JPH11140223A - Treatment of halogen-containing plastic and apparatus therefor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To perform efficient decomposition of halogen-containing plastics without corrosion of the treatment vessel by carrying out the pretreatment of dehalogenation reaction before the treatment of the halogen-containing plastic with a supercritical fluid. SOLUTION: A halogen-containing plastic as poly(vinyl chloride) is preliminarily dehalogenated to recover the halogen compounds separated from the plastic, then a super-critical fluid as water is used as a solvent to decompose the halogen-removed plastic. In the dehalogenation process, the plastic is heated in an inert atmosphere or under reduced pressure or eluted with sub-critical fluid. The halogen compound is recovered by collecting the gaseous halogen compound formed by dehalogenation reaction in the gaseous form, or by allowing the halogen compound formed in a gas form to be adsorbed into the absorption liquid, which is collected.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method and an apparatus for decomposing halogen-containing plastics such as polyvinyl chloride and bromine-containing epoxy resin for recycling.

[0002]

2. Description of the Related Art The amount of plastic used is increasing year by year, and the amount of waste is also rapidly increasing. It is difficult to establish a new waste treatment plant, and while its remaining capacity is tight, there is an urgent need to develop plastic recycling technology that reduces waste and effectively uses resources. .

[0003] Conventionally, separation and crushing techniques and regeneration techniques have been studied for the purpose of material recycling, and oil conversion and oligomerization / monomerization techniques by thermal decomposition and catalytic decomposition have been studied for the purpose of thermal recycling and chemical recycling. In recent years, as a new plastic decomposition technology, a decomposition technology using a supercritical fluid as a solvent has been developed.

[0004] Among these, the plastic decomposition method using a supercritical fluid can easily obtain a high decomposition rate in a very short time and suppress the generation of harmful gases and the like. It is expected as. A supercritical fluid is a state that is taken when a substance reaches a temperature and a pressure higher than a critical point, and has a property intermediate between a liquid and a gas. Near the critical point, many physical properties of a material change significantly. For example, water hardly dissolves nonpolar organic substances below the critical point, but has a very low dielectric constant in a supercritical state, making it an excellent solvent for nonpolar substances. Also, since supercritical fluids have extremely active molecular motion, various reactions proceed very quickly in them. Stable substances such as plastics are also rapidly decomposed and dissolved in many supercritical fluids typified by supercritical water by a hydrolysis reaction or an addition reaction.

[0005]

In the decomposition of plastics by such a supercritical fluid, there is a problem that it is difficult to directly treat a plastic containing halogen in a supercritical fluid. This is because the halogen contained in the plastic is released by the supercritical treatment and becomes a halogen molecule or an acid containing a halogen, thereby corroding the container.

[0006] Corrosion due to halogen occurs even in a region where the concentration of halogen in the supercritical fluid is relatively low, and when it is directly processed, a very large amount of supercritical fluid per plastic processing amount must be taken. Processing was difficult.

[0007]

The above problems can be solved by dehalogenating a halogen-containing plastic and recovering a halogen compound separated from the plastic.

As a means for dehalogenation, heating in an inert atmosphere or under reduced pressure, elution in a subcritical fluid, or the like can be applied. Means for recovering the halogen compound include a method of collecting the halogen compound generated in a gaseous state by dehalogenation as a gas, a method of absorbing the gaseous halogen compound in a liquid and collecting the solution, and a method of collecting the solution. A method in which a halogenated compound formed in a liquid by halogenation is collected as a liquid, and a salt is formed by a neutralization reaction by reacting a gaseous halogenated compound formed by dehalogenation or a solution thereof with a compound containing an alkaline element or an atomic group. A method of generating the salt and collecting the salt or a solution of the salt can be applied.

