A reactor and process for producing hydrocarbon compounds by catalytic cracking of waste plastics

Abstract

The application discloses a kind of reactors and process methods for preparing hydrocarbon compounds by catalytic cracking of waste plastics, comprising reactor body and exhaust collection unit;The reactor body is communicated by at least two double screw extruders in series from head to tail, forming a closed material circulation loop;At least one double screw extruder is provided with a feeding unit;Double screw extruder is provided with at least one gas inlet and at least one exhaust port.The application can realize uniform dispersion of solid catalyst in high viscosity melt by the strong shear mixing and self-cleaning characteristics of double screw extruder during operation, eliminate the problem of local catalyst concentration uneven, effectively reduce the coking and carbon deposition caused by material stickiness;At the same time, the closed loop circulation loop formed by multiple extruders makes the material realize overall circulation flow on the basis of axial push conveying, repeatedly experience shear mixing process, significantly improve the reaction rate of catalytic cracking.

Description

Technical Field

[0001] This invention relates to the field of chemical engineering and polymer resource recycling technology, and in particular to a reactor and process for the catalytic cracking of waste plastics to produce hydrocarbon compounds. Background Technology

[0002] Existing methods for recycling waste plastics through energy recovery, such as incineration for power generation or heating, are effective in reducing volume and weight. However, these methods easily generate pollutants such as dioxins, HCl, and fly ash, resulting in high carbon emissions. They are more suitable for treating waste plastics that are almost impossible to reuse. Physical recycling, also known as mechanical recycling, involves melting and reprocessing waste plastics. This method has low investment, mature technology, simple equipment, and relatively low environmental risks. However, it can only process single, clean, and non-severely polluted plastics, and the performance deteriorates after multiple melting processes, limiting the number of times it can be recycled. Chemical recycling uses chemical reactions to degrade mixed waste plastic molecules, generating monomers and other small-molecule basic chemicals with properties consistent with virgin materials. These are then polymerized back into plastics, allowing for almost unlimited recycling. Therefore, it has advantages such as wide applicability to various types of plastics, good carbon reduction effects, and alignment with the circular economy.

[0003] Currently, the main chemical recycling methods for waste plastics include thermal pyrolysis, catalytic pyrolysis, and solvent hydrolysis. Thermal pyrolysis and catalytic pyrolysis are suitable for almost all plastics, including thermosetting plastics, while solvent hydrolysis is mainly suitable for some heterochain polymers synthesized by condensation and polyaddition, such as polyesters and polyamides. Thermal pyrolysis is simple, but it requires high temperatures, consumes a lot of energy, has poor reaction selectivity, a wide product distribution, and the equipment is prone to coking and carbon buildup, requiring frequent cleaning.

[0004] Catalytic cracking operates at lower temperatures, produces less coking, and consumes significantly less energy than thermal cracking. Catalysts not only provide active sites, greatly improving cracking efficiency, but also offer relatively good controllability of product distribution. However, this method is not yet widely used, primarily due to the following insurmountable problems: a lack of efficient reactors; currently used or demonstrated equipment typically directly utilizes thermal cracking units from petrochemical or coal chemical processes. Catalysts are difficult to disperse and mix uniformly in high-viscosity plastic melts, and the main chains of plastic macromolecules are difficult to effectively contact the catalyst's active sites and quickly leave after the reaction. Furthermore, it is difficult to flexibly adjust the residence time of materials in the reactor according to the requirements of the dominant product to avoid over- or under-cracking or excessive side reactions. Summary of the Invention

[0005] The purpose of this invention is to overcome the shortcomings of the prior art by providing a reactor and process method for the catalytic cracking of waste plastics to produce hydrocarbon compounds.

[0006] The objective of this invention is achieved through the following technical solution: a reactor for the catalytic cracking of waste plastics to produce hydrocarbon compounds, comprising a reactor body and an exhaust gas collection unit; the reactor body consists of at least two twin-screw extruders connected in series to form a closed material circulation loop; at least one twin-screw extruder is equipped with a feeding unit; the twin-screw extruder is provided with at least one air inlet and at least one exhaust outlet, the air inlet and the exhaust outlet being arranged sequentially at intervals along the material conveying direction of the twin-screw extruder; the air inlet is used to introduce reaction control gas into the twin-screw extruder, and each exhaust outlet is connected to the exhaust gas collection unit.

[0007] Preferably, when the reactor body has two twin-screw extruders, the two twin-screw extruders are arranged in opposite parallel directions; when the reactor body has more than two twin-screw extruders, the extruders are arranged in a polygonal closed arrangement.

