JPS61275232A - Storage of polymerizable substance - Google Patents

Abstract

PURPOSE:To suppress the polymerization reaction and evaporation by cooling the liquid-phase part of a polymerizable substance in a storage tank and to suppress the condensation of vapor and prevent the lowering of the quality of the polymerizable substance by heating the wall surface corresponding to the vapor-phase part in the upper part of the tank. CONSTITUTION:A cooling pipe 4 is provided at the bottom of the storage tank 1 to cool the liquid-phase part of the polymerizable substance, and a heating pipe 2 is attached to the outside of the top plate 1A to prevent the condensation of the polymerizable substance. The refrigerant discharged from the cooling pipe 4 is passed through the heat-exchanger 15 and delivered by the compressor 7 at 10-12kg/cm<2> pressure and 70-80 deg.C. It is then transferred to the heating pipe 2 via the three-way valve 10. When the temperature of the substance mea sured by the temperature sensor 3 is higher than a prescribed value, the three- way valve 10 is operated by the controller 11 to direct the flow of the regrigerant to the by-pass 12. The refrigerant passed through the pipe 2 or the by-pass 12 is passed successively through the heat-exchanger 13 (cooled by seawater, ground water, etc.) and the heat-exchanger 15 (cooled by the refrig erant sent through the pipe 4) and sent to the pipe 4.

Description

Detailed Description of the Invention [Field of Industrial Application] The present invention relates to a method for storing polymerizable substances that are room temperature liquids that easily polymerize, such as styrene monomer, α-methylstyrene monomer, acrylonitrile monomer, etc. The present invention relates to an improvement in a method for storing a polymerizable substance that prevents the generation of polymer due to a polymerization reaction of the polymerizable substance in a container and avoids deterioration of quality.

[Background Art and Problems] Conventionally, various methods have been devised for storing polymerizable substances, which are room temperature liquids that easily polymerize, such as styrene monomer, α-methylstyrene monomer, and acrylonitrile monomer, in tanks. For example, in order to prevent a polymerization reaction in the liquid phase portion of a polymerizable substance in a tank, it is common to add a polymerization inhibitor and to cool the reaction to suppress the reaction.

Paratertiary butylcatechol (TBC) and sulfur were commonly used as polymerization inhibitors, but today more superior nitrosamine compounds (Japanese Patent Publication No. 52-39016
) and a mixture of 2.4 dinitrophenol and 2.6 dinitrophenol (Japanese Patent Publication No. 17583/1983) are known.

On the other hand, methods of cooling include spraying water on the outer surface of the tank, or extracting a portion of the liquid inside the tank, cooling it, and then returning it to the tank.

However, these methods are effective only for polymerizable substances in the liquid phase portion of the tank, and are not effective for polymerizable substances that exist in the vapor phase above the liquid level.

In other words, the polymerizable substance in the gas phase part is affected by the temperature of the wall surface corresponding to the gas phase part at the top of the tank, so the cooling effect is not affected, and the boiling point of the additive used as a polymerization inhibitor is , which is generally higher than the boiling point of the polymerizable substance, means that only the polymerizable substance evaporates. Therefore, when the outside temperature drops, the polymerizable substances in the gas phase are cooled from those near the wall surface and condense on the wall surface, but these condensed droplets contain almost no polymerization inhibitor; The polymerizable substance within the droplet easily initiates a polymerization reaction and becomes a polymer. At this time, the polymer grows downward due to gravity, so it grows in the shape of an icicle on the inner surface of the top plate, and eventually peels off under its own weight, falls down, and mixes into the stored liquid. Furthermore, the polymer on the side wall grows downward along the side wall, eventually reaching the liquid level and dissolving into the storage liquid. On the other hand, when additional 1-polymerizable substances are stored and the liquid level rises, the polymer growing on the wall surface may be immersed in the liquid and dissolved. In either case, the polymer may be mixed into the stored liquid. , a problem arises in that it becomes an impurity.

In general, the polymer content when a monopolymerizable substance is commercially available is regulated to about 1 to 10 ppm. Conventionally, in order to avoid losing commercial value as a polymerizable substance due to the contamination of the polymer, it was necessary to While cleaning and reprocessing polymerizable substances were carried out, research was being conducted on methods to prevent polymer formation on the inner walls of the tank.

For example, in addition to the conventional addition of a polymerization inhibitor and cooling of the polymerizable substance in the liquid phase, this polymerizable substance containing the polymerization inhibitor is pumped up and sprayed onto the top plate at the top of the tank, and the wall surface is washed. There is a known method (Japanese Unexamined Patent Publication No. 58-42601) that prevents condensation and actively liquefies and recovers polymerizable substances in the gas phase near the top plate by cooling the top plate.

