Method for catalyzing degradation of polyolefin mixed plastic by using molten salt

Abstract

The invention discloses a method for catalyzing degradation of polyolefin mixed plastic by using molten salt. The catalyst is composed of gallium chloride or gallium chloride and other metal chlorides, has a low melting point, high fluidity and strong Lewis acidity, and can degrade polyethylene (PE), polypropylene (PP), polystyrene (PS) plastics and mixtures thereof at 70-170 DEG C under a solvent-free condition to obtain C4-C16 + alkane, olefin and aromatic hydrocarbon. The method is suitable for actual waste plastic resource recovery, and has the advantages of mild conditions, low energy consumption, product controllability and the like.

Description

Technical Field

[0001] This invention belongs to the field of waste plastic recycling, and specifically discloses a method for the degradation of polyolefin mixed plastics by molten salt catalysis. Background Technology

[0002] Plastics, due to their excellent properties such as light weight, corrosion resistance, easy processing, and low cost, have become an indispensable basic material in modern society. However, the "white pollution" caused by large amounts of waste plastics has become a global environmental problem that urgently needs to be solved. Among them, mixed plastics are difficult to sort due to their complex origins, mixed components, and often contain impurities, making their recycling a persistent pain point in the industry. In particular, polyethylene (PE), polypropylene (PP), and polystyrene (PS), as general-purpose plastics accounting for over 65% of production, each face unique recycling obstacles: PE and PP have low C(sp) content. 3 )-C(sp 3 The skeleton of PS is chemically inert and difficult to activate under mild conditions; traditional methods require high temperature and pressure for pyrolysis. Although PS is relatively easy to degrade, its recycling efficiency is reduced due to component interference when blended with PE and PP, further exacerbating the difficulty of processing mixed plastics. Direct landfilling or incineration of these plastics not only wastes valuable petroleum-based resources but also exacerbates soil and water pollution, threatening ecological balance and human health. Achieving efficient recycling of these plastics has significant environmental and economic value. Current mixed plastic recycling technologies have many shortcomings: mechanical recycling methods produce products with poor mechanical properties, which can only be used at a lower grade; thermal pyrolysis has high energy consumption, complex product composition, and is prone to coking; solvent dissolution methods have problems with solvent toxicity and high recycling costs; existing Lewis acid catalysts (such as AlCl3) have high melting points, low contact efficiency with plastics, and mass transfer limitations, making it difficult to adapt to the unique structural characteristics of PE, PP, and PS and the complex requirements of mixed systems. Gallium chloride, as a salt with a suitable melting point and good thermal stability, may possess unique catalytic activity and mediating properties in its molten state, which is expected to overcome many bottlenecks in existing technologies. However, there are currently no reports on the application of gallium chloride molten salt to the recycling of mixed plastics. Therefore, developing a mixed plastic recycling method based on gallium chloride molten salt is of great significance for promoting the efficient, low-consumption, and environmentally friendly recycling of mixed plastics. Summary of the Invention

[0003] To address the problems in the background art, this invention discloses a method for the degradation of polyolefin mixed plastics by molten salt catalysis, so as to realize the generation of liquid hydrocarbons from waste plastics under mild conditions.

[0004] The technical solution adopted in this invention is: A method for molten salt catalytic degradation of polyolefin mixed plastics includes the following steps: adding a certain amount of waste plastic (polyethylene, polypropylene, or polystyrene and their different proportions of mixed plastics) to a container; adding gallium chloride or a mixed salt of gallium chloride and different chlorides in different masses to the container; and, without the need for external solvents, catalytic degradation at 70-170 °C. o At a temperature of C, the reaction takes 3 minutes to 12 hours, during which single or mixed plastics can undergo a degradation reaction in the presence of a catalyst, transforming into hydrocarbon products. After the reaction, chromatographic analysis reveals that the liquid hydrocarbon products in the organic phase are distributed in the C4-C6 region. 16+ Alkanes, alkenes, and aromatics.

[0005] Furthermore, the mixed plastic is polyethylene, polypropylene, and polystyrene.

