CN112920456B

CN112920456B - Separation and recycling method of waste PET (polyethylene terephthalate) methanol alcoholysis ionic liquid catalyst

Info

Publication number: CN112920456B
Application number: CN202110145287.7A
Authority: CN
Inventors: 辛加余; 黄俊杰; 晏冬霞; 吕兴梅; 张旗; 荣嘉诚; 周清; 张锁江
Original assignee: Institute of Process Engineering of CAS
Current assignee: Institute of Process Engineering of CAS
Priority date: 2021-02-02
Filing date: 2021-02-02
Publication date: 2022-04-29
Anticipated expiration: 2041-02-02
Also published as: CN112920456A

Abstract

The invention relates to a method for separating and recycling a waste PET (polyethylene terephthalate) methanolysis ionic liquid catalyst, which comprises the following specific steps of firstly removing a solvent methanol and a byproduct ethylene glycol by means of atmospheric distillation and reduced pressure distillation, and separating and removing a product DMT (dimethyl terephthalate), so that the ionic liquid catalyst is separated and recycled: 1) degrading the waste PET by adopting a methanol alcoholysis method, and obtaining impurity-containing DMT after the reaction is finished; 2) removing methanol component in DMT containing impurities by atmospheric distillation; 3) removing the glycol component in the DMT containing impurities by adopting a reduced pressure distillation mode; 4) and separating and removing the DMT product by adopting a reduced pressure distillation mode, wherein the main component of the remainder is an alcoholysis ionic liquid catalyst which can be directly used for degrading the waste PET. The method has simple process, the catalytic performance of the obtained regenerated catalyst is kept good, and the separation and the cyclic utilization of the waste PET methanol alcoholysis ionic liquid catalyst are realized.

Description

Separation and recycling method of waste PET (polyethylene terephthalate) methanol alcoholysis ionic liquid catalyst

Technical Field

The invention belongs to the field of solid waste resource utilization, and relates to a method for separating and recycling a waste PET (polyethylene terephthalate) methanol alcoholysis catalyst.

Background

Polyethylene terephthalate (PET) is widely used in the fields of food and beverage packaging, fibers, films, substrates, and the like because of its characteristics of light weight, high strength, good air tightness, high transparency, and the like. As the first major world of PET production and consumption, china consumes up to several million tons of PET per year, with the production of large quantities of waste PET. Therefore, efficient recycling of PET is a major challenge facing our society. At present, the recovery methods of PET mainly comprise a physical recovery method, a chemical recovery method and a pyrolysis method, wherein the physical recovery method has low cost but is difficult to obtain high-quality recycled PET, and the pyrolysis method is difficult to control the reaction process, so that high-purity PET monomer cannot be obtained, and the closed-loop recovery of plastics cannot be realized. In contrast, the chemical recovery method is not limited by PET raw materials, and the regenerated PET product has high quality and wide application, and accords with the development concept of modern green economy and circular economy. However, at present, the operation cost is high due to the overhigh energy consumption of the purification section of the PET degradation product and the overlarge output of three wastes, and the chemical recovery of PET is difficult to realize large-scale industrial application. Among them, the separation of the PET degradation catalyst and the PET monomer (for example, methanolysis, the obtained PET monomer is dimethyl terephthalate, DMT) is the most troublesome part of the purification section of the PET degradation product.

For heterogeneous catalytic reaction systems, the active substances (mostly metal salts or metal oxides) in the catalyst are often supported on a support material with a certain mechanical strength and can be separated by simple filtration after the reaction is finished. However, since heterogeneous catalytic reaction mostly occurs on the surface of the catalyst, the catalyst has fewer active sites and lower catalytic efficiency. For a homogeneous catalytic reaction system, active sites of the catalyst can be fully exposed and utilized, and the catalytic efficiency is high, but the separation of the catalyst and reaction products is difficult. There are two common methods for separating the catalyst in a homogeneous system, one is to precipitate the catalyst by changing the conditions of temperature, pH, etc. or adding a precipitant, and the other is to separate the reaction product by distillation, and the remaining catalyst can be recycled. The former often needs the participation of organic solvent or auxiliary agent sensitive to temperature, the discharge amount of three wastes and the treatment difficulty are greatly increased, and the catalyst obtained by adding the precipitator and separating still needs further purification treatment and then can be reused. The latter only needs to regulate and control the distillation condition to distill off each component in the homogeneous system one by one to separate out the catalyst. In the case of an ionic liquid catalyst, since the catalyst is mostly in a liquid state under normal temperature and pressure conditions, if separation is performed by precipitation, the structure of the catalyst itself may be destroyed and the catalyst may be deactivated. On the contrary, because the vapor pressure of the ionic liquid is extremely low and the stability is good, if the catalyst is separated by adopting a mode of distilling to remove other components in a homogeneous system, not only can the purification of the product and the cyclic utilization of the solvent and the by-products be realized, but also the structure of the catalyst can be ensured not to be damaged, the catalytic activity can be maintained, the catalyst can be recycled, and the ionic liquid has important practical significance and wide application prospect. The invention has the following advantages:

(1) the ionic liquid catalyst for alcoholysis of waste PET methanol is separated from the reaction product and recycled, so that the production cost and the subsequent treatment cost of the catalyst can be greatly reduced, and the three-waste pollution generated in the production process can be reduced.