This method can significantly prevent condensation of polymerizable substances on the inner wall of the tank, but it also poses installation-related problems such as difficulty in spraying uniformly, as well as problems such as clogging of the spray nozzle or polymerization in gaps in complicated piping. It has been difficult to deal with problems such as the accumulation of harmful substances only in the piping inside the tank.

Other methods include introducing an inert gas such as nitrogen into the tank to reduce the partial pressure of the polymerizable substance in the gas phase to limit evaporation, and coating the inner wall of the tank to prevent droplets from condensing. There are methods to suppress condensation by reducing the protrusions that tend to become nuclei, but none of them are definitive and can only be used in conjunction with other methods.

[Objective of the Invention] An object of the present invention is to prevent the polymerization reaction of the polymerizable substance in the liquid phase in a tank, suppress evaporation from the liquid surface, and prevent polymerization in the gas phase when storing the polymerizable substance. Polymerization can suppress the polymerization reaction within droplets due to condensation on the wall surface corresponding to the upper gas phase part of the tank, preventing the generation of polymers and making it easier to avoid quality deterioration. The object of the present invention is to provide a method for storing sexual substances.

[Means and effects for solving the problems] The present invention has the following features:
Among the polymerizable substances in the storage tank, by cooling the liquid phase part, the polymerization reaction and evaporation of the polymerizable substance are suppressed, and by heating the wall surface corresponding to the gas phase part in the upper part of the tank, the liquid phase part of the polymerizable substance is suppressed. This prevents condensation on the walls and avoids deterioration in quality due to polymerization, which was a problem when storing polymerizable substances.

[Example] Examples of the method for storing a polymerizable substance of the present invention will be described below based on the drawings.

FIG. 1 is a schematic diagram showing a storage tank apparatus according to the method for storing polymerizable substances of the present invention.

In the figure, tank 1 stores a liquid obtained by adding paratertiary butylcatechol (TBC) as a polymerization inhibitor to the polymerizable substance L/7 monomer. A heating pipe 2 as a heating section is provided on the outside of the corn roof type top plate IA of this tank 1, and a temperature sensor 3 for detecting the top plate temperature is attached. Furthermore, the inner surfaces of the top plate IA and side wall surfaces IB are smoothed by coating, so that other substances are less likely to adhere to them.

On the other hand, inside the bottom of the tank 1, a cooling pipe 4 serving as a cooling section is provided in a coil shape, and a temperature sensor 5 for detecting the liquid temperature is attached. Furthermore, a stirring pump 6 is connected through the suction pipe 6A and the discharge pipe 6B, and the jet flow from the discharge pipe 6B constantly stirs the liquid in the tank 1, so that the temperature distribution becomes uniform and the cooling effect is enhanced. ing. These pipes are installed in a double pipe structure, taking into consideration the durability of the tank side wall surface IB.

Freon-22 (R-22) is fed into the heating pipe 2 and the cooling pipe 4 as a refrigerant, and other parts will be explained following the movement of this refrigerant.

A compressor 7 is connected to the outlet side of the cooling pipe 4, that is, the upper end side in the figure, via a heat exchanger 15, and this compression lR7
In this case, the suction side pressure is kept almost constant 1, for example 0.
It is driven by a motor (not shown) that is controlled to have a refrigerant of 5 to 1.0 kg/Ctrl, and compresses the refrigerant.
Discharge side pressure 10-12 kg/cm', temperature 70
Deliver at ~80°C.

The sent refrigerant passes through the three-way valve lO, and then enters the heat radiation section piping 2.
The heat is sent to the upper end side, passes through this heat radiation section piping 2, and radiates heat to the top plate IA. At this time, if the temperature detected by the temperature sensor 3 is higher than the specified value, the three-way valve 10 is switched by the control device 11 to protect the top plate IA, and the refrigerant passes through the bypass 12, so that the heat dissipation pipe 2 No refrigerant passes through, no heating occurs, and the temperature of the top plate does not rise any further.

The refrigerant that has passed through the heat radiation section piping 2 or the bypass 12 enters the heat exchanger 13, but the refrigerant passes through the heat exchanger piping 2 or the bypass 12.
A cooling liquid such as seawater or ground water flows through the cooling pipe 4, whereby the refrigerant is cooled to a certain degree, and then enters the heat exchanger 15 where it is cooled by the refrigerant from the cooling pipe 4. On the other hand, the refrigerant in the cooling pipe 4 is heated and completely vaporized, so that the refrigerant will not be introduced into the compression Ia7 in a liquid phase and damage the compressor 7.

