Method and system for preparing low-chlorine pyrolytic oil from plastic mixture

Abstract

The invention relates to a method and system for preparing low-chlorine pyrolytic oil from a plastic mixture. Chlorine-containing plastic and additive-containing plastic enter first screw type heating conveying equipment to be subjected to dehydration, degassing and volume reduction treatment, and the obtained dehydrated, degassed and volume-reduced plastic enters second screw type heating conveying equipment to be subjected to liquefaction treatment and dechlorination treatment; the obtained liquefied dechlorinated plastic is subjected to visbreaking treatment, and visbreaking plastic oil and first dry gas are obtained; heating the visbreaking plastic oil and then carrying out pyrolytic reaction to obtain a pyrolysis product and coke; separating the pyrolysis product to obtain second dry gas, liquefied gas and pyrolysis oil; wherein the additives are oxides, hydroxides and salts of alkali metals / alkaline earth metals. According to the method, the alkali metal / alkaline earth metal compound in the additive-containing plastic added in the pyrolysis dechlorination process can adsorb HCl released by decomposition of the chlorine-containing compound at high temperature in the whole process in situ, generation of organic chlorides is reduced, and large-scale and continuous production of low-chlorine pyrolytic oil from the chlorine-containing waste plastic is effectively achieved.

Description

Technical Field

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

[0002] At present, there are nearly 1 billion tons of waste plastics in urgent need of disposal in China, and the global accumulated waste plastics are about 9 billion tons. The "white pollution" caused by waste plastics, such as marine pollution, water and soil pollution, and ecological environment damage, is severe. Traditional treatment methods for waste plastics include landfill and incineration, which pollute the environment and cause huge economic value losses. Chemical recycling can convert waste plastics into chemicals by applying different technologies such as pyrolysis, catalytic decomposition, solvent decomposition and gasification. Despite this, the development of cost-effective and environmentally friendly chemical upgrading and recycling methods to convert plastic waste into valuable products is still highly welcomed.

[0003] Chemical recycling is generally considered to be a sustainable technology that can achieve high-value resource utilization of waste plastics. However, globally, the development of this technology is still in its early stages, accounting for only 1% of the waste plastics treatment volume. With the changes in global environmental policies, especially the proposal and implementation of commitments such as carbon emission reduction, carbon peak, and carbon neutrality, refining companies in various countries have gradually turned their attention to the chemical recycling of waste plastics, with the EU countries being the most prominent. For example, BUSF, BP, and Shell have all developed chemical recycling technologies for waste plastics. It is expected that by 2030, the chemical recycling technology for waste plastics will increase to 13%. At this stage, the mainstream treatment technology is still pyrolysis technology. Due to its advantages such as simple process, low cost, and wide adaptability of raw materials, the pyrolysis technology of waste plastics has certain economic advantages and technical feasibility. Waste plastics that can be treated by pyrolysis technology mainly include stale plastics dug out of landfills and waste plastics in dynamic daily garbage. However, due to the presence of these mixed plastics PVC and chlorine-containing additives, the chlorine content in the pyrolysis oil is relatively high, reaching more than 4000 mg / kg, and most of them are organic chlorides, which greatly affects the quality of the oil. At the same time, some plastics containing alkaline substances such as calcium carbonate, such as calcium plastic boards, are difficult to chemically recycle due to low plastic content and high content of organic impurities such as calcium carbonate. The alkaline substances in waste plastics containing alkaline substances can absorb HCl released by chlorine-containing compounds such as PVC during pyrolysis, which can reduce the generation of organic chlorides. Therefore, it is urgent to develop a technology for co-pyrolysis of waste plastics containing alkaline substances and chlorine-containing waste plastics to prepare low-chlorine pyrolysis oil, which 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. According to the method, the chlorine-containing waste plastics are dechlorinated in a dechlorination device in the form of a shaftless stirring screw, isolated from the air and at 180°C to 320°C to obtain a molten material and chlorine-containing gas; the molten material is then pyrolyzed in a pyrolysis device under vacuum conditions at 500°C to 700°C to produce pyrolytic charcoal and pyrolytic steam. Due to the low heat transfer efficiency, uneven heating and low dechlorination temperature of 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 feeding device heats the waste plastics to 100°C to 250°C and enters a dechlorination diverter for dechlorination reaction. Since the dechlorination reaction of PVC and the addition reaction of olefins are carried out at the same time, the dechlorination rate is not high under the condition of separating HCl without external force; and the waste plastics are only softened into a plastic high-density material at 250°C, and its physical phase is a non-self-flowing non-liquid plastic solid, which is difficult to output from the dechlorination diverter.

[0006] CN201810272820.4 discloses a method for preparing low-chlorine plastic cracking oil, which gradually heats mixed plastics containing PVC in sections, and after completely removing the released hydrogen chloride by nitrogen purging or vacuum extraction within the temperature range of PVC decomposition, a composite catalyst is added to perform deep dechlorination and catalytic thermal cracking of the remaining materials to obtain low-chlorine plastic cracking oil. This method is an intermittent reaction, and it is impossible to achieve large-scale and continuous production of low-chlorine pyrolysis oil from chlorine-containing waste plastics. Because its dechlorination equipment also has problems such as low heat transfer efficiency, uneven heating and local overheating, the dechlorination is not thorough and it is difficult to avoid the production of more organic chlorides, and the chlorine content in the pyrolysis light oil is still high. Summary of the invention

[0007] The technical problem to be solved by the present 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. The co-pyrolysis of waste plastics containing additives and waste plastics containing chlorine can be effectively achieved, and low-chlorine pyrolysis oil can be produced on a large scale and continuously.

[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, the chlorine-containing plastic and the additive-containing plastic enter the first screw-type heating and conveying equipment separately or together for dehydration, degassing and volume reduction treatment to obtain a dehydrated, degassed and volume-reduced plastic;

[0010] S2, allowing the dehydrated, degassed and volume-reduced plastic to enter a second screw-type heating and conveying device for liquefaction and dechlorination treatment to obtain a liquefied dechlorinated plastic;

[0011] S3, allowing the liquefied dechlorinated plastic to enter a visbreaking unit for visbreaking treatment to obtain visbreaking plastic oil and a first dry gas;

[0012] S4, allowing the viscous and cracked plastic oil to enter a heating unit for heating treatment to obtain heated plastic oil;

[0013] S5, allowing the heated plastic oil to enter a pyrolysis reaction unit for pyrolysis reaction to obtain pyrolysis products and coke;

[0014] S6, allowing the pyrolysis product to enter a separation unit for separation to obtain a second dry gas, liquefied gas and pyrolysis oil;

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

[0016] In the method provided by the present invention, the chlorine-containing plastic refers to chlorine-containing 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 limit on the PVC content, and the Cl content in the chlorine-containing plastic is greater than 0.5% by weight. The chlorine-containing plastic in the present disclosure can be directly made of waste plastic in a landfill.

