JP2003103108A - Distillation method for easily polymerizable substance and manhole structure of distillation column - 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 and a manhole structure of a distillation column. SOLUTION: This distillation method for the easily polymerizable substance comprises heating a manhole of the distillation column, thereby preventing the polymerization of the easily polymerizable substance in performing the distillation of the easily polymerizable substance. This manhole structure has a manhole shell plate 3 which is attached to a wall surface 1 of the distillation column and protrudes from the wall surface 1, a cap 5 which closes the front end opening of the manhole shell plate 3 and heating means 10 which is disposed at the manhole shell plate 3 and heats the manhole shell plate 3.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a distillation method for an easily polymerizable substance represented by a vinyl compound having a double bond in the molecule and a manhole structure of a distillation column used for the distillation of the easily polymerizable substance.

[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. 4 shows a distillation column normally used for distilling easily polymerizable substances. This distillation column is provided with packed layers 30 and 31 filled with packing. The raw material is supplied from the raw material supply port 33 into the tower. On the other hand, steam is introduced from the lower steam inlet 34, rises in countercurrent contact with the raw material, and is discharged from the upper steam outlet 35. Further, 36 is a reflux liquid inlet, and 37 is a liquid outlet.

In such a distillation column, a plurality of manholes 38, 39, ... 44 are provided for extracting the packing material and the like. FIG. 5 shows the structure of such a manhole. The manhole body plate 46 is attached to the wall surface 45 of the tower and protrudes from the wall surface 45, the flange 47 attached to the outer periphery of the tip of the manhole body plate 46, and the manhole. It comprises a lid portion 48 that closes the tip end opening of the body plate 46, and a gasket 49 that is interposed between the lid portion 48 and the flange 47. Then, the bolt 50 is passed through the bolt insertion holes provided in the lid portion 48 and the flange 47 and screwed with the nut 51 to close the tip opening of the manhole body plate 46 with the lid portion 48. A handle 52 is attached to the surface of the lid portion 48.

When the easily polymerizable substance was distilled using the above distillation apparatus, a polymer was sometimes formed at the manhole site. When a polymer is produced in the distillation step, it becomes a nucleus and gradually grows and accumulates to increase the pressure in the column, which eventually blocks the column. 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.

[0006]

DISCLOSURE OF THE INVENTION The main object of the present invention is to distill a readily polymerizable substance typified by a vinyl compound, to reduce the production of a polymer and to enable continuous operation of a distillation column. Is to provide a method. Another object of the present invention is to provide a manhole structure of a distillation column which reduces the production of polymer and enables continuous operation of the distillation column.

[0007]

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. Then, by heating the manhole installed in the distillation column, the vapor containing the easily polymerizable substance is prevented from condensing at a portion such as the manhole portion which is difficult to contact with the liquid containing the polymerization inhibitor, thereby distilling. The inventors have found that it is possible to prevent the formation of a portion where the easily polymerizable substance is easily polymerized in the tower, and have completed the present invention.

That is, the method for distilling the easily polymerizable substance of the present invention is characterized by heating the manhole of the distillation column when the easily polymerizable substance is distilled.

The polymerization inhibitor is usually mixed with the reflux liquid and supplied from the top of the distillation column. Since the polymerization inhibitor is substantially non-volatile, the polymerization inhibitor is not contained in the condensate generated by the vapor condensation in the distillation column. Therefore, the condensate is very unstable and easy to polymerize. This condensate is stabilized by being contacted with and mixed with a liquid containing a polymerization inhibitor flowing down from the upper part of the distillation column to prevent polymerization.
Therefore, as described above, the site where the vapor is condensed in the distillation column and the liquid is easily accumulated in the absence of the polymerization inhibitor is the site where the easily polymerizable substance is easily polymerized.

As a result of further studies on the cause of the polymerization in the distillation column, the present inventors have found that the manhole part of the distillation column is convexly projected from the space inside the column as shown in FIG. Since the projecting portion 53 is cooled by the influence of the outside air, the vapor containing the easily polymerizable substance is likely to condense, and the manhole portion is less likely to come into contact with the reflux liquid containing the polymerization inhibitor, so that the manhole portion is condensed. It was found that the liquid is very unstable and a polymer is easily generated. In the present invention, as described above, the manhole of the distillation column is heated to give the steam a heat amount equal to or more than the heat radiation amount, thereby preventing the steam containing the easily polymerizable substance from being cooled. This makes it difficult to contact the reflux liquid containing the polymerization inhibitor like the manhole part of the distillation column,
It is possible to prevent condensation of the easily polymerizable substance at the site where polymerization is very easy, and prevent polymerization at the site.

