Method for preparing aviation kerosene by directional preparation of polyolefin plastics under ambient temperature condition

Abstract

The present application relates to the technical field of polymer degradation, waste plastic resource recycling, green catalytic conversion and aviation fuel preparation, and particularly relates to a method for cracking polyolefin plastics to direct preparation of aviation kerosene under normal temperature conditions, comprising the following steps: mixing polyolefin plastics with cyclohexane, chloroaluminate ionic liquid catalyst and chlorinated tertiary butane, and performing reaction under room temperature or low temperature conditions to make the polyolefin plastics undergo chain scission and cracking, and further make the low-carbon olefins or active hydrocarbon intermediates generated by cracking undergo alkylation conversion to generate liquid-phase products containing C8-C16 aviation kerosene range hydrocarbons. The recycling method can realize directional conversion of waste polyethylene, polypropylene, polyvinyl chloride, polystyrene and other waste polyolefin plastics to aviation kerosene components under normal pressure and room temperature conditions, and has the advantages of mild reaction conditions, low energy consumption, high product selectivity, high resource utilization value and the like.

Description

Technical Field

[0001] This invention relates to the fields of polymer degradation, waste plastic resource recycling, green catalytic conversion, and aviation fuel preparation technology, and particularly to a method for the directional preparation of aviation kerosene by pyrolysis of polyolefin plastics under ambient temperature conditions. Background Technology

[0002] Polyolefins are a class of petroleum-based polymers formed by the polymerization of olefin monomers. Broadly speaking, they include polyethylene, polypropylene, polyvinyl chloride, and polystyrene, and are among the most widely produced and consumed general-purpose plastics. They are widely used in food packaging, films, household products, automotive parts, medical consumables, electronics, and pipes. Due to their advantages such as chemical resistance, excellent processing performance, and low cost, polyolefin products are widely used in daily life and industrial production. However, polyolefin materials have high chemical stability and are difficult to degrade in the natural environment. Large quantities of waste polyolefin plastics entering landfills, incineration systems, or the natural environment cause problems such as land occupation, increased carbon emissions, microplastic release, and environmental pollution. Therefore, developing efficient, low-emission, and high-value-added methods for the resource recovery of waste polyolefins is of great significance.

[0003] Currently, the main recycling methods for waste polyolefin plastics include mechanical recycling, thermal cracking recycling, and chemical catalytic recycling. Mechanical recycling typically involves steps such as sorting, washing, crushing, melt granulation, and reprocessing. While the process is relatively simple, it requires high purity raw materials, and the recycled materials are prone to mechanical property degradation due to thermo-oxidative aging, impurity contamination, and molecular weight reduction. Therefore, it is generally only suitable for low-value-added products and difficult to achieve high-value recycling. Traditional thermal cracking technology can convert waste polyolefins into liquid oils, gases, and waxy products, achieving a certain degree of higher value-added recycling. However, the breaking of C–C bonds in the polyolefin molecular chain usually requires overcoming a high energy barrier, thus relying on high reaction temperatures to provide the energy needed for chain breaking. Furthermore, the products have a wide carbon number distribution and contain a large amount of olefins, branched hydrocarbons, and heavy components. If the target product is C8–C16 aviation kerosene hydrocarbons, further hydrorefining, isomerization, or fractionation is usually required to obtain hydrocarbon components that meet fuel requirements. Therefore, existing thermal cracking technologies still struggle to simultaneously achieve mild reaction conditions, low energy consumption, and the targeted generation of fuel-range hydrocarbons. Summary of the Invention

[0004] In view of this, the technical problem to be solved by the present invention is to provide a method for the directional preparation of aviation kerosene by pyrolyzing polyolefin plastics under room temperature conditions, which addresses the problems existing in the current waste polyolefin plastic recycling technology, such as the decline in mechanical recycling quality, the wide distribution of traditional pyrolysis products, the low selectivity of aviation kerosene components, the complexity of subsequent refining processes, and the lack of high-value utilization.

