A method and system for preparing low-chlorine pyrolysis oil from plastic mixtures

Abstract

This disclosure relates to a method and system for preparing low-chlorine pyrolysis oil from plastic mixtures. Chlorine-containing plastics and additive-containing plastics are fed into a first screw-type heating and conveying device for dehydration, degassing, and volume reduction treatment. The resulting dehydrated, degassed, and volume-reduced plastics are then fed into a second screw-type heating and conveying device for liquefaction and dechlorination treatment. The resulting liquefied and dechlorinated plastics undergo viscosity-reducing cracking treatment to obtain viscosity-reduced cracked plastic oil and a first dry gas. The viscosity-reduced cracked plastic oil is then heated and subjected to a pyrolysis reaction to obtain pyrolysis products and coke. The pyrolysis products are separated to obtain a second dry gas, liquefied gas, and pyrolysis oil. The additives are oxides, hydroxides, and salts of alkali metals / alkaline earth metals. In this invention, the alkali metal / alkaline earth metal compounds added to the additive-containing plastics during the pyrolysis and dechlorination process can adsorb HCl released from the high-temperature decomposition of chlorine-containing compounds in situ, reducing the generation of organochlorides and effectively realizing the large-scale, continuous production of low-chlorine pyrolysis oil from chlorine-containing waste plastics.

Description

Technical Field

[0001] This invention belongs to the technical field of waste plastic resource utilization and green environmental protection, specifically relating to a method and system for preparing low-chlorine pyrolysis oil by co-pyrolysis of waste plastics containing alkaline additives and chlorine-containing waste plastics. Background Technology

[0002] Currently, nearly 1 billion tons of waste plastics urgently need to be disposed of in China, while the global cumulative amount is approximately 9 billion tons. "White pollution," caused by waste plastics, including marine pollution, water and soil pollution, and ecological damage, is a serious problem. Traditional methods of waste plastic disposal include landfill and incineration, which pollute the environment and cause significant economic losses. Chemical recycling can transform waste plastics into chemical products by applying various technologies such as pyrolysis, catalytic decomposition, solvent decomposition, and gasification. Nevertheless, developing cost-effective and environmentally friendly chemical recycling methods to transform plastic waste into valuable products remains highly desirable.

[0003] Chemical recycling is widely considered a sustainable technology capable of high-value utilization of waste plastics. However, globally, its development is still in its early stages, accounting for only 1% of waste plastic processing. With changes in global environmental policies, particularly the commitments to carbon reduction, carbon peaking, and carbon neutrality, refining companies worldwide are increasingly focusing on chemical recycling of waste plastics, especially in EU countries. Companies like BUSF, BP, and Shell have developed chemical recycling technologies for waste plastics, and it is projected that by 2030, chemical recycling technology will account for 13% of waste plastic recycling. Currently, pyrolysis remains the mainstream processing technology. Its simplicity, low cost, and wide adaptability to raw materials give it economic advantages and technical feasibility. Waste plastics that can be processed by pyrolysis mainly include aged plastics excavated from landfills and waste plastics from dynamic household waste. However, the presence of mixed plastics like PVC and chlorine-containing additives results in high chlorine content in the pyrolysis oil, reaching over 4000 mg / kg, with the majority being organochlorides, significantly impacting oil quality. Meanwhile, some plastics containing alkaline substances such as calcium carbonate, like calcium-plastic boards, are difficult to chemically recycle due to their low plastic content and high content of organic impurities such as calcium carbonate. However, utilizing the alkaline substances in waste plastics can adsorb the HCl released during the pyrolysis of chlorine-containing compounds such as PVC, thus reducing the formation of organochlorine compounds. Therefore, developing a technology for co-pyrolyzing alkaline and chlorine-containing waste plastics to prepare low-chlorine pyrolysis oil is urgently needed, as this technology is of great significance for achieving closed-loop recycling of waste plastics.

[0004] CN202010457518.3 discloses a method and system for treating chlorine-containing waste plastics. The method involves dechlorinating the chlorine-containing waste plastics in a dechlorination device using a shaftless stirring screw, isolating it from air, and at a temperature of 180℃~320℃ to obtain molten material and chlorine-containing gas. The molten material is then pyrolyzed in a pyrolysis device under vacuum conditions at 500℃~700℃ to produce pyrolytic carbon and pyrolysis steam. However, due to problems such as low heat transfer efficiency, uneven heating, and low dechlorination temperature in the dechlorination device, the chlorine removal rate of the dechlorinated molten plastic is low, only 70%.

[0005] CN201610606090.8 discloses a device and method for harmless treatment of waste plastics. In this method, a large screw feeder heats the waste plastics to 100℃~250℃ and feeds them into a dechlorination separator for dechlorination reaction. Since the dechlorination reaction of PVC and the addition reaction of olefins occur simultaneously, the dechlorination rate is not high under the condition of separating HCl without external force. Moreover, at 250℃, the waste plastics only soften into a plastic high-molecular-weight material, and its phase is a non-flowing, non-liquid plastic solid, which is difficult to output from the dechlorination separator.

[0006] CN201810272820.4 discloses a method for preparing low-chlorinated plastic pyrolysis oil. This method involves staged, stepwise heating of a mixed plastic containing PVC. Within the temperature range where PVC decomposes and releases hydrogen chloride, the released hydrogen chloride is completely removed using nitrogen purging or vacuum extraction. A composite catalyst is then added to perform deep dechlorination and catalytic pyrolysis on the remaining material to obtain low-chlorinated plastic pyrolysis oil. However, this method is an intermittent reaction and cannot achieve large-scale, continuous production of low-chlorinated pyrolysis oil from chlorinated waste plastics. Furthermore, the dechlorination equipment suffers from low heat transfer efficiency, uneven heating, and localized overheating, resulting in incomplete dechlorination and the unavoidable production of a significant amount of organochlorides, leading to a still relatively high chlorine content in the pyrolysis light oil. Summary of the Invention

[0007] The technical problem to be solved by this invention is to provide a method and system for preparing low-chlorine pyrolysis oil by co-pyrolysis of waste plastics containing additives and waste plastics containing chlorine. This method can effectively achieve the co-pyrolysis of waste plastics containing additives and waste plastics containing chlorine, enabling large-scale, continuous production of low-chlorine pyrolysis oil.

[0008] To achieve the above objectives, in a first aspect, the present invention provides a method for preparing low-chlorine pyrolysis oil from a plastic mixture, comprising the following steps:

[0009] S1. Chlorine-containing plastics and additive-containing plastics are fed separately or together into the first screw-type heating and conveying equipment for dehydration, degassing and volume reduction treatment to obtain dehydrated, degassing and volume-reduced plastics.

[0010] S2. The dehydrated, degassed, and volume-reduced plastic is fed into a second screw-type heating and conveying device for liquefaction and dechlorination treatment to obtain liquefied and dechlorinated plastic.

[0011] S3. The liquefied dechlorinated plastic is fed into the viscosity reduction cracking unit for viscosity reduction cracking treatment to obtain viscosity reduction cracked plastic oil and first dry gas.

[0012] S4. The viscosity-reducing cracked plastic oil is fed into a heating unit for heating treatment to obtain heated plastic oil;

[0013] S5. The heated plastic oil is introduced into the pyrolysis reaction unit to carry out the pyrolysis reaction, and pyrolysis products and coke are obtained.

[0014] S6. The pyrolysis products are separated in a separation unit to obtain second dry gas, liquefied gas and pyrolysis oil.

[0015] The additives are oxides, hydroxides, and salts of alkali metals / alkaline earth metals.

