Method for producing C6-C8 cycloalkane mixture and C15 cycloalkane by directional depolymerization of mixed plastics

Abstract

The present invention discloses a method for the directional depolymerization of mixed plastics to produce a C6-C8 cycloalkane mixture and C15 cycloalkane, belonging to the technical field of solid waste recycling and utilization. Among them, the mixed plastics include various oxygen-containing aromatic polymers. The rhodium-based niobium pentoxide catalyst is used to carry out a hydrodeoxygenation reaction to depolymerize the mixed plastics in two stages with a programmed temperature rise in a hydrogen atmosphere in an organic solvent system. In the first stage, the hydrodeoxygenation reaction is carried out at a temperature of 120-250 °C to prepare and separate C15 cycloalkane. In the second stage, the hydrodeoxygenation reaction is continued at a temperature of 220-300 °C to prepare and separate the C6-C8 cycloalkane mixture. The present invention can maximize the retention of the carbon skeleton of each oxygen-containing aromatic plastic, has atom economy, solves the problems of high energy consumption and high cost in the pretreatment step of chemical depolymerization of mixed plastics, and provides a sustainable technical route for the resource recovery of polluted mixed plastics.

Description

Technical Field

[0001] The present invention belongs to the technical field of solid waste recycling, and particularly relates to a method for the directional depolymerization of mixed plastics to produce a C6-C8 cycloalkane mixture and C15 cycloalkane. Background Art

[0002] With the development of industry and the improvement of people's living standards, the demand for plastic products has increased significantly. The annual output of plastic products is large, and the waste rate is high. Efficient recycling of waste plastics is an inevitable direction for realizing resource circulation and sustainable development. Physical recycling is currently the most direct and effective method for recycling waste plastics. However, complex pretreatment steps such as classification and cleaning not only increase the energy consumption cost but also lead to a decline in the performance of plastics during the treatment process. In contrast, chemical-based directional upgrading recycling is a more effective recycling method for realizing the recycling of carbon resources at the molecular level.

[0003] Oxygen-containing aromatic polymers are an important class of polymers in plastics, including common polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polyphenylene oxide (PPO), polycarbonate (PC), etc., and are widely used in the electronics and electrical industries, packaging industry, automotive industry, aerospace, construction industry, medical industry, textile industry, etc. If waste oxygen-containing aromatic polymers are directly incinerated or landfilled, it will cause serious environmental pollution and resource waste. Therefore, it is necessary to develop an efficient method for the upgrading and recycling of waste oxygen-containing aromatic polymers. Currently, extensive research has been conducted on the upgrading and recycling of single-component oxygen-containing aromatic polymers. For example, PET and PBT can be upgraded to terephthalic acid (TPA), dimethyl terephthalate (DMT), terephthalamide (TAM), and light aromatic hydrocarbon mixtures (BTX) such as benzene, toluene, and xylene, cycloalkanes, etc. through hydrolysis, alcoholysis, ammonolysis, glycolysis, hydrodeoxygenation (HDO), etc. PC can be upgraded to bisphenol A or polycyclic cycloalkanes, and PPO can be upgraded to dimethylphenol or m-dimethylcyclohexane. Among the above upgrading and recycling products, cycloalkanes have unique chemical structures and physical properties and can be widely used as gasoline, aviation and jet fuels, liquid organic hydrogen carriers (LOHCs), precursors for polymer monomer synthesis, etc. However, there is less research on the upgrading and recycling of mixed plastics in the prior art. In fact, most waste plastics are mixtures. In addition, the current chemical-based directional upgrading recycling of plastics still has the following problems:

[0004] (1) The cleavage of C-C bonds caused by non-precious metal active centers such as Ni and Co results in a decrease in the number of C atoms in the target product, reducing the effective utilization rate of carbon resources in oxygen-containing aromatic polymers (patent literature CN117531508A, etc.). The noble metal catalyst system still needs to be developed (the current noble metal catalyst system only focuses on Ru-based catalysts).

[0005] (2) None of the current mixed plastic catalytic systems has a suitable catalytic heating-up step to maximize the retention of the carbon skeletons of each plastic.