(2) The catalyst regeneration method is simple, and the recovery of alcoholysis byproducts and the separation of products can be realized in the regeneration process, so that the production cost is reduced.

(3) Because the vapor pressure of the ionic liquid is extremely low and the stability is good, the loss rate of the catalyst in the distillation separation process is low, the catalytic activity is kept good, and the activity of the catalyst is not obviously reduced after the catalyst is separated and recycled for 10 times.

Disclosure of Invention

The invention aims to provide a method for separating and recycling a waste PET (polyethylene terephthalate) methanol alcoholysis ionic liquid catalyst, and aims to solve the problems of difficult separation of products and the catalyst, low utilization rate of the catalyst, difficult subsequent treatment of a metal catalyst and the like in the existing PET chemical recovery process.

In order to achieve the purpose, the invention adopts the following technical scheme:

a method for separating and recycling a waste PET methanolysis ionic liquid catalyst, the method comprising the steps of:

(1) degrading PET by adopting a methanol alcoholysis method, and obtaining impurity-containing DMT after the reaction is finished;

(2) distilling the impurity-containing DMT obtained in the step (1) at normal pressure to remove a methanol component in the impurity-containing DMT;

(3) carrying out reduced pressure distillation on the DMT containing impurities obtained in the step (2) to remove glycol components in the DMT containing impurities;

(4) and (4) carrying out reduced pressure distillation on the impurity-containing DMT obtained in the step (3) to remove the DMT product, wherein the main component of the remainder is alcoholysis ionic liquid catalyst, and the collected catalyst is used as a regenerated catalyst to be reused for alcoholysis of waste PET methanol.

The method for separating and recycling the waste PET methanol alcoholysis ionic liquid catalyst provided by the invention has the advantages of simple process flow and convenience in operation, and can effectively separate and recycle the catalyst and realize recycling of the waste alcoholysis catalyst.

Detailed Description

The present invention will be described below with reference to specific examples, but the application of the present invention is not limited to the scope of the examples, and variations and implementations are included in the technical scope of the present invention without departing from the spirit of the invention.

1. Preparation of DMT containing impurities by alcoholysis of PET with methanol

Examples 1 to 4:

the reaction equation for DMT preparation by methanolysis of PET is as follows:

putting PET bottle chips and 0.5 mass percent of 1-butyl-3-methylimidazole tetrachlorozincate, 1-butyl-3-methylimidazole tetrachlorocobaltate, 1-butyl-3-methylimidazole trichloromanganate and 1-butyl-3-methylimidazole tetrachloroferrate catalyst into a degradation kettle, adding the components in a mass ratio of 4: 1, the reaction temperature is 180 ℃, the reaction pressure is 2.7MPa, and the reaction time is 2 h. After the reaction is finished, the impurity-containing DMT is obtained and is used for subsequent distillation purification. The results of different catalysts for catalyzing alcoholysis of PET with methanol are detailed in the numbers 1-4 in Table 1.

TABLE 1 examples 1-4 results of PET methanolysis to make DMT-containing impurities

Examples	Catalyst and process for preparing same	PET conversion/%)	DMT yield/%
				1	1-butyl-3-methylimidazol tetrachlorozincate	100	88.5
2	1-butyl-3-methylimidazolium tetrachlorocobaltate	100	90.3
				3	1-butyl-3-methylimidazole trichloromanganate	100	82.3
4	1-butyl-3-methylimidazolium tetrachloroferrate	100	79.8

2. Separation and recycle of ionic liquid catalyst

Example 5:

the embodiment provides a method for separating and recycling a waste PET methanolysis ionic liquid catalyst, which comprises the following steps:

(1) the DMT containing impurities obtained in example 1 was subjected to atmospheric distillation at 80 ℃ and the residue in the round-bottomed flask was used for subsequent purification;

(2) carrying out reduced pressure distillation on the residue obtained in the step (1), wherein the operating pressure is-0.06 MPa, the operating temperature is 160 ℃, and the residue in the round-bottom flask is used for subsequent purification;

(3) and (3) carrying out reduced pressure distillation on the residues obtained in the step (2), wherein the operating pressure is-0.1 MPa, the operating temperature is 200 ℃, the distillate is refined DMT, and the distillation residues are mainly ionic liquid catalyst and are collected to be used as regenerated ionic liquid catalyst for later use.

