Waste plastic pyrolysis process

Abstract

The present application relates to the technical field of waste plastic chemical treatment, and discloses a waste plastic pyrolysis method.The method comprises the following steps: (1) mixing waste plastic with solvent oil for thermal dissolution to obtain a waste plastic solution; wherein the total content of monocyclic aromatic hydrocarbons and bicyclic aromatic hydrocarbons in the solvent oil is 10-80 wt%; (2) pyrolyzing the waste plastic solution to obtain pyrolysis mixed gas, pyrolysis oil and semi-coke; (3) rectifying the pyrolysis oil to obtain light oil and heavy oil with a boiling point of greater than or equal to 350 DEG C; (4) catalytically hydrogenating the heavy oil to obtain hydrogenated mixed gas and an oil phase; wherein the oil phase is returned to step (1) as solvent oil.The waste plastic pyrolysis method provided in the present application can reduce the amount of semi-coke generated, improve the pyrolysis oil yield and the product quality of the pyrolysis oil, thereby improving the economic benefits of waste plastic pyrolysis and being suitable for industrialization and popularization.

Description

Technical Field

[0001] This invention relates to the field of chemical treatment technology for waste plastics, and specifically to a waste plastic pyrolysis method that can reduce the amount of coke produced. Background Technology

[0002] Waste plastic pyrolysis technology is currently a relatively mature chemical treatment method for waste plastics, attracting much attention due to its advantages such as low technical threshold, low investment, and low operating costs. In recent years, with the increasing awareness of environmental protection, waste plastic pyrolysis technologies have emerged in large numbers, among which rotary kiln pyrolysis technology is the most widely used. Some enterprises and research institutes have also developed different process technologies such as fluidized bed and rotating cone pyrolysis. Although the technology types are different, most technologies have the same drawbacks: high pyrolysis coke production, low pyrolysis oil yield, and poor oil quality that requires further processing before it can be put into use. Taking the traditional rotary kiln pyrolysis technology as an example, the waste plastic pyrolysis oil yield is about 30-70%, and the semi-coke yield is about 20-30%. Moreover, the high coke production rate easily leads to frequent shutdowns of the reaction unit for coking, which seriously affects the economic benefits of enterprises.

[0003] Therefore, there is an urgent need to provide a waste plastic pyrolysis method with low pyrolysis coke production, high pyrolysis oil yield, and good quality. Summary of the Invention

[0004] The purpose of this invention is to solve the problems of high coke production, low pyrolysis oil yield and poor quality in waste plastic pyrolysis, and to provide a waste plastic pyrolysis method.

[0005] To achieve the above objectives, the present invention provides a method for pyrolyzing waste plastics, the method comprising the following steps:

[0006] (1) Waste plastics are mixed with solvent oil and thermally dissolved to obtain a waste plastic solution; wherein the total content of monocyclic aromatic hydrocarbons and bicyclic aromatic hydrocarbons in the solvent oil is 10-80 wt%;

[0007] (2) The waste plastic solution is pyrolyzed to obtain pyrolysis mixed gas, pyrolysis oil and semi-coke;

[0008] (3) The pyrolysis oil is distilled to obtain light oil and heavy oil; wherein the boiling point of the heavy oil is ≥350℃;

[0009] (4) Catalytically hydrogenate the heavy oil to obtain a hydrogenated gas mixture and an oil phase; wherein the oil phase is returned to step (1) as a solvent oil.

[0010] The beneficial technical effects achieved by the present invention through the above technical solution are as follows:

[0011] 1) The waste plastic pyrolysis method provided in this invention can reduce the amount of semi-coke generated, improve the pyrolysis oil yield and the product quality of pyrolysis oil by selecting a solvent with a total content of 10-80 wt% of monocyclic aromatic hydrocarbons and bicyclic aromatic hydrocarbons to dissolve waste plastics, thereby improving the economic benefits of waste plastic pyrolysis and making it suitable for industrial promotion.