[0006] (3) The vast majority of the work still focuses on treating single-component, pre-sorted, pre-cleaned, pre-decolored, or transparent oxygen-containing aromatic waste plastics. However, in the actual treatment of waste oxygen-containing aromatic plastics, the additional pre-sorting, pre-cleaning, and pre-decoloring make the recycling cumbersome and increase the post-treatment cost (Patent Document CN118791367A, etc.).

[0007] Therefore, for mixed oxygen-containing aromatic waste plastics (including various truly contaminated plastics of colored, black, and transparent materials that have not been pre-sorted, pre-cleaned, or pre-decolored), there is an urgent need to develop an efficient chemical recycling system without pretreatment that can maximize the retention of the carbon skeletons of each plastic. Summary of the Invention

[0008] To solve the deficiencies existing in the above-mentioned prior art, the present invention provides a method for the directional depolymerization of mixed plastics to produce a C6-C8 cycloalkane mixture and C15 cycloalkane. This method uses a rhodium-based niobium pentoxide catalyst to catalytically carry out a stepwise temperature-raising reaction of the mixed plastics to obtain high-value cycloalkane products directionally, and the catalyst can be recycled, with good atom economy.

[0009] The specific technical solutions adopted are as follows:

[0010] A method for the directional depolymerization of mixed plastics to produce a C6-C8 cycloalkane mixture and C15 cycloalkane, wherein the mixed plastics include various oxygen-containing aromatic polymers. Using a rhodium-based niobium pentoxide catalyst, a hydrodeoxygenation reaction is carried out in two stages with a programmed temperature increase in an organic solvent system under a hydrogen atmosphere to depolymerize the mixed plastics. In the first stage, a hydrodeoxygenation reaction is carried out at a temperature of 120 - 250 °C to prepare and separate C15 cycloalkane. In the second stage, the hydrodeoxygenation reaction is continued at a temperature of 220 - 300 °C to prepare and separate a C6-C8 cycloalkane mixture;

[0011] The rhodium-based niobium pentoxide catalyst includes a carrier acidic solid oxide Nb2O5 and zero-valent rhodium supported thereon, and the rhodium loading is 4 wt% - 6 wt% (obtained by ICP testing).

[0012] The zero-valent rhodium on the Rh / Nb2O5 catalyst has excellent ability to activate and dissociate hydrogen, promoting the hydrogenation of C=C bonds; the acidic solid oxide Nb2O5 has a strong affinity for benzene rings and C=O bonds, which is beneficial to the hydrogenolysis of C-O bonds.

[0013] Specifically, the mixed plastics include polyphenylene ether, polycarbonate, polyethylene terephthalate, and polybutylene terephthalate.

[0014] Preferably, the rhodium loading in the rhodium-based niobium pentoxide catalyst is 5 wt%, and the mass ratio of the mixed plastic to the rhodium-based niobium pentoxide catalyst is 1:0.005 - 5, further 1:0.5 - 5. Under the above condition parameters, the rhodium-based niobium pentoxide catalyst has good catalytic effect and can prepare the product C6-C8 cycloalkane mixture and C15 cycloalkane in high yield, which helps to efficiently utilize the carbon resources in the waste mixed plastic.

[0015] Preferably, the rhodium-based niobium pentoxide catalyst is prepared by the following method: Prepare a mixture containing rhodium chloride, acidic solid oxide niobium pentoxide and deionized water, stir the mixture at room temperature until dry, then further dry it by heating, and reduce the dried solid in a reducing gas atmosphere at 300 - 400 °C for 4 - 5 h to obtain the rhodium-based niobium pentoxide catalyst.

[0016] More preferably, the reducing gas atmosphere is a hydrogen-argon mixed atmosphere, and the heating rate during the reduction process is 1 - 3 °C / min.

[0017] The rhodium-based niobium pentoxide catalyst has good catalytic activity and stability and can be recycled multiple times. After the reacted catalyst is recovered, washed and dried, it can be directly reused and still can prepare the target product in high yield. Experiments prove that after being reused 6 times, the yield of the target product obtained by the catalytic depolymerization of the mixed plastic by this catalyst is still >90%.

[0018] Preferably, the organic solvent is decane.

[0019] More preferably, the dosage ratio of the mixed plastic to the decane solvent is 1 g:2 - 200 mL, further 1 g:80 - 200 mL.