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

[0018] Optionally, the chlorine-containing plastic enters the first screw-type heating and conveying device for chlorine-containing plastic for treatment, with an outlet temperature of 100°C to 250°C and a residence time of 4min to 20min, to obtain a dehydrated, degassed and reduced-volume chlorine-containing plastic; preferably, the outlet temperature of the first screw-type heating and conveying device for chlorine-containing plastic is 150 to 200°C, and the residence time is 5min to 16min; the pressure inside the screw is 0.1MPa to 6MPa, more preferably 0.1MPa to 4MPa. The additive-containing plastic enters the first screw-type heating and conveying device for additive-containing plastic for treatment, with an outlet temperature of 120°C to 400°C and a residence time of 4min to 20min, to obtain a dehydrated, degassed and reduced-volume additive-containing plastic; preferably, the outlet temperature of the first screw-type heating and conveying device for additive-containing plastic is 150°C to 380°C, the residence time is 5min to 16min, and the pressure inside the screw is 0.1MPa to 6MPa, more preferably 0.1MPa to 4MPa. The treated material enters the second screw-type heating and conveying device.

[0019] Preferably, the outlet temperature of the first screw heating and conveying device for plastics containing additives is 10°C to 180°C higher than that of the first screw heating and conveying device for plastics containing chlorine, and preferably 20°C to 150°C higher.

[0020] In the method provided by the present invention, liquefaction treatment and dechlorination treatment are carried out in the second screw-type heating and conveying equipment to obtain liquefied dechlorinated plastic, the outlet temperature of the second screw-type heating and conveying equipment is 280°C to 450°C, and the residence time is 5min to 30min; preferably, the outlet temperature of the second screw-type heating and conveying equipment is 300°C to 430°C, the residence time is 6min to 25min, and the pressure inside the screw is 0.0001MPa to 5MPa, more preferably 0.1MPa to 3MPa.

[0021] In the method provided by the present invention, the visbreaking unit described in step S3 adopts an adiabatic visbreaking reactor to carry out the visbreaking treatment, the reaction temperature is 350°C to 450°C, and the residence time is 15min to 150min; preferably, the reaction temperature is 360°C to 430°C, and the residence time is 20min to 120min.

[0022] In the method provided by the present invention, the heating unit described in step S4 includes a heating furnace, the outlet temperature of the heating furnace is 430°C to 570°C, preferably 450°C to 550°C, and water vapor is injected into the heating furnace. The steam injection amount is 0.5% to 5% by weight based on the weight of the viscous cracked plastic oil entering the heating furnace.

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

[0024] Optionally, in step S2, the gas generated in the second screw heating and conveying device enters the hydrogen chloride absorption unit under the action of the vacuum system, and contacts with the hydrogen chloride absorbent to remove hydrogen chloride, wherein 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 chlorine-containing plastic includes PVC; the additive-containing plastic refers to calcium plastic materials containing additives, incinerable plastic garbage bags, soft polyethylene wires, polyethylene soles, plastic agricultural films, antibacterial plastics or thermally conductive plastics; preferably, the additives are selected from alkali metal / alkaline earth metal oxides, hydroxides, carbonates, 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 the additive-containing plastic to the chlorine-containing plastic is such that the mass ratio of the additive to chlorine is 1:0.5-20, preferably 1:1-8.

[0027] In a second aspect, the present invention provides a system for preparing low-chlorine pyrolysis oil from a plastic mixture, 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 visbreaking unit, a heating unit, a pyrolysis reaction unit, and a separation unit;

[0028] The first screw-type heating and conveying device for chlorine-containing plastics and the first screw-type heating and conveying device for additive-containing plastics are arranged in parallel, and include an inlet and an outlet; the first screw-type heating and conveying device for chlorine-containing plastics is configured to perform dehydration, degassing and volume reduction treatment on the chlorine-containing plastics; the first screw-type heating and conveying device for additive-containing plastics is configured to perform dehydration, degassing and volume reduction treatment on the additive-containing plastics;

[0029] The outlet of the first screw-type heating and conveying device for chlorine-containing plastics and the outlet of the first screw-type heating and conveying device for additive-containing plastics are respectively connected to the second screw-type heating and conveying device;

[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 perform liquefaction and dechlorination treatment on the dehydrated, degassed and volume-reduced plastic to obtain the dechlorinated plastic;

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

[0032] The heating unit comprises a visbreaking plastic oil inlet and a heated plastic oil outlet, wherein the visbreaking plastic oil inlet is connected to the visbreaking plastic oil outlet of the visbreaking unit; the heating unit is configured to heat the visbreaking plastic oil to obtain heated plastic oil;

[0033] The pyrolysis reaction unit comprises a heated plastic oil inlet and a pyrolysis product outlet; the heated plastic oil inlet is connected to the heated plastic oil outlet of the heating unit; the pyrolysis reaction unit is configured to perform pyrolysis reaction on the heated 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 product to obtain dry gas, liquefied gas and pyrolysis oil.

[0035] Through the above technical scheme, the present invention provides a method and system for preparing low-chlorine pyrolysis oil by co-pyrolysis of waste plastics containing alkaline substances and waste plastics containing chlorine. By dehydrating, degassing and reducing the volume of waste plastics containing alkaline substances and waste plastics containing chlorine, liquefying and dechlorinating, and reducing viscosity and cracking, the viscosity and chlorine content of the liquefied waste plastics are reduced without coking and excessive cracking, forming a uniform, fluid low-chlorine fluidized waste plastic that can be transported by a pump; then, it is treated by a heating furnace or the like to quickly reach the pyrolysis reaction temperature, and the high-temperature liquefied waste plastic is transported to a pyrolysis tower for pyrolysis reaction. The alkaline substance in the waste plastic containing alkaline substances added in the pyrolysis dechlorination process of the present invention can in situ absorb HCl released by the decomposition of chlorine-containing compounds at high temperature in the whole process, reduce the generation of organic chlorides, and obtain low-chlorine pyrolysis oil.

[0036] Other features and advantages of the present invention will be described in detail in the following detailed description. BRIEF DESCRIPTION OF THE DRAWINGS

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

[0038] Figure 1The present invention is a process flow chart of an embodiment of a method for preparing low-chlorine pyrolysis oil from a plastic mixture.

