JPH0978070A - Method for recycling plastic and method for producing carbon material for producing carbon electrode - Google Patents

Abstract

(57) [Abstract] [PROBLEMS] To provide a method for recycling plastics, which allows the thermal decomposition residue of plastics to be used for a new purpose. SOLUTION: A carbonaceous solid decomposition residue remaining after thermally decomposing a plastic to recover a decomposition product is treated at 700 ° C.
The above is heat-treated to obtain coke-like carbon. The coke-like carbon is mixed with a decomposition product, and molded and sintered to form a carbon electrode having a desired shape. Pyrolysis is carried out in the presence of alkali,
The solid decomposition residue is washed with water before heat treatment. [Effect] Use of the decomposition residue of plastic as an end material for electrode production has been found, and treatment of waste plastic is easy to put into practical use.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to the treatment and recycling of waste plastics contained in industrial wastes, especially waste plastics containing polyvinyl chloride resin.

[0002]

2. Description of the Related Art In recent years, a technique has been developed in which a thermoplastic is pyrolyzed and pyrolyzed and reused as a fuel oil, and it is regarded as a promising method for recycling a large amount of waste plastic. The solid decomposition residue obtained by thermally decomposing waste plastic is used for landfills, road paving, etc.

[0003]

However, when halogen-containing plastic such as polyvinyl chloride resin is contained in the waste plastic, halides such as chlorine gas are generated. An alkali such as sodium is added. As a result, the decomposition residue contains excess alkali along with halogen-neutralized salt.Therefore, in order to use the decomposition residue for landfilling, etc. Need to be removed sufficiently. But,
Since it takes time and cost to remove excess alkali, it is not economically economical to use the residue for landfill treatment. However, if there are other uses that can produce economically more valuable products from the residue, the practical application of recycling of waste plastics by thermal decomposition will be promoted. Therefore, there is a demand for the development of new uses for decomposition residues.

The present invention has been made in order to solve the problems of the prior art as described above, and an object thereof is to provide a method for recycling plastics, which enables the thermal decomposition residue of the plastics to be used for a new purpose. It is what

[0005]

[Means for Solving the Problems] In order to achieve the above object, the inventors of the present invention have conducted extensive studies, and as a result, found that a carbonaceous solid residue obtained after thermal decomposition can be used for producing a carbon electrode. The inventors have invented a method for recycling the invention.

The plastic recycling method of the present invention is
A thermal decomposition step of thermally decomposing the plastic to obtain an oily product and a carbonaceous solid decomposition residue;
A heat treatment step of heating at not less than 0 ° C., a molding step of mixing the solid decomposition residue with the oily product to form a residual molded article, and a sintering step of sintering the residual molded article to generate a carbon electrode. Is to have.

In the method for producing a carbon material for producing a carbon electrode of the present invention, the carbonaceous solid decomposition residue remaining after the thermal decomposition of the plastic to recover the decomposition products is heat-treated at 700 ° C. or higher. .

In the above, the plastic is thermally decomposed in the presence of an alkali, and before the heat treatment step, there is a water washing step of washing the solid decomposition residue with water.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION By heating a solid decomposition residue obtained by thermally decomposing a plastic to obtain a fuel oil as a thermal decomposition product at 700 ° C. or higher, the residue becomes coke-like carbon,
By adding fuel oil to coke-like carbon, shaping, sintering, and shaping, a carbon electrode having a desired shape is produced.

Hereinafter, the present invention will be described in more detail.

When polyvinyl chloride (PVC) resin is heated, desorption of the chlorine element occurs at around 300 ° C. to generate hydrogen chloride, and at about 400 to 500 ° C., oil is decomposed by thermal decomposition (when the degree of decomposition is low, Also produces solids) and gaseous decomposition products are produced. After the thermal decomposition is completed, a solid decomposition residue remains. Polyolefin-based plastics and other resins are also thermally decomposed at about 400 to 500 ° C. to produce oil, and decomposition residues remain. The oil obtained by the thermal decomposition of plastic is a fatty acid having 5 to 22 carbon atoms,
It contains paraffin and is suitable for use as fuel oil. The plastic can be dechlorinated by heating the plastic in advance at around 300 ° C. before thermal decomposition.

