Process for preparing oil product by using molten salt to distill and degrade waste plastics

Abstract

The invention belongs to the technical field of waste plastic resource recovery and heterogeneous catalytic distillation, and discloses a process for preparing an oil product by degrading waste plastic through molten salt distillation. Polyolefin waste plastic is used as a raw material, directional cracking of polyolefin is realized through a distillation degradation reaction under the catalysis and heat transfer synergistic effect of a molten salt system, and segmented separation of an oil product is synchronously completed. According to the process disclosed by the invention, by virtue of high-efficiency catalytic activity and excellent heat transfer performance of a molten salt system, high-efficiency degradation of the polyolefin waste plastics can be realized under relatively mild reaction conditions, and high-quality oil products can be directionally prepared; meanwhile, the preparation process of the molten salt system is simple, convenient and controllable, cyclic regeneration can be realized, the process cost is greatly reduced, and large-scale production is easy to realize. The method provides a brand new technical path for resource conversion of polyolefin waste plastics, has dual values of environmental protection treatment and resource recovery, and has an important application prospect in the fields of solid waste treatment and energy chemical industry.

Description

Technical Field

[0001] This invention belongs to the field of waste plastic resource recycling and multiphase catalytic distillation technology, and relates to a process for molten salt distillation to degrade waste plastics into oil products. Background Technology

[0002] Polyolefin plastics are widely used in packaging, building materials, automobiles, and other fields due to their excellent physical and chemical properties. However, their slow degradation leads to "white pollution" from large quantities of waste, which has become a global environmental challenge. Meanwhile, petroleum products, as a core energy carrier, are indispensable in industrial production and daily life. Converting waste polyolefin plastics into high-quality petroleum products, achieving the dual goals of "solid waste resource utilization" and "energy supplementation," is an important technological direction that balances environmental protection and efficient resource utilization.

[0003] Currently, the mainstream technologies for converting waste plastics into petroleum products include thermal cracking, catalytic cracking, and solvent depolymerization. Among these, thermal cracking and catalytic cracking have become research hotspots due to their significant industrialization potential. However, existing technological bottlenecks urgently need to be overcome: one is that the thermal cracking process requires maintaining a temperature of 600°C. o In high-temperature environments above 450°C, energy consumption is high and the product system is complex. In addition to oil phase products, a large amount of cracked gas and carbon deposits are also generated. The overall oil yield is usually less than 60%, and the proportion of heavy components in the oil phase products exceeds 30%. The content of impurities such as sulfur and nitrogen is unstable, requiring multiple processing steps such as hydrorefining and distillation separation, which significantly increases the total production cost. Secondly, traditional catalytic cracking processes mostly use solid acidic catalysts such as ZSM-5 and Y-type molecular sieves, although they can reduce the reaction temperature to 450°C. o C ~ 550 o C. However, the carbon deposits generated during the cracking of polyolefins are prone to accumulate on the active sites of the catalyst, leading to a rapid decline in catalytic activity. Catalyst regeneration requires complex processes such as calcination and acid washing, which not only cause the loss of active components but also generate secondary pollutants such as acidic wastewater. Third, some existing processes still require the introduction of organic solvents as reaction media, which increases the complexity of the process and the cost of raw materials, limiting large-scale promotion. In addition, solvent depolymerization technology has problems such as slow reaction kinetics, difficulty in solvent recovery, and narrow applicability to plastics, making it difficult to meet the needs of industrial mass production.

[0004] In research on the catalytic degradation of waste plastics to produce oil products, some technologies employ homogeneous or composite catalytic systems. While these can improve oil yield, they suffer from drawbacks such as difficulty in separating the catalyst from the product, significant catalyst loss, and cumbersome subsequent purification processes. To improve reaction efficiency, some systems require the introduction of hydrogen for hydrorefining, which not only increases hydrogen consumption and equipment investment but also raises process safety risks. Furthermore, some processes rely on specialized heating equipment such as microwaves and ultrasound, which present bottlenecks including high equipment investment, poor heating uniformity, and difficulties in large-scale scaling. A comparison with existing patented technologies reveals these shortcomings: Although patent CN113502174 has achieved the directional preparation of aviation-grade fuel, it has problems such as complicated reaction process and the need for multiple hydrogenation refining steps to improve product quality, resulting in high process cost.