[0039] Description of Reference Numerals

[0040] 1-Chlorine-containing plastics 2-Chlorine-containing plastics first screw heating and conveying equipment

[0041] 3-Plastics containing additives 4-Plastics containing additives The first screw type heating and conveying equipment

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

[0043] 9-Hydrogen chloride absorption unit 10-Visbreaking unit

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

[0045] 13-Separation unit DETAILED DESCRIPTION

[0046] The specific embodiments of the present invention are described in detail below. It should be understood that the specific embodiments described herein are only used to illustrate and explain the present invention, and are not used to limit the present invention.

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

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

[0049] S1, the chlorine-containing plastic and the additive-containing plastic enter the first screw-type heating and conveying equipment separately or together for dehydration, degassing and volume reduction treatment to obtain a dehydrated, degassed and volume-reduced plastic;

[0050] S2, allowing the dehydrated, degassed and volume-reduced plastic to enter a second screw-type heating and conveying device for liquefaction and dechlorination treatment to obtain a liquefied dechlorinated plastic;

[0051] S3, allowing the liquefied dechlorinated plastic to enter a visbreaking unit for visbreaking treatment to obtain visbreaking plastic oil and a first dry gas;

[0052] S4, allowing the viscous and cracked plastic oil to enter a heating unit for heating treatment to obtain heated plastic oil;

[0053] S5, allowing the heated plastic oil to enter a pyrolysis reaction unit for pyrolysis reaction to obtain pyrolysis products and coke;

[0054] S6, allowing the pyrolysis product to enter a separation unit for separation to obtain a second dry gas, liquefied gas and pyrolysis oil;

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

[0056] In the method provided by the present 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 in the present invention can be directly waste plastics in landfills.

[0057] Additive-containing plastics refer to plastics containing plastic additives. Plastic additives are some compounds that must be added to synthetic resins during molding to improve their processing properties or to improve the insufficient properties of the resin itself. For example, calcium carbonate is added to plastic processing. They can improve the stability, heat resistance, hardness and rigidity of plastic products, improve plastic processing properties, and reduce the cost of plastic products. The amount added to plastics can reach more than 60% by weight. Adding 30% by weight of specially treated calcium oxide to plastic products can make the notched impact strength of the products reach 10% to 120%, and the thermoplasticity, elastomer and toughness reach the same level as the modified products. Zinc oxide has many applications in plastics, such as enhancing the mechanical properties of plastics, preventing ultraviolet radiation, improving processability and manufacturing electrical conductive materials.

[0058] In a specific embodiment, the additive in the additive-containing plastic is 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 a mixture thereof. It also includes a mixture containing alkali metal and / or alkaline earth metal compounds such as talc, bentonite, clay, magnesia, glass powder and asbestos. The content of the additive in the additive-containing plastic is 0.1% to 90% by weight, preferably 1% to 70% by weight.

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

[0060] In a specific embodiment, chlorine-containing 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°C to 380°C, and the residence time is 5min to 16min to obtain a dehydrated, degassed and volume-reduced plastic; the conveying line speed of the first screw-type heating and conveying device is 0.0025m / s to 0.008m / s, the pressure inside the screw is 0.1Mpa to 4MPa, and the feed rate is 30g / s to 200g / s.

[0061] In a preferred embodiment, two first screw heating and conveying devices are used for processing. Figure 1 As shown, the chlorine-containing plastic 1 enters the first chlorine-containing plastic screw heating and conveying device 2 for treatment, the outlet temperature is 150°C to 200°C, the residence time is 5min to 16min, the conveying line speed is 0.0025m / s to 0.008m / s, more preferably 0.003m / s to 0.007m / s, the pressure in the screw is 0.1MPa to 4MPa, and the feed rate is 20g / s to 100g / s to obtain a dehydrated, degassed and reduced-volume chlorine-containing plastic; the additive-containing plastic 3 enters the additive-containing plastic The material is processed in the first screw heating and conveying device 4 with an outlet temperature of 150°C to 380°C, a residence time of 5min to 16min, a conveying line speed of 0.0025m / s to 0.008m / s, more preferably 0.003m / s to 0.007m / s, a screw internal pressure of 0.1Mpa to 4MPa, and a feed rate of 10g / s to 100g / s to obtain a dehydrated, degassed, and volume-reduced plastic containing additives; the processed materials enter the second screw heating and conveying device 8 separately or after mixing.

[0062] In a preferred embodiment, the outlet temperature of the first screw heating and conveying device for plastics containing additives is 10°C to 180°C higher than that of the first screw heating and conveying device for plastics containing chlorine, and more preferably 20°C to 150°C higher.

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

[0064] In one embodiment, in step S2, the outlet temperature of the second screw heating and conveying equipment 3 is 280°C to 450°C, and the residence time is 5min to 30min; optionally, the conveying line speed of the second screw heating and conveying equipment is 0.003m / s to 0.008m / s, and the pressure inside the screw is 0.0001MPa to 5MPa.

[0065] In a preferred embodiment, in step S2, the outlet temperature of the second screw heating conveying device 3 is 300°C to 430°C, the residence time is 6min to 25min, the conveying line speed is 0.003m / s to 0.008m / s, and the pressure inside the screw is 0.1MPa to 3MPa. The waste plastics are treated according to the optimized liquefaction and dechlorination conditions in this embodiment, which can further improve the liquefaction and dechlorination efficiency.

[0066] In one embodiment, the additive in the additive-containing plastic is 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 hydroxide is 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 carbonate is 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 alkali metal / alkaline earth metal silicate is sodium silicate and / or magnesium silicate.

[0071] In one embodiment, in step S2, the outlet temperature of the second screw heating and conveying device is 280°C to 450°C, preferably 300°C to 430°C, and the residence time is 6 min to 25 min.

[0072] In one embodiment, the visbreaking unit in step S4 uses a visbreaking reactor to perform visbreaking treatment, and the visbreaking reactor is an adiabatic visbreaking reactor; the process conditions of the visbreaking treatment are conventional visbreaking reaction conditions in the art, and optionally, the reaction temperature is 350°C to 450°C, preferably 360°C to 430°C, and more preferably 370°C to 410°C; the residence time is 15min to 150min, preferably 20min to 120min.

[0073] In one embodiment, in step S4, the heating unit includes a heating furnace; the process conditions of the 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; water vapor is injected along with the heated material, and the steam injection amount is 0.5% by weight to 5% by weight, preferably 1% by weight to 3% by weight.

