Method and apparatus for converting plastics into oil.

Abstract

The present invention provides a plastic liquefaction method and apparatus that reduce the risk of fire and produce low-molecular-weight recycled oil in the process of thermally decomposing waste plastics into plastic liquefaction. [Solution] This method for converting plastics into oil is characterized by thermally decomposing uncrushed waste plastics in a thermal decomposition furnace and then contacting the resulting gas with a catalyst in the thermal decomposition furnace to reduce its molecular weight.

Description

Technical Field

[0001] This invention relates to a method for plastic oilification and a plastic oilification apparatus.

Background Art

[0002] Plastics derived from petroleum are used in various applications today, and as a result, the amount of plastic waste is increasing year by year worldwide. Since petroleum is a finite resource and plastic pollution of the marine environment is a matter of concern, technologies for recycling or reusing waste plastics have attracted attention.

[0003] Plastic oilification is a method of decomposing waste plastics into recycled oil and has attracted attention as a type of chemical recycling. For example, Patent Document 1 discloses a method of cooling and liquefying the gas obtained by thermally decomposing waste plastics to obtain recycled oil. Further, Patent Document 2 describes a plastic oilification method using supercritical carbon dioxide, and Patent Document 3 describes a method of dissolving waste plastics in a raw material oil and then performing a decomposition process. Furthermore, as described in Patent Document 4, it is known that in plastic oilification technology, a catalyst can be used to reduce the molecular weight of recycled oil.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Patent Document 2

Patent Document 3

Patent Document 4

Summary of the Invention

Problems to be Solved by the Invention

[0005] In recent years, the risk of fire at plastic liquefaction sites has become a major problem. Typically, waste plastics discharged from households and other sources are formed into bales to facilitate transportation and storage. After being transported to a decomposition plant, the baled waste plastics are crushed and fed into the decomposition equipment. Fires in plastic liquefaction are often caused during this crushing process when flammable foreign objects mixed in with the plastic, such as lighters, dry cell batteries, or rechargeable batteries, are destroyed and ignite.

[0006] Furthermore, in conventional low-molecular-weight methods using catalysts, the catalytic activity is sometimes insufficient, resulting in the recycled oil's molecular weight not being sufficiently reduced. In such cases, the recycled oil becomes highly viscous and solidifies at low temperatures. Consequently, it not only fails to meet the required oil quality standards but also causes clogging of the equipment.

[0007] The present invention aims to provide a method and apparatus for converting plastics into oil that reduces the risk of fire during plastic crushing and produces recycled oil that is sufficiently low in molecular weight and viscosity. [Means for solving the problem]

[0008] The inventors of this invention diligently studied how to solve the above problems and, as a result, discovered that the above problems can be solved by pyrolyzing uncrushed waste plastic in a pyrolysis furnace and then contacting the resulting gas with a catalyst in the pyrolysis furnace to reduce its molecular weight, thereby completing the present invention.

[0009] In other words, the gist of this invention is as follows: [1] A method for converting plastics into oil, comprising a pyrolysis step of heating uncrushed waste plastics in a pyrolysis furnace to generate pyrolysis gas, and a condensation step of cooling the pyrolysis gas to obtain recycled oil, wherein the pyrolysis gas comes into contact with a catalyst installed inside the pyrolysis furnace to be reduced in molecular weight, and is then sent to the condensation step. [2] The plastic oil conversion method according to [1] above, wherein the uncrushed waste plastic includes at least one selected from polyethylene, polypropylene, and polystyrene. [3] The plastic oil conversion method according to [1] above, wherein the uncrushed waste plastic contains foreign matter. [4] The method for converting plastics into oil according to [1] above, characterized in that an inert gas is introduced into the furnace during the pyrolysis step. [5] The method for liquefying plastics according to [1] above, wherein the catalyst is at least one selected from silica-alumina, synthetic zeolite, and natural zeolite. [6] The method for converting plastics into oil according to [1] above, further comprising a gas re-decomposition step in which the pyrolysis gas is passed through a catalyst installed outside the pyrolysis furnace to decompose the pyrolysis gas into smaller molecules. [7] The method for converting plastics into oil according to [1] above, further comprising a recycled oil demolition step in which recycled oil is brought into contact with a catalyst installed outside the pyrolysis furnace to demolition the recycled oil into low molecular weight oil. [8] The method for liquefying plastics according to [6] or [7] above, wherein the catalyst is at least one selected from silica-alumina, synthetic zeolite, and natural zeolite. [9] A plastic oil conversion apparatus comprising a pyrolysis furnace that pyrolyzes plastic to produce pyrolysis gas, and a condenser that cools the pyrolysis gas to obtain recycled oil, wherein a metal container containing uncrushed waste plastic and a catalyst case containing a catalyst are arranged inside the pyrolysis furnace.