[0016] In the method provided by this invention, the chlorinated plastic refers to chlorinated waste plastic, including polyvinyl chloride (PVC) and a mixture of one or more selected from low-density polyethylene (LDPE), high-density polyethylene (HDPE), polystyrene (PS), and polypropylene (PP). There is no limitation on the PVC content, and the chlorinated plastic contains more than 0.5% by weight of Cl. The chlorinated plastic disclosed herein can be directly sourced from waste plastics in landfills.

[0017] Optionally, the chlorine-containing plastic is first crushed and impurity removed before entering the first screw-type heating and conveying equipment for dehydration, degassing, and volume reduction treatment; the additive-containing plastic is first crushed and impurity removed before entering the first screw-type heating and conveying equipment for dehydration, degassing, and volume reduction treatment.

[0018] Optionally, chlorinated plastics are processed in a first screw-type heating and conveying device for chlorinated plastics, with an outlet temperature of 100℃~250℃ and a residence time of 4min~20min, to obtain dehydrated, degassed, and volume-reduced chlorinated plastics. Preferably, the outlet temperature of the first screw-type heating and conveying device for chlorinated plastics is 150~200℃, the residence time is 5min~16min, and the screw internal pressure is 0.1MPa~6MPa, more preferably 0.1MPa~4MPa. Additive-containing plastics are processed in a first screw-type heating and conveying device for additive-containing plastics, with an outlet temperature of 120℃~400℃ and a residence time of 4min~20min, to obtain dehydrated, degassed, and volume-reduced additive-containing plastics. Preferably, the outlet temperature of the first screw-type heating and conveying device for additive-containing plastics is 150℃~380℃, the residence time is 5min~16min, and the screw internal pressure is 0.1MPa~6MPa, more preferably 0.1MPa~4MPa. The processed material then enters a second screw-type heating and conveying device.

[0019] Preferably, the outlet temperature of the first screw-type heating conveyor for plastic containing additives is 10°C to 180°C higher than that of the first screw-type heating conveyor for plastic containing chlorine, and more preferably 20°C to 150°C higher.

[0020] In the method provided by the present invention, liquefaction and dechlorination are performed in a second screw-type heating and conveying device to obtain liquefied dechlorinated plastic. The outlet temperature of the second screw-type heating and conveying device is 280℃~450℃, and the residence time is 5min~30min. Preferably, the outlet temperature of the second screw-type heating and conveying device is 300℃~430℃, the residence time is 6min~25min, and the screw internal pressure is 0.0001MPa~5MPa, more preferably 0.1MPa~3MPa.

[0021] In the method provided by the present invention, the viscosity reduction cracking unit in step S3 is used to carry out the viscosity reduction cracking treatment in an adiabatic viscosity reduction cracking reactor, with a reaction temperature of 350℃~450℃ and a residence time of 15min~150min; preferably, the reaction temperature is 360℃~430℃ and the residence time is 20min~120min.

[0022] In the method provided by the present invention, the heating unit in step S4 includes a heating furnace with an outlet temperature of 430°C to 570°C, preferably 450°C to 550°C. Steam is injected into the heating furnace, and the amount of steam injected is 0.5% to 5% by weight, based on the weight of the viscosity-reducing cracked plastic oil entering the heating furnace.

[0023] In the method provided by the present invention, the pyrolysis reaction unit in step S5 adopts a pyrolysis tower with a tower top pressure of 0.05MPa to 0.6MPa, a pyrolysis reaction temperature of 430℃ to 550℃, and a pyrolysis reaction time of 20s to 80s, preferably 20s to 60s.

[0024] Optionally, in step S2, under the action of a vacuum system, the gas generated in the second screw-type heating and conveying device enters the hydrogen chloride absorption unit and contacts the hydrogen chloride absorbent to remove hydrogen chloride. The hydrogen chloride absorbent is water or an alkaline solution. Optionally, the alkaline solution is selected from one or more of sodium hydroxide solution, potassium hydroxide solution, calcium hydroxide solution, sodium bicarbonate solution, sodium carbonate solution, and ammonia water.

[0025] Optionally, the chlorinated plastic includes PVC; the additive-containing plastic refers to calcium-plastic materials containing additives, incinerable plastic garbage bags, flexible polyethylene wires, polyethylene shoe soles, plastic agricultural films, antibacterial plastics, or thermally conductive plastics; preferably, the additives are selected from alkali metal / alkaline earth metal oxides, hydroxides, carbonates, and silicates; preferably, the additives are selected from one or more of calcium carbonate, calcium oxide, calcium hydroxide, zinc oxide, and magnesium oxide; the content of the additives is 0.1% to 90% by weight, preferably 1% to 70% by weight.

[0026] Optionally, the ratio of additive-containing plastic to chlorine-containing plastic is such that the mass ratio of additive to chlorine is 1:0.5 to 20, preferably 1:1 to 8.

[0027] In a second aspect, the present invention provides a system for preparing low-chlorine pyrolysis oil from plastic mixtures, comprising a first screw-type heating and conveying device for chlorine-containing plastics, a first screw-type heating and conveying device for additive-containing plastics, a second screw-type heating and conveying device, a viscosity-reducing cracking unit, a heating unit, a pyrolysis reaction unit, and a separation unit;

[0028] A first screw-type heating and conveying device for chlorinated plastics and a first screw-type heating and conveying device for additive-containing plastics are connected in parallel, including an inlet and an outlet; the first screw-type heating and conveying device for chlorinated plastics is configured to perform dehydration, degassing and volume reduction treatment on chlorinated plastics; the first screw-type heating and conveying device for additive-containing plastics is configured to perform dehydration, degassing and volume reduction treatment on additive-containing plastics.

[0029] The outlets of the first screw-type heating conveyor for chlorinated plastics and the first screw-type heating conveyor for additive-containing plastics are respectively connected to the second screw-type heating conveyor.

[0030] The second screw-type heating and conveying device is provided with a dechlorinated plastic outlet; the second screw-type heating and conveying device is configured to liquefy and dechlorinate the dehydrated, degassed, and volume-reduced plastic to obtain dechlorinated plastic;

[0031] The viscosity-reducing cracking unit includes a dechlorinated plastic inlet and a viscosity-reducing cracked plastic oil outlet; the dechlorinated plastic inlet is connected to the dechlorinated plastic outlet of the second screw-type heating conveying device; the viscosity-reducing cracking unit is configured to perform viscosity-reducing cracking treatment on the dechlorinated plastic to obtain viscosity-reducing cracked plastic oil;

[0032] The heating unit includes a viscosity-reducing cracked plastic oil inlet and a heated plastic oil outlet, wherein the viscosity-reducing cracked plastic oil inlet is connected to the viscosity-reducing cracked plastic oil outlet of the viscosity-reducing cracking unit; the heating unit is configured to heat the viscosity-reducing cracked plastic oil to obtain heated plastic oil.

[0033] The pyrolysis reaction unit includes a heating plastic oil inlet and a pyrolysis product outlet; the heating plastic oil inlet is connected to the heating plastic oil outlet of the heating unit; the pyrolysis reaction unit is configured to perform a pyrolysis reaction on the heating plastic oil to obtain pyrolysis products and coke.

[0034] The separation unit includes a pyrolysis product inlet, a dry gas outlet, a liquefied gas outlet, and a pyrolysis oil outlet; the pyrolysis product inlet is connected to the pyrolysis product outlet of the pyrolysis reaction unit; the separation unit is configured to separate the pyrolysis products to obtain dry gas, liquefied gas, and pyrolysis oil.

