JPH10251660A - Method for preventing polymerization of conjugated diene - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for preventing the polymn. of conjugated dienes whereby the formation of polymers in an extractive distillation apparatus is inhibited and soiling in the apparatus, pipe clogging, lowering in heat efficiency, etc., are made hardly to occur. SOLUTION: In a process for separating conjugated dienes by the extractive distillation of a petroleum fraction contg. conjugated dienes with an extractive distillation tower by using dimethylformamide contg. t-butylcatechol, the fraction contg. conjugated dienes is supplied to an intermediate stage of the distillation tower; the oxygen concn. of a vapor phase of a distillate coming out through the exit port of a condenser at the top of the tower is measured; and a part of the vapor phase is taken out, mixed with the fraction, and resupplied to the intermediate stage of the tower to adjust the oxygen concn. to 20ppm or lower.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for preventing polymerization of conjugated dienes, and more particularly, to a method for purifying conjugated dienes such as isoprene and butadiene of high purity from petroleum fractions. The present invention relates to a method for preventing the polymerization of conjugated dienes, which suppresses the production of a polymer in (1), prevents the distillation column from being fouled, and makes it difficult to cause clogging of pipes and a decrease in thermal efficiency.

[0002]

2. Description of the Related Art Conjugated dienes such as 1,3-butadiene, isoprene and chloroprene are accidentally porous and insoluble in both liquid and gaseous phases, so-called popcorn polymers and rubbery polymers (dirt). ) Easy to occur. In particular, in industrial distillation, various conditions that easily cause polymerization, such as appropriate operation temperature, high monomer purity, coexistence of gas phase and liquid phase, mixing of water and presence of iron rust, are provided.

[0003] When the polymer begins to occur, it exponentially grows using the polymer as a nucleus and rapidly blocks the inside of the apparatus. Also, the polymer is insoluble in all known solvents,
It is a tough polymer that does not melt when heated. There is no better way to remove this polymer than cleaning by mechanical means. For this cleaning, it is necessary to temporarily stop the apparatus, which is economically disadvantageous.
In addition, since the polymer cannot be completely removed by mechanical cleaning, when the operation is restarted, the growth starts again with a small amount of the polymer that could not be removed as a nucleus.

[0004] In order to prevent polymerization of petroleum fractions containing conjugated dienes in a distillation apparatus, a method for distilling C5 hydrocarbons in the presence of di-lower alkylhydroxylamine has been proposed (see, for example, Japanese Patent Application Laid-Open No. H11-157556). JP-A-50-11230
No. 4). It is disclosed that the generation of popcorn polymer during the distillation of isoprene is suppressed by this method.

As a method for purifying isoprene or butadiene, JP-B-47-41323 and JP-B-45-196 are disclosed.
No. 82 discloses a method of extracting and distilling a conjugated diene hydrocarbon. In this case, it is disclosed that a polymerization inhibitor or a polymerization chain transfer agent can be added to the extraction solvent.

Further, JP-A-56-81526 and JP-B-43-20281 disclose a method of extracting and distilling furfural and a furfural condensate in a solvent.

However, in the extractive distillation of conjugated dienes, the conventional method in which only a polymerization inhibitor or furfural is present in the extractant increases the production of the polymer in the extractive distillation apparatus, particularly in a reflux condenser or an evaporator. It could not be prevented over a period of time, causing pipe clogging and reducing the thermal efficiency of condensation or evaporation.

[0008]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a conjugated diene for suppressing the production of a polymer in an extractive distillation apparatus, and for preventing the occurrence of dirt, clogging of pipes and a decrease in thermal efficiency in the apparatus. An object of the present invention is to provide a method for preventing polymerization. The present inventors have conducted intensive studies in order to achieve the above object, and as a result, a part of this gas phase has been removed so that the oxygen concentration in the gas phase of the top distillate of the extractive distillation column does not increase. It has been found that the above object can be achieved by extracting, preferably returning to a petroleum fraction containing a conjugated diene, and performing extractive distillation again. Based on this finding, the present invention has been completed.