[0005] Patent CN118546429 achieves 350 by introducing a specific metal oxide catalyst. o C ~ 450 o The low-temperature degradation of C reduces energy consumption, but the homogeneous catalytic system used in this process has drawbacks such as difficulty in catalyst separation and recovery and easy product contamination, which limits its large-scale application.

[0006] Patent CN117186926 improves product selectivity by utilizing the shape-selective catalytic performance of ZSM-5, but traditional ZSM-5 molecular sieves have a single pore size and uneven surface acidity distribution, resulting in severe carbon deposition during the reaction process and rapid decay of catalytic activity.

[0007] Therefore, developing a process for producing oil from waste plastics that features mild reaction conditions, low energy consumption, high oil yield and good selectivity, while also considering catalyst stability and easy recyclability, is of great significance for promoting the resource utilization of polyolefin waste plastics and optimizing the energy structure. To address the above issues, this invention aims to provide a process route for the degradation of polyolefin waste plastics into oils via molten salt distillation. Utilizing the highly efficient catalytic activity, excellent heat transfer performance, and high-temperature stability of molten salts, combined with distillation fractional separation technology, this method achieves directional pyrolysis of polyolefin plastics and precise product separation, overcoming the problems of high energy consumption, rapid catalyst deactivation, poor product selectivity, complex processes, and limited scalability in existing technologies. Summary of the Invention

[0008] The purpose of this invention is to provide a process route and application for the molten salt distillation degradation of polyolefin waste plastics to produce oil. Specifically, it involves using polyolefin waste plastics as raw materials, and under the synergistic effect of catalysis and heat transfer in a molten salt system, at 400... o C ~600 oC. Directional cracking of polyolefins is achieved under inert atmosphere and normal pressure. Gasoline and diesel fractions (corresponding to light and medium fuel oil components, respectively) conforming to national standards for gasoline (C5-C12) and diesel (C13-C22) are then separated through precise distillation. This process significantly improves the yield and selectivity of the target fuel oil fraction, reduces reaction energy consumption and production costs, and enables efficient catalyst recovery and recycling. It addresses the core shortcomings of existing technologies, such as wide carbon number distribution of oil products, low proportion of target fractions, and complex separation processes.

[0009] This invention constructs a molten salt catalytic system, which regulates the acidity and alkalinity of the system and the density of catalytic active sites through the synergistic effect of salt components. The high-temperature fluidity of the molten salt enables full contact between the raw materials and the catalyst, enhancing the mass and heat transfer process. At the same time, it integrates distillation separation technology, which enables precise fractional collection of gasoline and diesel fractions through temperature gradient control, thereby improving product quality.

[0010] The technical solution of the present invention: A process route for the degradation of polyolefin waste plastics by molten salt distillation to produce oil products includes the following steps: Using polyolefin waste plastics as reaction substrates, a distillation-catalytic degradation reaction is carried out in the presence of a molten salt system under an inert atmosphere and normal pressure to achieve directional cracking of polyolefin waste plastics to produce oil products, and the products are separated by fractional distillation.

[0011] The molten salt system consists of one or two combinations of alkali metal nitrates (including NaNO3, KNO3, and LiNO3), with the addition of alkali metal chlorides (including NaCl, KCl, and LiCl) or alkaline earth metal chlorides (including CaCl2, MgCl2, and BaCl2).

[0012] The molten salt system may contain performance-modifying additives, including transition metal oxides (ZnO, Fe2O3, Co3O4, NiO, CuO), nitrides (h-BN, Si3N4, AlN, ZrN), carbides (WC, Mo2C, TiC, SiC), etc. The amount of catalyst additive added is 1% to 15% of the total mass of the molten salt system.