[0035] Through the above technical solution, this invention provides a method and system for preparing low-chlorine pyrolysis oil by co-pyrolysis of alkaline and chlorine-containing waste plastics. By subjecting the alkaline and chlorine-containing waste plastics to dehydration, degassing, volume reduction, liquefaction, dechlorination, and viscosity reduction cracking treatments, the viscosity and chlorine content of the liquefied waste plastics are reduced without coking or excessive cracking, forming a uniform, highly fluid low-chlorine liquefied waste plastic that can be pumped. Then, it is rapidly heated to the pyrolysis reaction temperature using a furnace or similar method, and the high-temperature liquefied waste plastic is transported to a pyrolysis tower for the pyrolysis reaction. In this invention, the alkaline substances added to the alkaline waste plastics during the pyrolysis dechlorination process can adsorb HCl released from the high-temperature decomposition of chlorine compounds in situ, reducing the formation of organochlorides and resulting in low-chlorine pyrolysis oil.

[0036] Other features and advantages of the present invention will be described in detail in the following detailed description section. Attached Figure Description

[0037] The accompanying drawings are provided to further understand the present disclosure and form part of the specification. They are used together with the following detailed description to explain the present disclosure, but do not constitute a limitation thereof.

[0038] Figure 1This is a process flow diagram of one implementation method for preparing low-chlorine pyrolysis oil from plastic mixtures.

[0039] Explanation of reference numerals in the attached figures

[0040] 1-Chlorinated plastics 2-Chlorinated plastics first screw heating conveyor equipment

[0041] 3-Plastics containing additives 4-Plastics containing additives First screw-type heating conveyor equipment

[0042] 5, 6, 7 - Pipelines 8 - Second screw type heating and conveying equipment

[0043] 9-Hydrogen chloride absorption unit; 10-Viscosity reduction cracking unit

[0044] 11-Heating unit 12-Pyrolysis reaction unit

[0045] 13-Separation Unit Detailed Implementation

[0046] The following provides a detailed description of specific embodiments of the present invention. It should be understood that the specific embodiments described herein are for illustrative and explanatory purposes only and are not intended to limit the scope of the invention.

[0047] In this invention, all pressures involved are apparent pressures.

[0048] As attached Figure 1 As shown, the present invention provides a method for preparing low-chlorine pyrolysis oil from plastic mixtures, comprising the following steps:

[0049] S1. Chlorine-containing plastics and additive-containing plastics are fed separately or together into the first screw-type heating and conveying equipment for dehydration, degassing and volume reduction treatment to obtain dehydrated, degassing and volume-reduced plastics.

[0050] S2. The dehydrated, degassed, and volume-reduced plastic is fed into a second screw-type heating and conveying device for liquefaction and dechlorination treatment to obtain liquefied and dechlorinated plastic.

[0051] S3. The liquefied dechlorinated plastic is fed into the viscosity reduction cracking unit for viscosity reduction cracking treatment to obtain viscosity reduction cracked plastic oil and first dry gas.

[0052] S4. The viscosity-reducing cracked plastic oil is fed into a heating unit for heating treatment to obtain heated plastic oil;

[0053] S5. The heated plastic oil is introduced into the pyrolysis reaction unit to carry out the pyrolysis reaction, and pyrolysis products and coke are obtained.

[0054] S6. The pyrolysis products are separated in a separation unit to obtain second dry gas, liquefied gas and pyrolysis oil.

[0055] The additives are oxides, hydroxides, and salts of alkali metals / alkaline earth metals.

[0056] In the method provided by this invention, the chlorine-containing plastic includes polyvinyl chloride (PVC) and one or more selected from low-density polyethylene (LDPE), high-density polyethylene (HDPE), polystyrene (PS), and polypropylene (PP). The plastic used in this invention can be directly sourced from waste plastics in landfills.

[0057] Additive-containing plastics refer to plastics containing plastic additives. Plastic additives are compounds added during the molding and processing of synthetic resins to improve their processing performance or to address deficiencies in the resin's inherent properties. For example, adding calcium carbonate during plastic processing can improve the stability, heat resistance, hardness, and rigidity of plastic products, improve processing performance, and reduce product costs; the addition amount can reach over 60% by weight. Adding 30% by weight of specially treated calcium oxide to plastic products can increase the notched impact strength to 10%–120%, and achieve the same level of thermoplasticity, elastomerism, and toughness as modified products. Zinc oxide has many applications in plastics, such as enhancing mechanical properties, preventing ultraviolet radiation, improving processability, and manufacturing electrically conductive materials.

[0058] In one specific embodiment, the additives in the additive-containing plastic are selected from oxides, hydroxides, carbonates, and silicates of alkali metals and / or alkaline earth metals, such as calcium oxide, aluminum oxide, iron oxide, magnesium oxide, zinc oxide, nickel oxide, copper oxide, calcium hydroxide, sodium hydroxide, potassium hydroxide, magnesium hydroxide, iron hydroxide, aluminum hydroxide, calcium carbonate, sodium carbonate, potassium carbonate, magnesium carbonate, zinc carbonate, barium carbonate, magnesium carbonate, copper carbonate, ammonium carbonate, sodium silicate, and magnesium silicate, or mixtures thereof. It also includes mixtures containing alkali metals and / or alkaline earth metal compounds such as talc, bentonite, clay, magnesia, glass powder, and asbestos. The additive content in the additive-containing plastic is 0.1% to 90% by weight, preferably 1% to 70% by weight.

[0059] The amount of additive-containing plastic is determined based on the relative amount of additive and chlorine content in the chlorine-containing plastic, such that the mass ratio of alkali metal and / or alkaline earth metal compounds to chlorine is 1:0.5 to 20, preferably 1:1 to 8.

[0060] In one specific embodiment, chlorinated plastic and additive-containing plastic enter a first screw-type heating and conveying device. The outlet temperature of the first screw-type heating and conveying device is 150℃~380℃, and the residence time is 5min~16min, resulting in dehydrated, degassed, and volume-reduced plastic. The conveying line speed of the first screw-type heating and conveying device is 0.0025m / s~0.008m / s, the screw internal pressure is 0.1MPa~4MPa, and the feeding rate is 30g / s~200g / s.

[0061] In a preferred embodiment, two first screw-type heating conveyor devices are used for processing. (See attached diagram) Figure 1 As shown, chlorinated plastic 1 enters the first screw-type heating and conveying device 2 for processing. The outlet temperature is 150℃~200℃, the residence time is 5min~16min, the conveying line speed is 0.0025m / s~0.008m / s, more preferably 0.003m / s~0.007m / s, the screw internal pressure is 0.1MPa~4MPa, and the feed rate is 20g / s~100g / s, resulting in dehydrated, degassed, and volume-reduced chlorinated plastic. Additive-containing plastic 3 then enters the additive-containing plastic... The material is processed in the first screw-type heating and conveying equipment 4, with an outlet temperature of 150℃~380℃, a residence time of 5min~16min, a conveying line speed of 0.0025m / s~0.008m / s, more preferably 0.003m / s~0.007m / s, a screw internal pressure of 0.1Mpa~4MPa, and a feeding rate of 10g / s~100g / s, to obtain dehydrated, degassed, reduced-volume plastic containing additives; the processed material is then fed into the second screw-type heating and conveying equipment 8, either separately or in combination.

[0062] In a preferred embodiment, the outlet temperature of the first screw-type heating conveyor for additive-containing plastic is 10°C to 180°C higher than that of the first screw-type heating conveyor for chlorinated plastic, and more preferably 20°C to 150°C higher.

[0063] In a preferred embodiment, as shown in the appendix Figure 1 As shown, the outlet of the first screw-type heating and conveying device for chlorinated plastics is connected to the inlet of the second screw-type heating and conveying device 8. The degassed, dehydrated, and volume-reduced chlorinated plastics enter the second screw-type heating and conveying device through the inlet. The second screw-type heating and conveying device 8 is sequentially equipped with a first inlet 5, a second inlet 6, and a third inlet 7 for degassed, dehydrated, and volume-reduced plastics containing additives along the material conveying direction. The degassed, dehydrated, and volume-reduced plastics containing additives enter the second screw-type heating and conveying device multiple times and mix with the treated chlorinated plastics.