In the distillation method of the present invention, the manhole temperature is preferably heated to a temperature higher than the temperature inside the column, more preferably higher than the temperature inside the column, and within a temperature range not exceeding 100 ° C. from the temperature inside the column. Good to do. This can prevent the easily polymerizable substance from condensing and polymerizing in the manhole portion.

The manhole structure of the distillation column of the present invention is the structure of the manhole provided in the distillation column for distilling the easily polymerizable substance. The manhole body plate is attached to the wall of the distillation column and protrudes from the wall, It is characterized in that it is provided with a lid portion that closes the front end opening of the manhole body plate, and a heating means for heating the manhole body plate and / or the lid portion provided in the manhole.

As the heating means, the outer surface of the body plate and / or the lid portion of the manhole is brought into contact with a trace pipe for passing a heat medium, or the outer surface of the body plate and / or the lid portion of the manhole is heated. A jacket is preferable.

[0014]

BEST MODE FOR CARRYING OUT THE INVENTION One embodiment of the present invention is shown in FIG. FIG. 1 is an exploded sectional view showing a manhole structure according to this embodiment.

The manhole shown in FIG. 1 is provided in a distillation column for distilling the above-mentioned easily polymerizable substance. A cylindrical manhole body plate 3 is integrally attached to the outer peripheral edge of the opening 2 provided in the column wall 1 of the distillation column by welding or the like. A flange 4 is attached to the outer periphery of the tip of the manhole body plate 3 by welding or the like. A gasket 6 is interposed between the flange 4 and the lid 5, and a bolt 7 is inserted in a bolt insertion hole provided in the flange 4 and the lid 5.
Through, and is screwed with the nut 8 to close the front end opening of the manhole body plate 3 with the lid portion 5. A handle 9 is provided on the surface of the lid 5.
Is attached.

A trace pipe 10 for passing a heat medium is spirally wound around the manhole body plate 3. If necessary, trace piping may be installed on the manhole cover. The heat medium is supplied from the supply port 10a, and the discharge port 1
It is discharged from 0b. If necessary, the supply port and the discharge port may be reversed and used. Due to the heat transmitted from the heat medium in the trace pipe 10 to the manhole body plate 3, the manhole body plate 3 is maintained at a temperature substantially equal to or higher than the tower temperature, preferably higher than the tower temperature. More preferably, the temperature is higher than the temperature inside the column, and is maintained within a temperature range not exceeding 100 ° C from the temperature inside the column, and more preferably, is higher than the temperature inside the column, and is more preferably maintained within a temperature range not exceeding 20 ° C from the temperature inside the column. To be done. This can prevent the easily polymerizable substance from condensing in the manhole portion. If continuous operation is performed for a long period of time in a temperature range in which the temperature of the manhole body plate 3 is excessively higher than the temperature inside the tower, it is disadvantageous in terms of energy, and a problem may occur such that the polymerization inhibitor and the attached polymer are burnt. It is not preferable.

As the heat medium passed through the trace pipe 10, hot water, steam, oil or the like can be used.

FIG. 2 is an exploded sectional view schematically showing a manhole structure according to another embodiment of the present invention. A cylindrical manhole body plate 13 is integrally attached by welding or the like to the outer peripheral edge of the opening 12 provided in the column wall 11 of the distillation column shown in FIG. On the outside of the manhole body plate 13, a heating jacket 15 through which a heat medium (hot water, steam, oil, etc. described above) passes is attached. If desired, a heating jacket may be installed on the manhole cover. On the surface of the heating jacket 15, a heat medium supply port 1
5a and a discharge port 15b are provided respectively. If necessary, the supply port and the discharge port may be reversed and used.
Due to the heat transmitted from the heat medium in the heating jacket 15 to the manhole shell plate 13, the manhole shell plate 13 is maintained at a temperature substantially equal to or higher than the tower internal temperature, preferably higher than the tower internal temperature. More preferably, the temperature is higher than the temperature inside the column and is maintained within a temperature range not exceeding 100 ° C. from the temperature inside the column, and more preferably, is maintained at a temperature higher than the temperature inside the column and not exceeding 20 ° C. from the temperature inside the column. To be done.