[0074] In one embodiment, in step S5, the pyrolysis reaction unit adopts 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°C to 550°C, preferably 450°C to 520°C.

[0075] In a second aspect, the present invention provides a system for preparing low-chlorine pyrolysis oil from a plastic mixture, as shown in the attached Figure 1 As shown, the system includes a first screw heating and conveying device 2 for chlorine-containing plastic, a first screw heating and conveying device 4 for additive-containing plastic, a second screw heating and conveying device 8, a visbreaking unit 10, a heating unit 11, a pyrolysis reaction unit 12 and a separation unit 13;

[0076] The first screw-type heating and conveying device 2 for chlorine-containing plastic and the first screw-type heating and conveying device 4 for additive-containing plastic are arranged in parallel, and include an inlet and an outlet; the first screw-type heating and conveying device 2 for chlorine-containing plastic is configured to perform dehydration, degassing and volume reduction treatment on the chlorine-containing plastic; the first screw-type heating and conveying device 4 for additive-containing plastic is configured to perform dehydration, degassing and volume reduction treatment on the additive-containing plastic;

[0077] The outlet of the first screw-type heating and conveying device for chlorine-containing plastics and the outlet of the first screw-type heating and conveying device 4 for additive-containing plastics are respectively connected to the second screw-type heating and conveying device;

[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 perform liquefaction and dechlorination treatment on the dehydrated, degassed and volume-reduced plastic to obtain the dechlorinated plastic;

[0079] The visbreaking unit 10 includes a dechlorinated plastic inlet and a visbreaking plastic oil outlet; the dechlorinated plastic inlet is connected to the dechlorinated plastic outlet of the second screw heating and conveying device 8; the visbreaking unit 10 is configured to perform visbreaking treatment on the dechlorinated plastic to obtain visbreaking plastic oil;

[0080] The heating unit 11 comprises a visbreaking plastic oil inlet and a heated plastic oil outlet, and the visbreaking plastic oil inlet is connected to the visbreaking plastic oil outlet of the visbreaking unit 10; the heating unit 11 is configured to heat the visbreaking plastic oil to obtain heated plastic oil;

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

[0083] The method provided by the present invention is described in detail below with examples, but the present invention is not limited thereby.

[0084] Example 1

[0085] according to Figure 1 According to the process flow shown, a mixed plastic containing 20 wt% LDPE, 20 wt% HDPE, 40 wt% PP, 16 wt% PS and 4 wt% PVC (chlorine content is 2 wt%, and analysis method adopts X-ray fluorescence spectrometry) is crushed and impurity removed to obtain chlorine-containing waste plastic particles, and the chlorine-containing plastic is subjected to dehydration, degassing and volume reduction treatment by a first screw-type heating and conveying equipment to obtain a dehydrated, degassed and volume-reduced chlorine-containing plastic, wherein the feed rate of the chlorine-containing plastic is 100 g / s, the outlet temperature of the first screw-type heating and conveying equipment is 200°C, the pressure inside the screw is 0.5 MPa, the conveying line speed is 0.005 m / s, and the material residence time is 8 min. An antibacterial plastic containing 4 wt% calcium carbonate and 96 wt% polyethylene is crushed and impurity-removed (the composition and content of additives in the plastic are determined by a combination of infrared spectroscopy, thermogravimetric method and X-ray fluorescence spectroscopy), and is dehydrated, degassed and reduced in volume by a first screw-type heating and conveying device for the additive-containing plastic to obtain a dehydrated, degassed and reduced-volume plastic containing additives, wherein the outlet temperature of the first screw-type heating and conveying device is 200°C, the pressure inside the screw is 0.4MPa, the conveying line speed is 0.005m / s, the material residence time is 10min, and the feed rate of the chlorine-containing plastic is 50g / s.

[0086] Then, the dehydrated, degassed and reduced-volume chlorine-containing plastic is mixed with the dehydrated, degassed and reduced-volume additive-containing plastic at the input end 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°C, the residence time is 6 minutes, and liquefied dechlorinated waste plastic is obtained; 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 to a hydrogen chloride absorption unit to contact with a hydrogen chloride absorbent (NaOH solution) for hydrogen chloride absorption treatment.

[0088] The liquefied dechlorinated waste plastic is sent to an adiabatic visbreaking reactor for visbreaking treatment to obtain visbreaking liquefied plastic oil and the first dry gas. The visbreaking treatment temperature is 380° C. and the residence time is 60 minutes to obtain liquefied dechlorinated plastic oil.

[0089] The dechlorinated plastic oil is first heated in a heating furnace to obtain high-temperature liquefied plastic, and the outlet temperature of the heating furnace is 500°C; the steam injection amount is 1 weight%; then the high-temperature liquefied plastic is sent to a pyrolysis tower for pyrolysis reaction, and pyrolysis is performed at 490°C for 40s. The obtained pyrolysis products are separated and treated by a separation unit to obtain pyrolysis oil, coke and pyrolysis gas, etc., wherein the chlorine content analysis results of the pyrolysis oil are shown in Table 1 (the analysis method adopts X-ray fluorescence spectrometry).

[0090] Example 2

[0091] according to Figure 1 According to the process flow shown, a mixed plastic (chlorine content of 0.5 weight %) containing LDPE, HDPE, PP, PS and PVC is crushed and impurized to obtain chlorine-containing waste plastic particles, and the mixed plastic is dehydrated, degassed and reduced in volume by a first screw-type heating and conveying device for chlorine-containing plastics to obtain dehydrated, degassed and reduced-volume chlorine-containing waste plastics. The feed rate of the chlorine-containing plastic is 100 g / s, the outlet temperature of the first screw-type heating and conveying device is 180°C, the pressure inside the screw is 1 MPa, the conveying line speed is 0.004 m / s, and the material residence time is 10 min. An incinerator plastic bag containing 25 weight % of calcium carbonate and 75 weight % of polyethylene is crushed and impurity-removed, and is dehydrated, degassed and reduced in volume by a first screw-type heating and conveying device for plastics containing additives to obtain dehydrated, degassed and reduced-volume waste plastics containing additives, wherein the feed rate of the plastics containing additives is 20 g / s, the outlet temperature of the first screw-type heating and conveying device is 300°C, the pressure inside the screw 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 plastics are mixed with the dehydrated, degassed and reduced-volume alkaline waste plastics 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°C, and the residence time is 5 minutes to obtain liquefied dechlorinated waste plastics. The vacuum degree of the screw-type heating and conveying equipment is 150 mmHg.