[0006] Furthermore, the catalyst includes, but is not limited to, gallium chloride and its mixture with chloride salts, wherein the chloride salt mixed with gallium chloride is selected from magnesium chloride (MgCl2), calcium chloride (CaCl2), sodium chloride (NaCl), and potassium chloride (KCl).

[0007] Furthermore, the molar ratio of chloride to gallium chloride in the mixed salt catalyst is 1:1 to 1:6.

[0008] Furthermore, when the chloride salt in the mixed salt catalyst is a divalent chloride (MgCl2, CaCl2), the preferred molar ratio with GaCl3 is 1:4; when the chloride salt is a monovalent chloride (NaCl, KCl), the preferred molar ratio with GaCl3 is 1:2.

[0009] Furthermore, the preferred reaction temperature is 100-170°C. o C.

[0010] Furthermore, the preferred reaction time is 15 minutes to 12 hours.

[0011] Furthermore, the reaction system requires no external solvent and the catalyst does not need to be prepared in advance.

[0012] Furthermore, the preferred ratio of the amount of polyolefin plastic to the amount of polystyrene plastic in the mixed plastic is 5:5.

[0013] Furthermore, the liquid hydrocarbon includes, but is not limited to, C4-C4 hydrocarbons. 16+ Alkanes (chain alkanes and cyclic alkanes), alkenes (chain alkenes and cyclic alkenes), and aromatic hydrocarbons (benzene, monocyclic aromatics and polycyclic aromatics).

[0014] Compared with the prior art, the beneficial effects of the present invention are as follows: This invention discloses a method for degrading and recycling mixed plastics. Under low-temperature, solvent-free conditions, it achieves efficient pyrolysis and directional conversion of plastics through sufficient contact between low-melting-point gallium chloride molten salt and the plastic, and the catalytic effect of a strong Lewis acid. Polystyrene (PS) can be completely converted, and the conversion rates of polyethylene (PE) and polypropylene (PP) exceed 70.0 wt.%, with the conversion rate of their mixture exceeding 85.0 wt.%. The liquid hydrocarbon products cover C4-C... 16+ This invention relates to alkanes, alkenes, and aromatics. It requires no external solvent or hydrogen, operates at a significantly lower reaction temperature than traditional pyrolysis, and can directly process post-consumer mixed plastics, avoiding complex sorting processes. This provides a feasible approach for the clean, efficient, and selective chemical recycling of mixed waste plastics. Detailed Implementation

[0015] To better understand the present invention, the following embodiments further illustrate the content of the invention, but the scope of protection of the present invention is not limited to the following embodiments. Numerous specific details are set forth in the following description to provide a more thorough understanding of the invention. However, it will be apparent to those skilled in the art that the present invention can be practiced without one or more of these details.

[0016] Unless otherwise specified, the methods in the following examples are conventional methods, and the sources of the drugs are shown in the table below.

[0017] Drug source

[0018] Example 1: Molten salt catalyst catalyzes the degradation of polyethylene (PE) plastics

[0019] Weigh out 1.32 g of gallium chloride and different masses of magnesium chloride (0 g to 0.72 g, with a molar ratio of magnesium chloride to gallium chloride of 0:1 to 1:6) or other chloride salts of different types (including sodium chloride, potassium chloride, and calcium chloride) and add them to a pressure-resistant tube equipped with a PTFE rubber ring. Weigh out 1.0 g of polyethylene and add it to the pressure-resistant tube equipped with a PTFE rubber ring. Perform tests at different temperatures (70°C) without adding any external solvent. o C to 170 o C) Reaction time (3 min to 300 min).

[0020] The products were tested using the following method: Low-boiling-point liquid products (C4-C 38After the reaction was complete, the system was cooled and deionized water, dichloromethane, and the internal standard cis-decahydronaphthalene were added. The mixture was stirred until phase separation was achieved. A small amount of the organic phase solution was neutralized with sodium bicarbonate solution and filtered. The liquid products (C4-C4) in the organic phase were analyzed using a Shimadzu GC-MS 2010 (equipped with an SH-5 capillary column 30 m × 0.25 mm × 0.25 μm). 38 ).