[0064] In one embodiment, in step S2, the outlet temperature of the second screw-type heating conveyor 3 is 280℃~450℃, and the residence time is 5min~30min; optionally, the conveying linear speed of the second screw-type heating conveyor is 0.003m / s~0.008m / s, and the screw internal pressure is 0.0001MPa~5MPa.

[0065] In a preferred embodiment, in step S2, the outlet temperature of the second screw-type heating conveyor 3 is 300℃~430℃, the residence time is 6min~25min, the conveying line speed is 0.003m / s~0.008m / s, and the screw internal pressure is 0.1MPa~3MPa. Treating waste plastics according to the optimized liquefaction and dechlorination conditions of this embodiment can further improve liquefaction and dechlorination efficiency.

[0066] In one embodiment, the additives in the additive-containing plastic are selected from one or more of alkali metal / alkaline earth metal oxides, hydroxides, carbonates, and silicates;

[0067] Optionally, the alkali metal / alkaline earth metal oxide is selected from one or more of calcium oxide, aluminum oxide, iron oxide, magnesium oxide, zinc oxide, nickel oxide and copper oxide;

[0068] The alkali metal / alkaline earth metal hydroxides are selected from one or more of calcium hydroxide, sodium hydroxide, potassium hydroxide, magnesium hydroxide, iron hydroxide, and aluminum hydroxide;

[0069] The alkali metal / alkaline earth metal carbonates are selected from one or more of calcium carbonate, sodium carbonate, potassium carbonate, magnesium carbonate, zinc carbonate, barium carbonate, magnesium carbonate, copper carbonate, and ammonium carbonate.

[0070] The silicates of the alkali metals / alkaline earth metals are sodium silicate and / or magnesium silicate.

[0071] In one embodiment, the outlet temperature of the second screw-type heating conveyor in step S2 is 280℃~450℃, preferably 300℃~430℃, and the residence time is 6min~25min.

[0072] In one embodiment, the viscosity reduction cracking unit in step S4 uses a viscosity reduction reactor for viscosity reduction cracking treatment, wherein the viscosity reduction reactor is an adiabatic viscosity reduction reactor; the process conditions for the viscosity reduction cracking treatment are conventional viscosity reduction cracking reaction conditions in the art, optionally, the reaction temperature is 350℃~450℃, preferably 360℃~430℃, more preferably 370℃~410℃; the residence time is 15min~150min, preferably 20min~120min.

[0073] In one embodiment, in step S4, the heating unit includes a heating furnace; the process conditions for heating treatment are conventional operating conditions in the art, and optionally, the outlet temperature of the heating furnace is 430°C to 570°C, preferably 450°C to 550°C; steam is injected along with the heated material, and the steam injection amount is 0.5% to 5% by weight, preferably 1% to 3% by weight.

[0074] In one embodiment, in step S5, the pyrolysis reaction unit is a pyrolysis tower, and the pyrolysis reaction process conditions adopt conventional operating conditions in the art. Optionally, the top pressure of the pyrolysis tower is 0.05MPa to 0.6MPa, preferably 0.1MPa to 0.4MPa; the pyrolysis reaction temperature is 430℃ to 550℃, preferably 450℃ to 520℃.

[0075] Secondly, the present invention provides a system for preparing low-chlorine pyrolysis oil from plastic mixtures, as shown in the attached figure. Figure 1 As shown, the system includes a first screw-type heating and conveying device 2 for chlorinated plastics, a first screw-type heating and conveying device 4 for additive-containing plastics, a second screw-type heating and conveying device 8, a viscosity-reducing cracking unit 10, a heating unit 11, a pyrolysis reaction unit 12, and a separation unit 13;

[0076] A first screw-type heating and conveying device 2 for chlorinated plastics and a first screw-type heating and conveying device 4 for additive-containing plastics are connected in parallel, including an inlet and an outlet; the first screw-type heating and conveying device 2 for chlorinated plastics is configured to perform dehydration, degassing and volume reduction treatment on chlorinated plastics; the first screw-type heating and conveying device 4 for additive-containing plastics is configured to perform dehydration, degassing and volume reduction treatment on additive-containing plastics.

[0077] The outlet of the first screw-type heating conveyor for chlorinated plastics and the outlet of the fourth screw-type heating conveyor for additive-containing plastics are respectively connected to the second screw-type heating conveyor.

[0078] The second screw-type heating and conveying device 8 is provided with a dechlorinated plastic outlet; the second screw-type heating and conveying device is configured to liquefy and dechlorinate the dehydrated, degassed, and volume-reduced plastic to obtain dechlorinated plastic;

[0079] The viscosity-reducing cracking unit 10 includes a dechlorinated plastic inlet and a viscosity-reducing cracked plastic oil outlet; the dechlorinated plastic inlet is connected to the dechlorinated plastic outlet of the second screw-type heating and conveying device 8; the viscosity-reducing cracking unit 10 is configured to perform viscosity-reducing cracking treatment on the dechlorinated plastic to obtain viscosity-reducing cracked plastic oil.

[0080] The heating unit 11 includes a viscosity-reducing cracked plastic oil inlet and a heated plastic oil outlet. The viscosity-reducing cracked plastic oil inlet is connected to the viscosity-reducing cracked plastic oil outlet of the viscosity-reducing cracked unit 10. The heating unit 11 is configured to heat the viscosity-reducing cracked plastic oil to obtain heated plastic oil.

[0081] The pyrolysis reaction unit 12 includes a heating plastic oil inlet and a pyrolysis product outlet; the heating plastic oil inlet is connected to the heating plastic oil outlet of the heating unit 11; the pyrolysis reaction unit 11 is configured to perform a pyrolysis reaction on the heating plastic oil to obtain pyrolysis products and coke.

[0082] The separation unit 13 includes a pyrolysis product inlet, a dry gas outlet, a liquefied gas outlet, and a pyrolysis oil outlet; the pyrolysis product inlet is connected to the pyrolysis product outlet of the pyrolysis reaction unit 12; the separation unit 13 is configured to separate the pyrolysis products to obtain dry gas, liquefied gas, and pyrolysis oil.

[0083] The following examples illustrate the method provided by the present invention in detail, but the present invention is not limited thereto.

[0084] Example 1

[0085] according to Figure 1 The process flow shown involves pulverizing and removing impurities from a mixed plastic containing 20 wt% LDPE, 20 wt% HDPE, 40 wt% PP, 16 wt% PS, and 4 wt% PVC (chlorine content of 2 wt%, analyzed by X-ray fluorescence spectrometry) to obtain chlorine-containing waste plastic particles. These particles are then dehydrated, degassed, and reduced in volume using a first screw-type heated conveyor for chlorine-containing plastics, resulting in dehydrated, degassed, and reduced-volume chlorine-containing plastics. The feed rate of the chlorine-containing plastics is 100 g / s, the outlet temperature of the first screw-type heated conveyor is 200℃, the screw internal pressure is 0.5 MPa, the conveying linear speed is 0.005 m / s, and the material residence time is 8 min. Antibacterial plastic containing 4% by weight calcium carbonate and 96% by weight polyethylene was pulverized and impurities removed (the composition and content of additives in the plastic were determined by a combination of infrared spectroscopy, thermogravimetric analysis, and X-ray fluorescence spectroscopy). The resulting plastic was then dehydrated, degassed, and reduced in volume using a first screw-type heated conveyor for additive-containing plastics. The outlet temperature of the first screw-type heated conveyor was 200℃, the screw internal pressure was 0.4MPa, the conveying linear speed was 0.005m / s, the material residence time was 10min, and the feed rate of the chlorinated plastic was 50g / s.