A flange 14 is attached to the outer periphery of the end of the heating jacket 15 by welding or the like. A gasket 6 is interposed between the flange 14 and the lid 5, and a bolt 7 is passed through a bolt insertion hole provided in the flange 14 and the lid 5 and screwed with a nut 8 to open the tip opening of the manhole body plate 13. Is covered with the lid 5. A handle 9 is attached to the surface of the lid 5.

FIG. 3 is an exploded sectional view showing a manhole structure according to still another embodiment of the present invention.

The manhole shown in FIG. 3 is provided in a distillation column for distilling the above-mentioned easily polymerizable substance. That is, a cylindrical flange portion 21 is integrally attached to the outer peripheral edge of the opening 2 provided in the column wall 1 of the distillation column by welding or the like. On the surface of the flange portion 21, a plurality of standing bolts 22 are provided upright along the circumferential direction at appropriate intervals.

The inner surface of the peripheral edge of the lid portion 23 abuts on the surface of the flange portion 21 via a gasket 27 to close the opening 2 of the distillation column. The lid 23 is a circular plate-shaped body.
A heating jacket 24 for passing a heat medium (hot water or the like) is attached to the upper surface of the lid portion 23. A heating medium supply port 24a and a heating medium discharge port 24b are provided on the surface of the heating jacket 24, respectively. The heating jacket 24 maintains the lid portion 23 at least at a temperature substantially equal to or higher than the temperature inside the column, preferably higher than the temperature inside the column, more preferably higher than the temperature inside the column, and more preferably higher than the temperature inside the column. Temperature range from the internal temperature to not exceeding 100 ° C, more preferably at a temperature higher than the internal temperature and from the internal temperature to 20 ° C
Is maintained within a temperature range not exceeding When the temperature of the lid portion 23 is lower than the temperature in the tower, the condensed liquid adheres to the lid portion 23, and the polymerized material and the condensed material are likely to accumulate.

A bolt insertion hole 25 corresponding to the stand-up bolt 22 is provided on the peripheral edge of the lid portion 23. Then, the nut 26 is attached to the stand-up bolt 22 of the flange portion 21 which is projected by being inserted through the bolt insertion hole 25.
Are screwed together. As a result, the lid portion 23 is replaced with the flange portion 21.
It can be pressed and fixed to the surface of. In addition, it is preferable that the inner surface of the lid portion 23 and / or the surface of the flange portion be lined.

As described above, in the present invention, by providing the trace pipe 10 and the heating jacket 15, the manhole body plate and / or the lid portion is maintained at a temperature higher than the temperature inside the tower. As a result, the vapor of the easily polymerizable substance does not condense to form a liquid pool in the manhole portion, and thus it is possible to prevent the generation of the polymer.

The manhole structure of the present invention is applied to an ordinary distillation column as shown in FIG. 4, and is particularly suitable for use as a manhole for discharging a packing which undergoes severe polymerization. Also,
In the distillation operation, the polymerization inhibitor may be added to the reflux liquid or the supply liquid and supplied. Examples of the polymerization inhibitor include one kind or two or more kinds of metal salts of dibutyldithiocarbamic acid (copper, manganese, etc.), phenothiazine, methoquinone, hydroquinone and the like.

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, 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.).

As the heating means for the manhole body plate 3, other heating means such as an electric heater may be adopted instead of the trace pipe 10 described above.

[0028]

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 1 In a distillation column for distilling acrylic acid as shown in FIG. 4, the packing extraction manhole was changed to the structure as shown in FIG. 1, and long-term continuous operation was performed. This distillation apparatus is a packed column equivalent to 6 theoretical plates, and the top pressure is 55 torr.
The operation was performed under the conditions of r, a distillation rate of 80%, and a reflux ratio of 0.8. At this time, a small amount of phenothiazine and metoquinone as polymerization inhibitors were added to the reflux liquid, and a constant amount of air was supplied to the liquid portion of the can portion for operation. Hot water was passed through the trace pipe 10, and the manhole body plate 3 was maintained at 74 to 77 ° C, which is a temperature 2 to 5 ° C higher than the temperature inside the tower. During the continuous operation, the tendency of pressure increase in the distillation column and the state of adhesion of the polymer to the manhole were periodically examined.

Example 2 Long-term continuous operation was carried out in the same manner as in Example 1 except that hot water was passed through the trace pipe 10 and the manhole shell plate 3 was maintained at 92 ° C. which was 20 ° C. higher than the temperature inside the tower. I went. During the continuous operation, the tendency of pressure increase in the distillation column and the state of adhesion of the polymer to the manhole were periodically examined.