[0008] Preferably, the reaction control gas is hydrogen or nitrogen. By introducing nitrogen, the hydrocarbon gases generated by the cracking reaction in the twin-screw extruder are quickly removed from the active sites of the catalyst to avoid over-reaction or side reactions. By introducing hydrogen, the hydrogen-to-carbon ratio of the reaction products is increased, and the content of aromatics in the reaction products is reduced.

[0009] Preferably, the twin-screw extruder implements segmented temperature control along the material conveying direction. The twin-screw extruder is divided into a first temperature control section and a second temperature control section. The first temperature control section is located on the side of the twin-screw extruder closest to the feeding unit, and the section of the twin-screw extruder other than the first temperature control section is the second temperature control section. When the raw material undergoes a pyrolysis reaction, the temperature range of the first temperature control section is 180~220℃, and the temperature range of the second temperature control section is 220~350℃. The second temperature control section includes a pyrolysis section with a temperature of 280~350℃.

[0010] Preferably, each temperature control zone on the outside of the twin-screw extruder is equipped with a cooling device to cool the area, thereby creating a temperature difference inside the twin-screw extruder along the material conveying direction.

[0011] Preferably, the exhaust collection unit includes an exhaust chamber body, a condenser, a gas storage tank, and a liquid storage tank. The exhaust chamber body is connected to the exhaust port on the twin-screw extruder. Each exhaust chamber body is connected to the condenser through a pipe. The liquid phase separated by the condenser is stored in the liquid storage tank, and the gas phase separated by the condenser is stored in the gas storage tank.

[0012] Preferably, the screw in the twin-screw extruder is a modular self-cleaning screw, which is arranged in a cyclic pattern along its axial direction as a conveying section, a compression section, a kneading section, and / or a combination of the above sections; the feeding unit is located at one end of the twin-screw extruder near the conveying section, and the other end of the twin-screw extruder is equipped with a die head, which is used for cleaning coking or residue inside the twin-screw extruder and for discharging and regenerating deactivated catalyst.

[0013] A process for producing hydrocarbon compounds from waste plastics by catalytic cracking includes the following specific steps:

[0014] S1: Waste plastics are processed into particles within a set particle size range, and the waste plastic particles are mixed with a catalyst to obtain a mixed raw material; S2: Preheat the twin-screw extruder to the set preheating temperature. During the preheating process, nitrogen gas is introduced into each twin-screw extruder to replace the internal air. After the set preheating temperature is reached, the feeding unit is opened to feed the mixed raw materials into the twin-screw extruder. The feeding speed is adjusted according to the load of the extruder to ensure the safe operation of the system. S3: Heat the twin-screw extruder to the catalytic cracking reaction temperature, open the corresponding air inlet according to the reaction requirements, and introduce reaction control gas into the twin-screw extruder through the air inlet; S4: Based on the structural and compositional requirements of the target hydrocarbon products, select the target exhaust port and open it; the material circulates and undergoes catalytic cracking reaction in the series-connected twin-screw extruders, and the generated gaseous hydrocarbon reaction products enter the exhaust collection unit through the exhaust port. The exhaust collection unit condenses and separates the gaseous hydrocarbon reaction products to obtain liquid hydrocarbon products and gaseous hydrocarbon products.

[0015] Preferably, in step S4, when deactivated catalyst and coking material are generated during the reaction process, the exhaust port near the die head is switched to vacuum exhaust mode, and the deactivated catalyst and coking material are discharged by the die head; the volatiles carried in during the discharge of deactivated catalyst and coking material are transported to the waste gas treatment device through the exhaust channel set near the die head.

[0016] Preferably, in step S2, the preheating temperature is set to 180~300℃; in step S3, the catalytic cracking reaction temperature is 180~350℃, and the screw speed in the twin-screw extruder is 10-1200 rpm.

[0017] The beneficial effects of this invention are: 1. This invention addresses the core pain points of difficult catalyst dispersion and insufficient contact between plastic macromolecules and catalyst active sites in high-viscosity plastic melts. By utilizing the strong shear mixing characteristics of a twin-screw extruder during operation, this invention achieves uniform dispersion of solid catalysts in high-viscosity melts, eliminating the problem of uneven catalyst concentration in certain areas. Simultaneously, a closed-loop circulation circuit composed of multiple extruders enables overall material circulation on an axially pushed conveying basis, repeatedly undergoing shear mixing processes to continuously renew the contact interface between plastic macromolecules and catalyst active sites, significantly improving the catalytic cracking reaction rate. Furthermore, the introduction of reaction-regulating gases (such as nitrogen) through intermittently spaced air inlets can promptly desorb and separate small-molecule hydrocarbon gases from the catalyst surface, achieving rapid renewal of active sites, preventing over-reaction or carbon buildup and deactivation of products, and further enhancing catalytic efficiency.