[0086] Then, the dehydrated, degassed, and reduced-volume chlorinated plastic is mixed with the dehydrated, degassed, and reduced-volume additive-containing plastic at the inlet of the second screw-type heating and conveying equipment. The mass ratio of calcium carbonate to chlorine is 1:1. The outlet temperature of the second screw-type heating and conveying equipment is 400℃, and the residence time is 6 minutes, resulting in liquefied dechlorinated waste plastic. The vacuum degree of the screw-type heating and conveying equipment is 150 mmHg.

[0087] During the dechlorination process, a vacuum system is used to extract the gaseous material containing hydrogen chloride and send it into the hydrogen chloride absorption unit, where it comes into contact with the hydrogen chloride absorbent (NaOH solution) for hydrogen chloride absorption treatment.

[0088] The liquefied dechlorinated waste plastic is fed into an adiabatic de-viscosity reactor for de-viscosity cracking treatment to obtain de-viscosity cracked liquefied plastic oil and first dry gas. The de-viscosity cracking treatment temperature is 380℃ and the residence time is 60min to obtain liquefied dechlorinated plastic oil.

[0089] The dechlorinated plastic oil was first heated in a furnace to obtain high-temperature liquefied plastic. The furnace outlet temperature was 500℃, and the steam injection rate was 1% by weight. Then, the high-temperature liquefied plastic was sent to a pyrolysis tower for pyrolysis reaction at 490℃ for 40s. The pyrolysis products were separated by a separation unit to obtain pyrolysis oil, coke, and pyrolysis gas. The chlorine content analysis results of the pyrolysis oil are shown in Table 1 (X-ray fluorescence spectrometry was used for analysis).

[0090] Example 2

[0091] according to Figure 1 The process flow shown involves crushing and removing impurities from a mixed plastic containing LDPE, HDPE, PP, PS, and PVC (chlorine content of 0.5% by weight) to obtain chlorine-containing waste plastic particles. These particles are then dehydrated, degassed, and reduced in volume using a first screw-type heated conveyor for chlorine-containing plastics, resulting in dehydrated, degassed, and reduced-volume chlorine-containing waste plastics. The feed rate of the chlorine-containing plastics is 100 g / s, the outlet temperature of the first screw-type heated conveyor is 180°C, the screw internal pressure is 1 MPa, the conveying line speed is 0.004 m / s, and the material residence time is 10 min. Combustible plastic bags containing 25% by weight calcium carbonate and 75% by weight polyethylene are crushed and impurities are removed. The bags are then dehydrated, degassed, and reduced in volume using a first screw-type heated conveyor for plastics containing additives. The resulting dehydrated, degassed, and reduced-volume waste plastics containing additives are obtained. The feed rate of the plastics containing additives is 20 g / s, the outlet temperature of the first screw-type heated conveyor is 300℃, the screw internal pressure is 0.2 MPa, the conveying line speed is 0.008 m / s, and the material residence time is 5 min.

[0092] Then, the dehydrated, degassed, and reduced-volume plastic is mixed with the dehydrated, degassed, and reduced-volume alkaline waste plastic in the middle section of the second screw-type heating and conveying equipment. The mass ratio of calcium carbonate to chlorine is 1:1. The outlet temperature of the second screw-type heating and conveying equipment is 400℃, and the residence time is 5 minutes, to obtain liquefied dechlorinated waste plastic. The vacuum degree of the screw-type heating and conveying equipment is 150 mmHg.

[0093] During the dechlorination process, a vacuum system is used to extract the gaseous material containing hydrogen chloride and send it into the hydrogen chloride absorption unit, where it comes into contact with the NaOH solution, a hydrogen chloride absorbent, for hydrogen chloride absorption treatment.

[0094] The liquefied dechlorinated waste plastic is fed into an adiabatic de-viscosity reactor for de-viscosity cracking treatment to obtain de-viscosity cracked liquefied waste plastic oil and first dry gas. The de-viscosity cracking treatment temperature is 380℃, and the residence time is 60min to obtain liquefied dechlorinated plastic oil.

[0095] The dechlorinated plastic oil was first heated in a furnace to obtain high-temperature liquefied plastic. The furnace outlet temperature was 500℃, and the steam injection rate was 1% by weight. Then, the high-temperature liquefied waste plastic was sent to a pyrolysis tower for pyrolysis reaction. Pyrolysis was carried out at 470℃ for 50s. The obtained pyrolysis products were separated by a separation unit to obtain pyrolysis oil, coke, and pyrolysis gas. The chlorine content analysis results of the pyrolysis oil are shown in Table 1.

[0096] Example 3

[0097] according to Figure 1 The process flow shown involves crushing and removing impurities from a mixed plastic containing LDPE, HDPE, PP, PS, and PVC (chlorine content of 5% by weight) to obtain chlorine-containing waste plastic particles. These particles are then dehydrated, degassed, and reduced in volume using a first screw-type heated conveyor for chlorine-containing plastics, resulting in dehydrated, degassed, and reduced-volume chlorine-containing plastics. The feed rate of the chlorine-containing plastics is 100 g / s, the outlet temperature of the first screw-type heated conveyor is 180°C, the screw internal pressure is 1 MPa, the conveying line speed is 0.006 m / s, and the material residence time is 7 min. Thermally conductive plastic containing 10% by weight magnesium oxide and 90% by weight polypropylene plastic is crushed and impurities are removed. Then, it is dehydrated, degassed, and reduced in volume by a first screw-type heating and conveying device for plastics with additives, resulting in dehydrated, degassed, and reduced-volume plastics with additives. The feed rate of the plastics with additives is 50 g / s, the outlet temperature of the first screw-type heating and conveying device is 350℃, the screw internal pressure is 1 MPa, the conveying linear speed is 0.007 m / s, and the material residence time is 6 min.

[0098] Then, the dehydrated, degassed, and reduced-volume chlorinated plastic is mixed with the dehydrated, degassed, and reduced-volume additive-containing plastic at the front end of the second screw-type heating and conveying equipment and then enters the second screw-type heating and conveying equipment. The mass ratio of magnesium oxide to chlorine is 1:1. The outlet temperature of the second screw-type heating and conveying equipment is 400℃, and the residence time is 5 minutes, resulting in liquefied dechlorinated plastic. The vacuum degree of the screw-type heating and conveying equipment is 150 mmHg.

[0099] During the dechlorination process, a vacuum system is used to extract the gaseous material containing hydrogen chloride and send it into the hydrogen chloride absorption unit, where it comes into contact with the NaOH solution, a hydrogen chloride absorbent, for hydrogen chloride absorption treatment.

[0100] The liquefied dechlorinated waste plastic is fed into an adiabatic de-viscosity reactor for de-viscosity cracking treatment to obtain de-viscosity cracked liquefied waste plastic oil and first dry gas. The de-viscosity cracking treatment temperature is 400℃ and the residence time is 45min to obtain liquefied dechlorinated plastic oil.

[0101] The dechlorinated plastic oil was first heated in a furnace to obtain high-temperature liquefied plastic. The outlet temperature of the furnace was 510℃, and the steam injection rate was 2% by weight. Then, the high-temperature liquefied plastic was sent to a pyrolysis tower for pyrolysis reaction. The pyrolysis was carried out at 460℃ for 60s. The pyrolysis products were separated by a separation unit to obtain pyrolysis oil, coke, and pyrolysis gas. The chlorine content analysis results of the pyrolysis oil are shown in Table 1.

