A method for recovering PE plastic by low-temperature oxidation cracking

Abstract

The present invention belongs to the technical field of plastic recycling, and discloses a method for low-temperature oxidation cracking and recycling of PE plastic, which comprises the following steps: S1: dispersing PE plastic and a catalyst in water to obtain a dispersion liquid mixed with the catalyst and PE plastic; S2: transferring the above dispersion liquid to a high-pressure reactor, performing a catalytic reaction at a set air pressure and a set temperature, and reacting for a set time to convert the PE dispersed in the water into a low-molecular-weight fatty carboxylic acid in one step; S3: after the above reaction is completed, post-processing is performed to collect the cracking product. The present invention has mild conditions, a high yield of high-value oil products, and is suitable for polyethylene products of different molecular weights and densities. The present invention solves the problem that PE plastic is difficult to crack and recycle, and solves the problem of mixed cracking and recycling of PE plastics of different sources and different molecular weights.

Description

Technical Field

[0001] The invention belongs to the technical field of plastic cracking and recycling, and in particular relates to a method for low-temperature oxidation cracking and recycling of polyethylene (PE) plastic. Background Art

[0002] In view of the strong chemical stability, difficulty in recycling and large scale of PE plastics, chemical recycling methods for PE plastic cracking have received increasing attention and research in recent years. In 2020, Scott et al. reported the catalytic degradation of PE (M) at 280 °C using Pt / γ-Al2O3 as a catalyst. w ,3.52×10 3 g / mol) for 24 h, and the aromatized long-chain alkane compound (~C 30 )(Science 2020,370,437-441). In 2022, Liang Wang et al. reported the low-temperature conversion of polyethylene into olefins. By reacting rationally designed ZSM-5 zeolite nanosheets with PE raw materials under flowing hydrogen as carrier gas at 280°C, light hydrocarbons (C1-C7) were obtained with a yield of 74.6% (J.Am.Chem.Soc.2022,144,31,14269-4277). In recent years, research on high-value recycling of PE plastics has begun to show results, mainly focusing on hydrogenolysis and direct pyrolysis methods. However, the reaction temperatures of hydrogenolysis and direct pyrolysis methods are relatively high, often ≥200°C, and the energy consumption is relatively high. Therefore, given the inherent chemical stability and large scale of PE plastics, it is still necessary to find new methods that are more economical and have milder conditions.

[0003] Therefore, the present invention proposes a new method that can crack polyethylene plastic into low molecular weight and high-value chemicals at a lower temperature, providing an effective strategy for achieving economic recycling of polyethylene. Summary of the invention

[0004] The purpose of the present invention is to provide a method for low-temperature oxidative cracking and recycling of PE plastics, which solves the problem of difficult recycling of PE plastics through comprehensive improvement and coordinated work of components, ratios and process conditions.

[0005] The present invention provides the following technical solutions:

[0006] A method for low-temperature oxidative cracking and recovery of PE plastics, characterized in that it comprises the following steps:

[0007] S1: dispersing PE plastic and catalyst into water to obtain a dispersion of the catalyst and PE plastic;

[0008] S2: transferring the above dispersion into a high-pressure reactor, performing a catalytic reaction at a set air pressure and a set temperature, and reacting for a set time, so that the PE dispersed in the water is converted into a low molecular weight fatty carboxylic acid in one step;

[0009] S3: After the above reaction is completed, post-treatment is performed to collect the cleavage products.

[0010] The PE plastic in step S1 includes: low-density polyethylene (LDPE), high-density polyethylene (HDPE), including PE plastic material products and mixed PE plastic materials.

[0011] The mixed PE plastic is a mixed plastic of LDPE and HDPE in equal mass ratio.

[0012] The catalyst in step S1 is a supported catalyst, with TiO2 as a carrier and loaded with Ru and Pt elements.

[0013] In step S1, the mass ratio of the catalyst to the PE plastic is 1:2.

[0014] The temperature set in step S2 is 160° C., the air pressure set is 1.5 MPa, and the reaction time set is 12-48 hours.

[0015] The reaction products in step S3 include liquid, gaseous and solid products.

[0016] Compared with the prior art, the present invention has the following beneficial effects:

[0017] 1. The low-temperature oxidative cracking and recovery method provided by the present invention can crack polyethylene plastic into low-molecular-weight, high-value chemicals at a lower temperature through comprehensive improvement and coordinated work of components, ratios and process conditions, thereby solving the problem of difficulty in recycling PE plastics and providing an effective strategy for achieving economic recycling of polyethylene.

