A method for hydrolyzing waste PET polyester by CO2 catalysis

Abstract

The present invention discloses a CO 2 A method for catalyzing the hydrolysis of waste PET polyester involves the comprehensive utilization of waste resources. The method uses high-pressure CO 2 Gas is used as a catalyst for the hydrolysis of waste PET polyester. 2 Carbonic acid is formed with water. After the reaction is completed, the carbonic acid is regenerated into CO 2 The gas is recycled, and the reaction obtains pure terephthalic acid (TPA) crystals and ethylene glycol (EG) aqueous solution, thereby realizing resource utilization of waste PET. The products of the method of the present invention are terephthalic acid and ethylene glycol aqueous solution. The present invention can be used for depolymerization and upgrading of waste PET polyester materials, and the obtained raw material monomer terephthalic acid can be used for recycling PET to realize system closed loop, and the ethylene glycol aqueous solution is used in the field of wastewater biological treatment as an external carbon source. In addition, the catalyst is cheap and easy to obtain, the catalyst has high catalytic efficiency in the reaction, is easy to recover, can be reused, and effectively reduces costs.

Description

Technical Field

[0001] The present invention relates to a CO2-catalyzed hydrolysis of waste PET polyester to produce terephthalic acid and an ethylene glycol aqueous solution, which involves the comprehensive utilization of waste resources. More specifically, the present invention relates to a method for catalytic hydrolysis of PET to obtain terephthalic acid and an ethylene glycol aqueous solution of a certain purity. Background Art

[0002] Polyethylene terephthalate (PET) is a common polyester material with an annual global production of 360 million tons. It is widely used in bottled beverages, synthetic fibers, and food packaging. After the use of PET materials, a large amount of waste PET waste is generated. Recycling can effectively reduce waste PET plastic pollution and avoid excessive consumption of fossil resources. At present, the recycling method of waste PET plastic is mainly mechanical recycling, which has the problem of gradually decreasing product quality and low product value. Overall, PET recycling faces the dilemma of "serious overcapacity at the low end and scarcity of high-value utilization technology." Waste PET chemical conversion technology with high-value chemicals as the target product is an inevitable trend of future development.

[0003] The hydrolysis and alcoholysis of PET are currently the most widely studied and applied. Hydrolysis involves water acting as a nucleophile to attack the C=O bonds in the polyester, producing terephthalic acid and ethylene glycol. Hydrolysis methods are categorized into acidic, alkaline, and neutral hydrolysis. Neutral hydrolysis is typically performed in water or steam. Without the addition of a catalyst, it requires high temperature and high pressure. The addition of an alkali metal catalyst can effectively increase the reaction rate. Acidic hydrolysis is typically performed in inorganic acids such as concentrated sulfuric acid, nitric acid, or phosphoric acid, while alkaline hydrolysis is typically performed in aqueous NaOH or KOH solutions. While acidic / base catalysis results in relatively relaxed reaction conditions, the acidic / alkaline wastewater must be treated and presents significant equipment corrosion risks. Most of these hydrolysis methods introduce metal elements or strong acids and bases, making the system less environmentally friendly and leading to issues such as catalyst contamination and reuse, limiting the industrial application of PET hydrolysis methods. Summary of the Invention

[0004] In response to the demand for green depolymerization and recycling of waste PET polyester and the defects of the existing technology, the present invention provides a method for hydrolyzing waste PET polyester using CO2. The method uses high-pressure CO2 gas as a catalyst for the PET hydrolysis reaction. Carbonic acid is formed by CO2 and water at high temperature. After the reaction is completed, the carbonic acid is regenerated into CO2 gas and recycled. Pure terephthalic acid (TPA) crystals and ethylene glycol (EG) aqueous solution are obtained by the reaction, thereby realizing resource utilization of waste PET polyester.

[0005] The specific technical solutions adopted in the present invention are as follows:

[0006] A method for hydrolyzing waste PET polyester using CO2 catalysis, the specific steps are as follows:

[0007] Crushed waste PET polyester and water solvent are placed in a reactor, and high-pressure CO2 gas is introduced as a depolymerization catalyst for PET. The reactor is then placed at a depolymerization temperature of 200-220°C for 6-24 hours. After the reaction is completed, the temperature is cooled to room temperature to obtain a depolymerization product containing terephthalic acid crystals and ethylene glycol.

