of the present invention have been described above, the present invention is not limited to these embodiments, and may be implemented in various modes without departing from the scope of the present invention. Of course.

For example, in the above-described embodiment, the raw material C
₄ fractions, separating the C ₄ compounds, although the purifying butadiene, from the raw material C ₅ fraction, C ₅
The compound may be separated and the isoprene may be purified.

[0063]

The present invention will be described in detail below with reference to examples, but the scope of the present invention is not limited by these examples.

The amount of the sulfur-containing compound contained in the raw material (sulfur atom weight concentration) is determined by the sulfur chemiluminescence detector (SC
It was measured by gas chromatography (GC) equipped with D). For this GC analysis, TC manufactured by GL Sciences Inc.
-1 column (length 60 m, inner diameter 0.25 mm, film thickness 1.
0 μm) was used. Helium as a carrier gas 2.
Flowed at a flow rate of 0 ml / min. Sample inlet temperature is 150 ℃
And the split ratio was 10: 1. The oven temperature was kept at 50 ° C. for 5 minutes, then the temperature was raised at a rate of 10 ° C./minute, and after reaching 250 ° C., the oven temperature was kept for 5 minutes. The combustion temperature of the SCD detector was set to 800 ° C.

Example 1 Raw material containing butadiene (C ₄ component in naphtha) B
BF (content of sulfur-containing compound: 100 wtppm)
Was treated in an alkaline washing tank containing a 5 wt% NaOH aqueous solution and washed with soft water to obtain a raw material BBF after the alkaline treatment in which the content of the sulfur-containing compound was reduced. When the content of the sulfur-containing compound in the raw material BBF after the alkali treatment was analyzed by gas chromatography (SCD-GC), it was 15 wtppm.

In this way, the raw material BBF with the reduced content of the sulfur-containing compound was supplied to the evaporation tower 2 of the separation and purification apparatus 1 shown in FIG. 1 to gasify the raw material BBF.

The gasified raw material BBF was supplied to the first extractive distillation column 4 together with dimethylformamide (DMF) as an extraction solvent. The feed position of the raw material BBF was approximately in the middle stage of the first extractive distillation column 4, and the feed position of DMF was above the feed position of the gasified raw material BBF. Along with these supplies, heating was carried out in a reboiler arranged at the bottom of the first extractive distillation column 4 to perform the first stage extractive distillation. In the first extractive distillation column 4, the column bottom pressure was 6 atm in absolute pressure, and the column bottom temperature was controlled at 125 ° C. And the first extractive distillation column 4
From the column top, the residual gas BBR obtained by separating the butadiene content from the raw material BBF was taken out as the first distillate. on the other hand,
From the bottom of the first extractive distillation column 4, a high-concentration butadiene extract was taken out as a first bottom product.

Next, the first canned product taken out is released into the stripping tower 8
Was supplied to approximately the middle stage of the above, and was distilled by heating with a reboiler arranged at the bottom of the stripping column 8. Then, from the bottom of the stripping tower 8, the solvent separated from the first bottom product was discharged as the second bottom product. On the other hand, from the top of the stripping tower 8, butadiene,
A stripped gas containing a large amount of higher acetylene and allene hydrocarbons was taken out as the second distillate.

Next, the extracted second distillate is supplied to the vicinity of the lower stage of the second extractive distillation column 12 and heated by the reboiler arranged at the bottom of the second extractive distillation column 12 to produce the second extractive distillation column 12. The extractive distillation of the first stage was performed. In the second extractive distillation column 12, the column bottom pressure was maintained at 5 atm in absolute pressure, and the column bottom temperature was controlled at 128 ° C.
The column top temperature in this case was 45 ° C. Then, from the top of the second extractive distillation column 12, a gas containing a high concentration of butadiene was taken out as a third distillate. On the other hand, from the bottom of the second extractive distillation column 12, impurities having a volatility (solubility) of butadiene or less were taken out as a third bottom product.

Next, the extracted third distillate is supplied to the substantially middle stage of the low boiling point removal tower 16 and heated by a reboiler arranged at the bottom of the low boiling point removal tower 16 for distillation. went. In the low boiling point substance removing column 16, the column bottom pressure was kept at 4 atm in absolute pressure, and the column bottom temperature was kept at 50 ° C. Then, a distillation gas containing more butadiene, cis-2-butene, pentene and the like was taken out as a fourth bottom product from the bottom of the low boiling point substance removing column 16. On the other hand, methylacetylene, which is an impurity having a boiling point lower than that of butadiene, was taken out as a fourth distillate from the top of the low boiling point removal column 16.

Next, the removed fourth bottom product is fed to the middle stage of the high-boiling-point removing tower 18 and heated by a reboiler arranged at the bottom of the high-boiling-point removing tower 18 for distillation. went. In the high boiling point removal tower 18, the tower bottom pressure was maintained at 5 atm in absolute pressure, and the tower bottom temperature was maintained at 60 ° C. Then, from the bottom of the high boiling point removal column 18, a fraction containing a large amount of impurities having a boiling point higher than that of butadiene, for example, cis-2-butene or pentene, was taken out as a fifth bottom product. On the other hand, from the top of the high-boiling-point removing column 18, a fraction in which butadiene was highly concentrated was taken out as a fifth distillate. The concentration of butadiene in the obtained fifth distillate was 99% or more. For this reason,
It was finally confirmed that the fifth distillate was useful as a raw material such as polybutadiene as high-purity butadiene.

