JP2667542B2 - Method for purifying tetrafluoroethylene - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention relates to a fluorine-containing polymer, specifically, a tetrafluoroethylene useful as a monomer for producing a fluorine-containing resin and a fluorine-containing elastomer having excellent heat resistance and chemical resistance. And a method for purifying the same.

(Prior art) Tetrafluoroethylene is a very useful monomer, and gives a polymer with remarkably excellent heat resistance, chemical resistance, etc. by homopolymerization or copolymerization. Are used for various purposes. For the production of tetrafluoroethylene, industrially, a method of thermally decomposing chlorodifluoromethane at a temperature of 600 ° C. or higher is generally used. The thermal decomposition product generated by thermal decomposition contains various kinds of fluorohydrocarbons in addition to the raw materials chlorodifluoromethane and tetrafluoroethylene, and the target high-purity tetrafluoroethylene is purified by distillation.

However, it is known that high-purity tetrafluoroethylene is very easily polymerized, particularly when it contains a trace amount of oxygen, and sometimes explosively. Therefore, when purifying and storing tetrafluoroethylene, a polymerization inhibitor typified by terpinoids such as pinene, limonene, camphene, cymene and terpinene is used in an amount of 100 to 100.
It has been conventionally performed to add about 00 ppm (US Pat. No. 2,737,533).

When tetrafluoroethylene stabilized by such a polymerization inhibitor is used for polymerization, a method of absorbing the polymerization inhibitor with concentrated sulfuric acid before being used for polymerization is adopted, but waste sulfuric acid having a reduced absorption efficiency is used. It has a problem of treatment, a problem of improvement of absorption efficiency due to gas-liquid absorption, and a problem of equipment such as removal of contained mist. In addition, in general, a method of contacting with an adsorbent such as zeolite is used for removing organic substances in a gas, but in the case of tetrafluoroethylene, when contacting with a packed layer of zeolite, the heat of adsorption of tetrafluoroethylene is reduced. Therefore, there have been problems that tetrafluoroethylene is polymerized and it is difficult to continue the adsorption due to heat of polymerization, and that zeolite is blackened and the adsorption efficiency is lowered. In order to prevent this, a device for arranging a large number of cooling water pipes for cooling in the adsorption layer can be considered, but it has been difficult to solve the problem only on the device side.

(Problems to be solved by the invention) An object of the present invention is to solve the above-mentioned problems of the prior art,
Another object of the present invention is to provide a method of removing a polymerization inhibitor in tetrafluoroethylene that can be industrially carried out.

(Means for Solving the Problems) The present invention has been made to solve the above-mentioned problems, and zeolite brought into contact with chlorofluorohydrocarbon is brought into contact with tetrafluoroethylene containing a polymerization inhibitor. The present invention provides a method for purifying tetrafluoroethylene, which comprises removing a polymerization inhibitor.

The chloro-fluoro hydrocarbons used in the present invention, freon -11 (CCl _3), freon -12 (CCl ₃ F _2), Freon -13
(CClF ₃ ), Freon-22 (CF ₂ HCl), Freon-23 (CH
F ₃ ), CFC-113 (CCl ₂ FCClF ₂ ), CFC-114 (CClF
₂ CClF ₂ ), CFC-115 (CClF ₂ · CF ₃ ), CFC-116
(CF ₃ · CF _3), freon -142b (CH ₃ CClF _2), Freon -15
2a (CH ₃ · CHF ₂ ) etc. Of these chlorofluorohydrocarbons, particularly preferred is that chlorofluorohydrocarbons used in the treatment of zeolite may be mixed in a very small amount into tetrafluoroethylene. It does not adversely affect the polymer obtained from. From this viewpoint, in the case of tetrafluoroethylene, CFC-13, CFC-114 and CFC-11, which are widely used as solvents for copolymerization, are used.
Is preferably used as the chlorofluorohydrocarbon in the present invention.

As the zeolite used in the present invention, known zeolite can be adopted without any limitation. Examples thereof include fluorite, ryohite, soda-fluorite, mordenite, tobuffite, and buccuite, and zeolite commercially available under the trade name of Monocular Sieve is particularly suitable. Due to the size of the pores of the molecular sieve,
There are 4A, 5A, 13X and the like, but 13X having a large pore is preferably used in the present invention because it does not adsorb tetrafluoroethylene very much and adsorbs the polymerization inhibitor well.