[0013] In the preparation of the catalyst, salt raw materials are mixed in a certain proportion and heated to 350°C. o C ~ 500 o C is used to completely melt the molten salt, and the mixture is stirred under an inert atmosphere for 60 min to 240 min to obtain a homogeneous and stable molten salt system.

[0014] The reaction raw materials are polyolefin waste plastics, including one or more of low-density polyethylene (high branching), high-density polyethylene (low branching), polypropylene, polybutene-1, and polyisobutylene.

[0015] The mass ratio of the molten salt catalytic system to polyolefin waste plastic is 1:1 to 1:5, and the optimal material mass ratio (molten salt: plastic) is 1:1 to 1:3.

[0016] After mixing the molten salt system with polyolefin waste plastics, grind the mixture. Add 1-5 mL of anhydrous ethanol as a dispersant. Grind for 5-10 minutes, then place in a vacuum oven at 40°C. o C ~ 60 o Keep at C for 1 h to remove ethanol.

[0017] Reaction temperature: 400 o C ~ 600 o C, Optimal reaction temperature: 450 o C ~ 550 o C. Reaction time: 0.5 h ~ 4 h, optimal reaction time: 1 h ~ 2 h. Reaction pressure: atmospheric pressure. Reaction atmosphere: inert atmosphere (nitrogen or argon).

[0018] Gasoline fraction collection section: Fractionating unit 120 o C ~ 180 o C-section condensate corresponds to light fuel oil components. Diesel fraction collection area: Fractionating unit 180. o C ~ 360 o C-section condensate corresponds to medium-quality fuel oil components. Pipe bottom residue: mainly wax oil and undegraded polyolefin residue.

[0019] The beneficial effects of this invention are: (1) This invention exhibits excellent performance in the degradation of polyolefins to produce oil products, with a total oil yield of over 70% and excellent product quality.

[0020] (2) The molten salt system used in this invention has both catalytic and heat transfer functions. Compared with traditional solid catalysts, it has the characteristics of strong resistance to carbon deposition and excellent stability.

[0021] (3) The preparation process of the molten salt system is simple and controllable, and no complex synthesis equipment is required. The reaction is carried out under normal pressure and inert atmosphere, with low equipment requirements, safe operation, and easy to achieve large-scale industrial production.

[0022] (4) The present invention integrates distillation and fractional separation technology to achieve online separation of products, avoiding subsequent complex separation and purification processes, and further reducing production energy consumption and costs.

[0023] (5) The catalyst additives added in this invention can form a synergistic effect with the molten salt system, supplement the catalytic active sites, improve the selectivity of the target fraction, and at the same time enhance the system's resistance to carbon deposition and extend the catalytic life.

[0024] In summary, the molten salt distillation process for degrading polyolefin waste plastics to produce oil products provided by this invention has excellent catalytic performance, resource conversion efficiency, and economic efficiency. It provides a new approach for the efficient utilization of polyolefin waste plastics in industry and has significant application prospects in the fields of solid waste treatment and energy chemical industry. Attached Figure Description

[0025] Figure 1 The chromatograms of products C5-C12 from Example 1 were obtained using gas chromatography-mass spectrometry (GC-MS). Figure 2 The spectra of products C13-C22 from Example 1 were obtained using gas chromatography-mass spectrometry (GC-MS). Detailed Implementation

[0026] The specific embodiments of the present invention will be further described below with reference to the accompanying drawings and technical solutions.