[0005] To achieve the above objectives, the present invention provides a method for the directional preparation of aviation kerosene by pyrolysis of polyolefin plastics under ambient temperature conditions, comprising the following steps:

[0006] Polyolefin plastics are mixed with cyclohexane, chloroaluminate ionic liquid catalyst and tert-butane chloride, and stirred at room temperature or low temperature to cause chain scission and cracking of the polyolefin plastics. The low-carbon olefins or active hydrocarbon intermediates generated by cracking are further alkylated to produce liquid-phase products rich in C8-C16 aviation kerosene hydrocarbons.

[0007] This invention utilizes the exothermic nature of alkylation to couple the polyolefin cracking process with the alkylation process. The heat released during alkylation helps compensate for the energy required for polyolefin chain scission and cracking, reducing the system's dependence on external high-temperature heating. This promotes carbon chain growth, branching, and rearrangement of low-carbon olefins, thereby further converting low-carbon hydrocarbons into fuel-grade hydrocarbons with higher carbon numbers. Simultaneously, the low-carbon olefins or reactive hydrocarbon intermediates produced by cracking can be promptly consumed by the alkylation reaction and further participate in carbon chain construction and structural rearrangement, thus reducing the disordered generation of low-carbon gases and broadly distributed liquid oils and promoting the enrichment of products into C8-C16 aviation kerosene hydrocarbons. Therefore, through the energy coupling between the endothermic cracking process and the exothermic alkylation process, and the kinetic matching between the generation and consumption of low-carbon cracking intermediates, it is expected to achieve the directional conversion of waste polyolefin plastics into aviation kerosene components under low-temperature or even room-temperature conditions.

[0008] Based on this, the present invention develops a method for promoting chain scission of polyolefin plastics at room temperature and simultaneously inducing alkylation conversion of low-carbon pyrolysis products, which can achieve highly selective and high-value-added conversion of waste polyolefin plastics into aviation kerosene components at room temperature.

[0009] The polyolefin plastic refers to a thermoplastic plastic whose main components are homopolymers, copolymers, or blends obtained by coordination polymerization, free radical polymerization, or ionic polymerization of one or more olefin monomers (such as ethylene, propylene, 1-butene, 1-hexene, 1-octene, and other α-olefins). The polyolefin plastic may be used unmodified or may further contain additives (such as antioxidants, light stabilizers, lubricants, antistatic agents, pigments, fillers, flame retardants, foaming agents, crosslinking agents, etc.), as long as the additives do not substantially alter the performance characteristics of the polyolefin. This invention does not specifically limit the type of polyolefin plastic, including but not limited to one or more of the following: waste polyethylene plastic, waste polypropylene plastic, waste polyvinyl chloride plastic, and waste polystyrene plastic.

[0010] Preferably, the polyolefin plastic is pretreated in the following way:

[0011] Waste polyolefin plastics are sorted, cleaned, dried and crushed to remove metals, paper scraps, inorganic fillers, pigments, oil and other impurities, resulting in pretreated polyolefin raw materials.

[0012] The polyolefin plastic was then mixed with cyclohexane, aluminochloroaluminate ionic liquid catalyst, and tert-butane chloride for reaction.

[0013] The reaction temperature is preferably 10~55℃, more preferably 25~55℃, and for example, it can be 10, 25, 40, or 55℃, with the most preferred temperature being 25, 40, or 55℃.

[0014] The stirring reaction time is preferably 2 to 24 hours, more preferably 6 to 24 hours, and for example, it can be 6, 12, or 24 hours.

[0015] The mass ratio of the polyolefin plastic to cyclohexane is preferably 1:1 to 12, more preferably 1:4 to 12, and for example, it can be 1:4, 1:8, or 1:12.

[0016] The mass ratio of the polyolefin plastic to the chloroaluminate ionic liquid catalyst is preferably 1:1 to 16, more preferably 1:4 to 16, and for example, it can be 1:4, 1:8, or 1:16.

