JP2001019646A - Dechlorination of aromatic chloride - Google Patents

Abstract

PROBLEM TO BE SOLVED: To detoxicate the catalyst in the reaction system including a platinum group catalyst supported by a carbon carrier and aromatic chlorine compound by carrying out the dechlorination reaction of aromatic chlorine compounds in the presence of a reducing substance, for example, hydrogen under irradiation with microwaves. SOLUTION: The reaction system including a platinum group catalyst supported by a carbon carrier (activated carbon, graphite, carbon black, carbon fiber, activated carbon fiber, meso-carbon or the like) (in addition to platinum, palladium and the platinumcarbon catalyst prepared by heating together platinum chloride and carbon powder may be used) and aromatic chlorine compounds as dioxin (preferably in an aqueous solution) is irradiated with microwaves in the presence of a reducing substance, for example, hydrogen, alcohols or hydrocarbons.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for dechlorinating an aromatic chlorine compound such as dioxin.

[0002]

2. Description of the Related Art Aromatic chlorine compounds such as polychlorinated dibenzodioxin (PCDD) and polychlorinated dibenzofuran (PCDF), which are collectively called dioxins, are used for industrial waste, incineration of municipal garbage or plastics, chlorine bleaching of paper, generation of agricultural chemicals. It occurs in various processes such as. These aromatic chlorine compounds are extremely harmful to living bodies including the human body, and are hardly decomposed in the environment. In particular, 2,3,7,8-tetrabenzodioxin tetrachloride (TCDD) is 10,000 times more acutely toxic than potassium cyanide, and is known to enhance carcinogenicity, teratogenicity, and cause immune abnormalities. I have.

[0003] Therefore, in an incineration plant, it is necessary to operate at a furnace temperature of 900 ° C or higher to suppress the generation of dioxin. However, continuous operation at such a high temperature causes the furnace to deteriorate quickly and has a small population. Many municipalities and SMEs do not have facilities with such processing capabilities.
Therefore, microwaves are irradiated to the incinerated ash to 400 to 600
Various dechlorination techniques or detoxification techniques have been proposed, such as a method of decomposing harmful organic chlorine compounds by heating at a low temperature of ℃ (JP-A-4-284885).

[0004]

However, the above-mentioned Japanese Patent Application Laid-Open No.
In the examples described in -284885, benzene which should be produced by decomposition has not been confirmed, and it is highly likely that the benzene is not actually decomposed but merely volatilized.
Therefore, at present, there is no practically available dechlorination technology or detoxification technology including other proposed technologies. Therefore, an object of the present invention is to provide a practically feasible method for dechlorinating and detoxifying an aromatic chlorine compound.

[0005]

In order to achieve the object, a method for dechlorinating an aromatic chlorine compound according to the present invention comprises:
A reaction system comprising a platinum group catalyst and an aromatic chlorine compound supported on a carbon-based catalyst carrier is irradiated with microwaves in the presence of a reducing substance such as hydrogen.

According to the method of the present invention, the aromatic chlorine compound is decomposed at a remarkably faster rate than the reduction reaction by ordinary heating. The mechanism is unclear, but when the carbon in the catalyst carrier is irradiated with microwaves, an eddy current is generated and the temperature becomes extremely high. Therefore, it is considered that the platinum group catalyst adhering to the surface is activated to accelerate the decomposition of the aromatic chlorine compound. That is, according to the microwave irradiation, even when the reaction system is a solution, the temperature can be locally and quickly raised to the boiling point or higher, so that hydrogen is activated.

[0007] Preferred as the catalyst carrier is activated carbon having a large adsorbing power and a large catalyst supporting power. A preferred form of the reaction system is an aqueous solution. This is because the activity of the platinum group catalyst is not reduced because the hydrogen chloride generated during the reaction is dissolved.

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS In addition to the above-mentioned activated carbon, graphite, carbon black, carbon fiber, activated carbon fiber, mesocarbon and the like may be used as the catalyst carrier. The catalyst is not limited to platinum, but may be palladium or platinum supported by heating chloroplatinic acid together with carbon powder. In addition, hydrogen is generally used as the reducing substance, but other reducing substances such as alcohol and hydrocarbon may be used.