[0027] Example 1 Weigh 0.69 g LiNO3, 1.70 g NaNO3, and 0.95 g MgCl2 according to a LiNO3-NaNO3-MgCl2 molar ratio of 1:2:1. Grind them in an agate mortar for 10 min, then transfer them to a quartz tube reactor. Argon gas is introduced as a protective gas, and the reactor is stirred by bubbling at 1000°C. o The temperature was increased from room temperature to 450 °C / min. o C was used to completely melt the salt, and the mixture was stirred and bubbled for 120 min before being naturally cooled to room temperature to obtain molten salt particles. Then, 1 g of these molten salt particles were weighed, and 1 g of low-density polyethylene powder and 0.08 g of ZnO catalyst were added. 5 mL of anhydrous ethanol was added dropwise as a dispersant, and the mixture was ground for 10 min. The composite material was collected and placed in a 50°C container. o After evaporating to remove ethanol in a vacuum drying oven at C for 1 h, the product is placed in a quartz tube reactor with a distillation column. Argon gas is introduced for 20 min to replace the air in the tube, followed by... o The temperature was increased from room temperature to 550 °C / min. o The reaction was carried out at atmospheric pressure for 1 hour, with argon gas continuously purging during the process. Simultaneously, the liquid products were separated by a distillation temperature gradient. o C~180 o Section C collects gasoline fractions, 180 o C~360 oDiesel fraction was collected in section C, and the residue at the bottom of the quartz tube reactor was collected separately for testing. The liquid obtained from the reaction of the collected gasoline (C5-C12), diesel (C13-C22) fractions, etc., was analyzed by gas chromatography-mass spectrometry.

[0028] Example 2 Weigh out 0.69 g LiNO3, 2.20 g KNO3, and 0.59 g NaCl according to a LiNO3-KNO3-NaCl molar ratio of 1:2:1. Grind them in an agate mortar for 10 min, then place them in a quartz tube reactor. Argon gas is introduced as a protective gas, and the reactor is stirred by bubbling at 1000°C. o Heat to 450 °C / min o C was used to completely melt the salt, and the mixture was stirred and bubbled for 120 min before being naturally cooled to room temperature to obtain molten salt particles. Then, 1 g of these molten salt particles were weighed, and 1 g of low-density polyethylene powder and 0.08 g of ZnO catalyst were added. 5 mL of anhydrous ethanol was added dropwise as a dispersant, and the mixture was ground for 10 min. The composite material was collected and placed in a 50°C container. o After evaporating and removing ethanol in a vacuum drying oven at C for 1 hour, the product is placed in a quartz tube reactor with a distillation column. Argon gas is introduced for 20 minutes to purge the air from the tube. Then, 10... o The temperature was increased from room temperature to 550 °C / min. o The reaction was carried out at atmospheric pressure for 1 hour, with argon gas continuously purging during the process. Simultaneously, the liquid products were separated by a distillation temperature gradient. o C~180 o Section C collects gasoline fractions, 180 o C~360 o Diesel fraction was collected in section C, and the residue at the bottom of the quartz tube reactor was collected separately for testing. The liquid obtained from the reaction of the collected gasoline (C5-C12), diesel (C13-C22) fractions, etc., was analyzed by gas chromatography-mass spectrometry.

[0029] Example 3 Weigh 0.69 g LiNO3, 1.70 g NaNO3, and 0.95 g MgCl2 according to a LiNO3-NaNO3-MgCl2 molar ratio of 1:2:1. Grind them in an agate mortar for 10 min, then transfer them to a quartz tube reactor. Argon gas is introduced as a protective gas, and the reactor is stirred by bubbling at 1000°C. o Heat to 450 °C / min oC was used to completely melt the salt, and the mixture was stirred and bubbled for 120 min before being naturally cooled to room temperature to obtain molten salt particles. Then, 1 g of these molten salt particles were weighed, and 1 g of low-density polyethylene powder and 0.14 g of Si3N4 catalyst were added. 5 mL of anhydrous ethanol was added dropwise as a dispersant, and the mixture was ground for 10 min. The composite material was collected and placed in a 50°C container. o After evaporating to remove ethanol in a vacuum drying oven at C for 1 h, the product is placed in a quartz tube reactor with a distillation column. Argon gas is introduced for 20 min to replace the air in the tube, followed by... o The temperature was increased from room temperature to 550 °C / min. o The reaction was carried out at atmospheric pressure for 1 hour, with argon gas continuously purging during the process. Simultaneously, the liquid products were separated by a distillation temperature gradient. o C~180 o Section C collects gasoline fractions, 180 o C~360 o Diesel fraction was collected in section C, and the residue at the bottom of the quartz tube reactor was collected separately for testing. The liquid obtained from the reaction of the collected gasoline (C5-C12), diesel (C13-C22) fractions, etc., was analyzed by gas chromatography-mass spectrometry.

