JP4783530B2 - Distillation method of easily polymerizable substance and distillation apparatus used therefor - Google Patents

Description

【００３３】
表１の結果から明らかなように、比較例と比較して、実施例１および２では重合物の生成が低減されていることがわかる。
【００３４】
【発明の効果】
本発明によれば、還流液を加熱するための加熱手段を設けることで、還流管周辺や液分配器の表面（特に下側）等の重合禁止剤を含む還流液と接触しにくい部位で、易重合性物質を含む蒸気が凝縮することを防止することができるため、これらの内部での重合物の生成が低減され、蒸留塔の連続運転が可能になるという効果がある。
【図面の簡単な説明】
【図１】本発明の蒸留装置を示す概略図である。
【図２】本発明の一実施形態である加熱手段と蒸留塔塔頂部周辺を示す概略図である。
【図３】本発明の他の実施形態である加熱手段と蒸留塔塔頂部周辺を示す概略図である。
【図４】本発明のさらに他の実施形態である加熱手段と蒸留塔塔頂部周辺を示す概略図である。
【図５】通常の蒸留装置を示す概略図である。
【図６】通常の蒸留塔塔頂部周辺を示す概略図である。
【符号の説明】
１ 加熱手段
２ 熱交換器
３ トレース配管
３ａ 供給口
３ｂ 排出口
４ 加熱ジャケット
４ａ 供給口
４ｂ 排出口[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for distilling an easily polymerizable substance typified by a vinyl compound having a double bond in the molecule, and a distillation apparatus used therefor.
[Prior art]
[0002]
Since an easily polymerizable substance has a property of being easily polymerized by light, heat, or the like, it is extremely easily polymerized by a treatment at a high temperature such as a distillation step. If polymerization occurs in the distillation column, it not only leads to a loss, but also hinders continuous operation and decreases productivity. Accordingly, prevention of polymerization is a very important technique in the purification of easily polymerizable substances by distillation, and many methods for preventing polymerization have been proposed in relation to the type, amount, and combination of polymerization inhibitors.
[0003]
FIG. 5 shows a distillation apparatus commonly used for distillation of easily polymerizable substances. This distillation apparatus includes a distillation column having packed beds 30 and 31 filled with packing inside, a condenser 40 for condensing discharged steam, and the like. In the distillation tower, 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, rising while making countercurrent contact with the raw material, and discharged from the upper tower top 35.
[0004]
The discharged steam is sent to the condenser 40 through the conduit 39 and cooled to become a condensate. The condensate containing an easily polymerizable substance is usually supercooled to a temperature lower than the condensing temperature for the purpose of lowering the temperature for stabilization. A part of this condensate is returned to the tower 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 is adjusted by adjusting valves 44 and 45. Reference numeral 37 denotes a bottom discharge outlet for discharging the bottom discharge liquid. The bottom discharge liquid is cooked by a reboiler, and the cooked steam is introduced into the tower through the steam inlet 34.
[0005]
FIG. 6 is an enlarged schematic view of the inside of the distillation tower around the tower top 35. As described above, the reflux liquid cooled by the condenser 40 is introduced into the tower from the reflux liquid inlet 36 and supplied to the liquid distributor 47 through the reflux pipe 46. The liquid distributor 47 is provided to uniformly supply the reflux liquid from above the packed bed 30. Instead of the liquid distributor 47, it is also possible to uniformly disperse the reflux liquid using a branched pipe or a spray nozzle.
The reflux liquid supplied to the liquid distributor 47 flows down to the packed bed 30 through the packing presser 50 as indicated by an arrow 48. On the other hand, the steam introduced from the steam inlet 34 (FIG. 5) and rising in the packed bed 31 comes into countercurrent contact with the reflux liquid in the packed bed 30 as indicated by an arrow 49. Thereafter, the steam rises further in the tower top 35 and is sent to the condenser 40 through the conduit 39.
[0006]
When the easily polymerizable substance is distilled using the distillation apparatus, a polymer may be generated around the reflux tube 46 and the liquid distributor 47. When a polymer is generated in the vicinity of the reflux pipe 46 and the liquid distributor 47, it becomes a nucleus and gradually grows and accumulates, increasing the pressure in the tower and eventually closing the inside of the tower. This not only increases product loss, but also hinders continuous operation of the distillation apparatus and is a major factor in reducing productivity. Moreover, it is very difficult to remove the produced polymer, and the removal cost is high.
