JP3497915B2 - Chemical decomposition method of polychlorobiphenyl by phase transfer catalyst - Google Patents

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a decomposition method for detoxifying a mixture of polychlorobiphenyl (PCB) obtained by chlorinating biphenyl.

[0002]

2. Description of the Related Art Conventionally, since a mixture of polychlorobiphenyl (hereinafter abbreviated as PCB) has good electric characteristics, a heat medium, a solvent for carbonless paper, an insulating oil plasticizer for a transformer, a lubricating oil. It was widely used as such.
However, since this PCB contains a large amount of a mixture having an average number of chlorine atoms of 3 to 4, it has a high persistence to the environment and is extremely toxic to the human body. Therefore, its use is prohibited except for a part thereof.

However, with respect to the PCB-using products that have already been used for many years, proper storage is becoming difficult as the storage period becomes long, and environmental safety cannot be secured only by storage. Fear is happening. Therefore, today, there is a demand for urgent disposal of the products using the PCB.

Therefore, conventionally, as a treatment method for making PCB harmless, generally, a complete incineration method, a hydrothermal decomposition method,
A dechlorination method using light or radiation is known.

However, in PCB, H of biphenyl is C
Substituted with L, CL has a minimum of 1 to a maximum of 10, and therefore, there are many isomers depending on the CL number and position, and a CL number of 3 or more is virtually nonflammable.

[0006]

[Chemical 1] And, this PCB is (1) strongly resistant to heat, oxidation, acid, and alkali, (2) hard to burn, (3) has good adhesiveness, (4) low volatility, (5) insulating property. Etc. have excellent electrical characteristics.

[0007] Therefore, the problem of how to detoxify such a PCB is only the problem of how to remove chlorine from the benzene ring.
Chemically, chlorine on the benzene ring is hard to remove. For example, when trying to react ammonia or sodium hydroxide, which is a general reagent, with chlorobenzene, the substitution reaction does not occur under severe conditions.

[0008]

[Chemical 2] To date, a treatment method known as a PCB detoxification method is as follows. (A) Low-concentration PCB When draining a substance containing a low-concentration PCB, the following method is known. 1. Method of decomposing by radiation 2. Method of degrading with microorganisms 3. Adsorption Method (B) High Concentration PCB When draining a substance containing a high concentration PCB, the following method is known. 1. Incineration method 2. Method of thermal decomposition at high temperature in alkaline aqueous solution 3. Method of decomposing with a compound of sodium and naphthalene 4. Dechlorination method (C) or other detoxification method of PCB by irradiation of light or radiation 1. Dechlorination Method by Reduction Reaction (Sending One Electron to PCB Molecule) This method breaks an aromatic carbon-chlorine bond having low reactivity. That is, the aromatic carbon-chlorine bond is
Irradiation with light in a suitable solvent causes reduction and substitution.

[0009]

[Chemical 3] in this case,

[0010]

[Chemical 4] Acts as a strong reducing agent that sends one electron to the PCB molecule.

Therefore, according to this method, when PCB is irradiated with light in 2-propanol in which sodium hydroxide is dissolved, the chain is dechlorinated. However, this method has a problem that NaCl is deposited on the jacket of the light source.

Further, in this method, as the PCB,
For example, KC-300 (Kanefuchi Chemical Co., Ltd., a mixture of chlorobiphenyls containing an average of 3.14 chlorine atoms) was added to NaO.
Irradiation in H- (CH ₃ ) ₂ CHOH under a 100 W high pressure mercury lamp (N ₂ ) results in dechlorination as follows.

[0013]

[Chemical 5] In this case, the absorbance of PCB is large, and the light required for decomposition is <300 nm. 2. Naphthalene (polynuclear aromatic compound) and alkali metal
Dechlorination method by the combination of

[0014]

[Chemical 6] To use.

In this case, 0.5 liter of naphthalene C ₁₀ H ₈ was added to 1 liter of THF under N ₂ at 0 ° C.
Is reacted with 0.5 mol to form a dark green electron transfer reducing agent.

In this method, as the PCB, for example, KC-400 (Kanefuchi Chemical Co., Ltd., chlorine content 48.7%)
Is added dropwise to a predetermined amount of THF solution in N ₂ gas at 0 ° C. and stirred. The reaction is then stopped by adding the minimum amount of water required for decolorization of the reaction mixture. In this case, the amounts of sodium and naphthalene greatly affect dechlorination. Chlorine of PCB is desorbed within 30 minutes by using a reducing agent in an amount 1.5 times or more (molar ratio of sodium and naphthalene to 1 CL). Therefore, the average molecular weight of the residue excluding naphthalene is 400 to 600.

