JP3941151B2 - Method for preventing polymerization of conjugated dienes - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for preventing the polymerization of conjugated dienes, and more specifically, it suppresses the formation of a polymer in a purification apparatus when purifying conjugated dienes such as isoprene and butadiene having a high purity from petroleum fractions. The present invention relates to a method for preventing polymerization of conjugated dienes, which prevents contamination of a distillation column and makes it difficult to cause clogging of piping and a decrease in thermal efficiency.
[0002]
[Prior art]
Conjugated dienes such as 1,3-butadiene, isoprene, and chloroprene tend to accidentally generate porous insoluble polymers, so-called popcorn polymers and rubber-like polymers (stains) in both the liquid phase and the gas phase. . In particular, in industrial distillation, there are various conditions that are liable to cause polymerization, such as an appropriate operating temperature, high monomer purity, coexistence of a gas phase and a liquid phase, mixing of moisture and the presence of iron rust.
[0003]
When this polymer begins to occur, it grows exponentially using this as a nucleus, and the inside of the apparatus is rapidly blocked. This polymer is a tough polymer that is insoluble in all known solvents and does not melt even when heated. In order to remove this polymer, there is no good method other than cleaning by mechanical means. For this cleaning, it is necessary to temporarily stop the apparatus, and an economic disadvantage cannot be avoided. In addition, since the polymer cannot be completely removed by mechanical cleaning, when the operation is resumed, growth starts again with a small amount of polymer that could not be removed as a nucleus.
[0004]
Thus, in order to prevent the 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 (Japanese Patent Laid-Open No. Sho). 50-112304). It is disclosed that this method can suppress the generation of popcorn polymer during distillation of isoprene.
[0005]
Further, as methods for purifying isoprene and butadiene, Japanese Patent Publication No. 47-41323, Japanese Patent Publication No. 45-19682, etc. disclose a method of extracting and distilling conjugated diene hydrocarbons. It is disclosed that a polymerization chain transfer agent can be added.
[0006]
Further, JP-A-56-81526 and JP-B-43-20281 disclose a method of performing extractive distillation in the presence of furfural and a furfural condensate in a solvent.
[0007]
However, in the extractive distillation of conjugated dienes, the conventional method in which a polymerization inhibitor or furfural is present in the extraction solvent prevents the formation of polymers in the extractive distillation apparatus, particularly in the reflux and evaporators, for a long period of time. It could not be exhausted, resulting in clogging of the piping, reducing the thermal efficiency of condensation or evaporation.
[0008]
[Problems to be solved by the invention]
An object of the present invention is to provide a method for preventing polymerization of conjugated dienes to suppress the formation of a polymer in an extractive distillation apparatus and to prevent the occurrence of dirt, piping clogging, and decrease in thermal efficiency in the apparatus. .
As a result of intensive studies to achieve the above object, the present inventors have determined a part of this gas phase so that the oxygen concentration in the gas phase of the extract at the top of the extractive distillation column does not increase. It was found that the above-mentioned object can be achieved by extracting, preferably returning to a petroleum fraction containing a conjugated diene, and performing extractive distillation again, and the present invention has been completed based on this finding.
[0009]
[Means for Solving the Problems]
Thus, according to the present invention, (1) in the step of separating a conjugated diene by extracting and distilling a petroleum fraction containing a conjugated diene by an extractive distillation tower using an extraction solvent,
A petroleum fraction containing conjugated dienes is supplied to an intermediate stage of an extractive distillation column;
Measure the oxygen concentration in the gas phase of the distillate from the top of the extractive distillation column,
A method for preventing polymerization of conjugated dienes is provided, wherein a part of the gas phase is extracted so that the oxygen concentration is 20 ppm or less.
[0010]
As a preferred embodiment of the present invention, the following polymerization prevention method is provided.
(2) The method for preventing polymerization according to the above (1), wherein the extraction solvent is an amide compound.
(3) The method for preventing polymerization according to the above (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 (4) to (5) above, 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. .
[0011]
(7) The polymerization prevention 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 method for preventing polymerization according to the above (4) to (6), wherein the polycondensate of a heterocyclic aldehyde or the polycondensate of an aromatic aldehyde is a furfural polycondensate.
[0012]
(9) The polymerization preventing method according to the above (1) to (8), wherein the polymerization inhibitor is continuously supplied from a position above the extraction solvent supply stage.
(10) The method for preventing polymerization according to (9), wherein the polymerization inhibitor is one which inhibits or suppresses polymerization by a chain transfer reaction.
(11) The method for preventing polymerization according to (9), wherein the polymerization inhibitor is di-lower alkylhydroxylamine.
[0013]
(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 tower top condenser.
(13) The method for preventing polymerization according to the above (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 on the basis of the extraction solvent.
[0014]
(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 the above (14), wherein the oxygen scavenger is nitrite.
