A processing method and processing system for reducing viscosity and pyrolyzing waste plastics

Abstract

The present disclosure relates to a processing method and a processing system for viscosity reduction and pyrolysis cracking of waste plastics. The method includes the following steps: S1, enabling the waste plastics to be processed to enter a waste plastic liquefaction unit for liquefaction treatment to obtain liquefied waste plastics; S2, enabling the liquefied waste plastics to enter a waste plastic visbreaking unit for visbreaking cracking treatment to obtain visbroken liquefied waste plastic oil; S3, enabling the visbroken liquefied waste plastic oil to enter a material heating unit for heating treatment to obtain high-temperature liquefied waste plastics; S4, enabling the high-temperature liquefied waste plastics to enter a pyrolysis reaction unit for pyrolysis reaction to obtain pyrolysis products and coke; S5, enabling the pyrolysis products to enter a separation unit for separation treatment to obtain dry gas, liquefied gas, gasoline fraction, diesel fraction and wax oil fraction. It can effectively realize the resource utilization of waste plastics and reduce the generation of coke.

Description

Technical Field

[0001] The present disclosure relates to the field of waste plastic resource recycling, and in particular, to a processing method and a processing system for reducing the viscosity and pyrolyzing waste plastics. Background Art

[0002] At present, with the progress of technology and the development of industry, plastics, as packaging materials, have appeared in large quantities in human daily life. Used waste plastics cannot decompose by themselves in nature. Only a few types of waste plastics can be reprocessed and utilized through specific recycling channels, while a large amount of waste plastics enter landfills in the form of domestic waste. Since waste plastics are not easily decomposed, they occupy a large amount of space. In recent years, in particular, the generation amount of waste plastics has increased, and it has become an urgent task to quickly and greenly recycle waste plastics.

[0003] The simplest chemical method for treating waste plastics is direct incineration, but direct incineration will produce toxic gases harmful to the human body, causing secondary environmental pollution. The waste plastic oilification technology is to pyrolyze waste plastics under anaerobic or anoxic conditions by heating or in the presence of a catalyst, so that the high polymers are pyrolyzed into low-molecular substances, obtaining gasoline, kerosene, diesel fractions and some pyrolysis gases, etc. The waste plastic oilification technology, on the one hand, alleviates the pollution problem caused by waste plastics, and on the other hand, realizes the recycling of waste plastics, which is an important direction for the resource treatment of waste plastics.

[0004] At present, the waste plastic oilification recycling technologies mainly include waste plastic pyrolysis, catalytic pyrolysis and pyrolysis catalytic upgrading technologies, etc. The pyrolysis method has the advantages of simple process, relatively less equipment investment, no need for a catalyst, and short reaction process, etc., making the pyrolysis method have the lowest unit oilification cost compared with the other two technologies. The general waste plastics in domestic waste undergo high-temperature pyrolysis reactions between 380 and 500 °C, with a relatively fast pyrolysis rate and relatively single product components, which can be used as oil products or chemical raw materials.

[0005] CN109401774A discloses a continuous pyrolysis system for waste plastics and its pyrolysis method. The system includes a feeding device, a feeding device, a pyrolysis reactor, and a slag discharging device connected in sequence. Since plastics are macromolecular polymers and form non-Newtonian fluids during the heating process, a screw propeller is used. In this process, there is uneven heating during the plastic liquefaction process, and coking and fouling are likely to occur. CN10461030A discloses a coking method for producing fuel oil from waste plastics. In this method, high-aromatic components and waste plastics or plastic oil are preheated in a raw material buffer tank and then enter a tubular heating furnace to be heated up, and then sprayed into a delayed coking tower for coking reaction. The waste plastics mentioned in this method are one or several of polyethylene, polypropylene, and polystyrene, and do not include polyvinyl chloride. Therefore, waste plastic raw materials mixed with polyvinyl chloride cannot be processed. CN112538363A discloses a method for co-converting waste plastics in a delayed coking unit. This method co-converts waste plastics with petroleum residue raw materials. The waste plastics are selected from polyethylene, polypropylene, polystyrene, PET, and multi-layer plastics added with metals, and also do not include waste plastics containing polyvinyl chloride. Since waste plastics form a high-viscosity polymer melt during the melting process and there is a density difference with hydrocarbon raw materials, the mixed fluid of hydrocarbons and polymer melt can cause problems such as blockage and coking of the tubes of the delayed coking heating furnace. CN106118707B discloses an equipment and method for harmless treatment of waste plastics. In this method, a large screw feeding device is used to heat the waste plastics to 100-250°C and then enter a dechlorination splitter 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, when the waste plastics are at 250°C, they only soften into a plasticized high-molecular material, and their phase is a non-flowable non-liquid plastic solid state, making it difficult to output from the dechlorination splitter.

[0006] One of the difficulties in the pyrolysis recovery of waste plastics: When polyvinyl chloride in waste plastics is decomposed by heat into HCl, it can quickly react with double bonds in the raw materials to form chlorohydrocarbons, making it difficult for traditional reaction devices to efficiently remove chlorine from waste plastics. Difficulty two: Waste plastics belong to macromolecular polymers. Due to their huge molecular weight and being solid, heat transfer inside the plastics is very slow. Traditional heating methods will cause excessive cracking of the outside of the plastics, while the inside of the plastics remains solid, resulting in a relatively high coking rate and high gas yield during the pyrolysis of waste plastics. Difficulty three: The density of waste plastics is relatively low, and the feeding rate of waste plastics into the reaction device is relatively low. The processing scale of existing technologies is small and cannot meet the needs of modern large-scale recycling.

[0007] For the first difficulty, a special device is used to quickly heat the polyvinyl chloride-containing material to decompose it, and the vacuum method is used to quickly separate the decomposed HCl from the reactor, thereby improving the dechlorination efficiency. For the second difficulty, a special device is used to increase the heating area by strong extrusion and agitation and quickly heat the waste plastic to a flowable liquid state, and the viscosity is reduced so that it can be pumped. When the waste plastic is quickly liquefied, due to the significant increase in the thermal conductivity of the liquid state, heating equipment such as a heating furnace can be used to carry out pyrolysis reaction on the liquid waste plastic, and a high liquid yield and a low coking rate can be obtained. For the third difficulty: after the waste plastic is liquefied, the conveying density of the raw material is significantly increased compared with that of the solid waste plastic. Therefore, not only can the large-scale processing of waste plastic be realized, but also the continuous pyrolysis recovery of waste plastic can be realized. Summary of the Invention

[0008] The purpose of the present disclosure is to provide a processing method and a processing system for viscosity reduction and pyrolysis cracking of waste plastics, which can effectively realize the resource utilization, large-scale and continuous utilization of waste plastics, and reduce the generation of coke.

[0009] To achieve the above purpose, the first aspect of the present disclosure provides a processing method for viscosity reduction and pyrolysis cracking of waste plastics, the method comprising the following steps: S1, feeding the waste plastics to be processed into a waste plastic liquefaction unit for liquefaction treatment to obtain liquefied waste plastics; S2, feeding the liquefied waste plastics into a waste plastic viscosity reduction unit for viscosity reduction cracking treatment to obtain viscosity reduction cracked liquefied waste plastic oil; S3, feeding the viscosity reduction cracked liquefied waste plastic oil into a material heating unit for heating treatment to obtain high-temperature liquefied waste plastics; S4, feeding the high-temperature liquefied waste plastics into a pyrolysis reaction unit for pyrolysis reaction to obtain pyrolysis products and coke; S5, feeding the pyrolysis products into a separation unit for separation treatment to obtain dry gas, liquefied gas, gasoline fraction, diesel fraction and wax oil fraction.