[0009]

FIG. 1 shows an application example of the present invention.
An example of a process outline when water is used as a supercritical fluid will be described. The halogen-containing plastic adjusted to an appropriate particle size is stored in a storage container 1 and sent to a dehalogenation tank 2 as needed. The dehalogenation tank 2 is equipped with a heater facility and has a structure that can be heated, and it is possible to make an inert atmosphere by introducing nitrogen from the nitrogen introduction pipe 3 after deaeration by the vacuum pump 4. It is. When the halogen-containing plastic is heated to a temperature of about 200 ° C. or more in an inert atmosphere in a state where the halogen-containing plastic is in the dehalogenation tank 2, the halogen-containing plastic releases a halogen or a halogen compound. The halogen or the halogen compound desorbed from the plastic enters the absorption tank 7 through the halogen transfer pipe 6. Water is contained in the absorption tank 7 through the water introduction pipe 5, and a stirring mechanism is attached. The halogen or the halogen compound is bubbled by being introduced from the lower end of the absorption tank 7, is absorbed by water, and becomes an acid containing halogen. The acid is subsequently introduced into the neutralization tank 9 where it undergoes a neutralization reaction with the alkali solution added through the alkali introduction tube 8 to form a halogen-containing salt. The absorption tank 7 and the neutralization tank 9 may be one tank, and a halogen compound may be introduced into an alkaline solution and bubbling may be performed to form a halogen salt. The aqueous solution containing the halogen-containing salt passes through the drier 10 to remove water, and becomes a solid halogen-containing salt. This salt is transported by the transport equipment 11 to the halogen salt storage tank 12 for storage.

On the other hand, the plastic subjected to the dehalogenation treatment is sent from the dehalogenation tank 2 to the storage tank 14 through the transport pipe 13. From here, it is supplied to the mixing tank 16 as needed. In the mixing tank 16, an amount of water required for supercritical processing is added via a water introduction pipe 15, and the mixture is slurried and introduced into a supercritical processing tank 18 by a slurry pump 17.
In addition, plastics, such as polyvinyl chloride, which melt at the temperature of the dehalogenation treatment, are directly transferred to the mixing tank 16 without being transferred to the storage tank, and are simultaneously solidified and slurried, or after solidification. It needs to be crushed and introduced into the mixing tank 16. The supercritical processing tank 18 is provided with a heating facility to keep the supplied slurry in a supercritical state, and has a sufficient pressure resistance against the pressure in the supercritical state. The plastic is decomposed in the supercritical processing tank 18, and the product is cooled by a cooler 20, and separated into a gas product 21 and a liquid product 22 by a gas-liquid separator 23.

In this process outline, the means for dehalogenating a halogen-containing plastic corresponds to the dehalogenation tank 2 and its associated equipment and the operations performed therein, and means for recovering the halogen compound separated from the plastic. Corresponds to the absorption tank 7, the neutralization tank 9, the dryer 10, the transport equipment 11, and the halogen salt storage tank 12, and the operations performed therein.

FIG. 2 shows an outline of another process using water as a supercritical fluid as an example to which the present invention is applied. In this example, the plastic is thermoplastic. The halogen-containing plastic powder is stored in a storage container 1 and transferred to a dehalogenation tank 2 equipped with a heating facility capable of providing a temperature difference between an upper portion and a lower portion. The transferred object is a mesh 24 finer than the powder particle size.
Is held on. In the dehalogenation tank 2, nitrogen is replaced by a vacuum pump 4 and a nitrogen introduction pipe 3. Thereafter, water is stored from the water introduction pipe 27 to the lower part of the tank. The amount of water is such that the water surface is below the mesh 24. When the dehalogenation tank is heated to about 200 ° C. in this state, a part of the halogen compound is desorbed from the halogen-containing plastic, and the gas component is stored in the gas halogen compound storage tank 26 through the gas halogen compound outlet pipe 25. When raising the temperature, a temperature difference is provided between the upper and lower portions of the tank so that all the water under the mesh 24 does not evaporate. As the plastic melts, it falls from the mesh 24 into the water below. Then, the plastic is solidified in a lump, and the remaining halogen component is dissolved in water to form a halogen compound aqueous solution. The aqueous solution of the halogen compound is connected to the halogen compound aqueous solution outlet pipe 28.
Is stored in the halogen compound aqueous solution storage tank 29.

