JPH1067991A - Conversion of plastic waste into oil and apparatus therefor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a technique of economically carrying out a method for decomposing plastic wastes at a high speed, converting the plastic wastes into an oil and treating the plastic waste in a large amount in the treatment of the plastic wastes according to a supercritical water method and perform the industrialization of the treatment of the plastic wastes according to the supercritical water method. SOLUTION: A thermoplastic plastic waste 1 is used as a raw material to melt the plastic. Steam 8 at a temperature above the critical temperature under a pressure above the critical pressure fed from a boiler 7 to the molten plastic 3 is then added thereto. The decomposing reaction of the plastic 3 is carried out at 400-600 deg.C temperature under 22.1-50MPa pressure for <=10min reactional time using water in the supercritical region as a reactional medium. An oil or a mixture thereof with a combustible gas is then recovered from the resultant reactional product 9.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method and an apparatus for decomposing plastic waste into oil by a reaction using water in a supercritical region as a reaction medium. More particularly, the present invention relates to a method and an apparatus for decomposing plastic waste into oil by the above reaction using high-pressure steam such as a power generation boiler.

[0002]

2. Description of the Related Art Conventionally, most of various plastic wastes have been subjected to landfill or incineration, and are not effectively used as resources. In addition, landfill disposal has problems such as difficulty in securing land for landfill and instability of the ground after landfilling, and incineration has caused problems such as furnace damage, generation of harmful gases and odors. For this reason, the Containers and Packaging Waste Law was enacted in 1995, and the collection and reuse of plastics has become mandatory. In recent years, attempts have been made to recycle plastic waste in accordance with these circumstances, and one of them is a reaction using supercritical water (supercritical water) as a reaction medium (supercritical water). (Referred to as “reaction”), a method of decomposing plastic waste to oil and recovering useful oils (referred to as supercritical water method) has been proposed (Japanese Patent Application Laid-Open (JP-A) No. 56-501205, Japanese Patent Application Laid-open No.
-4225, JP-A-5-31000, JP-A-6-2
No. 79762 (see gazette)).

[0003] Supercritical water or supercritical steam means that the temperature is higher than the critical temperature (374 ° C) and the pressure is the critical pressure (22.1
MPa) Water or steam in the above state.
Since supercritical water easily penetrates into molten plastic oil droplets, the supercritical water method has a faster reaction than pyrolysis under normal pressure, produces less gas and residues, and achieves a high oil conversion rate. can do.

[0004] However, the technology for the treatment of plastic waste by the supercritical water method has not been sufficiently established at present, and particularly the problems of high-speed reaction, large-scale treatment of waste, and heating equipment. Overcoming and industrializing is urgent.
That is, in the conventional processing of plastic waste by the supercritical water method, batch processing is performed at a temperature of about 400 ° C. using a small cell.
It takes a long time of 0 minute or more, it is difficult to carry out a large amount of treatment, and the melting of plastic, reaction equipment and heat treatment therefor hindered industrialization of plastic waste treatment.

[0005]

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and is directed to a method for treating plastic waste by a supercritical water method in which plastic waste is decomposed, oiled, and mass-processed at high speed. It is an object of the present invention to provide a technology for economically processing plastic waste and to industrialize the processing of plastic waste by a supercritical water method.

[0006]

Means for Solving the Problems In order to achieve the above-mentioned object, the present inventors have developed a high-speed, large-scale, continuous, and economical method for decomposing and oiling plastic waste by supercritical water reaction. As a result of examining the means that can be carried out, the reaction was carried out under supercritical water conditions at a temperature of 420 ° C. or higher for polystyrene and 500 ° C. or higher for polyethylene, polypropylene, polyvinyl chloride, etc. In this case, for example, it has been found that plastic is decomposed and turned into oil in a short time of 2 minutes or less. As for the means of treating plastic waste by the supercritical water method, it has been found that a large amount can be treated by using a tubular continuous reactor, and furthermore, in order to obtain supercritical water, high-pressure steam from a power generation boiler or the like is used. In particular, it is economically advantageous to use steam having a temperature higher than the critical temperature and pressure and to melt the plastic waste by utilizing the heat of the reaction product. It has been found that the use of combustible gas and oil as fuel can generate more steam than used steam, and the present invention has been completed.

That is, according to the present invention, a thermoplastic resin waste containing at least one of polyethylene, polypropylene, polyvinyl chloride, and polystyrene is used as a raw material to melt the plastic, and then the critical temperature supplied from the boiler to the molten plastic is obtained. The above steam is added to perform a plastic decomposition reaction at a temperature of 400 to 600 ° C., a pressure of 22.1 to 50 MPa, and a reaction time of 10 minutes or less, using water in a supercritical region as a reaction medium. And apparatus for liquefying plastic waste to recover a mixture of flammable gas and plastic, and furthermore, plastic waste using oil or flammable gas obtained from liquefaction of plastic waste as fuel for the boiler An object of the present invention is to provide a method and an apparatus for liquefying a product.