[0010] Optionally, before step S1, the method further comprises: feeding the chlorine-containing waste plastic raw material into a waste plastic preliminary melting, liquefaction and dechlorination unit for hot melt dechlorination treatment to obtain a gas-phase material containing hydrogen chloride and a dechlorinated waste plastic material; feeding the dechlorinated waste plastic material into the waste plastic liquefaction unit; or subjecting the dechlorinated waste plastic material to cooling treatment and crushing treatment in sequence to obtain dechlorinated waste plastic particles; feeding the dechlorinated waste plastic particles into the waste plastic liquefaction unit.

[0011] Optionally, the method further includes: introducing the hydrogen chloride-containing gas into a hydrogen chloride absorption unit, contacting with a hydrogen chloride absorbent for hydrogen chloride absorption treatment to obtain a chlorine-containing absorbent and dechlorinated dry gas; optionally, introducing the hydrogen chloride-containing gas into the hydrogen chloride absorption unit under the action of a vacuum system; wherein the hydrogen chloride absorbent is water or an alkali solution with a pH greater than 7; optionally, the alkali solution includes one or more of sodium hydroxide solution, potassium hydroxide solution, calcium hydroxide solution, sodium bicarbonate solution, sodium carbonate solution, and ammonia water.

[0012] Optionally, the method further includes: returning at least a part of the wax oil fraction from the separation unit to the waste plastic visbreaking unit for recycling; preferably, the weight ratio of the recycled wax oil fraction to the waste plastic to be treated is 0.2-5.0:1, preferably 0.2-2:1; preferably, the fraction with a distillation range greater than 350 °C separated by the separation unit is used as the wax oil fraction.

[0013] Optionally, in step S1, the waste plastic liquefaction unit uses a rapid heating liquefaction conveying device for the liquefaction treatment; optionally, the rapid heating liquefaction conveying device includes a first screw-type heating conveying device; preferably, the first screw-type heating conveying device is selected from a double-screw type or a single-screw type heating conveying device with heating; preferably, the process conditions for the liquefaction treatment include: the outlet temperature is 370-500 °C, preferably 380-450 °C; the residence time is 5-20 min, preferably 5-15 min.

[0014] Optionally, in step S2, the waste plastic visbreaking unit uses a visbreaking reactor for the visbreaking cracking treatment, preferably, the visbreaking reactor is an adiabatic visbreaking reactor; preferably, the process conditions for the visbreaking cracking treatment include: the reaction temperature is 370-450 °C, preferably 380-420 °C, more preferably 390-420 °C; the residence time is 2-120 min, preferably 30-70 min.

[0015] Optionally, in step S3, the material heating unit includes a heating furnace; preferably, the process conditions for the heating treatment include: the outlet temperature of the heating furnace is 450 °C - 550 °C, preferably 460 °C - 520 °C; the steam injection amount is 0.5-5 wt%, optimized to 1-3 wt%.

[0016] Optionally, in step S4, the process conditions for the pyrolysis reaction include: the pressure at the top of the pyrolysis tower is 0.05-0.6 MPa, preferably 0.1-0.3 Mpa; the pyrolysis reaction temperature is 450-520 °C, preferably 480-520 °C.

[0017] Optionally, the preliminary melting, liquefaction, and dechlorination unit for waste plastics includes a second screw-type heating and conveying device and a vacuum device communicated with the second screw-type heating and conveying device; preferably, the second screw-type heating and conveying device is selected from a twin-screw type or a single-screw type conveying device; the process conditions for the hot-melt dechlorination treatment include: the feeding rate is 5-5000 kg / h, preferably 100-4000 kg / h; the outlet temperature is 150-370 °C, preferably 300-330 °C, the reaction time is 0.1-0.5 h, preferably 0.1-0.3 h; the vacuum degree of the preliminary melting, liquefaction, and dechlorination unit for waste plastics is 50-300 mmHg, preferably 50-150 mmHg; preferably, the particle size of the dechlorinated waste plastic particles obtained by the crushing treatment is 100-2000 μm.

[0018] Optionally, the waste plastics to be treated include one or more of LDPE, HDPE, PS, PP, PET, and PVC; optionally, the content of PVC in the waste plastics to be treated is less than 10% by weight; the ash content in the waste plastics to be treated is 1-40% by weight, preferably 3-30% by weight.

[0019] The second aspect of the present disclosure provides a processing system for viscosity reduction and pyrolysis cracking of waste plastics, which includes: a waste plastic liquefaction unit, a waste plastic viscosity reduction unit, a material heating unit, a pyrolysis reaction unit, and a separation unit; the waste plastic liquefaction unit includes an inlet for waste plastics to be treated and an outlet for liquefied waste plastics, and the waste plastic liquefaction unit is configured to perform liquefaction treatment on the waste plastics to be treated; the waste plastic viscosity reduction unit includes an inlet for liquefied waste plastics and an outlet for liquefied waste plastic oil, and the waste plastic viscosity reduction unit is configured to perform viscosity reduction and cracking treatment on the liquefied waste plastics; the material heating unit includes a heating inlet and a heating outlet, the heating inlet is communicated with the outlet for liquefied waste plastic oil of the waste plastic viscosity reduction unit, and the heating unit is configured to perform heating treatment on the liquefied waste plastic oil after viscosity reduction and cracking; the pyrolysis reaction unit includes a pyrolysis reactant inlet and a pyrolysis product outlet, the pyrolysis reactant inlet is communicated with the heating outlet of the heating unit, and the pyrolysis reaction unit is configured to perform pyrolysis reaction treatment on the high-temperature liquefied waste plastics; the separation unit includes a separation inlet, a dry gas outlet, a liquefied gas outlet, a gasoline fraction outlet, a diesel fraction outlet, and a wax oil fraction outlet; the separation inlet is communicated with the pyrolysis product outlet of the pyrolysis reaction unit, and the separation unit is configured to perform separation treatment on the pyrolysis products.

[0020] Optionally, the system further includes a preliminary melting, liquefaction, and dechlorination unit for waste plastics and a hydrogen chloride absorption unit; the preliminary melting, liquefaction, and dechlorination unit for waste plastics includes an inlet for raw materials of chlorine-containing waste plastics, an outlet for gaseous materials containing hydrogen chloride, and an outlet for dechlorinated waste plastics in liquid phase. The preliminary melting, liquefaction, and dechlorination unit for waste plastics is configured to perform hot melting and dechlorination treatment on the raw materials of chlorine-containing waste plastics; the outlet for dechlorinated waste plastics in liquid phase is communicated with the inlet for waste plastics to be treated of the waste plastics liquefaction unit; the hydrogen chloride absorption unit includes an inlet for gaseous materials containing hydrogen chloride, a hydrogen chloride absorbent, and an outlet for dechlorinated dry gas; the inlet for gaseous materials containing hydrogen chloride is communicated with the outlet for gaseous materials containing hydrogen chloride of the preliminary melting, liquefaction, and dechlorination unit for waste plastics; preferably, the waste plastics liquefaction includes a heating and liquefaction conveying device; optionally, the heating and liquefaction conveying device includes a first screw-type heating conveying device; preferably, the first screw-type heating conveying device is selected from a double-screw type or single-screw type heating conveying device with heating; preferably, the preliminary melting, liquefaction, and dechlorination unit for waste plastics includes a second screw-type heating conveying device and a vacuum device communicated with the second screw-type heating conveying device; preferably, the second screw-type heating conveying device is selected from a double-screw type or single-screw type conveying device; preferably, the waste plastics viscosity reduction unit further includes a circulating oil inlet; the circulating oil inlet is communicated with the outlet of the wax oil fraction of the separation unit; optionally, the preliminary melting, liquefaction, and dechlorination unit for waste plastics further includes a non-condensable gas outlet.