[0012] 2) The waste plastic pyrolysis method provided in this invention can obtain high-quality light oil. Only heavy oil needs to be catalytically hydrogenated, which can avoid excessive hydrogenation of light oil, reduce hydrogen consumption, and further improve economic benefits. Attached Figure Description

[0013] Figure 1 This is a process flow diagram of a preferred embodiment provided by the present invention. Detailed Implementation

[0014] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0015] This invention provides a method for pyrolyzing waste plastics, the method comprising the following steps:

[0016] (1) Waste plastics are mixed with solvent oil and thermally dissolved to obtain a waste plastic solution; wherein the total content of monocyclic aromatic hydrocarbons and bicyclic aromatic hydrocarbons in the solvent oil is 10-80 wt%;

[0017] (2) The waste plastic solution is pyrolyzed to obtain pyrolysis mixed gas, pyrolysis oil and semi-coke;

[0018] (3) The pyrolysis oil is distilled to obtain light oil and heavy oil; wherein the boiling point of the heavy oil is ≥350℃;

[0019] (4) The heavy oil is subjected to catalytic hydrogenation to obtain a hydrogenated gas mixture and an oil phase; wherein the oil phase is returned to step (1) as a solvent oil, as follows. Figure 1 As shown.

[0020] The inventors of this invention discovered through research that dissolving waste plastics with a solvent (solvent oil and / or oil phase) containing 10-40 wt% monocyclic and bicyclic aromatic hydrocarbons can reduce the amount of semi-coke generated, improve the yield of pyrolysis oil and the product quality of pyrolysis oil, thereby improving the economic benefits of waste plastic pyrolysis.

[0021] In step (1):

[0022] In one embodiment of the present invention, the waste plastic contains at least one of PE, PP, PS and optionally PVC.

[0023] In one embodiment of the present invention, the waste plastic contains at least one of PE, PP, PS and PVC; wherein, based on the total amount of the waste plastic, the PVC content is ≤2.5wt%, preferably ≤1wt%.

[0024] In one embodiment of the present invention, the particle size of the waste plastic is 1-500 mm, preferably 1-50 mm.

[0025] In one embodiment of the present invention, the mechanical impurity content of the waste plastic is ≤10wt%, preferably ≤3wt%; and the moisture content is ≤5wt%, preferably ≤1wt%.

[0026] In one embodiment of the present invention, the total content of monocyclic aromatic hydrocarbons and bicyclic aromatic hydrocarbons in the solvent oil is preferably 15-50 wt%.

[0027] In one embodiment of the present invention, the solvent oil is preferably selected from one or more of straight-run diesel oil, coal tar distillate oil, LCO (catalytic cracking light cycle oil), HLCO (catalytic cracking heavy cycle oil), VGO (vacuum-fired diesel oil), HVGO (hydro-vacuum-fired diesel oil), and waste plastic pyrolysis oil, and is more preferably selected from one of straight-run diesel oil, catalytic cracking heavy cycle oil, and waste plastic pyrolysis oil.

[0028] In this invention, the terms "straight-run diesel oil, coal tar distillate oil, catalytic cracking light cycle oil, catalytic cracking heavy cycle oil, vacuum diesel oil, hydrotreated vacuum diesel oil, and waste plastic pyrolysis oil" have meanings known in the art, and are generally distillate oils rich in aromatics. In this invention, the solvent oil is preferably a distillate oil whose total content of monocyclic and bicyclic aromatic hydrocarbons is between 10-80 wt%. In one embodiment of this invention, the mass ratio of waste plastic to solvent oil is 1-10:1, preferably 3-7:1.

[0029] In one embodiment of the present invention, the operating conditions for hot dissolution include: hot dissolution temperature of 180-390℃, preferably 250-350℃; hot dissolution pressure of 0.1-2MPa, preferably 0.5-1.5MPa; and hot dissolution time of 10-50min, preferably 25-35min.