Comparative Example A long-term continuous operation was carried out in the same manner as in Example 1 except that the distillation column shown in FIG. 4 equipped with the manhole shown in FIG. 4 was used. During the continuous operation, the tendency of pressure increase in the distillation column and the state of adhesion of the polymer to the manhole were periodically examined.

Table 1 shows the long-term continuous operation results of Examples 1, 2 and Comparative Example.

[Table 1]

As a result of the long-term continuous operation of Example 1, the pressure in the distillation column started to rise after 3 months. Further, as a result of visual observation, although the polymer was slightly produced, the lid 5 could be easily opened. As a result of long-term continuous operation of Example 2, no pressure increase in the distillation column was observed even after 4 months. In addition, as a result of visual observation, no production of a polymer was found, and the lid 5 could be easily opened. As a result of long-term continuous operation of the comparative example, the pressure in the distillation column started to rise after 2 months. Further, since the polymer was accumulated in the manhole, the manhole cover 5 could not be opened without a jig.

As described above, it was found that by heating the manhole of the distillation column to a temperature equal to or higher than the internal temperature of the column, the production of the polymer is suppressed.

[0035]

According to the present invention, the manhole body plate and / or the lid portion is provided with a heating means such as a trace pipe and a heating jacket to maintain the manhole body plate and / or the lid portion at a temperature higher than the temperature in the tower. Therefore, it is possible to prevent the vapor containing the easily polymerizable substance from condensing at the site. In the manhole part, since it is difficult to contact with the reflux liquid containing the polymerization inhibitor, the vapor containing the easily polymerizable substance is very unstable and easily polymerized, but in the present invention, as described above, the vapor containing the easily polymerizable substance is vaporized. Since it can be prevented from condensing, the production of the polymer in the manhole is reduced, and the distillation column can be continuously operated.

[Brief description of drawings]

FIG. 1 is an exploded cross-sectional view showing a manhole structure according to an embodiment of the present invention.

FIG. 2 is an exploded sectional view schematically showing a manhole structure according to another embodiment of the present invention.

FIG. 3 is an exploded cross-sectional view schematically showing a manhole structure which is another embodiment of the present invention.

FIG. 4 is a schematic view showing an ordinary distillation column.

FIG. 5 is an exploded sectional view showing a conventional manhole structure.

[Explanation of symbols]

1 tower wall 2 openings 3 Manhole body plate 4 flange 5 Lid 6 gasket 7 volts 8 nuts 9 handle 10 Trace piping (heating means) 10a supply port 10b outlet 11 tower wall 12 openings 13 Manhole body plate 14 Flange 15 Heating jacket (heating means) 15a supply port 15b outlet

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Hideki Gondo             Sumitomo Chemical 5-1, Soukai-cho, Niihama-shi, Ehime             Industry Co., Ltd. F-term (reference) 4D076 AA01 AA13 AA16 AA22 BB01                       BB03 CD41 CD43 DA14 DA22                       JA02                 4H006 AA02 AA04 AD11 BD82 BS10

Claims (7)

[Claims] 1. A method for distilling a readily polymerizable substance, which comprises heating a manhole of a distillation column when distilling the easily polymerizable substance. 2. The method for distilling a readily polymerizable substance according to claim 1, wherein the temperature of the manhole is heated to a temperature higher than the temperature inside the tower. 3. The method for distilling a readily polymerizable substance according to claim 1, wherein the temperature of the manhole is heated to a temperature higher than the temperature inside the column and within a temperature range not exceeding 100 ° C. from the temperature inside the column. 4. The method for distilling an easily polymerizable substance according to claim 1, wherein the easily polymerizable substance is a vinyl compound. 5. A structure of a manhole provided in a distillation column for distilling a readily polymerizable substance, the manhole body plate being attached to a wall surface of the distillation column and protruding from the wall surface, and closing a front end opening of the manhole body plate. A manhole structure for a distillation column, comprising a lid and a heating means for heating the manhole body plate and / or the lid provided in the manhole. 6. The manhole structure according to claim 5, wherein the heating means is such that a trace pipe for passing a heat medium is brought into contact with the outer surface of the manhole body plate and / or the lid portion. 7. The manhole structure according to claim 5, wherein the heating means is provided with a heating jacket for passing a heat medium on the outer surface of the manhole body plate and / or the lid portion.