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail.
The types of plastics that can be processed in the present invention are mainly thermoplastic resins, including partially cured resins, and can be single types, mixtures, or composite materials such as alloys. You may. As the thermoplastic resin, polyethylene, polypropylene, poly-4-methylpentene-1, ionomer, polystyrene, AS resin, AB
Examples include S resin, polyvinyl chloride, polyvinylidene chloride, methacrylic resin, polyvinyl alcohol, EVA, and cellulosic plastic. Preferably, it is a plastic waste containing at least one general-purpose plastic such as polyethylene, polypropylene, polystyrene, or polyvinyl chloride.

The plastic waste is pulverized if necessary.
After performing pretreatment such as separation and separation, it is heated and melted. When a gas such as hydrogen chloride is generated at the time of thermal melting, the gas can be separated and removed, washed and recovered, or neutralized. The plastic waste may be supplied to a vertical or horizontal melting tank using a feeder or the like. Melting of plastic waste is 200-400 ° C., preferably 250-3
Performed at 50 ° C. Heat melting is performed in a melting tank, may be melted alone with plastic, may be melted in a dispersed state in heated water, may be dissolved in oil obtained by the reaction, or may be dissolved in oil. The dissolved matter may be dispersed in the heated water.

When the plastic is melted alone or dissolved in the oil obtained by the reaction, these may be mixed with water after leaving the melting tank and dispersed in heated water. . For transporting molten plastic alone,
A press-fitting device with a single or twin screw can be used. Chlorine-containing plastics such as polyvinyl chloride generate hydrogen chloride gas at the time of heat melting and reaction, and generate hydrochloric acid when condensed water is generated, resulting in significant corrosion of the material. Therefore, it is desirable to separate and remove the generated hydrogen chloride in the gas phase. Furthermore, equipment using an acid-resistant material such as Hastelloy C or carbait is required. Alternatively, a basic substance, for example, ammonia, caustic soda, sodium carbonate, or the like can be added in an amount corresponding to the acidic substance generated during melting or reaction.

The advantage of dissolving plastic waste in the obtained oil is that pretreatment such as cutting of plastic waste is unnecessary or reduced, dissolution is easy, processing can be performed in a short time, and the obtained liquid Is easy to transport because the viscosity is reduced. In addition, high melting point resin in plastic waste,
Non-melting materials such as thermosetting resins, inorganic fillers, especially short fibers, long fibers or whiskers such as glass and carbon, or mixed metal pieces are easily removed from plastics to be melted by filtration means, centrifugal separation means, etc. can do. These oils naturally do not hinder the cracking reaction.

The temperature of the reaction using water in the supercritical region as a reaction medium is 400 ° C. or higher, preferably 500 ° C. or higher. It is about 600 ° C. from the point. The reaction temperature depends on the type of plastic and the processing time, for example,
In the case of polystyrene, at 420 ° C or higher, polyethylene,
In the case of polypropylene, polyvinyl chloride or the like, the plastic is decomposed and turned into oil in a short time of 2 minutes or less when the reaction is performed at 500 ° C. or higher. The reaction pressure was 22.1
~ 50MPa, preferably 23 ~ 30MPa,
It depends on the type of the plastic and the processing time.

When the weight ratio of plastic waste / water is too low, it is economically disadvantageous if it is less than 0.1. Since a high-viscosity material is formed, preferably 0.15
０．５0.5. The treatment time (reaction time with supercritical water) is 0.1 to 10 minutes, preferably 2 minutes or less.
What is supplied to the reaction zone may be the molten plastic alone, may be dispersed in high-temperature water, may be dissolved in oil, or may be dissolved in oil dispersed in heated water. It may be in the state of being done. The decomposition conditions are
It is selected depending on the temperature, pressure, and amount of steam that can be used, the type and amount of plastic waste, the time to be treated, and the like, and the combustible gas / oil ratio and the heavy / light oil ratio of the oil component can be widely changed.

As the reactor, various types such as a tube type, a tower type, a tank type, and a multi-stage tank type can be used. The reaction operation can be performed in a continuous or semi-batch mode, or a quasi-continuous batch mode such as tank type switching. By using a tubular continuous reactor as the reactor, it is possible to increase the speed of the reaction, mass-process the reactor, and reduce the size of the reactor. The material of the reactor is metal,
Ceramics, carbates, glass, or linings thereof may be used. As a metal material,
Special steels such as Ni, Cr, V, and Mo, and austenitic stainless steels may be used.