[0007]
[Problems to be solved by the invention]
The main object of the present invention is to provide a distillation method that reduces the formation of polymerized products and enables continuous operation of a distillation column when performing distillation of easily polymerizable substances typified by vinyl compounds.
Another object of the present invention is to provide a distillation apparatus that 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 inventors of the present invention have a portion where the easily polymerizable substance is easily polymerized in the distillation column. It has been found that it is a site where a liquid pool is likely to be formed in the absence. Then, by heating the reflux liquid, the vapor containing the easily polymerizable substance is prevented from condensing at a site that is difficult to come into contact with the liquid containing the polymerization inhibitor around the reflux pipe or the liquid distributor. The present inventors have found that formation of a site where an easily polymerizable substance is easily polymerized can be prevented, and the present invention has been completed.
[0009]
That is, the method for distilling an easily polymerizable substance of the present invention is characterized in that when the easily polymerizable substance is distilled while refluxing, the reflux liquid is heated.
[0010]
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 just by condensing the vapor in the distillation column. Therefore, the condensate is very unstable and easily polymerized. This condensate is stabilized by contacting and mixing with a liquid containing a polymerization inhibitor flowing down from the upper part of the distillation column, thereby preventing polymerization. Therefore, as described above, the portion where the vapor is condensed in the distillation column and a liquid pool is easily formed in the absence of the polymerization inhibitor is the portion where the easily polymerizable substance is easily polymerized.
[0011]
As described above, the condensate containing an easily polymerizable substance is usually supercooled to a temperature lower than the condensing temperature for the purpose of stabilizing the temperature by lowering the temperature. As a result of further intensive studies on the cause of polymerization in the distillation column, the present inventors have found that in FIG. 6, when the vapor rises in the column top 35, it is cooled by the reflux liquid having a temperature lower than the vapor temperature. Thus, the vapor containing the easily polymerizable substance is condensed on the surfaces of the reflux pipe 46 and the liquid distributor 47, and a condensate liquid containing no polymerization inhibitor can be collected around the reflux pipe 46 and the liquid distributor 47, It was found that the easily polymerizable material forms a site that is easily polymerized. In the present invention, the reflux liquid is heated so that the vapor containing the easily polymerizable substance does not condense around the reflux pipe or the liquid distributor, which is a part that is difficult to come into contact with the liquid containing the polymerization inhibitor. This prevents the formation of a portion where an easily polymerizable substance is easily polymerized in the distillation column, and prevents polymerization in the distillation column.
[0012]
In the distillation method of the present invention, it is preferable to heat the reflux liquid so that it is in a range of ± 10 ° C. with respect to the temperature at the top of the distillation column. Thereby, it can suppress that an easily polymerizable substance superposes | polymerizes substantially in the said tower top part.
[0013]
The distillation apparatus of the present invention includes a heating means for heating the reflux liquid in at least a part of the reflux path, and can be suitably used in the distillation method. Moreover, a heat exchanger is suitable as the heating means.
[0014]
DETAILED DESCRIPTION OF THE INVENTION
One embodiment of the present invention is shown in FIG. FIG. 1 is a schematic view showing a distillation apparatus according to this embodiment.
[0015]
As shown in FIG. 1, the distillation apparatus of the present invention includes a distillation column having packed beds 30 and 31 filled with a packing therein, a condenser 40 for condensing discharged steam, and a reflux liquid for heating. It consists of heating means 1 and the like.
[0016]
The steam discharged from the top 35 of the distillation tower is cooled by the condenser 40 to become a condensate. A part of this condensate is heated in the heating means 1 provided in at least a part of the reflux path, and then introduced into the tower top 35 from the reflux liquid inlet 36 as a reflux liquid. The remaining condensate is recovered as a distillate through the pipe 43. Here, the column top portion 35 refers to a portion located above the uppermost packed bed 30 of the packed portion intended for distillation separation in the distillation column. The reflux path refers to a path located between the valve 44 and the reflux liquid inlet 36.