[0021] Through the above technical solutions, the present disclosure provides a processing method and a processing system for viscosity reduction and pyrolysis cracking of waste plastics. By subjecting the waste plastics to be treated to rapid liquefaction treatment and viscosity reduction cracking treatment, the viscosity of the liquefied waste plastics is reduced under the conditions of no coking and excessive cracking, forming a uniform and well-flowing fluidized waste plastics that can be transported by a pump; then, it is rapidly heated to the pyrolysis reaction temperature by means of a heating furnace or the like, and the high-temperature liquefied waste plastics are transported to a pyrolysis tower for pyrolysis reaction, realizing the resource utilization of waste plastics and reducing the generation of coke. Through the processing method of the present disclosure, the waste plastics in landfills can be dehydrated and dechlorinated and reduced in place, and the subsequent cracking and recovery can be centrally processed, which is easy to expand the production scale and reduce the processing cost; the process flow is simple, the equipment investment is relatively small, and large-scale, continuous, and green resource recovery of waste plastics is realized.

[0022] Other features and advantages of the present disclosure will be described in detail in the subsequent specific implementation section. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] The drawings are used to provide a further understanding of the present disclosure, and constitute a part of the specification, and are used together with the following specific implementation to explain the present disclosure, but do not constitute a limitation to the present disclosure. In the drawings:

[0024] Figure 1 It is an exemplary flowchart of a processing method and system for reducing viscosity and pyrolyzing waste plastics provided by the present disclosure.

[0025] Description of Reference Numerals

[0026] 1 - Waste plastic storage tank, 2 - Preliminary melting, liquefaction and dechlorination unit for waste plastics, 3 - Quick heating, liquefaction and transportation equipment, 4 - Adiabatic viscosity reduction reactor, 5 - Heating furnace, 6 - Pyrolysis reaction unit, 7 - Separation unit, 8 - Hydrogen chloride absorption unit, 9 - Pipeline, 10 - Pipeline, 11 - Pipeline, 12 - Pipeline, 13 - Pipeline, 14 - Pipeline, 15 - Pipeline, 16 - Pipeline, 17 - Pipeline, 18 - Pipeline. Specific Embodiments

[0027] The following details the specific embodiments of the present disclosure. It should be understood that the specific embodiments described herein are only for the purpose of illustrating and explaining the present disclosure, and are not intended to limit the present disclosure.

[0028] The first aspect of the present disclosure provides a processing method for reducing viscosity and pyrolyzing waste plastics, the method comprising the following steps:

[0029] S1. Feed the waste plastics to be processed into a waste plastic liquefaction unit for liquefaction treatment to obtain liquefied waste plastics;

[0030] S2. Feed the liquefied waste plastics into a waste plastic viscosity reduction unit for viscosity reduction cracking treatment to obtain viscosity reduction cracked liquefied waste plastic oil;

[0031] S3. Feed the viscosity reduction cracked liquefied waste plastic oil into a material heating unit for heating treatment to obtain high-temperature liquefied waste plastics;

[0032] S4. Feed the high-temperature liquefied waste plastics into a pyrolysis reaction unit for pyrolysis reaction to obtain pyrolysis products and coke;

[0033] S5. Feed the pyrolysis products into a separation unit for separation treatment to obtain dry gas, liquefied gas, gasoline fraction, diesel fraction and wax oil fraction.

[0034] The present disclosure provides a processing method for reducing viscosity and pyrolyzing waste plastics. By performing liquefaction treatment and viscosity reduction cracking treatment on the waste plastics to be processed, the viscosity of the liquefied waste plastics is reduced; then, through heating treatment, the temperature for pyrolysis reaction is reached, and a uniform and good-flowing material stream is formed; the high-temperature liquefied waste plastics are subjected to pyrolysis reaction, realizing the resource utilization of waste plastics and reducing coke generation; through the processing method of the present disclosure, waste plastics in landfills can be dehydrated and dechlorinated and reduced in quantity on-site, and subsequent cracking and recovery can be centrally processed, which is easy to expand the production scale and reduce the processing cost; the process flow is simple, the equipment investment is relatively small, and green resource recovery of waste plastics is achieved.

[0035] In a specific embodiment, the waste plastics to be processed include one or more of low-density polyethylene (LDPE), high-density polyethylene (HDPE), polystyrene (PS), polypropylene (PP), polyethylene terephthalate (PET), and polyvinyl chloride (PVC);

[0036] Optionally, the content of PVC in the waste plastics to be processed is less than 10% by weight; the ash content in the waste plastics to be processed is 1-40% by weight, preferably 3-30% by weight. The waste plastic raw materials in the present disclosure can directly use the waste plastics in landfills.

[0037] In a preferred embodiment, before step S1, the method further includes:

[0038] Feeding the chlorine-containing waste plastic raw materials into a waste plastic preliminary melting, liquefying and dechlorination unit for hot-melt dechlorination treatment to obtain a gas-phase material containing hydrogen chloride and a dechlorinated waste plastic material;

[0039] Feeding the dechlorinated waste plastic material into the waste plastic liquefaction unit; or

[0040] Cooling and pulverizing the dechlorinated waste plastic material in sequence to obtain dechlorinated waste plastic particles; feeding the dechlorinated waste plastic particles into the waste plastic liquefaction unit.

[0041] In the present disclosure, the hot-melt dechlorination step and the waste plastic liquefaction step can adopt the same fast heating, liquefying and conveying equipment, or each adopt a fast heating, liquefying and conveying equipment; for example, the fast heating, liquefying and conveying equipment is a screw-type heating and conveying equipment with heating, etc.

[0042] In an embodiment, the method further includes:

[0043] Feeding the hydrogen chloride-containing gas into a hydrogen chloride absorption unit to contact with a hydrogen chloride absorbent for hydrogen chloride absorption treatment to obtain a chlorine-containing absorbent and dechlorinated dry gas;

[0044] Optionally, under the action of a vacuum system, feeding the hydrogen chloride-containing gas into the hydrogen chloride absorption unit.

[0045] In the present disclosure, the chlorine in the chlorine-containing waste plastic PVC is decomposed into the gas phase through the waste plastic preliminary melting, liquefying and dechlorination unit, and the hydrogen chloride can be quickly separated using a vacuum system, avoiding the secondary reaction of hydrogen chloride, improving the dechlorination efficiency of waste plastics, and reducing the anti-corrosion pressure of subsequent equipment.

[0046] In a specific embodiment, the hydrogen chloride absorbent is water or an alkaline solution with a pH greater than 7; optionally, the alkaline solution includes one or more of sodium hydroxide solution, potassium hydroxide solution, calcium hydroxide solution, sodium bicarbonate solution, sodium carbonate solution, and ammonia water.

[0047] In a preferred embodiment, the method further includes:

[0048] Returning at least part of the wax oil fraction from the separation unit to the waste plastic visbreaking unit for recycling;

[0049] Preferably, the fraction with a distillation range greater than 350 °C separated by the separation unit is used as the wax oil fraction. Processing according to this embodiment can further improve the utilization efficiency of waste plastic resources; and introducing the wax oil fraction into the waste plastic visbreaking unit is also beneficial to the visbreaking and cracking treatment of waste plastics.