As a method for treating zeolite with chlorofluorohydrocarbon, a method of passing gaseous chlorofluorohydrocarbon as it is or by diluting it with an inert gas such as nitrogen and passing the packed bed of zeolite at room temperature, or liquid chlorofluorohydrocarbon If so, a method in which the zeolite is immersed in chlorofluorohydrocarbon at room temperature and the chlorofluorohydrocarbon is sufficiently adsorbed, then the zeolite is filtered off and dried to remove excess chlorofluorohydrocarbon is adopted. You. In particular, in order to perform the treatment in a short time, a method of immersion in a liquid chlorofluorohydrocarbon is preferable.

It is considered that the chlorofluorohydrocarbon is partially adsorbed on the zeolite by this treatment and the effect of the present invention is exhibited, but the adsorption amount is 0.01 to 10% by weight, preferably 0.1 to 5% by weight based on the zeolite. It is enough.

The zeolite thus obtained is then contacted with tetrafluoroethylene containing a polymerization inhibitor.

The polymerization inhibitor is not particularly limited as long as it is a compound used to prevent polymerization of tetrafluoroethylene. Generally, limonene, pinene, camphene, cymene,
Tempene hydrocarbons such as terpinene; terpene alcohols such as citronellol, terpineol and borneol;
Monoterpenoids such as terpene aldehyde; terpene ketone: sesquiterpenoids: terpenoids such as diterpenoids are used.

The method of contacting the zeolite with the tetrafluoroethylene containing the polymerization inhibitor is not limited at all, but a packed tower system that is industrially employed is suitably employed. The packing amount of the zeolite in contact with chlorofluorohydrocarbon and the contact time in the packed column are determined by the concentration of the polymerization inhibitor contained in tetrafluoroethylene, but if the concentration is about 500 ppm, the space velocity will be When the contact is performed at ¹ to 20 min- ¹ , the concentration of the polymerization inhibitor in tetrafluoroethylene having a volume of 50,000 to 100,000 times the volume of the packed bed can be removed by adsorption to 0.1 ppm or less.
It is preferable that the temperature at the time of contact is under cooling because the amount of adsorption increases, but it becomes complicated in terms of the apparatus. The effects of the present invention are sufficiently exhibited even at room temperature. The pressure at the time of contact may be atmospheric pressure to 20 kg / cm ² for ventilation.

The zeolite after the saturated adsorption may be regenerated by heating, but may be discarded without being regenerated because of its high processing capacity.

(Effect) The polymerization inhibitor in tetrafluoroethylene can be removed by the method of the present invention by a simpler method than the conventional method. Also,
The polymer obtained from the purified tetrafluoroethylene has no difference in heat resistance and mechanical properties from the polymer obtained from tetrafluoroethylene containing no polymerization inhibitor.

Example -1 put mono sieve 13X pellets (Kishida Chemical Co., Ltd. 1/16 pellets) 5 to the vessel was further added Freon therein -113 a (CF ₂ Cl · CFCl ₂₎ until immersed mono sieve . The container was sealed and immersed at room temperature for 3 hours. Then, CFC-113 was removed, and the mixture was left at room temperature to dry. Inner diameter of dried monocular sieve 1
A 5 cm, 60 cm long stainless steel cylindrical container was filled to form an adsorption tower. Thereafter, the pressure in the adsorption tower was reduced by a vacuum pump at room temperature for 5 hours to remove excess Freon-113. The amount of CFC-113 adsorbed was determined from the change in weight of the monocular sieve and found to be 5% by weight.

On the other hand, tetrafluoroethylene (purity 99.99% or more)
Was introduced into the bottom of the container containing limonene from the bomb, and tetrafluoroethylene was discharged from the top of the container to produce tetrafluoroethylene containing limonene.

The upper part of the limonene container and the upper part of the adsorption tower subjected to the decompression treatment were connected by a pipe, and an adsorption test was performed so that tetrafluoroethylene could be discharged from the bottom of the adsorption tower.

300 / hr including tetrafluoroethylene of flowing pressure in the adsorption tower at atmospheric pressure, where then flowed as 4 kg / cm ² pressure, limonene concentration in the adsorption tower top is 700 ppm, it is discharged from the lower adsorption tower The concentration of limonene in tetrafluoroethylene is 0.1 ppm or less.
Was 100 ppm. Also, in order to seek processing capacity,
When the adsorption test was continuously performed, the limonene concentration in tetrafluoroethylene rapidly increased to 3 ppm at 80,000 times the volume of the used monocular sieve. or,
Although the temperature change in the adsorption tower slightly increased at the beginning of the flow of tetrafluoroethylene, the adsorption test could be continued without a temperature increase.

