Chemical degradation and resource utilization method of waste polyester plastic

Abstract

The invention discloses a waste polyester plastic chemical degradation and resource utilization method, which comprises: (1) adding waste polyester plastic subjected to physical resolution into a reaction kettle, adding NaOH and monoethanolamine as alcoholysis catalysts, introducing nitrogen gas to remove air, and heating to carry out a catalytic degradation reaction; (2) after the reaction is finished, carrying out reduced pressure distillation on a reaction system to respectively obtain a low-boiling-point small-molecule fraction, a mixture of monoethanolamine and sodium hydroxide, an ethylene glycol fraction, residual N, N '-bis (2-ethoxyl) terephthalamide in the system or residual N, N'-bis (2-ethoxyl) terephthalamide and polyester plastic which is not completely degraded; if two components remain in the system, the two components are separated through reduced pressure filtration. The method provided by the invention realizes efficient catalytic degradation and reutilization of the waste polyester plastic under mild conditions, and has the advantages of short process route, proper reaction conditions, high degradation efficiency, capability of realizing resource reutilization of wastes and the like.

Description

Technical Field

[0001] The present invention relates to the technical field of chemical recycling of organic chemical products, and more specifically, to a method for chemical degradation and resource utilization of waste polyester plastics. Background Art

[0002] The development of synthetic chemistry has played an important role in promoting the progress of human civilization. Polymer materials represented by plastics have developed rapidly in the 20th century, greatly improving the living standards of modern humans. Among them, representative polymer materials include: polyolefins polymerized with ethylene and propylene as monomers, which are often used as shopping bags and food cling films; polyesters polymerized with terephthalic acid and ethylene glycol as monomers, which are often used as materials for white plastic bottles and polyester clothing; resins polymerized with styrene, butadiene, acrylonitrile, etc. as monomers can be used as hard shells, with advantages such as light weight, corrosion resistance, and high cost performance, and can replace metal materials in whole or in part. However, the widespread use of these polymer materials has also brought serious environmental pollution problems. The use of plastics is huge, and they have the advantages of being inexpensive and durable, but they are often abandoned in the environment after use, and the number of recycling times is relatively small. In the natural environment, the life cycle of these materials can reach hundreds of years, and they are difficult to be naturally degraded, and some small particles can gradually become microplastics, enter the internal organs of fish and shrimps and then enter the human body. Therefore, chemical degradation of these polymer materials, obtaining monomers or other useful small molecules, and reusing them not only has good environmental benefits, but also has significant economic value.

[0003] For materials that are difficult to degrade, such as polyethylene and polypropylene, the current research focus is on high-temperature pyrolysis or catalytic degradation, converting them into small molecules such as carbon monoxide and hydrogen, which can then be used to synthesize other types of chemicals. The difficulty of this method is that the molecular structure of these polymer materials is relatively stable, and the breaking of CC and CH chemical bonds in the molecules requires higher reaction temperatures and energy. Therefore, the economic efficiency of this method needs to be improved.

[0004] For polymer compounds containing ester bonds or ether bonds, such as polyesters and polyethers, the current research focus is on using liquid alkalis such as sodium hydroxide and potassium hydroxide as catalysts to convert these polymer materials into sodium carboxylates or sodium alcoholates at high temperatures, such as Figure 1 The difficulty of the research lies in the fact that this type of catalytic reaction requires a high reaction temperature and a long reaction time, and at this time, the reactants and reaction intermediates are prone to produce by-products containing double bonds, aldehyde groups and other functional groups, which causes the final product to turn black and deteriorate in performance, making it difficult to function as a chemical raw material again, and the economic efficiency is low.

[0005] Therefore, if the catalytic degradation and recycling of polymer materials can be achieved under relatively mild reaction conditions (using appropriate reaction temperature, pressure, and suitable catalyst), it will have higher environmentally friendly benefits and economic value, and conform to the development concept of green environmental protection and circular economy. Summary of the invention

[0006] The purpose of the present invention is to overcome the deficiencies of the above-mentioned prior art and provide a method for chemical degradation and resource utilization of waste polyester plastics. According to the structural characteristics of polyester-based polymer materials, waste polyester plastics (copolymers of terephthalic acid and ethylene glycol) with a molecular weight between 20,000 and 50,000 are selected, and a suitable catalytic reaction system and a catalyst with excellent performance are used to achieve efficient degradation of the raw materials under mild reaction conditions, converting them into N,N'-bis(2-hydroxyethyl)terephthalamide and ethylene glycol. By using suitable separation and purification technology, the two products can be efficiently separated and reused, and ideal experimental results have been achieved.

[0007] In order to achieve the above object, the present invention adopts the following technical solution:

[0008] A method for chemical degradation and resource utilization of waste polyester plastics, comprising the following steps:

[0009] (1) Chemical catalytic degradation of waste polyester plastics: waste polyester plastics that have been physically split are added to a reactor, NaOH and monoethanolamine are added as alcoholysis catalysts, nitrogen is introduced to remove air in the system, and then the temperature is raised to carry out a catalytic degradation reaction;

[0010] (2) Separation and purification of catalytic degradation products: After the reaction is completed, the reaction system is subjected to vacuum distillation to obtain a low-boiling point small molecule fraction, a mixture of monoethanolamine and sodium hydroxide, and an ethylene glycol fraction, respectively. The remaining N,N'-bis(2-hydroxyethyl)terephthalamide or the remaining N,N'-bis(2-hydroxyethyl)terephthalamide and polyester plastic that has not been completely degraded in the system; if two components remain in the system after vacuum distillation, they are separated by vacuum filtration.