[0020] Preferably, the hydrodeoxygenation reaction is carried out under the condition of a pressure of 1 - 2 MPa.

[0021] Specifically, the method for the directional depolymerization of mixed plastic to produce C6-C8 cycloalkane mixture and C15 cycloalkane specifically includes the following steps:

[0022] S1. Use the mixed plastic, rhodium-based niobium pentoxide catalyst and organic solvent decane to construct a reaction system, place the reaction system under a hydrogen atmosphere and at a temperature of 120 - 250 °C for the first-stage hydrodeoxygenation reaction for 8 - 24 hours. After the reaction is completed, quench and cool down, and perform solid-liquid separation on the obtained reaction solution. Separate C15 cycloalkane (1,1'-(1-methylethylidene)bicyclohexane) from the liquid (including C15 cycloalkane and organic solvent decane), and the solid (including the unreacted remaining mixed plastic and rhodium-based niobium pentoxide catalyst) is continued to be used;

[0023] S2. Use the solid obtained in step S1 and the organic solvent decane to construct a reaction system. Place this reaction system under a hydrogen atmosphere and carry out a second-stage hydrodeoxygenation reaction at a temperature of 220 - 300 °C for 8 - 32 hours. After the reaction is completed, quench and cool down, and perform solid-liquid separation on the resulting reaction solution. Separate C6 - C8 cycloalkanes from the liquid (including C6 - C8 cycloalkanes and decane), and the solid (including the catalyst) can be recycled after recovery.

[0024] In the above steps S1 and S2, rotary evaporation can be used to separate the target product and the organic solvent decane in the liquid, and the separated decane can be recycled.

[0025] Specifically, the mixed plastic is waste mixed plastic in the form of pre-crushed flakes, granules or powders (millimeter scale). Correspondingly, the mixed plastic can be directly depolymerized by the method of the present invention without washing. The reaction catalytic system of the present invention has strong anti-interference ability, and can produce the target product with high yield even in the case of contaminated raw materials. The mixed plastic may include PPO white particles, PC optical discs, PET water bottles, PBT white bandages, or colored contaminated PPO black particles, PC insulating boxes, PET colored water bottles, PBT colored bandages, etc. Of course, the corresponding pure chemicals can also be used to construct the reaction system.

[0026] Preferably, the conditions for the first-stage hydrodeoxygenation reaction are 1 - 2 MPa, 160 - 200 °C, and 14 - 18 h.

[0027] Preferably, the conditions for the second-stage hydrodeoxygenation reaction are 1 - 2 MPa, 250 - 270 °C, and 22 - 26 h.

[0028] The present invention also provides a method for treating waste mixed plastic, including treating waste mixed plastic by using the method for producing a C6 - C8 cycloalkane mixture and a C15 cycloalkane by the directional depolymerization of the mixed plastic described above.

[0029] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0030] (1) The present invention overcomes the cleavage of C - C bonds caused by non-noble metal active centers such as Ni and Co, increases the number of C atoms in the target product, improves the effective utilization rate of carbon resources in oxygen-containing aromatic polymers, and develops a noble metal catalyst system for the complete hydrogenation of mixed plastics, which is conducive to understanding the reaction pathway of the degradation of oxygen-containing aromatic plastics and guiding the design and development of subsequent other HDO catalysts.

[0031] (2) The present invention constructs a multi-stage programmed temperature catalytic process, which avoids the cleavage of the C-C bond between the bicyclics of polycarbonate, obtains C15 cycloalkane products that are more valuable than monocyclic products, maximally retains the carbon skeleton of each plastic, has atom economy, and the catalyst used in the system can be recycled without calcination reduction, which is beneficial to the circular economy.

[0032] (3) The reaction system developed by the present invention is applicable to the degradation of actual waste oxygen-containing aromatic plastics, without additional pre-sorting, pre-cleaning, and pre-decolorization, has strong anti-interference ability, and still has excellent effects when applied to the depolymerization of various truly contaminated plastics, and has good industrial application prospects. Description of the Drawings

[0033] Figure 1 It is an XRD characterization result diagram of a rhodium-based niobium pentoxide Rh / Nb2O5 catalyst (Rh loading is 5 wt%).

