Method for preparing high-quality oil from plastic

Abstract

The invention provides a method for preparing high-quality oil from plastic. The method comprises a heating pyrolysis gasification stage and a gas phase catalytic modification stage, in the heating pyrolysis gasification stage, waste plastics are placed in a reaction container to be subjected to high-temperature heating pyrolysis to generate gaseous substances, and in the gas phase catalytic modification stage, the gaseous substances are introduced into a modification device to be subjected to catalytic modification to obtain high-quality oil; according to the method, pyrolysis is performed firstly, and then catalytic upgrading is performed, so that compared with direct catalytic pyrolysis, the dosage of a catalyst is reduced, and the cost is saved. The catalyst is not in direct contact with the waste plastic, the service life of the catalyst can be prolonged, separation, recovery, activation and recycling of the catalyst are facilitated, meanwhile, collection and subsequent conversion and utilization of solid components generated by first-step pyrolysis are facilitated, and maximum utilization of waste plastic resources is achieved.

Description

Technical Field

[0001] This invention relates to the field of plastic processing technology, and more particularly to a method for preparing high-quality oil from plastics. Background Technology

[0002] Traditional waste plastic treatment methods, such as landfill and incineration, while capable of managing waste plastics to some extent, suffer from numerous problems: landfill occupies large amounts of land and easily causes secondary pollution; incineration easily produces harmful gases, causing air pollution. Furthermore, existing waste plastic recycling processes are costly, have low economic value, and result in insufficient profits for enterprises, leading to slow development of waste plastic resource recycling. To address these issues, chemical conversion of waste plastics has become an effective means to achieve rapid recycling and conversion. Among these methods, pyrolysis has attracted widespread attention due to its environmental friendliness and high yield. However, existing pyrolysis processes still have some problems, such as high Cl and Si impurities in the pyrolysis oil, leading to easy corrosion of pipelines and equipment in subsequent processes, easy catalyst deactivation, and low oil quality that cannot meet the requirements of downstream processes for pyrolysis products.

[0003] CN106349500B discloses a method for dechlorinating chlorinated plastics. In an inert atmosphere, alkaline substances (iron oxides, alkali metal oxides, alkali metal hydroxides, alkaline earth metal oxides, and alkaline earth metal hydroxides) undergo a pyrolysis reaction with the chlorinated plastics to yield chloride salts and hydrocarbons. The direct addition of alkaline substances to the pyrolysis system, coupled with the molten state of the waste plastics, easily deactivates the porous structure of these alkaline adsorbent / catalytic substances. Furthermore, separation, recovery, and recycling become more difficult.

[0004] CN118272125A provides a method for treating waste plastics and heavy oil. First, the waste plastics are pretreated to remove impurities and grease from their surface. Then, the waste plastics and heavy oil are fed into a mixing unit for mixing. Finally, the first slurry obtained from the mixture of waste plastics and heavy oil undergoes a first pyrolysis treatment and a second pyrolysis treatment sequentially. This method achieves co-pyrolysis of the waste plastics and heavy oil components and continuous processing of the waste plastics, while reducing the chlorine content in the pyrolysis products. However, this method requires pretreatment of the waste plastics, and during the co-pyrolysis of the waste plastics and heavy oil mixture, the heavy oil preferentially participates in the pyrolysis, which does not effectively achieve single-stage pyrolysis and impurity removal of the waste plastics.

[0005] Therefore, developing a new method for treating waste plastics is of great significance for improving the quality of recycled resources. Summary of the Invention

[0006] The technical problem to be solved by this invention is that the oil produced by existing waste plastic treatment processes is of low quality and contains a lot of impurities.

[0007] To address the aforementioned technical problems, this invention provides a method for preparing high-quality oil from plastics. The method includes a heating pyrolysis and gasification stage and a gas-phase catalytic modification stage. The heating pyrolysis and gasification stage involves placing waste plastics in a reaction vessel for high-temperature heating and pyrolysis to generate gaseous substances. The gas-phase catalytic modification stage involves passing the gaseous substances into a modification device for catalytic modification to obtain high-quality oil.

[0008] The method provided by this invention can effectively remove chlorine from waste plastics, reducing both organic and inorganic chlorine to a few ppm, achieving the standard of less than 10 mg / L chlorine content in liquid oil. This reduces corrosion and abnormal reactions in subsequent processing and refining, providing a better foundation for future utilization. The process is simple, and the dechlorination catalyst and adsorbent are easy to separate, recover, and recycle, saving costs. During the catalytic reforming process, the pyrolysis products undergo reactions such as alkane isomerization, cyclization, and olefin aromatization, which can increase the light components and reduce the heavy components in fuel oil, thereby increasing the octane rating of gasoline and improving the quality of fuel oil.