[0093] During the dechlorination process, the gaseous material containing hydrogen chloride is extracted by a vacuum system and sent to a hydrogen chloride absorption unit to contact with a hydrogen chloride absorbent NaOH solution for hydrogen chloride absorption treatment.

[0094] The liquefied dechlorinated waste plastic is sent to an adiabatic visbreaking reactor for visbreaking treatment to obtain visbreaking liquefied waste plastic oil and the first dry gas. The visbreaking treatment temperature is 380° C. and the residence time is 60 minutes to obtain liquefied dechlorinated plastic oil.

[0095] The dechlorinated plastic oil was first heated in a heating furnace to obtain high-temperature liquefied plastic, and the outlet temperature of the heating furnace was 500°C; the steam injection amount was 1 weight%; then the high-temperature liquefied waste plastic was sent to a pyrolysis tower for pyrolysis reaction, and pyrolyzed at 470°C for 50s. The obtained pyrolysis products were separated and treated 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.

[0096] Example 3

[0097] according to Figure 1 According to the process flow shown, a mixed plastic containing LDPE, HDPE, PP, PS and PVC (chlorine content is 5 weight%) is crushed and impurized to obtain chlorine-containing waste plastic particles, and the chlorine-containing plastic is dehydrated, degassed and reduced in volume by a first screw-type heating and conveying device to obtain a dehydrated, degassed and reduced-volume chlorine-containing plastic, wherein the feed rate of the chlorine-containing plastic is 100 g / s, the outlet temperature of the first screw-type heating and conveying device is 180°C, the pressure inside the screw is 1 MPa, the conveying line speed is 0.006 m / s, and the material residence time is 7 min. The thermal conductive plastic containing 10 weight % of magnesium oxide and 90 weight % of polypropylene plastic is crushed and impurity-removed, and is dehydrated, degassed and reduced in volume by a first screw-type heating and conveying device for the additive-containing plastic to obtain a dehydrated, degassed and reduced-volume plastic containing additives, wherein the feed rate of the additive-containing plastic is 50 g / s, the outlet temperature of the first screw-type heating and conveying device is 350°C, the pressure inside the screw is 1 MPa, the conveying line speed is 0.007 m / s, and the material residence time is 6 min.

[0098] Then, the dehydrated, degassed and reduced-volume chlorine-containing plastic is mixed with the dehydrated, degassed and reduced-volume plastic containing additives 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°C, the residence time is 5 minutes, and liquefied dechlorinated plastic is obtained; the vacuum degree of the screw-type heating and conveying equipment is 150 mmHg.

[0099] During the dechlorination process, the gaseous material containing hydrogen chloride is extracted by a vacuum system and sent to a hydrogen chloride absorption unit to contact with a hydrogen chloride absorbent NaOH solution for hydrogen chloride absorption treatment.

[0100] The liquefied dechlorinated waste plastic is sent to an adiabatic visbreaking reactor for visbreaking treatment to obtain visbreaking liquefied waste plastic oil and the first dry gas. The visbreaking treatment temperature is 400° C. and the residence time is 45 minutes to obtain liquefied dechlorinated plastic oil.

[0101] The dechlorinated plastic oil was first heated in a heating furnace to obtain high-temperature liquefied plastic, and the outlet temperature of the heating furnace was 510°C; the steam injection amount was 2% by weight; then the high-temperature liquefied plastic was sent to a pyrolysis tower for pyrolysis reaction, and pyrolyzed at 460°C for 60s. The obtained pyrolysis products were separated and treated 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.

[0102] Example 4

[0103] according to Figure 1 The process flow shown in the figure is to crush and remove impurities from a mixed plastic containing LDPE, HDPE, PP, PS and PVC (chlorine content is 6 weight%) to obtain chlorine-containing waste plastic particles, and then carry out dehydration, degassing and volume reduction treatment through a first screw-type heating and conveying device for chlorine-containing plastics to obtain dehydrated, degassed and volume-reduced chlorine-containing waste plastics, wherein the feed rate of the chlorine-containing plastics is 100 g / s, the outlet temperature of the first screw-type heating and conveying device is 150°C, the pressure inside the screw is 2 MPa, the conveying line speed is 0.005 m / s, and the material residence time is 8 min. The agricultural film containing 10 weight % of calcium oxide and 90 weight % of polyethylene is crushed and impurity-removed, and is dehydrated, degassed and reduced in volume by a first screw-type heating and conveying device containing additive plastics to obtain dehydrated, degassed and reduced-volume waste plastics containing additives, wherein the feed rate of the additive-containing plastics is 20 g / s, the outlet temperature of the first screw-type heating and conveying device is 220°C, the pressure inside the screw is 0.1 MPa, the conveying line speed is 0.01 m / s, and the material residence time is 4 min.

[0104] Then, the dehydrated, degassed and reduced-volume chlorine-containing plastic is mixed with the dehydrated, degassed and reduced-volume additive-containing plastic at the input end 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°C, the residence time is 5 minutes, and liquefied dechlorinated waste plastic is obtained; the vacuum degree of the screw-type heating and conveying equipment is 150 mmHg.

[0105] During the dechlorination process, the gaseous material containing hydrogen chloride is extracted by a vacuum system and sent to a hydrogen chloride absorption unit to contact with a hydrogen chloride absorbent NaOH solution for hydrogen chloride absorption treatment.

[0106] The liquefied dechlorinated waste plastic is sent to an adiabatic visbreaking reactor for visbreaking treatment to obtain visbreaking liquefied plastic oil and the first dry gas. The visbreaking treatment temperature is 430° C. and the residence time is 20 minutes to obtain liquefied dechlorinated plastic oil.

[0107] The dechlorinated plastic oil was first heated in a heating furnace to obtain high-temperature liquefied plastic, and the outlet temperature of the heating furnace was 520°C; the steam injection amount was 3% by weight; then the high-temperature liquefied plastic was sent to a pyrolysis tower for pyrolysis reaction, and pyrolyzed at 520°C for 20s. The obtained pyrolysis products were separated and treated by a separation unit to obtain pyrolysis oil, coke and pyrolysis gas, etc., wherein the chlorine content analysis results of the pyrolysis oil are shown in Table 1.