[0009]

EXAMPLES [Experimental Methods of Examples 1 to 7] Example 1
In the experiments from to the comparative example 7, the effect of the type of the catalyst and the heating means on the reduction reaction was examined. Example 1 50 mg of 80 to 100 mesh activated carbon (Pt / C: Wako Pure Chemical Industries, Ltd.) supporting 5 wt% of platinum was suspended in 20 ml of a 75 mM aqueous solution of parachlorophenol, and the frequency was increased to 2 while blowing hydrogen gas. Microwave of 45 GHz and irradiation energy of 650 watts was irradiated. A 100 ml flask equipped with a reflux condenser was used as a reaction vessel. The microwave was alternately irradiated for one minute and left for one minute. The reaction time described below is the total time of these.

Comparative Example 1 A reaction was performed under the same conditions as in Example 1 except that heating was performed in an oil bath instead of microwave irradiation. The temperature of the reaction system was approximately 95 ° C. -Comparative Example 2-Platinum black (PtB: Nippon Engelhard) 50 instead of Pt / C
The reaction was carried out under the same conditions as in Example 1 except that mg was used. Comparative Example 3 A reaction was performed under the same conditions as in Comparative Example 2 except that heating was performed in an oil bath instead of microwave irradiation.

Comparative Example 4 5 wt% of nickel was supported on activated carbon (manufactured by Wako Pure Chemical Industries) by reduction of nickel nitrate. This nickel-supported activated carbon (Ni
/ C) The reaction was carried out under the same conditions as in Example 1 except that 50 mg was used in place of Pt / C. Comparative Example 5 A reaction was performed under the same conditions as in Comparative Example 4, except that heating was performed in an oil bath instead of microwave irradiation. -Comparative Example 6-Raney nickel (RNi: manufactured by Wako Pure Chemical Industries) 50 mg instead of Pt / C
The reaction was carried out under the same conditions as in Example 1 except that was used. Comparative Example 7 A reaction was performed under the same conditions as in Comparative Example 6, except that heating was performed in an oil bath instead of microwave irradiation.

[Results of Example 1 to Comparative Example 7] A solution after reaction for a predetermined time is converted into a gas chromatography mass spectrometer (hereinafter GC-M) using PEG-20M as a capillary column.
MS) to determine the conversion of parachlorophenol to a dechlorinated compound. Table 1 shows the analysis results. In addition, about Example 1 and the comparative example 1, the analysis result for every time until 40 minutes after reaction start was spotted in FIG. In the figure, ■ and △
Indicates the amount of unreacted parachlorophenol in Example 1 and Comparative Example 1, respectively, and ● and ○ indicate the amount of phenol produced in Example 1 and Comparative Example 1, respectively.

[0013]

[Table 1]

In all of the reaction systems except Comparative Examples 4 and 5, the products were mostly phenol and hydrogen chloride, and no other chlorine-containing compounds were found to be formed by GC-MS analysis. . The generation of hydrogen chloride is presumed from the fact that the pH of the aqueous solution decreases as the reaction time elapses.

As shown in FIG. 1, in a reaction system using Pt / C as a catalyst, microwave irradiation (Example 1)
The reduction rate of chlorophenol was almost twice that of the case of heating in an oil bath (Comparative Example 1), and chlorophenol disappeared almost completely in a reaction time of 40 minutes. Therefore, it is clear that microwave irradiation is significantly more effective for the decomposition reaction of the aromatic chlorine compound than the conventional heating method.

As can be seen from Table 1, in the case of oil bath heating, PtB (Comparative Example 3) shows the same activity as Pt / C (Comparative Example 1), but in the case of microwave irradiation (Comparative Example 1). Example 2)
On the contrary, the conversion rate fell. In any case of Ni / C (Comparative Example 4 and Comparative Example 5), the reduction reaction did not proceed. On the other hand, when RNi was used, microwaves (Comparative Example 6)
However, even in the oil bath (Comparative Example 7), the reaction proceeded very quickly by any heating method, and chlorophenol disappeared in about 10 minutes of the reaction time. However, since the color of the reaction solution changed to green, it was recognized that Ni metal was oxidized to Ni ions at the same time, and the reaction did not become catalytic. Therefore, it is clear that the catalyst that acts on the reaction to decompose the aromatic chlorine compound by microwave irradiation is limited to the platinum group supported on the carbon-containing carrier.