[0030] Example 4 Weigh 0.69 g LiNO3, 1.70 g NaNO3, and 0.95 g MgCl2 according to a LiNO3-NaNO3-MgCl2 molar ratio of 1:2:1. Grind them in an agate mortar for 10 min, then transfer them to a quartz tube reactor. Argon gas is introduced as a protective gas, and the reactor is stirred by bubbling at 1000°C. o Heat to 450 °C / min o C was used to completely melt the salt, and the mixture was stirred and bubbled for 120 min before being naturally cooled to room temperature to obtain molten salt particles. Then, 1 g of these molten salt particles were weighed, and 1 g of low-density polyethylene powder and 0.20 g of Mo2C catalyst were added. 5 mL of anhydrous ethanol was added dropwise as a dispersant, and the mixture was ground for 10 min. The composite material was collected and placed in a 50°C container. o After evaporating to remove ethanol in a vacuum drying oven at C for 1 h, the product is placed in a quartz tube reactor with a distillation column. Argon gas is introduced for 20 min to replace the air in the tube, followed by... o The temperature was increased from room temperature to 550 °C / min. o The reaction was carried out at atmospheric pressure for 1 hour, with argon gas continuously purging during the process. Simultaneously, the liquid products were separated by a distillation temperature gradient. o C~180 o Section C collects gasoline fractions, 180 o C~360 oDiesel fraction was collected in section C, and the residue at the bottom of the quartz tube reactor was collected separately for testing. The liquid obtained from the reaction of the collected gasoline (C5-C12), diesel (C13-C22) fractions, etc., was analyzed by gas chromatography-mass spectrometry.

[0031] Example 5 Weigh 0.69 g LiNO3, 1.70 g NaNO3, and 0.95 g MgCl2 according to a LiNO3-NaNO3-MgCl2 molar ratio of 1:2:1. Grind them in an agate mortar for 10 min, then transfer them to a quartz tube reactor. Argon gas is introduced as a protective gas, and the reactor is stirred by bubbling at 1000°C. o Heat to 450 °C / min o C was used to completely melt the salt, and the mixture was stirred and bubbled for 120 min before being naturally cooled to room temperature to obtain molten salt particles. Then, 1 g of these molten salt particles were weighed, and 1 g of low-density polyethylene powder and 0.16 g of Fe2O3 catalyst were added. 5 mL of anhydrous ethanol was added dropwise as a dispersant, and the mixture was ground for 10 min. The composite material was collected and placed in a 50°C container. o After evaporating to remove ethanol in a vacuum drying oven at C for 1 h, the product is placed in a quartz tube reactor with a distillation column. Argon gas is introduced for 20 min to replace the air in the tube, followed by... o The temperature was increased from room temperature to 550 °C / min. o The reaction was carried out at atmospheric pressure for 1 hour, with argon gas continuously purging during the process. Simultaneously, the liquid products were separated by a distillation temperature gradient. o C~180 o Section C collects gasoline fractions, 180 o C~360 o Diesel fraction was collected in section C, and the residue at the bottom of the quartz tube reactor was collected separately for testing. The liquid obtained from the reaction of the collected gasoline (C5-C12), diesel (C13-C22) fractions, etc., was analyzed by gas chromatography-mass spectrometry.