[0018] 2. Addressing the shortcomings of traditional pyrolysis reactors, such as easy coking on the inner wall and the need for frequent shutdowns for slag removal, this invention structurally reduces the risk of coking. Firstly, the twin-screw extruder adopts a modular self-cleaning configuration, with minimal gap between the screw elements and the inner wall of the twin-screw extruder barrel. During operation, it continuously scrapes away material retained on the wall, achieving high-speed dynamic renewal of the wall and screw surfaces, preventing long-term high-temperature retention and coking. Secondly, the closed-loop circulation working mode eliminates dead zones, ensuring all materials are in a state of continuous flow and renewal, eliminating the stagnant coking zones on the walls of traditional batch reactors. Simultaneously, during the catalytic reaction, deactivated catalyst, coke, and other non-volatile solid residues within the twin-screw extruder can be discharged intermittently or continuously through the die head, eliminating the need for shutdown and disassembly of screens and other components for slag removal. This significantly reduces cleaning difficulty and greatly improves the continuous operating time and maintenance efficiency of the unit. Attached Figure Description

[0019] Figure 1 This is a schematic diagram of the reactor for the catalytic cracking of waste plastics to produce hydrocarbon compounds according to the present invention.

[0020] Figure 2 This is a graph showing the change in the composition of gaseous products with catalytic cracking reaction time in Example 2 of the present invention.

[0021] Figure 3 This is a graph showing the change in the composition of gaseous products with catalytic cracking reaction time in Example 5 of the present invention.

[0022] In the diagram: 11. Twin-screw extruder, 12. Feeding unit, 13. Die head, 14. Air inlet, 15. Exhaust outlet, 21. Exhaust chamber body, 22. Condenser, 23. Liquid storage tank, 24. Gas storage tank. Detailed Implementation

[0023] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention are within the scope of protection of the present invention.

[0024] Those skilled in the art should understand that, in the disclosure of this invention, the terms "longitudinal," "lateral," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," and "outer," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, the above terms should not be construed as limiting this invention.

[0025] It is understood that the term "a" should be understood as "at least one" or "one or more", that is, in one embodiment, the number of an element can be one, while in another embodiment, the number of the element can be multiple, and the term "a" should not be understood as a limitation on the number.

[0026] like Figure 1 As shown, a reactor for catalytic cracking of waste plastics to produce hydrocarbon compounds includes a reactor body and an exhaust gas collection unit. The reactor body consists of at least two twin-screw extruders 11 connected in series to form a closed material circulation loop. At least one twin-screw extruder 11 is equipped with a feeding unit 12. The twin-screw extruder 11 is equipped with at least one air inlet 14 and at least one exhaust outlet 15, which are arranged sequentially at intervals along the material conveying direction of the twin-screw extruder 11. The air inlet 14 is used to introduce reaction control gas into the twin-screw extruder 11, and each exhaust outlet 15 is connected to the exhaust gas collection unit.

[0027] This invention addresses the core pain points of catalyst dispersion difficulties and insufficient contact between plastic macromolecules and catalyst active sites in high-viscosity plastic melts. By utilizing the strong shear mixing characteristics of a twin-screw extruder 11 during operation, the invention achieves uniform dispersion of solid catalysts in high-viscosity melts, eliminating the problem of uneven catalyst concentration in certain areas. Simultaneously, a closed-loop circulation circuit composed of multiple extruders allows the material to circulate and repeatedly undergo shear mixing processes while being conveyed axially, continuously renewing the contact interface between plastic macromolecules and catalyst active sites, significantly improving the catalytic cracking reaction rate. Furthermore, the introduction of reaction control gas (such as nitrogen) through spaced air inlets 14 promptly removes small-molecule hydrocarbon gases from the catalyst surface, achieving rapid renewal of active sites, preventing over-reaction or carbon buildup and deactivation of the product, and further enhancing catalytic efficiency.

[0028] During catalytic cracking operation, the material circulation rate can be adjusted by controlling the screw speed inside the twin-screw extruder 11. Combined with opening the exhaust ports 15 at different positions, the number of times the material circulates in the closed loop and the total reaction residence time can be flexibly changed, achieving precise control of the cracking depth. By opening the upstream exhaust port 15 (the exhaust port 15 is closer to the feeding unit 12), hydrocarbon products with higher carbon numbers can be obtained. By opening the downstream exhaust port 15 (the exhaust port 15 is further away from the feeding unit 12), the material undergoes a longer reaction time, resulting in deeply cracked small molecule hydrocarbons, meeting the production needs of products with different carbon numbers.