[0017] The chloroaluminate ionic liquid catalyst is preferably prepared by reacting triethylamine hydrochloride with anhydrous aluminum chloride.

[0018] The preferred molar ratio of anhydrous aluminum chloride to triethylamine hydrochloride is 1.2 to 2.5:1.

[0019] The mass ratio of the polyolefin plastic to tert-butane chloride is preferably 1:0 to 0.5, more preferably 1:0.05 to 0.5, and for example, it can be 1:0.05, 1:0.1, 1:0.3, 1:0.5, and most preferably 1:0.1 to 0.5.

[0020] Preferably, after the alkylation conversion is completed, the organic product layer and the catalyst layer are allowed to stand and separate to obtain a liquid-phase product rich in hydrocarbons in the C8-C16 aviation kerosene range.

[0021] The carbon number range of aviation kerosene hydrocarbon products in the product layer obtained by the present invention is mainly distributed in the range of C8 to C16, preferably in the range of C9 to C15.

[0022] The present invention also provides an aviation kerosene prepared by the above method.

[0023] The hydrocarbons in the aviation kerosene preferably include one or more of C8-C16 isoalkanes, cycloalkanes, and straight-chain alkanes, with isoalkanes and cycloalkanes being the main components.

[0024] The aviation kerosene prepared by this invention can be used as aviation fuel, aviation kerosene blending component, or liquid hydrocarbon fuel component.

[0025] See Figure 1 As shown, Figure 1 The flowchart for the directional preparation of aviation kerosene from recycled polyolefin plastics provided by the present invention mainly includes the following three steps: (1) sorting, cleaning, drying and crushing waste polyolefin plastics to remove metals, paper scraps, inorganic fillers, oil stains and other impurities, and obtaining pretreated waste polyolefin raw materials; (2) mixing the waste polyolefin raw materials with cyclohexane, chloroaluminate ionic liquid catalyst and chlorotert-butane, and carrying out a constant temperature stirring reaction at room temperature or low temperature to cause chain cleavage of waste polyolefins, and further causing alkylation, carbon chain growth, branching and rearrangement reactions of the low carbon olefins or active hydrocarbon intermediates produced by cleavage; (3) after the reaction is completed, separating the organic product layer from the catalyst layer by static separation to obtain a liquid phase product rich in C8 to C16 aviation kerosene hydrocarbons.

[0026] Compared with the prior art, the present invention provides a method for the directional preparation of aviation kerosene by cracking polyolefin plastics under room temperature conditions, comprising the following steps: mixing polyolefin plastics with cyclohexane, chloroaluminate ionic liquid catalyst and tert-butane chloride, and reacting at room temperature or low temperature to cause chain scission cracking of polyolefin plastics, and further alkylating the low-carbon olefins or active hydrocarbon intermediates generated by cracking to generate liquid-phase products containing hydrocarbons in the range of C8 to C16 aviation kerosene.

[0027] This recycling method can realize the directional conversion of waste polyethylene, polypropylene, polyvinyl chloride, polystyrene and other waste polyolefin plastics into aviation kerosene components under room temperature and normal pressure conditions. It has the advantages of mild reaction conditions, low energy consumption, high product selectivity and high resource utilization value. Attached Figure Description

[0028] Figure 1 A flowchart of the polyolefin plastic upgrading and recycling method provided by the present invention;

[0029] Figure 2 This is a physical image of the chloroaluminate ionic liquid catalyst in the embodiments of the present invention;

[0030] Figure 3 The yield results of the products in the embodiments of the present invention;

[0031] Figure 4 The above are the gas chromatography-mass spectrometry results of the products in the embodiments of the present invention. Detailed Implementation

[0032] To further illustrate the present invention, a detailed description is provided below with reference to embodiments. However, it should be understood that these descriptions are merely for further illustrating the features and advantages of the present invention, and not for limiting the scope of the claims.