[0034] Figure 2 It is a roadmap of the first-stage hydrodeoxygenation reaction.

[0035] Figure 3 It is a gas chromatogram of the C15 cycloalkane obtained in Example 1.

[0036] Figure 4 It is a roadmap of the second-stage hydrodeoxygenation reaction.

[0037] Figure 5 It is a gas chromatogram of the C6-C8 cycloalkane mixture obtained in Example 1. Detailed Description of the Invention

[0038] To make the objectives, features, and advantages of the present invention more obvious and understandable, the following provides a detailed description through specific embodiments. Many specific details are set forth in the following description to fully understand the present invention. However, the present invention can be implemented in many other ways different from those described herein, and those skilled in the art can make similar improvements without departing from the connotation of the present invention. Therefore, the present invention is not limited by the specific embodiments disclosed below. The technical features in each embodiment of the present invention can be combined accordingly without conflict.

[0039] The operating methods of the following examples without specific conditions are generally carried out under conventional conditions or according to the conditions recommended by the manufacturer. The content not described in detail in this specification belongs to the prior art well-known to those skilled in the art. The experimental materials used in the following examples can be obtained from conventional biochemical reagent companies without special instructions.

[0040] In the following examples, the rhodium-based niobium pentoxide catalyst (Rh / Nb2O5 catalyst) was prepared by the following incipient wetness impregnation method:

[0041] In a 100 mL beaker, rhodium chloride, Nb2O5, and a small amount (5 - 10 mL) of deionized water were added, and the mixture was continuously stirred at room temperature until dry, and then dried in an oven at 60 °C for 12 h. The dried solid was ground evenly and placed in a tubular furnace for reduction at 350 °C for 4 h (reduction gas: 5% H2 / 95% Ar; heating rate: 2 °C / min; gas flow rate: 30 mL / min) to obtain the Rh / Nb2O5 catalyst.

[0042] In the Rh / Nb2O5 catalyst, the carrier is the acidic solid oxide Nb2O5, and the rhodium loading can be adjusted by changing the feeding amount of rhodium chloride. The rhodium loading is generally controlled at 4 wt% - 6 wt%. Experiments have shown that the best catalytic performance for the depolymerization reaction can be achieved when the rhodium loading is 5 wt%.

[0043] The XRD characterization results of the corresponding active metals of the Rh / Nb2O5 catalyst (Rh loading of 5 wt%) and the acidic solid oxide Nb2O5 are as Figure 1 shown (the PDF#27 - 1312 marked in the figure refers to the XRD standard card data), and no diffraction peak corresponding to Rh 0 (zero-valent rhodium) was detected, indicating that Rh 0 is highly dispersed on Nb2O5.

[0044] Nb2O5 can be purchased or synthesized in the laboratory.

[0045] Example 1

[0046] In a high-pressure autoclave reactor equipped with a magnetic stirrer, a thermocouple, and a programmable temperature controller, 0.05 g of mixed plastic powder (0.0125 g each of PPO, PC, PET, and PBT), 0.05 g of Rh / Nb2O5 catalyst (Rh loading of 5 wt%), and 5 mL of decane solvent were added. After sealing the high-pressure autoclave reactor, the gas in the autoclave was replaced with hydrogen three times, and then hydrogen was pressurized and filled at ambient temperature to a pressure of 1.5 MPa. Stirring and heating were started to raise the temperature of the reaction system to 180 °C, and the reaction was carried out at this temperature for 16 h (the reaction roadmap is as Figure 2 shown). After the reaction, the high-pressure autoclave was quenched to ambient temperature in an ice-water bath. The solid-liquid mixture after the reaction was filtered. The solid was unreacted plastic and catalyst, and the liquid was analyzed by gas chromatography (GC) with dodecane as the internal standard and methyl formate as the co-solvent to obtain C15 cycloalkanes (the GC spectrum is as Figure 3As shown, where the truncated peak is the solvent peak and has no effect on the illustrated information), the yield is 100% (relative to the reactant PC plastic component).