[0029] Each air inlet 14 and exhaust outlet 15 of the twin-screw extruder 11 is equipped with a valve to control the opening and closing of the air inlet 14 or the exhaust outlet 15.

[0030] The screw inside the twin-screw extruder 11 is a modular self-cleaning screw, which is arranged in a cyclic pattern along its axial direction as a conveying section, a compression section, a kneading section, and / or a combination of the above sections. The feeding unit 12 is located on one end of the twin-screw extruder 11 near the conveying section, and the other end of the twin-screw extruder 11 is equipped with a die head 13. The die head 13 is used for cleaning coking or residue inside the twin-screw extruder 11 and for discharging and regenerating deactivated catalyst.

[0031] Among them, the modular self-cleaning screw is a screw structure used in the twin-screw extruder 11. It consists of standardized independent threaded elements splined onto a solid mandrel, which can be freely disassembled and reassembled. It relies on the full meshing structure of the twin screws to achieve automatic anti-accumulation, anti-sticking, and anti-carbonization during operation, while taking into account process adjustability and online self-cleaning capability.

[0032] A conveying thread element with a deep groove and long pitch is used near the feeding unit 12, namely the conveying section. A compression section and a kneading section are arranged after the conveying section. For systems with multiple air inlets 14 and air outlets, the conveying section, compression section, kneading section and other thread elements can be combined in a cyclic manner, with the air outlet set on the conveying section after the kneading section and the air inlet 14 set before the kneading section.

[0033] The specific composition of each type of threaded element can also be adjusted as needed. Typically, a kneading section threaded element can be composed of different shearing elements such as 30°, 45°, 60°, 90° and reverse thread elements. The number and composition of these elements can be adjusted as needed to achieve the corresponding kneading strength.

[0034] To address the drawbacks of traditional pyrolysis reactors, such as easy coking on the inner wall and the need for frequent shutdowns for slag removal, this invention structurally reduces the risk of coking. Firstly, the twin-screw extruder adopts a modular self-cleaning configuration, with extremely small gaps between the screw elements and the inner wall of the twin-screw extruder 11 barrel. During operation, it continuously scrapes away material retained on the wall, achieving high-speed dynamic renewal of the wall and screw surfaces, thus preventing long-term high-temperature retention and coking. Secondly, the closed-loop circulation working mode eliminates dead zones, ensuring all materials are in a state of continuous flow and renewal, thus eliminating the stagnant coking zones on the walls of traditional batch reactors.

[0035] Meanwhile, during the catalytic reaction, the deactivated catalyst, coke and other non-volatile solid residues in the twin-screw extruder 11 can be discharged intermittently or continuously through the die head 13, without the need to stop the machine to disassemble the screen and other parts for cleaning, which greatly reduces the difficulty of cleaning and significantly improves the continuous running time and maintenance efficiency of the unit.

[0036] When using a long-lasting catalyst, after feeding in a certain amount of a mixture of waste plastic and catalyst, granular waste plastic is continuously fed in batches through the feeding units of one or more twin-screw extruders 11, while simultaneously obtaining liquid and gaseous products continuously. Meanwhile, non-volatile materials such as degraded catalyst, filler, and coke can be discharged intermittently or continuously from the die 13 of the twin-screw extruder 11 under vacuum exhaust conditions at the exhaust port 15 near the die head.

[0037] An exhaust duct is provided near the die head 13, with one end aligned with the die head 13 and the other end connected to a waste gas treatment device. When the die head 13 opens and discharges the non-volatile solid residue inside the twin-screw extruder 11, the volatile substances (volatile gases) entrained therein are transported to the waste gas treatment device through the exhaust duct provided near the die head 13.

[0038] The reaction control gas is either hydrogen or nitrogen. Introducing nitrogen allows hydrocarbon gases generated by the cracking reaction within the twin-screw extruder 11 to quickly leave the catalyst's active sites, preventing over-reaction or side reactions. Introducing hydrogen increases the hydrogen-to-carbon ratio of the reaction products and reduces the aromatic content. The air inlets 14, spaced apart along the material flow direction, allow for independent control of the gas composition. Nitrogen, hydrogen, or a mixture of gases can be introduced at different reaction stages to achieve targeted effects such as inert protection, controlling the hydrogen-to-carbon ratio of the products, and suppressing aromatic formation, further precisely controlling the product's structure, composition, and quality.