The refrigerant cooled by the two heat exchangers 41113.15 expands and vaporizes adiabatically through the 11 tension valve 16, absorbs the heat of vaporization in the cooling section piping 4, and cools the polymerizable substance at the bottom of the tank. As the expansion valve 16, one with large hysteresis is used to prevent pulsation, and furthermore, a control device 17 is used.
It has a mechanism that adjusts the opening degree using override control.

FIG. 2 shows the flow of adjusting the valve opening of the expansion valve 16 by the override control.

In the figure, a control device 1 receives a temperature T1 from a temperature sensor 3 for detecting the temperature of the top plate and a temperature T2 from a temperature sensor 5 for detecting the liquid temperature in a tank l.
7, the temperature difference (TI-T2) is first calculated by the calculator 17A, and the valve opening degree A1 is determined by comparing the temperature difference (Tl-T2) with the specified value Td by the regulator 17B. On the other hand, the regulator 17C compares the temperature T2 and the specified value Tc to obtain the valve opening A2, and the comparator (high select) 17D selects the larger one of the valve openings AI and A2, and according to that value. The opening degree of the expansion valve 16 is controlled in a direction that increases the cooling capacity of the cooling pipe 4. At this time, the specified value Td is a target value for the temperature difference between the top plate temperature and the liquid temperature in the tank 1, and is preferably 10°C or more, and the specified value Td is
c is the target value of the liquid temperature in tank 1, and in order to suppress the polymerization reaction of the polymerizable substance, it should be 20℃ or less, preferably 1
It is desirable to keep the temperature below 0°C.

Following the flow of the refrigerant again, the refrigerant that has exited the cooling pipe 4 enters the heat exchanger 15, cools the refrigerant from the heat exchanger 13, and then returns to the compressor 7, forming the cycle described above.

FIG. 3 is a schematic diagram showing the heat exchanger 15. In the figure,
The refrigerant that exits the heating pipe 2 and passes through the heat exchanger 13 enters through the inlet 15A and is cooled, and exits through the outlet 15B and reaches the expansion valve 16. On the other hand, the refrigerant from the cooling pipe 4 flows through the inlet 1
It enters from 5C, absorbs heat, exits from outlet 150 and reaches compressor 7. At this time, most of the refrigerant that exits the cooling pipe 4 is in the gas phase, but there is also some liquid phase mixed in, and if this is sent to the compressor 7 as it is, the If the oil becomes too cold, or in the worst case, the compression 4i17 may be damaged due to liquid compression, so a rise is provided in front of the inlet 15C as shown in the figure.
C is connected so that it is lower than the outlet 15D to stop it from passing through in a liquid phase.

In the apparatus of this embodiment, a cooling pipe 4 is provided in the liquid phase portion of the polymerizable substance in the tank l to keep the temperature of the liquid phase low, thereby suppressing the polymerization reaction and preventing evaporation from the liquid surface. By heating the gas phase portion by providing heating piping 2 that heats the tank top plate IA, it is possible to prevent condensation of the polymerizable substance in the gas phase on the inner wall surface of the tank 1, and to heat the tank top plate IA. Since polymerization reactions of stored polymerizable substances can be reliably prevented, deterioration in quality can be easily avoided.

Since the heating and cooling are realized by a refrigeration cycle using a refrigerant, the device can be made compact, and since both the heating and cooling of the refrigeration cycle are effectively used, energy costs can be reduced. . These cycles also include temperature sensors 3 and 5 and control device 1.
1.17, it can be controlled to the optimum state according to the settings.

In the control, the valve opening degree Al was obtained by comparing the temperature difference between the top plate temperature TI and the liquid temperature T2 (TI-T2) with the specified value Td, and the liquid temperature T2 was obtained by comparing the specified value TC. Comparator (High Select) 1 for the larger valve opening degree A2
7D and by operating the opening degree of the expansion valve 16 according to the value, the liquid phase portion in the tank 1 can be kept at a sufficiently low temperature, suppressing the polymerization reaction and preventing evaporation from the liquid surface. It can be suppressed. Furthermore, by providing an interlock mechanism to prevent overheating using the three-way valve lO and the bypass 12, the heating pipe 2 may overheat and damage the top plate IA and other equipment, or the liquid phase portion in the tank l may be damaged. It can prevent the effects of heat from reaching up to