[0102] Example 4

[0103] according to Figure 1 The process flow shown involves crushing and removing impurities from a mixed plastic containing LDPE, HDPE, PP, PS, and PVC (chlorine content of 6% by weight) to obtain chlorine-containing waste plastic particles. These particles are then dehydrated, degassed, and reduced in volume using a first screw-type heated conveyor for chlorine-containing plastics, resulting in dehydrated, degassed, and reduced-volume chlorine-containing waste plastics. The feed rate of the chlorine-containing plastics is 100 g / s, the outlet temperature of the first screw-type heated conveyor is 150°C, the screw internal pressure is 2 MPa, the conveying line speed is 0.005 m / s, and the material residence time is 8 min. Agricultural film containing 10% by weight calcium oxide and 90% by weight polyethylene was crushed and impurities removed. It was then dehydrated, degassed, and reduced in volume using a first screw-type heated conveyor for plastics containing additives. The resulting dehydrated, degassed, and reduced-volume waste plastics containing additives were obtained. The feed rate of the plastics containing additives was 20 g / s, the outlet temperature of the first screw-type heated conveyor was 220℃, the screw internal pressure was 0.1 MPa, the conveying line speed was 0.01 m / s, and the material residence time was 4 min.

[0104] Then, the dehydrated, degassed, and reduced-volume chlorinated plastic is mixed with the dehydrated, degassed, and reduced-volume additive-containing plastic at the inlet of the second screw-type heating and conveying equipment. The mass ratio of zinc oxide to chlorine is 1:3. The outlet temperature of the second screw-type heating and conveying equipment is 400℃, and the residence time is 5 minutes, resulting in liquefied dechlorinated waste plastic. The vacuum degree of the screw-type heating and conveying equipment is 150 mmHg.

[0105] During the dechlorination process, a vacuum system is used to extract the gaseous material containing hydrogen chloride and send it into the hydrogen chloride absorption unit, where it comes into contact with the NaOH solution, a hydrogen chloride absorbent, for hydrogen chloride absorption treatment.

[0106] The liquefied dechlorinated waste plastic is fed into an adiabatic de-viscosity reactor for de-viscosity cracking treatment to obtain de-viscosity cracked liquefied plastic oil and first dry gas. The de-viscosity cracking treatment temperature is 430℃, and the residence time is 20min to obtain liquefied dechlorinated plastic oil.

[0107] The dechlorinated plastic oil was first heated in a furnace to obtain high-temperature liquefied plastic. The furnace outlet temperature was 520℃, and the steam injection rate was 3% by weight. The high-temperature liquefied plastic was then sent to a pyrolysis tower for pyrolysis reaction. The pyrolysis was carried out at 520℃ for 20 seconds. The pyrolysis products were separated by a separation unit to obtain pyrolysis oil, coke, and pyrolysis gas. The chlorine content analysis results of the pyrolysis oil are shown in Table 1.

[0108] Example 5

[0109] according to Figure 1 The process flow shown involves crushing and removing impurities from a mixed plastic containing LDPE, HDPE, PP, PS, and PVC (chlorine content of 6% by weight) to obtain chlorine-containing waste plastic particles. These particles are then dehydrated, degassed, and reduced in volume using a first screw-type heated conveyor for chlorine-containing plastics, resulting in dehydrated, degassed, and reduced-volume chlorine-containing waste plastics. The feed rate of the chlorine-containing plastics is 100 g / s, the outlet temperature of the first screw-type heated conveyor is 200°C, the screw internal pressure is 2 MPa, the conveying line speed is 0.005 m / s, and the material residence time is 8 min. Calcium-plastic board containing 60% by weight calcium carbonate and 40% by weight polyethylene is crushed and impurities are removed. Then, it is dehydrated, degassed, and reduced in volume by a screw-type heated conveyor with additives to obtain dehydrated, degassed, and reduced-volume plastic with additives. The feed rate of the plastic with additives is 10 g / s, the outlet temperature of the screw-type heated conveyor is 320℃, the screw internal pressure is 1.5 MPa, the conveying line speed is 0.008 m / s, and the material residence time is 5 min.

[0110] Then, the dehydrated, degassed, and volume-reduced waste plastic is mixed with the dehydrated, degassed, and volume-reduced waste plastic containing additives in the middle section of the second screw-type heating and conveying equipment. The mass ratio of calcium oxide to chlorine is 1:3. The outlet temperature of the second screw-type heating and conveying equipment is 400℃, and the residence time is 5 minutes, to obtain liquefied dechlorinated plastic. The vacuum degree of the screw-type heating and conveying equipment is 150 mmHg.

[0111] During the dechlorination process, a vacuum system is used to extract the gaseous material containing hydrogen chloride and send it into the hydrogen chloride absorption unit, where it comes into contact with the NaOH solution, a hydrogen chloride absorbent, for hydrogen chloride absorption treatment.

[0112] The liquefied dechlorinated waste plastic is fed into an adiabatic de-viscosity reactor for de-viscosity cracking treatment to obtain de-viscosity cracked liquefied waste plastic oil and first dry gas. The de-viscosity cracking treatment temperature is 380℃ and the residence time is 60min to obtain liquefied dechlorinated waste plastic oil.

[0113] The dechlorinated waste plastic oil was first heated in a furnace to obtain high-temperature liquefied plastic. The outlet temperature of the furnace was 500℃, and the steam injection rate was 1% by weight. Then, the high-temperature liquefied plastic was sent to a pyrolysis tower for pyrolysis reaction. Pyrolysis was carried out at 480℃ for 60s. The pyrolysis products were separated by a separation unit to obtain pyrolysis oil, coke, and pyrolysis gas. The chlorine content analysis results of the pyrolysis oil are shown in Table 1.

[0114] Example 6

[0115] according to Figure 1The process flow shown involves crushing and removing impurities from a mixed plastic containing LDPE, HDPE, PP, PS, and PVC (chlorine content of 8% by weight) to obtain chlorine-containing waste plastic particles. These particles are then dehydrated, degassed, and reduced in volume using a first screw-type heated conveyor for chlorine-containing plastics, resulting in dehydrated, degassed, and reduced-volume chlorine-containing waste plastics. The feed rate of the chlorine-containing plastics is 90 g / s, the outlet temperature of the first screw-type heated conveyor is 170°C, the screw internal pressure is 0.8 MPa, the conveying line speed is 0.004 m / s, and the material residence time is 10 min. Soft polyethylene wire containing 15% by weight calcium hydroxide and 85% by weight polyethylene was crushed and impurities removed. It was then dehydrated, degassed, and reduced in volume using a first screw-type heated conveyor for additive-containing plastics, yielding dehydrated, degassed, and reduced-volume waste plastic containing additives. The feed rate of the additive-containing plastic was 16 g / s, the outlet temperature of the first screw-type heated conveyor was 360℃, the screw internal pressure was 1.0 MPa, the conveyor line speed was 0.008 m / s, and the material residence time was 5 min. Then, the dehydrated, degassed, and reduced-volume chlorinated plastic was mixed with the dehydrated, degassed, and reduced-volume chlorinated plastic containing additives, with a calcium hydroxide to chlorine mass ratio of 1:3. This mixture was then fed into a second screw-type heated conveyor for dechlorination and liquefaction treatment. The outlet temperature of the second screw-type heated conveyor was 420℃, and the residence time was 6 min, yielding liquefied dechlorinated waste plastic. The vacuum degree of the screw-type heated conveyor was 150 mmHg.

[0116] During the dechlorination process, a vacuum system is used to extract the gaseous material containing hydrogen chloride and send it into the hydrogen chloride absorption unit, where it comes into contact with the NaOH solution, a hydrogen chloride absorbent, for hydrogen chloride absorption treatment.