[0018] 2. The present invention uses Ru / TiO2 as a catalyst and water as a dispersant at 160°C and an air pressure of 1.5MPa to directly convert PE into low molecular weight fatty acids. The conditions are mild and the steps are simple and efficient.

[0019] 3. The high-value oil product of the present invention has a high yield, reaching a ratio of 80% (oil product quality / original feed PE quality) or above, and the product has a high selectivity for carboxylic acid.

[0020] 4. The method provided by the present invention has mild conditions, high yield of high-value oil products, and is applicable to polyethylene products of different molecular weights and densities. It is not only applicable to LDPE, but also to HDPE, and exhibits high activity to PE mixtures of different types and sources, and has good substrate universality. The present invention not only solves the problem that PE plastics are difficult to crack and recycle, but also solves the problem of mixed cracking and recycling of PE plastics of different sources and different molecular weights.

[0021] 5. The present invention reasonably matches the reaction materials, catalysts and reaction conditions to make them work together. The solid product content after the reaction is extremely small, and it is mainly concentrated in the high-value liquid product, thereby improving the recovery efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 Schematic diagram of a specific oxidative cracking process according to an embodiment of the present invention.

[0023] Figure 2 It is the infrared spectrum (FTIR) diagram of the oil product of Examples 5-9 of the present invention.

[0024] Figure 3 The nuclear magnetic resonance of the oil product of Examples 5-9 of the present invention is 1 H spectrum. DETAILED DESCRIPTION

[0025] The present invention is further described below in conjunction with the accompanying drawings, but the present invention is not limited thereto. The experimental methods used in the following examples are conventional methods unless otherwise specified. Unless otherwise specifically stated, the various raw materials, reagents, instruments and equipment used in the present invention can be purchased from the market or can be prepared by existing methods.

[0026] The following is combined with Figure 1-3 The present invention is described in detail through Examples 1-10.

[0027] Embodiment 1:

[0028] See attached Figure 1 The method for low-temperature oxidative cracking and recycling of PE plastics provided in this embodiment is specifically an oxidative cracking method for LDPE particles, which specifically includes the following steps:

[0029] (1) Dispersing LDPE particles and catalyst in water to obtain a dispersion of the catalyst and LDPE particles: Specifically, 50 mg of LDPE particles (M w ,2259g / mol), 25mg catalyst Ru / TiO2 was added into 10mL H2O to obtain a dispersion.

[0030] (2) The dispersion was transferred to a high-pressure reactor, filled with 1.5 MPa high-purity air, stirred at 400 r, and the temperature was raised to 160°C at a rate of 5°C / min and maintained for 12 h to directly convert the LDPE component into low molecular weight fatty acids.

[0031] (3) After the reaction reaches the set time, the reaction mixture is cooled to room temperature and then post-processed: the reaction mixture is collected with ethanol and dichloromethane in sequence, mixed and filtered, and the filtrate is concentrated by vacuum distillation to collect a high-value brown-yellow liquid product;

[0032] (4) The structure of the recovered yellow liquid product was characterized by NMR and IR, and its molecular weight distribution was characterized by gel permeation chromatography. It can be found that the mass percentage of the liquid product after 12 hours of reaction in this example / the mass percentage of the original input LDPE particles is 67%, and the product components in the brown-yellow liquid are low molecular weight fatty carboxylic acids.

[0033] Embodiment 2:

[0034] The method for low-temperature oxidative cracking and recycling of PE plastic provided in this embodiment is based on Example 1, and further oxidative cracking is performed on LDPE particles, which specifically includes the following steps:

[0035] (1) Take 50 mg of LDPE particles (M w ,2259g / mol), 25mg catalyst Ru / TiO2 was added into 10mL H2O to prepare a dispersion.

[0036] (2) The dispersion was transferred to a high-pressure reactor, filled with 1.5 MPa high-purity air, stirred at 400 r, and the temperature was raised to 160°C at a rate of 5°C / min and maintained for 24 h to directly convert the LDPE component into low molecular weight fatty acids.

[0037] (3) After the reaction is completed, the temperature naturally drops to room temperature and post-treatment is performed: the reaction solution is collected with ethanol and dichloromethane in sequence, mixed and filtered, and the filtrate is concentrated by distillation under reduced pressure to collect a high-value brown-yellow liquid product.

[0038] (4) The structure of the liquid product was characterized by NMR and IR, and its molecular weight distribution was characterized by GPC. The mass of the liquid product after 24 hours of reaction was 90% of the mass of the original LDPE particles, and the product structure was low molecular weight fatty carboxylic acid.