Example-2 Monocular sieve 13X was treated with Freon-1 in the same manner as in Example 1.
It was immersed in 1 (CFCl ₃ ) and then at room temperature for 4 hours. An adsorption tower was prepared by using the same operation and apparatus as in Example 1. Adsorption amount of CFC-11 to molecular sieve 13X is 0.5% by weight
Met.

Using pinene instead of limonene used in Example-1,
An adsorption test was conducted in the same manner.

When tetrafluoroethylene was flowed at a flow rate of 400 / hr, the pinene concentration in tetrafluoroethylene was 550 ppm
It became. Approximately 100 tetrafluoroethylene was flowed into the adsorption tower at atmospheric pressure in the same manner as in Example 1, and then the pressure in the adsorption tower was flowed at 3 kg / cm ² , and the pinene concentration at the adsorption tower outlet was 0.1 ppm or less. The concentration of Freon-11 was 50 ppm.
It was possible to process 10,000 times more tetrafluoroethylene. On the other hand, no rise in temperature in the adsorption tower was observed.

Example 3 In order to make molecular sieve 13X1 come into contact with gaseous chlorofluorocarbon, the stainless steel cylindrical container of Example 1 was used as an adsorption tower. Next, to make contact with CFCs, CFC-114
(CF ₂ Cl / CF ₂ Cl) is introduced from the upper part of the adsorption tower at atmospheric pressure at a flow rate of 0.5 / hr for 10 hours, and CFC-114 discharged from the lower part is introduced.
Was collected through a container cooled with dry ice-methanol. The amount of adsorption was determined from the weight loss of the cylinder and the weight of the collected Freon-114. The amount of adsorption was 1% by weight.

Next, in order to conduct an adsorption test, tetrafluoroethylene containing cymene was prepared by using cymene instead of limonene used in Example 1.

The obtained tetrafluoroethylene containing cymene was 100
When flow was carried out at atmospheric pressure at a flow rate of / hr, the concentration of cymene was about 400 ppm at the top of the adsorption tower, 0.2 ppm at the exit of the adsorption tower, and the concentration of Freon-114 was 150 ppm, and the volume of the molecular sieve used was 5 ppm. Ten times more tetrafluoroethylene can be processed.

Example 4 A contact and adsorption test with CFCs was performed in the same manner as in Example 3 using CFC-22 (CF ₂ HCl) instead of CFC-114, and the amount of CFC-22 adsorbed on the molecular sieve 13X was 0.1. % By weight. In addition, in the adsorption test, the concentration of tetramethylene in the tetrafluoroethylene at the outlet of the adsorption tower was 0.1 ppm, and it was possible to treat tetrafluoroethylene having a volume of 80,000 times the used molecular sieve volume.

Example-5 A polymerization experiment was performed using the purified tetrafluoroethylene of the present invention and tetrafluoroethylene containing no polymerization inhibitor.

To a stainless steel pressure vessel equipped with a 250 cc stirrer, 110 g of CFC-113, 5 g of CF ₂ = CFOCF ₂ CF ₂ CF ₃ was added. Next, in order to deoxidize the pressure vessel, the contents are cooled and solidified,
Then, the operation of degassing was repeated three times. Then, as a polymerization initiator 0.4 g, and tetrafluoroethylene 3 kg / cm ²
Then, the mixture was pressure-injected and the polymerization was carried out at 18 ° C for 4 hours. This experiment was performed on the purified tetrafluoroethylene of the present invention (Example-1) and tetrafluoroethylene containing no polymerization inhibitor. The results are shown in the table below.

Comparative Example 1 An adsorption test was performed on the molecular sieve 13X in Example 1 without making contact with Freon-113. Tetrafluoroethylene containing limonene at atmospheric pressure, 100 / hr
Immediately after the addition, the temperature in the adsorption tower rapidly increased, and the adsorption test was stopped. When the inside of the adsorption tower was opened and the molecular sieve was taken out, the molecular sieve pellets were locally formed as a black mass. This lump was dissolved with hydrofluoric acid, and a small amount of the remaining residue was analyzed.As a result, it was a polymer of tetrafluoroethylene. It was presumed to have advanced.

Claims (1)

(57) [Claims] 1. A process for purifying tetrafluoroethylene, comprising contacting zeolite in contact with chlorofluorohydrocarbon and tetrafluoroethylene containing a polymerization inhibitor to remove the polymerization inhibitor.