[0117] The liquefied dechlorinated waste plastic is fed into an adiabatic de-viscosity reactor for de-viscosity cracking treatment to obtain de-viscosity cracked liquefied waste plastic oil and first dry gas. The de-viscosity cracking treatment temperature is 360℃ and the residence time is 120min to obtain liquefied dechlorinated plastic oil.

[0118] The dechlorinated waste plastic oil was first heated in a furnace to obtain high-temperature liquefied plastic. The outlet temperature of the furnace was 460℃, and the steam injection rate was 1% by weight. Then, the high-temperature liquefied plastic was sent to a pyrolysis reaction tower and pyrolyzed at 480℃ for 50s. The pyrolysis products were separated by a separation unit to obtain pyrolysis oil, coke, and pyrolysis gas. The chlorine content analysis results of the pyrolysis oil are shown in Table 1.

[0119] Example 7

[0120] according to Figure 1The process flow shown involves crushing and removing impurities from a mixed plastic containing 2DPE, HDPE, PP, PS, and PVC (chlorine content of 1% by weight) to obtain chlorine-containing waste plastic particles. These particles are then dehydrated, degassed, and reduced in volume using a first screw-type heated conveyor for chlorine-containing plastics, resulting in dehydrated, degassed, and reduced-volume chlorine-containing waste plastics. The feed rate of the chlorine-containing plastics is 100 g / s, the outlet temperature of the first screw-type heated conveyor is 170°C, the screw internal pressure is 0.8 MPa, the conveying line speed is 0.004 m / s, and the material residence time is 10 min. A polyethylene shoe sole containing 1% by weight calcium carbonate and 99% by weight polyethylene is crushed and impurity removed. It is then dehydrated, degassed, and reduced in volume using a screw-type heated conveyor system for additive-containing plastics. The resulting dehydrated, degassed, and reduced-volume additive-containing plastic has the following characteristics: feed rate of 100 g / s; outlet temperature of the screw-type heated conveyor system: 210℃; screw internal pressure: 2.5 MPa; conveyor linear speed: 0.005 m / s; material residence time: 8 min.

[0121] Then, the dehydrated, degassed, and reduced-volume chlorine-containing waste plastic is mixed with the dehydrated, degassed, and reduced-volume additive-containing waste plastic at the inlet of the second screw-type heating and conveying equipment. The mass ratio of calcium carbonate to chlorine is 1:1. The outlet temperature of the second screw-type heating and conveying equipment is 390℃, and the residence time is 6 minutes, resulting in liquefied dechlorinated waste plastic. The screw-type heating and conveying equipment is not vacuumed.

[0122] During the dechlorination process, a vacuum system is used to extract the gaseous material containing hydrogen chloride and send it into the hydrogen chloride absorption unit, where it comes into contact with the hydrogen chloride absorbent (NaOH solution) for hydrogen chloride absorption treatment.

[0123] The liquefied dechlorinated waste plastic is fed into a viscosity reduction tank for viscosity reduction cracking treatment to obtain liquefied waste plastic oil and first dry gas. The viscosity reduction cracking treatment temperature is 380℃ and the residence time is 60min to obtain liquefied dechlorinated waste plastic oil.

[0124] The dechlorinated waste plastic oil is first heated in a furnace to obtain high-temperature liquefied waste plastic. The outlet temperature of the furnace is 500℃ and the steam injection rate is 1% by weight. Then, the high-temperature liquefied waste plastic is sent to a pyrolysis reaction device and pyrolyzed at 500℃ for 35s. The pyrolysis products are separated by a separation unit to obtain pyrolysis oil, coke and pyrolysis gas, etc. The chlorine content analysis results of the pyrolysis oil are shown in Table 1.

[0125] Comparative Example 1

[0126] according to Figure 1The process flow shown involves crushing and removing impurities from a mixture of waste plastics containing 20 wt% LDPE, 20 wt% HDPE, 40 wt% PP, 16 wt% PS, and 4 wt% PVC to obtain chlorinated waste plastic granules. These granules are then dehydrated, degassed, and reduced in volume using a first screw-type heated conveyor to obtain dehydrated, degassed, and reduced-volume chlorinated waste plastics. The feed rate of the chlorinated plastics is 100 g / s, the outlet temperature of the first screw-type heated conveyor is 200℃, the screw internal pressure is 0.5 MPa, the conveyor linear speed is 0.005 m / s, and the material residence time is 8 min.

[0127] Then, the dehydrated, degassed, and volume-reduced waste plastic is directly liquefied and dechlorinated in the third screw-type heating and conveying equipment without adding any additives. The outlet temperature of the second screw-type heating and conveying equipment is 400℃, and the residence time is 8 minutes, resulting in liquefied and dechlorinated waste plastic. The vacuum degree of the screw-type heating and conveying equipment is 150 mmHg.

[0128] During the dechlorination process, a vacuum system is used to extract the gaseous material containing hydrogen chloride and send it into the hydrogen chloride absorption unit, where it comes into contact with the hydrogen chloride absorbent (NaOH solution) for hydrogen chloride absorption treatment.

[0129] The liquefied dechlorinated waste plastic is fed into a viscosity reduction tank for viscosity reduction cracking treatment to obtain liquefied waste plastic oil and first dry gas. The viscosity reduction cracking treatment temperature is 380℃ and the residence time is 60min to obtain liquefied dechlorinated waste plastic oil.

[0130] The dechlorinated waste plastic oil is first heated in a furnace to obtain high-temperature liquefied waste plastic. The outlet temperature of the furnace is 500℃ and the steam injection rate is 1% by weight. Then, the high-temperature liquefied waste plastic is sent to a pyrolysis reaction device and pyrolyzed at 480℃ for 40s. The pyrolysis products are separated by a separation unit to obtain pyrolysis oil, coke and pyrolysis gas, etc. The chlorine content analysis results of the pyrolysis oil are shown in Table 1.

[0131] Comparative Example 2

[0132] according to Figure 1 The process flow shown involves crushing and removing impurities from a mixed plastic comprising 20 wt% LDPE, 20 wt% HDPE, 40 wt% PP, 16 wt% PS, and 4 wt% PVC to obtain chlorine-containing waste plastic granules. These granules are then dehydrated, degassed, and reduced in volume using a first screw-type heated conveyor to obtain dehydrated, degassed, and reduced-volume chlorine-containing waste plastic. The feed rate of the chlorine-containing plastic is 100 g / s, the outlet temperature of the first screw-type heated conveyor is 200℃, the screw internal pressure is 0.5 MPa, the conveyor linear speed is 0.005 m / s, and the material residence time is 8 min.

[0133] Then, the dehydrated, degassed, and volume-reduced waste plastic is directly liquefied and dechlorinated in a second screw-type heating and conveying device without adding waste plastic containing additives. The outlet temperature of the second screw-type heating and conveying device is 400℃, and the residence time is 10 minutes, resulting in liquefied and dechlorinated waste plastic. The screw-type heating and conveying device is not vacuumed.

[0134] During the dechlorination process, a vacuum system is used to extract the gaseous material containing hydrogen chloride and send it into the hydrogen chloride absorption unit, where it comes into contact with the hydrogen chloride absorbent (NaOH solution) for hydrogen chloride absorption treatment.

[0135] The liquefied dechlorinated waste plastic is fed into a viscosity reduction tank for viscosity reduction cracking treatment to obtain liquefied waste plastic oil and first dry gas. The viscosity reduction cracking treatment temperature is 380℃ and the residence time is 60min to obtain liquefied dechlorinated waste plastic oil.