[0032] Example 6 Weigh 0.69 g LiNO3, 1.70 g NaNO3, and 0.95 g MgCl2 according to a LiNO3-NaNO3-MgCl2 molar ratio of 1:2:1. Grind them in an agate mortar for 10 min, then transfer them to a quartz tube reactor. Argon gas is introduced as a protective gas, and the reactor is stirred by bubbling at 1000°C. o Heat to 450 °C / min oC was used to completely melt the salt, and the mixture was stirred and bubbled for 120 min before being naturally cooled to room temperature to obtain molten salt particles. Then, 1 g of these molten salt particles were weighed, and 1 g of polypropylene powder and 0.08 g of ZnO catalyst were added. 5 mL of anhydrous ethanol was added dropwise as a dispersant, and the mixture was ground for 10 min. The composite material was collected and placed in a 50°C container. o After evaporating and removing ethanol in a vacuum drying oven at C for 1 hour, the product is placed in a quartz tube reactor with a distillation column. Argon gas is introduced for 20 minutes to purge the air from the tube. Then, 10... o The temperature was increased from room temperature to 550 °C / min. o The reaction was carried out at atmospheric pressure for 1 hour, with argon gas continuously purging during the process. Simultaneously, the liquid products were separated by a distillation temperature gradient. o C~180 o Section C collects gasoline fractions, 180 o C~360 o Diesel fraction was collected in section C, and the residue at the bottom of the quartz tube reactor was collected separately for testing. The liquid obtained from the reaction of the collected gasoline (C5-C12), diesel (C13-C22) fractions, etc., was analyzed by gas chromatography-mass spectrometry.

[0033] Example 7 Weigh 0.69 g LiNO3, 1.70 g NaNO3, and 0.95 g MgCl2 according to a LiNO3-NaNO3-MgCl2 molar ratio of 1:2:1. Grind them in an agate mortar for 10 min, then transfer them to a quartz tube reactor. Argon gas is introduced as a protective gas, and the reactor is stirred by bubbling at 1000°C. o Heat to 450 °C / min o C was used to completely melt the salt, and the mixture was stirred and bubbled for 120 min before being naturally cooled to room temperature to obtain molten salt particles. Then, 1 g of these molten salt particles were weighed, and 1 g of polyvinyl chloride powder and 0.08 g of ZnO catalyst were added. 5 mL of anhydrous ethanol was added dropwise as a dispersant, and the mixture was ground for 10 min. The composite material was collected and placed in a 50°C container. o After evaporating to remove ethanol in a vacuum drying oven at C for 1 h, the product is placed in a quartz tube reactor with a distillation column. Argon gas is introduced for 20 min to replace the air in the tube, followed by... o The temperature was increased from room temperature to 550 °C / min. o The reaction was carried out at atmospheric pressure for 1 hour, with argon gas continuously purging during the process. Simultaneously, the liquid products were separated by a distillation temperature gradient. o C~180 o Section C collects gasoline fractions, 180 o C~360 oDiesel fraction was collected in section C, and the residue at the bottom of the quartz tube reactor was collected separately for testing. The liquid obtained from the reaction of the collected gasoline (C5-C12), diesel (C13-C22) fractions, etc., was analyzed by gas chromatography-mass spectrometry.

[0034] Comparative Example 1 Weigh 0.69 g of LiNO3 and 1 g of low-density polyethylene powder, add 5 mL of anhydrous ethanol as a dispersant and grind for 10 min, then place in a 50°C container. o After evaporating to remove ethanol in a vacuum drying oven at C for 1 h, the product is placed in a quartz tube reactor with a distillation column. Argon gas is introduced for 20 min to replace the air in the tube, followed by... o The temperature was increased from room temperature to 550 °C / min. o The reaction was carried out at atmospheric pressure for 1 hour, with argon gas continuously purging during the process. Simultaneously, the liquid products were separated by a distillation temperature gradient. o C~180 o Section C collects gasoline fractions, 180 o C~360 o Diesel fraction was collected in section C, and the residue at the bottom of the quartz tube reactor was collected separately for testing. The liquid obtained from the reaction of the collected gasoline (C5-C12), diesel (C13-C22) fractions, etc., was analyzed by gas chromatography-mass spectrometry.