[0009]

Thus, according to the present invention, (1) a petroleum fraction containing a conjugated diene is extracted and distilled by an extractive distillation column using an extraction solvent to separate the conjugated diene. In the process, a petroleum fraction containing conjugated dienes is supplied to an intermediate stage of the extractive distillation column, and the oxygen concentration in the gas phase of the distillate coming out of the extractive distillation column is measured, and the oxygen concentration is 20 ppm. As described below, there is provided a method for preventing polymerization of conjugated dienes, which comprises extracting a part of the gas phase.

As a preferred embodiment of the present invention, the following polymerization prevention method is provided. (2) The method for preventing polymerization according to (1), wherein the extraction solvent is an amide compound. (3) The method for preventing polymerization according to (2), wherein the amide compound is dimethylformamide. (4) The method for preventing polymerization according to the above (1) to (3), wherein a heterocyclic aldehyde, aromatic nitro or aromatic aldehyde is further present in the extraction solvent. (5) The method for preventing polymerization according to (4), wherein the heterocyclic aldehyde, aromatic nitro or aromatic aldehyde is furfural. (6) The method for preventing polymerization according to the above (4) to (5), wherein a polycondensate of a heterocyclic aldehyde or a polycondensate of an aromatic aldehyde is further present in the extraction solvent in an amount of 0.5 to 10% by weight based on the extraction solvent. .

(7) The method according to the above (6), wherein the total amount of the heterocyclic aldehyde, aromatic nitro or aromatic aldehyde and the polycondensate thereof in the extraction solvent is 1 to 10% by weight. (8) The polymerization prevention method according to the above (4) to (6), wherein the polycondensate of the heterocyclic aldehyde or the aromatic aldehyde is a furfural polycondensate.

(9) The method for preventing polymerization according to (1) to (8), wherein the polymerization inhibitor is continuously supplied from a position above the supply stage of the extraction solvent. (10) The method for preventing polymerization according to (9), wherein the polymerization inhibitor inhibits or suppresses polymerization by a chain transfer reaction. (11) The method for preventing polymerization according to the above (9), wherein the polymerization inhibitor is di-lower alkylhydroxylamine.

(12) The method for preventing polymerization according to the above (9) to (11), wherein the polymerization inhibitor is continuously supplied from the inlet of the condenser at the top of the tower. (13) The method for preventing polymerization according to (1) to (12), wherein the extraction solvent in the extraction solvent supply stage is adjusted so that 50 to 1000 ppm of water is present based on the extraction solvent.

(14) The method for preventing polymerization according to the above (1) to (13), wherein the extraction solvent contains an oxygen scavenger. (15) The method for preventing polymerization according to (14), wherein the oxygen scavenger is a nitrite. (16) The polymerization prevention method according to any one of (1) to (15), wherein the extracted gas-phase component is mixed with a petroleum fraction, and the mixture is re-supplied to an intermediate stage of the extractive distillation column.

[0015]

BEST MODE FOR CARRYING OUT THE INVENTION The method for preventing the polymerization of conjugated dienes according to the present invention comprises a step of extracting and distilling a petroleum fraction containing conjugated dienes by an extraction distillation column using an extraction solvent to separate the conjugated dienes. In the above, a petroleum fraction containing conjugated dienes is supplied to the intermediate stage of the extractive distillation column, and the oxygen concentration in the gas phase of the distillate coming out of the extractive distillation column top, preferably from the condenser is measured. So that the oxygen concentration is below a certain value
It is characterized in that a part of the gas phase is extracted.

[0016] Extractive distillation tower (preferably exiting the condenser)
The measurement of the oxygen concentration in the gas phase of the fraction coming out of the reactor is not particularly limited by the method. For example, a part of the gas phase is extracted from a line connected to the outlet of the extractive distillation column top (or condenser). The measurement may be performed, or the measurement may be performed at all times by burying an oxygen concentration measurement device in the line.