[0108] Example 5

[0109] according to Figure 1 According to the process flow shown, a mixed plastic containing LDPE, HDPE, PP, PS and PVC (chlorine content is 6 weight%) is crushed and impurized to obtain chlorine-containing waste plastic particles, and the chlorine-containing plastic is dehydrated, degassed and reduced in volume by a first screw-type heating and conveying device to obtain dehydrated, degassed and reduced in volume chlorine-containing waste plastic, wherein the feed rate of the chlorine-containing plastic is 100 g / s, the outlet temperature of the first screw-type heating and conveying device is 200°C, the pressure inside the screw is 2 MPa, the conveying line speed is 0.005 m / s, and the material residence time is 8 min. A calcium plastic plate containing 60 weight % of calcium carbonate and 40 weight % of polyethylene is crushed and impurity removed, and is dehydrated, degassed and reduced in volume by a first screw-type heating and conveying device for the additive-containing plastic to obtain a dehydrated, degassed and reduced-volume additive-containing plastic, wherein the feed rate of the additive-containing plastic is 10 g / s, the outlet temperature of the first screw-type heating and conveying device is 320°C, the pressure inside the screw 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 reduced-volume waste plastics are mixed with the dehydrated, degassed and reduced-volume waste plastics 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°C, and the residence time is 5 minutes to obtain liquefied dechlorinated plastics. The vacuum degree of the screw-type heating and conveying equipment is 150 mmHg.

[0111] During the dechlorination process, the gaseous material containing hydrogen chloride is extracted by a vacuum system and sent to a hydrogen chloride absorption unit to contact with a hydrogen chloride absorbent NaOH solution for hydrogen chloride absorption treatment.

[0112] The liquefied dechlorinated waste plastic is sent to an adiabatic visbreaking reactor for visbreaking treatment to obtain visbreaking liquefied waste plastic oil and the first dry gas. The visbreaking treatment temperature is 380° C. and the residence time is 60 minutes to obtain liquefied dechlorinated waste plastic oil.

[0113] The dechlorinated waste plastic oil is first heated in a heating furnace to obtain high-temperature liquefied plastic, and the outlet temperature of the heating furnace is 500°C; the steam injection amount is 1 weight%; then the high-temperature liquefied plastic is sent to a pyrolysis tower for pyrolysis reaction, and pyrolysis is carried out at 480°C for 60s. The obtained pyrolysis products are separated and treated by a separation unit to obtain pyrolysis oil, coke and pyrolysis gas, etc., wherein the chlorine content analysis results of the pyrolysis oil are shown in Table 1.

[0114] Example 6

[0115] according to Figure 1According to the process flow shown, a mixed plastic (chlorine content of 8 weight %) including LDPE, HDPE, PP, PS and PVC is crushed and impurized to obtain chlorine-containing waste plastic particles, and the chlorine-containing plastic is dehydrated, degassed and reduced in volume by a first screw-type heating and conveying device to obtain dehydrated, degassed and reduced-volume chlorine-containing waste plastic, wherein the feed rate of the chlorine-containing plastic is 90 g / s, the outlet temperature of the first screw-type heating and conveying device is 170°C, the pressure inside the screw is 0.8 MPa, the conveying line speed is 0.004 m / s, and the material residence time is 10 min. The soft polyethylene wire containing 15 wt% calcium hydroxide and 85 wt% polyethylene is crushed and impurities are removed, and the first screw-type heating and conveying equipment containing additives is used for dehydration, degassing and volume reduction treatment to obtain dehydrated, degassed and volume-reduced waste plastic containing additives, wherein the feed rate of the additive-containing plastic is 16 g / s, the outlet temperature of the first screw-type heating and conveying equipment is 360°C, the pressure in the screw is 1.0 MPa, the conveying line speed is 0.008 m / s, and the material residence time is 5 min. Then the dehydrated, degassed and volume-reduced chlorine-containing plastic is mixed with the dehydrated, degassed and volume-reduced plastic containing additives, the mass ratio of calcium hydroxide to chlorine is 1:3, and enters the second screw-type heating and conveying equipment for dechlorination and liquefaction treatment, the outlet temperature of the second screw-type heating and conveying equipment is 420°C, the residence time is 6 min, and liquefied dechlorinated waste plastic is obtained; the vacuum degree of the screw-type heating and conveying equipment is 150 mmHg.

[0116] During the dechlorination process, the gaseous material containing hydrogen chloride is extracted by a vacuum system and sent to a hydrogen chloride absorption unit to contact with a hydrogen chloride absorbent NaOH solution for hydrogen chloride absorption treatment.

[0117] The liquefied dechlorinated waste plastic is sent to an adiabatic visbreaking reactor for visbreaking treatment to obtain visbreaking liquefied waste plastic oil and the first dry gas. The visbreaking treatment temperature is 360° C. and the residence time is 120 minutes to obtain liquefied dechlorinated plastic oil.

[0118] The dechlorinated waste plastic oil is first heated in a heating furnace to obtain high-temperature liquefied plastic, and the outlet temperature of the heating furnace is 460°C; the steam injection amount is 1 weight%; then the high-temperature liquefied plastic is sent to a pyrolysis reaction tower and pyrolyzed at 480°C for 50s. The pyrolysis products are separated and treated 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.

[0119] Example 7

[0120] according to Figure 1According to the process flow shown, a mixed plastic (chlorine content of 1 weight %) including 2DPE, HDPE, PP, PS and PVC is crushed and impurized to obtain chlorine-containing waste plastic particles, and the chlorine-containing plastic is dehydrated, degassed and reduced in volume by a first screw-type heating and conveying device to obtain dehydrated, degassed and reduced-volume chlorine-containing waste plastic, wherein the feed rate of the chlorine-containing plastic is 100 g / s, the outlet temperature of the first screw-type heating and conveying device is 170°C, the pressure inside the screw is 0.8 MPa, the conveying line speed is 0.004 m / s, and the material residence time is 10 min. The polyethylene sole containing 1 wt% calcium carbonate and 99 wt% polyethylene was crushed and impurities were removed, and the plastic containing additives was dehydrated, degassed and reduced in volume by the first screw-type heating and conveying device to obtain the dehydrated, degassed and reduced-volume plastic containing additives, wherein the feed rate of the plastic containing additives was 100 g / s, the outlet temperature of the first screw-type heating and conveying device was 210°C, the pressure inside the screw was 2.5 MPa, the conveying line speed was 0.005 m / s, and the material residence time was 8 min.

[0121] Then, the dehydrated, degassed and reduced-volume chlorine-containing waste plastics are mixed with the dehydrated, degassed and reduced-volume plastics containing additives at the input end 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°C, the residence time is 6 minutes, and liquefied dechlorinated waste plastics are obtained; 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 to a hydrogen chloride absorption unit to contact with a hydrogen chloride absorbent (NaOH solution) for hydrogen chloride absorption treatment.