[0039] When there are two twin-screw extruders 11 in the reactor body, the two twin-screw extruders 11 are arranged in opposite parallel directions; when there are more than two twin-screw extruders 11 in the reactor body, each extruder is arranged in a polygonal closed arrangement.

[0040] The twin-screw extruder 11 implements segmented temperature control along the material conveying direction. The twin-screw extruder 11 is divided into a first temperature control section and a second temperature control section. The first temperature control section is located on the side of the twin-screw extruder 11 closest to the feeding unit. The section of the twin-screw extruder 11 other than the first temperature control section is the second temperature control section. When the raw material undergoes a pyrolysis reaction, the temperature range of the first temperature control section is 180~220℃, and the temperature range of the second temperature control section is 220~350℃. The second temperature control section includes a pyrolysis section with a temperature of 280~350℃.

[0041] Cooling devices are distributed in various temperature control zones on the outside of the barrel of the twin-screw extruder 11. These devices cool their respective locations to create temperature differences within the twin-screw extruder 11 along the material conveying direction. The cooling devices can be water-cooled jackets, which can be installed at different locations on the outside of the barrel of the twin-screw extruder 11 to form a distributed cooling mechanism. By controlling the cooling effect of different water-cooled jackets (the cooling effect is adjusted by the flow rate of the cooling water), precise segmented temperature control of the twin-screw extruder 11 can be achieved.

[0042] The exhaust collection unit includes an exhaust chamber body 21, a condenser 22, a gas storage tank 24, and a liquid storage tank 23. The exhaust chamber body 21 is connected to the exhaust port 15 on the twin-screw extruder 11. Each exhaust chamber body 21 is connected to the condenser 22 through a pipe. The liquid phase separated by the condenser 22 is stored in the liquid storage tank 23, and the gas phase separated by the condenser 22 is stored in the gas storage tank 24.

[0043] A process for producing hydrocarbon compounds from waste plastics by catalytic cracking includes the following specific steps: S1: Process waste plastics into particles within a set particle size range, mix the waste plastic particles with a catalyst to obtain a mixed raw material.

[0044] In this step, waste plastic is crushed into particles or fragments smaller than 10mm, large pieces exceeding the set particle size range are screened out, and the waste plastic is mixed with catalyst particles in a predetermined ratio using a mixer and then fed into a twin-screw extruder through a feeding unit.

[0045] S2: Preheat each temperature control zone of the twin-screw extruder to the set preheating temperature. During the preheating process, nitrogen can be introduced into each twin-screw extruder to replace the internal air. After the set preheating temperature is reached, start the twin-screw main unit as usual and start the feeding unit. Feed the mixed raw materials into the twin-screw extruder through the feeding unit. The feeding speed is adjusted at any time according to the load of the extruder to ensure the safe operation of the system.

[0046] S3: Heat the twin-screw extruder to the catalytic cracking reaction temperature, open the corresponding air inlet according to the reaction requirements, and introduce reaction control gas into the twin-screw extruder through the air inlet.

[0047] In step S3, the catalytic cracking reaction temperature is 180-350℃, and the screw speed in the twin-screw extruder is 10-1200 rpm.

[0048] S4: Based on the structural and compositional requirements of the target hydrocarbon products, select the target exhaust port and open it; the material circulates and undergoes catalytic cracking reaction in the series-connected twin-screw extruders, and the generated gaseous hydrocarbon reaction products enter the exhaust collection unit through the exhaust port. The exhaust collection unit condenses and separates the gaseous hydrocarbon reaction products to obtain liquid hydrocarbon products and gaseous hydrocarbon products.

[0049] In this step, when deactivated catalyst and coking material are generated during the reaction, the exhaust port near the die head is switched to vacuum exhaust mode, and the die head discharges the deactivated catalyst and coking material; the volatiles carried in during the discharge of deactivated catalyst and coking material are transported to the waste gas treatment device through the exhaust channel set near the die head.