(16) The method for preventing polymerization according to the above (1) to (15), wherein the extracted gas phase component is mixed with the petroleum fraction and re-supplied to the intermediate stage of the extractive distillation column.
[0015]
DETAILED DESCRIPTION OF THE INVENTION
The method for preventing polymerization of a conjugated diene according to the present invention includes the step of separating a conjugated diene by extracting and distilling a petroleum fraction containing the conjugated diene by an extractive distillation tower using an extraction solvent. The oil fraction to be fed is supplied to the middle stage of the extractive distillation column, and the oxygen concentration in the gas phase of the distillate coming out from the top of the extractive distillation column, preferably from the condenser, is measured, and the oxygen concentration is below a specific value. Thus, a part of the gas phase is extracted.
[0016]
The measurement of the oxygen concentration in the gas phase of the fraction coming out from the top of the extractive distillation column (preferably from the condenser) is not particularly limited by the method. For example, the outlet of the top of the extractive distillation column (or the condenser) A part of the gas phase may be extracted from a line connected to the part, and the measurement may be performed. Alternatively, an oxygen concentration measuring device may be embedded in the line and the measurement may be performed constantly.
[0017]
In the present invention, a part of the gas phase is extracted so that the oxygen concentration is 20 ppm or less, preferably 10 ppm or less, more preferably 5 ppm or less. The extracted gas phase may be discharged from a flare stack or the like, but it is mixed with a petroleum fraction containing a conjugated diene as a feedstock and supplied to the extractive distillation tower again. It is preferable for increasing the separation and purification yield. When the oxygen concentration exceeds 20 ppm, a polymer is generated in a condenser or the like, and the apparatus is contaminated to cause clogging.
[0018]
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-methylrolldamine, N-ethylsuccinimide, 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 Examples include cyanoacetate, ethyl acetoacetate, ethyl acetate, dimethyl malonate, propylene carbonate, methyl carbitol, triethyl phosphate, diethylene glycol monomethyl ether, dimethyl sulfoxide, and γ-butyrolactone. Of these, amide compounds, particularly dimethylformamide, are preferred.
[0019]
The amount of the extraction solvent is usually 100 to 1000 parts by weight, preferably 200 to 800 parts by weight with respect to 100 parts by weight of the petroleum fraction containing the conjugated diene.
The extraction solvent is usually supplied to the extractive distillation column from an extraction solvent supply stage provided at an upper stage than a stage for supplying a petroleum fraction containing a conjugated diene (petroleum fraction supply stage).
[0020]
In the present invention, the amount of water in the extraction solvent in the extraction solvent supply stage is usually 50 to 1000 ppm, preferably 100 to 500 ppm, based on the extraction solvent. If the amount of water is too small, the polymer is liable to occur and the equipment piping is likely to be clogged. On the other hand, if the amount of water is too large, corrosion of the device is likely to be accelerated.
[0021]
Since water is also contained in the petroleum distillate supplied as a raw material, the amount of water in the extraction solvent increases when the extractive distillation of conjugated dienes is operated for a long time. When the amount of water increases, the corrosion of the apparatus is promoted and the life of the apparatus is shortened, which is not preferable. Conventionally, in the process of recovering and purifying the extraction solvent, the removal of impurities in the extraction solvent and the complete removal of water have been prevented to prevent the corrosion of the apparatus, but in the present invention, the above range is adjusted. It is preferable to do.
[0022]
In the present invention, in order to further prevent the occurrence of the 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, nitro having a benzene ring or aldehyde having a benzene ring.
Heterocyclic aldehydes include furfural, 5-methylfurfural, 5- (hydroxymethyl) furfural; thiophene carbaldehyde; nicotinaldehyde, pyridoxal, and the like. Of these, furfural is preferred.
[0023]
Examples of aromatic aldehydes include benzaldehyde, tolualdehyde, cuminaldehyde, phenylacetaldehyde, ginnamaldehyde, phthalaldehyde, isophthalaldehyde, terephthalaldehyde, and the like. Of these, benzaldehyde is preferred.
[0024]
Examples of the aromatic nitro include nitrobenzene, nitrotoluene, α-nitrotoluene, nitroxylene, nitromesitylene, dinitrobenzene, dinitrotoluene, dinitroxylene, trinitrobenzene, and trinitroxylene. Of these, nitrobenzene is preferred.
[0025]
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.
[0026]
In addition, 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; a combined solvent of the extraction solvent and the heterocyclic aldehyde or aromatic aldehyde A tar such as a heterocyclic aldehyde or aromatic aldehyde polycondensate is added and used. In particular, it is preferable to add a tar such as a heterocyclic aldehyde or an aromatic aldehyde polycondensate to a combined solvent of an extraction solvent and a heterocyclic aldehyde or an aromatic aldehyde.
[0027]
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.