[0009] The plastics used in this invention are generally dried and pulverized. The gaseous substance is generally a gaseous hydrocarbon. The reaction vessel can be a reaction kettle.

[0010] Preferably, the high-temperature heating temperature is 350-400℃, for example, 350℃, 360℃, 370℃, 380℃, 390℃ or 400℃.

[0011] Preferably, the high-temperature heating time is 0.5 to 2 hours, for example, it can be 0.5 hours, 1 hour, or 2 hours.

[0012] In this invention, the high-temperature heating residence time is matched with the temperature of this stage. Lower temperatures require a longer time to achieve better impurity removal and pyrolysis effects. Excessively high temperatures and excessively long residence times in this stage will also reduce the final pyrolysis oil yield. This stage can remove more than 90% of impurities.

[0013] Preferably, the temperature for catalytic modification is 300–400°C, for example, 300°C, 320°C, 350°C, 380°C, or 400°C.

[0014] Preferably, the catalytic modification time is 20 to 40 minutes, for example, 20 minutes, 25 minutes, 30 minutes, 35 minutes, or 40 minutes.

[0015] Preferably, the catalytic modification process includes a catalyst.

[0016] In this invention, the catalyst plays a dual role of catalysis and adsorption. The products, after cooling and fractionation, can yield gasoline, kerosene, diesel oil, and gases. The yield is 80%–90%, and the chlorine content in the oil is less than 10 ppm.

[0017] Preferably, the catalyst comprises a zeolite molecular sieve or an alkali metal oxide. Alkali metal oxides play a dual role in catalysis and adsorption during the catalytic process, reacting with HCl produced during pyrolysis to generate corresponding metal chloride salts, thereby fixing chlorine into the solid product and reducing the chlorine content of the liquid product. Zeolite molecular sieves, a type of natural aluminosilicate molecular sieve, are commonly used in the pyrolysis of waste plastics due to their porous structure and high cracking activity towards various polymers.

[0018] Preferably, the zeolite molecular sieve includes any one or a combination of at least two of ZMS-5 or HZMS-5.

[0019] Preferably, the alkali metal oxide includes any one or a combination of at least two of Al2O3, ZnO, CaO, Fe2O3, Fe3O4, PbO, or La2O3.

[0020] Preferably, the mass of the catalyst is 5% to 15% of the mass of the plastic, for example, it can be 5%, 7%, 10%, 12% or 15%.

[0021] Implementing this invention has the following beneficial effects:

[0022] The method of the present invention increases the light components and reduces the heavy components in fuel oil, thereby improving the quality of fuel oil.

[0023] This invention utilizes a pre-pyrolysis followed by catalytic upgrading, which reduces catalyst usage and saves costs compared to direct catalytic pyrolysis. The catalyst does not directly contact the waste plastics, extending its lifespan and facilitating its separation, recovery, activation, and recycling. Furthermore, it allows for the collection and subsequent conversion of the solid components generated in the first pyrolysis step, maximizing the utilization of waste plastic resources.

[0024] This invention combines pyrolysis and catalysis to remove impurities such as chlorine from waste plastic oil to the greatest extent possible, facilitating subsequent processing and use of the oil. Detailed Implementation

[0025] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0026] Example 1

[0027] Waste plastic particles are placed in a reactor and heated to 380°C. The reaction is carried out at this temperature for 1 hour to produce gaseous hydrocarbons. The hydrocarbons are then introduced into a catalytic decomposition tank containing ZMS-5 catalyst, with the amount of catalyst being 10% of the mass of the plastic. The catalytic reforming temperature is controlled at 350°C and the reaction is carried out at this temperature for 30 minutes. The gaseous hydrocarbons produced by pyrolysis are decomposed into light hydrocarbons by the catalyst. After condensation, fuel oil and fuel gas can be obtained.

[0028] Example 2

[0029] Waste plastic particles are placed in a reactor and heated to 350°C. The reaction is carried out at this temperature for 1 hour to produce gaseous hydrocarbons. The gaseous hydrocarbons are then introduced into a catalytic decomposition tank containing an Al2O3 catalyst, with the catalyst amount being 8% of the plastic mass. The catalytic reforming temperature is controlled at 400°C and the reaction is carried out at this temperature for 20 minutes. The gaseous hydrocarbons produced by pyrolysis are decomposed into light hydrocarbons by the catalyst. After condensation, fuel oil and fuel gas can be obtained.

