JP2003103105A - 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 and a distillation apparatus. SOLUTION: This distillation method for the easily polymerizable substance comprises heating a column apex and a conduit, thereby preventing the polymerization of the easily polymerizable substance in refining the easily polymerizable substance by distillation. This distillation apparatus is a distillation apparatus provided with the conduit 39 for discharge at the column apex 35 and has heating means 1 and 2 in at least portions of the column apex 35 and the conduit 39.

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 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 so far with respect to the type, amount, combination and the like of polymerization inhibitors.

FIG. 3 shows a distillation column commonly used for the distillation of 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 while coming into countercurrent contact with the raw material, and is discharged from the upper tower portion 35 in the upper part.

The discharged vapor is sent to a condenser 40 through a conduit 39 and cooled to be a condensed liquid. A part of this condensate is re-supplied into the column as a reflux liquid from the reflux liquid inlet 36 through the pipe 42 by the pump 41, and the rest is recovered as a distillate through the pipe 43. The ratio of the reflux liquid to the distillate liquid is adjusted by adjusting valves 44 and 45. Incidentally, 37 is a bottom liquid outlet for discharging bottom liquid, the bottom liquid is cooked by a reboiler, and the steam thus cooked is introduced from the steam inlet 34 into the tower.

The high-temperature steam introduced from the steam inlet 34 is brought into countercurrent contact with the above-mentioned raw material and reflux liquid to carry out distillation purification. When the easily polymerizable substance was distilled using the above-mentioned distillation apparatus, a polymer was sometimes produced in the tower top 35 and the conduit 39.

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,
Eventually the inside of the tower will be blocked. This not only increases product loss, but also becomes a major factor that impedes continuous operation of the distillation column and reduces productivity. Also,
It is very difficult to remove the produced polymer, and the removal cost is great.

[0007]

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 distillation apparatus which reduces the production of polymer and enables continuous operation of the distillation column.

[0008]

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 at least a part of the column top and / or the conduit, it is possible to prevent the vapor containing the easily polymerizable substance from condensing at a portion of the column top or the conduit which is difficult to contact with the liquid containing the polymerization inhibitor. As a result, they have found that it is possible to prevent the formation of a portion where the easily polymerizable substance is easily polymerized in the distillation column, and have completed the present invention.

That is, the method of distilling the easily polymerizable substance of the present invention is a distillation method for distilling the easily polymerizable substance in a distillation column, wherein vapor containing the easily polymerizable substance is passed from the top of the column through a conduit. At the time of discharging, at least a part of the column top and / or the conduit is heated.

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 condensation liquid does not contain the polymerization inhibitor only when the vapor is condensed in the distillation column. Therefore,
The condensate is very unstable and easy to polymerize. This condensate is
The solution containing the polymerization inhibitor flowing down from the upper part of the distillation column is stabilized by being brought into contact with and mixed with the solution to prevent polymerization. Therefore, as described above, the vapor is condensed in the distillation column,
The site where the easily-polymerizable substance is easily polymerized is a site where a liquid pool is easily formed in the absence of the polymerization inhibitor.

As a result of further diligent studies on the cause of polymerization in the distillation column, the present inventors have found that the column top of the distillation column and the conduit connecting the column top and the condenser (condenser) contain a reflux containing a polymerization inhibitor. Since it is difficult to contact with the liquid, it has been found that, as described above, when the vapor containing the easily polymerizable substance is condensed at this site, it is very unstable and easily polymerizes.

Since the top vapor of the distillation column is saturated,
When the steam is cooled, some or all of it condenses. Since the distillation operation is usually performed at a temperature higher than the external atmosphere,
The temperature difference between the temperature of the distillation apparatus and the ambient temperature of the outside is used as a driving force to release heat from the distillation apparatus to the outside. this is,
Since heat loss is usually caused by blocking heat from the distillation equipment and the outside with a heat insulating material, this method cannot completely eliminate heat dissipation, and the tower top and conduit are cooled by the influence of outside air. Then, the vapor containing the easily polymerizable substance is condensed. In the present invention, as described above, the cooling of the vapor is prevented by heating at least a part of the top of the distillation column and / or the conduit to give the vapor a heat amount equal to or higher than the heat radiation amount. Thereby, it is possible to prevent condensation of the easily polymerizable substance at a portion which is difficult to contact with the reflux liquid containing the polymerization inhibitor and which is very easy to be polymerized such as a conduit, and to prevent the polymerization at the portion. You can

In the distillation method of the present invention, the temperature at the top of the column and / or the conduit is preferably at least the internal temperature of the column, more preferably at least the internal temperature of the column, and at a temperature not exceeding 100 ° C. from the internal temperature of the column. It is better to heat to the range. This can prevent the easily polymerizable substance from condensing and polymerizing at the column top and / or the conduit.