[0030] In one embodiment of the present invention, the thermal dissolution is carried out in a dissolution device, which is selected from a kettle-type dissolution device; the heating method of the dissolution device is selected from internal heating or external heating.

[0031] In step (2):

[0032] In one embodiment of the present invention, the operating conditions for pyrolysis include: a pyrolysis temperature of 400-600℃, preferably 450-550℃; a pyrolysis pressure of 0.1-6MPa, preferably 2-4MPa; and an average residence time of 10-50min, preferably 25-35min.

[0033] In one embodiment of the present invention, the pyrolysis is carried out in a reactor, which is selected from at least one of a moving bed reactor, a slurry bed reactor, and a fluidized bed reactor, preferably a slurry bed reactor.

[0034] The inventors of this invention discovered through research that by carrying out thermal dissolution and pyrolysis in different devices, the yield of semi-coke can be further reduced.

[0035] In one embodiment of the present invention, pyrolysis mixed gas is extracted from the upper part of the pyrolysis reactor, and a mixture including pyrolysis oil and semi-coke is extracted from the lower part of the pyrolysis reactor. Solid-liquid separation is performed on the mixture to obtain pyrolysis oil and semi-coke.

[0036] In one embodiment of the present invention, the yield of the pyrolysis mixture is 2-15%, the yield of the pyrolysis oil is 75-85%, and the yield of the semi-coke is 5-15%.

[0037] In step (3):

[0038] In one embodiment of the present invention, the light oil is a fraction with a boiling point <350°C, and the heavy oil preferably has a boiling point ≥350°C. The present invention does not impose special limitations on the cutting of the light oil; it can be cut according to actual needs to obtain different products, or the fraction with a boiling point <350°C can be extracted entirely.

[0039] In one embodiment of the present invention, the distillation conditions are not specifically limited and can be performed according to conventional operations in the art, and will not be described in detail here.

[0040] In step (4):

[0041] In one embodiment of the present invention, the catalytic hydrogenation is carried out in a fixed-bed reactor along the flow direction of the heavy oil. The fixed-bed reactor is sequentially filled with a desilication catalyst, a hydrogenation catalyst, and a dechlorination catalyst. The mass ratio of the desilication catalyst, the hydrogenation catalyst, and the dechlorination catalyst is 0.1-2:0.1-2:1, preferably 0.5-1:0.5-1:1.

[0042] In one embodiment of the present invention, the desilication catalyst comprises 5-15 parts by weight, preferably 10-15 parts by weight of an active component and 85-95 parts by weight, preferably 85-90 parts by weight of a support; wherein the active component is selected from one or more of W, Ni, Mo, and Co, and the support is selected from aluminum oxide and / or silicon dioxide.

[0043] In one embodiment of the present invention, the desilication catalyst may be a commercially available product, preferably selected from one of RSi-1, FHRS-1, HPS-02, ACT961, DC series, TK-400 series, and AT series, and more preferably RSi-1 and / or FHRS-1. The desilication catalyst may also be prepared using conventional catalyst preparation methods; the preparation methods will not be elaborated upon in this invention.

[0044] In one embodiment of the present invention, the hydrogenation catalyst comprises 16-35 parts by weight, preferably 16-30 parts by weight, of an active component and 65-84 parts by weight, preferably 70-74 parts by weight, of a support; wherein the active component is selected from one or more of W, Ni, Mo, Co, Pt, and Pd, and the support is selected from one or more of alumina, modified alumina, activated carbon, diatomaceous earth, aluminum silicate, magnesium silicate, activated clay, and molecular sieve.

[0045] In one embodiment of the present invention, the hydrogenation catalyst may be a commercially available product, preferably selected from RS-2100, FH series, FF series, 3936, 3996, 3987, 3962, CK-2, DBS series, HDN-1, HDS-1, S-12H, and Resid-1, and more preferably RS-2100, FH series, or Resid-1. The hydrogenation catalyst may also be prepared using conventional catalyst preparation methods; the preparation methods will not be elaborated upon in this invention.

