JP2005154517A - Method for chemical recycling of waste plastic and apparatus therefor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To ensure stable continuous operations of plants in a chemical recycling method for pyrolyzing waste plastics to reutilize them as raw materials for petrochemistry. <P>SOLUTION: A plurality of catalytic decomposition tanks filled with a silicate catalyst are installed and switched in turn to be repeatedly subjected alternately to a catalytic decomposition reaction operation and a catalyst generation reaction operation. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention has 2 to 4 carbon atoms that can be reused as a plastic raw material by treating mainly polyolefin-based plastics (polyethylene, polypropylene, etc.) among waste plastics, particularly waste plastics contained in waste such as municipal waste. Aromatic hydrocarbons such as olefin gas, fuel for fuel cells, hydrogen that can be reused as hydrogenation / desulfurization raw materials, and benzene, toluene, and xylene (hereinafter referred to as BTX) that can be reused as chemical / pharmaceutical raw materials. The present invention relates to a chemical recycling method for waste plastic that can be recovered with high efficiency.

  In recent years, a large amount of polymer waste (waste plastic) has been generated as waste such as municipal waste, and the disposal of such waste plastic has become a major social problem. The plastic production volume is the largest for polyolefin plastics (polyethylene, polypropylene, etc.), and the amount of waste plastic generated for this reason is the largest for polyolefin plastics. In recent years, separation and collection of PET bottles and foam containers has been promoted, but various plastic containers, plates, bags, strips, etc. are processed in a batch without being separated. .

Conventionally, as a method of recycling such waste plastic, a blast furnace raw material method, an oil conversion method, a gasification method, and the like have been considered.
In the blast furnace raw material production method, waste plastic is added to the blast furnace raw material to be used as a reducing agent at the time of iron making, but it is finally discharged as carbon dioxide (CO ₂ ).
In the oil conversion method, waste plastic is thermally decomposed by heat treatment in the presence of an activated carbon catalyst supporting iron or platinum or in the absence of a catalyst, and then condensed by a condenser to contain carbon containing hydrogen (H ₂ ). A recovered oil in which various compositions of several 1 to 20 are mixed is obtained. This recovered oil is directly used as fuel in various combustion facilities, or is refined to obtain gasoline, and further, olefin gas, chemical / pharmaceutical raw materials, and the like are obtained.
In the gasification method, waste plastic is heated and decomposed at 600 to 1400 ° C., and the resulting decomposition gas is used as a raw material for synthesizing methanol and ammonia.

In the above blast furnace raw material production method, waste plastic is simply used as a reducing agent during iron making, but the amount used as a reducing agent in the blast furnace is limited, and is used in view of the amount of generated waste plastic. The amount is very small and the expected effect is small. In addition, waste plastic added as a reducing agent is simply emitted as carbon dioxide (CO ₂ ), so plastics made from petroleum resources are not recycled as petrochemical raw materials and are simply consumed. There is a problem of being done.

Also, in the oil production method, it is difficult to recover a specific compound because the composition of the recovered oil to be obtained is diverse. In particular, olefin gas used as a plastic raw material, fuel for fuel cells, hydrogenation / desulfurization The recovery rate of hydrogen (H ₂ ) that can be used as a starting material, and benzene, toluene, and xylene (BTX) that can be used as a chemical / pharmaceutical raw material was low. In addition, since the composition of the recovered oil is diverse, a complicated refining process for extracting necessary components is required. Therefore, it is practically limited only to use as a fuel oil. In this case as well, there is a problem that it is simply recycled without being recycled as a petrochemical raw material.

In the gasification method, it is necessary to heat the waste plastic at a high temperature of 600 to 1400 ° C. in order to gasify the waste plastic by pyrolysis, which increases energy consumption and is also heat resistant for the production of the reactor. There is a problem that the cost of the apparatus is increased due to the necessity of the conductive material. The gasification method generates hydrogen (H ₂ ) and carbon monoxide (CO) by decomposing at high temperature, but more energy is required when synthesizing methanol, ammonia, etc. There is a problem of becoming. Such a method that requires a large amount of energy and equipment is difficult to adopt as a method for recycling waste plastic.