[10] The plastic oil liquefaction apparatus according to [9] above, wherein the catalyst is at least one selected from silica-alumina, synthetic zeolite, and natural zeolite. [Effects of the Invention]

[0010] According to the present invention's oil conversion method and apparatus, there is no need to crush waste plastics, thus significantly reducing the risk of fire. Furthermore, according to the present invention's oil conversion method and apparatus, it is possible to enhance catalytic activity, thereby obtaining high-quality recycled oil with low molecular weight and high fluidity. [Brief explanation of the drawing]

[0011] [Figure 1] A schematic diagram of an example of a batch-type pyrolysis furnace. [Figure 2] A schematic diagram of an example of a continuous pyrolysis furnace. [Modes for carrying out the invention]

[0012] The embodiments of the present invention will be described in detail below. Note that the following description is merely an example (representative example) of the embodiments of the present invention, and the present invention is not limited to these contents unless it exceeds the essence of the invention.

[0013] The present invention provides a method for converting plastics into oil, which first includes a step (thermal decomposition step) in which waste plastics are thermally decomposed in a thermal decomposition furnace to obtain thermal decomposition gas. The waste plastic used in this invention preferably contains at least one selected from polyethylene, polypropylene, and polystyrene. Furthermore, while compressed waste plastic in the form of a bale approximately 1 meter on each side can be used, uncompressed waste plastic can also be used. The waste plastic may also contain foreign matter, such as metal parts found in plastic furniture, batteries found in toys, mobile batteries, lighters, etc. In the method of this invention, the waste plastic does not need to be crushed as preparation before being fed into the pyrolysis furnace; it can be processed in the pyrolysis furnace in the form of bale-shaped waste plastic or furniture.

[0014] A batch-type or continuous-type pyrolysis furnace can be used as the pyrolysis furnace in the oil conversion method of the present invention.

[0015] FIG. 1 is a schematic view of an example of a batch-type pyrolysis furnace. The pyrolysis furnace 1 shown in FIG. 1 includes a metal container 12 containing uncrushed waste plastic 11 and a catalyst case 22 containing a catalyst 21 inside. The pyrolysis furnace 1 also includes a metal container loading / unloading port 31, an inert gas inlet 32, a pyrolysis gas outlet 33, and a gas recovery line 34, and has a heat source 41 outside. The pyrolysis furnace 1 can also include a thermometer, an oxygen concentration system, and a heat source adjustment device not shown.

[0016] In the pyrolysis process using the batch-type pyrolysis furnace, the uncrushed waste plastic 11 is loaded onto the metal container 12 and carried into the pyrolysis furnace 1 through the metal container loading / unloading port 31. By heating the pyrolysis furnace 1 to a predetermined temperature, the waste plastic 11 is pyrolyzed to generate pyrolysis gas. The temperature and time of pyrolysis are set as appropriate, but it is preferable that the temperature inside the pyrolysis furnace is 350 to 550 °C and the treatment is carried out for about 9 hours. When the generated pyrolysis gas passes through the catalyst case 22, it contacts the high-temperature catalyst 21 and is reduced in molecular weight, and is discharged from the pyrolysis gas outlet 33 to the pyrolysis gas recovery line 34. Therefore, the catalyst case 22 needs to have a structure through which the pyrolysis gas can pass. Also, the catalyst case 22 is preferably arranged so that substantially all of the generated pyrolysis gas can contact the catalyst 21. As one aspect, the catalyst case 22 can be arranged in contact with the pyrolysis gas outlet 33 and covering the pyrolysis gas outlet 33 as shown in FIG. 1. As another aspect, the catalyst case 22 can be installed on top of the metal container 12 as a lid member of the metal container 12 (not shown). The catalyst 21 is granular and is at least one selected from silica-alumina, synthetic zeolite, and natural zeolite. From the perspective of cost, it is preferable to use natural zeolite as the catalyst of the present invention. The size of the catalyst 21 particles is preferably 3.3 to 6.3 mm from the perspectives of treatment speed, yield, and the properties of the obtained recycled oil. The amount of the catalyst used is preferably 50 to 60% of the weight of the waste plastic. In the present invention, since the catalyst case 22 is installed inside the pyrolysis furnace 1, the temperature of the catalyst 21 is kept high, so the activity of the catalyst increases, and it becomes possible to sufficiently reduce the molecular weight of the pyrolysis gas.