[0030] Example 3

[0031] Waste plastic particles are placed in a reactor and heated to 400°C. The reaction is carried out at this temperature for 0.8 hours to produce gaseous hydrocarbons. The gaseous hydrocarbons are then introduced into a catalytic decomposition tank containing a PbO catalyst. The amount of catalyst is 15% of the mass of the plastic. The catalytic reforming temperature is controlled at 300°C and the reaction is carried out at this temperature for 40 minutes. The gaseous hydrocarbons produced by pyrolysis are decomposed into light hydrocarbons by the catalyst. After condensation, fuel oil and fuel gas can be obtained.

[0032] Example 4

[0033] The difference between this embodiment and Example 1 is that the catalyst is replaced with La2O3.

[0034] Example 5

[0035] The difference between this embodiment and Embodiment 1 is that the high-temperature heating temperature is 500℃.

[0036] Example 6

[0037] The difference between this embodiment and Embodiment 1 is that the high-temperature heating temperature is 300℃.

[0038] Example 7

[0039] The difference between this embodiment and Embodiment 1 is that the temperature for catalytic modification is 200°C.

[0040] Example 8

[0041] The difference between this embodiment and Embodiment 1 is that the temperature for catalytic modification is 500℃.

[0042] Example 9

[0043] The difference between this embodiment and Example 1 is that the catalyst is replaced with CaO.

[0044] Comparative Example 1

[0045] The difference between this comparative example and Example 1 is that it does not include the catalyst ZMS-5.

[0046] Comparative Example 2

[0047] The difference between this comparative example and Example 1 is that the high-temperature heating process in the first stage is not included.

[0048] The above samples were subjected to fuel yield calculation and chlorine content testing. Fuel yield = (mass of obtained fuel / mass of waste plastic input) × 100%, and chlorine content was determined by the combustion-microcoulometric method.

[0049] Table 1

[0050]

[0051]

[0052] As can be seen from the data in the above embodiments and comparative examples:

[0053] Zeolite molecular sieves or alkali metal oxides can both achieve catalytic pyrolysis and dechlorination of waste plastics, with slight differences in effectiveness and operating conditions among different catalysts. When no catalyst is used, the reaction efficiency decreases significantly; the fuel oil yield is highest when ZMS-5 or Al2O3 is used as the catalyst.

[0054] The pyrolysis stage produces a small amount of aromatics, and excessively high temperatures and residence times during this stage can reduce the final pyrolysis oil yield. The temperature and residence time during the catalytic upgrading stage directly affect the yield of the final target product. The optimal temperature range is between 300 and 400°C. Excessively high temperatures are detrimental to tar production and have a relatively small impact on the dechlorination rate.

[0055] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for preparing high-quality oil from plastics, characterized in that, The method includes a heating pyrolysis gasification stage and a gas-phase catalytic reforming stage; the heating pyrolysis gasification stage involves placing waste plastics in a reaction vessel for high-temperature heating and pyrolysis to generate gaseous substances, and the gas-phase catalytic reforming stage involves passing the gaseous substances into a reformer for catalytic reforming to obtain high-quality oil.

2. The method according to claim 1, characterized in that, The high-temperature heating temperature is 350-400℃.

3. The method according to claim 1, characterized in that, The high-temperature heating time is 0.5 to 2 hours.

4. The method according to claim 1, characterized in that, The temperature for catalytic reforming is 300–400°C.

5. The method according to claim 1, characterized in that, The catalytic reforming time is 20–40 min.

6. The method according to claim 1, characterized in that, The catalytic reforming process includes a catalyst.

7. The method according to claim 6, characterized in that, The catalyst includes zeolite molecular sieves or alkali metal oxides.

8. The method according to claim 7, characterized in that, The zeolite molecular sieve includes any one or a combination of at least two of ZMS-5 or HZMS-5.

9. The method according to claim 7, characterized in that, The alkali metal oxides include any one or a combination of at least two of Al2O3, ZnO, CaO, Fe2O3, Fe3O4, PbO, or La2O3.

10. The method according to claim 6, characterized in that, The catalyst is used in an amount of 5% to 15% of the mass of the plastic.

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