[0047] Add the solid after the first-stage reaction (unreacted plastic and catalyst) and 5 mL of decane solvent to the autoclave reactor. After sealing, replace the gas in the autoclave with hydrogen three times, and then pressurize and fill with hydrogen at ambient temperature to make the pressure reach 1.5 MPa. Turn on the stirring and heating to raise the temperature of the reaction system to 250 °C and react at this temperature for 24 h (the reaction route diagram is as Figure 4 shown). After the reaction is completed, quench the autoclave in an ice-water bath to ambient temperature. Filter the solid-liquid mixture after the reaction. The solid is the catalyst, and the liquid uses dodecane as the internal standard and methyl formate as the co-solvent, and then analyze it by gas chromatography (GC) to obtain a C6-C8 cycloalkane mixture (the GC chromatogram is as Figure 5 shown, where the truncated peak is the solvent peak and has no effect on the illustrated information), the yield is 100% (relative to the reactant PPO, PET, PBT plastic components), among which the yield of cyclohexane is 11.7%, the yield of methylcyclohexane is 21.9%, and the yield of dimethylcyclohexane is 66.4%.

[0048] Example 2

[0049] Add 0.05 g of transparent actual mixed plastic (0.0125 g each of PPO white particles, PC CD, PET water bottle, PBT white bandage), 0.05 g of Rh / Nb2O5 catalyst (Rh loading is 5 wt%), and 5 mL of decane solvent into an autoclave reactor equipped with an electromagnetic stirrer, thermocouple, and programmable temperature controller. After sealing the autoclave reactor, replace the gas in the autoclave with hydrogen three times, and then pressurize and fill with hydrogen at ambient temperature to make the pressure reach 1.5 MPa. Turn on the stirring and heating to raise the temperature of the reaction system to 180 °C and react at this temperature for 16 h. After the reaction is completed, quench the autoclave in an ice-water bath to ambient temperature. Filter the solid-liquid mixture after the reaction. The solid is the unreacted plastic and catalyst, and the liquid uses dodecane as the internal standard and methyl formate as the co-solvent, and then analyze it by gas chromatography (GC) to obtain a C15 cycloalkane yield of 100% (relative to the reactant PC plastic component).

[0050] The solid after the first-stage reaction (unreacted plastics and catalyst), 5 mL of decane solvent were added to an autoclave reactor. After sealing, the gas in the autoclave was replaced with hydrogen three times, and then hydrogen was pressurized and filled into the autoclave at ambient temperature to make the pressure reach 1.5 MPa. Stirring and heating were started to raise the temperature of the reaction system to 250 °C, and the reaction was carried out at this temperature for 24 h. After the reaction, the autoclave was quenched to ambient temperature in an ice-water bath. The solid-liquid mixture after the reaction was filtered. The solid was the catalyst, and the liquid was analyzed by gas chromatography (GC) with dodecane as the internal standard and methyl formate as the co-solvent. The yield of C6-C8 cycloalkane mixture was 93.2% (relative to the PPO, PET, and PBT plastic components of the reactants), among which the yield of cyclohexane was 38.0%, the yield of methylcyclohexane was 15.1%, and the yield of dimethylcyclohexane was 40.1%.

[0051] Example 3

[0052] 0.05 g of contaminated colored actual mixed plastics (0.0125 g each of PPO black particles, PC insulating box, PET colored water bottle, and PBT colored bandage), 0.05 g of Rh / Nb2O5 catalyst (Rh loading of 5 wt%), and 5 mL of decane solvent were added to an autoclave reactor equipped with an electromagnetic stirrer, a thermocouple, and a programmable temperature controller. After sealing the autoclave reactor, the gas in the autoclave was replaced with hydrogen three times, and then hydrogen was pressurized and filled into the autoclave at ambient temperature to make the pressure reach 1.5 MPa. Stirring and heating were started to raise the temperature of the reaction system to 180 °C, and the reaction was carried out at this temperature for 16 h. After the reaction, the autoclave was quenched to ambient temperature in an ice-water bath. The solid-liquid mixture after the reaction was filtered. The solid was unreacted plastics and catalyst, and the liquid was analyzed by gas chromatography (GC) with dodecane as the internal standard and methyl formate as the co-solvent. The yield of C15 cycloalkane was 100% (relative to the PC plastic component of the reactants).

