JP2003103103A - Distillation method for easily polymerizable substance and distillation apparatus used for the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a distillation method which makes the continuous operation of a distillation column possible by reducing the formation of a polymer in performing distillation of an easily polymerizable substance, as represented by a vinyl compound, such as an acrylic acid, and a distillation apparatus used for the same. SOLUTION: In performing distillation while refluxing the easily polymerizable substance, a reflux liquid is made to flow down from an aperture 1b disposed atop a reflux pipe 1 inserted into the distillation column while wetting an external wall surface 1a of the reflux pipe. As a result, the easily polymerizable substance is prevented from concentrating and growing a polymer on the external wall surface of the reflux pipe.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a method for distilling a readily polymerizable substance represented by a vinyl compound such as acrylic acid having a double bond in the molecule, and a distillation apparatus used therefor.

[Prior art]

[0002] Since the easily polymerizable substance has a property of being easily polymerized by light, heat, etc., it is extremely easily polymerized at a high temperature such as a distillation step. When polymerization occurs in the distillation column,
Not only will it lead to loss, but it will also hinder continuous operation and reduce productivity. Therefore, prevention of polymerization is a very important technique in the distillation and purification of the easily polymerizable substance, and many methods for preventing polymerization have been proposed in the past regarding the type, amount, combination and the like of the polymerization inhibitors.

FIG. 3 shows a distillation apparatus usually used for distilling easily polymerizable substances. This distillation apparatus comprises a distillation column having packed beds 30, 31, 32 filled with Raschig rings and the like, a condenser 40 for condensing discharged vapor, and the like. In the distillation column, the raw material is supplied into the column through the raw material supply ports 33, 33. On the other hand, steam is introduced from the lower steam inlet 34, rises while coming into countercurrent contact with the raw material, and is discharged from the upper tower portion 35 in the upper part.

The discharged steam is sent to a condenser 40 through a circulation pipe 39 and cooled by cooling water to become a condensed liquid. A part of this condensate is supplied to the inside of the tower as a reflux liquid from the reflux liquid inlet 36 through the circulation pipe 42 by the pump 41, and the rest is recovered as a distillate liquid through the pipe 43. The ratio of the reflux liquid and the distillate is adjusted by the adjusting valve 44,
Adjusted by 45. Reference numeral 37 is a bottom liquid outlet for discharging the bottom liquid, and 38 is a manhole provided for withdrawing the filling material and the like.

FIG. 5 is a schematic view showing an example inside the distillation column around the column top 35. As described above, the reflux liquid cooled by the condenser 40 is supplied to the reflux liquid inlet 36.
Liquid distributor 4 from the opening 46b provided on the lower surface of the reflux pipe 46 that is introduced into the column from the
7 is supplied. The liquid distributor 47 is provided to uniformly disperse and supply the reflux liquid from the upper portion of the packed bed 30. The reflux liquid supplied to the liquid distributor 47 passes through the packing presser 50 as shown by an arrow 48, and the packed bed 3
Run down to zero. On the other hand, the steam introduced from the steam inlet 34 (FIG. 3) and rising in the packed beds 32 and 31 is
As shown in FIG. 9, in the packed bed 30, the reflux liquid is brought into gas-liquid contact. Then, the vapor further rises in the tower top portion 35 and is sent to the condenser 40 through the pipe 39.

FIG. 6 is a schematic view showing another example of the inside of the distillation column around the column top 35. As mentioned above,
The reflux liquid is introduced into the tower through the reflux liquid inlet 36 and is supplied to the liquid distributor 47 through the opening 51 b of the reflux pipe 51.

When the easily polymerizable substance was distilled using the above-mentioned distillation apparatus, a polymer was sometimes produced in the reflux pipe for supplying the reflux liquid to the top of the distillation column. If the polymer generated here falls and accumulates in the liquid distributor, the liquid distributor will be clogged, making it difficult to uniformly distribute and supply the reflux liquid to the packed bed. A part with poor liquid wettability occurs. As described above, usually, a polymerization inhibitor is added to the reflux liquid and the effect of preventing polymerization is seen, but since there is almost no polymerization inhibitor in the poor liquid wettability portion, the filling surface Also, a polymer is easily formed. When the polymer is generated in this manner, it becomes a nucleus and gradually grows and accumulates to increase the pressure in the tower, and finally the inside of the tower is blocked. This not only increases product loss, but also becomes a major factor that impedes continuous operation of the distillation column and reduces productivity. Further, it is very difficult to remove the produced polymer, and the removal cost is great.

[0008]

SUMMARY OF THE INVENTION The main object of the present invention is to reduce the production of polymer and to continuously operate the distillation column when distilling easily polymerizable substances represented by vinyl compounds such as acrylic acid. It is to provide a distillation method that enables it. Another object of the present invention is to provide a distillation apparatus which reduces the production of polymer and enables continuous operation of the distillation column.