A basic metal hydroxide is added to the thermally decomposable plastic as a neutralizing agent in order to trap hydrogen halide and prevent the formation of organic chlorine compounds. As the basic metal hydroxide, specifically, sodium hydroxide, potassium hydroxide, calcium hydroxide, magnesium hydroxide,
Examples thereof include alkalis such as barium hydroxide and lithium hydroxide, and particularly strong alkalis such as sodium hydroxide and potassium hydroxide are used. The amount of alkali to be added is set in the range of 0.01 to 1.5 times the halogen contained in the plastic to be treated in terms of molar ratio. When decomposing plastics by batch processing, if the plastics are not agitated, it is necessary to add 1 to 1.5 times the molar amount of alkali, and if the plastics are dechlorinated beforehand, the amount of alkalis added to the plastics Can be suppressed to 0.5 times mol or less of the initially contained halogen. The addition of the metal hydroxide also has a function of promoting the decomposition of ether bonds and ester bonds of the polyester resin or the epoxy resin and promoting oil conversion. In addition, when the plastic is thermally decomposed, anhydrides of plasticizers (phthalic acid diester, etc.) usually contained in PVC resins are also generated, but addition of alkali prevents clogging of pipes and the like due to anhydrides, and oil recovery rate Is improved. For these reasons, alkali addition is effective for the thermal decomposition of waste plastic.

After the thermal decomposition of the plastic, a solid decomposition residue remains, and the decomposition residue of the polyolefin plastic is P
Although the amount produced is smaller than in the case of VC resin, the amount of decomposition residue increases extremely when PVC coexists. Such a solid decomposition residue is carbonaceous, and when it is thermally decomposed in the presence of an alkali, the decomposition residue contains excess alkali and neutralized salts such as sodium chloride.

The state of the decomposition residue varies depending on the reaction conditions at the time of decomposition. Particularly, the decomposition residue of PVC becomes solid and difficult to handle when no alkali is present during the decomposition, but alkali is added. In some cases, a residue that is relatively easy to grind is obtained. Furthermore, when the decomposition residue is ignited in the presence of an appropriate amount of alkali, the surface activity of the solid residue is improved.

Excess alkali and salt contained in the decomposition residue are eluted and separated by washing with water or warm water. Some plastics contain a trace amount of a metal component such as lead, and the metal component contained in the decomposition residue due to this is also removed by washing with water.

When the solid residue is further ignited at about 700 ° C. or higher, preferably around 1000 ° C., the residue becomes a coke-like carbon content. Coke-like residue has high surface activity,
Further, it is easy to crush and can be easily subjected to molding and the like, which is most suitable for use in the production of carbon electrodes. The appropriate heating time depends on the difference in heat transfer due to the size of the batch, but it is effective to maintain the heating for about 1 hour or longer.

The coke-like carbon content is molded into a predetermined shape such as a rod shape by adding the oil content containing the paraffin component obtained by the above-mentioned thermal decomposition. After molding the carbon content, the oil content may be permeated into the molded product. If necessary, graphite, pitch or the like may be mixed with the coke-like carbon component so as to facilitate the molding process or to appropriately adjust the physical properties of the obtained carbon electrode. After that, the molded product is sintered in a sintering furnace at a temperature of about 1000 to 1200 ° C., cooled, and the shape of the sintered product is adjusted by cutting or the like to obtain a rod-shaped or plate-shaped carbon material. This carbon material is suitable for use as an artificial graphite electrode.

Through the above manufacturing process, the specific resistance value is 1
A rod-shaped graphite electrode having a bending strength of not more than 0.0 μΩm and a bending strength of 1275 N / cm ² can be obtained. In the case of a plate electrode, the specific resistance value is 11.0 μΩm or less and the bending strength is 1765N.
/ Cm ² can be obtained (reference: JIS R
7201).

FIG. 1 shows an apparatus 1 for recycling plastics. By using this apparatus, the plastics can be thermally decomposed and the decomposition residues can be adjusted to carbon materials for electrode production.

A delivery pipe 5 is connected to the thermal decomposition tank 3 of the recycling apparatus 1, and an additive tank 7 is attached via a valve 9. The additive tank 7 contains a metal hydroxide for capturing and neutralizing hydrogen halide generated when the plastic containing the halogen-containing resin is decomposed. Further, water, a catalyst, etc. may be stored. In the thermal decomposition tank 3, a delivery pipe 11 is further provided.
Are connected via a pressure control valve 13, and the delivery pipe 11 is connected to a container 15. Further, the delivery pipe 11 has a constant temperature part 1
7. A temperature control device 19 is attached. The temperature control device 19 sends a medium having a predetermined temperature to the constant temperature part 17 to keep the temperature of the constant temperature part constant. As the medium, those commonly used such as air, water and liquid compounds can be used.

A pump 21 is further provided in the delivery pipe 11 of the above apparatus.
Is provided, and the pressure control valve 23 is attached to the container 15. These are used when carrying out thermal decomposition in two steps. In this case, the pressure control valve 13 is opened and the container 1
5 is equipped with a heating means so that the same operation as the thermal decomposition tank 3 can be performed. Performing thermal decomposition in multiple steps is effective for obtaining a higher quality product.