[0021] Solid products: Anhydrous ethanol is added to the organic phase to precipitate all the solid phase. The solid residue is then filtered, collected, and dried. The collected residual solid is characterized by infrared spectroscopy. If the peaks are the same as those of the raw material, the conversion rate is calculated based on the mass of the residual solid. If the peaks are different from those of the raw material, it proves that the plastic has been completely converted.

[0022] High-boiling-point liquid products (C 39+ The filtrate was collected and evaporated using a rotary evaporator at 8 mbar pressure, 80 °C heating, and 100 rpm for 3 hours to separate the low-boiling hydrocarbon products from the heavy product. The heavy product obtained by rotary evaporation has approximately C64 carbon atoms. 16+ The heavy product was dissolved in dichloromethane, with 10 μL of cyclohexane added as an internal standard. Quantitative analysis was performed using gas chromatography (GC). The mass of the heavy product minus the mass of the volatile components calculated from the GC signal yielded the high-boiling-point liquid product (C2). 39+ (quality)

[0023] Quantitative calculation of plastic conversion rate:

[0024] Quantitative calculation of liquid and solid phase products:

[0025] Among them, liquid product C i The specific quantitative method is as follows:

[0026] The internal standard was cis-decahydronaphthalene.

[0027] Unless otherwise specified, reactant conversion, product yield, and selectivity in the following examples are calculated using the formulas above.

[0028] The results after the reaction are shown in the table below:

[0029] The results showed that the solid residues after the reaction were all white solids. Infrared spectroscopy confirmed that the solid residues were still polyethylene raw materials, and GPC analysis showed no significant decrease in molecular weight. At a reaction time of 15 min, GaCl3 and its molten salt catalysts catalyzed polyethylene at different reaction temperatures (70°C). o C-170 o C) All showed some reactivity, with the highest conversion rate reaching 80.8 wt.%. Polyethylene at 130 o The conversion rate was 70.4 wt.% at 300 min for C4-C4 reaction, and the liquid product contained C4-C4. 15 Component selectivity reaches 50.0 wt.%, in C4-C 15 The selectivity of hydrocarbon products was 86.3 wt.% for alkanes (including chain alkanes and cyclic alkanes), 13.0 wt.% for alkenes (including chain alkenes and cyclic alkenes), and 0.7 wt.% for aromatic hydrocarbons.

[0030] Example 2: Molten salt catalyst catalyzes the degradation of polypropylene (PP) plastics

[0031] 0.18 g of anhydrous MgCl2 and 1.32 g of anhydrous GaCl3 (molar ratio 1:4) were weighed and added to a pressure-resistant tube equipped with a PTFE rubber ring. 1.0 g of polypropylene was also weighed and added to the pressure-resistant tube. The mixture was heated to 130°C without any added solvent. o Reacting at C for different times (3 min to 300 min).

[0032] The results after the reaction are shown in the table below:

[0033] The results showed that the solid residue after the reaction was a white solid. Infrared spectroscopy confirmed that the solid residue was still polypropylene raw material, and GPC analysis showed no significant decrease in its molecular weight. The conversion rate of polypropylene after 300 min of reaction was calculated to be 76.3 wt.%, and the liquid product contained C4-C... 15 The component selectivity reached 55.0 wt.%, in the C4-C range. 15 The selectivity of hydrocarbon products was 90.6 wt.% for alkanes (including chain alkanes and cyclic alkanes), 8.9 wt.% for alkenes (including chain alkenes and cyclic alkenes), and 0.5 wt.% for aromatic hydrocarbons.

[0034] Example 3: Molten Salt Catalysis of Polystyrene (PS) Plastic Degradation

[0035] Weigh out 1.32 g of gallium chloride and different masses of magnesium chloride (0 g to 0.72 g, with a molar ratio of magnesium chloride to gallium chloride of 0:1 to 1:6) or other chloride salts of different types (including sodium chloride, potassium chloride, and calcium chloride) and add them to a pressure-resistant tube equipped with a PTFE rubber ring. Weigh out 1.0 g of polystyrene and add it to the pressure-resistant tube equipped with a PTFE rubber ring. Perform tests at different temperatures (70°C) without adding any external solvent. o C to 170 o C) Reaction time (3 min to 300 min).