[Examples 2 to 4] Examples 2 to 4 are experiments in which the reaction according to the dechlorination method of the present invention proceeds to see what progresses. -Example 2-The same 50 mg of Pt / C and 100 mg as used in Example 1
Was irradiated with microwaves under the same conditions as in Example 1 for 3 minutes in the same reaction vessel as in Example 1 under a hydrogen gas atmosphere. After the completion of the reaction, the reaction solution was washed with methanol to extract a product.

The conversion was 52%. From the results of analysis by GC-MS, the product was phenol at 37% of the product, and the balance was cyclohexanol, 1,1'-oxybiscyclohexane and other unidentified hydrides. It was recognized that there was. Therefore, it is considered that parachlorophenol is mainly dechlorinated to phenol and further reduced to lose aromaticity.

Example 3 The same 50 mg of Pt / C as used in Example 1 was mixed with 10 ml of monochlorobenzene (hereinafter referred to as CB) and 10 ml of water in a 100 ml flask equipped with a reflux condenser. Was suspended in the mixture separated. Pt / C appears to have actually aggregated at the two-phase interface. Then, heating was performed in an oil bath under the same conditions as in Example 1 while blowing hydrogen gas, or microwave irradiation was performed. 1,2-dichloro- in place of CB
The same operation was performed for benzene (hereinafter, 1,2-DCB) and 1,2,4-trichlorobenzene (hereinafter, 1,2,4-TCB). However, heating in an oil bath was different from that in Example 1, and the reaction time was 20 minutes, and the temperature of the reaction system was 90 ° C.

After the reaction for a predetermined time, the solution was analyzed by GC-MS in the same manner as in Example 1 to determine the reaction rate and the product composition of the dechlorination reaction of each chlorobenzene. Table 2 shows the analysis results
Shown in The reaction rate was defined as a reaction amount (mmol) per 1 g of Pt / C when the reaction time was converted to one hour.

[0021]

[Table 2]

As can be seen from Table 2, no matter which chlorobenzene was used as the substrate, it was almost selectively dechlorinated to benzene, and the reaction solution was separated into three layers: a chlorobenzene layer, an aqueous layer and a benzene layer. did. The reaction rate was much faster in microwave irradiation than in oil bath heating. Moreover, it turned out that chlorine is dechlorinated step by step in the polychloro form.

Example 4 The same 200 mg of Pt / C and 0.2 mM as used in Example 1
Pentachlorophenol in ethanol solution,
After drying by removing the ethanol using an evaporator, microwave irradiation was performed for 10 minutes while blowing hydrogen gas. After completion of the reaction, the product was extracted by washing with methanol.

Although the course of the reaction is unknown, analysis by GC-MS of the solution after the reaction revealed that cyclohexanol and phenol were formed at a ratio of about 1: 1 assuming that a radical derived from ethanol was added to the phenol. I was From these facts, it is considered that pentachlorophenol was once dechlorinated to phenol and further reduced to lose aromaticity.

From the results of Examples 2 to 4, according to the dechlorination method of the present invention, as long as the compound is an aromatic chlorine compound, regardless of the chlorine substitution amount and the presence or absence of other functional groups. It can be seen that after the dechlorination proceeds preferentially, it undergoes a process of undergoing reduction to lose aromaticity. Therefore,
It is clear that the present invention is also applicable to dioxin dechlorination.

[0026]

As described above, the aromatic chlorine compound can be dechlorinated at a low temperature and in a short time, so that harmful chlorine compounds such as dioxin can be detoxified by general-purpose equipment.

[Brief description of the drawings]

FIG. 1 is a graph showing the dechlorination rate of parachlorophenol by microwave irradiation or oil bath heating.

 ────────────────────────────────────────────────── ─── Continuing from the front page (72) Takayuki Kitamura 3-9-9-203 Higashi Onohara, Minoh-shi, Osaka (72) Yuji Wada 2-6-643 Nishi Midorioka, Toyonaka-shi, Osaka F-term ( Reference) 2E191 BA12 BD11 BD13 BD17 4D004 AA47 AB07 CA36 CA37 CA50 4H006 AA02 AC13 BA22 BA55 BA95 BE20

Claims (2)

[Claims] 1. A method comprising irradiating a reaction system containing a platinum group catalyst supported on a carbon-based catalyst carrier and an aromatic chlorine compound with microwaves in the presence of a reducing substance such as hydrogen. A method for dechlorination of a group III chlorine compound. 2. The method according to claim 1, wherein said catalyst carrier is activated carbon.