[0017] In a batch-type pyrolysis furnace, the heat source 41 is arranged outside the pyrolysis furnace 1. The pyrolysis furnace 1 is directly heated from the outside by the heat source 41 or heated through a heat medium by the heat source 41. As the heat source 41, a burner can be used.

[0018] Further, the pyrolysis furnace 1 has an inert gas inlet 32, and an inert gas such as nitrogen can be introduced into the interior. It is preferable to perform pyrolysis while introducing an inert gas, and the risk of fire can be reduced.

[0019] FIG. 2 shows a schematic view of an example of a continuous pyrolysis furnace. The continuous pyrolysis furnace 51 shown in FIG. 2 is a tunnel-shaped pyrolysis furnace partitioned into a first unit 52, a second unit 53, and a third unit 54 by partitions 55a and 55b. A metal container 62 containing uncrushed waste plastic 61 is conveyed through the tunnel from the first unit toward the third unit. Further, the pyrolysis furnace 51 includes a catalyst case 72 containing a catalyst 71, a metal container inlet 81, an inert gas inlet 82, a pyrolysis gas outlet 83, a gas recovery line 84, and a metal container outlet 85, and has a heat source 91 outside. Further, the pyrolysis furnace 1 can include a thermometer, an oxygen concentration system, and a heat source adjustment device not shown.

[0020] The metal container 62 containing the uncrushed waste plastic 61 is first brought into the first unit 52 from the metal container entrance 81 with partitions 55a and 55b closed. The first unit 52 is a preheating unit. The waste plastic 61 in the metal container 62 is heated to a predetermined preheating temperature in the first unit 52, after which partition 55a is opened and the metal container 62 is transported to the second unit 53. However, if other metal containers are contained in the second unit 53 and thermal decomposition is being carried out, partition 55a is opened only after the thermal decomposition is complete and the other metal containers have been transported from the second unit 53 to the third unit 54. Here, the preheating temperature is set as appropriate, but it is preferably 200 to 250°C. Once the metal container 62 is transported to the second unit 53, partition 55a is closed again.

[0021] The second unit 53 is a unit for the main heating process. By heating the second unit 53 to a predetermined temperature, the waste plastic 61 is thermally decomposed, generating pyrolysis gas. The temperature and time of pyrolysis are set as appropriate, but it is preferable that the temperature inside the pyrolysis furnace be 350-550°C for about 7 hours. The generated pyrolysis gas comes into contact with the high-temperature catalyst 71 as it passes through the catalyst case 72, is broken down into smaller molecules, and is discharged from the pyrolysis gas outlet 83 to the pyrolysis gas recovery line 84. Therefore, the catalyst case 72 needs to have a structure that allows the pyrolysis gas to pass through. It is also preferable that the catalyst case 72 be positioned so that substantially all of the generated pyrolysis gas comes into contact with the catalyst 71. In one embodiment, the catalyst case 72 can be positioned in contact with the pyrolysis gas outlet 83 and cover the pyrolysis gas outlet 83, as shown in Figure 2. In another embodiment, the catalyst case 72 may be installed on top of the metal container 62 as a lid member of the metal container 62 (not shown). The catalyst 71 is granular and is at least one selected from silica-alumina, synthetic zeolite, and natural zeolite. From the viewpoint of cost, it is preferable that the catalyst of the present invention uses natural zeolite. The particle size of the catalyst 71 is preferably 3.3 to 6.3 mm from the viewpoint of processing speed, yield, and the properties of the recycled oil obtained. The amount of catalyst used is preferably 50 to 60% of the weight of the waste plastic. In this invention, the catalyst case 72 is installed inside the pyrolysis furnace 51, which keeps the temperature of the catalyst 71 at a high temperature. This increases the activity of the catalyst, making it possible to sufficiently reduce the molecular weight of the pyrolysis gas.

[0022] In a continuous pyrolysis furnace, the heat source 91 is located outside the pyrolysis furnace 51. The pyrolysis furnace 51 is heated directly from the outside by the heat source 91, or heated by the heat source 91 via a heat transfer medium. A burner can be used as the heat source 91.

[0023] Furthermore, the pyrolysis furnace 51 has an inert gas inlet 82, allowing an inert gas such as nitrogen to be introduced into the second unit 53 during pyrolysis. It is preferable to carry out pyrolysis while introducing an inert gas, which can reduce the risk of fire.

[0024] Once the thermal decomposition is complete, the partition 55b is opened, and the metal container 62, still containing the waste plastic decomposition residue, is transported to the third unit 54. The third unit 54 is a cooling unit, and after the metal container 62 has cooled to a predetermined temperature, it is discharged from the metal container outlet 85.