[0039] Embodiment 3:

[0040] The method for low-temperature oxidative cracking and recycling of PE plastics provided in this embodiment is based on Examples 1 and 2, and oxidative cracking is performed on LDPE particles, which specifically includes the following steps:

[0041] (1) Take 50 mg of LDPE particles (Mw ,2259g / mol), 25mg catalyst Ru / TiO2 was added into 10mL H2O to prepare a dispersion.

[0042] (2) The dispersion was transferred to a high-pressure reactor, filled with 1.5 MPa high-purity air, stirred at 400 r, and raised to 160°C at a rate of 5°C / min and maintained for 36 h, so that the LDPE component was directly converted into low molecular weight fatty acids.

[0043] (3) The reaction mixture is cooled to room temperature naturally and then post-processed. The reaction solution is collected with ethanol and dichloromethane in turn, mixed and filtered, and the filtrate is concentrated by vacuum distillation to collect a high-value brown-yellow liquid product.

[0044] (4) The structure of the liquid product was characterized by NMR and IR, and its molecular weight distribution was characterized by GPC. The mass of the liquid product after 36 hours of reaction was 76% of the mass of the original LDPE particles, and the product structure was low molecular weight fatty carboxylic acid.

[0045] Embodiment 4:

[0046] The method for low-temperature oxidative cracking and recycling of PE plastics provided in this embodiment is based on Examples 1-3, and oxidative cracking is performed on LDPE particles, which specifically includes the following steps:

[0047] (1) 50mg LDPE granules (M w ,2259 g / mol), 25 mg of catalyst Ru / TiO2 was added into 10 mL of H2O to prepare a dispersion.

[0048] (2) The dispersion was transferred to a high-pressure reactor, filled with 1.5 MPa high-purity air, stirred at 400 r, and raised to 160°C at a rate of 5°C / min and maintained for 48 h, so that the LDPE component was directly converted into low molecular weight fatty acids.

[0049] (3) The reaction mixture is cooled to room temperature naturally and then post-processed. The reaction solution is collected with ethanol and dichloromethane in turn, mixed and filtered, and the filtrate is concentrated by vacuum distillation to collect a high-value brown-yellow liquid product.

[0050] (4) The structure of the liquid product was characterized by NMR and IR, and its molecular weight distribution was characterized by GPC. The mass of the liquid product after 36 hours of reaction was 70% of the mass of the original LDPE particles, and the product structure was low molecular weight fatty carboxylic acid.

[0051] Embodiment 5:

[0052] The method for low-temperature oxidative cracking and recycling of PE plastic provided in this embodiment is based on Examples 1-4, and the final product (actual product) of PE prepared by low-temperature oxidative cracking of the rubber-tipped dropper is subjected to low-temperature oxidative cracking, which specifically includes the following steps:

[0053] (1) Take 50 mg of rubber dropper fragment (M w ,117029g / mol), 25mg catalyst Ru / TiO2 was added into 10mL H2O to prepare a dispersion.

[0054] (2) The dispersion was transferred to a high-pressure reactor, filled with 1.5 MPa high-purity air, stirred at 400 r, and heated to 160° C. at a rate of 5° C. / min and maintained for 24 h, so that the PE component was directly converted into low molecular weight fatty acids.

[0055] (3) The reaction mixture is cooled to room temperature naturally and then post-processed. The reaction solution is collected with ethanol and dichloromethane in turn, mixed and filtered, and the filtrate is concentrated by vacuum distillation to collect a high-value brown-yellow liquid product.

[0056] (4) The structure of the liquid product was characterized by NMR and IR, and its molecular weight distribution was characterized by GPC. The mass percentage of the liquid product of the reaction / the mass percentage of the original rubber-head dropper fragments was 86%, M w It is 1055g / mol, and the product structure is low molecular weight fatty carboxylic acid.

[0057] Embodiment 6:

[0058] The method for low-temperature oxidative cracking and recycling of PE plastic provided in this embodiment is based on Examples 1-5, and low-temperature oxidative cracking is performed on the actual PE product plastic ziplock bag, which specifically includes the following steps:

[0059] (1) Take 50 mg of plastic ziplock bag fragments (M w ,126388g / mol), 25mg catalyst Ru / TiO2 was added into 10mL H2O to prepare a dispersion.

[0060] (2) The dispersion was transferred to a high-pressure reactor, filled with 1.5 MPa high-purity air, stirred at 400 r, and heated to 160° C. at a rate of 5° C. / min and maintained for 24 h, so that the PE component was directly converted into low molecular weight fatty acids.

[0061] (3) The reaction mixture is cooled to room temperature naturally and then post-processed. The reaction solution is collected with ethanol and dichloromethane in turn, mixed and filtered, and the filtrate is concentrated by vacuum distillation to collect a high-value brown-yellow liquid product.