On the other hand, the dehalogenated plastic is washed with water from the water introduction pipe 27 as necessary after the entire amount of the halogen compound aqueous solution has been sent. Thereafter, it is sent to the storage tank 14 and subjected to the supercritical decomposition treatment as in the example of FIG.

In the outline of this process, the means for dehalogenating a halogen-containing plastic corresponds to the dehalogenation tank 2 and its associated equipment and the operation thereof, and the means for recovering the halogen compound includes the dehalogenation tank 2 And the associated equipment, the gaseous halogen compound storage tank 26 and the halogen compound aqueous solution storage tank 29 and the operations performed therein.

FIG. 3 shows an example of still another process outline when the present invention is applied and water is used as a supercritical fluid. In this example, the halogen-containing plastic is thermoset. The halogen-containing plastic powder is transferred from the storage tank 1 to the dehalogenation tank 2. The dehalogenation tank 2 has a heating facility capable of forming a subcritical state of water and pressure resistance. The dehalogenation tank 2 is degassed by a vacuum pump 4,
After the inside is made into an inert atmosphere by introducing nitrogen from the nitrogen introduction pipe 3, water is introduced into the inside through the water introduction pipe 27. By heating in this state to form a subcritical state of water, the halogen component is eluted from the plastic to form a halogen compound aqueous solution. The aqueous solution passes through a halogen compound aqueous solution outlet pipe 28 and is stored in a halogen compound aqueous solution storage tank 29.

On the other hand, the plastic from which the halogen is eluted is again supplied with water in an amount necessary for the supercritical treatment through the water introduction pipe 27, mixed, and introduced into the supercritical treatment tank 18 by the slurry pump 17. The plastic is decomposed in the supercritical processing tank 18, and the product is cooled by a cooler 20, and separated into a gas product 21 and a liquid product 22 by a gas-liquid separator 23. In this example, the dehalogenation tank and the supercritical processing tank 18 can be combined into one vessel.

In this process outline, the means for dehalogenating a halogen-containing plastic corresponds to the dehalogenation tank 2 and its associated equipment and the operation thereof, and the means for recovering the halogen compound is defined as a halogen compound aqueous solution. This corresponds to the storage tank 29 and the operation there.

In the halogen-containing plastic, compared to the binding energy such as carbon-carbon bond, carbon-hydrogen bond, carbon-oxygen bond, etc. which form the skeleton structure of the plastic,
Since the carbon-halogen bond is relatively small, the bond is easily broken. Therefore, dehalogenation occurs under milder conditions than decomposition of the plastic skeleton structure. That is, as a means for dehalogenation, mild treatment such as heating in an inert atmosphere or under reduced pressure, elution in a subcritical fluid, or the like that does not decompose the plastic can be applied. For example, in the case of polyvinyl chloride, a dechlorination reaction occurs at about 190 ° C. in an inert atmosphere. By previously removing the halogen from the plastic, corrosion of the container due to release of the halogen from the plastic in the supercritical state can be prevented.

Subsequently, by recovering the halogen compound removed from the plastic, not only the organic compound which is the main component of the plastic but also the halogen component can be recycled, and the overall efficiency of material recycling from the plastic can be improved. Can be enhanced. As a method of recovering a halogen component, when a gaseous halogen compound is generated by the dehalogenation treatment, the halogen compound is collected as a solution as it is or as a solution after absorbing it in a liquid. When a liquid halogen compound is produced, the liquid is collected as a liquid. The halogen compounds obtained using these methods are highly reactive and can be reused for various chemical processes. Further, a method in which a halogen compound generated by dehalogenation is reacted and collected as a relatively stable salt can also be applied. As a substance which reacts with halogen to form a salt, a compound containing an alkaline element or an alkaline atomic group can be used. Here, the alkaline element indicates an alkali metal or an alkaline earth metal, and the alkaline atomic group indicates a basic polyatomic ion such as an ammonium ion or a pyridinium ion. Such a halogen salt of an alkaline element or an atomic group is a stable substance and is easy to handle.