[0017]
FIG. 2 is a schematic view when a heat exchanger 2 is used as the heating means in the present invention. The heat exchanger 2 is not particularly limited as long as the reflux liquid and the heat medium exchange heat through a partition such as a tube or a flat plate. For example, a multi-tube cylindrical heat exchange that is a partition type heat exchanger is used. A heat exchanger, a plate heat exchanger, a spiral heat exchanger, etc. can be used. In addition to these, as the heat exchanger 2, for example, a pipe in which a trace pipe for passing a heat medium is spirally wound around a pipe through which a reflux liquid flows or a heating jacket for passing a heat medium can be used. .
[0018]
Hot water, steam, oil, or the like can be used as the heat medium.
[0019]
Using the heat exchanger 2 and the heat medium as described above, the reflux liquid has a temperature range of −10 ° C. to 10 ° C. with respect to the temperature of the tower top 35, preferably the temperature of the tower top 35. The heating is preferably controlled so as to be in the temperature range of −5 ° C. to 5 ° C. As a result, the temperature difference between the temperature of the steam present at the tower top 35 and the reflux liquid is reduced, so that it is included in the steam indicated by the arrow 49 in the vicinity of the reflux pipe and on the surface of the liquid distributor (particularly on the lower side). The easily polymerizable substance can be made difficult to condense, and thereby the formation of a polymer can be suppressed.
[0020]
When the temperature of the reflux liquid is higher than the above range with respect to the temperature of the tower top 35, the distillation separation ability is reduced due to vaporization of the reflux liquid, and furthermore, it cannot flow down to the packed bed 30, or the tower top 35 This causes problems such as excessively raising the temperature of the steam and requiring extra energy for condensation by the condenser 40.
[0021]
On the other hand, when the temperature of the reflux liquid becomes lower than the above range with respect to the temperature of the tower top 35, as described above, reflux including a polymerization inhibitor around the reflux pipe and the surface (particularly the lower side) of the liquid distributor. This is not preferable because the vapor containing the easily polymerizable substance is condensed at a site that is difficult to come into contact with the liquid and an environment in which a polymer is easily generated is generated.
[0022]
FIG. 3 is a schematic view when the above-described trace pipe 3 is used as the heat exchanger 2. As shown in FIG. 3, a trace pipe 3 through which a heat medium (warm water, steam, oil, etc.) passes is spirally wound around the pipe 42 through which the reflux liquid flows. The heat medium is supplied from the supply port 3a and discharged from the discharge port 3b. If necessary, the supply port and the discharge port may be reversed. Due to the heat transferred from the heat medium in the trace pipe 3 to the inside of the pipe 42, the temperature of the reflux liquid is within a temperature range of ± 10 ° C. with respect to the temperature of the tower top 35, preferably ± 5 with respect to the temperature of the tower top 35. Controlled to a temperature range of ° C.
[0023]
FIG. 4 is a schematic view when the above-described heating jacket 4 is used as the heat exchanger 2. As shown in FIG. 4, a heating jacket 4 through which a heat medium (warm water, steam, oil, etc.) passes is attached outside the pipe 42 through which the reflux liquid flows. The heating jacket 4 is provided with a heat medium supply port 4a and a discharge port 4b. If necessary, the supply port and the discharge port may be reversed. The reflux liquid is controlled in the same temperature range as described above by the heat transferred from the heat medium in the heating jacket 4 to the inside of the pipe 42.
[0024]
As described above, in the present invention, the reflux liquid is heated by the heat exchanger such as the multi-tube cylindrical heat exchanger, the trace pipe 3, and the heating jacket 4, and the temperature of the reflux liquid is controlled within the above range. This makes it difficult for the vapor containing the easily polymerizable substance to condense and form a liquid pool at a site that is difficult to contact with the reflux liquid containing the polymerization inhibitor such as the periphery of the reflux pipe or the surface of the liquid distributor (particularly the lower side). Therefore, this can suppress polymerization.
[0025]
Examples of the polymerization inhibitor include one or more of dibutyldithiocarbamate metal salts (copper, manganese, etc.), phenothiazine, methoquinone, hydroquinone and the like.
[0026]
Examples of the readily polymerizable substances include acrylic acid, conjugated acids such as methacrylic acid or esters thereof, amides, derivatives such as nitrile (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- Examples include diolefins (butadiene, isoprene, etc.), ethylene and alkyl-substituted ethylene (propylene, etc.).