The thermal decomposition tank 3 may be provided with a stirring device used for stirring the plastic during the thermal decomposition reaction and scraping and crushing the residue after the reaction. Further, a filter for separating the contents of the opening / closing shutter for controlling the discharge of the contents in the tank can be provided at the bottom of the thermal decomposition tank 3.

Using the above apparatus, plastics are processed, for example, according to the flow shown in FIG. First, the waste plastic A that has been appropriately pretreated such as crushed is supplied from the delivery pipe 5 to the thermal decomposition tank 3, and an additive such as a metal hydroxide B is added to the resin from the additive tank 7. The amount of the additive is appropriately adjusted by the valve 9. Waste plastic is a thermal decomposition tank 3
It is heated inside to undergo thermal decomposition (25), and the thermal decomposition tank 3 is filled with gaseous decomposition products. When the pressure in the thermal decomposition tank 3 exceeds a predetermined pressure, the pressure control valve 13 is opened and a gaseous decomposition product is released to the delivery pipe 11, whereby the reaction system is regulated to a predetermined pressure. Therefore, by maintaining the thermal decomposition tank 3 at a constant temperature, the reaction proceeds under constant conditions. The released decomposition products are cooled and condensed in the constant temperature unit 17,
It is accumulated in the container 15 as a liquid decomposition product C such as fuel oil.

Water E is added from the additive tank 7 to the mixture D of the decomposition residue, excess metal hydroxide and salt in the thermal decomposition tank 3 to wash it (27). The cleaning liquid F containing the metal hydroxide and the salt is separated and removed from the decomposition residue G after cleaning. The decomposition residue G in the thermal decomposition tank 3 is further heated at 700 ° C. or higher (29),
A coke-like residue H is obtained. This coke residue H
Is washed with water E'to further remove metal components as needed (27 '), and the washing solution F'is removed to obtain coke-like carbon H'.

The coke-like carbon H'is discharged from the thermal decomposition tank 3 and, after being appropriately dried, graphite I and pitch J are added, and decomposition product C is added and sufficiently mixed (29). The mixture is molded using a molding machine (31) and 1000-1200 in a sintering furnace.
After sintering (33) at 0 ° C., the carbon rod or carbon plate K is obtained by cutting (35) and shaping it into a desired shape. This is used as an electrode.

[0026]

EXAMPLES The present invention will be described in more detail below with reference to experimental examples. The unit "%" in the following examples is all based on weight.

(Experimental Example 1) Using the apparatus shown in FIG. 1, 11 kg of sodium hydroxide was added to 50 kg of waste plastic containing polyvinyl chloride, and heated at 450 ° C. for 200 minutes in a decomposition tank. The gas generated by the thermal decomposition of the waste plastic was cooled by the condenser and 30 kg of liquid was obtained. This liquid was a fat containing a paraffin component. About 20 kg of black solid residue remained in the decomposition tank.

100 L of water was added to the above black solid residue to obtain 6
After boiling for 0 minutes, water and solid residue were separated, and the separated water was discharged from the decomposition tank. The weight of black solid residue is 15
It was reduced to kg (converted to dry weight). Sodium hydroxide was eluted in the separated water. Further, the black residue was well pulverized and pulverized, and then 15 L of pure water was used to wash the pulverized residue 10 times to remove residual metal components and salts. When the black residue after washing was heated at 1000 ° C. for 2 hours and then cooled, 14 kg of coke-like carbon was obtained. Furthermore, this series of operations is repeated for a total of 56k.
g of coke-like carbon was obtained.

4 kg of natural graphite and 4 pitches were added to the above carbon content.
16 kg of fats and oils obtained by pyrolysis
g was mixed and mixed well, and processed into a rod shape using a molding machine. This rod-shaped molded product is heated to 1100 ° C. for 120 hours in a sintering furnace.
Heat and bake for a minute. This was cut to form a rod-shaped electrode (nominal diameter = 75 mm, nominal length = 1000 mm).

The coke-like carbon content obtained by repeating the same operation as above using another waste plastic containing polyvinyl chloride was similarly mixed with natural graphite, pitch and fat and oil, and the mixture was molded into a plate shape. And sinter the plate electrode (length = 2
50 mm, width = 50 mm, thickness = 20 mm).

Both the rod-shaped electrode and the plate-shaped electrode are
No scratches, cracks, or cracks harmful to use were found. The specific resistance and bending strength of these electrodes were measured. Table 1 shows the results
Shown in

[0032]

[Table 1] ------------------ Specific resistance, bending strength, ash content --------------- −−−−−−−−−−−−−−−−−−−− Rod electrode 9.0 μΩm 1500 N / m ² 0.8% Plate electrode 9.0 μΩm 1900 N / m ² 0.15% --- ---------------------------------------- The results in Table 1 were in conformity with the criteria described in JIS R7201.