[0123] The liquefied dechlorinated waste plastic is sent to a visbreaking tank for visbreaking treatment to obtain visbreaking liquefied waste plastic oil and the first dry gas. The visbreaking treatment temperature is 380° C. and the residence time is 60 minutes to obtain liquefied dechlorinated waste plastic oil.

[0124] The dechlorinated waste plastic oil was first heated in a heating furnace to obtain high-temperature liquefied waste plastic, and the outlet temperature of the heating furnace was 500°C; the steam injection amount was 1 weight%; then the high-temperature liquefied waste plastic was sent to a pyrolysis reaction equipment and pyrolyzed at 500°C for 35s. The obtained pyrolysis products were separated and treated by a separation unit to obtain pyrolysis oil, coke and pyrolysis gas, etc., wherein 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 in the figure is to crush and remove impurities from mixed waste plastics containing 20 wt% LDPE, 20 wt% HDPE, 40 wt% PP, 16 wt% PS and 4 wt% PVC to obtain chlorine-containing waste plastic particles, and then dehydrate, degas and reduce the volume by a first screw-type heating and conveying device to obtain dehydrated, degassed and reduced-volume chlorine-containing waste plastics. The feed rate of the chlorine-containing plastic is 100 g / s, the outlet temperature of the first screw-type heating and conveying device is 200°C, the pressure inside the screw is 0.5 MPa, the conveying line speed is 0.005 m / s, and the material residence time is 8 min.

[0127] Then, the dehydrated, degassed and volume-reduced waste plastics are directly liquefied and dechlorinated in the third screw-type heating and conveying equipment without adding plastics containing additives. The outlet temperature of the second screw-type heating and conveying equipment is 400°C, and the residence time is 8 minutes to obtain liquefied dechlorinated waste plastics; 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 to a hydrogen chloride absorption unit to contact with a hydrogen chloride absorbent (NaOH solution) for hydrogen chloride absorption treatment.

[0129] The liquefied dechlorinated waste plastic is sent to a visbreaking tank for visbreaking treatment to obtain visbreaking liquefied waste plastic oil and the first dry gas. The visbreaking treatment temperature is 380° C. and the residence time is 60 minutes to obtain liquefied dechlorinated waste plastic oil.

[0130] The dechlorinated waste plastic oil was first heated in a heating furnace to obtain high-temperature liquefied waste plastic, and the outlet temperature of the heating furnace was 500°C; the steam injection amount was 1 weight%; then the high-temperature liquefied waste plastic was sent to a pyrolysis reaction equipment and pyrolyzed at 480°C for 40s. The obtained pyrolysis products were separated and treated by a separation unit to obtain pyrolysis oil, coke and pyrolysis gas, etc., wherein 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 in the figure is to crush and remove impurities from a mixed plastic containing 20 wt% LDPE, 20 wt% HDPE, 40 wt% PP, 16 wt% PS and 4 wt% PVC to obtain chlorine-containing waste plastic particles, and then dehydrate, degas and reduce the volume by a first screw-type heating and conveying device 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 heating and conveying device is 200°C, the pressure inside the screw is 0.5 MPa, the conveying line speed is 0.005 m / s, and the material residence time is 8 min.

[0133] Then, the dehydrated, degassed and volume-reduced waste plastics are directly liquefied and dechlorinated in the second screw-type heating and conveying equipment without adding waste plastics containing additives. The outlet temperature of the second screw-type heating and conveying equipment is 400° C., and the residence time is 10 minutes to obtain liquefied dechlorinated waste plastics; the screw-type heating and conveying equipment is not vacuumed.

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

[0135] The liquefied dechlorinated waste plastic is sent to a visbreaking tank for visbreaking treatment to obtain visbreaking liquefied waste plastic oil and the first dry gas. The visbreaking treatment temperature is 380° C. and the residence time is 60 minutes to obtain liquefied dechlorinated waste plastic oil.

[0136] The dechlorinated waste plastic oil was first heated in a heating furnace to obtain high-temperature liquefied waste plastic, and the outlet temperature of the heating furnace was 500°C; the steam injection amount was 1 weight%; then the high-temperature liquefied waste plastic was sent to a pyrolysis reaction equipment and pyrolyzed at 480°C for 40s. The obtained pyrolysis products were separated and treated by a separation unit to obtain pyrolysis oil, coke and pyrolysis gas, etc., wherein the chlorine content analysis results of the pyrolysis oil are shown in Table 1.

[0137] Table 1 Chlorine content in pyrolysis oil in 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, from Examples 1 to 7, and by comparing with Comparative Examples 1 to 2, it can be seen that additive-containing plastics are added during the pyrolysis dechlorination process, and the additives are oxides, hydroxides and salts of alkali metals / alkaline earth metals, wherein the additives can in situ adsorb HCl released by the decomposition of chlorine-containing compounds at high temperatures in the whole process, reduce the generation of organic chlorides, and effectively realize 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 the present disclosure are described in detail above; however, the present disclosure is not limited to the specific details in the above embodiments. Within the technical concept of the present disclosure, a variety of simple modifications can be made to the technical solution of the present disclosure, and these simple modifications all fall within the protection scope of the present disclosure.

Claims

1. A method for preparing low-chlorine pyrolysis oil from a plastic mixture, characterized in that: The following steps are involved: S1, the chlorine-containing plastic and the additive-containing plastic enter the first screw-type heating and conveying equipment separately or together for dehydration, degassing and volume reduction treatment to obtain a dehydrated, degassed and volume-reduced plastic; S2, allowing the dehydrated, degassed and volume-reduced plastic to enter a second screw-type heating and conveying device for liquefaction and dechlorination treatment to obtain a liquefied dechlorinated plastic; S3, allowing the liquefied dechlorinated plastic to enter a visbreaking unit for visbreaking treatment to obtain visbreaking plastic oil and a first dry gas; S4, allowing the viscous and cracked plastic oil to enter a heating unit for heating treatment to obtain heated plastic oil; S5, allowing the heated plastic oil to enter a pyrolysis reaction unit for pyrolysis reaction to obtain pyrolysis products and coke; S6, allowing the pyrolysis product to enter a separation unit for separation to obtain a second dry gas, liquefied gas and pyrolysis oil; Wherein, the additives are oxides, hydroxides and salts of alkali metals / alkaline earth metals.