In addition, as described above, many containers containing halogen elements are mixed, such as containers and other materials molded with polyvinyl chloride, or bags and sheets that have been surface-treated with halogen elements to block air permeability. doing.
Waste plastics containing such halogen elements must be treated by separating and removing the halogen elements reliably due to the problem of environmental pollution. Generally, however, a method of simply incineration at high temperatures has been adopted. A new environmental pollution problem has occurred.

On the other hand, a chemical recycling method that effectively recycles waste plastic as a basic material of plastic has also been proposed (see, for example, Patent Document 1).
In view of the above circumstances, the present applicant also treated waste plastic with a dehalogenating element to reliably remove the halogen element, and from the dehalogenated waste plastic, olefin gas and hydrogen as a plastic raw material, and chemical / pharmaceutical A chemical recycling method and apparatus for waste plastic that can effectively recover BTX as a raw material has been proposed (see, for example, Patent Document 2).
This method includes a pretreatment step (I) for separating polyolefin plastics from other plastics from waste plastic, a thermal decomposition step (II) for vaporizing polyolefin plastics by pyrolysis, and gallium from the pyrolysis gas. Alternatively, the catalytic cracking step of reacting in the presence of a silicate catalyst containing boron to produce a gas phase component composed of an olefin component having 2 to 4 carbon atoms and hydrogen and a liquid phase component mainly composed of aromatic hydrocarbons. (III), a gas-liquid separation step (IV) for separating the gas phase component and the liquid component obtained in the catalyst decomposition step (III), and a gas phase component obtained in the gas-liquid separation step (IV) And a separation step (VI) for separating and obtaining benzene, toluene and xylene from the liquid phase component obtained in the gas-liquid separation step (IV) It is.

  According to the present invention, in the pretreatment process, the polyolefin plastic, which occupies most of the waste plastic, is effectively separated into other plastics, and the polyolefin plastic is vaporized in the thermal decomposition process. The pyrolysis gas is thermally decomposed in the presence of a silicate catalyst containing gallium or boron, so that the gas phase component mainly composed of hydrogen and olefins having 2 to 4 carbon atoms and the aromatic hydrocarbon are mainly composed. After generating a liquid phase component and then separating the gas phase component and the liquid phase component, hydrogen and olefin gas having 2 to 4 carbon atoms are obtained from the gas phase component, and BTX is fractionally obtained from the liquid phase component. Therefore, olefin gas having 2 to 4 carbon atoms can be reused as a raw material for plastics, and hydrogen can be reused as a fuel for fuel cells and as a raw material for hydrogenation / desulfurization. Can, the liquid phase can be reused as a chemical / pharmaceutical material by separating benzene, toluene, xylene by distillation. Therefore, there is an advantage that waste plastic can be effectively and efficiently chemically recycled.

Furthermore, if a dehalogenation element treatment step is performed between the pretreatment step and the thermal decomposition step to remove the halogen element by heating the polyolefin-based plastic separated in the pretreatment step, the waste plastic containing no halogen element is then added. In addition, since the waste plastic is in a molten state by heating in the dehalogenating element treatment step, there is an advantage that handling properties such as subsequent conveyance can be remarkably improved.
JP 2002-20533 A JP 2002-121318 A

  However, since only one catalytic cracking tank is installed in the above-mentioned chemical recycling method for waste plastics, the catalytic activity gradually decreases as the operation continues for a long time, and the target olefinic gas and aromatic hydrocarbons are reduced. The yield decreased, and eventually the operation had to be stopped and the catalyst regeneration treatment operation had to be performed, and the process could not be operated continuously, leading to an increase in time and required energy.

  The present invention improves the chemical recycling method for waste plastic, and by installing a plurality of catalytic cracking tanks, the catalytic cracking tanks for performing catalytic catalytic cracking reaction and catalyst regeneration treatment are switched alternately and continuously. This makes it possible to perform chemical recycling processing of plastics.