[0053] The solid after the first-stage reaction (unreacted plastics and catalyst), 5 mL of decane solvent were added to an autoclave reactor. After sealing, the gas in the autoclave was replaced with hydrogen three times, and then hydrogen was pressurized and filled into the autoclave at ambient temperature to make the pressure reach 1.5 MPa. Stirring and heating were started to raise the temperature of the reaction system to 260 °C, and the reaction was carried out at this temperature for 24 h. After the reaction, the autoclave was quenched to ambient temperature in an ice-water bath. The solid-liquid mixture after the reaction was filtered. The solid was the catalyst, and the liquid was analyzed by gas chromatography (GC) with dodecane as the internal standard and methyl formate as the co-solvent. The yield of C6-C8 cycloalkane mixture was 90.9% (relative to the PPO, PET, and PBT plastic components of the reactants), among which the yield of cyclohexane was 30.4%, the yield of methylcyclohexane was 19.8%, and the yield of dimethylcyclohexane was 40.7%.

[0054] Example 4

[0055] In an autoclave reactor equipped with an electromagnetic stirrer, a thermocouple, and a programmable temperature controller, 0.05 g of mixed plastic powder (0.0125 g each of PPO, PC, PET, and PBT), 0.05 g of Rh / Nb2O5 catalyst (Rh loading is 5 wt%), and 5 mL of decane solvent were added. After sealing the autoclave reactor, the gas in the autoclave was replaced with hydrogen three times, and then hydrogen was pressurized and filled into the autoclave at ambient temperature to make the pressure reach 1.5 MPa. Stirring and heating were started to raise the temperature of the reaction system to 160 °C, and the reaction was carried out at this temperature for 18 h. After the reaction, the autoclave was quenched to ambient temperature in an ice-water bath. The solid-liquid mixture after the reaction was filtered. The solid was unreacted plastic and catalyst, and the liquid was analyzed by gas chromatography (GC) with dodecane as the internal standard and methyl formate as the co-solvent, and the yield of C15 cycloalkanes was obtained as 90.3% (relative to the PC plastic component of the reactants).

[0056] The solid (unreacted plastic and catalyst) after the first-stage reaction and 5 mL of decane solvent were added to the autoclave reactor. After sealing, the gas in the autoclave was replaced with hydrogen three times, and then hydrogen was pressurized and filled into the autoclave at ambient temperature to make the pressure reach 1.5 MPa. Stirring and heating were started to raise the temperature of the reaction system to 240 °C, and the reaction was carried out at this temperature for 28 h. After the reaction, the autoclave was quenched to ambient temperature in an ice-water bath. The solid-liquid mixture after the reaction was filtered. The solid was the catalyst, and the liquid was analyzed by gas chromatography (GC) with dodecane as the internal standard and methyl formate as the co-solvent, and the yield of C6-C8 cycloalkane mixture was obtained as 93.2% (relative to the PPO, PET, and PBT plastic components of the reactants), among which the yield of cyclohexane was 19.3%, the yield of methylcyclohexane was 27.9%, and the yield of dimethylcyclohexane was 46.0%.

[0057] Example 5

[0058] In an autoclave reactor equipped with an electromagnetic stirrer, a thermocouple, and a programmable temperature controller, 0.05 g of mixed plastic powder (0.0125 g each of PPO, PC, PET, and PBT), 0.2 g of Rh / Nb2O5 catalyst (Rh loading of 5 wt%), and 10 mL of decane solvent were added. After sealing the autoclave reactor, the gas in the autoclave was replaced with hydrogen three times, and then hydrogen was pressurized and filled at ambient temperature to a pressure of 1.5 MPa. Stirring and heating were started, and the reaction system was heated to 200 °C and reacted at this temperature for 10 h. After the reaction, the autoclave was quenched to ambient temperature in an ice-water bath. The solid-liquid mixture after the reaction was filtered. The solid was unreacted plastic and catalyst, and the liquid was analyzed by gas chromatography (GC) using dodecane as the internal standard and methyl formate as the co-solvent, and the yield of C15 cycloalkanes was obtained as 95.3% (relative to the PC plastic component of the reactants).

