Method for preparing low-carbon olefin through co-conversion of waste plastics and heavy oil

Abstract

The invention relates to a method for preparing low-carbon olefin through co-conversion of waste plastics and heavy oil. The method comprises the following steps: S1, preparing a uniform mixed slurry from waste plastics, a catalyst and heavy oil in a raw material tank, and preheating to form a uniform liquid-phase mixture; s2, the uniform liquid-phase mixture enters from the bottom of the tubular reactor to be subjected to a hydrocracking reaction, light distillate oil and heavy distillate oil are obtained through separation, and the heavy distillate oil serves as first fuel oil to be discharged out of the device; s3, the light distillate oil is subjected to a catalytic cracking reaction from the lower end of the catalytic cracking riser reactor, a reaction product is subjected to fractionation through a fractionating tower, dry gas, low-carbon olefin, gasoline and diesel oil fractions, recycle oil and catalytic slurry oil are obtained, the recycle oil is returned to the catalytic cracking riser reactor for continuous reaction, and the catalytic slurry oil is obtained. One part of catalytic slurry oil enters the tubular reactor as a raw material for continuous reaction, and the rest is discharged out of the device as second fuel oil. According to the method, efficient co-conversion of the waste plastics and the heavy oil is realized through a combined process of multiphase flow hydrocracking pretreatment and fluidized bed catalytic cracking.

Description

Technical Field

[0001] This invention belongs to the field of waste resource utilization technology, specifically relating to a method for co-converting waste plastics and heavy oil to produce low-carbon olefins. Background Technology

[0002] In real life, plastic waste is disposed of through landfill, incineration or pyrolysis, leading to environmental pollution and resource waste.

[0003] Chemical recycling can not only transform waste plastics into clean oils, but also upgrade and recycle them into important chemical raw materials such as high-value-added aromatics.

[0004] Patent CN 113604244 A discloses a system and method for in-situ catalytic pyrolysis of waste plastics. The system includes a three-stream impinging flow mixer, a pyrolysis reactor, a high-density circulating fluidized bed, a multiphase flow riser, and a separation device connected in sequence. The raw waste plastic and solid heat carrier catalyst are thoroughly mixed in the three-stream impinging flow mixer, and then passed through the pyrolysis reactor at a temperature of 500-600℃. Hydrogen chloride in the product reacts with the catalyst to generate calcium chloride. The pyrolysis gas is introduced into the gas recirculation device of the high-density circulating fluidized bed, where the heat carrier and semi-coke are heated to a predetermined temperature. The heat carrier and semi-coke then enter the multiphase flow riser to separate and recover large-particle catalyst, while maximizing the yield of high-quality liquid fuel. However, due to the characteristics of waste plastics, such as easy softening and adhesion, and high chlorine content, problems exist, including feed system blockage, equipment corrosion, inability to operate the device for long periods, and low added value of the product. Summary of the Invention

[0005] To achieve high-value utilization of waste resources and overcome the shortcomings of existing technologies, this invention provides a method for co-converting waste plastics and heavy oil to produce low-carbon olefins. This method is based on the dispersing effect of heavy oil on waste plastic particles and the synergistic effect of hydrocarbons in the reaction process. Through a combination of multiphase flow hydrocracking pretreatment and fluidized bed catalytic cracking, the method achieves efficient co-conversion of waste plastics and heavy oil. This not only effectively solves the technical problems of easy agglomeration of waste plastics during transportation, low heat transfer efficiency, and difficulty in treating chlorine-containing components, but also successfully converts two types of low-value resources into high-value-added low-carbon olefins, resulting in significant economic and environmental benefits.