[0050] The following are specific embodiments of the present invention: Example 1: Using a mixer, 1 kg of low-density polyethylene (LDPE) granules with a size of 2-10 mm are mixed with 100 g of ZSM-5 molecular sieve catalyst granules of similar size in a certain proportion, and then the additives are added. Figure 1The reactor body shown consists of two parallel twin-screw extruders (screw diameter 26mm, length-to-diameter ratios 56:1 and 40:1, respectively). The feed unit of one of the twin-screw extruders is fed into the hopper. Simultaneously, the extruder, after nitrogen purging, is preheated to 200°C, and the cooling device on the outside of the barrel is activated. The screw speed is set to 300 rpm, the feed unit is opened, and the frequency of the feed unit's inverter is set to 10 Hz. The aforementioned waste plastic / catalyst mixture is fed into the twin-screw extruder via the feed unit. The feeding speed is adjusted according to the extruder load to ensure safe system operation. The twin-screw extruder is further heated to 300°C. The valve at the designated exhaust port is opened, and the material circulates between the two twin-screw extruders, undergoing catalytic cracking and other reactions to generate small-molecule hydrocarbons which enter each exhaust chamber 21. Some of these hydrocarbons are condensed by the condenser 22 and enter the liquid product storage tank 23, while the uncondensed gaseous hydrocarbons enter the gas product storage tank 24. After running for 2 hours, a total of 60g of liquid sample and 99g of gas sample were collected from each collection port. Gas chromatography determined that alkanes, alkenes and aromatics accounted for 7.3wt%, 7.1wt% and 1.5wt% respectively.

[0051] Example 2: Using a mixer, 1 kg of low-density polyethylene (LDPE) granules with a size of 2-10 mm are mixed with 100 g of ZSM-5 molecular sieve catalyst granules of similar size in a certain proportion, and then the additives are added. Figure 1 The feed unit of one of the twin-screw extruders in the reactor body, which consists of two parallel twin-screw extruders (screw diameter 26 mm, length-to-diameter ratios of 56:1 and 40:1 respectively), is fed into the hopper of the feed unit. Simultaneously, the extruder, after being purged with nitrogen, is preheated to 200°C, and the cooling device on the outside of the barrel is turned on. The screw speed is set to 300 rpm, the feed unit is turned on, and the frequency of the frequency converter of the feed unit is set to 10 Hz. The above-mentioned waste plastic / catalyst mixture is fed into the twin-screw extruder through the feed unit. The feeding speed is adjusted according to the extruder load to ensure safe system operation. The twin-screw extruder is then heated to 300℃. The valve at the designated air inlet is opened, allowing nitrogen to be introduced at a flow rate of 20 L / min. The valve at the designated exhaust outlet is also opened. The material circulates between the two twin-screw extruders, undergoing catalytic cracking reactions to produce small-molecule hydrocarbons, which enter each exhaust chamber 21. Some of these hydrocarbons are condensed by the condenser 22 and enter the liquid product storage tank 23, while the uncondensed gaseous hydrocarbons enter the gas product storage tank 24. The composition of the mixed gas sample at each collection port is measured using a gas chromatography-mass spectrometry (GC-MS) instrument as a function of catalytic cracking time. Figure 2 As shown; after running for 2 hours, a total of 133g of liquid sample and 664g of gas sample were collected from each collection port. Gas chromatography determined that alkanes, alkenes and aromatics accounted for 20.8wt%, 57.1wt% and 1.8wt% respectively.

[0052] Example 3: Using a mixer, 1 kg of high-density polyethylene (HDPE) granules with a size of 2-10 mm are mixed with 100 g of ZSM-5 molecular sieve catalyst granules of similar size in a certain proportion, and then the additives are added. Figure 1 The feed unit of one of the twin-screw extruders in the reactor body, which consists of two parallel twin-screw extruders (screw diameter 26 mm, length-to-diameter ratios of 56:1 and 40:1 respectively), is fed into the hopper of the feed unit. Simultaneously, the extruder, after being purged with nitrogen, is preheated to 200°C, and the cooling device on the outside of the barrel is turned on. The screw speed is set to 300 rpm, the feed unit is turned on, and the frequency of the frequency converter of the feed unit is set to 10 Hz. The above-mentioned waste plastic / catalyst mixture is fed into the twin-screw extruder through the feed unit. The feeding speed is adjusted according to the extruder load to ensure safe system operation. The twin-screw extruder is then heated to 300℃. The valve at the designated air inlet is opened to introduce nitrogen gas, with a flow rate set to 20L / min. The valve at the designated exhaust outlet is also opened. The material circulates between the two twin-screw extruders while undergoing catalytic cracking and other reactions to generate small-molecule hydrocarbon compounds, which then enter the exhaust chambers. Some of these compounds are condensed by condenser 22 and enter the liquid product storage tank 23, while the uncondensed gaseous hydrocarbon compounds enter the gas product storage tank. After 2 hours of operation, 157g of liquid sample and 574g of gas sample are collected from the various collection ports. Gas chromatography analysis shows that alkanes, alkenes, and aromatics account for 17.6wt%, 54.4wt%, and 1.1wt%, respectively.