[0062] (4) The structure of the liquid product was characterized by NMR and IR, and its molecular weight distribution was characterized by GPC. The mass of the liquid product of the reaction / the mass percentage of the original ziplock bag fragments was 88%, M w It is 1414 g / mol, and the product structure is low molecular weight fatty carboxylic acid.

[0063] Embodiment 7:

[0064] The method for low-temperature oxidative cracking and recycling of PE plastic provided in this embodiment is based on Examples 1-6, and low-temperature oxidative cracking is performed on commercial LDPE powder, which specifically includes the following steps:

[0065] (1) Take 50 mg of commercial LDPE powder (M w ,64598g / mol), 25mg catalyst Ru / TiO2 was added into 10mL H2O to prepare a dispersion.

[0066] (2) The dispersion was transferred to a high-pressure reactor, filled with 1.5 MPa high-purity air, stirred at 400 r, and the temperature was raised to 160°C at a rate of 5°C / min and maintained for 24 h to directly convert the LDPE component into low molecular weight fatty acids.

[0067] (3) The reaction mixture is cooled to room temperature naturally and then post-processed. The reaction solution is collected with ethanol and dichloromethane in turn, mixed and filtered, and the filtrate is concentrated by vacuum distillation to collect a high-value brown-yellow liquid product.

[0068] (4) The structure of the liquid product was characterized by NMR and IR, and its molecular weight distribution was characterized by GPC. The mass of the liquid product of the reaction was 90% of the mass of the original commercial LDPE powder. w The product structure is low molecular weight fatty carboxylic acid.

[0069] Embodiment 8:

[0070] The method for low-temperature oxidative cracking and recycling of PE plastic provided in this embodiment is based on Examples 1-7, and low-temperature oxidative cracking is performed on HDPE powder, which specifically includes the following steps:

[0071] (1) Take 50 mg HDPE powder (M w ,106935g / mol), 25mg catalyst Ru / TiO2 was added into 10mL H2O to prepare a dispersion.

[0072] (2) The dispersion was transferred to a high-pressure reactor, filled with 1.5 MPa high-purity air, stirred at 400 r, and raised to 160°C at a rate of 5°C / min and maintained for 24 h, so that the HDPE component was directly converted into low molecular weight fatty acids.

[0073] (3) The reaction mixture is cooled to room temperature naturally and then post-processed. The reaction solution is collected with ethanol and dichloromethane in turn, mixed and filtered, and the filtrate is concentrated by vacuum distillation to collect a high-value brown-yellow liquid product.

[0074] (4) The structure of the liquid product was characterized by NMR and IR, and its molecular weight distribution was characterized by GPC. The mass percentage of the liquid product of the reaction / the mass percentage of the original HDPE powder input was 107%, M w It is 609 g / mol, and the product structure is low molecular weight fatty carboxylic acid.

[0075] Embodiment 9:

[0076] The method for low-temperature oxidative cracking and recycling of PE plastics provided in this embodiment is based on Examples 1-8, and the PE mixed plastics are subjected to low-temperature oxidative cracking, which specifically comprises the following steps:

[0077] (1) 10 mg each of LDPE pellets, commercial LDPE powder, rubber-tipped dropper fragments, ziplock bag fragments, and HDPE powder and 25 mg of catalyst Ru / TiO2 were added to 10 mL of H2O to prepare a dispersion.

[0078] (2) The dispersion was transferred to a high-pressure reactor, filled with 1.5 MPa high-purity air, stirred at 400 r, and the temperature was raised to 160°C at a rate of 5°C / min and maintained for 24 h to directly convert the PE component into low molecular weight fatty acids.

[0079] (3) The reaction mixture is cooled to room temperature naturally and then post-processed. The reaction solution is collected with ethanol and dichloromethane in turn, mixed and filtered, and the filtrate is concentrated by vacuum distillation to collect a high-value brown-yellow liquid product.

[0080] (4) The structure of the liquid product was characterized by NMR and IR, and its molecular weight distribution was characterized by GPC. The mass of the liquid product in the reaction was 110% of the mass of the original PE input. w It is 515g / mol, and the product structure is low molecular weight fatty carboxylic acid.

[0081] Embodiment 10:

[0082] The method for low-temperature oxidative cracking and recycling of PE plastic provided in this embodiment is based on Examples 1 and 2, and the low-temperature oxidative cracking of LDPE particles is carried out, which specifically comprises the following steps:

[0083] (1) Take 50 mg of LDPE particles (M w ,2259g / mol), 25mg catalyst Pt / TiO2 was added into 10mL H2O to prepare a dispersion.