That is, the method for chemical recycling of waste plastic according to the present invention includes a pretreatment step for separating polyolefin plastic and other plastics from waste plastic, and a thermal decomposition step for vaporizing the separated polyolefin plastic by thermal decomposition. The pyrolysis gas obtained in the pyrolysis step is pyrolyzed in the presence of a silicate catalyst, and a gas phase component composed of hydrogen and a lower hydrocarbon having 2 to 4 carbon atoms and an aromatic hydrocarbon as main components. Obtained in the catalytic cracking step for producing a liquid phase component to be obtained, a step of separating hydrogen from the gas phase component leaving the catalytic cracking step to obtain lower hydrocarbons having 2 to 4 carbon atoms, and the catalytic cracking step Recycling of waste plastics with a process of separating the liquid phase components into aromatic hydrocarbons mainly composed of benzene, toluene and xylene In law, the catalyst decomposition step catalytic decomposition using multiple catalytic decomposition vessel and the chemical recycling process of sequentially repeating waste plastics steps of catalyst regeneration and optionally wait.
At least two catalyst decomposition tanks are installed. If there are two catalyst cracking tanks, the catalyst can be regenerated in the other catalyst cracking tank while the catalyst decomposition reaction of waste plastic is performed in one catalyst cracking tank. It becomes possible to perform chemical recycling processing of waste plastics.

  Furthermore, if a plurality of catalyst decomposition tanks of 3 or more are used, a standby process can be taken in addition to the catalyst decomposition reaction and the catalyst regeneration process. Therefore, the catalyst regeneration process can be performed regardless of the time required for each process. The necessary time can be ensured and the catalytic activity can be completely recovered, so that the target olefin gas component and aromatic hydrocarbon component acquisition rate can be maintained high.

  In the waste plastic chemical recycling method of the present invention, for example, it is preferable to operate by installing five catalyst decomposition tanks. In this case, if the catalyst decomposition reaction is 8 hours, the catalyst regeneration process is 24 hours and the standby time is 8 hours, and the total 40 hours is sequentially switched as one cycle, operation with a high acquisition rate that fully recovers the catalyst activity. Can be maintained continuously.

Further, the catalyst regeneration treatment is initially performed by a method comprising two steps of heating to 500 to 550 ° C. in air having an oxygen concentration of 5% or less, and normally heating to 525 ± 25 ° C. in air. preferable.
This is because the coking product adhered to the catalyst surface is burned and completely removed to recover the catalyst activity.

The waste plastic chemical recycling apparatus of the present invention includes a pretreatment facility for separating polyolefin-based plastic and other plastics from waste plastic, and melting for heating and melting the separated polyolefin-based plastic and supplying it to a thermal decomposition facility. An extruder, a pyrolysis tank that vaporizes the supplied molten polyolefin plastic by pyrolysis, and a pyrolysis gas obtained in the pyrolysis tank is thermally decomposed in the presence of a silicate catalyst to generate hydrogen and carbon number A plurality of catalytic cracking tanks for producing 2-4 lower hydrocarbons and aromatic hydrocarbons, a refluxer for separating high-boiling components from the gas exiting the plurality of catalytic cracking tanks, A gas phase component mainly composed of hydrogen and a lower hydrocarbon having 2 to 4 carbon atoms and a liquid phase mainly composed of an aromatic hydrocarbon by cooling the gas from which the gas is removed A condenser for separating the gas component, a gas separation device for separating a gas phase component separated by the condenser into hydrogen and a lower hydrocarbon having 2 to 4 carbon atoms, and a liquid phase component separated by the condenser as benzene, toluene, xylene A waste plastic chemical recycling device having a fractionation device for separating aromatic hydrocarbons such as the above.
Each catalyst decomposition tank is connected by piping, and a control valve is provided at the entrance and exit so that it can be switched to a catalyst decomposition tank that performs a catalyst decomposition reaction based on the operation schedule.
Since the waste plastic chemical recycling apparatus of the present invention has two or more catalyst decomposition tanks, the catalyst decomposition reaction and the catalyst regeneration treatment can be performed simultaneously in any of the catalyst decomposition tanks. It becomes possible to continuously maintain the chemical recycling operation of waste plastic with a high acquisition rate with the activity fully recovered.

  According to the present invention, it becomes possible to continuously maintain the chemical recycling operation of waste plastic with a high acquisition rate with the catalyst activity completely recovered, and the energy required for recycling is greatly reduced. As a result, the recycling of waste plastics can be performed more smoothly.