[0053] Example 4: Using a mixer, 1 kg of isotactic polypropylene (i-PP) particles with a size of 2-10 mm are mixed with 100 g of ZSM-5 molecular sieve catalyst particles of similar size in a certain proportion, and then the additives are added. Figure 1The feed unit of one of the twin-screw extruders in the reactor body, which consists of two parallel twin-screw extruders (screw diameter 26 mm, length-to-diameter ratios of 56:1 and 40:1 respectively), is fed into the hopper of the feed unit. Simultaneously, the extruder, after being purged with nitrogen, is preheated to 200°C, and the cooling device on the outside of the barrel is turned on. The screw speed is set to 300 rpm, the feed unit is turned on, and the frequency of the frequency converter of the feed unit is set to 10 Hz. The above-mentioned waste plastic / catalyst mixture is fed into the twin-screw extruder through the feed unit. The feeding speed is adjusted according to the extruder load to ensure safe system operation. The twin-screw extruder is then heated to 300℃. The valve at the designated air inlet is opened to introduce nitrogen gas, with a flow rate set to 20L / min. The valve at the designated exhaust outlet is also opened. The material circulates between the two twin-screw extruders while undergoing catalytic cracking and other reactions to generate small-molecule hydrocarbon compounds, which then enter each exhaust chamber. Some of these compounds are condensed by condenser 22 and enter the liquid product storage tank 23, while the uncondensed gaseous hydrocarbon compounds enter the gas product storage tank. After 2 hours of operation, 23g of liquid sample and 145g of gas sample are collected from each sampling port. Gas chromatography analysis shows that alkanes, alkenes, and aromatics account for 9.1wt%, 7.0wt%, and 0.7wt%, respectively.

[0054] Example 5: Using a mixer, 1 kg of LDPE particles with a size of 2-10 mm are mixed with 100 g of ZSM-5 molecular sieve catalyst particles of similar size in a certain proportion, and then the additives are added. Figure 1The feed unit of one of the twin-screw extruders in the reactor body, which consists of two parallel twin-screw extruders (screw diameter 26 mm, length-to-diameter ratios of 56:1 and 40:1, respectively), is fed into the hopper of the feed unit. Simultaneously, the twin-screw extruder, after being purged with nitrogen, is preheated to 200°C, and the cooling device on the outside of the barrel is turned on. The screw speed is set to 300 rpm, the valve of the feed unit 12 is opened, and the frequency of the frequency converter of the feed unit is set to 10 Hz. The above-mentioned waste plastic / catalyst mixture is fed into the extruder through the feed unit. The feeding speed is adjusted according to the extruder load to ensure safe system operation. The extruder is then heated to 300℃. The valve at the designated air inlet is opened, allowing nitrogen to flow through at a rate of 20 L / min. The valve at the designated exhaust port 15 is opened, allowing the material to circulate between the two extruders. During this process, it undergoes catalytic cracking and other reactions to generate small-molecule hydrocarbons, which enter each exhaust chamber 21. Some of these hydrocarbons are condensed by the condenser 22 and enter the liquid product storage tank 23, while the uncondensed gaseous hydrocarbons enter the gas product storage tank 24. After one hour of reaction operation, 300g of LDPE granules are fed into the original extruder through its feeding unit 12 while the reactor remains in normal operation. This process is repeated for another hour, with another 300g of LDPE granules fed into the reactor through feeding unit 12. This process is repeated every hour, in five batches, to accumulate a total of 1500g of LDPE without introducing new catalyst. After a cumulative 6 hours of operation, 317g of mixed liquid sample and 1867g of gas sample were collected from each sampling port. The changes in the components of the mixed gas sample from each sampling port with catalytic cracking time were measured using gas chromatography-mass spectrometry (GC-MS). Figure 3 As shown.

[0055] This invention is not limited to the preferred embodiments described above. Anyone can derive other products in various forms under the guidance of this invention. However, regardless of any changes in shape or structure, any technical solution that is the same as or similar to this application falls within the protection scope of this invention.

Claims

1. A reactor for the catalytic cracking of waste plastics to produce hydrocarbon compounds, characterized in that, The reactor includes a reactor body and an exhaust collection unit. The reactor body consists of at least two twin-screw extruders connected in series to form a closed material circulation loop. At least one twin-screw extruder is equipped with a feeding unit. Each twin-screw extruder is equipped with at least one air inlet and at least one exhaust outlet, which are arranged sequentially at intervals along the material conveying direction of the twin-screw extruder. The air inlet is used to introduce reaction control gas into the twin-screw extruder, and each exhaust outlet is connected to the exhaust collection unit.

2. The reactor for catalytic cracking of waste plastics to produce hydrocarbon compounds according to claim 1, characterized in that, When the reactor body has two twin-screw extruders, the two twin-screw extruders are arranged in opposite parallel directions; when the reactor body has more than two twin-screw extruders, the extruders are arranged in a polygonal closed arrangement.