[0033] There are no particular restrictions on the source of any raw materials used in this invention; they can be purchased from the market or prepared using conventional methods known to those skilled in the art.

[0034] The conversion rate of polyolefins, the yield of hydrocarbon products, and the selectivity of C8–C16 hydrocarbon products are calculated using formulas 1, 2, and 3:

[0035] (1)

[0036] (2)

[0037] (3)

[0038] Synthesis of chloroaluminate ionic liquid catalysts:

[0039] Under dry, anhydrous conditions, triethylamine hydrochloride was placed in a three-necked flask and stirred at 200 rpm under nitrogen protection. Anhydrous aluminum chloride was then slowly added in batches. The molar ratio of anhydrous aluminum chloride to triethylamine hydrochloride was 1.2–2.5:1. The system temperature was controlled to not exceed 40 °C during the addition process to avoid excessive local exothermic reactions. After the anhydrous aluminum chloride was added, the reaction was continued at room temperature for 0.5–6 h until a homogeneous transparent or homogeneous light-colored liquid was formed, thus obtaining the aluminochloride ionic liquid catalyst. Figure 2 As shown. The resulting catalyst should be stored in a sealed container and kept away from moisture in the air.

[0040] In the following examples, the pretreatment of waste polyolefin plastics is as follows:

[0041] Waste polyolefin plastics are sorted, cleaned, dried and crushed to remove metals, paper scraps, inorganic fillers, pigments, oil and other impurities, resulting in pretreated polyolefin raw materials.

[0042] Examples 1-4: Effect of reaction temperature on the pyrolysis-alkylation process of polyolefin plastics

[0043] Pretreated waste polyolefin plastics, cyclohexane, chloroaluminate ionic liquid catalyst, and tert-butane chloride were added to a reaction vessel, with the mass ratios of waste polyolefin plastics to cyclohexane being 1:4, to chloroaluminate ionic liquid catalysts being 1:4, and to tert-butane chloride being 1:0.1. The reaction was carried out at 10 °C, 25 °C, 40 °C, and 55 °C under stirring conditions for 12 h at a stirring speed of 1200 rpm. After the reaction, unreacted solid residue was first separated by filtration, then dried to constant weight under vacuum conditions, and its mass was recorded for calculating the conversion rate of waste polyolefin plastics. The remaining organic product layer and catalyst layer were separated after standing and subjected to gas chromatography-mass spectrometry (GC-MS). Based on the GC-MS analysis results, the yields of liquid hydrocarbon products with different carbon number ranges were classified and statistically analyzed. The results are shown below. Figure 3 As shown, the total yield of liquid-phase hydrocarbon products and the selectivity of hydrocarbons in the C8–C16 aviation kerosene range were further calculated. See items 1–4 in Table 1 for details.

[0044] Table 1. Effect of reaction temperature on the pyrolysis-alkylation process of polyolefin plastics

[0045]

[0046] Examples 5-9: Effect of reaction time on the pyrolysis-alkylation process of polyolefin plastics

[0047] Pretreated waste polyolefin plastics, cyclohexane, chloroaluminate ionic liquid catalyst, and tert-butane chloride were added to a reaction vessel. The mass ratio of waste polyolefin plastics to cyclohexane was 1:4, the mass ratio of waste polyolefin plastics to chloroaluminate ionic liquid catalyst was 1:4, and the mass ratio of waste polyolefin plastics to tert-butane chloride was 1:0.1. The reaction was carried out under stirring conditions for 2 h, 4 h, 6 h, 12 h, and 24 h, respectively, at a reaction temperature of 25 ℃ and a stirring speed of 1200 rpm. After the reaction, unreacted solid residue was first separated by filtration, then dried to constant weight under vacuum conditions, and its mass was recorded for calculating the conversion rate of waste polyolefin plastics. The remaining organic product layer and catalyst layer were separated after settling and separation, and the organic products were analyzed by gas chromatography-mass spectrometry to calculate the yield of liquid-phase hydrocarbon products and the selectivity of hydrocarbons in the C8–C16 aviation kerosene range. Figure 4 The total ion current chromatogram of the organic product obtained in Example 8 of Table 2 and the corresponding mass spectrometry identification results are shown as typical examples of the compositional characteristics of the liquid hydrocarbon products obtained in this invention. The organic products obtained in other examples were all detected and calculated using the same method, and the results are detailed in Examples 5 to 9 of Table 2.