[0084] (2) The dispersion was transferred to a high-pressure reactor, filled with 1.5 MPa high-purity air, stirred at 400 r, and the temperature was raised to 160°C at a rate of 5°C / min and maintained for 24 h to directly convert the LDPE component into low molecular weight fatty acids.

[0085] (3) The reaction mixture is cooled to room temperature naturally and then post-processed. The reaction solution is collected with ethanol and dichloromethane in turn, mixed and filtered, and the filtrate is concentrated by vacuum distillation to collect a high-value brown-yellow liquid product.

[0086] (4) The structure of the liquid product was characterized by NMR and IR, and its molecular weight distribution was characterized by GPC. The mass of the liquid product after 24 hours of reaction was 84% ​​of the mass of the original LDPE particles, and the product structure was low molecular weight fatty carboxylic acid.

[0087] Comparative Example 1: Catalyst-free oxidative cracking process of LDPE particles.

[0088] (1) 50mg LDPE granules (M w ,2259g / mol) was added into 10mL H2O to prepare a dispersion, and the dispersion was transferred into a high-pressure reactor, filled with 1.5MPa high-purity air, stirred at 400r, and heated to 160℃ at a rate of 5℃ / min and maintained for 24h.

[0089] (2) The reaction mixture was cooled to room temperature and then post-processed. The reaction mixture was collected with ethanol and dichloromethane in turn, mixed and filtered, and the filtrate was concentrated by distillation under reduced pressure to collect the product.

[0090] (3) The amount of liquid product collected after 24 h of reaction was very small and was not characterized.

[0091] Comparative Example 2: Pyrolysis process of LDPE particles under N2 atmosphere.

[0092] (1) 50mg LDPE granules (M w ,2259g / mol) was added into 10mL H2O to prepare a dispersion, and the dispersion was transferred into a high-pressure reactor, filled with 1.5MPa high-purity N2, stirred at 400r, and heated to 160℃ at a rate of 5℃ / min and maintained for 24h.

[0093] (2) The reaction mixture was cooled to room temperature and then post-processed. The reaction mixture was collected with ethanol and dichloromethane in turn, mixed and filtered, and the filtrate was concentrated by distillation under reduced pressure to collect the product.

[0094] (3) There is no liquid product after 24 hours of reaction.

[0095] The main parameters of the above embodiments and comparative examples are shown in Table 1.

[0096] Table 1

[0097]

[0098] The plastic recycling method for low-molecular-weight fatty carboxylic acids obtained by low-temperature catalytic oxidation of polyethylene (PE) plastics provided in the above embodiments of the present invention solves the problem that PE plastics are difficult to crack and recycle, and solves the problem of mixed cracking and recycling of PE plastics of different molecular weights from different sources. The recycling method comprises the following steps: dispersing PE plastics and catalysts into water, transferring the dispersion into a high-pressure reactor, filling with air at a set pressure, stirring, reacting at a set temperature for several hours, and cracking the PE plastic into low-molecular-weight fatty acids. The method of the present invention has mild conditions, a high yield of high-value oil products, and is suitable for polyethylene products of different molecular weights and densities.

[0099] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A method for recovering PE plastic by low-temperature oxidation cracking, characterized in that: It includes the following steps: S1: dispersing PE plastic and catalyst into water to obtain a dispersion of the catalyst and PE plastic; The PE plastic includes: low-density polyethylene LDPE, high-density polyethylene HDPE, including PE plastic material products and mixed PE plastic materials; The catalyst is a supported catalyst, with TiO2 as the carrier and loaded with Ru and Pt elements; the mass ratio of the catalyst to the PE plastic is 1:2; S2: The above dispersion is transferred to a high-pressure reactor, and a catalytic reaction is carried out at an air pressure of 1.5 MPa and a temperature of 160°C for a set reaction time of 12-48 hours, so that the PE dispersed in the water is converted into a low molecular weight fatty carboxylic acid in one step; S3: After the above reaction is completed, post-processing is performed to collect the cleavage products; the cleavage reaction products include liquid, gaseous and solid products; the content of the solid product after the reaction is very small, and it is mainly concentrated in the high-value liquid product; The post-treatment comprises: collecting the reaction solution with ethanol and dichloromethane in sequence, filtering after mixing, distilling and concentrating the filtrate under reduced pressure, and collecting a high-value brown-yellow liquid product, wherein the product component is a low-molecular-weight fatty carboxylic acid.

2. The method for recovering PE plastic by low-temperature oxidation cracking according to claim 1, characterized in that: The mixed PE plastic is a mixed plastic of LDPE and HDPE in equal mass ratio.

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