[0050] In a specific embodiment, the weight ratio of the recycled wax oil fraction to the waste plastic to be treated is 0.2 - 5.0:1, preferably 0.2 - 2:1.

[0051] In one embodiment, in step S1, the waste plastic liquefaction unit uses a rapid heating liquefaction and conveying device for the liquefaction treatment; optionally, the rapid heating liquefaction and conveying device includes a first screw type heating and conveying device; preferably, the first screw type heating and conveying device is selected from a double screw type or a single screw type heating and conveying device with heating. The rapid heating liquefaction and conveying device adopted in the present disclosure is beneficial to the rapid liquefaction treatment of solid waste plastics.

[0052] In a preferred embodiment, the process conditions of the liquefaction treatment include: the outlet temperature is 370 - 500 °C, preferably 380 - 450 °C; the residence time is 5 - 20 min, preferably 5 - 15 min.

[0053] In one embodiment, in step S2, the waste plastic visbreaking unit uses a visbreaking reactor for the visbreaking and cracking treatment, preferably an adiabatic visbreaking reactor. The visbreaking reactor in the present disclosure can be any reactor known in the art, such as an up - flow visbreaking reactor or a down - flow visbreaking reactor.

[0054] In a preferred embodiment, the process conditions of the visbreaking and cracking treatment include: the reaction temperature is 370 - 450 °C, preferably 380 - 420 °C, more preferably 390 - 420 °C; the residence time is 2 - 120 min, preferably 30 - 70 min, further preferably 50 - 70 min.

[0055] In one embodiment, in step S3, the material heating unit includes a heating furnace;

[0056] Preferably, the process conditions of the heating treatment include: the outlet temperature of the heating furnace is 450 °C - 550 °C, preferably 460 °C - 520 °C; the steam injection amount is 0.5 - 5 wt%, preferably 1 - 3 wt%.

[0057] In one embodiment, in step S4, the process conditions of the pyrolysis reaction include: the pressure at the top of the pyrolysis tower is 0.05 - 0.6 MPa, preferably 0.1 - 0.3 Mpa; the pyrolysis reaction temperature is 450 - 520 °C, preferably 480 - 520 °C.

[0058] In the present disclosure, the pyrolysis reaction unit may include multiple pyrolysis towers arranged in parallel.

[0059] In one embodiment, the preliminary melting, liquefaction and dechlorination unit of waste plastics includes a second screw-type heating and conveying device and a vacuum device communicated with the second screw-type heating and conveying device; preferably, the second screw-type heating and conveying device is selected from a twin-screw type or a single-screw type conveying device.

[0060] In a preferred embodiment, the process conditions of the hot melt dechlorination treatment include: the feeding rate is 5 - 5000 kg / h, preferably 100 - 4000 kg / h; the outlet temperature is 150 - 370 °C, preferably 300 - 330 °C, the reaction time is 0.1 - 0.5 h, preferably 0.1 - 0.3 h; the vacuum degree of the preliminary melting, liquefaction and dechlorination unit of waste plastics is 50 - 300 mmHg, preferably 50 - 150 mmHg;

[0061] Preferably, the particle size of the dechlorinated waste plastic particles obtained by the crushing treatment is 100 - 2000 μm.

[0062] In the present disclosure, the devices and methods for the cooling treatment and the crushing treatment may be conventional devices and methods in the art.

[0063] In the second aspect of the present disclosure, there is provided a processing system for reducing the viscosity and pyrolyzing waste plastics, as Figure 1 shown, the processing system includes: a waste plastic liquefaction unit, a waste plastic viscosity reduction unit, a material heating unit, a pyrolysis reaction unit and a separation unit;

[0064] The waste plastic liquefaction unit includes an inlet for waste plastics to be treated and an outlet for liquefied waste plastics, and the waste plastic liquefaction unit is configured to perform liquefaction treatment on the waste plastics to be treated;

[0065] The waste plastic viscosity reduction unit includes an inlet for liquefied waste plastics and an outlet for liquefied waste plastic oil, and the waste plastic viscosity reduction unit is configured to perform viscosity reduction cracking treatment on the liquefied waste plastics;

[0066] The material heating unit includes a heating inlet and a heating outlet, the heating inlet is communicated with the outlet of the liquefied waste plastic oil of the waste plastic viscosity reduction unit, and the heating unit is configured to perform heating treatment on the liquefied waste plastic oil subjected to viscosity reduction cracking;

[0067] The pyrolysis reaction unit includes a pyrolysis reactant inlet and a pyrolysis product outlet. The pyrolysis reactant inlet is connected to the heating outlet of the heating unit. The pyrolysis reaction unit is configured to perform pyrolysis reaction treatment on high-temperature liquefied waste plastics;

[0068] The separation unit includes a separation inlet, a dry gas outlet, a liquefied gas outlet, a gasoline fraction outlet, a diesel fraction outlet, and a wax oil fraction outlet; the separation inlet is connected to the pyrolysis product outlet of the pyrolysis reaction unit. The separation unit is configured to perform separation treatment on the pyrolysis products.

[0069] In a preferred embodiment, the waste plastic visbreaking unit further includes a recycle oil inlet; the recycle oil inlet is connected to the wax oil fraction outlet of the separation unit.

[0070] In one embodiment, as Figure 1 shown, the system further includes a waste plastic preliminary melting, liquefaction and dechlorination unit and a hydrogen chloride absorption unit;

[0071] The waste plastic preliminary melting, liquefaction and dechlorination unit includes a chlorine-containing waste plastic raw material inlet, a gas-phase material outlet containing hydrogen chloride, and a dechlorinated waste plastic liquid-phase material outlet. The waste plastic preliminary melting, liquefaction and dechlorination unit is configured to perform hot-melt dechlorination treatment on the chlorine-containing waste plastic raw material; the dechlorinated waste plastic liquid-phase material outlet is connected to the waste plastic to-be-treated inlet of the waste plastic liquefaction unit;

[0072] The hydrogen chloride absorption unit includes a gas-phase material inlet containing hydrogen chloride, a hydrogen chloride absorbent, and a dechlorinated dry gas outlet; the gas-phase material inlet containing hydrogen chloride is connected to the gas-phase material outlet containing hydrogen chloride of the waste plastic preliminary melting, liquefaction and dechlorination unit.

[0073] In a specific embodiment, the waste plastic liquefaction unit includes a heating, liquefaction and conveying device; optionally, the heating, liquefaction and conveying device includes a first screw-type heating and conveying device; preferably, the first screw-type heating and conveying device is selected from a double-screw-type or single-screw-type heating and conveying device with heating;

[0074] The waste plastic preliminary melting, liquefaction and dechlorination unit includes a second screw-type heating and conveying device and a vacuum device connected to the second screw-type heating and conveying device; preferably, the second screw-type heating and conveying device is selected from a double-screw-type or single-screw-type conveying device.

[0075] In a preferred embodiment, the waste plastic preliminary melting, liquefaction and dechlorination unit and the waste plastic liquefaction unit share one heating, liquefaction and conveying device, which includes a first screw-type heating and conveying device. A gas outlet is provided in the middle of the screw-type heating and conveying device and is connected to the vacuum device.

[0076] In a specific embodiment, the waste plastic preliminary melting, liquefaction and dechlorination unit further includes a non-condensable gas outlet for leading out non-condensable gas.