[0011] Furthermore, in step (1), the mass ratio of the waste polyester plastic added to the reaction system to the sodium hydroxide and monoethanolamine is 1:0.4:4.

[0012] Furthermore, the catalytic degradation reaction temperature is 60-90° C., and the reaction time is 3-6 hours.

[0013] Furthermore, in step (2), the heating temperatures during the reduced pressure distillation are 50, 90, and 140° C., respectively, the vacuum degree of the circulating water pump is 0.096 MPa, and the reduced pressure distillation time at the three temperatures is 2 h.

[0014] Furthermore, the waste polyester plastic is physically cut, split, cleaned, and air-dried to obtain physically split waste polyester plastic.

[0015] Furthermore, the waste polyester plastic is polyethylene terephthalate with a molecular weight between 20,000 and 50,000.

[0016] Furthermore, the method further comprises step (3): reusing the mixture of monoethanolamine and sodium hydroxide obtained in step (2) for the catalytic degradation reaction in step (1).

[0017] The beneficial effects of the present invention are:

[0018] (1) Under relatively mild experimental conditions, efficient catalytic degradation and reuse of waste polyester plastics were achieved, completing the recycling of waste polymer materials;

[0019] (2) The two-component catalyst used is abundant in source, low in price and has little environmental impact;

[0020] (3) The entire process route is short, the reaction conditions are suitable, and the degradation efficiency is high, which has significant environmental significance and market promotion value. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 The reaction roadmap for the traditional degradation of waste polyester;

[0022] Figure 2 The figure is a reaction route diagram for the catalytic degradation of waste polyester according to the present invention. DETAILED DESCRIPTION

[0023] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0024] Comparative Example 1

[0025] The waste polyester plastic raw materials were physically split and cleaned, cut into 5*5mm shapes, washed with tap water, then washed with deionized water, and air-dried; 100g was transferred to a 1L reactor, and 40g NaOH was added as an alcoholysis catalyst; nitrogen was introduced to remove the air in the system, and then the temperature was raised to 90°C for catalytic degradation reaction for 6 hours. The results showed that the polyester plastic did not degrade.

[0026] Comparative Example 2

[0027] The waste polyester plastic raw materials were physically split and cleaned, cut into 5*5mm shapes, washed with tap water, then washed with deionized water, and air-dried; 100g was transferred to a 1L reactor, and 400g of monoethanolamine was added as an alcoholysis catalyst; nitrogen was introduced to remove the air in the system, and then the temperature was raised to 90°C for catalytic degradation reaction for 6 hours. The results showed that the polyester plastic did not degrade.

[0028] Example 1

[0029] The waste polyester plastic raw materials are physically split and cleaned: the waste polyester plastic is cut into 5*5mm shapes and sizes, washed with tap water, then washed with deionized water, and air-dried; 100g of the physically split waste polyester plastic is transferred to a 1L reactor, and 40g NaOH and 400g monoethanolamine are added as alcoholysis catalysts; nitrogen is introduced to remove the air in the system, and then the temperature is raised to 90°C to carry out catalytic degradation reaction for 3h; after the reaction, the above system is subjected to reduced pressure distillation (the vacuum degree of the circulating water pump is 0.096Mpa, the operating temperatures are 50, 90, and 140°C, and the time is 2h), respectively obtaining a low-boiling point small molecule fraction, a mixture of monoethanolamine and sodium hydroxide, and an ethylene glycol fraction, and the remaining components in the system are N,N'-bis(2-hydroxyethyl)terephthalamide.

[0030] Example 2

[0031] The waste polyester plastic raw materials are physically split and cleaned: the waste polyester plastic is cut into 5*5mm shapes and sizes, washed with tap water, then washed with deionized water, and air-dried; 100g of the physically split waste polyester plastic is transferred to a 1L reactor, and 40g NaOH and 400g monoethanolamine are added as alcoholysis catalysts; nitrogen is introduced to remove the air in the system, and then the temperature is raised to 80°C to carry out catalytic degradation reaction for 4h; after the reaction, the above system is subjected to reduced pressure distillation (the vacuum degree of the circulating water pump is 0.096Mpa, the operating temperatures are 50, 90, and 140°C, and the time is 2h), respectively, to obtain a low-boiling point small molecule fraction, a mixture of monoethanolamine and sodium hydroxide, and an ethylene glycol fraction, and the remaining components in the system are N,N'-bis(2-hydroxyethyl)terephthalamide.