(Experimental Example 2) Using the apparatus shown in FIG. 1, 15.4 kg of sodium potassium hydroxide was added to 50 kg of waste plastic containing polyvinyl chloride, and the mixture was heated to 450.degree.
Heat for 0 minutes. The gas generated by the thermal decomposition of the waste plastic was cooled by the condenser and 30 kg of liquid was obtained. This liquid was a fat containing a paraffin component. About 25 kg of black solid residue remained in the decomposition tank.

100 L of water was added to the above black solid residue to obtain 6
After boiling for 0 minutes, water and solid residue were separated, and the separated water was discharged from the decomposition tank. The weight of black solid residue is 15
It was reduced to kg (converted to dry weight). Potassium hydroxide was eluted in the separated water. Further, the black residue was well pulverized and pulverized, and then 15 L of pure water was used to wash the pulverized residue 10 times to remove residual metal components and salts. When the black residue after washing was heated at 1000 ° C. for 2 hours and then cooled, 14 kg of coke-like carbon was obtained. Furthermore, repeating this series of operations, a total of 56 kg
Coke-like carbon content was obtained.

Oil and fat 16k obtained by pyrolyzing the above carbon content
g, 4 kg of natural graphite and 4 kg of pitch were mixed and mixed well, and processed into a rod shape using a molding machine. This rod-shaped molded product was heated to 1100 ° C. for 120 minutes in a sintering furnace to be baked and solidified. By cutting this, a rod-shaped electrode (nominal diameter = 75 mm,
Nominal length = 1000 mm) was formed.

Coke-like carbon content obtained by repeating the same operation as above using another waste plastic containing polyvinyl chloride is similarly mixed with fat and oil, and the mixture is subjected to a forming / sintering step to obtain a plate-like electrode. (Length = 250 mm, width = 50 mm, thickness = 20 mm) were similarly formed.

Both the rod-shaped electrode and the plate-shaped electrode are
No scratches, cracks, or cracks harmful to use were found. The specific resistance and bending strength of these electrodes were measured. Table 2 shows the results
Shown in

[0038]

[Table 2] ------------------ Specific resistance Bending strength Ash ---------- −−−−−−−−−−−−−−−−−−−− Rod electrode 9.0 μΩm 1500 N / m ² 0.9% Plate electrode 9.0 μΩm 1900 N / m ² 0.15% --- ----------------------------------------- The results in Table 2 were in conformity with the criteria described in JIS R7201.

[0039]

As described above, in the plastic recycling method of the present invention, the solid residue produced by the thermal decomposition reaction has a high adsorption ability and can be used as a gas / liquid purification adsorbent. Becomes Waste plastic contained in industrial waste can be recycled without waste, and its industrial value is extremely large.

[Brief description of drawings]

FIG. 1 is a conceptual diagram showing an example of a thermal decomposition apparatus for carrying out the recycling method of the present invention.

FIG. 2 is a flow chart showing an example of a process for producing a carbon electrode from a carbon material obtained according to the recycling method of the present invention.

[Explanation of symbols]

 1 Thermal Decomposition Device 3 Thermal Decomposition Tank 7 Additives Tank 15 Container 17 Constant Temperature Section 19 Temperature Control Device 21 Pump

Continuation of front page (51) Int.Cl. ⁶ Identification code Internal reference number FI Technical display area C08J 11/12 ZAB 9547-4H C10G 1/10 11/16 CEV H01M 4/96 B C10G 1/10 C25B 11 / 12 H01M 4/96 B09B 3/00 ZAB // C25B 11/12 302A

Claims (3)

[Claims] 1. A thermal decomposition step of thermally decomposing a plastic to obtain an oily product and a carbonaceous solid decomposition residue; a heat treatment step of heating the solid decomposition residue at 700 ° C. or higher; A method for recycling plastics, comprising: a molding step of mixing with an oily product to form a residual molded article; and a sintering step of sintering the residual molded article to generate a carbon electrode. 2. A carbonaceous solid decomposition residue remaining after the decomposition product is recovered by thermally decomposing a plastic at 700 ° C.
A method for producing a carbon material for producing a carbon electrode, which is characterized by performing heat treatment as described above. 3. The method according to claim 1, wherein the plastic is thermally decomposed in the presence of an alkali in the thermal decomposition step, and a washing step of washing the solid decomposition residue with water is further carried out before the heat treatment step. .