If the polycondensate is too much, the extraction efficiency tends to decrease, and if it is too little, a large amount of heterocyclic aldehyde or aromatic aldehyde in dimethylformamide is consumed, which is uneconomical.
[0028]
The extraction solvent used in the present invention preferably contains an oxygen scavenger. Nitrites such as calcium nitrite and sodium nitrite; amines such as hydroxylamine and hydrazine; dithionates such as sodium dithionite; sulfites such as calcium sulfite, potassium sulfite, manganese sulfite and sodium sulfite Can do. Of these, nitrite is preferred. Oxygen scavenger removes oxygen in the extraction solvent and prevents the generation of radicals, thereby increasing the polymerization inhibition effect. Further, when a part of the gas phase of the distillate at the top of the extractive distillation column is re-supplied to the extractive distillation column, oxygen in the gas phase is removed by the oxygen scavenger in the extraction solvent circulating in the extractive distillation column, The oxygen concentration 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 with respect to 1000 parts by weight of the extraction solvent.
[0029]
In the present invention, it is preferable to continuously add a polymerization inhibitor from a position above the extraction solvent supply stage in order to prevent polymerization of conjugated dienes.
[0030]
The polymerization inhibitor used in the present invention can prevent polymerization of conjugated dienes. Specifically, polymerization is inhibited or suppressed by capturing radicals with stable radicals, such as 1,1-diphenyl-2-picrylhydrazyl, 1,3,5-triphenylferdazyl, 2,6-dit -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;
[0031]
Polymers that inhibit or inhibit polymerization by chain transfer reactions include active NHs such as diphenylpicrylhydrazine, diphenylamine, diethylhydroxylamine, dimethylhydroxylamine, methylethylhydroxylamine, dipropylhydroxylamine, dibutylhydroxylamine, dipentylhydroxylamine. Having a bond; 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;
[0032]
Examples of polymerization inhibition or suppression by addition reaction include oxygen, sulfur, anthracene, 1,2-benzanthracene, tetracene, chloranil; p-benzoquinone, 2,6-dichlorobenzoquinone, and 2,5-dichlorobenzoquinone. Nitro compounds such as benzoquinone derivatives, furfludene malononitrile, trinitrobenzene, m-dinitrobenzene; nitroso compounds such as nitrosobenzene and 2-methyl-2-nitrosopropane;
Furthermore, metal salts such as ferric chloride and ferric bromide can be mentioned.
[0033]
Among these polymerization inhibitors, those which inhibit or inhibit polymerization by chain transfer reaction, particularly di-lower alkylhydroxylamine, specifically diethylhydroxylamine are preferred.
[0034]
The amount of the polymerization inhibitor is usually 0.1 to 20 ppm, preferably 0.5 to 10 ppm based on the total amount of the petroleum fraction containing the conjugated diene and the extraction solvent.
[0035]
Examples of the position at which the polymerization inhibitor is supplied to the extractive distillation column include the side of the extractive distillation column above the extraction solvent feed stage and the inlet or outlet of the condenser at the top of the extractive distillation column. Among these, it is preferable to provide at the inlet of the tower top condenser because the production of the polymer in the condenser can be suppressed and the production of the polymer can also be suppressed in the next step after the separator.
[0036]
The petroleum fraction used in the present invention contains conjugated dienes. The petroleum fraction is usually a C4 or C5 fraction obtained by cracking naphtha and separating C2 and C3 hydrocarbons such as ethylene and propylene, preferably extracting the concentration of conjugated dienes in these fractions. Increased by distillation or the like. The method of the present invention is particularly preferably used for a fraction containing butadiene. The petroleum fraction containing conjugated dienes is usually fed to the intermediate stage of the extractive distillation column.
[0037]
【Example】
EXAMPLES Hereinafter, the present invention will be described more specifically with reference to examples and comparative examples. However, the present invention is not limited only to these examples. Parts and% are based on weight unless otherwise specified.
[0038]
Example 1
Experiments were conducted using a purification experiment apparatus for C4 fraction containing butadiene as shown in FIG.
(First extractive distillation)
The gasified C4 fraction is fed to the intermediate stage of the first extractive distillation column 101, and dimethylformamide (hereinafter referred to as 1% heterocyclic aldehyde or aromatic aldehyde, 200 ppm water and 0.05% sodium nitrite) , Simply referred to as an extraction solvent) was supplied from the tube 102 and heated at the bottom by the reheater 105 to perform first-stage extractive distillation. The gas taken out from the top of the column was condensed by the condenser 103 and partly refluxed and returned to the top. The remainder is taken out from the tube 104 as a distillate containing a large amount of butane, butylene and the like. The pressure in the first extractive distillation column is usually 1 to 10 atm, and the column bottom temperature is usually 100 to 160 ° C. A butadiene extract containing higher acetylene and allene-based hydrocarbons was taken out from the bottom of the column, and this extract was supplied to the top of the stripping column 107 via a pipe 106. Distillation was carried out by heating and evaporating with a reboiler 109 at the bottom of the stripping tower. The pressure of the stripping tower 107 was usually 1 to 2 atmospheres, and the tower bottom temperature was the boiling point at that pressure.