[0006] To achieve the above objectives, the present invention adopts the following technical solution: A method for co-converting waste plastics and heavy oil to produce low-carbon olefins includes the following steps; Step S1: Waste plastic 1, catalyst 2 and heavy oil 3 are mixed in raw material tank 4 to form a uniform slurry. The mixture is then pressurized and transported by raw material pump 5. Most of the mixture is returned to raw material tank 4 through the circulation pipeline to enhance mixing. A portion of the mixture is preheated by preheater 6 to melt and liquefy the waste plastic, forming a uniform liquid phase mixture. Step S2: A homogeneous liquid mixture enters from the bottom of the tubular reactor 7 for hydrocracking reaction. The reaction products are separated by the primary separator 8 and the secondary separator 9 to obtain light distillate oil 10 and heavy distillate oil 11. Light distillate oil 10 is used as the first feedstock for catalytic cracking, and a portion of the heavy distillate oil 11 is returned to the feedstock tank 4 to continue the reaction, while the remainder is used as the first fuel oil and exits the unit. Step S3: Light distillate oil 10 undergoes catalytic cracking reaction at the lower end of catalytic cracking riser reactor 12. The reaction products are fractionated by fractionation tower 13 to obtain dry gas 14, low carbon olefins 15, gasoline and diesel fractions 16, recycled oil 17 and catalytic slurry 18. Among them, recycled oil 17 is returned to catalytic cracking riser reactor 12 for further reaction, a portion of catalytic slurry 18 is used as feedstock to enter tubular reactor 7 for further reaction, and the remainder is used as second fuel oil exiting the device.

[0007] The waste plastic 1 mentioned in step S1 is one or more mixtures of PP and PE, in granular form, with a particle size range of 5-150μm and an average particle size of 75μm.

[0008] The heavy oil 3 mentioned in step S1 is one or more of atmospheric residue oil, vacuum wax oil, coking wax oil, hydrocracking tail oil and waste oil.

[0009] The catalyst 2 mentioned in step S1 is α-FeOOH, and the amount added accounts for 0.1~1% of the total feed mass.

[0010] In step S1, the raw material tank 4 is controlled at a temperature of 50-150℃, and the mass fraction of waste plastic 1 in the mixed slurry does not exceed 50%. Controlling the raw material tank temperature at 50-150℃ primarily reduces the viscosity of the heavy oil while ensuring the plastic does not soften, thus preventing the plastic from softening and sticking together, and improving the mixing effect between the plastic and heavy oil. The preheater temperature is controlled at 200-350℃, mainly to achieve melting, softening, and liquefaction of the plastic by increasing the temperature, while simultaneously reducing the viscosity of the plastic-heavy oil mixture. The preheater temperature is controlled at 200-380℃ to melt and liquefy the waste plastic, forming a homogeneous liquid phase mixture.

[0011] In step S2, the tubular reactor 7 consists of 1-3 suspended bed or fluidized bed reactors connected in series. The reaction conditions are: temperature 370-450℃, pressure 2-10MPa, and liquid hourly space velocity 0.3-3.0h. -1 Hydrogen-to-oil ratio: 800~1500 NL / kg.

[0012] The reaction products described in step S2 are separated by a primary separator 8 and a secondary separator 9 to obtain light distillate oil 10 and heavy distillate oil 11, wherein the final boiling point of the light distillate oil is not higher than 500°C, and it is used as feedstock for catalytic cracking.

[0013] In step S2, the circulation rate of the heavy distillate oil 11 is adjusted according to the product properties, catalyst activity and concentration. The circulation rate is calculated based on the total feed mass fraction and does not exceed 30%. The remaining part is used as the first fuel oil and exits the device.

[0014] The reaction conditions of the catalytic cracking riser reactor 12 in step S3 are: temperature 480-550℃, regeneration temperature 650-750℃, pressure 0.1-0.3MPa, agent-to-oil ratio 15-30, and reaction time 0.2-3 seconds.

[0015] The catalyst used for catalytic cracking in step S3 is at least one of Y-type molecular sieve, ZSM-5 molecular sieve, and β-molecular sieve.

[0016] The yield of low-carbon olefin 15 in the catalytic cracking reaction products described in step S3 is 30-70%.

[0017] The catalytic cracking reaction product catalytic slurry 18 described in step S3 contains polycyclic aromatic hydrocarbon components, which are returned to the system as an excellent hydrogen donor solvent to promote the hydrogenation reaction.

[0018] In steps S2 and S3, the first fuel oil and the second fuel oil can be mixed or used alone as fuel oil 19 in the device, depending on their properties.