[0136] The dechlorinated waste plastic oil is first heated in a furnace to obtain high-temperature liquefied waste plastic. The outlet temperature of the furnace is 500℃ and the steam injection rate is 1% by weight. Then, the high-temperature liquefied waste plastic is sent to a pyrolysis reaction device and pyrolyzed at 480℃ for 40s. The pyrolysis products are separated by a separation unit to obtain pyrolysis oil, coke and pyrolysis gas, etc. The chlorine content analysis results of the pyrolysis oil are shown in Table 1.

[0137] Table 1. Chlorine content in pyrolysis oil in the examples and comparative examples.

[0138] Instance number Chlorine content of pyrolysis oil (μg / g) Example 1 55 Example 2 10 Example 3 88 Example 4 256 Example 5 172 Example 6 138 Example 7 23 Comparative Example 1 630 Comparative Example 2 1840

[0139] As can be seen from Table 1, and from Examples 1 to 7, and compared with Comparative Examples 1 to 2, it can be seen that adding plastic containing additives during the pyrolysis dechlorination process, wherein the additives are oxides, hydroxides and salts of alkali metals / alkaline earth metals, can adsorb HCl released by the decomposition of chlorinated compounds at high temperatures throughout the process in situ, reducing the generation of organochlorines. This can effectively achieve the co-pyrolysis of waste plastics containing alkaline additives and waste plastics containing chlorine, and produce low-chlorine pyrolysis oil on a large scale and continuously.

[0140] The preferred embodiments of this disclosure have been described in detail above. However, this disclosure is not limited to the specific details of the above embodiments. Within the scope of the technical concept of this disclosure, various simple modifications can be made to the technical solutions of this disclosure, and these simple modifications all fall within the protection scope of this disclosure.

Claims

1. A method for preparing pyrolysis oil from a plastic mixture, characterized in that, Includes the following steps: S1. Chlorine-containing plastics and additive-containing plastics are fed separately or together into the first screw-type heating and conveying equipment for dehydration, degassing and volume reduction treatment to obtain dehydrated, degassing and volume-reduced plastics. S2. The dehydrated, degassed, and volume-reduced plastic is fed into a second screw-type heating and conveying device for liquefaction and dechlorination treatment to obtain liquefied and dechlorinated plastic. S3. The liquefied dechlorinated plastic is fed into a viscosity-reducing cracking unit for viscosity-reducing cracking treatment to obtain viscosity-reduced cracked plastic oil and first dry gas; the reaction temperature is 350℃~450℃ and the residence time is 15min~60min. S4. The viscosity-reducing cracked plastic oil is fed into a heating unit for heating treatment to obtain heated plastic oil; S5. The heated plastic oil is introduced into the pyrolysis reaction unit for pyrolysis reaction to obtain pyrolysis products and coke; the pyrolysis reaction unit adopts a pyrolysis tower with a tower top pressure of 0.05MPa~0.6MPa, a pyrolysis reaction temperature of 430℃~550℃, and a pyrolysis reaction time of 20s-60s. S6. The pyrolysis products are separated in a separation unit to obtain second dry gas, liquefied gas and pyrolysis oil. Wherein, in the additive-containing plastic, the content of the additive is 0.1% to 90% by weight, the additive is zinc oxide, or the additive is selected from oxides, hydroxides and salts of alkali metals / alkaline earth metals; the ratio of additive-containing plastic to chlorine-containing plastic is such that the mass ratio of additive to chlorine is 1:0.5 to 20.

2. The method for preparing pyrolysis oil from plastic mixtures according to claim 1, characterized in that, Chlorinated plastics are processed in a first screw-type heating and conveying equipment for chlorinated plastics, with an outlet temperature of 100℃~250℃ and a residence time of 4min~20min, resulting in dehydrated, degassed, and volume-reduced chlorinated plastics. Additive-containing plastics are processed in a first screw-type heating and conveying equipment for additive-containing plastics, with an outlet temperature of 120℃~380℃ and a residence time of 4min~20min, resulting in dehydrated, degassed, and volume-reduced additive-containing plastics. The processed materials are then fed into a second screw-type heating and conveying equipment.

3. The method for preparing pyrolysis oil from plastic mixtures according to claim 2, characterized in that, The outlet temperature of the first screw-type heating and conveying device for chlorinated plastics is 150℃~200℃, the residence time is 5min~16min, and the internal pressure of the screw is 0.1MPa~6MPa; the outlet temperature of the first screw-type heating and conveying device for additive-containing plastics is 150℃~380℃, the residence time is 5min~16min, and the internal pressure of the screw is 0.1MPa~6MPa.

4. The method for preparing pyrolysis oil from plastic mixtures according to claim 3, characterized in that, The outlet temperature of the first screw-type heating conveyor for plastics containing additives is 10℃~180℃ higher than that of the first screw-type heating conveyor for plastics containing chlorine.

5. The method for preparing pyrolysis oil from plastic mixtures according to claim 4, characterized in that, The outlet temperature of the first screw-type heating conveyor for plastics containing additives is 20℃~150℃ higher than that of the first screw-type heating conveyor for plastics containing chlorine.

6. The method for preparing pyrolysis oil from a plastic mixture according to any one of claims 1-5, characterized in that, The outlet temperature of the second screw-type heating conveyor is 280℃~450℃, and the residence time is 5min~30min.

7. The method for preparing pyrolysis oil from plastic mixtures according to claim 6, characterized in that, The outlet temperature of the second screw-type heating conveyor is 300℃~430℃, the residence time is 5min~20min, and the internal pressure of the screw is 0.0001MPa~5MPa.

8. The method for preparing pyrolysis oil from a plastic mixture according to any one of claims 1-5, characterized in that, The viscosity reduction cracking unit mentioned in step S3 uses an adiabatic viscosity reduction cracking reactor to carry out the viscosity reduction cracking treatment. The reaction temperature is 360℃~430℃ and the residence time is 20min~60min.

9. The method for preparing pyrolysis oil from a plastic mixture according to any one of claims 1-5, characterized in that, The heating unit mentioned in step S4 includes a heating furnace with an outlet temperature of 430°C to 570°C. Water vapor is injected into the heating furnace, and the amount of steam injected is 0.5% to 5% by weight, based on the weight of the viscosity-reducing cracked plastic oil entering the heating furnace.

10. The method for preparing pyrolysis oil from a plastic mixture according to claim 9, characterized in that, The outlet temperature of the heating furnace is 450℃~550℃.

11. The method for preparing pyrolysis oil from a plastic mixture according to any one of claims 1-5, characterized in that, In step S2, under the action of the vacuum system, the gas generated in the second screw heating and conveying device enters the hydrogen chloride absorption unit and comes into contact with the hydrogen chloride absorbent to remove hydrogen chloride. The hydrogen chloride absorbent is water or an alkaline solution.

12. The method for preparing pyrolysis oil from a plastic mixture according to any one of claims 1-5, characterized in that, The chlorine-containing plastics include PVC; the additive-containing plastics refer to calcium-plastic materials containing additives, incinerable plastic garbage bags, flexible polyethylene wires, polyethylene shoe soles, plastic agricultural films, antibacterial plastics or thermally conductive plastics, wherein the content of the additives is 1% to 70% by weight.

13. The method for preparing pyrolysis oil from a plastic mixture according to any one of claims 1-5, characterized in that, The additives are selected from one or more of calcium carbonate, calcium oxide, calcium hydroxide, and magnesium oxide.

14. The method for preparing pyrolysis oil from a plastic mixture according to any one of claims 1-5, characterized in that, The ratio of additive-containing plastics to chlorine-containing plastics results in a mass ratio of additives to chlorine of 1:1-8.

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