FIG. 1 shows a basic flow of the chemical recycling method for waste plastic according to the present invention.
In FIG. 1, reference numeral 1 denotes a pretreatment apparatus for pretreatment step (I) for carrying out waste plastic separation pretreatment. The pretreatment apparatus 1 converts at least waste plastic into polyolefin-based plastic and other plastics. A sorting device for separation is provided. As the sorting device, a light sorting method and a specific gravity difference sorting method are adopted. At this time, waste plastic contains a large number of containers made of polyolefin-based plastic. Therefore, it is preferable to sort such relatively large containers in advance by a light sorting method. Further, it is preferable that bags, belts or other broken plastic pieces contained in the waste plastic are crushed into a required size and sorted by a specific gravity difference sorting method.
In addition, it is necessary to wash a container or the like in which the contents remain in the waste plastic. For this purpose, the pretreatment device 1 includes a crushing device for crushing waste plastic in advance, or a crushed waste plastic. It is preferable to provide a cleaning device or the like that cleans.

In recent years, separation and collection of trash in each municipality has progressed, and at the same time, the Containers and Packaging Recycling Law has been enforced, and waste plastics have been collected. Currently, the annual discharge of waste plastics is about 9.8 million tons, of which about 50% is polyolefin plastics such as polyethylene and polypropylene. If polyolefin plastics, which account for a large proportion of waste plastics, can be converted into aromatic hydrocarbons (so-called BTX) and hydrogen, or lower olefins, which are the key raw materials of petrochemical industry, it can greatly contribute to the establishment of a recycling society. .
Analyzing the contents of waste plastic waste collected separately, polyethylene (PE) 18-37%, polypropylene (PP) 24-36%, polystyrene (PS) 11-36%, polyethylene terephthalate ( The actual situation is that 8-14% of PET), 1-2% of polyvinyl chloride (PVC), and 6-12% of foreign matters such as paper, disposable chopsticks and metal are included.

Among these waste plastic wastes, polyvinyl chloride contains about 73% of chlorine by weight, and a large amount of hydrogen chloride gas and harmful dioxins are generated when thermally decomposed at a high temperature of 300 to 600 ° C. Besides this, fluorine-based resin and waste coated with fluororesin also emit harmful fluorine gas when thermally decomposed at high temperatures.
Therefore, waste plastic waste containing halogen elements such as chlorine and fluorine must be treated with dedicated equipment equipped with exhaust gas treatment equipment such as chlorine and fluorine. It is also economically advantageous.
In the chemical recycling method for waste plastics using silicate catalysts, the presence of halogen elements such as chlorine, fluorine and bromine not only reduces the catalytic activity, making it impossible to maintain stable operation for a long time. And the recovery rate of aromatic hydrocarbons decreases. Therefore, in the present invention, in a chemical recycling method for recovering hydrogen, lower hydrocarbons, and BTX useful as chemical raw materials from waste plastic at low cost, the content of the plastic containing halogen element by separating waste plastic in a pretreatment step Is preferably less than 5 wt%. Further, the halogen element content is preferably less than 0.5 wt%, desirably less than 0.1 wt%.

  Waste plastic that has been sorted by the sorting device of the pretreatment device 1 and mostly made of polyolefin plastic is sent to the thermal cracking process (II) through the melt extruder 2 and is pyrolyzed for vaporization by thermal cracking. 3 is supplied. Further, other plastics than the polyolefin-based plastic selected by the pretreatment device 1 are separately processed by being routed to a separate process route that is equipped with a halogen element treatment device.

The melt extruder 2 is composed of a screw conveyor around which an electric heater is wound. The melted polyolefin plastic is heated to a temperature of about 200 ° C. or more and about 250 ° C. to be melted and supplied to the pyrolysis tank 3. is there.
When the polyolefin-based plastic is supplied in a solid state, a gas such as air is entrained to foam the molten bath, making it difficult to maintain a stable decomposition reaction. In order to prevent gas from being entrained, there is a method of supplying gas by extracting air to the decompression-like body, but there is a problem that supply is intermittent. Therefore, it is preferable to melt the polyolefin-based plastic and supply it to the thermal decomposition tank because it can prevent gas entrainment and can be continuously supplied while arbitrarily adjusting the supply speed. The heat-melted polyolefin-based plastic has a density of about 0.95 g / cm ³ and a viscosity of about 10 poise (p).