[0017]

[Chemical 7]

[0018]

[Chemical 8] The feature of this method is that (1) rapid and complete dechlorination proceeds at room temperature and atmospheric pressure, and (2) the treated product does not contain any organic chlorine, so that it can be completely treated in an ordinary incinerator. Is. 3. Dechlorination Method by Bireh Reduction Method In this method, Na is changed to liquid ammonium (boiling point-
33 ° C.) (in this case, dark blue). Metallic sodium dissolved in the obtained liquid ammonium,
If there is a person who accepts the electrons, they can easily deliver the electrons.

[0019]

[Chemical 9] This causes the sodium electrons to move to the PCB and break the aromatic carbon-chlorine bond.

For example, when PCB and Na-OH ₃ are reacted under vacuum at -33 ° C., PCB is rapidly dechlorinated, and when CL / Na = 1/2, the dechlorination rate is 100%.
Becomes 4. Dechlorination method by hydrothermal decomposition reaction In this method, 1 g of PCB was added to 12.5% of methanol.
Dissolve in ml, then add 5 moles of NaOH and react under high pressure and at 300-320 ° C to decompose PCB in minutes.

[0021]

[Chemical 10]

[0022]

However, the above-mentioned conventional PCB dechlorination method involves enormous temperature conditions, pressure conditions, processing time, and the like, and is disadvantageous in terms of processing efficiency and economic efficiency. .

Therefore, as a result of intensive studies, the present inventors have found that when PCB and KOH are reacted in the presence of tetrabutylammonium chloride (TBAC) which is a phase transfer catalyst, PCB is produced under milder conditions than before. I found out that it can be disassembled.

That is, when a halogen in the reductive dehalogenation reaction and a slightly excess amount of alkali are coexistent, the halogen of the aromatic compound is generally difficult to separate,
Therefore, high temperature is required. Therefore, it is desirable to lower the reaction temperature because halogen transfer may occur.
It has been found that the method according to the invention is suitable as a reductive dehalogenation method in such cases.

However, in order to carry out the nucleophilic substitution reaction of the aromatic halogen compound in the liquid phase, various measures are required. PCB
Is an oil, and KOH, NaOH, and generally anionic reagents that react with it are soluble in water and do not dissolve in oil, so the possibility of collision of two molecules necessary for the reaction to occur. There is almost no.

Therefore, as a phase transfer catalyst, C16H36C is used.
1N (Tetrabutylammonium chloride-TBAC
-) · Formula weight 277.92 CAS [1112-67-0]
By using the above, the anion was activated in the organic phase, the ionic reaction was promoted, and the PCB was chemically decomposed by the nucleophilic substitution reaction of the KOH / TBAC system, and an extremely effective dechlorination treatment was achieved. We were able to.

For example, the BCD method (Base Catal)
yes Decomposition Procedures
s) is an organic chlorine compound such as PCB added with an alkaline agent such as caustic soda, a carbon catalyst, and a hydrogen donor substance to give 300
It requires a chemical reaction under heating conditions of up to 350 ° C., and requires a reaction time of 6 hours. On the other hand, according to the above-described method of the present invention, the intended purpose can be achieved with the reaction time of 2 hours and the reaction temperature of 130 ° C. as the lower limit.

Therefore, it is an object of the present invention to provide a method for chemically decomposing polychlorobiphenyl by a phase transfer catalyst capable of decomposing PCB rapidly and economically under milder conditions than before.

[0029]

In order to achieve the above object, a method for chemically decomposing polychlorobiphenyl (PCB) by a phase transfer catalyst according to the present invention comprises reacting PCB and KOH in the presence of the phase transfer catalyst. It is characterized by

In this case, tetrabutylammonium chloride (TBAC) can be used as the phase transfer catalyst.

For PCB-containing substances, at least 5% TBAC aqueous solution and at least 5% KOH aqueous solution are used in the presence of N ₂ gas at a reaction temperature of 100 to 13%.
The decomposition treatment of PCB can be effectively achieved by reacting for 1 hour under the condition of 0 ° C.

The phase transfer catalyst used in the method of the present invention has the following constitution and reaction. That is, a system in which two liquid phases of water that dissolves the salt M ⁺ Nu ^{− serving} as a nucleophile and a hydrophobic organic solvent that dissolves the organic base R—X come into contact with each other can be applied to both phases of the quaternary ammonium. When QX containing dissolved cation Q ⁺ is added, anion exchange first occurs in the aqueous phase.

[0033]

[Chemical 11] Since Q ⁺ Nu ⁻ is soluble in both phases, it migrates to the organic solvent phase where it undergoes subsequent anion exchange, resulting in the product R-Nu in the organic solvent phase.

[0034]

[Chemical 12] In this case, QX returns to the water phase again.