[0032] Example 3

[0033] The waste polyester plastic raw materials were physically split and cleaned: the waste polyester plastic was cut into 5*5mm shapes and sizes, washed with tap water, then washed with deionized water, and air-dried; 100g of the physically split waste polyester plastic was transferred to a 1L reactor, and 40g NaOH and 400g monoethanolamine were added as alcoholysis catalysts; nitrogen was introduced to remove the air in the system, and then the temperature was raised to 70°C for catalytic degradation reaction for 5h; after the reaction, the system was subjected to reduced pressure distillation (the vacuum degree of the circulating water pump was 0.096Mpa, the operating temperatures were 50, 90, and 140°C, and the time was 2h), respectively, to obtain low-boiling point small molecule fractions, a mixture of monoethanolamine and sodium hydroxide, and ethylene glycol fractions, and the remaining components in the system were N,N'-bis(2-hydroxyethyl)terephthalamide and polyester plastic raw materials that had not yet completely reacted. The remaining two components were separated by reduced pressure filtration.

[0034] Example 4

[0035] The waste polyester plastic raw materials were physically split and cleaned: the waste polyester plastic was cut into 5*5mm shapes and sizes, washed with tap water, then washed with deionized water, and air-dried; 100g was transferred to a 1L reactor, and 40g NaOH and 400g monoethanolamine were added as alcoholysis catalysts; nitrogen was introduced to remove the air in the system, and then the temperature was raised to 60°C for catalytic degradation reaction for 6h; after the reaction, the above system was subjected to reduced pressure distillation (the vacuum degree of the circulating water pump was 0.096Mpa, the operating temperatures were 50, 90, and 140°C, and the time was 2h), respectively, to obtain low-boiling point small molecule fractions, a mixture of monoethanolamine and sodium hydroxide, and ethylene glycol fractions, and the remaining components in the system were N,N'-bis(2-hydroxyethyl)terephthalamide and polyester plastic raw materials that had not yet completely reacted. The remaining two components were separated by reduced pressure filtration.

[0036] Table 1 shows the degradation test results of waste polyester plastic raw materials of Comparative Example 1-Comparative Example 2 and Example 1-Example 4. It can be seen that the present invention achieves efficient catalytic degradation and repeated reuse of waste polyester plastics under mild experimental conditions.

[0037] Table 1: Test results of the products

[0038]

[0039] The waste polyester plastic raw material in each comparative example and embodiment of the present invention is polyethylene terephthalate with a molecular weight between 20,000 and 50,000; the catalytic degradation reaction route is as follows Figure 2 The mixture of monoethanolamine and sodium hydroxide obtained in the embodiment can be reused for catalytic degradation reaction.

[0040] The above is only a preferred embodiment of the present invention, and the protection scope of the present invention is not limited to the above embodiments. All technical solutions under the concept of the present invention belong to the protection scope of the present invention. It should be pointed out that for ordinary technicians in this technical field, some improvements and modifications without departing from the principle of the present invention should also be regarded as the protection scope of the present invention.

Claims

1. A method for chemical degradation and resource utilization of waste polyester plastics, characterized in that: The following steps are involved: (1) Chemical catalytic degradation of waste polyester plastics: waste polyester plastics after physical splitting are added to a reactor, and then NaOH and monoethanolamine are added as alcoholysis catalysts, nitrogen is introduced to remove air in the system, and then the temperature is increased to carry out catalytic degradation reaction; (2) Separation and purification of catalytic degradation products: After the reaction is completed, the reaction system is subjected to vacuum distillation to obtain a low-boiling point small molecule fraction, a mixture of monoethanolamine and sodium hydroxide, and an ethylene glycol fraction, respectively. The remaining N,N'-bis(2-hydroxyethyl)terephthalamide or the remaining N,N'-bis(2-hydroxyethyl)terephthalamide and polyester plastic that has not been completely degraded in the system; if two components remain in the system after vacuum distillation, they are separated by vacuum filtration.

2. The method for chemical degradation and resource utilization of waste polyester plastics according to claim 1, characterized in that: In step (1), the mass ratio of the waste polyester plastic added to the reaction system to the sodium hydroxide and monoethanolamine is 1:0.4:

4.

3. The method for chemical degradation and resource utilization of waste polyester plastics according to claim 1, characterized in that: The catalytic degradation reaction temperature is 60-90°C and the reaction time is 3-6h.

4. The method for chemical degradation and resource utilization of waste polyester plastics according to claim 1, characterized in that: In step (2), the heating temperatures during the reduced pressure distillation are 50, 90, and 140° C., respectively, the vacuum degree of the circulating water pump is 0.096 MPa, and the reduced pressure distillation time at the three temperatures is 2 h.

5. The method for chemical degradation and resource utilization of waste polyester plastics according to claim 1, characterized in that: The waste polyester plastic is physically cut, split, cleaned, and air-dried to obtain the waste polyester plastic after physical splitting treatment.

6. The method for chemical degradation and resource utilization of waste polyester plastics according to claim 1, characterized in that: Waste polyester plastic is polyethylene terephthalate with a molecular weight between 20,000 and 50,000.

7. A method for chemical degradation and resource utilization of waste polyester plastics according to any one of claims 1 to 6, characterized in that: The method further comprises step (3): reusing the mixture of monoethanolamine and sodium hydroxide obtained in step (2) for the catalytic degradation reaction in step (1).

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