After continuously operating these steps for one month, the bottom of the first extractive distillation column 4 (high temperature part) and the bottom of the second extractive distillation column 12 (high temperature part) are observed. As a result, the rubber-like polymer was slightly generated in all cases, and the stain was small. Also, the top of the second extractive distillation column 12 (low temperature part)
And the bottom (low temperature part) of the low boiling point removal tower 16 and the top (low temperature part) of the high boiling point removal tower 18 were observed. Was few.

Example 2 A treatment solution was prepared in the same manner as in Example 1 except that a 3 wt% NaOH aqueous solution was used and the contact time in the alkaline washing tank was set to (2/3) times that in Example 1. The content of the sulfur-containing compound was analyzed by SCD-GC. As a result, 30 wt
It was ppm. Thus, the raw material BBF in which the content of the sulfur-containing compound was reduced was separated and purified in the same manner as in Example 1. As a result, the high temperature part was slightly contaminated, but the low temperature part was less contaminated.

Example 3 The same procedure as in Example 1 was carried out except that an aqueous 8 wt% NaOH solution was used, and the contact time in the alkaline washing tank was set to be three times as long as that in Example 1. Content of S
It was analyzed by CD-GC. As a result, 0.5 wtppm
Met. Thus, the raw material BBF in which the content of the sulfur-containing compound was reduced was separated and purified in the same manner as in Example 1.
As a result, the high temperature part was extremely dirty and the low temperature part was slightly dirty.

Comparative Example 1 The same treatment as in Example 1 was carried out except that the alkali washing treatment in Example 1 was omitted, and the content of the sulfur-containing compound in the treatment liquid was analyzed by SCD-GC. As a result, 100 wtp
It was pm. This raw material BBF was separated and purified in the same manner as in Example 1. As a result, when the top of the second extractive distillation column 12 (low temperature part), the bottom of the low boiling point removal column 16 (low temperature part), and the top of the high boiling point removal column 18 (low temperature part) were observed, The amount of popcorn polymer generated was very small in all places, and the stain was extremely small. On the other hand, when the bottom of the first extractive distillation column 4 (high temperature part) and the bottom of the second extractive distillation column 12 (high temperature part) were observed, generation of a rubber-like polymer was observed at any place. There was a lot of dirt. This confirmed the superiority of Examples 1 to 3.

Comparative Example 2 A treatment solution was prepared in the same manner as in Example 1 except that a 2 wt% NaOH aqueous solution was used and the contact time in the alkaline washing tank was set to (3/5) times that of Example 1. The content of the sulfur-containing compound was analyzed by SCD-GC. As a result, 50wt
It was ppm. Thus, the raw material BBF in which the content of the sulfur-containing compound was reduced was separated and purified in the same manner as in Example 1. As a result, the same result as in Comparative Example 1 was obtained. This confirmed the superiority of Examples 1 to 3.

Comparative Example 3 A sulfur-containing compound in the treatment liquid was treated in the same manner as in Example 1 except that a 9 wt% NaOH aqueous solution was used and the contact time in the alkaline washing tank was set to be four times that in Example 1. Content of S
It was analyzed by CD-GC. As a result, 0.2 wtppm
Met. Thus, the raw material BBF in which the content of the sulfur-containing compound was reduced was separated and purified in the same manner as in Example 1.
As a result, when the bottom of the first extractive distillation column 4 (high temperature part) and the bottom of the second extractive distillation column 12 (high temperature part) were observed,
The generation of the rubber-like polymer was very small in all places, and the stain was extremely small. On the other hand, the second extractive distillation column 1
The top of 2 (low temperature part), the bottom of low boiling point removal column 16 (low temperature part), and the top of high boiling point removal column 18 (low temperature part) were observed. Was observed, and there was a lot of dirt. This confirmed the superiority of Examples 1 to 3. The results of Examples 1 to 3 and Comparative Examples 1 to 3 are shown in Table 1 above.

[0078]

[Table 1]

[Brief description of drawings]

FIG. 1 is a schematic diagram showing the overall configuration of a separation and purification apparatus used in this embodiment.

[Explanation of symbols]

1 ... Separation and purification device 2 ... Evaporating tower 4 ... First extractive distillation column 8 ... Dispersion tower 10 ... Compressor 12 ... Second extractive distillation column 13 ... First diffusion tower 14 ... Second diffusion tower 16 ... Low boiling point removal tower 18 ... High boiling point removal tower

Claims (4)

[Claims] 1. A method of distilling a raw material containing an unsaturated hydrocarbon and a sulfur-containing compound to separate and purify a target unsaturated hydrocarbon, wherein the amount of the sulfur-containing compound is 0.5 wtppm or more in terms of sulfur atom. A method for separating and purifying unsaturated hydrocarbons, characterized in that the raw material of 30 wtppm or less is used. 2. The method for separating and purifying unsaturated hydrocarbons according to claim 1, wherein the raw material in which the amount of the sulfur-containing compound is reduced to 0.5 wtppm or more and 30 wtppm or less in terms of sulfur atom is used. 3. The method for separating and purifying unsaturated hydrocarbons according to claim 1, wherein the raw material is a C ₄ fraction or a C ₅ fraction. 4. The method for separating and purifying unsaturated hydrocarbons according to claim 1, wherein the sulfur-containing compound is a mercaptan.