A distillate containing butadiene, higher acetylene and allenic hydrocarbons is taken out from the top of the stripping tower 107 and liquefied by the cooler 108, and a part thereof is refluxed to the top of the stripping tower 107. Then, the gas was sent to the water washing tower 132 and to the compressor 112. The extraction solvent was taken out from the bottom of the stripping tower, and was circulated to the first extraction tower 101 or the second extractive distillation tower 114 by the pump 110 through the cooler 111 and the pipe 102 or the pipe 130.
[0039]
(Second extractive distillation)
The gas exiting the cooler 108 was supplied to the intermediate stage of the second extractive distillation column 114 via the compressor 112 and the pipe 113. Dimethylformamide containing 1% of a heterocyclic aldehyde or aromatic aldehyde, 200 ppm of water and 0.05% of sodium nitrite is supplied from a pipe 130, and diethyl hydroxyl is supplied from a pipe 160 provided in front of the condenser 115 inlet. Amine was fed. The bottom portion was heated by a reheater 117 to perform second-stage extractive distillation.
[0040]
The liquid taken out 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.
[0041]
The bottoms taken out from the bottom of the recovery tower are 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 taken out from the top of the stripping tower 125. The distillate was liquefied by the condenser 126, a part of which was refluxed to the stripping tower 125, and the remainder was supplied to the intermediate stage of the washing tower 132 via the pipe 131.
[0042]
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 pipe 102 and the pipe 130 was 200 ppm. The extraction solvent prepared by dehydration merges with the extraction solvent flowing from the pipe 129 and the pipe 137 via the pipe 138 and is circulated through the pipe 102 and the pipe 130.
[0043]
The gas taken out from the top of the second extractive distillation column was condensed by the condenser 115. A 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 from the condenser was returned to the inlet of the compressor 112, and the measured value of the oxygen concentration was adjusted to 5 ppm or less. The remaining liquid was supplied to the first distillation column (not shown) through the pipe 116.
[0044]
The distillate discharged from the top of the first distillation column was condensed by a condenser (not shown) and partly refluxed, and the remainder was incinerated as boiler fuel or flare stack.
The bottoms discharged from the bottom of the first distillation column was supplied to the second distillation column (not shown).
[0045]
The distillate discharged from the top of the second distillation column was condensed by a condenser (not shown), a part of the distillate was refluxed, and the remainder was fed as a high-purity butadiene to a raw material such as polybutadiene.
[0046]
This purification method was operated continuously for 2 years. Popcorn polymer and rubber-like polymer are generated little in each part of the purification equipment such as piping, extractive distillation tower, condenser, reheater (reboiler), etc., and there is little contamination inside the equipment and no corrosion has occurred. It was.
[0047]
Comparative Example 1
In Example 1, even when the measured value of the oxygen concentration was 20 ppm or more, C4 was the same as Example 1 except that part of the gas phase that came out of the condenser 115 was not returned to the inlet of the compressor 112. Extractive distillation of the fraction was performed.
This purification method was operated continuously for 2 years. A large amount of popcorn polymer and rubber-like polymer were generated in each part of the purifier, particularly the condenser 115, the pipe 116, and the second distillation column, and there were many stains. Since the condenser 115 was blocked after one and a half years, it had to be disassembled and cleaned.
[0048]
【The invention's effect】
According to the polymerization prevention method of the present invention, in the purification of petroleum fractions containing conjugated dienes, there is little occurrence of popcorn polymer or rubbery polymer, the inside of the apparatus is not soiled, piping is not clogged, a condenser, Since the thermal efficiency in the reboiler and the like does not decrease and the period during which cleaning is not required is long, continuous operation for a long period of time is possible and economical separation and purification of conjugated dienes is 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.

Claims (3)

In the process of separating conjugated dienes by extracting and distilling petroleum fractions containing conjugated dienes using an extraction solvent by an extractive distillation column equipped with a condenser at the top of the extractive distillation column.
A petroleum fraction containing conjugated dienes is supplied to an intermediate stage of an extractive distillation column;
When the distillate from the top of the extractive distillation column is condensed by the condenser and refluxed to the top of the extractive distillation column , the oxygen concentration in the gas phase after being condensed by the condenser is measured, A method for preventing polymerization of conjugated dienes, wherein a part of the gas phase is extracted so that the oxygen concentration is 20 ppm or less.   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.   The method for preventing polymerization of conjugated dienes according to claim 1 or 2, wherein the extraction solvent contains an oxygen scavenger.

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