[0019] The beneficial effects of this invention are: This invention achieves uniform dispersion of waste plastics by mixing them at low temperatures, forming a homogeneous slurry. The raw material tank maintains a temperature of 50-150℃ based on the viscosity of the heavy oil, ensuring its low viscosity. During the mixing process, the heavy oil not only dilutes and disperses the plastic particles, preventing adhesion and clumping, but also acts as a heat carrier, ensuring uniform heating of the plastics and preventing uneven heating that could lead to softening and adhesion. This fundamentally solves the problems of adhesion, coking, and pipe blockage during high-temperature feeding of waste plastics, laying the foundation for stable operation of subsequent processes.

[0020] This invention constructs a complete "hydrocracking-catalytic cracking" synergistic process system through the innovative coupling of tubular reactor and catalytic cracking reactor, achieving deep deimpurification and directional conversion of products, and has advantages such as strong adaptability to raw materials, short process flow and low energy consumption.

[0021] This invention establishes an internal circulation system between heavy distillate oil and catalytic slurry, which not only fully utilizes the continuous activity of the catalyst, but also takes advantage of the hydrogen-donating solvent effect of polycyclic aromatic hydrocarbon components in the catalytic slurry, forming a synergistic effect within the system and significantly improving the conversion efficiency of heavy oil and the yield of low-carbon olefins. Attached Figure Description

[0022] Figure 1This is a schematic diagram of the process flow for the co-conversion of waste plastics and heavy oil to produce low-carbon olefins according to the present invention.

[0023] 1-Waste plastics; 2-Heavy oil; 3-Catalyst; 4-Raw material tank; 5-Raw material transfer pump; 6-Preheater; 7-Tube reactor; 8-Primary separator; 9-Secondary separator; 10-Light distillate oil; 11-Heavy distillate oil; 12-Catalytic cracking riser reactor; 13-Fracturing tower; 14-Dry gas; 15-Low carbon olefins; 16-Gasoline and diesel fractions; 17-Recycled oil; 18-Catalytic slurry; 19-Fuel oil. Detailed Implementation

[0024] The present invention will now be described in further detail with reference to the accompanying drawings.

[0025] The system for co-converting waste plastics and heavy oil to produce low-carbon olefins provided by this invention is as follows: Figure 1 As shown, waste plastic 1, catalyst 2, and heavy oil 3 are mixed in raw material tank 4 at 50-150℃. This temperature is lower than the softening and sticking temperature of the waste plastic, ensuring that the waste plastic is uniformly dispersed in the heavy oil in the form of solid particles, forming a stable slurry. The slurry is transported by raw material pump 5, with part of it returning to raw material tank 4 through the circulation pipeline for continuous mixing to prevent solid material deposition, and part entering preheater 6 to be preheated to 200-380℃, so that the waste plastic is completely melted and liquefied, forming a homogeneous liquid-phase mixture with the heavy oil. Subsequently, it enters tubular reactor 7 for hydrocracking reaction, effectively removing impurities such as sulfur, nitrogen, chlorine, and metals.

[0026] The reaction products are separated by a primary separator 8 and a secondary separator 9 to obtain light distillate oil 10 and heavy oil 11. Light distillate oil 10 enters the catalytic cracking riser reactor 12 for catalytic cracking reaction. The reaction products are separated by a fractionation tower 13 to obtain dry gas 14, low-carbon olefins 15, gasoline and diesel fractions 16, recycled oil 17, and catalytic slurry 18. Among them, recycled oil 17 is returned to the lower end of the catalytic cracking riser reactor 12 for further reaction, and part of the catalytic slurry 18 and heavy oil 11 are recycled back to the system for further reaction, while part is discharged from the unit as fuel oil 19.

[0027] The technical solutions and effects of the present invention will be further illustrated below with reference to the embodiments, but the present invention shall not be limited thereto.

[0028] Example 1 PP plastic granules with a particle size of 100 μm were mixed with vacuum wax oil at a mass ratio of 3:7 in a feed tank, and 0.5% α-FeOOH catalyst was added. The mixture was stirred at 80°C to form a homogeneous slurry. The slurry was preheated to 350°C and then fed into a two-stage series suspended bed reactor for hydrocracking at 400°C, 6 MPa, and a hydrogen-to-oil ratio of 1000 NL / kg. Light distillate oil (final boiling point 460°C) was then catalytically cracked in contact with ZSM-5 molecular sieve catalyst at 520°C, 0.2 MPa, and a catalyst-to-oil ratio of 20.