[0008] The reaction formula of the above depolymerization reaction can be expressed as:

[0009]

[0010] Preferably, the waste PET polyester is one or more of PET discarded bottles, PET non-woven fabrics, PET colored ropes, PET woven belts, and PET transparent films.

[0011] Preferably, the gas pressure after high-pressure CO2 gas is introduced into the reactor is 1 to 5 MPa.

[0012] Preferably, the amount of the aqueous solvent added is 1 to 5 mL / mol of waste PET polyester.

[0013] Preferably, the depolymerization temperature is 200°C.

[0014] Preferably, the depolymerization reaction time is 12 hours.

[0015] Compared with the prior art, the present invention has the following beneficial effects:

[0016] (1) The present invention uses CO2 as a catalyst for the hydrolysis of PET. CO2 is a widely existing greenhouse gas. During the reaction process, it is used to react with water to form carbonic acid, which then acid-catalyzes the hydrolysis of PET to produce terephthalic acid (TPA) and ethylene glycol (EG). After the reaction is completed, CO2 is released from the system, thereby achieving recycling. The CO2 catalytic system has the advantages of high efficiency and is non-corrosive. It does not require high materials for the reactor. At the same time, it is clean, zero-toxic, and pollution-free, meeting the requirements of clean production. The present invention targets the greenhouse gas CO2 and develops a novel way to utilize CO2, providing a new way to achieve the "dual carbon" goal.

[0017] (2) The catalytic system used in the present invention is easy to separate and recycle because CO2, EG, and TPA are in the gas, liquid, and solid phases, respectively. The inexpensive and easily recyclable CO2 catalyst is used and can be collected and reused after the reaction is completed. There is no need to consider the separation of the catalyst from the system. Theoretically, it can be reused indefinitely, meeting the requirements of sustainable development.

[0018] (3) The product of the present invention is an aqueous solution of TPA and EG. The purified TPA crystals can be used for the polymerization and regeneration of PET. The aqueous solution of ethylene glycol contains no metals or acid-base catalysts, making the system green and pure, and can be used as an external carbon source for biological denitrification in sewage treatment plants. The production process is zero-toxic and free of pollutant emissions. The product is easy to separate and has high value, thus providing good economic and environmental benefits. DETAILED DESCRIPTION

[0019] In order to make the above-mentioned objects, features and advantages of the present invention more clearly understood, a detailed description is given below through specific embodiments. In the following description, many specific details are set forth to facilitate a full understanding of the present invention. However, the present invention can be implemented in many other ways than those described herein, and those skilled in the art can make similar improvements without violating the connotation of the present invention. Therefore, the present invention is not limited to the specific embodiments disclosed below. The technical features in the various embodiments of the present invention can be combined accordingly without conflicting with each other.

[0020] The present invention provides a method for hydrolyzing waste PET polyester by using CO2 as catalyst, which comprises:

[0021] First, crushed waste PET polyester and water solvent are placed in a reactor, and high-pressure CO2 gas is introduced as a depolymerization catalyst for PET; then the reactor is placed at a depolymerization temperature of 200-220°C for 6-24 hours for a depolymerization reaction. After the reaction is completed, the temperature is cooled to room temperature to obtain a depolymerization product containing terephthalic acid crystals and ethylene glycol.

[0022] The above-mentioned waste PET polyester can be any PET waste, such as one or more of PET waste bottles, PET non-woven fabrics, PET colored ropes, PET woven tapes, or PET transparent films. Of course, the method can also be used to hydrolyze PET polyester in other non-waste forms.

[0023] In the above-mentioned reactor, the specific process parameters can be optimized and adjusted according to actual conditions. Specifically: after high-pressure CO2 gas is introduced into the reactor, the gas pressure is controlled to be 1-5 MPa; the amount of water solvent added to the reactor is controlled to be 1-5 mL / mol of waste PET polyester; the depolymerization temperature is preferably 200°C, and the depolymerization reaction time is preferably 12 h.

[0024] This method uses high-pressure CO₂ gas as a catalyst for the hydrolysis of waste PET polyester. At high temperatures, the CO₂ reacts with water to form carbonic acid, which is then regenerated into CO₂ gas and recycled. Pure terephthalic acid (TPA) crystals and an ethylene glycol (EG) aqueous solution are obtained, achieving resource utilization of waste PET. Several examples and comparative examples are provided below to demonstrate the technical benefits of the present invention.