By dehalogenating the halogen-containing plastic and recovering the generated halogen compound, it is possible to avoid remarkable corrosion of the container in the supercritical treatment, and to increase the amount of substances that can be reused by chemical recycling. be able to.

Hereinafter, the present invention will be described specifically with reference to examples.

(Embodiment 1) Using the apparatus shown in FIG.
A vinyl chloride-vinyl acetate copolymer plastic containing about 42% by weight of chlorine was heat-treated at 220 ° C. in a nitrogen atmosphere. The evolved gas was absorbed into water and the solution was contacted with calcium hydroxide. As a result of powder X-ray diffraction analysis, almost all the substance obtained from the dryer was calcium chloride. The amount of calcium chloride obtained was about 0.64 g per g of plastic. If all the chlorine comes out of this plastic and it is all calcium chloride, the theoretical amount is 0.657 g / g-plastic, and almost all the chlorine can be recovered from the plastic by this treatment. I understood. A part of the dechlorinated plastic was recovered, and the amount of chlorine in the plastic was determined using an ion chromatograph after bomb combustion. As a result, it was 170 ppm. This indicates that almost all chlorine in the plastic is desorbed by the dechlorination treatment as described above.

The dechlorinated plastic is crushed once,
Water was mixed with the mixture at a ratio of plastic: water = 1: 9 and supercritically treated at 300 ° C. for 30 minutes. The container after the treatment was cut and the cross section was observed with a scanning electron microscope. In the container, an altered layer having a slightly different composition was observed at a portion several micrometers from the inner surface, but no other change was observed.

On the other hand, as a result of performing the same supercritical treatment without performing the dechlorination treatment, the inner surface of the container after the treatment is several hundred μm
A corrosion layer was observed over m. In the corroded layer, several μm ~
In addition to a large number of large and small pits having a size of several hundreds of mm, many cracks having a length of several hundreds of μm were generated, and it was difficult to use the container repeatedly.

From these facts, by applying the present invention, it is possible to remove the halogen component from the plastic in advance, thereby suppressing the corrosion of the container in the supercritical treatment.

(Embodiment 2) Using the apparatus shown in FIG.
A polyvinyl chloride resin having a chlorine content of about 45% (weight ratio) was dechlorinated and then supercritically decomposed. The dehalogenation tank 2 with glass lining inside is pumped by a vacuum pump 4 to 0.1T.
After reducing the pressure to orr, nitrogen was introduced at 3 kg / cm ² . After water was introduced into the lower part of the tank, the temperature inside the tank was raised, and the temperature was adjusted so that the temperature near the mesh became 195 ° C and the temperature near the surface of the water became 80 ° C. Under this condition, the resin melts and generates hydrogen chloride while dripping from the mesh. A part of the generated hydrogen chloride remains in a gaseous state, and a part thereof adheres to the dropped polyvinyl chloride and dissolves in water.

The amount of chlorine in the dechlorinated plastic was determined by ion chromatography after bomb burning, and was 0.4% by weight. It was found that most of the chlorine could be removed by this dechlorination treatment.

(Embodiment 3) Using the apparatus shown in FIG.
An epoxy resin of brominated bisphenol A type having a bromine content of about 12% by weight was debrominated, and this was subjected to supercritical decomposition. The epoxy resin finely pulverized to about 200 mesh was put into a dehalogenation tank 2 having a pressure-resistant structure, and was replaced with nitrogen by using a vacuum pump 4, water was added, and the mixture was heated to 250 ° C. After holding for 45 minutes, the temperature was lowered, and the aqueous solution was taken out and analyzed. As a result, hydrogen bromide was recognized. The amount of bromine contained in the debrominated resin was determined using an ion chromatograph after bomb burning, and as a result, was 0.9% by weight.