In the present invention, the oxygen concentration is 20
Part of the gas phase is extracted so as to be at most 10 ppm, preferably at most 10 ppm, more preferably at most 5 ppm. The extracted gas phase may be discharged from a flare stack or the like, but it is necessary to mix it with a petroleum fraction containing a conjugated diene as a feedstock and supply it to the extractive distillation column again.
It is preferable to increase the separation and purification yield of conjugated dienes. When the oxygen concentration exceeds 20 ppm, a polymer is generated in a condenser or the like, fouling the apparatus and causing blockage.

The extraction solvent used in the present invention is capable of dissolving and extracting conjugated dienes. Specifically, water, acetone, methyl ethyl ketone, dioxane,
Isoprene cyclic sulfone, acetonitrile, alcohol, glycol, N-methyl rolldamine, N-
Ethyl succinimide, N-methylpyrrolidone, N-methyl-2-pyrrolidone, hydroxylethylpyrrolidone, N-methyl-5-methylpyrrolidone, furfural, 2-heptenone, dimethylformamide, dimethylacetamide, N, N-dimethylacetoneacetamide ,
Morpholine, N-formylmorpholine, N-methylmorpholin-3-one, sulfolane, methyl carbitol,
Tetrahydrofuran, aniline, N-methyloxazolidone, N-methylimidazole, N, N'-dimethylimidazolin-2-one, 1-oxo-1-methylphospholine, methyl cyanoacetate, ethyl acetoacetate, ethyl acetate, dimethyl malonate ester,
Examples include propylene carbonate, methyl carbitol, triethyl phosphate, diethylene glycol monomethyl ether, dimethyl sulfoxide, and γ-butyrolactone. Of these, amide compounds, particularly dimethylformamide, are preferred.

The amount of the extraction solvent is usually from 100 to 100 parts by weight based on 100 parts by weight of a petroleum fraction containing conjugated dienes.
0 parts by weight, preferably 200 to 800 parts by weight. The extraction solvent is usually supplied to the extraction distillation column from an extraction solvent supply stage provided at an upper position than a stage for supplying a petroleum fraction containing a conjugated diene (a petroleum fraction supply stage).

In the present invention, the amount of water in the extraction solvent in the extraction solvent supply stage is usually 50 to 50% based on the extraction solvent.
It is preferably 1000 ppm, preferably 100 to 500 ppm. If the amount of water is too small, a polymer is likely to be generated, and clogging of the device piping is likely to occur. On the other hand, if the amount of water is too large, corrosion of the device is likely to be promoted.

Since water is also contained in a petroleum fraction supplied as a raw material, if the extractive distillation of conjugated dienes is operated for a long time, the amount of water in the extraction solvent increases.
When the amount of water increases, corrosion of the device is accelerated, and the life of the device is shortened, which is not preferable. Conventionally, in the step of recovering and purifying the extraction solvent, the removal of impurities in the extraction solvent and the complete removal of water were carried out to prevent the corrosion of the apparatus and the like. Is preferred.

In the present invention, in order to further prevent the occurrence of a polymer, it is preferable that a heterocyclic aldehyde, aromatic nitro or aromatic aldehyde is present in the extraction solvent. The heterocyclic aldehyde, aromatic nitro or aromatic aldehyde used in the present invention is an aldehyde having a heterocyclic ring, a nitro having a benzene ring or an aldehyde having a benzene ring. Examples of the heterocyclic aldehyde include furfural, 5-methylfurfural, 5- (hydroxymethyl) furfural; thiophene carbaldehyde; nicotinaldehyde, pyridoxal, and the like. Of these, furfural is preferred.

Examples of the aromatic aldehyde include benzaldehyde, tolualdehyde, cuminaldehyde, phenylacetaldehyde, ginnamaldehyde, phthalaldehyde, isophthalaldehyde, terephthalaldehyde and the like. Of these, benzaldehyde is preferred.

As the aromatic nitro, nitrobenzene,
Examples include nitrotoluene, α-nitrotoluene, nitroxylene, nitromesitylene, dinitrobenzene, dinitrotoluene, dinitroxylene, trinitrobenzene, trinitroxylene, and the like. Of these, nitrobenzene is preferred.