[0046] In one embodiment of the present invention, the dechlorination catalyst comprises 25-70 parts by weight, preferably 30-50 parts by weight, of an active component and 30-75 parts by weight, preferably 50-70 parts by weight, of a support; wherein the active component is selected from one or more of sodium hydroxide, potassium hydroxide, calcium oxide, calcium hydroxide, magnesium oxide, magnesium hydroxide, strontium oxide, strontium hydroxide, barium oxide, and ferric oxide, and the support is selected from one or more of alumina, silicon dioxide, and ceramics. In this invention, ceramics refer to porous ceramic materials, such as honeycomb ceramic materials.

[0047] In one embodiment of the present invention, the dechlorination catalyst may be a commercially available product, preferably selected from WGL-A, NC-H, JX-5A, KT406-1, and PURASPEC6250, and more preferably WGL-A and / or NC-H. The dechlorination catalyst may also be prepared using conventional catalyst preparation methods; the preparation methods will not be elaborated upon in this invention.

[0048] In one embodiment of the present invention, the operating conditions of the catalytic hydrogenation reaction include: a catalytic hydrogenation temperature of 320-380°C, preferably 340-360°C; a catalytic hydrogenation pressure of 4-10 MPa, preferably 6-8 MPa; a volume hourly space velocity (VHSV) of 2-16 / h, preferably 6-10 / h, based on the hydrogenation catalyst; and a volume hydrogen-to-oil ratio of 50-200:1, preferably 120-180:1. Wherein, the catalytic hydrogenation temperature in this invention refers to the average temperature of the catalyst bed.

[0049] In one embodiment of the present invention, the total content of monocyclic aromatic hydrocarbons and bicyclic aromatic hydrocarbons in the oil phase is preferably 10-80 wt%, and more preferably 15-50 wt%.

[0050] In one embodiment of the present invention, when the oil phase is returned to step (1) as solvent oil, the use of solvent oil can be stopped and the oil phase can be used to completely replace the solvent oil, or the amount of solvent oil can be reduced and the oil phase and solvent oil can be mixed and used together.

[0051] In one embodiment of the present invention, the method further includes step (5) separating the pyrolysis mixture and / or the hydrogenation mixture to obtain pyrolysis gas and hydrogen.

[0052] In one embodiment of the present invention, the hydrogen obtained in step (5) is returned to step (4).

[0053] The present invention will be described in detail below through embodiments.

[0054] In the embodiments, the mechanical impurities and moisture content in waste plastics were determined using the "Industrial Analysis Methods for Coal" (GB212-91).

[0055] In this embodiment, the relative content of different plastic components in the waste plastic was estimated using flotation. Random samples were taken from the waste plastic, and the mixed plastics were separated by flotation, wherein PP and PE had densities of 0.85-1 g / mL; PS had a density of 1-1.15 g / mL; and PVC had a density >1.35 g / mL. The mass content of each component in the mixed plastic was calculated based on the flotation results. In this invention, PP and PE have similar pyrolytic properties, therefore no further differentiation between PP and PE is necessary.

[0056] Pyrolysis Test Example 1

[0057] (1) Waste plastics excavated from landfills in Yunfu, Guangdong Province are dried and removed from mechanical impurities and then crushed into 20-30mm pieces. The crushed waste plastics contain approximately 92wt% PE and PP, approximately 2wt% PS, approximately 2wt% PVC, approximately 1wt% moisture, and approximately 3wt% mechanical impurities.

[0058] A portion of the above-mentioned waste plastics was mixed with solvent oil (straight-run diesel oil purchased from Beijing Yanshan Branch of China Petroleum & Chemical Corporation, composition as shown in Table 1) at a mass ratio of 1:5 and sent to a dissolving kettle. The mixture was stirred and dissolved for 30 minutes at 300℃ and 1MPa to obtain a waste plastic solution.