The flammable gas and oil obtained by the above decomposition treatment vary depending on the type of raw material and the processing conditions. In the case of polystyrene, however, the flammable gas content is small, the decomposition product oil is mostly contained, and polyethylene and polypropylene are used. 1 if
5-20% of a hydrocarbon-based flammable gas and the remainder of the cracked product oil are produced. The total yield of these fuels is 90 to 100%, none of them contain sulfur, heavy metals, etc., and the total heat of combustion shows a calorific value comparable to heavy oil. Therefore, for example, if fuel is obtained by treating the plastic waste / water at a weight ratio of 1/3, about 300 kg of fuel can be obtained from 1 / 3t of plastic waste and 1t of steam, which is a supercritical fuel. This corresponds to the fuel required to generate about 3 tons of steam in the state.

The steam used is a large private power generation boiler,
Boilers from electric utility boilers can be used. Even if the temperature and pressure are both above the critical point, the pressure is below the critical pressure, but the temperature is superheated above the critical temperature and added to the molten plastic or mixture of molten plastic and water, Any steam capable of performing a plastic decomposition reaction using water in a critical region as a reaction medium can be used. Specifically, such steam has a temperature of 500 ° C. or higher, a pressure of 8 MPa, a temperature of 570 ° C.,
For a boiler for electric power business with a high output of 17.4 MPa, the temperature is 542 to 567 ° C. and the pressure is 2
5.1MPa, especially the most recent boilers for thermal power generation are above the critical point, and the supercritical state from the once-through boiler of the supercritical pressure variable pressure operation and the supercritical pressure combined circulation type variable pressure once-through boiler Is preferably used.

Therefore, the apparatus of the present invention can be attached to an existing boiler, or by simultaneously constructing and using the apparatus and the boiler, to use steam economically and to use the obtained fuel such as oil effectively. Can be used for Since the reaction mass after the decomposition reaction is at a high temperature, it is used for heating the melted plastic and further used for melting the plastic waste. Large private power generation boiler,
For power business boilers, etc., the amount of generated steam is several hundred t / hr.
To several thousand t / hr, while the throughput of plastic waste is several hundred kg / hr to several thousand kg / hr. As described above, since the weight ratio of plastic waste / water is practically in the range of 0.15 to 0.5, equipment such as a large private power generation boiler and a boiler for an electric power business includes steam for power generation. Although there is a small decrease in the volume, it is possible to share steam for plastic waste treatment in view of the importance of plastic waste treatment and the effective use of the obtained fuel.

FIG. 1 shows an example of the method and the apparatus of the present invention.
This will be described with reference to FIG. The plastic waste 1 that has been pre-treated as necessary is supplied to a melting tank 2 having a stirrer (not shown). For example, 250 ° C.
Hot, pressurized water, and the molten plastic and water are stirred to form dispersion 3. The melting tank 2 is provided with a heat exchange pipe 4 such as a coil and a coiled pipe inside. The dispersion is heated by a plastic decomposition product by supercritical water flowing through the heat exchange pipe 4. The dispersion (molten plastic) 3 discharged from the melting tank 2 is heated through a preheater 5 if necessary, and supplied to a reactor 6. On the other hand, high-temperature steam 8 is supplied from a boiler 7 to the reactor 6, and a decomposition reaction by supercritical water occurs to generate a reaction product 9.

The reaction product 9 discharged from the reactor 6 is cooled by the preheater 5, supplied to the melting tank 2 and used for melting the plastic waste 1, and further cooled by the heat exchanger 10 if necessary. Is supplied to a gas-liquid separator 11 to be separated into a gas component 13 and a liquid component. The liquid component is further separated in a separator 12 into an oil layer 14 and an aqueous layer 15. The water layer 15 is reused for melting the plastic waste 1. The oil layer 14 may be used as fuel for the boiler 7 as it is,
It may be fractionated and divided into various boiling components. The gas component 13 can be generated by the fuel of the boiler 7, and when hydrogen gas or the like is contained, the gas component 13 may be passed through a post-processor 16 or the like for removal. As another method, the reaction product 9 is supplied to the melting tank 2 and used for melting the plastic waste 1, and then, by flash distillation or the like, a high-boiling residue oil, a gas, a low-boiling fraction oil, and water are used. And the high boiling residual oil may be used for dissolving the plastic waste 1. The obtained gas and oil content, when used for fuel, is less sulfur and heavy metal content causing pollution compared to heavy oil and coal,
The calorific value during combustion is also high. The oil can also be used as a hydrocarbon-based solvent.