The amount of the heterocyclic aldehyde, aromatic nitro or aromatic aldehyde is usually 0.01 to 10% by weight, preferably 0.05 to 5% by weight, based on the extraction solvent in the extraction solvent supply stage. is there.

Further, in order to prevent contamination of the extractive distillation apparatus, a solvent obtained by adding monoethanolamine, monomethylamine, dimethylamine, trimethylamine or ethylenediamine to the extraction solvent; or a mixture of the extraction solvent with a heterocyclic aldehyde or an aromatic aldehyde. A tar such as a polycondensate of a heterocyclic aldehyde or an aromatic aldehyde is added to the solvent used in the above. Particularly, it is preferable to add a tar such as a heterocyclic aldehyde or an aromatic aldehyde polycondensate to a solvent used in combination with the extraction solvent and the heterocyclic aldehyde or the aromatic aldehyde.

The amount of the heterocyclic aldehyde polycondensate or aromatic aldehyde polycondensate is usually 0.5 to 10% by weight, preferably 1 to 5% by weight, based on the extraction solvent in the extraction solvent supply stage. is there. If the amount of the polycondensate is too large, the extraction efficiency tends to decrease. If the amount is too small, a large amount of heterocyclic aldehyde or aromatic aldehyde in dimethylformamide is consumed, which is uneconomical.

The extraction solvent used in the present invention preferably contains an oxygen scavenger. Nitrites such as calcium nitrite and sodium nitrite; hydroxylamine,
Amines such as hydrazine; dithionites such as sodium dithionite; sulfites such as calcium sulfite, potassium sulfite, manganese sulfite and sodium sulfite. Of these, nitrite is preferred. The oxygen scavenger removes oxygen in the extraction solvent and inhibits the generation of radicals, thereby increasing the polymerization inhibiting effect. Also, when a part of the gas phase of the distillate at the top of the extractive distillation column is resupplied to the extractive distillation column, oxygen in the gaseous phase is removed by the oxygen scavenger in the extractant circulating in the extractive distillation column, The concentration of oxygen in the gas phase of the distillate can be reduced. The amount of the oxygen scavenger is usually 0.1 to 1.5 parts by weight, preferably 0.2 to 0.8 parts by weight, per 1000 parts by weight of the extraction solvent.
Parts by weight.

In the present invention, it is preferable to continuously add the polymerization inhibitor from the position above the extraction solvent supply stage in order to prevent the polymerization of conjugated dienes.

The polymerization inhibitor used in the present invention can prevent polymerization of conjugated dienes. Specifically, 1,1-diphenyl-2-picrylhydrazyl, 1,3,5-triphenylferdazyl, as polymerization inhibition or suppression by trapping of radicals by stable radicals,
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) -feldadyl;

Examples of compounds that inhibit or inhibit polymerization by a chain transfer reaction include diphenylpicrylhydrazine, diphenylamine, diethylhydroxylamine, dimethylhydroxylamine, methylethylhydroxylamine, dipropylhydroxylamine, dibutylhydroxylamine, and dipentylhydroxylamine. Those having an active NH bond; those having a phenolic OH bond such as hydroquinone and t-butylcatechol;
Dithiobenzoyl disulfide, p, p'-ditolyl trisulfide, p, p'-ditolyl tetrasulfide,
Dibenzyltetrasulfide, tetraethylthiuram disulfide;

Examples of those which inhibit or inhibit polymerization by addition reaction include oxygen, sulfur, anthracene, 1,2-benzanthalacene, tetracene, and chloranil; p-benzoquinone, 2,6-dichlorobenzoquinone, and 2,5-diphenyl. Nitro compounds such as benzoquinone derivatives such as chlorobenzoquinone, frifludenmalononitrile, trinitrobenzene and m-dinitrobenzene; nitroso compounds such as nitrosobenzene and 2-methyl-2-nitrosopropane; further, ferric chloride and bromide And metal salts such as ferric iron.

Among these polymerization inhibitors, those which inhibit or inhibit the polymerization by a chain transfer reaction, particularly di-lower alkylhydroxylamine, specifically diethylhydroxylamine, are preferred.