[0059] The solid (unreacted plastic and catalyst) after the first-stage reaction and 10 mL of decane solvent were added to the autoclave reactor. After sealing, the gas in the autoclave was replaced with hydrogen three times, and then hydrogen was pressurized and filled at ambient temperature to a pressure of 1.5 MPa. Stirring and heating were started, and the reaction system was heated to 280 °C and reacted at this temperature for 22 h. After the reaction, the autoclave was quenched to ambient temperature in an ice-water bath. The solid-liquid mixture after the reaction was filtered. The solid was the catalyst, and the liquid was analyzed by gas chromatography (GC) using dodecane as the internal standard and methyl formate as the co-solvent, and the yield of C6-C8 cycloalkane mixture was obtained as 100% (relative to the PPO, PET, and PBT plastic components of the reactants), where the yield of cyclohexane was 31.5%, the yield of methylcyclohexane was 31.7%, and the yield of dimethylcyclohexane was 36.8%.

[0060] Example 6

[0061] In an autoclave reactor equipped with an electromagnetic stirrer, a thermocouple, and a programmable temperature controller, 0.05 g of mixed plastic powder (0.0125 g each of PPO, PC, PET, and PBT), 0.2 g of Rh / Nb2O5 catalyst (Rh loading of 5 wt%), and 2 mL of decane solvent were added. After sealing the autoclave reactor, the gas in the autoclave was replaced with hydrogen three times, and then hydrogen was pressurized and filled at ambient temperature to a pressure of 2 MPa. Stirring and heating were started, and the reaction system was heated to 180 °C and reacted at this temperature for 24 h. After the reaction, the autoclave was quenched to ambient temperature in an ice-water bath. The solid-liquid mixture after the reaction was filtered. The solid was unreacted plastic and catalyst, and the liquid was analyzed by gas chromatography (GC) using dodecane as the internal standard and methyl formate as the co-solvent, and the yield of C15 cycloalkanes was obtained as 96.7% (relative to the PC plastic component of the reactants).

[0062] The solid after the first-stage reaction (unreacted plastics and catalyst), along with 2 mL of decane solvent, was added to an autoclave reactor. After sealing, the gas inside the autoclave was replaced with hydrogen three times, and then hydrogen was pressurized and filled into the autoclave at ambient temperature until the pressure reached 2 MPa. Stirring and heating were started, and the reaction system was heated to 220 °C and reacted at this temperature for 32 h. After the reaction ended, the autoclave was quenched to ambient temperature in an ice-water bath. The solid-liquid mixture after the reaction was filtered. The solid was the catalyst, and the liquid used dodecane as the internal standard and methyl formate as the co-solvent, and then was analyzed by gas chromatography (GC). The yield of the C6-C8 cycloalkane mixture was 89.4% (relative to the PPO, PET, and PBT plastic components of the reactants), among which the yield of cyclohexane was 26.3%, the yield of methylcyclohexane was 24.7%, and the yield of dimethylcyclohexane was 38.4%.

[0063] Comparative Example 1

[0064] In an autoclave reactor equipped with an electromagnetic stirrer, a thermocouple, and a programmable temperature controller, 0.05 g of mixed plastic powder (0.0125 g each of PPO, PC, PET, and PBT), 0.05 g of Rh / Nb2O5 catalyst (Rh loading of 5 wt%), and 5 mL of decane solvent were added. After sealing the autoclave reactor, the gas inside the autoclave was replaced with hydrogen three times, and then hydrogen was pressurized and filled into the autoclave at ambient temperature until the pressure reached 1.5 MPa. Stirring and heating were started, and the reaction system was heated to 260 °C and reacted at this temperature for 24 h. After the reaction ended, the autoclave was quenched to ambient temperature in an ice-water bath. The solid-liquid mixture after the reaction was filtered. The solid was the catalyst, and the liquid used dodecane as the internal standard and methyl formate as the co-solvent, and then was analyzed by gas chromatography (GC). A C6-C9 cycloalkane mixture was obtained with a yield of 100%, among which the yield of cyclohexane was 22.2%, the yield of methylcyclohexane was 19.5%, the yield of dimethylcyclohexane was 30.4%, the yield of ethylcyclohexane was 11.8%, and the yield of isopropylcyclohexane was 16.2%.