[0077] In a specific embodiment, as Figure 1 shown, the system includes: a preliminary melting, liquefaction and dechlorination unit for waste plastics, a hydrogen chloride absorption unit, a waste plastics liquefaction unit, a waste plastics visbreaking unit, a material heating unit, a pyrolysis reaction unit and a separation unit;

[0078] Among them, the waste plastics liquefaction unit includes an inlet for waste plastics to be treated and an outlet for liquefied waste plastics, and the waste plastics liquefaction unit is configured to perform liquefaction treatment on the waste plastics to be treated;

[0079] The waste plastics visbreaking unit includes an inlet for liquefied waste plastics, an inlet for recycle oil and an outlet for liquefied waste plastics oil, and the waste plastics visbreaking unit is configured to perform visbreaking cracking treatment on the liquefied waste plastics;

[0080] The material heating unit includes a heating inlet and a heating outlet, the heating inlet is communicated with the outlet of the liquefied waste plastics oil of the waste plastics visbreaking unit, and the heating unit is configured to perform heating treatment on the visbroken and cracked liquefied waste plastics oil;

[0081] The pyrolysis reaction unit includes a pyrolysis reactant inlet and a pyrolysis product outlet, the pyrolysis reactant inlet is communicated with the heating outlet of the heating unit, and the pyrolysis reaction unit is configured to perform pyrolysis reaction treatment on the high-temperature liquefied waste plastics;

[0082] The separation unit includes a separation inlet, a dry gas outlet, a liquefied gas outlet, a gasoline fraction outlet, a diesel fraction outlet and a wax oil fraction outlet; the separation inlet is communicated with the pyrolysis product outlet of the pyrolysis reaction unit, and the separation unit is configured to perform separation treatment on the pyrolysis product; the wax oil fraction outlet of the separation unit is communicated with the recycle oil inlet of the waste plastics visbreaking unit;

[0083] The preliminary melting, liquefaction and dechlorination unit for waste plastics includes an inlet for chlorine-containing waste plastics raw materials, an outlet for gas-phase materials containing hydrogen chloride and an outlet for dechlorinated waste plastics liquid-phase materials, and the preliminary melting, liquefaction and dechlorination unit for waste plastics is configured to perform hot-melt dechlorination treatment on the chlorine-containing waste plastics raw materials; the outlet of the dechlorinated waste plastics liquid-phase materials is communicated with the inlet for waste plastics to be treated of the waste plastics liquefaction unit;

[0084] The hydrogen chloride absorption unit includes an inlet for gas-phase materials containing hydrogen chloride, a hydrogen chloride absorbent and a dechlorinated dry gas outlet; the inlet for gas-phase materials containing hydrogen chloride is communicated with the outlet for gas-phase materials containing hydrogen chloride of the preliminary melting, liquefaction and dechlorination unit for waste plastics.

[0085] In the present disclosure, the process flow of the system provided by the above specific embodiment specifically includes, as Figure 1 shown:

[0086] The waste plastics or dehydrated and dechlorinated waste plastic particles stored in the waste plastic storage tank 1 enter the waste plastic preliminary melting, liquefaction and dechlorination unit 2. After dehydration, deaeration and dechlorination, a gaseous material containing hydrogen chloride and a dechlorinated waste plastic material are obtained. The gaseous material containing hydrogen chloride is pumped into the hydrogen chloride absorption unit 8 by a vacuum system to contact with a hydrogen chloride absorbent for hydrogen chloride absorption treatment, obtaining a chlorine-containing absorbent and dechlorinated dry gas. A small amount of non-condensable gas is discharged through pipeline 9. The waste plastic liquefaction unit uses a rapid heating liquefaction and conveying device 3. The dechlorinated waste plastic liquid-phase material from the waste plastic preliminary melting, liquefaction and dechlorination unit 2 can be sent out of the device for cooling treatment and crushing treatment to obtain dechlorinated waste plastic particles, or directly enter the rapid heating liquefaction and conveying device 3 (waste plastic liquefaction unit) to obtain a molten dechlorinated waste plastic liquid-phase material; the molten dechlorinated waste plastic liquid-phase material enters the adiabatic visbreaking reactor 4 (waste plastic visbreaking unit) for visbreaking cracking treatment to obtain visbroken liquefied waste plastic oil, or the wax oil fraction from the separation unit 7 can also be simultaneously fed into the adiabatic visbreaking reactor 4 for recycling; the visbroken liquefied waste plastic oil is sent to the heating furnace 5 (heating unit) through pipeline 10. After being heated and raised in temperature by the heating furnace 5, the high-temperature liquefied waste plastic enters the pyrolysis reaction unit 6 through pipeline 11 for pyrolysis reaction to obtain pyrolysis products and coke; the pyrolysis products enter the subsequent separation unit 7 through pipeline 12 for separation treatment: among them, the dry gas is sent out of the device through pipeline 15, the liquefied gas and gasoline fraction are sent out of the device through pipeline 14, and the diesel fraction is sent out of the device through pipeline 13; the wax oil fraction at the bottom of the tower is led out of the separation unit through pipeline 16, and part of the wax oil fraction can also be returned to the adiabatic visbreaking reactor 4 (waste plastic visbreaking unit) through pipeline 15 for recycling, or can be led out of the device as a product through pipeline 17.

[0087] The present disclosure is further described in detail below by way of examples. The raw materials used in the examples can all be obtained through commercial channels.

[0088] Among them, the analysis method for the chlorine content in the liquefied waste plastic is: Q / SH 3360 270-2018.

[0089] The analysis methods for other elements in the liquefied waste plastic are: for carbon and hydrogen elements, SH / T 0656-2017; for oxygen element, SH / T0986; for nitrogen element, SH / T 0704-2010; for sulfur element, SH / T 0842-2010.

[0090] The pyrolysis product distribution is obtained by the simulated distillation NB / SH / T 0829-2010 method.

[0091] The density analysis method for diesel wax oil is SH / T0604-2000; the pyrolysis gas composition is determined by the RIPP 78-90 method; the hydrocarbon composition of naphtha, diesel, etc. is analyzed and determined by chromatography.

[0092] In the following embodiments, the particle size range of the particles obtained by comminution treatment is 100 - 2000 μm.

[0093] Example 1

[0094] Mix LDPE, HDPE, PS, PP, and PVC in a mass percentage of 4:4:8:3:1, crush and dry the mixed plastic packaging materials. The chlorine content of the mixed plastics is 2.9 wt%. Use a twin-screw heating and conveying device as the equipment for preliminary melting, liquefaction, and dechlorination of waste plastics, with a feeding rate of approximately 100 kg / h. During the test process, change the outlet temperature. The treatment time under each outlet temperature condition is 0.1 h, and the vacuum degree of the screw-type heating and conveying device is 100 mmHg. Test the morphology and chlorine content of the waste plastics after conveying under different outlet temperature conditions to obtain the liquefied dechlorinated waste plastics DCl-1 to DCl-5 series. The properties of the obtained liquefied dechlorinated waste plastics DCl-1 to DCl-5 are shown in Table 1.

[0095] During the dechlorination treatment process, use a vacuum system to extract the gas-phase material containing hydrogen chloride and send it to the hydrogen chloride absorption unit to contact with the hydrogen chloride absorbent (NaOH solution) for hydrogen chloride absorption treatment.

