JPH0160482B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION This invention provides styrene, acrylonitrile, α
-Relates to a method for storing a room-temperature liquid substance that easily polymerizes (hereinafter referred to as a polymerizable substance) such as methylstyrene in a tank.

Such polymerizable substances not only easily initiate polymerization during storage, but also generate considerable heat of polymerization during this polymerization, and when the temperature rises due to this heat of polymerization, the polymerization rate increases rapidly, and once Once polymerization begins to proceed, it proceeds explosively. For this reason, when storing such polymerizable substances, a polymerization inhibitor is added to prevent such explosive polymerization, and the tank is further cooled for safety reasons.

Conventionally, methods for cooling this tank include spraying cooling water on the outer wall of the tank, pumping out some of the liquid in the tank and returning it to the tank, or installing a cooling coil inside the tank. Methods such as circulating refrigerant have been used.

However, in these conventional methods, even if the tank cooling is sufficiently controlled and the polymerization inhibitor content is maintained at a sufficient concentration, the vapor of polymerizable substances remains in the internal space above the tank liquid level. When the temperature of the tank wall changes due to changes in atmospheric temperature, etc., the vapor of the polymerizable substance condenses on the tank top and side walls above the liquid level, forming droplets. Since these droplets do not substantially contain polymerization inhibitors, they are easily polymerized, and the resulting polymer adheres to the inner wall of the tank and gradually grows. When the polymer content rose, the polymer content in the liquid sometimes suddenly increased dramatically. By the way, when a polymerizable substance is commercially available, the polymer content is usually regulated to be 1 to 10 ppm or less as a standard, and if the polymer content of the polymerizable substance exceeds this value, it loses its commercial value. For this reason, in the past, in addition to controlling tank cooling and controlling the polymerization inhibitor content, cleaning work was carried out to periodically scrape off and remove the polymer adhering to the inner wall of the tank, and to prevent the polymer content from increasing. In such cases, they were reprocessed, but this cleaning work and reprocessing required a large amount of money.

The inventors of the present invention have conducted extensive research on methods for preventing the polymer content from increasing during storage in tanks, and for preventing polymers from adhering to and growing on the inner walls of tanks. The present invention was completed by discovering a method to effectively utilize the polymerization inhibitor contained in the polymerizable material stored in the container.

That is, the present invention extracts a polymerizable substance containing a polymerization inhibitor from a tank, and sprays some or all of the extracted polymerizable substance onto the inner wall surface of the tank above the liquid level with or without cooling. This solves various problems in conventional storage methods.

Hereinafter, the method of the present invention will be explained in detail based on the accompanying drawings.

The drawing shows an example of the storage method of the present invention, and shows a branch path 9 from between the pump 2 and the indirect heat exchanger 3 to the distribution pipe 8 in the tank 1 via the flow meter 7.
A part of the polymerizable substance extracted by the pump 2 is continuously sprayed from the spray pipe 8 onto the inner surface of the tank top plate 1a, and the remaining polymeric substance extracted by the pump 2 is indirectly sprayed. The polymerizable substance in the tank 1 is cooled in a type heat exchanger 3 and jetted obliquely upward from a nozzle 11 provided at the bottom of the tank 1 . In addition, a bypass 5a is provided in the return path of the refrigerant circulation path 5 that circulates a refrigerant such as frozen water in the indirect heat exchanger 3, and a tank top plate 1a is provided.
A cooling coil 10 is installed on the inner surface of the bypass 5.
By a, the frozen water on the outlet side of the indirect heat exchanger 3 is circulated through the cooling coil 10, thereby cooling the gas phase above the tank liquid level.

In this example, a branch path 9 is provided in the circulation path 4 between the pump 2 and the indirect heat exchanger 3, and the pump 2
A part of the polymerizable substance extracted by the method is directly sprayed onto the inner surface of the tank top plate 1a through the spray pipe 8 without being cooled. A branch 9' may be provided in the circuit 4 after the exchanger 3. In this case, since the cooled polymerizable substance is sprayed, tank 1
Great effect in cooling the internal air phase.

Further, the spraying from the spray tube 8 and the jetting from the nozzle 11 do not necessarily have to be continuous, but if they are intermittent, it is preferable not to leave intervals of several hours or more. Further, although it is not always necessary to perform the spraying and ejection at the same time, it is more efficient to perform them at the same time.

The spray pipe 8 is preferably provided with a plurality of spray nozzles so that the polymerizable substance is sprayed as uniformly as possible over the entire inner surface of the tank gas phase section, particularly the entire inner surface of the tank top plate 1a. Further, as the spray nozzle, a spray nozzle whose spray direction can be changed can be used, but a fixed nozzle with several small holes that spray the spray directly upward and diagonally upward is most suitable.

Furthermore, the amount of polymerizable material extracted from the tank is 1
1/200 to 1/2, preferably 1/100 to 1/10 of the total amount of polymerizable material stored in the tank per hour
is appropriate, and the spray amount is 0.01/hr or more, preferably 0.05 to ¹ m2 of the surface area of the tank top plate.
1 m ² /hr is appropriate, and when spraying and ejecting from the bottom of the tank are performed at the same time, it is preferable that the value of spray volume/spray volume is within the range of 0.05 to 2, and 0.5
It is more preferable to set it within the range of 1 to 1.