[0025] Example 1

[0026] In an autoclave reactor equipped with an electromagnetic stirrer, thermocouple, and programmable temperature controller, 0.192 g of PET powder (1 mmol) and 3 mL of distilled water were added. 1 MPa of CO₂ gas was then introduced. After the autoclave reactor was positioned, stirring and heating were initiated. The reaction system in the autoclave was heated to 200°C and allowed to react at this temperature for 12 hours. After completion of the reaction, the temperature was lowered to room temperature, and the resulting mixture was the product. The terephthalic acid and ethylene glycol contents of the product were determined, and their yields were calculated to be 70.3% and 65.2% respectively.

[0027] Example 2

[0028] In an autoclave reactor equipped with an electromagnetic stirrer, thermocouple, and programmable temperature controller, 0.192 g of PET powder (1 mmol) and 3 mL of distilled water were added, and 3 MPa of CO₂ gas was introduced. After the autoclave reactor was positioned, stirring and heating were initiated. The reaction system in the autoclave reactor was heated to 200°C and allowed to react at this temperature for 12 hours. After completion of the reaction, the temperature was lowered to room temperature, and the resulting mixture was the product. The terephthalic acid and ethylene glycol contents of the product were determined, and their yields were calculated to be 99.8% and 95.4% respectively.

[0029] Example 3

[0030] In an autoclave reactor equipped with an electromagnetic stirrer, thermocouple, and programmable temperature controller, 0.192 g of PET powder (1 mmol) and 3 mL of distilled water were added, and 5 MPa of CO₂ gas was introduced. After the autoclave reactor was positioned, stirring and heating were initiated. The reaction system in the autoclave reactor was heated to 200°C and allowed to react at this temperature for 12 hours. After completion of the reaction, the temperature was lowered to room temperature, and the resulting mixture was the product. The terephthalic acid and ethylene glycol contents of the product were determined, and their yields were calculated to be 90.6% and 92.7% respectively.

[0031] Comparative Example 1

[0032] In an autoclave reactor equipped with an electromagnetic stirrer, thermocouple, and programmable temperature controller, 0.192 g of PET powder (1 mmol) and 3 mL of distilled water were added. However, to provide a contrast with Example 2, two comparative experiments were conducted on the atmosphere within the reactor. In the first comparative experiment, the autoclave reactor was not filled with CO2 gas, retaining atmospheric air pressure, while in the second comparative experiment, the autoclave reactor was filled with 3 MPa of N2 gas instead of CO2 gas. After the gas treatment within the autoclave reactors was completed in both comparative experiments, the autoclave reactors were placed in place, and stirring and heating were initiated. The reaction system in the autoclave reactor was heated to 200°C and allowed to react at this temperature for 12 hours. After completion of the reaction, the temperature was cooled to room temperature, and the resulting mixed system was the product. The terephthalic acid and ethylene glycol contents in the product system were measured, and their yields were calculated. The yields were 49.7% and 53.7% when no CO2 gas was introduced, and 63.6% and 64.4% when 3 MPa of N2 gas was introduced. It can be seen that the high-pressure CO2 gas introduced into the autoclave reactor in the present invention acts as a catalyst for the hydrolysis reaction of waste PET polyester, and can improve the efficiency of the hydrolysis reaction of waste PET polyester.

[0033] Example 4

[0034] In an autoclave reactor equipped with an electromagnetic stirrer, thermocouple, and programmable temperature controller, 0.192 g of PET powder (1 mmol) and 5 mL of distilled water were added, and 3 MPa of CO₂ gas was introduced. After the autoclave reactor was positioned, stirring and heating were initiated. The reaction system in the autoclave reactor was heated to 200°C and allowed to react at this temperature for 12 hours. After completion of the reaction, the temperature was lowered to room temperature, and the resulting mixture was the product. The terephthalic acid and ethylene glycol contents of the product were determined, and their yields were calculated to be 98.6% and 92.2% respectively.

[0035] Example 5

[0036] In an autoclave reactor equipped with an electromagnetic stirrer, thermocouple, and programmable temperature controller, 0.192 g of PET plastic bottles (1 mmol, pre-crushed to the centimeter level) and 3 mL of distilled water were added. 3 MPa of CO₂ gas was then introduced. After the autoclave reactor was placed, stirring and heating were initiated. The reaction system in the autoclave was heated to 200°C and allowed to react at this temperature for 12 hours. After completion of the reaction, the temperature was cooled to room temperature, and the resulting mixture was the product. The terephthalic acid and ethylene glycol contents of the product were determined, and their yields were calculated to be 31.5% and 36.0%.