As described above, QX reciprocates between the two phases to promote the next reaction.

[0036]

[Chemical 13]

[0037]

EXAMPLES Next, examples of the method of the present invention will be described together with comparative examples.

Example 1 Insulating oil for transformer (containing PCB / 640 ppm) 1000
A 5% aqueous solution of tetrabutylammonium chloride (hereinafter abbreviated as TBAC) as a phase transfer catalyst was added to ml in the presence of N ₂ gas and stirred, and then the paraffin bath was heated to start, the outside temperature was 130 ° C., and the content was Reaction temperature 1
The temperature was adjusted to 00 ° C., 5% of KOH was further added, and the mixture was reacted on an oil bath for 1 hour.

After completion of the reaction, the mixture is cooled and filtered to obtain 600 parts of washing water.
After adding ml and mixing, the oil-water is separated, 300 ml of washing water is added again to the oil part and mixed, and then the oil-water is separated, the oil part is dehydrated, and a Gderna Danish concentrator is used. After degassing and concentration, the oil portion was used as a sample and calibrated by gas chromatography. As a result, the residual PCB is only 6
ppm was detected.

Example 2 In the same manner as in Example 1, insulating oil for a transformer (PCB / 64
(0 ppm content) to 1000 ml, TBAC 5% aqueous solution as a phase transfer catalyst was added in the presence of N ₂ gas, and K was further added.
6% of OH was added and the reaction temperature was 110 ° C. on an oil bath.
Then, it was reacted for 1 hour. After the reaction was completed, the residual PCB was calibrated by gas chromatography in the same manner as in Example 1. As a result, the residual PCB was 0 ppm.

Example 3 In the same manner as in Example 1, insulating oil for a transformer (PCB / 64
(0 ppm content) to 1000 ml, TBAC 5% aqueous solution as a phase transfer catalyst was added in the presence of N ₂ gas, and K was further added.
Add 6% of OH, reaction temperature 130 ℃ on oil bath
Then, it was reacted for 1 hour. After the reaction was completed, the residual PCB was calibrated by gas chromatography in the same manner as in Example 1. As a result, the residual PCB was 0 ppm.

Comparative Example 1 Under the same conditions as in Example 1, insulating oil for transformer (PCB
(/ 640 ppm content) in 1000 ml of a TBAC 3% aqueous solution as a phase transfer catalyst in the presence of N ₂ gas, KOH of 2% was further added, and the reaction temperature was 10 on an oil bath.
The reaction was carried out at 0 ° C for 1 hour. After completion of the reaction,
The residual PCB was calibrated by a gas chromatograph in the same manner as in. As a result, the residual PCB was 74 ppm.

Comparative Example 2 In the same manner as in Comparative Example 1, the insulating oil for the transformer (PCB /
640ppm content) 1000ml, TBAC 3% aqueous solution as a phase transfer catalyst was added in the presence of N ₂ gas, KOH 3% was further added, and the reaction temperature 100
The reaction was carried out at 0 ° C for 1 hour. After the reaction was completed, the residual PCB was calibrated by gas chromatography in the same manner as in Comparative Example 1. As a result, the residual PCB was 60 ppm.

[0044]

As is apparent from the above-described examples, according to the method for chemically decomposing polychlorobiphenyl (PCB) by the phase transfer catalyst according to the present invention, PCB and KOH are mixed with tetrabutyl which is a phase transfer catalyst. By reacting in the presence of ammonium chloride (TBAC),
Under a milder condition than before, which comprises a temperature condition of 100 to 130 ° C. and a reaction condition of 30 minutes to 2 hours, PC
B can be decomposed.

Therefore, according to the present invention, various conventional PCs are used.
Compared with the decomposition treatment method of B, it has an advantage that PCB can be decomposed rapidly and economically.

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁷ Identification code FI C07C 25/18 C07C 25/18 (56) References JP-A-49-32868 (JP, A) JP-A-6-234674 (JP , A) JP 56-133228 (JP, A) JP 56-133227 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) C07B 37/06 A62D 3/00 B01J 19/00 B01J 27/32 C07B 35/06 C07C 25/18

Claims (3)

(57) [Claims] 1. A method for chemically decomposing polychlorobiphenyl (PCB), which comprises reacting PCB and KOH in the presence of a phase transfer catalyst. 2. The chemical decomposition method according to claim 1, wherein tetrabutylammonium chloride (TBAC) is used as the phase transfer catalyst. 3. At least 5% TBAC aqueous solution in the presence of N ₂ gas and at least 5%, relative to the PCB content.
KOH aqueous solution of 100 to 130 ° C.
The chemical decomposition method according to claim 1, which comprises reacting for 1 hour under the conditions of.