[0096] Then further heat DCl-3 to 390 °C for 0.2 h using a screw-type heating and conveying device (liquefaction treatment process); then measure the rotational viscosity after holding at 390 °C for 30 min, 50 min, and 70 min (using an adiabatic up-flow visbreaking reactor) to obtain the visbroken liquefied waste plastic oil (denoted as DCl-3-30, DCl-3-50, DCl-3-70) respectively. The properties of the visbroken liquefied waste plastic oil are shown in Table 2.

[0097] First, heat the DCl-3-70 sample in a heating furnace to obtain high-temperature liquefied waste plastics, with the outlet temperature of the heating furnace being 390 °C; then send the obtained high-temperature liquefied waste plastics into a pyrolysis reaction device (pyrolysis tower) and pyrolyze at 480 °C for 2 h. After the obtained pyrolysis products are separated by a separation unit, conduct product distribution tests. The pyrolysis reaction product distribution is shown in Tables 4 - 5.

[0098] Comparative Example 1

[0099] Use the raw materials, dechlorination equipment, and methods of Example 1, with the difference that the outlet temperatures are set at 250 °C and 220 °C. Test the morphology and chlorine content of the waste plastics after conveying under different outlet temperature conditions to obtain the liquefied dechlorinated waste plastics DCl-6 and DCl-7, and their properties are listed in Table 1.

[0100] Heat DCl-6 to 250°C using a screw-type heating and conveying device and directly extrude it into an atmospheric pressure container with a gas outlet and an internal temperature of 250°C. Keep it warm for 60 minutes, and take a sample of DCl-6-60 to test the viscosity. Its viscosity is too high and exceeds the measurement range. Its form is a plastic solid and it cannot flow by itself.

[0101] Example 2

[0102] Use a twin-screw heating and conveying device as the equipment for preliminary melting, liquefaction, and dechlorination of waste plastics for waste agricultural film (chlorine content is 0.0162% by weight). The feeding rate is about 100 kg / h, the outlet temperature is 220°C, the treatment time is 0.1 h, and the vacuum degree of the screw-type heating and conveying device is 150 mmHg to obtain waste plastic DCl-8. The properties of the obtained waste plastic particles are shown in Table 3. The absorption process of the hydrogen chloride gas obtained from the dechlorination treatment is the same as that in Example 1.

[0103] Further heat DCl-8 to 400°C using a screw-type heating and conveying device for 0.1 h (liquefaction treatment process); sample and measure the rotational viscosity at 400°C for 30 min, 50 min, and 70 min (using an adiabatic up-flow visbreaking reactor) to obtain visbroken liquefied waste plastic oil (denoted as DCl-8-30, DCl-8-50, DCl-8-70) respectively. The viscosity is shown in Table 2.

[0104] First heat the DCl-8-50 sample in a heating furnace to obtain high-temperature liquefied waste plastic. The outlet temperature of the heating furnace is 500°C; the steam injection rate is 0.5% by weight; then send the obtained high-temperature liquefied waste plastic into a pyrolysis reaction device and pyrolyze it at 480°C for 2 h. The obtained pyrolysis products are separated by a separation unit and then the product distribution is tested. The pyrolysis reaction product distribution is shown in Tables 4 - 5.

[0105] Example 3

[0106] Use a twin-screw heating and conveying device as the equipment for preliminary melting, liquefaction, and dechlorination of waste plastics for real waste plastics (chlorine content is about 3% by weight). The feeding rate is about 100 kg / h, the outlet temperature is 300°C, the treatment time is 0.1 h, and the vacuum degree of the screw-type heating and conveying device is 70 mmHg to obtain liquefied dechlorinated waste plastic DCl-9. The absorption process of the hydrogen chloride gas obtained from the dechlorination treatment is the same as that in Example 1.

[0107] Further heat DCl-9 to 420°C using a screw-type heating and conveying device for 0.2 h (liquefaction treatment process); then keep it warm at 420°C for 30 min (using an adiabatic up-flow visbreaking reactor), sample and measure the rotational viscosity (denoted as DCl-9-30) to obtain visbroken liquefied waste plastic oil. The viscosity results are shown in Table 2.

[0108] The DCl-9-30 sample was first heated in a heating furnace to obtain high-temperature liquefied waste plastics, and the outlet temperature of the heating furnace was 480°C; then the obtained high-temperature liquefied waste plastics were sent to a pyrolysis reaction device and pyrolyzed at 480°C for 2 h. The pyrolysis products were separated by a separation unit and then subjected to product distribution tests. The product distributions of the pyrolysis reactions are shown in Tables 4 to 5.

[0109] Example 4

[0110] A medium-sized continuous pyrolysis device for waste plastics was used, with DCl-8 as the raw material. A twin-screw heating and conveying device was used as the equipment for liquefying waste plastics. The feeding rate was about 5 kg / h, and the outlet temperature was 300°C. It was directly sent to the next-stage screw heating and conveying device for further heating to 400°C, and then held at 380°C for a period of time for visbreaking treatment (using an adiabatic up-flow visbreaking reactor); then the obtained visbroken liquefied waste plastic oil was sent to a heating device (heating furnace), different heating furnace outlet temperatures were set, and pyrolysis was carried out under different temperature conditions (in this example, the pyrolysis temperature was the corresponding heating furnace outlet temperature). The pyrolysis products were separated by a separation unit and then subjected to product distribution tests. The reaction conditions and the product distributions of the pyrolysis reactions are shown in Table 6.

[0111] Example 5

[0112] A medium-sized continuous pyrolysis device for waste plastics was used, with DCl-8 as the raw material and a feeding rate of about 5 kg / h. DCl-8 was further heated to 400°C by a screw heating and conveying device for 0.2 h (liquefaction treatment process); then it was held for visbreaking treatment, the visbreaking temperature was 380°C, and the visbreaking time was 1 h (using an adiabatic up-flow visbreaking reactor); when the heating furnace outlet temperature (reaction temperature) was 500°C and the pyrolysis tower pressure (reaction pressure) was 0.15 MPa, the RPCC processing product distribution (dry ash-free basis treatment) of waste agricultural film particles is shown in Table 7, the gas-phase product distribution is shown in Table 8, the liquid product was cut to obtain naphtha, diesel, and wax oil components, and their properties are shown in Table 9, and the properties of the coke products are shown in Table 10.

[0113] Comparative Example 2

[0114] Referring to the process flow of Example 5, the same waste plastic raw material was used. The difference from Example 5 was that DCl-8 as the raw material was not subjected to liquefaction treatment and visbreaking treatment, but was directly introduced into the heating furnace for heating and then pyrolysis reaction was carried out. The specific process conditions were the same as those in Example 5. The product distribution (dry ash-free basis treatment) is shown in Table 7.

[0115] Table 1 Properties of Liquefied Waste Plastics

[0116] Sample Name DCl-1 DCl-2 DCl-3 DCl-4 DCl-5 DCl-6 DCl-7 Outlet Temperature 330 320 310 300 285 250 220 w(Cl) / (μg / g) 750 1630 1720 2900 6430 11410 20223 Dechlorination Rate / wt% 97.41 94.38 94.07 90.00 77.83 59.82 28.79

[0117] It can be seen from the data in Table 1 that by comparing DCl-1 to DCl-5 with DCl-6 and DCl-7 in Comparative Example 1, it is known that DCl-1 to DCl-5 meet the requirement that the dechlorination outlet temperature is 285 to 330 °C during the hot-melt dechlorination treatment of waste plastics, and the dechlorination rate of the obtained liquefied dechlorinated waste plastics is higher.