The thermal decomposition tank 3 has a stirring device 23 for stirring the waste polyolefin-based plastic inside, and is provided with a heater 12 on the outer periphery. The temperature of the waste plastic is about 650 ° C. or less, for example, about 500. It is heated to a temperature of ° C. and vaporized to generate a pyrolysis gas that lowers the molecular weight to a hydrocarbon having about 4 to 20 carbon atoms. In addition, when throwing the waste plastic into the thermal decomposition tank 3, an inert gas such as nitrogen gas is introduced into the thermal decomposition tank 3 in advance, and the waste plastic is heated in an inert gas atmosphere. preferable.
If a catalyst such as activated carbon or zeolite is used in the thermal decomposition tank 3, the heating temperature required for the reaction can be lowered, and the thermal decomposition rate of the waste plastic can be increased.

  The carbonaceous residue generated in the pyrolysis tank 3 is intermittently extracted into a decomposition residue discharge tank 4 provided at the bottom of the pyrolysis tank 3 and incinerated. At this time, when zeolite is used as the catalyst, the incinerated ash can be used again as the catalyst.

  The pyrolysis gas generated in the pyrolysis tank 3 is led to the catalyst decomposition step (III) through the filter 5. The filter 5 is obtained by heating a metal mesh having an opening of about 100 μm to about 500 ° C. The pyrolysis gas generated from the polyolefin-based plastic in a molten state in the pyrolysis tank 3 contains fine droplets. If the pyrolysis gas enters the catalyst reaction tank and adheres to the silicate catalyst as it is, the result is that the activity of the catalyst is impaired. . Therefore, it is preferable that fine droplets are captured by the filter 5 and reheated to be completely vaporized before being sent to the catalyst decomposition step (III).

In the catalyst decomposition step (III), a plurality of catalyst reaction tanks containing silicate catalysts are installed in parallel. In the catalyst decomposition step (III) of FIG. 1, an example is shown in which five catalytic reaction tanks (6-1, 6-2,... 6-5) are installed in parallel. These catalytic reaction tanks repeat the catalytic decomposition reaction, the regeneration reaction, and the standby according to a predetermined time schedule.
The catalyst reaction tank 6 includes a catalyst layer 8 filled with a silicate catalyst in an outer cylinder 7, and an internal temperature is arbitrarily set within a range of 350 to 600 ° C. by a heater 13 attached around the outer cylinder 7. It can be set.

As the silicate catalyst, a boron-containing silicate catalyst or a gallium-containing silicate catalyst can be used. The boron-containing silicate catalyst is preferably a proton-substituted H-type borosilicate, and the gallium-containing silicate catalyst is preferably H-type gallium silicate.
When a boron-containing silicate catalyst is used as the silicate catalyst, it has an effect of effectively generating a lower olefin gas having 2 to 4 carbon atoms from the pyrolysis gas, for example, 50 wt% or more, or 70% or more. Yields can be obtained. Thus, it is very advantageous in terms of plastic recycling to be able to obtain an olefin having 2 to 4 carbon atoms that can be reused as a raw material for plastic in a high yield.
Moreover, when using a gallium containing silicate catalyst as a silicate catalyst, it has the effect | action which produces | generates benzene, toluene, xylene, and hydrogen effectively.
Thus, what is necessary is just to use properly a silicate catalyst according to the kind of the collection | recovery raw material made into the objective.

  The catalytic decomposition reaction is performed by heating the pyrolysis gas generated in the pyrolysis tank 3 to 530 to 570 ° C. in the presence of a silicate catalyst. Since the catalytic decomposition reaction is an endothermic reaction, it is accompanied by a temperature drop of 65 to 75 ° C. with respect to the set temperature of the catalyst tank. The temperature drop is about the same whether using a gallium-containing silicate catalyst or a boron-containing silicate catalyst. If the amount of pyrolysis gas is constant, the temperature drop is also substantially constant, and stable operation can be maintained. Therefore, the constant supply of raw materials by the above-described melt extruder is effective.