The amount of the polymerization inhibitor is usually 0.1 to the total amount of the petroleum fraction containing the conjugated diene and the extraction solvent.
The amount is 1 to 20 ppm, preferably 0.5 to 10 ppm.

The position where the polymerization inhibitor is supplied to the extractive distillation column is, for example, at the side of the extractive distillation column above the extractive solvent feed stage, at the inlet or outlet of the condenser at the top of the extractive distillation column. Among them, the one provided at the inlet of the condenser at the top of the tower is preferable because the formation of the polymer in the condenser can be suppressed and the formation of the polymer can be suppressed in the next step after the separator.

The petroleum fraction used in the present invention contains conjugated dienes. The petroleum fraction is usually obtained by cracking naphtha and extracting C4 or C5 fractions obtained by separating C2 and C3 hydrocarbons such as ethylene and propylene, and preferably extracting the concentration of conjugated dienes in these fractions. It is increased by distillation or the like. The method of the present invention is particularly suitably used for a fraction containing butadiene. Petroleum fractions containing conjugated dienes are usually fed to the middle stage of an extractive distillation column.

[0037]

EXAMPLES The present invention will be described more specifically with reference to examples and comparative examples, but the present invention is not limited to only these examples. Parts and percentages are by weight unless otherwise specified.

Example 1 An experiment was carried out using a purification experiment apparatus for a C4 fraction containing butadiene shown in FIG. (First extractive distillation) The gasified C4 fraction is supplied to an intermediate stage of the first extractive distillation column 101, and 1% of a heterocyclic aldehyde or an aromatic aldehyde, 200 ppm of water, and 0.05% of sodium nitrite are used. The contained dimethylformamide (hereinafter, sometimes simply referred to as an extraction solvent) was supplied from a tube 102, and heated at the bottom with a reheater 105 to perform first-stage extractive distillation. The gas taken out from the top was condensed by the condenser 103, and part of the gas was refluxed and returned to the top. The remainder is pipe 1 as a distillate rich in butane, butylene, etc.
04. The pressure in the first extractive distillation column is usually 1 to 10 atm, and the bottom temperature is usually 100 to 160.
° C. An extract of butadiene containing higher acetylene and an allene-based hydrocarbon was taken out from the bottom of the tower, and this extract was supplied to the top of the stripping tower 107 via the pipe 106.
In the lower part of the stripping tower, distillation was performed by heating and evaporating with a reboiler 109. The pressure in the stripping tower 107 was usually 1 to 2 atm, and the bottom temperature was the boiling point at that pressure. A distillate containing butadiene, higher acetylene and allene-based hydrocarbons is taken out from the top of the stripping tower 107 and is cooled.
The liquid was liquefied at 8 and a part thereof was refluxed to the top of the stripping tower 107, the remaining part was sent to the washing tower 132 via the pipe 120, and the gas was sent to the compressor 112. The extraction solvent is taken out from the bottom of the stripping tower, and is passed through a condenser 111 by a pump 110 to a pipe 102.
Alternatively, it was circulated through the pipe 130 to the first extraction column 101 or the second extraction distillation column 114.

(Second Extractive Distillation) The gas exiting the cooler 108 is passed through a compressor 112 and a pipe 113 to the second extractive distillation column 1.
It was fed to 14 intermediate stages. Dimethylformamide containing 1% of a heterocyclic aldehyde or an aromatic aldehyde, 200 ppm of water and 0.05% of sodium nitrite in a tube 1
30 and further, diethylhydroxylamine was supplied from a tube 160 provided in front of the condenser 115 inlet.
The bottom portion was heated by a reheater 117 to perform a second-stage extractive distillation.

The liquid removed from the bottom of the second extractive distillation column was sent to the intermediate stage of the recovery column 119. The distillate taken out from the top of the recovery tower was sent to the compressor 112 via the pipe 121.