[0036] The results after the reaction are shown in the table below:

[0037] The results showed that, at a reaction time of 15 min, GaCl3 and its molten salt catalysts catalyzed polystyrene at different reaction temperatures (70°C and 100°C). o C-170 o C) All exhibited certain reactivity, with a reaction temperature of 100°C. o The conversion of C4-C4+ was relatively significant. After reacting for 30 minutes with a 1:4 molar ratio mixture of magnesium chloride and gallium chloride as a catalyst, the remaining solid was a brownish-green powder. Infrared spectroscopy confirmed that the solid residue was no longer polystyrene, and GPC analysis showed a significant decrease in the molecular weight of the remaining solid, indicating that the remaining solid was no longer a polymer. Polystyrene was considered completely converted. At 300 minutes of reaction, the solid yield was 17.4 wt.%, and the liquid yield was 83.6 wt.%. The liquid product contained C4-C4+. 15 The component selectivity reached 64.6 wt.%, in the C4-C range. 15 The selectivity for aromatic hydrocarbons in hydrocarbon products exceeds 99.5 wt.%, in the C6-C range. 15 Among the aromatic hydrocarbon products, the selectivity for benzene was 65.0 wt.%, the selectivity for monocyclic aromatic hydrocarbons was 23.9 wt.%, and the selectivity for polycyclic aromatic hydrocarbons was 11.1 wt.

[0038] Example 4: Co-degradation of PE and PS plastics catalyzed by molten salt catalyst

[0039] Weigh out 0.18 g of anhydrous MgCl2 and 1.32 g of anhydrous GaCl3 (molar ratio 1:4) and add them to a pressure-resistant tube equipped with a PTFE rubber ring. Weigh out 0.5 g of polyethylene and 0.5 g of polystyrene and add them to the pressure-resistant tube. Under conditions without added solvent, heat at 130°C... o Reacting at C for different times (3 min to 300 min).

[0040] The results after the reaction are shown in the table below:

[0041] The results showed that during the co-conversion of PE and PS mixtures, the residual solid infrared spectroscopy characterization indicated that the characteristic peaks of PS disappeared after 30 min of reaction, while the characteristic peaks of PE were retained, suggesting complete PS conversion. Calculations showed that after 300 min of reaction, the plastic conversion rate was 84.9 wt.%, the liquid product yield was 74.4 wt.%, and the C4-C... 15 The component selectivity was 47.8 wt.%, in the C4-C range. 15 The hydrocarbon products showed an alkane selectivity of 39.2 wt.% (with carbon numbers concentrated between C4 and C8), an aromatic hydrocarbon selectivity of 60.6 wt.%, and almost no alkenes. In the C6-C... 15 Among the aromatic hydrocarbon products, the selectivity for benzene was 43.0 wt.%, the selectivity for monocyclic aromatic hydrocarbons was 28.9 wt.%, and the selectivity for polycyclic aromatic hydrocarbons was 28.1 wt.

[0042] Example 5: Co-degradation of PP and PS plastics catalyzed by molten salt catalyst

[0043] 0.18 g of anhydrous MgCl2 and 1.32 g of anhydrous GaCl3 (molar ratio 1:4) were weighed and added to a pressure-resistant tube equipped with a PTFE rubber ring. 0.5 g of polypropylene and 0.5 g of polystyrene were also weighed and added to the pressure-resistant tube. The mixture was heated to 130 °C without any added solvent. o Reacting at C for different times (3 min to 300 min).