[0035] Comparative Example 2 Weigh 0.69 g of LiNO3 and 1.70 g of NaNO3 according to a LiNO3-NaNO3 molar ratio of 1:2, grind them in an agate mortar for 10 min, then put them into a quartz tube reactor. Argon gas is introduced as a protective gas, and the reactor is stirred by bubbling at 1000 rpm. o Heat to 450 °C / min o C was used to completely melt the salt, and the mixture was continued to bubble and stir for 120 min, then naturally cooled to room temperature to obtain molten salt particles. Subsequently, 1 g of the molten salt particles and 1 g of low-density polyethylene powder were weighed, and 5 mL of anhydrous ethanol was added dropwise as a dispersant. The mixture was then ground for 10 min and placed at 50°C. o After evaporating to remove ethanol in a vacuum drying oven at C for 1 h, the product is placed in a quartz tube reactor with a distillation column. Argon gas is introduced for 20 min to replace the air in the tube, followed by... o The temperature was increased from room temperature to 550 °C / min. o The reaction was carried out at atmospheric pressure for 1 hour, with argon gas continuously purging during the process. Simultaneously, the liquid products were separated by a distillation temperature gradient. o C~180 o Section C collects gasoline fractions, 180 o C~360 oDiesel fraction was collected in section C, and the residue at the bottom of the quartz tube reactor was collected separately for testing. The liquid obtained from the reaction of the collected gasoline (C5-C12), diesel (C13-C22) fractions, etc., was analyzed by gas chromatography-mass spectrometry.

[0036] Comparative Example 3 Weigh 0.69 g LiNO3, 1.70 g NaNO3, and 0.95 g MgCl2 according to a LiNO3-NaNO3-MgCl2 molar ratio of 1:2:1. Grind them in an agate mortar for 10 min, then transfer them to a quartz tube reactor. Argon gas is introduced as a protective gas, and the reactor is stirred by bubbling at 1000°C. o Heat to 450 °C / min o C was used to completely melt the salt, and the mixture was continued to bubble and stir for 120 min, then naturally cooled to room temperature to obtain molten salt particles. Subsequently, 1 g of these molten salt particles were weighed, 1 g of low-density polyethylene powder was added, and 5 mL of anhydrous ethanol was added dropwise as a dispersant. The mixture was ground for 10 min, and the composite material was collected. The composite material was then placed in a 50°C container. o After evaporating to remove ethanol in a vacuum drying oven at C for 1 h, the product is placed in a quartz tube reactor with a distillation column. Argon gas is introduced for 20 min to replace the air in the tube, followed by... o The temperature was increased from room temperature to 550 °C / min. o The reaction was carried out at atmospheric pressure for 1 hour, with argon gas continuously purging during the process. Simultaneously, the liquid products were separated by a distillation temperature gradient. o C~180 o Section C collects gasoline fractions, 180 o C~360 o Diesel fraction was collected in section C, and the residue at the bottom of the quartz tube reactor was collected separately for testing. The liquid obtained from the reaction of the collected gasoline (C5-C12), diesel (C13-C22) fractions, etc., was analyzed by gas chromatography-mass spectrometry.

[0037] The reaction performance data of Examples 1-8 and Comparative Examples 1-3 are shown in Table 1.