[0009]

Means for Solving the Problems As a result of intensive studies to solve the above-mentioned problems, the present inventors have found that a portion of the distillation column where the easily polymerizable substance is easily polymerized is vapor containing the easily polymerizable substance. It has been found that these are sites that are likely to condense and form a liquid pool in the absence of the polymerization inhibitor. Further, when the vapor rises in the top of the tower, the vapor comes into contact with the outer wall surface of the reflux pipe cooled by the low-temperature reflux liquid to be cooled, so that the easily polymerizable substance contained in the vapor on the outer wall surface of the reflux pipe. Have been found to condense. From these, by allowing the reflux liquid to flow down from the opening provided on the upper surface of the reflux pipe inserted inside the distillation column while wetting the outer wall surface of the reflux pipe, the vapor containing the easily polymerizable substance can flow into the reflux pipe. The present invention has been completed by discovering that it is possible to prevent the formation of easily polymerized substances in the distillation column by preventing condensation at the portions that are difficult to contact with the liquid containing the polymerization inhibitor, such as the outer wall surface, and completed the present invention. Came to let.

That is, in the method of distilling the easily polymerizable substance in the present invention, when the easily polymerizable substance is distilled while refluxing, the reflux liquid is refluxed from the opening provided on the upper surface of the reflux pipe inserted inside the distillation column. The feature is that the outer wall surface of the pipe is made to flow down while being wet.

As described above, the reflux liquid is made to flow down from the opening provided on the upper surface of the reflux pipe while wetting the outer wall surface, so that the easily polymerizable substance such as acrylic acid is condensed on the outer wall surface of the reflux pipe to form a polymer. Can be prevented.

The distillation apparatus of the present invention is a distillation apparatus equipped with a distillation column, a condenser for condensing the vapor discharged from the distillation column, and a circulation pipe connecting these, and distillation is performed from the pipe. It is characterized in that an opening is provided on the upper surface of the reflux pipe inserted into the inside of the column, and can be suitably used in the distillation method.

[0013]

BEST MODE FOR CARRYING OUT THE INVENTION One embodiment of the present invention is shown in FIG. FIG. 1 is a schematic diagram showing a configuration around a reflux pipe 1 in a distillation apparatus for distilling an easily polymerizable substance of the present invention.

A reflux pipe 1 used in the present invention shown in FIG.
Is located inside the column top portion 35 of the distillation column provided with the packed layers 30, 31, and 32 in which Raschig rings or the like are filled inside shown in FIG.

As described above, the vapor introduced from the vapor inlet 34 rises in countercurrent contact with the raw materials in the packed beds 30, 31, 32, and is discharged from the top 35 of the distillation column. The steam discharged from the tower top 35 is stored in the condenser 4
It is cooled by 0 and becomes a condensate. Some of this condensate is
It is introduced as a reflux liquid from the reflux liquid inlet 36 into the column top 35. The remaining condensate is recovered as a distillate through the pipe 43.

The reflux liquid introduced into the tower top 35 flows down along the outer wall surface 1a of the reflux pipe from the opening 1b provided on the upper surface of the reflux pipe 1. The flowing-down reflux liquid is supplied to the liquid distributor 47, and further flows down to the packed bed 30 via the packing presser 50 as shown by an arrow 48.

FIG. 2 is a partially enlarged plan view showing the return pipe 1. In FIG. 2, arrow 2 indicates the flow of reflux liquid. The reflux pipe 1 is provided with a plurality of holes 1b, and the reflux liquid overflowing from the holes 1b flows down along the reflux pipe outer wall surface 1a as shown by an arrow 2. In this way, the reflux liquid flows down while wetting the outer wall surface 1a of the reflux pipe, so that it is possible to prevent condensation of easily polymerizable substances such as acrylic acid on the outer wall surface 1a to form a polymer.

The number of holes 1b provided in the reflux pipe 1,
It is preferable to set the hole diameter, the hole interval, and the like so that almost all the surface of the reflux pipe 1 is wet with the reflux liquid, and may be determined in consideration of the reflux amount, the pipe diameter of the reflux pipe 1, the pipe length, and the like. Specifically, for example, the diameter of the return pipe 1 is generally about 20 to 65 mm, and the diameter of the hole 1b provided in the return pipe 1 is generally about 1 to 3 mm.

In the distillation operation, a polymerization inhibitor may be added to the reflux liquid. Examples of the polymerization inhibitor include dibutyldithiocarbamic acid metal salt (copper, manganese, etc.),
One or more of phenothiazine, metoquinone, hydroquinone and the like can be mentioned. The amount of polymerization inhibitor added is
It may be about 0.005 to 0.1 part by weight per 100 parts by weight of the reflux liquid.