[0044] The results after the reaction are shown in the table below:

[0045] The results showed that during the co-conversion of PP and PS, the residual solid infrared spectroscopy characterization indicated that the characteristic peak of PS disappeared after 30 min of reaction, while the characteristic peak of PE was retained, indicating that PS was considered to be completely converted. Calculations showed that after 300 min of reaction, the plastic conversion rate was 85.2 wt.%, the liquid product yield was 72.1 wt.%, and the C4-C... 15 The component selectivity was 57.7 wt.%, in the C4-C range. 15 The hydrocarbon products showed an alkane selectivity of 42.6 wt.% (with carbon numbers concentrated between C4 and C8), an aromatic hydrocarbon selectivity of 57.4 wt.%, and almost no alkenes. In the C6-C... 15 Among the aromatic hydrocarbon products, the selectivity for benzene was 40.5 wt.%, the selectivity for monocyclic aromatic hydrocarbons was 33.5 wt.%, and the selectivity for polycyclic aromatic hydrocarbons was 26.0 wt.

[0046] Example 6: Co-degradation of real mixed plastics catalyzed by molten salt catalyst

[0047] Weigh out 0.36 g of anhydrous MgCl2 and 2.64 g of anhydrous GaCl3 (molar ratio 1:4) and add them to a pressure-resistant tube equipped with a PTFE rubber ring. Weigh out 1 g of a real mixed plastic (a mixture of polyolefin and polystyrene plastics in different mass ratios, including a 1:1 mass ratio of polyethylene plastics (for disposable gloves and self-sealing bags) and polypropylene plastics (for disposable straws and centrifuge tubes), and a 1:1 mass ratio of polystyrene plastics (for foam boxes and packing boxes) and add it to the pressure-resistant tube. Heat the mixture at 170°C without any added solvent. o The reaction was carried out at C for 12 hours.

[0048] The results after the reaction are shown in the table below:

Claims

1. A method for molten salt catalytic degradation of polyolefin mixed plastics, comprising the following steps: adding a certain amount of waste plastic (polyethylene, polypropylene, or polystyrene and mixed plastics in different proportions) to a container; adding gallium chloride or a mixed salt of gallium chloride and different chlorides in different masses to the container; and, without the addition of external solvents, catalytic degradation at 70-170 °C. o At a temperature of C, the reaction takes 3 minutes to 12 hours, during which single or mixed plastics can undergo a degradation reaction in the presence of a catalyst, transforming into hydrocarbon products. After the reaction, chromatographic analysis reveals that the liquid hydrocarbon products in the organic phase are distributed in the C4-C6 region. 16+ Alkanes, alkenes, and aromatics.

2. The method according to claim 1, characterized in that, The mixed plastic is polyethylene, polypropylene, and polystyrene.

3. The method according to claim 1, characterized in that, The catalyst includes, but is not limited to, gallium chloride and its mixture with chloride salts, wherein the chloride salt mixed with gallium chloride is selected from magnesium chloride (MgCl2), calcium chloride (CaCl2), sodium chloride (NaCl), and potassium chloride (KCl).

4. The method according to claim 3, characterized in that, The molar ratio of chloride to gallium chloride in the mixed salt catalyst is 1:1 to 1:

6.

5. The method according to claim 3, characterized in that, When the chloride salt in the mixed salt catalyst is a divalent chloride (MgCl2, CaCl2), the molar ratio with GaCl3 is 1:4; when the chloride salt is a monovalent chloride (NaCl, KCl), the molar ratio with GaCl3 is 1:

2.

6. The method according to claim 1, characterized in that, The reaction temperature is 70-170°C. o C.

7. The method according to claim 1, characterized in that, The reaction time ranges from 3 minutes to 12 hours.

8. The method according to claim 1, characterized in that, The reaction system requires no external solvent and the catalyst does not need to be prepared in advance.

9. The method according to claim 1, characterized in that, The ratio of polyolefin plastic to polystyrene plastic in the mixed plastic is 9:1 to 3:

7.

10. The method according to claim 1, characterized in that, The liquid hydrocarbons include, but are not limited to, C4-C4 hydrocarbons. 16+ Alkanes (chain alkanes and cyclic alkanes), alkenes (chain alkenes and cyclic alkenes), and aromatic hydrocarbons (benzene, monocyclic aromatics and polycyclic aromatics).

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