The distillation apparatus of the present invention is a distillation apparatus having a conduit for discharging a polymerizable substance at the top of the tower, wherein at least a part of the tower and / or the conduit is provided with a heating means. And can be suitably used in the distillation method.

As the heating means, a heating jacket for passing a heat medium to the surface of the tower top and / or the conduit is brought into contact with the heating means, or a trace pipe for passing the heat medium to the surface of the tower top and / or the conduit. Those provided with are preferable.

[0016]

BEST MODE FOR CARRYING OUT THE INVENTION One embodiment of the present invention is shown in FIG. FIG. 1 shows a tower top 35 and a conduit 39 according to this embodiment.
It is a schematic diagram showing the structure of.

As shown in FIG. 1, a conduit 3 is provided at the top 35 of the tower.
9 is attached, and the vapor containing the easily polymerizable substance is discharged from the column top 35 and sent to the condenser 40 through the conduit 39. With this condenser 40,
The steam is cooled to a condensate. Here, the tower top 3
5 refers to a portion located above the uppermost packed layer (packed layer 30 in FIG. 3) for the purpose of separation by distillation in the distillation column.

As shown in FIG. 1, a tower top 35 and a conduit 39 are provided.
Heating jackets 3 and 4 for passing a heat medium are attached to the outside of the. The heating jackets 3 and 4 are provided with heat medium supply ports 3a and 4a and discharge ports 3b and 4b, 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 jackets 3 and 4 to the tower top portion 35 and the conduit 39, the tower top portion 35 and the conduit 39 are in a temperature range above the tower temperature, preferably above the tower temperature and above the tower temperature. It is maintained in a temperature range not exceeding 100 ° C, more preferably at a temperature not lower than the column internal temperature and not exceeding 20 ° C from the column internal temperature. Performing a long-term continuous operation in a temperature range in which the temperature of the tower top 35 and the conduit 39 is excessively higher than the temperature inside the tower is disadvantageous in terms of energy,
This is not preferable because there is a possibility that the polymerization inhibitor scattered as a mist and the adhered polymer may burn.

As the heat medium passed through the heating jackets 3 and 4, hot water, steam, oil or the like can be used.

FIG. 2 is a schematic view showing the structures of the column top portion 35 and the conduit 39 according to another embodiment of the present invention. As shown in FIG. 2, trace pipes 1 and 2 for passing a heat medium are spirally wound around the tower top 35 and the conduit 39, respectively. The heat medium is supplied from the supply ports 1a and 2a, and the discharge port 1
It is discharged from b and 2b. 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 pipes 1 and 2 to the tower top 35 and the conduit 39,
The tower top 35 and the conduit 39 are maintained at a temperature equal to or higher than the temperature inside the tower. This can prevent the easily polymerizable substance from condensing inside these. The tower top portion 35 and the conduit 39 are preferably maintained at a temperature higher than the temperature in the tower and in a temperature range not exceeding 100 ° C. from the temperature in the tower, more preferably at a temperature higher than the temperature in the tower and in the tower. It is preferable to maintain the temperature range of 20 ° C. or less.

As the heat medium to be passed through the trace pipes 1 and 2, hot water, steam, oil or the like can be used. As described above, in the present invention, by providing the trace pipes 1 and 2 and the heating jackets 3 and 4, the tower top portion 35 and the conduit 39 are maintained at a temperature equal to or higher than the tower internal temperature. As a result, the vapor of the easily polymerizable substance typified by a vinyl compound does not condense inside these to form a liquid pool in the absence of the polymerization inhibitor, so that the polymerization at the tower top 35 and the conduit 39 is prevented. can do.

As the polymerization inhibitor, for example, one or two of metal salts of dibutyldithiocarbamic acid (copper, manganese, etc.), phenothiazine, metquinone, hydroquinone, etc.
There are more than one species.