[0059] (2) The above waste plastic solution is sent to a slurry bed reactor and pyrolyzed at 450°C and 4MPa. The average residence time of the waste plastic solution is set to 30 min. The pyrolysis mixed gas is taken out from the top of the slurry bed reactor and a mixture including pyrolysis oil and semi-coke is taken out from the bottom. The mixture is filtered to obtain pyrolysis oil and semi-coke.

[0060] (3) The above pyrolysis oil is sent to a distillation column for distillation to obtain light oil with a boiling point <350℃ and heavy oil with a boiling point ≥350℃.

[0061] (4) The above heavy oil is sent to a fixed bed reactor for catalytic hydrogenation at a catalytic hydrogenation temperature of 350°C, a catalytic hydrogenation pressure of 7 MPa, a heavy oil volume hourly space velocity of 8.5 / h, and a hydrogen-to-oil ratio of 100:1 to obtain a hydrogenated mixed gas and an oil phase. Along the flow direction of the heavy oil, the fixed bed reactor is sequentially filled with a desilication catalyst RSi-1, a hydrogenation catalyst RS-2100, and a dechlorination catalyst WGL-A in a mass ratio of 0.8:0.7:1. The total content of monocyclic aromatic hydrocarbons and bicyclic aromatic hydrocarbons in the obtained oil phase is 36.4 wt%. The obtained oil phase replaces straight-run diesel oil as solvent oil and is returned to step (1) for subsequent treatment of waste plastics.

[0062] (5) The above pyrolysis mixture and the above hydrogenated mixture are mixed and then separated to obtain pyrolysis gas and hydrogen; wherein the separated hydrogen is returned to step (4).

[0063] Operations will cease once all waste plastics have been processed.

[0064] Blank test 1:

[0065] The same solvent oil (straight-run diesel) as in Example 1 was fed into a slurry bed reactor and pyrolyzed under the same conditions. The pyrolysis mixture, pyrolysis oil, and semi-coke were collected, and the product yield was calculated. The product yield of the blank test was calculated according to the following formula, and the results of the blank test are shown in Table 2.

[0066]

[0067]

[0068] y 空白-热解半焦 =100% - y 空白-热解油 -y 空白-热解气

[0069] In the formula, y 空白-热解油 : Yield of pyrolysis oil during blank test; m 空白-热解油 : The mass of pyrolysis oil collected during the blank test; m 空白-溶剂油 : The mass of solvent oil used in the blank test; y 空白-热解气 : Yield of pyrolysis gas during the blank test; m 空白-热解气 : The mass of pyrolysis gas collected during the blank experiment; y 空白-热解半焦 : Yield of pyrolysis semi-coke during blank test.

[0070] Based on the results of Example 1 and Blank Test 1, the yields of different products of waste plastic under the above conditions in Example 1 were calculated and converted into product yields based on dry ash-free plastic. The product yields based on the ash-free plastic and the dry ash-free plastic were calculated according to the following formulas, and the results are shown in Table 1.

[0071]

[0072]

[0073] y 塑料-热解半焦 =100% - y 塑料-热解油 -y 塑料-热解气

[0074] In the formula, y 塑料-热解油 : Yield of pyrolysis oil during the pyrolysis test; m 塑料-热解油 : The mass of pyrolysis oil collected during the pyrolysis experiment; m 溶剂油 : The mass of solvent oil used in the pyrolysis test; m 塑料 : The mass of the plastic used in the pyrolysis test; y 塑料-热解气 : Yield of pyrolysis gas during the pyrolysis experiment; m 塑料-热解气 : The mass of pyrolysis gas collected during the pyrolysis experiment; y 塑料-热解半焦 : Yield of pyrolysis semi-coke during blank test.