[0027]
As the heating means for the reflux liquid, other heating means such as an electric heater may be employed instead of the above-described heat exchanger.
[0028]
【Example】
EXAMPLES Hereinafter, although an Example and a comparative example are given and this invention is demonstrated in detail, this invention is not limited only to a following example.
[0029]
Example 1
In a distillation apparatus as shown in FIG. 1 for distilling acrylic acid, a double-pipe heat exchanger was provided as a heating means 1 for heating the reflux liquid, and a long-term continuous operation was performed. The distillation apparatus in FIG. 1 is a packed column corresponding to 6 theoretical plates, and was operated under the conditions of a tower top pressure of 55 torr, a distillation rate of 80%, and a reflux ratio of 0.8.
At this time, a small amount of phenothiazine and methoquinone as a polymerization inhibitor was added to the reflux liquid, and a fixed amount of air was supplied to the can part liquid layer part to operate.
The heat medium was circulated through the heat exchanger 2 and the reflux liquid was controlled to be in the range of −10 to 0 ° C. with respect to the tower top 35.
During the continuous operation, the tendency of pressure increase in the distillation column and the state of polymer adhering to the packed portion 30 and the reflux pipe 46 at the end of the operation were periodically examined.
[0030]
Example 2
A long-term continuous operation was carried out in the same manner as in Example 1 except that the temperature of the reflux liquid was controlled to be in the range of 0 to 5 ° C. with respect to the tower top 35.
During the continuous operation, the tendency of pressure increase in the distillation column and the state of polymer adhering to the packed portion 30 and the reflux pipe 46 at the end of the operation were periodically examined.
[0031]
Comparative Example A long-term continuous operation was performed in the same manner as in Example 1 except that a distillation apparatus as shown in FIG.
The temperature of the reflux liquid during long-term continuous operation was in the range of about 30-35 ° C. This was about 37 to 42 ° C. lower than the temperature at the top 35 of the column.
During the continuous operation, the tendency of pressure increase in the distillation column and the state of polymer adhering to the packed portion 30 and the reflux pipe 46 at the end of the operation were periodically examined.
[0032]
Table 1 shows long-term continuous operation results of Examples and Comparative Examples.
[Table 1]

[0033]
As is clear from the results in Table 1, it can be seen that the production of the polymer is reduced in Examples 1 and 2 as compared with the comparative example.
[0034]
【The invention's effect】
According to the present invention, by providing a heating means for heating the reflux liquid, it is difficult to come into contact with the reflux liquid containing a polymerization inhibitor such as the periphery of the reflux pipe and the surface of the liquid distributor (particularly the lower side). Since it is possible to prevent the vapor containing the easily polymerizable substance from condensing, there is an effect that the production of a polymerized product inside these is reduced, and the continuous operation of the distillation column becomes possible.
[Brief description of the drawings]
FIG. 1 is a schematic view showing a distillation apparatus of the present invention.
FIG. 2 is a schematic view showing the heating means and the vicinity of the top of the distillation column, which is an embodiment of the present invention.
FIG. 3 is a schematic view showing the heating means and the vicinity of the top of the distillation column, which is another embodiment of the present invention.
FIG. 4 is a schematic view showing a heating means and the vicinity of the top of a distillation column, which is still another embodiment of the present invention.
FIG. 5 is a schematic view showing a normal distillation apparatus.
FIG. 6 is a schematic view showing the vicinity of the top of a normal distillation column.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Heating means 2 Heat exchanger 3 Trace piping 3a Supply port 3b Discharge port 4 Heating jacket 4a Supply port 4b Discharge port

Claims (4)

A method for distilling an easily polymerizable substance, characterized in that when the easily polymerizable substance is distilled while refluxing, the reflux liquid is heated to a temperature range of ± 10 ° C with respect to the temperature at the top of the distillation column . The method for distilling an easily polymerizable substance according to claim 1 , wherein the easily polymerizable substance is a vinyl compound. The distillation apparatus used for the distillation method according to claim 1 or 2 , wherein heating means for heating the reflux liquid is provided in at least a part of the reflux path. The distillation apparatus according to claim 3 , wherein the heating means is a heat exchanger.

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