Since all these controls are processed electrically,
By centralizing the control system in one place, centralized management via remote control is also possible. Furthermore, an inverter-controlled compressor 7 is used to compress the refrigerant to improve energy efficiency, and a cooling section for cooling the liquid phase is provided in the tank 1 for direct cooling, reducing energy costs in this respect as well. can. In addition, by providing a stirring pump 6 that stirs the liquid phase part, it is possible to keep the temperature distribution of the liquid phase part of the polymerizable substance constant, and further shorten the cooling time of the polymerizable substance transferred at the time of arrival. In addition, the temperature of the polymerizable substance sent into the transfer pipe during shipping can be sent out at a low temperature similar to that in the tank, which has the effect of suppressing the polymerization reaction within the transfer pipe.

In addition, in the above embodiment, the cone roof type tank 1
Although we have shown an example of storage in a tank, it can also be applied to tanks with a dome-shaped or flat top plate, and the heating piping 2 installed on the top plate IA at the top of the tank is not limited to the top plate IA. It may be extended to a portion corresponding to the gas phase portion at the upper part of the side wall surface IB. Furthermore, the method of controlling the motor that drives the compression Ja7 is not limited to controlling the rotation speed using an inverter.
It may also be unload control or the like.

Furthermore, in the embodiment described above, the heating pipe 2 as the heating section and the cooling pipe 4 as the cooling section are configured by a series of refrigeration cycles, but the present invention is not limited to this. Other heating and cooling means may be used instead, such as using a simple heater and a heat pipe as the cooling part.In short, the wall surface corresponding to the gas phase part of the upper part of the tank L is heated, and the cooling part is heated and the cooling part is heated. Any device may be used as long as it can cool the liquid phase portion of the polymerizable substance. However, if configured as in the above embodiment, there is an advantage that polymerization can be efficiently prevented through a series of cycles.

Further, the polymerizable substance to be stored is not limited to styrene monomer, but may be, for example, α-methylstyrene monomer, acrylonitrile monomer, etc., and the refrigerant may be Freon-12 or the like in addition to Freon-22. Paratertiary butylcatechol (TB) is used as an inhibitor.
C) was added, which could be either sulfur or, even better, the nitrosamine compounds 2,4-dinitrophenol and 2,6-dinitrophenol [? It can be a thing.

[Effects of the Invention] As described above, according to the method for storing a polymerizable substance of the present invention, the polymerization reaction of the polymerizable substance in the tank is prevented, evaporation from the liquid surface is suppressed, and the polymerizability of the gas phase is reduced. By suppressing the polymerization reaction within the droplets due to the condensation of the substance within the tank, it is possible to prevent the generation of polymers and easily avoid deterioration in quality.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram showing an example of a storage tank device for carrying out the method of the present invention, FIG. 2 is a diagram showing the flow of control of the expansion valve in FIG. 1, and FIG. FIG. 2 is a schematic configuration diagram showing a heat exchanger. 1... Tank, IA... Top plate, 2... Heating piping, 3.5... Temperature sensor, 4... Cooling piping, 7.
...Compressor, 11.17...Control device, 13.15.
... Heat exchanger, 16... Expansion valve.

Claims (4)

[Claims] (1) In a storage tank for polymerizable substances, there is a cooling section for cooling the liquid phase portion of the polymerizable substance stored in the tank, and a heating section for heating the wall surface corresponding to the gas phase portion in the upper part of the tank. 1. A method for storing a polymerizable substance, the method comprising: (2) In claim 1, the refrigerant is adiabatically compressed by a compressor, radiated heat in a heating section, further cooled in a heat exchanger, expanded adiabatically by an adjustable expansion valve, and vaporized in a cooling section. A method for storing a polymerizable substance, the method comprising: forming a refrigeration cycle in which the compressor absorbs heat and returns to the compressor. (3) In claim 1 or 2, the temperature of the heating part and the temperature of the liquid phase part in the tank are detected, and the temperature difference between the temperature of the heating part and the temperature of the liquid phase part is determined in advance. The opening of the expansion valve is determined by comparing it with a preset value, and the opening of the expansion valve is determined by comparing the temperature of the liquid phase with a preset value. A method for storing a polymerizable substance, the method comprising controlling the system by adjusting an expansion valve according to the larger opening degree. (4) In claim 2 or 3, when the temperature of the heating section is higher than a preset value,
By switching the refrigerant flow path to avoid heating parts,
A method for storing a polymerizable substance characterized by preventing overheating of a heating section.