[0075]

[0076]

[0077] y 塑料-热解半焦(daf) =100% - y 塑料-热解油(daf) -y 塑料-热解油(daf)

[0078] In the formula, y 塑料-热解油(daf) : Yield of pyrolysis oil during the pyrolysis test, calculated based on a dry, ash-free basis; y 塑料-热解气(daf) : Yield of pyrolysis gas during the pyrolysis test, calculated based on a dry, ash-free basis; y 塑料-热解半焦(daf) : Yield of pyrolysis semi-coke during the pyrolysis test, calculated based on a dry, ash-free basis.

[0079] Pyrolysis Test Example 2

[0080] Similar to Example 1, except that the solvent oil in step (1) is HLCO purchased from Sinopec Shijiazhuang Refining & Chemical Branch, and the composition of HLCO is shown in Table 1.

[0081] Blank test 2:

[0082] The same solvent oil (HLCO) as in Example 2 was fed into a slurry bed reactor and pyrolyzed under the same conditions. The pyrolysis mixture, pyrolysis oil and semi-coke were collected and the product yield was calculated.

[0083] Based on the results of Example 2 and Blank Test 2, calculations were performed using the same formula as described in Blank Test 1. The yields of different products of waste plastics under the above conditions in Example 2 were then converted into product yields based on a dry, ash-free basis. The results are shown in Table 2.

[0084] Pyrolysis Test Example 3

[0085] Similar to Example 1, except that the solvent oil in step (1) is the waste plastic pyrolysis oil obtained in Comparative Example 1, and the composition of the waste plastic pyrolysis oil is shown in Table 1.

[0086] Blank Experiment 3:

[0087] The same solvent oil as in Example 3 was sent to a slurry bed pyrolysis reactor for pyrolysis under the same conditions. The pyrolysis mixture, pyrolysis oil and semi-coke were collected and the product yield was calculated.

[0088] Based on the results of Example 3 and Blank Experiment 3, calculations were performed using the same formula as described in Blank Experiment 1. The yields of different products of waste plastics under the above conditions in Example 3 were then converted into product yields based on a dry, ash-free basis. The results are shown in Table 2.

[0089] Comparative Example 1

[0090] The waste plastics from Example 1 were sent to a rotary kiln pyrolysis reaction system with continuous feed and discharge, and pyrolyzed at atmospheric pressure and 450°C. Pyrolysis oil, pyrolysis mixed gas and semi-coke were collected. The yield of pyrolysis products is shown in Table 2.

[0091] Comparative Example 2

[0092] Similar to Example 1, the difference is that the solvent oil in step (1) is Fischer-Tropsch light oil from the pilot plant of Qilu Petrochemical Fischer-Tropsch synthesis, and the composition of the Fischer-Tropsch light oil is shown in Table 1.

[0093] Comparative Example 2: Blank Test

[0094] The same mass of solvent oil as that in Comparative Example 2 was sent to a slurry bed pyrolysis reactor for pyrolysis under the same conditions. The pyrolysis mixture, pyrolysis oil and semi-coke were collected and the product yield was calculated.

[0095] Based on the results of Comparative Example 2 and the blank test of Comparative Example 2, the calculation was performed using the same formula as described in Blank Test 1. The yields of different products of waste plastic in Comparative Example 2 under the above conditions were then converted into product yields based on dry ash-free basis. The results are shown in Table 2.

[0096] Table 1

[0097]

[0098]

[0099] Table 2

[0100]

[0101] Note: A semi-coke yield of 0 in Table 2 means that no significant solids were obtained during filtration.

[0102] As shown in Table 2, the waste plastic pyrolysis method provided in this invention can reduce the amount of semi-coke generated during waste plastic pyrolysis, improve the pyrolysis oil yield and product quality, thereby improving the economic benefits of waste plastic pyrolysis. Comparative Example 2 shows that the choice of solvent oil significantly affects the yield of waste plastic pyrolysis products. When Fischer-Tropsch light oil, which contains almost no monocyclic or bicyclic aromatics, is selected, the waste plastic does not dissolve and disperse in the solvent oil, and the thermal conductivity during pyrolysis is poor, leading to localized hot spots that increase the semi-coke yield and decrease the pyrolysis oil yield. While a higher aromatic content in the solvent oil improves thermal dissolution and thermal conductivity during pyrolysis, thus helping to reduce the semi-coke yield, the high aromatic content solvent oil can also remove H free radicals generated during waste plastic pyrolysis. Therefore, although it has a limited effect in reducing coking, the effect is limited.