[0029] Example 2 PE plastic particles with a particle size of 100 μm were mixed with atmospheric residue oil at a mass ratio of 2:8 in a feed tank, and 0.3% α-FeOOH catalyst was added. The mixture was stirred at 100°C to form a homogeneous slurry. After being preheated to 350°C in a preheater, the slurry was fed into a fluidized bed reactor and subjected to hydrocracking at 420°C, 6 MPa, and a hydrogen-to-oil ratio of 1200 NL / kg. Light distillate oil (final boiling point 460°C) underwent catalytic cracking in contact with a β-molecular sieve catalyst at 500°C, 0.15 MPa, and a catalyst-to-oil ratio of 25.

[0030] Example 3 PP / PE mixed plastics with a particle size of 80 μm (mass ratio 1:1) were mixed with waste lubricating oil at a mass ratio of 4:6, and 0.8% α-FeOOH catalyst was added. The mixture was stirred at 120℃ to form a homogeneous slurry. The slurry was preheated to 350℃ and then fed into a three-stage series suspended bed reactor for hydrocracking at 420℃, 8 MPa, and a hydrogen-to-oil ratio of 800 NL / kg. Light distillate oil (final boiling point 500℃) was catalytically cracked by contacting a Y-type molecular sieve catalyst at 540℃, 0.25 MPa, and a catalyst-to-oil ratio of 18.

[0031] Example 4 PP / PE mixed plastics with a particle size of 100 μm (mass ratio 1:1) were mixed with waste lubricating oil at a mass ratio of 4:6, and 0.8% α-FeOOH catalyst was added. The mixture was stirred at 120℃ to form a homogeneous slurry. The slurry was preheated to 380℃ and then fed into a three-stage series suspended bed reactor for hydrocracking at 450℃, 8 MPa, and a hydrogen-to-oil ratio of 1200 NL / kg. Light distillate oil (final boiling point 500℃) was catalytically cracked by contacting a Y-type molecular sieve catalyst at 540℃, 0.25 MPa, and a catalyst-to-oil ratio of 20.

[0032] Table 1. Reaction conditions and product distribution of the examples. project Example 1 Example 2 Example 3 Example 4 Hydrocracking section Reaction temperature (°C) 400 420 420 450 Reaction pressure (MPa) 6 6 8 8 Hydrogen-to-oil ratio (NL / kg) 1000 1200 800 1200 Catalytic cracking section Reaction temperature (°C) 520 500 540 540 Agent-to-oil ratio 20 25 18 20 Product distribution (wt%) dry air 5.21 4.86 5.55 6.22 Liquefied gas 45.33 52.11 38.62 41.28 Gasoline and diesel fractions 40.84 35.54 44.95 40.09 fuel oil 5.53 4.58 7.43 8.16 coke 3.09 2.91 3.45 4.25 C2-C4 olefin yield (wt%) 42.82 48.9 34.74 39.13 ethylene 12.20 15.26 9.31 12.19 propylene 19.53 20.93 16.40 18.22 Butene 11.09 12.71 9.03 8.72 This invention employs a combined process of hydrocracking in a tubular reactor and catalytic cracking in a riser reactor. This effectively removes impurities such as sulfur, nitrogen, and chlorine while obtaining high-quality catalytic cracking feedstock, achieving efficient synergistic conversion of waste plastics and heavy oil. This method directionally converts two low-value feedstocks into high-value-added low-carbon olefins, achieving a liquefied petroleum gas (LPG) yield of 38.6%-52.1%, with low-carbon olefins accounting for over 93% of the total, demonstrating excellent product selectivity and directional conversion capability.

[0033] It should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and do not constitute a limitation on the scope of protection of the present invention. Various modifications or equivalent substitutions made to the technical solutions of the present invention without departing from the concept of the present invention should be considered to fall within the scope of protection of the present invention.