[0048] Table 2 Effect of reaction time on the pyrolysis-alkylation process of polyolefin plastics

[0049]

[0050] Examples 10-14: Effect of cyclohexane dosage on the pyrolysis-alkylation process of polyolefin plastics

[0051] Pretreated waste polyolefin plastics, cyclohexane, chloroaluminate ionic liquid catalyst, and tert-butane chloride were added to a reaction vessel. The mass ratio of waste polyolefin plastics to cyclohexane was 1:1–12, the mass ratio of waste polyolefin plastics to chloroaluminate ionic liquid catalyst was 1:4, and the mass ratio of waste polyolefin plastics to tert-butane chloride was 1:0.1. The reaction was carried out at 25 °C for 12 h with stirring at 1200 rpm. After the reaction, unreacted solid residues were first separated by filtration, then dried to constant weight under vacuum, and their mass was recorded for calculating the conversion rate of waste polyolefin plastics. The remaining organic product layer and catalyst layer were separated after settling and the organic products were analyzed by gas chromatography-mass spectrometry to calculate the yield of liquid-phase hydrocarbon products and the selectivity of hydrocarbons in the C8–C16 aviation kerosene range. See items 10–14 in Table 3 for details.

[0052] Table 3. Effect of cyclohexane dosage on the pyrolysis-alkylation process of polyolefin plastics

[0053]

[0054] Examples 15-19: Effect of catalyst dosage on the cracking-alkylation process of polyolefin plastics

[0055] Pretreated waste polyolefin plastics, cyclohexane, chloroaluminate ionic liquid catalyst, and tert-butane chloride were added to a reaction vessel. The mass ratio of waste polyolefin plastics to cyclohexane was 1:4, the mass ratio of waste polyolefin plastics to chloroaluminate ionic liquid catalyst was 1:1–16, and the mass ratio of waste polyolefin plastics to tert-butane chloride was 1:0.1. The reaction was carried out at 25 °C for 12 h with stirring at 1200 rpm. After the reaction, unreacted solid residues were first separated by filtration, then dried to constant weight under vacuum, and their mass was recorded for calculating the conversion rate of waste polyolefin plastics. The remaining organic product layer and catalyst layer were separated after standing and separation, and the organic products were analyzed by gas chromatography-mass spectrometry to calculate the yield of liquid-phase hydrocarbon products and the selectivity of hydrocarbons in the C8–C16 aviation kerosene range. See items 15–19 in Table 4 for details.

[0056] Table 4. Effect of catalyst dosage on the pyrolysis-alkylation process of polyolefin plastics

[0057]

[0058] Examples 20-24: Effect of tert-butane chloride dosage on the pyrolysis-alkylation process of polyolefin plastics

[0059] Pretreated waste polyolefin plastics, cyclohexane, chloroaluminate ionic liquid catalyst, and tert-butane chloride were added to a reaction vessel. The mass ratio of waste polyolefin plastics to cyclohexane was 1:4, the mass ratio of waste polyolefin plastics to chloroaluminate ionic liquid catalyst was 1:4, and the mass ratio of waste polyolefin plastics to tert-butane chloride was 1:0–0.5. The reaction was carried out at 25 °C for 12 h with stirring at 1200 rpm. After the reaction, unreacted solid residues were first separated by filtration, then dried to constant weight under vacuum, and their mass was recorded for calculating the conversion rate of waste polyolefin plastics. The remaining organic product layer and catalyst layer were separated after settling and the organic products were analyzed by gas chromatography-mass spectrometry to calculate the yield of liquid-phase hydrocarbon products and the selectivity of hydrocarbons in the C8–C16 aviation kerosene range. See items 20–24 in Table 5 for details.