  The duration of the catalytic cracking reaction is about 8 hours. If the operation is continued so much, the catalytic activity decreases. The decrease in the catalyst activity can be grasped from the composition of the recovered liquid and recovered gas generated by the catalytic decomposition reaction. In a normal and stable catalytic cracking reaction, the composition of the recovered liquid is 60 to 80 wt% as an aromatic hydrocarbon, and the composition of the recovered gas is 50 to 60 vol% of hydrogen gas as a main component. When the recovered liquid and recovered gas composition fall below the above values, it indicates that the catalyst activity has been reduced, and thus a catalyst regeneration process is required. When such a state is reached, the catalyst reaction tank having the catalyst layer that has been regenerated is switched to.

The catalyst regeneration treatment is performed by completely burning and removing the coking product adhered to the catalyst surface.
In the catalyst regeneration treatment, it is preferable to employ a method comprising two steps of initially heating to 500 to 550 ° C. in air having an oxygen concentration of 5% or less, and usually heating to 525 ± 25 ° C. in the latter period. The initial required time is approximately 10 hours, and the required time in the latter period is approximately 14 hours.
The catalyst regeneration reaction is an exothermic reaction accompanied by combustion, and the temperature in the catalyst reaction tank increases by 40 to 60 ° C. as the catalyst regeneration process proceeds. For this reason, it is preferable to initially suppress the oxygen amount to a low level to suppress a rapid temperature rise, and then increase the oxygen amount so that it is completely burned. This is because when the temperature is too high, the crystal structure of the catalyst changes and the catalytic activity decreases.

The progress of catalyst regeneration can be known by monitoring the gas composition. That is, the gas composition from the catalyst reaction tank is the same as the gas composition of the supply air by decreasing the CO and CO ₂ concentrations and increasing the O ₂ concentration. It takes about one day to complete the catalyst regeneration.

In order to completely recover the catalyst function, it is effective to perform a regeneration process taking a sufficient time. If there are two catalyst reaction tanks, alternate operation is possible for the time being, but there is a risk that regeneration of the catalyst may be insufficient. Therefore, it is preferable that the number of catalyst reaction tanks is large.
For example, in the present invention, an operation method is adopted in which the time required for the catalyst decomposition reaction and the catalyst regeneration process is taken into consideration, the standby time is set to 8 hours including the time required for other maintenance, and one cycle is performed for 40 hours. The method of continuous chemical recycling operation was adopted. In order to repeat one catalytic reactor in 40 hours per cycle, five catalytic reactors may be installed. The operation schedule of each catalyst reaction tank is shown in FIG.
As shown in FIG. 2, for example, while the No. 1 catalytic reactor is performing the catalytic decomposition reaction, the No. 2 catalytic reactor is in a standby state, and the No. 3 to No. 5 catalytic reactors are in two steps. The catalyst regeneration process is performed. That is, one unit is always in an operation state of the catalytic decomposition reaction, three units are in the regeneration process, and one unit is in a standby state.
By adopting such an operation schedule, it becomes possible to continuously perform chemical recycling operations of waste plastics, dramatically increase the processing capacity, and greatly reduce the required energy.

The gas emitted from the catalytic reaction step (III) is led to a refluxing device 14 which is a high boiling point component separation step (IV). In the reflux device 14, for example, a high boiling point component having a temperature of about 150 ° C. or higher is separated by condensation, and the separated high boiling point component is returned to the thermal decomposition tank 2.
The gas from which the high-boiling components have been removed by the reflux device 14 is led to a condenser 15 which is a gas-liquid separation step (V) and cooled, and a gas phase 16 mainly composed of an olefin gas having 2 to 4 carbon atoms and hydrogen, The liquid phase 17 is mainly composed of aromatic hydrocarbons such as benzene, toluene and xylene.
The gas phase from the condenser 15 is guided to a gas separation device 24 and separated into lower olefin gas having 2 to 4 carbon atoms and hydrogen by a cryogenic separation method or other methods.
Further, the liquid phase from the condenser 15 is led to the distillation column 18 to be separated into benzene, toluene and xylene (BTX).

According to the present invention, since an apparatus including a plurality of catalyst reaction tanks is used, a catalyst decomposition reaction can be performed in another catalyst reaction tank even during a catalyst regeneration process, and a continuous chemical recycling operation of waste plastic can be performed. It becomes possible, processing capacity increases dramatically, and required energy can be significantly reduced.
As a result, olefins having 2 to 4 carbon atoms, BTX and hydrogen are produced, and the olefin gas having 2 to 4 carbon atoms can be reused as a raw material for plastics, and hydrogen can be reused as a fuel for fuel cells and a raw material for hydrogenation / desulfurization. The liquid phase can be reused as a chemical / pharmaceutical raw material by separating it into benzene, toluene and xylene by a distillation column. Therefore, in the present invention, chemical recycling of waste plastic can be realized effectively and with high efficiency.