Claims

1. A method for co-converting waste plastics and heavy oil to produce low-carbon olefins, characterized in that, Includes the following steps; Step S1: Waste plastic (1), catalyst (2) and heavy oil (3) are mixed in the raw material tank (4) to form a uniform slurry. The slurry is then pressurized and transported by the raw material pump (5). Most of the mixture is returned to the raw material tank (4) through the circulation pipeline to enhance mixing. A portion of the mixture is preheated by the preheater (6) to melt and liquefy the waste plastic, forming a uniform liquid phase mixture. Step S2: A homogeneous liquid mixture enters from the bottom of the tubular reactor (7) for hydrocracking reaction. The reaction products are separated by a primary separator (8) and a secondary separator (9) to obtain light distillate oil (10) and heavy distillate oil (11). The light distillate oil (10) is used as the first feedstock for catalytic cracking, and part of the heavy distillate oil (11) is returned to the feedstock tank (4) to continue the reaction. The remainder is used as the first fuel oil and exits the unit. Step S3: Light distillate oil (10) undergoes catalytic cracking reaction from the lower end of catalytic cracking riser reactor (12). The reaction products are fractionated by fractionation tower (13) to obtain dry gas (14), low carbon olefins (15), gasoline and diesel fractions (16), recycled oil (17) and catalytic slurry (18). Among them, recycled oil (17) is returned to catalytic cracking riser reactor (12) to continue the reaction, and part of the catalytic slurry (18) is used as raw material to enter tubular reactor (7) to continue the reaction. The remainder is used as second fuel oil and exits the device.

2. The method for co-converting waste plastics and heavy oil to produce low-carbon olefins according to claim 1, characterized in that, The waste plastic (1) mentioned in step S1 is one or more of PP and PE, in granular form, with a particle size range of 5-150μm and an average particle size of 75μm; The heavy oil (3) mentioned in step S1 is one or more of atmospheric residue, vacuum wax oil, coking wax oil, hydrocracking tail oil and waste oil; The catalyst (2) mentioned in step S1 is α-FeOOH, and the amount added accounts for 0.1~1% of the total feed mass.

3. The method for co-converting waste plastics and heavy oil to produce low-carbon olefins according to claim 2, characterized in that, In step S1, the temperature of the raw material tank (4) is controlled at 50~150℃, and the mass fraction of waste plastic (1) in the mixed slurry does not exceed 50%; the temperature of the raw material tank (4) is controlled at 50-150℃, and the temperature of the preheater (6) is controlled at 200-350℃.

4. The method for co-converting waste plastics and heavy oil to produce low-carbon olefins according to claim 3, characterized in that, The tubular reactor (7) mentioned in step S2 consists of 1-3 suspended bed or fluidized bed reactors connected in series. The reaction conditions are: temperature 370~450℃, pressure 2~10MPa, and liquid hourly space velocity 0.3~3.0h. -1 Hydrogen-to-oil ratio: 800~1500 NL / kg.

5. The method for co-converting waste plastics and heavy oil to produce low-carbon olefins according to claim 4, characterized in that, The reaction products described in step S2 are separated by a primary separator (8) and a secondary separator (9) to obtain light distillate oil (10) and heavy distillate oil (11), wherein the final boiling point of the light distillate oil is not higher than 500°C, and it is used as a feedstock for catalytic cracking.

6. The method for co-converting waste plastics and heavy oil to produce low-carbon olefins according to claim 5, characterized in that, The heavy distillate oil (11) mentioned in step S2 is circulated according to the product properties, catalyst activity and concentration. The circulation volume is calculated based on the total feed mass fraction and does not exceed 30%. The remaining part is used as the first fuel oil to exit the device.

7. The method for co-converting waste plastics and heavy oil to produce low-carbon olefins according to claim 6, characterized in that, The reaction conditions of the catalytic cracking riser reactor (12) in step S3 are: temperature 480-550℃, regeneration temperature 650-750℃, pressure 0.1-0.3MPa, agent-to-oil ratio 15-30, and reaction time 0.2-3 seconds.

8. The method for co-converting waste plastics and heavy oil to produce low-carbon olefins according to claim 7, characterized in that, The catalyst used for catalytic cracking in step S3 is at least one of Y-type molecular sieve, ZSM-5 molecular sieve, and β molecular sieve; The yield of low-carbon olefins (15) in the catalytic cracking reaction products described in step S3 is 30-70%; The catalytic cracking reaction product catalytic slurry (18) described in step S3 contains polycyclic aromatic hydrocarbon components.

9. The method for co-converting waste plastics and heavy oil to produce low-carbon olefins according to claim 8, characterized in that, In steps S2 and S3, the first fuel oil and the second fuel oil can be mixed or used alone as fuel oil (19) according to their properties and composition.

Images