[0060] Table 5. Effect of tert-butane chloride dosage on the pyrolysis-alkylation process of polyolefin plastics

[0061]

[0062] In summary, the present invention has the following beneficial effects:

[0063] This invention provides an upgraded recycling method for waste polyolefin plastics, involving room-temperature pyrolysis and alkylation-directed conversion to prepare aviation kerosene components. This method features strong raw material adaptability, high selectivity of target products, controllable reaction process, mild alkylation conditions, low energy consumption, and high value utilization. The method converts waste polyolefins into olefin-rich intermediates and simultaneously utilizes alkylation to achieve carbon chain growth and branching structure control, thereby directionally upgrading the low-value waste polyolefin system into C8-C16 aviation kerosene hydrocarbon components. This effectively improves the problems of wide product distribution, low fuel quality, and complex post-processing associated with traditional pyrolysis methods. The resulting hydrocarbon products can be used as aviation fuel components, aviation kerosene blending components, or liquid hydrocarbon fuel components, providing a green and efficient technical path for the highly selective and high-value-added resource utilization of waste polyolefin plastics.

[0064] The above description of the embodiments is only for the purpose of helping to understand the method and core ideas of the present invention. It should be noted that those skilled in the art can make several improvements and modifications to the present invention without departing from the principles of the present invention, and these improvements and modifications also fall within the protection scope of the claims of the present invention.

Claims

1. A method for directionally preparing aviation kerosene by pyrolysis of polyolefin plastics at room temperature, comprising the following steps: Polyolefin plastics are mixed with cyclohexane, chloroaluminate ionic liquid catalyst and tert-butane chloride, and reacted at room temperature or low temperature to cause chain scission and cracking of the polyolefin plastics. The low-carbon olefins or active hydrocarbon intermediates generated by cracking are further alkylated to produce liquid-phase products containing hydrocarbons in the range of C8 to C16 aviation kerosene.

2. The method according to claim 1, characterized in that, The polyolefin plastics include one or more of the following: waste polyethylene plastics, waste polypropylene plastics, waste polyvinyl chloride plastics, and waste polystyrene plastics.

3. The method according to claim 1, characterized in that, The reaction temperature is 10~55℃; The reaction time is 2 to 24 hours.

4. The method according to claim 1, characterized in that, The mass ratio of the polyolefin plastic to cyclohexane is 1:1~12.

5. The method according to claim 1, characterized in that, The mass ratio of the polyolefin plastic to the chloroaluminate ionic liquid catalyst is 1:1~16.

6. The method according to claim 1, characterized in that, The mass ratio of the polyolefin plastic to tert-butane chloride is 1:0 to 0.

5.

7. The method according to claim 1, characterized in that, The chloroaluminate ionic liquid catalyst was prepared by reacting triethylamine hydrochloride with anhydrous aluminum chloride. The molar ratio of anhydrous aluminum chloride to triethylamine hydrochloride is 1.2 to 2.5:

1.

8. The method according to claim 1, characterized in that, The polyolefin plastic undergoes the following pretreatment: Waste polyolefin plastics are sorted, cleaned, dried and crushed to remove metals, paper scraps, inorganic fillers, pigments, oil and other impurities, resulting in pretreated polyolefin raw materials.

9. The method according to claim 1, characterized in that, After the alkylation conversion is completed, the organic product layer and the catalyst layer are separated by static separation to obtain a liquid product rich in C8-C16 aviation kerosene hydrocarbons.

10. An aviation kerosene, prepared by the method according to any one of claims 1 to 9; The hydrocarbons in the aviation kerosene include one or more of the following: C8-C16 isoalkanes, cycloalkanes, and straight-chain alkanes.

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