[0038] Table 1

[0039] As shown in the table above, the optimal catalyst system of LiNO3-NaNO3-MgCl2+ZnO (alkali metal and alkaline earth metal, artificially defined, addition ratio) used in this invention exhibits excellent catalytic activity and target product selectivity in the reaction of plastic degradation to prepare fuel oil products, and is highly adaptable to the three mainstream plastics: PE, PP, and PVC. Compared with simple salt catalytic systems such as single-salt systems, the optimal ternary salt catalyst system significantly improves the total oil yield and the proportion of target fuel oil fraction, solving the problem of insufficient activity in simple salt systems. Simultaneously, the catalyst promoter can form a synergistic effect with the ternary salt, supplementing active sites, guiding the reaction directionally, reducing by-products, and improving system stability and reducing carbon deposition, fundamentally solving the problems of insufficient activity and poor selectivity in simple salt systems. The LiNO3-NaNO3-MgCl2+ZnO catalyst system described in this invention has the core advantages of high catalytic activity, excellent target product selectivity, and wide plastic compatibility, and has good application value.

[0040] In summary, the molten salt distillation process for degrading polyolefin waste plastics to produce oil products provided by this invention exhibits significant advantages in terms of oil yield and product selectivity, overcomes the core defects of traditional processes, and has promising prospects for industrial application.

Claims

1. A process for degrading waste plastics to produce oil products by molten salt distillation, characterized in that, The steps are as follows: Using polyolefin waste plastics as reaction substrates, a distillation catalytic degradation reaction is carried out in the presence of a molten salt system under an inert atmosphere and normal pressure to achieve directional cracking of polyolefin waste plastics to produce oil products, and to complete the fractional distillation separation of the products.

2. The process according to claim 1, characterized in that, The temperature of the distillation catalytic degradation reaction is 400°C. o C ~600 o C, reaction time is 0.5 h ~ 4 h.

3. The process according to claim 1, characterized in that, The mass ratio of the molten salt system to polyolefin waste plastics is 1:1 to 1:

5.

4. The process according to claim 1, characterized in that, After mixing the molten salt system with polyolefin waste plastics, grind the mixture. Add 1-5 mL of anhydrous ethanol as a dispersant. Grind for 5-10 minutes, then place in a vacuum oven at 40°C. o C ~ 60 o Keep at C for 1 h to remove ethanol.

5. The process according to claim 1, characterized in that, The molten salt system consists of one or two combinations of alkali metal nitrates, with the addition of alkali metal chlorides or alkaline earth metal chlorides; the alkali metal chlorides are NaCl, KCl, and LiCl, the alkaline earth metal chlorides are CaCl2, MgCl2, and BaCl2, and the alkali metal nitrates are NaNO3, KNO3, and LiNO3.

6. The process according to claim 1, characterized in that, The polyolefin waste plastics mentioned above include one or more of low-density polyethylene, high-density polyethylene, polypropylene, polybutene-1, and polyisobutylene.

7. The process according to claim 1, characterized in that, A catalyst promoter is added to the molten salt system to regulate its surface activity and thermal stability. The catalyst promoter is one or more of transition metal oxides, nitrides, and carbides. The transition metal oxide is one of ZnO, Fe2O3, Co3O4, NiO, and CuO. The nitride is one of h-BN, Si3N4, AlN, and ZrN. The nitride is one of WC, Mo2C, TiC, and SiC. The amount of catalyst promoter added is 1% to 15% of the total mass of the molten salt system.

8. The process according to claim 1, characterized in that, The inert atmosphere is nitrogen or argon.

9. The process according to claim 1, characterized in that, The specific method for fractional distillation separation is as follows: controlling the temperature gradient within the fractionation apparatus to be 120°C. o C~360 o C, at 120 o C ~180 o C collects the gasoline fraction at 180 o C ~360 o C collects the diesel fraction, with the residue at the bottom of the pipe consisting of wax oil and undegraded polyolefin residue.

10. The process according to claim 1, characterized in that, The method for preparing the molten salt system is as follows: mixing one or more of alkali metal chlorides, alkaline earth metal chlorides, and alkali metal nitrates, and heating to 350°C. o C ~ 500 o C is used to completely melt the molten salt, and the mixture is stirred under an inert atmosphere for 60 to 240 minutes to obtain a homogeneous and stable molten salt system.

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