[0037] Example 6

[0038] In an autoclave reactor equipped with an electromagnetic stirrer, thermocouple, and programmable temperature controller, 0.192 g of PET nonwoven fabric (1 mmol, pre-crushed to the centimeter scale) and 3 mL of distilled water were added. 3 MPa of CO₂ gas was then introduced. After the autoclave reactor was placed, stirring and heating were initiated. The reaction system in the autoclave was heated to 200°C and allowed to react at this temperature for 12 hours. After completion of the reaction, the temperature was cooled to room temperature, and the resulting mixture was the product. The terephthalic acid and ethylene glycol contents of the product were determined, and their yields were calculated to be 47.2% and 63.2%.

[0039] Example 7

[0040] In an autoclave reactor equipped with an electromagnetic stirrer, thermocouple, and programmable temperature controller, 0.192 g of PET colored twine (1 mmol, pre-crushed to the centimeter scale) and 3 mL of distilled water were added. 3 MPa of CO₂ gas was then introduced. After the autoclave reactor was set up, stirring and heating were initiated. The reaction system in the autoclave was heated to 200°C and allowed to react at this temperature for 12 hours. After completion of the reaction, the temperature was cooled to room temperature, and the resulting mixture was the product. The terephthalic acid and ethylene glycol contents of the product were determined, and their yields were calculated to be 63.2% and 73.1%.

[0041] Example 8

[0042] In an autoclave reactor equipped with an electromagnetic stirrer, thermocouple, and programmable temperature controller, 0.192 g of PET braid (1 mmol, pre-crushed to the centimeter scale) and 3 mL of distilled water were added. 3 MPa of CO₂ gas was then introduced. After the autoclave reactor was placed, stirring and heating were initiated. The reaction system in the autoclave was heated to 200°C and allowed to react at this temperature for 12 hours. After completion of the reaction, the temperature was cooled to room temperature, and the resulting mixture was the product. The terephthalic acid and ethylene glycol contents of the product were determined, and their yields were calculated to be 57.0% and 60.7%.

[0043] Example 9

[0044] In an autoclave reactor equipped with an electromagnetic stirrer, thermocouple, and programmable temperature controller, 0.192 g of transparent PET film (1 mmol, pre-fragmented to the centimeter scale) and 3 mL of distilled water were added. 3 MPa of CO₂ gas was then introduced. After the autoclave reactor was positioned, stirring and heating were initiated. The reaction system in the autoclave was heated to 200°C and allowed to react at this temperature for 12 hours. After completion of the reaction, the temperature was cooled to room temperature, and the resulting mixture was the product. The terephthalic acid and ethylene glycol contents of the product were determined, and their yields were calculated to be 64.9% and 70.6% respectively.

[0045] The embodiment described above is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Persons skilled in the art may make various changes and modifications without departing from the spirit and scope of the present invention. Therefore, any technical solution obtained by equivalent substitution or equivalent transformation falls within the scope of protection of the present invention.

Claims

1. A method for hydrolyzing waste PET polyester by CO2 catalysis, characterized in that: Put crushed waste PET polyester and water solvent in a reactor, and introduce high-pressure CO2 gas as a depolymerization catalyst for PET, then place the reactor at a depolymerization temperature of 200-220°C for 6-24 hours of depolymerization reaction, and cool to room temperature after the reaction is completed to obtain a depolymerization product containing terephthalic acid crystals and ethylene glycol; After high-pressure CO2 gas is introduced into the reactor, the gas pressure is 1-5 MPa; the amount of water solvent added to the reactor is 1-5 mL / mol of waste PET polyester.

2. The method for hydrolyzing waste PET polyester by CO2 catalysis as claimed in claim 1, characterized in that: The waste PET polyester is one or more of PET waste bottles, PET non-woven fabrics, PET colored ropes, PET woven belts or PET transparent films.

3. The method for hydrolyzing waste PET polyester by CO2 catalysis as claimed in claim 1, characterized in that: The depolymerization temperature is 200°C.

4. The method for hydrolyzing waste PET polyester by CO2 catalysis as claimed in claim 1, characterized in that: The depolymerization reaction time is 12h.

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