[0103] Test Example 1

[0104] The total content of monocyclic and bicyclic aromatic hydrocarbons in the oil phases obtained in Examples 1-3 and Comparative Example 2 was tested, and the results are shown in Table 3:

[0105] Table 3

[0106] Total content of monocyclic and bicyclic aromatic hydrocarbons, wt% Example 1 36.4 Example 2 79.7 Example 3 20.2 Comparative Example 2 3.8

[0107] The preferred embodiments of the present invention have been described in detail above; however, the present invention is not limited thereto. Within the scope of the inventive concept, various simple modifications can be made to the technical solutions of the present invention, including combinations of various technical features in any other suitable manner. These simple modifications and combinations should also be considered as the content disclosed in the present invention and are all within the protection scope of the present invention.

Claims

1. A method for pyrolyzing waste plastics, characterized in that, The method includes the following steps: (1) Waste plastics are mixed with solvent oil and thermally dissolved to obtain a waste plastic solution; wherein the total content of monocyclic aromatic hydrocarbons and bicyclic aromatic hydrocarbons in the solvent oil is 15-50 wt%; the mass ratio of waste plastics to solvent oil is 1-10:1; (2) The waste plastic solution is pyrolyzed to obtain pyrolysis mixed gas, pyrolysis oil and semi-coke; (3) The pyrolysis oil is distilled to obtain light oil and heavy oil; wherein the boiling point of the heavy oil is ≥350℃; (4) Catalytically hydrogenate the heavy oil to obtain a hydrogenated mixed gas and an oil phase; wherein the oil phase is returned to step (1) as a solvent oil.

2. The method according to claim 1, wherein, The waste plastic contains at least one of PE, PP, PS and optionally PVC.

3. The method according to claim 1, wherein, The waste plastic contains at least one of PE, PP, PS and PVC; wherein, based on the total amount of the waste plastic, the PVC content is ≤2.5wt%.

4. The method according to claim 3, wherein, The PVC content is ≤1wt%.

5. The method according to claim 1, wherein, The waste plastic has a particle size of 1-500mm; the mechanical impurity content in the waste plastic is ≤10wt%; and the moisture content is ≤5wt%.

6. The method according to claim 1, wherein, The waste plastic has a particle size of 1-50 mm; the mechanical impurity content in the waste plastic is ≤3 wt%; and the moisture content is ≤1 wt%.

7. The method according to any one of claims 1-6, wherein, The solvent oil is selected from one or more of the following: straight-run diesel oil, coal tar distillate oil, catalytic cracking light cycle oil, catalytic cracking heavy cycle oil, vacuum diesel oil, hydrotreated vacuum diesel oil, and waste plastic pyrolysis oil.

8. The method according to any one of claims 1-6, wherein, The solvent oil is selected from one of the following: straight-run diesel oil, catalytic cracking heavy cycle oil, and waste plastic pyrolysis oil.

9. The method according to any one of claims 1-6, wherein, The mass ratio of the waste plastic to the solvent oil is 3-7:

1.

10. The method according to any one of claims 1-6, wherein, In step (1), the operating conditions for hot dissolution include: hot dissolution temperature of 180-390℃; hot dissolution pressure of 0.1-2MPa; and hot dissolution time of 10-50min.

11. The method according to claim 10, wherein, In step (1), the operating conditions for hot dissolution include: hot dissolution temperature of 250-350℃; hot dissolution pressure of 0.5-1.5MPa; and hot dissolution time of 25-35min.