It is a figure which shows the basic flow of the chemical recycling method of the waste plastic of this invention. It is a figure which shows the operation schedule of a catalyst reaction tank.

Explanation of symbols

I: Pretreatment step, II: Thermal decomposition step, III: Catalyst decomposition step, IV: High boiling point decomposition step, V: Gas-liquid separation step,
DESCRIPTION OF SYMBOLS 1 ... Pretreatment apparatus, 2 ... Melt extruder, 3 ... Thermal decomposition tank, 4 ... Decomposition residue discharge tank, 5 ... Filter, 6・ ・ ・ ・ ・ Catalyst reaction tank, 7 ・ ・ ・ outer cylinder, 8 ・ ・ ・ catalyst layer, 11 …… stirrer, 12 …… heater, 13 ・ ・ ・Heater, 14 ... reflux, 15 ... condenser, 16 ... gas phase, 17 ... liquid phase, 18 ... distillation column, 19 ... ..Heavy residue receiving tank

Claims (5)

  A pretreatment process for separating polyolefin plastic and other plastics from waste plastic, a thermal decomposition process for vaporizing the separated polyolefin plastic by thermal decomposition, and a thermal decomposition gas obtained in the thermal decomposition process A catalytic cracking step for generating a gas phase component composed of hydrogen and a lower hydrocarbon having 2 to 4 carbon atoms and a liquid phase component mainly composed of an aromatic hydrocarbon by thermal decomposition in the presence of a silicate catalyst; The step of separating hydrogen from the gas phase component leaving the catalytic cracking step to obtain a lower hydrocarbon having 2 to 4 carbon atoms, and the liquid phase component obtained in the catalytic cracking step are mainly composed of benzene, toluene and xylene. In the chemical recycling method of waste plastics having a step of separating into aromatic hydrocarbons, the catalytic decomposition step using a plurality of catalytic decomposition tanks Degradation, chemical recycling method of waste plastics, characterized by sequentially repeating the waiting step according to the catalyst regeneration and necessary.   The method for chemical recycling of waste plastics according to claim 1, wherein two catalyst decomposition tanks are provided, and the decomposition and regeneration steps are alternately repeated in the two catalyst decomposition tanks.   The waste plastic chemical recycling method according to claim 2, wherein five catalyst decomposition tanks are provided, and the steps of decomposition, regeneration, and standby are sequentially repeated in the five catalyst decomposition tanks.   The catalyst regeneration step comprises two steps: a first step of heating to 500 to 550 ° C. in air having an oxygen concentration of 5% or less, and a second step of heating to 525 ± 25 ° C. in air normally. The method for chemical recycling of waste plastic according to any one of claims 1 to 3, wherein the method is a chemical recycling method. A pretreatment facility for separating polyolefin plastic and other plastics from waste plastic, a melt extruder for heating and melting the separated polyolefin plastic and supplying it to a thermal decomposition facility, and the supplied molten polyolefin system A pyrolysis tank for vaporizing plastic by pyrolysis, and pyrolysis gas obtained in the pyrolysis tank is thermally decomposed in the presence of a silicate catalyst to produce hydrogen, lower hydrocarbons having 2 to 4 carbon atoms, and aromatic carbonization. A plurality of catalytic cracking tanks for generating hydrogen; a refluxer for separating high boiling point components from the gas exiting the plurality of catalytic cracking tanks; Capacitor for separating gas phase component mainly composed of lower hydrocarbons having 2 to 4 carbon atoms and liquid phase component mainly composed of aromatic hydrocarbons, and separation by the capacitor Gas separation device for separating the gas phase component into hydrogen and lower hydrocarbons having 2 to 4 carbon atoms, and fractionation for separating the liquid phase component separated by the condenser into aromatic hydrocarbons such as benzene, toluene and xylene A plastic recycling apparatus for waste plastics.

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