2. The method for preparing low-chlorine pyrolysis oil from a plastic mixture according to claim 1, characterized in that: The chlorine-containing plastic enters the first screw-type heating and conveying equipment for chlorine-containing plastics for treatment, with an outlet temperature of 100°C to 250°C and a residence time of 4min to 20min, to obtain a dehydrated, degassed and volume-reduced chlorine-containing plastic; the additive-containing plastic enters the first screw-type heating and conveying equipment for additive-containing plastics for treatment, with an outlet temperature of 120°C to 380°C and a residence time of 4min to 20min, to obtain a dehydrated, degassed and volume-reduced additive-containing plastic; the treated material enters the second screw-type heating and conveying equipment; Preferably, the outlet temperature of the first screw-type heating and conveying device for chlorine-containing plastic is 150°C to 200°C, the residence time is 5min to 16min, and the pressure inside the screw is 0.1MPa to 6MPa; The outlet temperature of the first screw-type heating and conveying device for the additive-containing plastic is 150° C. to 380° C., the residence time is 5 min to 16 min, and the pressure inside the screw is 0.1 MPa to 6 MPa.

3. The method for preparing low-chlorine pyrolysis oil from a plastic mixture according to claim 2, characterized in that: The outlet temperature of the first screw heating and conveying device for plastics containing additives is 10°C to 180°C higher than the outlet temperature of the first screw heating and conveying device for plastics containing chlorine, and preferably 20°C to 150°C higher.

4. The method for preparing low-chlorine pyrolysis oil from a plastic mixture according to claim 1, 2 or 3, characterized in that: The outlet temperature of the second screw heating and conveying device is 280°C to 450°C, and the residence time is 5min to 30min; Preferably, the outlet temperature of the second screw-type heating and conveying device is 300° C. to 430° C., the residence time is 5 min to 20 min, and the pressure inside the screw is 0.0001 MPa to 5 MPa.

5. The method for preparing low-chlorine pyrolysis oil from a plastic mixture according to claim 1, 2 or 3, characterized in that: The visbreaking unit in step S3 uses an adiabatic visbreaking reactor to perform the visbreaking treatment, the reaction temperature is 350° C. to 450° C., and the residence time is 15 min to 150 min; Preferably, the reaction temperature is 360° C. to 430° C., and the residence time is 20 min to 120 min.

6. The method for preparing low-chlorine pyrolysis oil from a plastic mixture according to claim 1, 2 or 3, characterized in that: The heating unit described in step S4 includes a heating furnace, the outlet temperature of the heating furnace is 430° C. to 570° C., water vapor is injected into the heating furnace, and the steam injection amount is 0.5% to 5% by weight based on the weight of the viscous cracked plastic oil entering the heating furnace; Preferably, the outlet temperature of the heating furnace is 450°C to 550°C.

7. The method for preparing low-chlorine pyrolysis oil from a plastic mixture according to claim 1, 2 or 3, characterized in that: The pyrolysis reaction unit described in step S5 adopts a pyrolysis tower, the tower top pressure is 0.05MPa~0.6MPa, the pyrolysis reaction temperature is 430℃~550℃, and the pyrolysis reaction time is 20s-60s.

8. The method for preparing low-chlorine pyrolysis oil from a plastic mixture according to claim 1, 2 or 3, characterized in that: In step S2, the gas generated in the second screw heating and conveying device enters the hydrogen chloride absorption unit under the action of the vacuum system, and contacts with the hydrogen chloride absorbent to remove hydrogen chloride, wherein 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.

9. The method for preparing low-chlorine pyrolysis oil from a plastic mixture according to claim 1, 2 or 3, characterized in that: The chlorine-containing plastic includes PVC; the additive-containing plastic refers to calcium plastic materials containing additives, incinerable plastic garbage bags, soft polyethylene wires, polyethylene soles, plastic agricultural films, antibacterial plastics or thermally conductive plastics, the additives are selected from alkali metal / alkaline earth metal oxides, hydroxides, carbonates, silicates, and the content of the additives is 0.1% to 90% by weight, preferably 1% to 70% by weight; Preferably, the additive is selected from one or more of calcium carbonate, calcium oxide, calcium hydroxide, zinc oxide and magnesium oxide.

10. The method for preparing low-chlorine pyrolysis oil from a plastic mixture according to claim 9, characterized in that: The ratio of the additive-containing plastic to the chlorine-containing plastic is such that the mass ratio of the additive to the chlorine is 1:0.5-20, preferably 1:1-8.

11. A system for preparing low-chlorine pyrolysis oil from a plastic mixture, characterized in that: The system comprises a first screw-type heating and conveying device (2) for chlorine-containing plastics, a first screw-type heating and conveying device (4) for additive-containing plastics, a second screw-type heating and conveying device (8), a visbreaking unit (10), a heating unit (11), a pyrolysis reaction unit (12) and a separation unit (13); The first screw-type heating and conveying device (2) for chlorine-containing plastic and the first screw-type heating and conveying device (4) for additive-containing plastic are arranged in parallel, and include an inlet and an outlet; the first screw-type heating and conveying device (2) for chlorine-containing plastic is configured to perform dehydration, degassing and volume reduction treatment on the chlorine-containing plastic; the first screw-type heating and conveying device (4) for additive-containing plastic is configured to perform dehydration, degassing and volume reduction treatment on the additive-containing plastic; The outlet of the first screw-type heating and conveying device for chlorine-containing plastics and the outlet of the first screw-type heating and conveying device for additive-containing plastics (4) are respectively connected to the second screw-type heating and conveying device; 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 perform liquefaction and dechlorination treatment on the dehydrated, degassed and volume-reduced plastic to obtain the dechlorinated plastic; The visbreaking unit (10) comprises a dechlorinated plastic inlet and a visbreaking 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 visbreaking unit (10) is configured to perform visbreaking treatment on the dechlorinated plastic to obtain visbreaking plastic oil; The heating unit (11) comprises a visbreaking plastic oil inlet and a heated plastic oil outlet, wherein the visbreaking plastic oil inlet is in communication with the visbreaking plastic oil outlet of the visbreaking unit (10); the heating unit (11) is configured to heat the visbreaking plastic oil to obtain heated plastic oil; The pyrolysis reaction unit (12) comprises a heated plastic oil inlet and a pyrolysis product outlet; the heated plastic oil inlet is connected to the heated plastic oil outlet of the heating unit (11); the pyrolysis reaction unit (11) is configured to perform a pyrolysis reaction on the heated plastic oil to obtain pyrolysis products and coke; The separation unit (13) comprises 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 product to obtain dry gas, liquefied gas and pyrolysis oil.

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