[0020]

EXAMPLES The present invention will now be described specifically with reference to examples, but the present invention is not limited to these examples. Examples 1 to 4 Melting and decomposition were carried out using the apparatus shown in FIG. 1 and plastic waste 1 and steam having the composition shown in Table 1. In addition, in Example 3, the oil added at the time of dissolution was used by collecting the flash distillation residue.

The results are shown in Table 1. As can be seen from Table 1, when the supercritical water reaction is performed, it is possible to continuously melt and decompose a large amount of plastic waste in a short period of time as compared with the case of thermal decomposition. It could be obtained in yield. The amount of the obtained fuel gas and oil was converted into a calorific value and was equal to or more than the calorific value of the steam used for dispersion. Also, by dissolving the raw plastic waste in the recovered oil, pretreatment such as shredding of the raw material is eased, the dissolving time is shortened, and the removal of foreign substances and inorganic fillers in the raw material is facilitated, The equipment can be operated continuously for a long time.

[Table 1]

[0022]

According to the present invention, plastic waste can be decomposed and turned into oil, and the obtained fuel can be reused in a boiler.
A technique has been obtained for treating plastic waste in large quantities, at high speed and economically.

[Brief description of the drawings]

FIG. 1 is a system flow diagram illustrating an example of the method and apparatus of the present invention.

[Explanation of symbols]

 Reference Signs List 1 plastic waste 2 melting tank 3 molten plastic 4 heat exchange pipe 5 preheater 6 reactor 7 boiler 8 water vapor 9 reaction product 10 heat exchanger 11 gas-liquid separator 12 separator 13 gas component 14 oil layer 15 water layer 16 after Processor

Claims (13)

[Claims] 1. A method for melting a plastic from a waste of thermoplastics as a raw material, and adding steam having a critical temperature and a pressure higher than a critical temperature supplied from a boiler to the molten plastic, thereby converting water in a supercritical region into a reaction medium. As temperature 400-6
A method for liquefying plastic waste in which a plastic decomposition reaction is performed at 00 ° C., a pressure of 2.1 to 50 MPa, and a reaction time is 10 minutes or less, and oil or a mixture of oil and flammable gas is recovered from the reaction product. 2. The thermoplastic resin is polyethylene,
The method for liquefying plastic waste according to claim 1, comprising at least one of polypropylene, polyvinyl chloride, and polystyrene. 3. Decomposition reaction is performed at 500-600 ° C., 22.1
The method for liquefying plastic waste according to claim 1 or 2, wherein the reaction is performed using water in a supercritical region of -40 MPa as a reaction medium. 4. The method according to claim 1, wherein the decomposition reaction time is 2 minutes or less. 5. The method according to claim 1, wherein the steam to be added is steam having a supercritical point or higher. 6. The method according to claim 1, wherein the boiler is a thermal boiler. 7. The method according to claim 1, wherein the raw material plastic waste is melted by heat exchange with a reaction product. 8. The method according to claim 1, wherein the raw plastic waste is melted by adding oil obtained by oiling the plastic waste. 9. The method according to claim 1, wherein water is added to the molten plastic to make a mixed dispersion of water and plastic, the mixture is preheated, and then steam is added. 10. The method for liquefying plastic waste according to claim 1, wherein oil or flammable gas obtained by liquefying plastic waste is used as fuel for the boiler. 11. A melting tank equipped with a stirrer and a heat exchange pipe, a reactor, a boiler, and a separator. The thermoplastic resin waste is used as a raw material to melt the plastic in the melting tank, and then supplied to the reactor. At the same time, add steam above the critical temperature and pressure supplied from the boiler to the reactor,
A plastic decomposition reaction is performed using water in the supercritical region as a reaction medium, and a reaction product is obtained.The reaction product is led to a heat exchange pipe of a melting tank, and the heat is used to melt the raw material plastic waste and then separated. An apparatus for liquefying plastic waste, which is configured to separate and collect water and oil or water, oil and flammable gas by a vessel. 12. An oil converting apparatus comprising a melting tank equipped with a stirrer and a heat exchange pipe, a reactor, and a separator is attached to a thermal power generation boiler. After melting in the tank, it is supplied to the reactor, and at the same time, steam over the critical temperature and pressure supplied from the thermal power boiler is added to the reactor, and the plastic decomposition reaction is performed using water in the supercritical region as the reaction medium. After the reaction product is obtained, the reaction product is led to a heat exchange pipe of a melting tank, and the raw material plastic waste is melted by the heat, and then separated into water and oil or water, oil and flammable gas by a separator. Separation, recovery, and oil purification equipment for plastic waste that uses the obtained oil or oil and combustible gas as boiler fuel. 13. The apparatus for liquefying plastic waste according to claim 11, wherein the reactor is a tubular continuous reactor.