In the above example, as well as cooling from the bottom of the tank, used frozen water is circulated through a cooling coil installed on the top of the tank, so the liquid polymerizable substance stored in the tank and the gas phase of the tank are It is possible to cool the tank at the same time as the steam, which allows the tank to be cooled extremely efficiently and to prevent polymerization more reliably, but the above cooling is omitted in seasons such as winter when the temperature inside the tank does not rise. Alternatively, one of the above cooling methods may be used.

According to the present invention, a part of the polymerizable substance containing the polymerization inhibitor extracted from the tank is sprayed onto the inner wall surface of the tank above the liquid level of the tank, and this sprayed polymerizable substance covers the inner wall surface of the tank. The vapor of the polymerizable substance, which evaporates above the tank liquid level and does not substantially contain the polymerization inhibitor, condenses on the inner wall of the tank and simultaneously dissolves the polymerization inhibitor. into the sprayed polymeric material containing. For this reason, it is possible to completely prevent polymerizable substances from polymerizing and forming polymers on the inner wall surface of the tank above the tank liquid level, which may result in a sudden increase in the polymer content in the liquid and loss of commercial value. This method has remarkable technical effects, such as eliminating the need to reprocess the polymerizable material with increased polymer content and to periodically clean the inside of the tank.

Furthermore, in the present invention, if not only the contents of the tank but also the outer wall of the tank are cooled using a refrigerant such as frozen water, the effect of suppressing evaporation of the polymerizable substance and the effect of lowering the polymerization rate will work even more effectively, thereby promoting polymerization. The prevention effect is improved. In addition, the technical effects of the present invention are as follows:
This is achieved by continuously, intermittently, or periodically spraying a polymerizable substance containing a polymerization inhibitor onto the inner wall of the tank, so it is difficult to store the aforementioned styrene, acrylonitrile, α-methylstyrene, etc. The method is not limited to this method and can be broadly applied to similar liquids.

The present invention will be specifically described below with reference to Examples.

EXAMPLE The technical effects of the present invention were tested using a styrene tank equipped with the storage mechanism of the present invention as shown in the drawings.

In the case of this example, 1/20 of the stored amount of polymerizable substance is extracted per hour, 60% of it is poured into the indirect heat exchanger side, 40% of it is poured into the distribution pipe side,
The entire amount of frozen water was flowed through the cooling coil installed on the top of the tank. The temperature of the frozen water circulating in the indirect heat exchanger is 13-15℃ at the inlet side and 15-20℃ at the outlet side.
It was warm at ℃. In addition, TBC is added to the styrene monomer stored in the styrene tank as a polymerization inhibitor.
(tertiary butylcatechol) 10-15ppm
Contained.

Regarding the liquid temperature in the styrene tank, there is no big difference between the conventional method and the method of the present invention.
The temperature was within the range of 23℃, but the temperature of the gas phase above the liquid level in the tank was the highest with the conventional method.
The temperature was 20.6°C and the average temperature was about 16°C, whereas in the case of the method of the present invention, the maximum temperature was 17.5°C and the average temperature was about 14°C.
In addition, the conventional method has the highest polymer content in styrene monomer.
8.4ppm and an average of about 6.26ppm, whereas in the case of the method of the present invention, the maximum was 3.8ppm and an average of about 6.26ppm.
It was 1.66ppm. These results show that according to the method of the present invention, the polymer content hardly increases during tank storage, and that by providing a cooling coil on the tank top plate and circulating frozen water, the upper part of the liquid level in the tank can be reduced. It was confirmed that temperature rise in the gas phase can be effectively prevented.

[Brief explanation of drawings]

The figure is a flow sheet showing an example of the storage method of the present invention. Description of symbols: 1...tank, 1a...tank top plate, 3...indirect heat exchanger.

Claims (1)

[Claims] 1. A room-temperature liquid polymerizable substance containing a polymerization inhibitor is extracted from a tank, and a part or all of the extracted polymerizable substance is cooled or not cooled to a level above the tank liquid level. A method for storing polymerizable substances characterized by spraying onto the inner wall of the tank and returning it into the tank. 2. A patent in which a portion of the polymerizable substance extracted from the tank is sprayed onto the inner wall of the tank, the remainder of the extracted polymeric substance is cooled, and the cooled polymerizable substance is jetted out from the bottom of the tank and returned into the tank. A method for storing a polymerizable substance according to claim 1. 3. The polymerizable material extracted from the tank is cooled by an indirect heat exchanger, and the refrigerant from the indirect heat exchanger is passed through a cooling coil installed on the top of the tank to cool the gas phase above the tank liquid level. A method for storing a polymerizable substance according to claim 1 or 2. 4. A method for storing a polymeric substance according to any one of claims 1 to 3, in which the polymeric substance is sprayed onto the inner surface of a tank top plate.