Water was mixed with the debrominated resin, which was subjected to a supercritical treatment at 400 ° C. for 30 minutes. Remove the treated container from the device, seal both ends, and press the hydrostatic press (CI
P), the container was repeatedly subjected to a pressure test at a pressure of 50 MPa. As a result, no damage was found in the container even after 10 pressure tests.

On the other hand, without performing the debromination treatment, a supercritical treatment was performed in the same manner. This container was also removed from the apparatus, both ends were sealed, and a pressure test was similarly performed by repeatedly applying pressure by CIP. As a result, after the second pressure test, the container was deformed such that the center portion was depressed. As a result of observing the cross section of this container with a scanning electron microscope, an altered layer of several hundred μm was formed on the inner surface of the container, and many corrosion holes were observed.

As described above, when the dehalogenation treatment according to the present invention is performed, corrosion does not occur in the container subjected to the supercritical treatment, so that no problem occurs in the container even if the pressure test is repeated.

[0032]

According to the present invention, the corrosion of the processing container can be prevented when supercritically processing a plastic containing halogen. In addition, the proportion of reusable parts of the plastic can be increased.

[Brief description of the drawings]

FIG. 1 is a schematic diagram of a process when water is used as a supercritical fluid in an example of the present invention.

FIG. 2 is a schematic diagram of another process when water is used as a supercritical fluid in an example of the present invention.

FIG. 3 is a schematic view showing still another process when water is used as a supercritical fluid in an example of the present invention.

[Explanation of symbols]

1 ... storage container, 2 ... dehalogenation tank, 3 ... nitrogen introduction pipe,
4: vacuum pump, 5: water introduction pipe, 6: halogen transfer pipe,
7 ... absorption tank, 8 ... alkali introduction pipe, 9 ... neutralization tank, 10 ...
Dryer, 11 ... Conveying equipment, 12 ... Halogen salt storage tank, 1
3 ... transport pipe, 14 ... storage tank, 15, 27 ... water introduction pipe, 1
6 Mixing tank, 17 Slurry pump, 18 Supercritical treatment tank, 19 Cooling water inlet pipe, 20 Cooler, 21 Gas product, 22 Liquid product, 23 Gas-liquid separation device, 24
Mesh, 25 ... Halogen compound outlet tube, 26 ... Gas halogen compound storage tank, 28 ... Halogen compound aqueous solution outlet tube, 29 ... Halogen compound aqueous solution storage tank.

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Isao Okochi 7-1-1, Omikacho, Hitachi City, Ibaraki Prefecture Inside Hitachi Research Laboratory, Hitachi, Ltd. (72) Inventor Hisao Yamashita 7-1 Omikacho, Hitachi City, Ibaraki Prefecture No. 1 Inside the Hitachi Research Laboratory, Hitachi, Ltd.

Claims (4)

[Claims] 1. A method of decomposing a halogen-containing plastic using a supercritical fluid as a solvent, the method comprising a step of previously dehalogenating an object to be treated and a step of recovering a halogen compound separated from the plastic. A method for treating halogen-containing plastics. 2. A method for treating a halogen-containing plastic according to claim 1, wherein the method for dehalogenation is heating in an inert atmosphere or under reduced pressure, or elution in a subcritical fluid. 3. The method for recovering a halogen compound according to claim 1, wherein (a) a method in which a halogen compound generated in a gaseous state by dehalogenation is collected in a gaseous state; A method of absorbing a halogen compound generated in a gaseous state into a liquid and collecting the solution,
(C) a method in which a halogen compound or a halogen compound solution produced in a liquid state by dehalogenation is collected in a liquid state, (d) a halogen compound produced by dehalogenation, or a solution of the compound and an alkaline element or alkaline A method for treating a halogen-containing plastic, wherein a salt is formed by a neutralization reaction with a compound containing an atomic group, and any one of methods for collecting the salt or a solution of the salt is used. 4. An apparatus for decomposing a halogen-containing plastic using a supercritical fluid, comprising means for previously removing and recovering the halogen before bringing the plastic into contact with the supercritical fluid. Plastic processing equipment.