The bottom product taken out from the bottom of the recovery tower is supplied to the top of the stripping tower 125 via the pump 123 and the pipe 124, the extraction solvent is recovered from the bottom of the stripping tower 125, and from the top of the stripping tower 125. The removed distillate is supplied to the condenser 126
And a part thereof was refluxed to the stripping tower 125, and the remaining part was supplied to an intermediate stage of the washing tower 132 through the pipe 131.

Water was supplied from the pipe 133 to the top of the washing tower 132 to purify the extraction solvent, and dehydration was adjusted so that the amount of water in the extraction solvent in the pipes 102 and 130 was 200 ppm. The extraction solvent prepared by dehydration merges with the extraction solvent flowing from the tubes 129 and 137 via the tube 138, and
And circulated through tube 130.

The gas extracted from the top of the second extractive distillation column was condensed by the condenser 115. Gas was extracted from the outlet of the condenser 115, and the oxygen concentration in the gas was measured by gas chromatography. A part of the distillate coming out of the condenser was refluxed to the top of the second extractive distillation column. A part of the gas phase of the distillate that came out of the condenser was returned to the inlet of the compressor 112, and adjusted so that the measured value of the oxygen concentration was 5 ppm or less. The residual liquid was supplied to a first distillation column (not shown) via a pipe 116.

The distillate discharged from the top of the first distillation column was condensed in a condenser (not shown) and partly refluxed, and the remainder was incinerated as boiler fuel or in a flare stack.
The bottom product discharged from the bottom of the first distillation column was supplied to a second distillation column (not shown).

The distillate discharged from the top of the second distillation column was condensed in a condenser (not shown), part of the distillate was refluxed, and the remainder was supplied as high-purity butadiene to raw materials such as polybutadiene.

The above-mentioned purification method was operated continuously for two years. The production of popcorn polymer and rubbery polymer in each part of the refining equipment such as pipes, extractive distillation towers, condensers, reheaters (reboilers) is slight, there is little dirt inside the equipment and no corrosion has occurred. Was.

COMPARATIVE EXAMPLE 1 The procedure of Example 1 was repeated except that a part of the gas phase coming out of the condenser 115 was not returned to the inlet of the compressor 112 even if the measured value of the oxygen concentration became 20 ppm or more. Extractive distillation of the C4 fraction was performed in the same manner as in Example 1. With this purification method,
It ran continuously for a year. Each part of the refining device, particularly the condenser 115,
In the pipe 116 and the second distillation column, a large amount of popcorn polymer and rubbery polymer was generated, and the amount of dirt was large. Since the condenser 115 was closed in one and a half years, it had to be disassembled and cleaned.

[0048]

According to the method for preventing polymerization of the present invention, in the purification of a petroleum fraction containing conjugated dienes, the occurrence of popcorn polymer and rubbery polymer is small, the inside of the apparatus is not contaminated, and the pipe is clogged. And the thermal efficiency in the condenser, reboiler, etc. does not decrease, and the period during which cleaning is not required is long, so long-term continuous operation is possible and economical separation and purification of conjugated dienes becomes possible. .

[Brief description of the drawings]

FIG. 1 is a conceptual diagram of a C4 fraction purification experiment apparatus used in Example 1 of the present invention.

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁶ Identification code FI C07C 17/383 C07C 17/383 17/42 17/42 21/21 21/21

Claims (3)

[Claims] 1. A step of extracting and distilling a petroleum fraction containing conjugated dienes by an extractive distillation tower using an extraction solvent to separate conjugated dienes, wherein the petroleum fraction containing conjugated dienes is extracted and distilled. Measure the oxygen concentration in the gas phase of the distillate supplied to the middle stage of the column and coming out from the top of the extractive distillation column, and extracting a part of the gas phase so that the oxygen concentration is 20 ppm or less. A method for preventing polymerization of conjugated dienes, characterized in that: 2. The method for preventing polymerization of conjugated dienes according to claim 1, wherein the extracted gas-phase component is mixed with a petroleum fraction and re-supplied to an intermediate stage of an extractive distillation column. 3. The method for preventing polymerization of conjugated dienes according to claim 1, wherein the extraction solvent contains an oxygen scavenger.