(4) The obtained regenerated ionic liquid catalyst is used for catalyzing alcoholysis of PET methanol. Putting PET bottle chips and a regenerated ionic liquid catalyst with the mass of 0.5 percent of that of the PET bottle chips into a degradation kettle, and adding a catalyst which is mixed with PET in a mass ratio of 4: 1, the reaction temperature is 180 ℃, the reaction pressure is 2.7MPa, and the reaction time is 2 h.

In the process of this example, the purity of the obtained purified DMT was 99.9%, and the content of the ionic liquid in the distillation residue was 98.4%. In the reaction of catalyzing alcoholysis of PET by methanol with the regenerated catalyst, the conversion rate of PET is 100 percent, and the yield of DMT is 88.1 percent.

Examples 6 to 8:

the procedure and conditions were the same as in example 5, except that the source of the DMT-containing impurity in step (1) was changed to examples 2 to 4. The results of separation and recycle of the ionic liquid catalyst are detailed in Table 2, Nos. 6-8.

TABLE 2 results of examples 6-8 regenerated catalyst catalyzed alcoholysis of PET with methanol

Example 9:

the procedure and conditions were the same as in example 5 except that the operating temperature of the atmospheric distillation in step (1) was adjusted to 50 ℃.

In the process of this example, the purity of the obtained purified DMT was 99.8%, and the content of the ionic liquid in the distillation residue was 97.9%. In the reaction of catalyzing alcoholysis of PET by methanol with the regenerated catalyst, the conversion rate of PET is 100 percent, and the yield of DMT is 87.9 percent.

Example 10:

the procedure and conditions were the same as in example 5 except that the operating pressure in the reduced pressure distillation in the step (2) was adjusted to-0.03 MPa and the operating temperature was adjusted to 180 ℃.

In the process of this example, the purity of the obtained purified DMT was 97.8%, and the content of the ionic liquid in the distillation residue was 98.1%. In the reaction of catalyzing alcoholysis of PET by methanol with the regenerated catalyst, the conversion rate of PET is 100 percent, and the yield of DMT is 87.5 percent.

Example 11:

the procedure and conditions were the same as in example 5 except that the operating pressure of the reduced pressure distillation in the step (3) was adjusted to-0.07 MPa and the operating temperature was adjusted to 260 ℃.

In the process of this example, the purity of the obtained purified DMT was 99.7%, and the content of the ionic liquid in the distillation residue was 95.5%. In the reaction of catalyzing alcoholysis of PET by methanol with the regenerated catalyst, the conversion rate of PET is 98.9%, and the yield of DMT is 86.4%.

Example 12:

the ionic liquid catalyst recovered from example 1 was subjected to a plurality of separation and recycling tests, which were performed in the same manner as in example 5, and the test results are detailed in table 3.

Table 3 example 12 results of multiple separation and recycle tests of ionic liquid catalysts

Number of cycles	0	1	2	3	4	5	6	7	8	9	10
												PET conversion/%)	100	100	99.8	100	99.7	100	99.5	100	99.8	99.3	98.7
DMT yield/%	88.5	88.1	88.0	88.3	87.9	87.2	88.1	87.5	87.2	86.3	85.9

The applicant states that the present invention is illustrated in detail by the above examples, but the present invention is not limited to the above detailed methods, i.e. it is not meant that the present invention must rely on the above detailed methods for its implementation. It should be understood by those skilled in the art that any modification of the present invention, equivalent substitutions of the raw materials of the product of the present invention, addition of auxiliary components, selection of specific modes, etc., are within the scope and disclosure of the present invention.

Claims

1. A separation and recycling method of a waste PET methanol alcoholysis ionic liquid catalyst is characterized by comprising the following specific steps:

(2) distilling the impurity-containing DMT obtained in the step (1) at normal pressure, wherein the operation temperature is 50-80 ℃ to remove a methanol component in the impurity-containing DMT;

(3) carrying out reduced pressure distillation on the impurity-containing DMT obtained in the step (2), wherein the operating temperature is 160-180 ℃, and the operating pressure is-0.03 to-0.06 MPa, so as to remove the glycol component in the impurity-containing DMT;

(4) and (4) carrying out reduced pressure distillation on the impurity-containing DMT obtained in the step (3), wherein the operating temperature is 200-260 ℃, the operating pressure is-0.07-0.1 MPa, so as to remove the DMT product, and the remainder mainly comprises an alcoholysis ionic liquid catalyst, and the catalyst is collected and used as a regenerated catalyst to be reused for alcoholysis of waste PET methanol.

2. The method of claim 1 for separating and recycling the waste PET methanolysis ionic liquid catalyst, wherein the method comprises the following steps: the ionic liquid catalyst comprises 1-butyl-3-methylimidazole tetrachlorozincate, 1-butyl-3-methylimidazole tetrachlorocobaltate, 1-butyl-3-methylimidazole trichloromanganate and 1-butyl-3-methylimidazole tetrachloroferrate.