Examples of the easily polymerizable substance include, in addition to acrylic acid, conjugated acids such as methacrylic acid or derivatives thereof such as esters, amides and nitriles (methyl acrylate, methyl methacrylate, acrylamide, acrylonitrile, etc.),
Conjugated aldehydes and ketones (acrolein, methacrolein, methyl vinyl ketone, etc.), vinyl halides (vinyl chloride, etc.), vinyl group-substituted aromatic compounds (styrene, etc.), vinyl carboxylates (vinyl acetate, etc.), vinyl ethers (methyl vinyl ether, etc.) ), 1,3-diolefins (butadiene, isoprene, etc.), ethylene and alkyl-substituted ethylene (propylene, etc.).

The opening is not limited to the one having a plurality of holes as shown in the above embodiment, and for example, a slit formed in the longitudinal direction of the pipe may be adopted. it can. Further, in the present invention, a ladder pipe 61 as shown in FIG. 4 can be used instead of the reflux pipe 1 shown in FIG. FIG. 4 is a plan view of the ladder pipe 61. This ladder pipe 6
Reference numeral 1 includes a main pipe 62 and a plurality of pipes 63 branched from the main pipe 62. A plurality of openings 64 are provided on the upper surfaces of the main pipe 62 and the pipe 63. When the reflux liquid is supplied from one end of the main pipe 62, the reflux liquid flows down from the opening 64 along the outer wall surfaces of the main pipe 62 and the pipe 63. Thereby, similarly to the reflux pipe 1, it is possible to prevent the easily polymerizable substance from condensing on the outer wall surfaces of the main pipe 62 and the pipe 63 to generate a polymer.

[0022]

The present invention will be described in detail below with reference to Examples and Comparative Examples, but the present invention is not limited to the following Examples.

EXAMPLE In order to purify acrylic acid by distillation, long-term continuous operation was carried out using a distillation apparatus equipped with a reflux pipe 1 having an opening on the upper surface as shown in FIG. At this time, a small amount of phenothiazine and metoquinone as polymerization inhibitors were added to the reflux liquid for operation. During the continuous operation, the tendency of increasing the differential pressure of the packed bed and the state of adhesion of the polymer to the liquid distributor 47, the packing, etc. were periodically examined.

COMPARATIVE EXAMPLE In order to purify acrylic acid by distillation, a distillation pipe similar to that of the embodiment was used except that a reflux pipe 46 having an opening on the lower surface was provided as shown in FIG. The liquid distributor 4 is operated to periodically increase the differential pressure of the packed bed, and the liquid distributor 4
7. The state of adhesion of the polymer to the filler was investigated.

Table 1 shows the long-term continuous operation results of Examples and Comparative Examples.

[Table 1]

[0026]

According to the present invention, the reflux liquid is made to flow down while wetting the outer wall surface from the opening provided on the upper surface of the reflux pipe, so that the easily polymerizable substance such as acrylic acid is condensed on the outer wall surface of the reflux pipe. It is possible to prevent the formation of a polymer, and it is possible to continuously operate the distillation column.

[Brief description of drawings]

FIG. 1 is a schematic view showing the periphery of a reflux pipe used in a distillation apparatus which is an embodiment of the present invention.

FIG. 2 is a partially enlarged plan view showing a reflux pipe which is an embodiment of the present invention.

FIG. 3 is a schematic diagram showing a distillation apparatus.

FIG. 4 is a plan view showing a ladder pipe.

FIG. 5 is a schematic view showing the periphery of a reflux pipe used in a conventional distillation apparatus.

FIG. 6 is a schematic view showing the periphery of a reflux pipe used in a conventional distillation apparatus.

[Explanation of symbols]

1 Return pipe 1a Return pipe outer wall surface 1b hole 2 Flow of reflux liquid

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Hideki Gondo             Sumitomo Chemical 5-1, Soukai-cho, Niihama-shi, Ehime             Industry Co., Ltd. F-term (reference) 4D076 AA07 AA16 AA21 BB04 CA11                       JA02                 4H006 AA02 AD11 BD82 BS10

Claims (4)

[Claims] 1. When distilling the easily polymerizable substance under reflux, the reflux liquid is made to flow down from an opening provided on the upper surface of the reflux pipe inserted in the distillation column while wetting the outer wall surface of the reflux pipe. And method for distilling easily polymerizable substances. 2. The method for distilling a readily polymerizable substance according to claim 1, wherein the opening comprises a plurality of holes. 3. The distillation method for an easily polymerizable substance according to claim 1, wherein the easily polymerizable substance is a vinyl compound. 4. A distillation apparatus comprising a distillation column, a condenser for condensing vapor discharged from the distillation column, and a circulation pipe connecting these, which is inserted into the distillation column through the pipe. The distillation apparatus used in the distillation method according to any one of claims 1 to 3, wherein an opening is provided on the upper surface of the reflux pipe.