3. The reactor for catalytic cracking of waste plastics to produce hydrocarbon compounds according to claim 1, characterized in that, The reaction control gas is hydrogen or nitrogen. By introducing nitrogen, the hydrocarbon gases produced by the cracking reaction in the twin-screw extruder are quickly removed from the active sites of the catalyst to prevent over-reaction or side reactions. By introducing hydrogen, the hydrogen-to-carbon ratio of the reaction products is increased, and the content of aromatics in the reaction products is reduced.

4. The reactor for catalytic cracking of waste plastics to produce hydrocarbon compounds according to claim 1, characterized in that, The twin-screw extruder implements segmented temperature control along the material conveying direction. The twin-screw extruder is divided into a first temperature control section and a second temperature control section. The first temperature control section is located on the side of the twin-screw extruder closest to the feeding unit, and the section of the twin-screw extruder other than the first temperature control section is the second temperature control section. When the raw material undergoes a pyrolysis reaction, the temperature range of the first temperature control section is 180~220℃, and the temperature range of the second temperature control section is 220~350℃. The second temperature control section includes a pyrolysis section with a temperature of 280~350℃.

5. The reactor for catalytic cracking of waste plastics to produce hydrocarbon compounds according to claim 4, characterized in that, The twin-screw extruder has cooling devices distributed in each temperature control zone outside the barrel. These devices cool the area to create a temperature difference inside the twin-screw extruder along the material conveying direction.

6. The reactor for catalytic cracking of waste plastics to produce hydrocarbon compounds according to claim 1, characterized in that, The exhaust collection unit includes an exhaust chamber body, a condenser, a gas storage tank, and a liquid storage tank. The exhaust chamber body is connected to the exhaust port on the twin-screw extruder. Each exhaust chamber body is connected to the condenser through a pipe. The liquid phase separated by the condenser is stored in the liquid storage tank, and the gas phase separated by the condenser is stored in the gas storage tank.

7. The reactor for catalytic cracking of waste plastics to produce hydrocarbon compounds according to claim 1, characterized in that, The screw in the twin-screw extruder is a modular self-cleaning screw, which is arranged in a cyclic pattern along its axial direction as a conveying section, a compression section, a kneading section, and / or a combination of the above sections. The feeding unit is located at one end of the twin-screw extruder near the conveying section, and the other end of the twin-screw extruder is equipped with a die head. The die head is used to clean coking or residue inside the twin-screw extruder and to discharge and regenerate deactivated catalyst.

8. A process for catalytic cracking of waste plastics to produce hydrocarbon compounds, based on the reactor for catalytic cracking of waste plastics to produce hydrocarbon compounds as described in claim 6, characterized in that, The specific steps include the following: S1: Waste plastics are processed into particles within a set particle size range, and the waste plastic particles are mixed with a catalyst to obtain a mixed raw material; S2: Preheat the twin-screw extruder to the set preheating temperature. During the preheating process, nitrogen is introduced into each twin-screw extruder to replace the internal air. After the set preheating temperature is reached, the feeding unit is opened to feed the mixed raw materials into the twin-screw extruder and then the feeding unit is closed. S3: Heat the twin-screw extruder to the catalytic cracking reaction temperature, open the corresponding air inlet according to the reaction requirements, and introduce reaction control gas into the twin-screw extruder through the air inlet; S4: Based on the structural and compositional requirements of the target hydrocarbon products, select the target exhaust port and open it; the material circulates and undergoes catalytic cracking reaction in the series-connected twin-screw extruders, and the generated gaseous hydrocarbon reaction products enter the exhaust collection unit through the exhaust port. The exhaust collection unit condenses and separates the gaseous hydrocarbon reaction products to obtain liquid hydrocarbon products and gaseous hydrocarbon products.

9. The process for producing hydrocarbon compounds from waste plastics by catalytic cracking according to claim 8, characterized in that, In step S4, when deactivated catalyst and coking material are generated during the reaction, the exhaust port near the die head is switched to vacuum exhaust mode, and the deactivated catalyst and coking material are discharged by the die head. The volatiles carried in during the discharge of deactivated catalyst and coking material are transported to the waste gas treatment device through the exhaust channel set near the die head.

10. The process for producing hydrocarbon compounds from waste plastics by catalytic cracking according to claim 8, characterized in that, In step S2, the preheating temperature is set to 180~300℃; in step S3, the catalytic cracking reaction temperature is 180~350℃, and the screw speed in the twin-screw extruder is 10~1200rpm.

Images