[0118] Furthermore, by comparing DCl-1 to DCl-4 with DCl-5, it is known that DCl-1 to DCl-4 meet the requirement that the dechlorination outlet temperature is 300 to 330 °C during the hot-melt dechlorination treatment of waste plastics, and the dechlorination rate of the obtained liquefied dechlorinated waste plastics is higher.

[0119] Table 2 Viscosity of visbreaking plastics

[0120]

[0121] It can be seen from the data in Table 2 that when the visbreaking treatment meets the reaction temperature of 390 to 420 °C and the residence time of 30 to 70 min, different visbreaking temperatures have different optimal visbreaking times.

[0122] Table 3 Properties of waste agricultural film particles

[0123] Item Value Ash Content / % 2.86 w(C) / % 83.28 w(H) / % 13.25 w(S) / % <0.1 w(N) / % 0.028 w(Cl) / % 0.0162 w(Si) / % 0.131 w(O) / % 1.45 w(Ca). %(W) 0.709

[0124] Table 4 Distribution of pyrolysis products of dry-ash-free waste plastics

[0125]

[0126]

[0127] Table 5 Mass composition of dry gas and liquefied gas in pyrolysis products of waste plastics

[0128] Example Example 1 Example 2 Example 3 Composition / wt% Dry Gas 35.34 32.42 52.4 Hydrogen 0.14 0.41 4.29 Methane 7.52 8.42 18 Ethane 16.42 13.05 22.54 Ethylene 11.26 10.54 7.57 Liquefied Gas 64.66 67.58 47.6 Propylene 29.28 23.61 17.47 Butene 17.18 17.01 15.44 Propane 12.95 17.64 10.27 Isobutane 0.63 0.42 0.8 n-Butane 4.62 8.90 3.62 Total 100.00 100 100.00

[0129] Table 6 Pyrolysis test in Example 4

[0130]

[0131]

[0132] It can be seen from Table 6 that by comparing Condition 1 to 3 with Condition 4 to 5, it is known that in Condition 1 to 3, it meets the requirements of "visbreaking residence time of 30 to 70 min; heating furnace outlet temperature and pyrolysis reaction temperature of 480 to 520 °C, and pyrolysis tower top pressure of 0.1 to 0.3 Mpa", and the total yield of coke and ash in the pyrolysis reaction products of Condition 1 to 3 is lower.

[0133] Comparing Condition 1 with Condition 6, it can be seen that the recycle of wax oil fraction is added in Condition 6, the yields of gas and light distillate oil in the pyrolysis reaction products of Condition 6 increase, and the total yields of coke and ash are lower.

[0134] Table 7 Pyrolysis Product Distribution of Example 5 and Comparative Example 1

[0135] Example 5 Comparative Example 2 Item Mass Fraction / % Mass Fraction / % CO 0.21 0.3 <![CDATA[CO2]]> 0.40 2.88 Dry Gas 6.10 8.73 Liquefied Gas 10.59 9.89 Naphtha fraction (<180 °C) 25.50 33.88 Diesel Fraction (180°C - 350°C) 32.68 21.53 Wax Oil Fraction (>350°C) 19.75 13.79 Coke 4.78 9.0 Total 100.00 100.00 Liquid Yield (including liquefied gas) 88.52 79.09

[0136] Table 8 Composition of Pyrolysis Gas of Example 5

[0137]

[0138]

[0139] Table 9 Properties of Pyrolysis Products of Example 5

[0140] Item Naphtha Diesel Wax Oil <![CDATA[Density (20 °C) / (kg / m 3 )]]> 740.1 798.7 844.7 Bromine Number / (gBr / 100mL) 43.1 15.7 PONA / % (Hydrocarbon Composition / %) Paraffin 25.96 42.3 47.3 Naphthene 7.13 Olefin 58.84 47.8 40.3 Aromatic 8.07 9.9 12.4 C / ％ 86.2 85.86 85.84 H / ％ 13.8 14.14 13.94 S / (mg / kg) 3.3 5.8 12 N / (mg / kg) 31 47 74 Cl / (mg / kg) 5.4 7.5 10 Si / (mg / kg) 5 7 9.5 O / (mg / L) 416 <300 0.22(％) Distillation Range / °C Initial Boiling Point 24.2 172.2 341.5 5％ 41.4 193.8 356.5 50％ 128.7 269.8 419.7 95％ 177.6 345.9 529.9 Final Boiling Point 197.0 360.8 581.5

[0141] Table 10 Properties of Coke

[0142] Item Value Ash Content, w% 45.96 Moisture Content, w% 0.96 Volatile Matter, w% 29.42 Lower Calorific Value / (kJ / kg) 10.74 <![CDATA[Bulk density / (kg / m 3 )]]> 672 C, w% 53.39 S, w% 0.65 Cl, w% 0.152 Metal Analysis / % Na 1.20 Mg 5.09 Al 2.18 Si 5.93 P 0.21 K 1.12 Ca 37.57 Ti 3.35 Fe 3.21 Zn 0.23 Ba 3.46

[0143] It can be seen from Example 1 that after the melting, liquefaction and dechlorination process of the mixed plastics by the twin-screw heating and conveying equipment, most of the chlorine in the plastics is removed; after the dechlorinated plastic DCl-3 is visbroken, the viscosity at 200 °C drops to 268.5 cp, the flow state of the sample is stable, and after heating to 480 °C, it enters the pyrolysis tower and is fractionated by the fractionating tower to obtain gas, gasoline, diesel, wax oil and coke yields of 3.71%, 49.50%, 29.53%, 16.16%, and 1.1%.

[0144] It can be seen from Example 2 that after the melting, liquefaction and dechlorination process of the real waste plastics by the twin-screw heating and conveying equipment, most of the chlorine in the plastic waste is removed; after the dechlorinated plastic DCl-6 is visbroken, the viscosity at 200 °C drops to 267.6 cp, the flow state of the sample is stable, and after heating to 480 °C, it enters the pyrolysis tower and is fractionated by the fractionating tower to obtain gas, gasoline, diesel, wax oil and coke yields of 5.39%, 29.21%, 23.21%, 10.91%, and 20.96%. Since the waste plastics contain a certain amount of polyester and have been oxidized for a long time, the raw materials contain a certain amount of oxygen, so there is a certain amount of CO and CO2 in the pyrolysis products.

[0145] As can be seen from Example 3, after the true waste plastics are melted, liquefied and dechlorinated by the twin-screw heating and conveying equipment, most of the chlorine in the plastic waste is removed; after the plastic DCl-7 is visbroken at 420 °C for 30 min after dechlorination, the viscosity drops to 282.8 cp at 200 °C, and the flow state of the sample is stable. After being heated to 480 °C, it enters the pyrolysis tower and is fractionated by the fractionating tower to obtain gas, gasoline, diesel, wax oil and coke with yields of 3.82%, 29.89%, 21.8%, 11.7% and 24.04% respectively. Since the waste plastics contain a certain amount of polyester and have been oxidized for a long time, the raw materials contain a certain amount of oxygen, so there is a certain amount of CO and CO2 in the pyrolysis products.

[0146] As can be seen from Example 5, after the waste agricultural film (granules) are processed by the process provided by the present disclosure, the liquid yield (including liquefied gas) of pyrolysis can reach 88.52%, and the coke yield is relatively small. From the properties of the obtained naphtha, diesel and wax oil, it can be known that the mass fraction of hydrogen element in each fraction oil is relatively high, the mass fraction of olefins is relatively high, the mass fraction of aromatics is relatively low, and the contents of chlorine and silicon heteroatoms are relatively low, and it can directly enter the refinery for further processing. The sum of the mass fractions of trienes in the pyrolysis gas is relatively high (>45 wt%), and the ash content of the coke is as high as 45.96 wt%, which cannot be sold as a product and can be co-fired as boiler fuel.