12. The method according to any one of claims 1-6, wherein, In step (2), the operating conditions for pyrolysis include: pyrolysis temperature of 400-600℃; pyrolysis pressure of 0.1-6MPa; and average residence time of pyrolysis of 10-50min.

13. The method according to claim 12, wherein, In step (2), the operating conditions for pyrolysis include: pyrolysis temperature of 450-550℃; pyrolysis pressure of 2-4MPa; and average residence time of pyrolysis of 25-35min.

14. The method according to any one of claims 1-6, wherein, The thermal dissolution is carried out in a dissolution device, which is selected from a kettle-type dissolution device; And / or, the pyrolysis is carried out in a reactor selected from at least one of a moving bed reactor, a slurry bed reactor, and a fluidized bed reactor.

15. The method according to claim 14, wherein, The reactor is a slurry bed reactor.

16. The method according to any one of claims 1-6, wherein, In step (4), the catalytic hydrogenation is carried out in a fixed-bed reactor along the direction of heavy oil flow. The fixed-bed reactor is sequentially filled with a desilication catalyst, a hydrogenation catalyst, and a dechlorination catalyst; wherein the mass ratio of the desilication catalyst, the hydrogenation catalyst, and the dechlorination catalyst is 0.1-2:0.1-2:

1.

17. The method according to claim 16, wherein, The mass ratio of the desilication catalyst, hydrogenation catalyst, and dechlorination catalyst is 0.5-1:0.5-1:

1.

18. The method according to claim 16, wherein, In step (4), the desilication catalyst comprises 5-15 parts by weight of an active component and 85-95 parts by weight of a support; wherein the active component is selected from one or more of W, Ni, Mo, and Co, and the support is selected from aluminum oxide and / or silicon dioxide.

19. The method according to claim 18, wherein, In step (4), the desilication catalyst comprises 10-15 parts by weight of active component and 85-90 parts by weight of support.

20. The method of claim 16, wherein, The hydrogenation catalyst comprises 16-35 parts by weight of an active component and 65-84 parts by weight of a support; wherein the active component is selected from one or more of W, Ni, Mo, Co, Pt, and Pd, and the support is selected from one or more of alumina, activated carbon, diatomaceous earth, aluminum silicate, magnesium silicate, activated clay, and molecular sieve.

21. The method according to claim 20, wherein, The hydrogenation catalyst comprises 16-30 parts by weight of an active component and 70-74 parts by weight of a support.

22. The method according to claim 16, wherein, The dechlorination catalyst comprises 25-70 parts by weight of an active component and 30-75 parts by weight of a support; wherein the active component is selected from one or more of sodium hydroxide, potassium hydroxide, calcium oxide, calcium hydroxide, magnesium oxide, magnesium hydroxide, strontium oxide, strontium hydroxide, barium oxide, and ferric oxide, and the support is selected from one or more of alumina, silicon dioxide, and ceramics.

23. The method according to claim 22, wherein, The dechlorination catalyst comprises 30-50 parts by weight of an active component and 50-70 parts by weight of a support.

24. The method according to any one of claims 1-6, wherein, In step (4), the operating conditions of the catalytic hydrogenation reaction include: catalytic hydrogenation temperature of 320-380℃; catalytic hydrogenation pressure of 4-10MPa; heavy oil space velocity of 2-16 / h based on hydrogenation catalyst; and volume hydrogen-to-oil ratio of 50-200:

1.

25. The method according to claim 24, wherein, In step (4), the operating conditions of the catalytic hydrogenation reaction include: catalytic hydrogenation temperature of 340-360℃; catalytic hydrogenation pressure of 6-8MPa; heavy oil space velocity of 6-10 / h based on hydrogenation catalyst; and volume hydrogen-to-oil ratio of 120-180:

1.

26. The method according to any one of claims 1-6, wherein, The method further includes step (5) separating the pyrolysis mixture and / or the hydrogenated mixture to obtain pyrolysis gas and hydrogen.

27. The method according to claim 26, wherein, Return the hydrogen obtained in step (5) to step (4).

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