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.).

As the heating means for the tower top portion 35 and the conduit 39, other heating means such as an electric heater may be adopted instead of the above trace pipes 1, 2. Further, the position (range) where the heating means is attached in the tower top portion 35 and the conduit 39 is not particularly limited. For example, when a part of the tower top portion 35 and the conduit 39 is covered with a heat insulating material and the heat insulating property can be secured, it suffices to attach the heating means only to other necessary portions.

[0025]

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. 3, the column top 35 and the conduit 39 were changed to the structure as shown in FIG. 1, and long-term continuous operation was performed. The distillation apparatus in FIG. 3 is a packed column corresponding to 12 theoretical plates, and the top pressure is 55 torr.
The operation was carried out under the conditions of r, a distillation rate of 50% and a reflux ratio of 1.1. 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. Warm water is passed through the heating jackets 3 and 4, and the tower top 35 and the conduit 39 are heated to 2 to more than the temperature inside the tower.
The temperature was maintained at 74 to 77 ° C, which is a temperature 5 ° C higher. During the continuous operation, the tendency of pressure increase in the distillation column and the state of adhesion of the polymer to the tower top 35 and the conduit 39 at the end of the operation were periodically examined.

Example 2 The same as Example 1 except that hot water was passed through the heating jackets 3 and 4 and the tower top 35 and the conduit 39 were maintained at 92 ° C., which is 20 ° C. higher than the temperature inside the column. For a long period of continuous operation. During the continuous operation, the tendency of pressure increase in the distillation column and the state of adhesion of the polymer to the tower top 35 and the conduit 39 at the end of the operation were periodically examined.

Comparative Example Example 1 except that the tower top 35 and conduit 39 were not heated.
The long-term continuous operation was performed in the same manner as in. During the continuous operation, the tendency of pressure increase in the distillation column and the state of adhesion of the polymer to the tower top 35 and the conduit 39 at the end of the operation were periodically examined.

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

[Table 1]

As is clear from the results in Table 1, it is understood that the production of the polymer is reduced in Examples 1 and 2 as compared with the Comparative Example.

[0031]

According to the present invention, by providing a heating means such as a heating jacket or a trace pipe on the tower top and the conduit, the tower top and the conduit can be maintained at a temperature higher than the internal temperature of the tower. It is possible to prevent the easily polymerizable substance from condensing, thereby reducing the production of the polymerized product and enabling the continuous operation of the distillation column.

[Brief description of drawings]

FIG. 1 is a schematic view showing a structure of a column top and a conduit which is an embodiment of the present invention.

FIG. 2 is a schematic view showing a structure of a column top and a conduit which is another embodiment of the present invention.

FIG. 3 is a schematic view showing an ordinary distillation column.

[Explanation of symbols]

1, 2 trace piping 1a, 2a supply port 1b, 2b outlet 3, 4 heating jacket 3a, 4a Supply port 3b, 4b outlet

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Kyosuke Kawasaki             Sumitomo Chemical 5-1, Soukai-cho, Niihama-shi, Ehime             Industry Co., Ltd. F term (reference) 4D076 AA07 AA16 AA21 BB04 CB03                       JA02                 4H006 AA02 AA04 AD11 BD82 BS10

Claims (7)

[Claims] 1. A distillation method for distilling an easily polymerizable substance in a distillation column, wherein when the vapor containing the easily polymerizable substance is discharged from the column top through a conduit, the column top and / or the conduit A method for distilling a readily polymerizable substance, which comprises heating at least a part of 2. The method for distilling a readily polymerizable substance according to claim 1, wherein the column top and / or the conduit is heated to a temperature higher than the temperature in the column. 3. The method for distilling a readily polymerizable substance according to claim 1, wherein the column top and / or the conduit is heated at 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 distillation apparatus having a conduit for discharging a polymerizable substance at the top of the column, wherein at least a part of the column and / or the conduit is equipped with a heating means. A distillation apparatus for use in the distillation method according to any one of to 4. 6. The distillation apparatus according to claim 5, wherein the heating means is provided with a heating jacket for passing a heat medium on the surface of the column top and / or the conduit. 7. The distillation apparatus 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 top of the column and / or the surface of the conduit.