[0147] Comparing Example 5 with Comparative Example 2, it can be known from the data in Table 7 that in the pyrolysis product distribution obtained by using the processing method of waste plastic viscosity reduction and pyrolytic cracking provided by the present disclosure, the liquid yield is higher and the coke yield is lower.

[0148] The preferred embodiments of the present disclosure have been described in detail above. However, the present disclosure is not limited to the specific details in the above embodiments. Within the scope of the technical concept of the present disclosure, various simple modifications can be made to the technical solutions of the present disclosure, and these simple modifications all belong to the protection scope of the present disclosure.

[0149] In addition, it should be noted that the various specific technical features described in the above specific embodiments can be combined in any suitable manner without conflict. To avoid unnecessary repetition, the present disclosure will not separately describe various possible combination methods.

[0150] In addition, any combination can be made between various different embodiments of the present disclosure as long as it does not violate the idea of the present disclosure, and it should also be regarded as the content disclosed by the present disclosure.

Claims

1. A processing method for viscosity reduction and pyrolysis cracking of waste plastics, characterized in that, The method comprises the following steps: S1. Feed the waste plastics to be processed into a waste plastic liquefaction unit for liquefaction treatment to obtain liquefied waste plastics; the waste plastic liquefaction unit uses a rapid heating liquefaction conveying device for the liquefaction treatment; the rapid heating liquefaction conveying device includes a first screw-type heating conveying device; the process conditions for the liquefaction treatment include: an outlet temperature of 370-500 °C and a residence time of 5-20 min; S2. Feed the liquefied waste plastics into a waste plastic visbreaking unit for visbreaking treatment to obtain visbroken liquefied waste plastic oil; the waste plastic visbreaking unit uses a visbreaking reactor for the visbreaking treatment; the process conditions for the visbreaking treatment include: a reaction temperature of 370-450 °C and a residence time of 30-70 min; S3. Feed the visbroken liquefied waste plastic oil into a material heating unit for heating treatment to obtain high-temperature liquefied waste plastics; the material heating unit includes a heating furnace; the outlet temperature of the heating furnace is 480-520 °C; S4. Feed the high-temperature liquefied waste plastics into a pyrolysis reaction unit for pyrolysis reaction to obtain pyrolysis products and coke; the process conditions for the pyrolysis reaction include: a pyrolysis tower top pressure of 0.1-0.3 Mpa; a pyrolysis reaction temperature of 480-520 °C; S5. Feed the pyrolysis products into a separation unit for separation treatment to obtain dry gas, liquefied gas, gasoline fraction, diesel fraction and wax oil fraction; Before step S1, the method further includes: Feed the chlorine-containing waste plastic raw materials into a waste plastic preliminary melting, liquefaction and dechlorination unit for hot melt dechlorination treatment to obtain a gas-phase material containing hydrogen chloride and dechlorinated waste plastic materials; Use the dechlorinated waste plastic materials as the waste plastics to be processed and feed them into the waste plastic liquefaction unit; or Cool and crush the dechlorinated waste plastic materials in sequence to obtain dechlorinated waste plastic particles; use the dechlorinated waste plastic particles as the waste plastics to be processed and feed them into the waste plastic liquefaction unit.

2. The processing method according to claim 1, characterized in that, The method further includes: Feed the gas-phase material containing hydrogen chloride into a hydrogen chloride absorption unit, and contact with a hydrogen chloride absorbent for hydrogen chloride absorption treatment to obtain a chlorine-containing absorbent and dechlorinated dry gas; Wherein the hydrogen chloride absorbent is water or an alkaline solution with a pH greater than 7.

3. The processing method according to claim 2, characterized in that, The method includes: Under the action of a vacuum system, feed the gas-phase material containing hydrogen chloride into the hydrogen chloride absorption unit.

4. The processing method according to claim 2, characterized in that, The alkaline solution includes one or more of sodium hydroxide solution, potassium hydroxide solution, calcium hydroxide solution, sodium bicarbonate solution, sodium carbonate solution and ammonia water.

5. The processing method according to claim 1, characterized in that, The method further includes: Return at least part of the wax oil fraction from the separation unit to the waste plastic visbreaking unit for recycling.

6. The processing method according to claim 5, characterized in that The weight ratio of the recycled wax oil fraction to the waste plastics to be processed is 0.2-5.0:

1.

7. The processing method according to claim 6, characterized in that, The weight ratio of the recycled wax oil fraction to the waste plastics to be processed is 0.2-2:

1.

8. The processing method according to claim 5, characterized in that, The method includes: Use the fraction with a distillation range greater than 350 °C separated by the separation unit as the wax oil fraction.

9. The processing method according to claim 1, wherein In step S1, the first screw-type heating conveying device is selected from a double-screw type or single-screw type heating conveying device with heating.

10. The processing method according to claim 9, characterized in that, The process conditions for the liquefaction treatment include: the outlet temperature is 380 - 450 °C, and the residence time is 5 - 15 min.

11. The processing method according to claim 1, characterized in that, In step S2, the visbreaking reactor is an adiabatic visbreaking reactor; the process conditions for the visbreaking treatment include: the reaction temperature is 380 - 420 °C.

12. The processing method according to claim 11, characterized in that, The process conditions for the visbreaking treatment include: the reaction temperature is 390 - 420 °C.

13. The processing method according to claim 1, wherein, In step S3, the process conditions for the heating treatment include: the steam injection rate is 0.5 - 5 wt%.

14. The processing method according to claim 13, wherein The steam injection rate is 1 - 3 wt%.

15. The processing method according to claim 1, characterized in that The preliminary melting, liquefaction and dechlorination unit for waste plastics includes a second screw-type heating and conveying device and a vacuum device communicated with the second screw-type heating and conveying device; The process conditions for the hot-melt dechlorination treatment include: the feeding rate is 5 - 5000 kg / h; the outlet temperature is 150 - 370 °C, and the reaction time is 0.1 - 0.5 h; the vacuum degree of the preliminary melting, liquefaction and dechlorination unit for waste plastics is 50 - 300 mmHg.

16. The processing method according to claim 15, wherein, The second screw-type heating and conveying device is selected from a twin-screw type or a single-screw type conveying device.

17. The processing method according to claim 15, characterized in that, The process conditions for the hot-melt dechlorination treatment include: the feeding rate is 100 - 4000 kg / h; the outlet temperature is 300 - 330 °C, and the reaction time is 0.1 - 0.3 h; the vacuum degree of the preliminary melting, liquefaction and dechlorination unit for waste plastics is 50 - 150 mmHg.

18. The processing method according to claim 15, characterized in that, The particle size of the dechlorinated waste plastic particles obtained by the pulverization treatment is 100 - 2000 μm.

19. The processing method according to claim 1, wherein The waste plastics to be treated include one or more of LDPE, HDPE, PS, PP, PET and PVC.

20. The processing method according to claim 19, characterized in that, The content of PVC in the waste plastics to be treated is less than 10 wt%; the ash content in the waste plastics to be treated is 1 - 40 wt%.

21. The processing method according to claim 20, characterized in that, The ash content in the waste plastics to be treated is 3 - 30 wt%.

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