[0025] The present invention's method for converting plastics into oil includes a step (condensation step) in which the pyrolysis gas generated in the pyrolysis step is cooled by a condenser to obtain recycled oil, following the pyrolysis step. The obtained recycled oil is sent to a storage tank and stored. Note that the recycled oil may contain water derived from water mixed in with the waste plastic. In that case, it is preferable to remove the water using an oil-water separator before storing it in the storage tank.

[0026] In one embodiment, the pyrolysis gas recovered from the pyrolysis furnace can be brought into contact with a catalyst again outside the pyrolysis furnace to further reduce its molecular weight (gas re-decomposition step). The catalyst used in the gas re-decomposition step is preferably at least one selected from silica-alumina, synthetic zeolite, and natural zeolite. At this time, in order to improve catalytic activity, the catalyst is preferably heated to 350-550°C with a heater or the like. After the reaction is complete, the pyrolysis gas is sent to a condenser.

[0027] In one embodiment, the molecular weight of recycled oil obtained in the condensation process can be reduced by contacting the recycled oil with a catalyst and heating it (recycled oil low molecular weight process). The contact method can be either by storing the recycled oil in a reaction vessel and adding a powdered catalyst, or by adding the recycled oil to a reaction vessel filled with a catalyst and then contacting it. The reaction is preferably carried out at 250 to 450°C for 4 to 5 hours while stirring. The catalyst used in the recycled oil low molecular weight process is preferably at least one selected from silica-alumina, synthetic zeolite, and natural zeolite. After the reaction is complete, the gasified recycled oil is again condensed and stored in a storage tank. [Industrial applicability]

[0028] According to the plastic oil conversion method or apparatus of the present invention, recycled oil with low viscosity and easy handling can be obtained using waste plastic as a raw material, while reducing the risk of fire during plastic crushing. [Explanation of Symbols]

[0029] 1, 51 Pyrolysis furnace 11. Waste Plastics 12 Metal containers 21, 71 Catalyst 22, 72 Catalytic converter case 31 Metal container loading / unloading entrance 32, 82 Inert gas inlet 33, 83 Pyrolysis gas outlet 34, 84 Gas recovery lines 41, 91 Heat source 52. Unit 1 53. Second Unit 54. The Third Unit 55a, 55b partition 61 Waste Plastics 62 Metal containers 81 Metal container loading entrance 85 Metal container exit

Claims

1. The pyrolysis process involves heating uncrushed waste plastic in a pyrolysis furnace to generate pyrolysis gas, A method for converting plastics into oil, comprising a condensation step of cooling the pyrolysis gas to obtain recycled oil, A method for converting plastics into oil, characterized in that the pyrolysis gas is brought into contact with a catalyst installed inside a pyrolysis furnace to be reduced to low molecular weight, and then sent to a condensation process.

2. The plastic liquefaction method according to claim 1, wherein the uncrushed waste plastic includes at least one selected from polyethylene, polypropylene, and polystyrene.

3. The method for converting plastic into oil according to claim 1, wherein the uncrushed waste plastic contains foreign matter.

4. The method for converting plastics into oil according to claim 1, characterized in that an inert gas is introduced into the furnace during the pyrolysis step.

5. The method for liquefying plastics according to claim 1, wherein the catalyst is at least one selected from silica-alumina, synthetic zeolite, and natural zeolite.

6. The method for converting plastics into oil according to claim 1, further comprising a gas re-decomposition step in which the pyrolysis gas is passed through a catalyst installed outside the pyrolysis furnace to decompose the pyrolysis gas into smaller molecules.

7. The method for converting plastics into oil according to claim 1, further comprising a step of reducing the molecular weight of recycled oil by contacting the recycled oil with a catalyst installed outside the pyrolysis furnace.

8. The method for liquefying plastics according to claim 6 or 7, wherein the catalyst is at least one selected from silica-alumina, synthetic zeolite, and natural zeolite.

9. A plastic oil conversion apparatus comprising a pyrolysis furnace that thermally decomposes plastic to produce pyrolysis gas, and a condenser that cools the pyrolysis gas to obtain recycled oil, A plastic liquefaction apparatus characterized in that a metal container containing uncrushed waste plastic and a catalyst case containing a catalyst are arranged inside the pyrolysis furnace.

10. The plastic oil liquefaction apparatus according to claim 9, wherein the catalyst is at least one selected from silica-alumina, synthetic zeolite, and natural zeolite.

Images