[0065] The above-described embodiments have elaborated on the technical solutions of the present invention. It should be understood that the above are only specific embodiments of the present invention and do not limit the present invention. Any modifications, supplements, or substitutions in a similar manner within the principle scope of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for the directional depolymerization of mixed plastics to produce a C6-C8 cycloalkane mixture and C15 cycloalkane, characterized in that, The described mixed plastics include various oxygen-containing aromatic polymers. Using a rhodium-based niobium pentoxide catalyst, a two-stage temperature-programmed hydrodeoxygenation reaction occurs in an organic solvent system under a hydrogen atmosphere to depolymerize the mixed plastics. In the first stage, the hydrodeoxygenation reaction is carried out at a temperature of 120 - 250 °C to prepare and separate C15 cycloalkanes. In the second stage, the hydrodeoxygenation reaction continues at a temperature of 220 - 300 °C to prepare and separate a C6 - C8 cycloalkane mixture; The rhodium-based niobium pentoxide catalyst includes the carrier acidic solid oxide Nb2O5 and zero-valent rhodium supported thereon, with the rhodium loading being 4 wt% - 6 wt%. The rhodium-based niobium pentoxide catalyst is prepared by the following method: Prepare a mixture containing rhodium chloride, the acidic solid oxide niobium pentoxide, and deionized water. Stir the mixture at room temperature until dry, then further dry it by heating. Reduce the dried solid in a reducing gas atmosphere at 300 - 400 °C for 4 - 5 h to obtain the rhodium-based niobium pentoxide catalyst; The mixed plastics include polyphenylene ether, polycarbonate, polyethylene terephthalate, and polybutylene terephthalate.

2. The method for producing a C6-C8 cycloalkane mixture and a C15 cycloalkane by the directional depolymerization of mixed plastics according to claim 1, characterized in that, The rhodium loading in the rhodium-based niobium pentoxide catalyst is 5 wt%, and the mass ratio of the mixed plastics to the rhodium-based niobium pentoxide catalyst is 1:0.005 - 5.

3. The method for producing C6-C8 cycloalkane mixture and C15 cycloalkane by the directional depolymerization of mixed plastics according to claim 1, characterized in that, The organic solvent is decane.

4. The method for producing C6-C8 cycloalkane mixture and C15 cycloalkane by depolymerizing mixed plastics in a directed manner according to claim 3, characterized in that, The dosage ratio of the mixed plastics to the decane solvent is 1 g:2 - 200 mL.

5. The method for producing C6-C8 cycloalkane mixture and C15 cycloalkane by the directional depolymerization of mixed plastics according to claim 1, characterized in that, The hydrodeoxygenation reaction is carried out under a pressure of 1 - 2 MPa.

6. The method for producing a C6-C8 cycloalkane mixture and a C15 cycloalkane by the directional depolymerization of mixed plastics according to claim 1, characterized in that, Specifically, it includes the following steps: S1. Construct a reaction system using the mixed plastics, the rhodium-based niobium pentoxide catalyst, and the organic solvent. Place the reaction system under a hydrogen atmosphere and carry out the first-stage hydrodeoxygenation reaction at a temperature of 120 - 250 °C for 8 - 24 hours. After the reaction is completed, quench and cool the temperature. Perform solid-liquid separation on the obtained reaction solution, separate C15 cycloalkanes from the liquid, and continue to use the solid; S2. Construct a reaction system using the solid obtained in step S1 and the organic solvent. Place the reaction system under a hydrogen atmosphere and carry out the second-stage hydrodeoxygenation reaction at a temperature of 220 - 300 °C for 8 - 32 hours. After the reaction is completed, quench and cool the temperature. Perform solid-liquid separation on the obtained reaction solution, and separate C6 - C8 cycloalkanes from the liquid; The described organic solvent is decane.

7. The method for producing C6-C8 cycloalkane mixture and C15 cycloalkane by the directional depolymerization of mixed plastics according to claim 1, characterized in that, The mixed plastics are pre-crushed millimeter-sized flaky, granular, or powdery waste mixed plastics.

8. A method for treating waste mixed plastics, characterized in that, It includes a method for treating waste mixed plastics by applying the method for the directional depolymerization of mixed plastics according to any one of claims 1 - 7 to produce a C6 - C8 cycloalkane mixture and C15 cycloalkanes.

Images