A method for upgrading polyester materials to dicarboxylic acid esters and ethylene carbonate

Abstract

The present invention discloses a method for upgrading polyester materials to dicarboxylic acid esters and ethylene carbonate, and relates to the comprehensive utilization of waste resources and the cascade utilization of raw materials. The method uses multiple types of green ionic liquid catalysts to catalyze the methanolysis reaction of PET, and then dimethyl carbonate captures the generated ethylene glycol in situ, forms a five-membered cyclic ethylene carbonate through nucleophilic cyclization, pulls the reaction equilibrium to move forward, and completely depolymerizes PET waste. The products of the method of the present invention are dimethyl terephthalate and five-membered cyclic ethylene carbonate. The present invention can be used for the depolymerization and upgrading of waste PET materials, and can also be used for other similar polyesters, such as polyethylene succinate, polyethylene adipate and polyethylene 2,5-furan dicarboxylate, which are also suitable for the recovery strategy of the present invention, and the products are the corresponding dimethyl succinate, dimethyl adipate and 2,5-furan dicarboxylate.

Description

Technical Field

[0001] The present invention relates to a method for producing dimethyl terephthalate and ethylene carbonate by depolymerizing PET with high selectivity, and relates to comprehensive utilization of waste resources and cascade utilization of raw materials. More specifically, the present invention relates to a method for depolymerizing various polyester raw materials including PET with methanol, and obtaining dicarboxylic acid esters and ethylene carbonate with high yield. Background Art

[0002] Landfill, incineration, mechanical recycling and chemical recycling are the four main methods for treating waste plastics. Generally, landfill and incineration treatment will not produce value-added products and are prone to secondary ecological pollution of the atmosphere and soil. Mechanical and physical recycling of waste has certain economic value, but the quality and performance of derived materials gradually decrease with the increase of recycling times. Compared with the above strategies, chemical recycling can cut the chemical bonds in waste plastics at the molecular level, reconstruct the molecular structure, and extend the material value chain. It has a milder treatment mode and lower production capacity consumption than other recycling methods. And this strategy focuses on the recovery of monomers, petroleum fuels and chemicals. It is a feasible strategy that takes both economy and environment into consideration, making the plastic recycling value chain more sustainable in the market. However, the ethylene glycol produced in the reaction is difficult to separate and recycle due to its high boiling point and is usually abandoned. But the ethylene glycol unit of PET also has great potential for conversion into high-value chemicals, and has been used to convert precursor materials into small molecule carboxylic acids and light olefins with higher added value. Therefore, the innovative recycling of ethylene glycol units is an important issue that needs to be solved in the field of PET depolymerization.

[0003] The methanol decomposition system has high pollution resistance, making it a cost-effective option for treating complex PET-based waste. However, methanol decomposition generally requires a higher temperature (generally ≥200°C) to promote the slow decomposition of PET depolymerization reaction, and the product DMT yield is only between 80-85%. In order to pursue a high yield of DMT, there are currently a small number of supercritical methanol or microwave-assisted methanol decomposition system research projects, but considering factors such as equipment operation and economic benefits, it is not recommended. In addition, this type of reaction often requires excess methanol or methanol as a solvent to promote the reaction, which is one of the limitations that urgently need to be overcome in the current field.

[0004] Ionic liquids are a class of excellent green catalysts that are non-volatile, thermally stable, and highly soluble. They are also designable and have been widely used in the fields of separation and catalysis. Therefore, it is worth paying attention to the development of mild and efficient methanol decomposition strategies using ionic liquids.

[0005] Ethylene carbonate (EC) is an organic solvent with excellent performance. It can dissolve a variety of polymers and is widely used in organic synthesis. Generally, ethylene carbonate can be obtained through the nucleophilic reaction of ethylene glycol and dimethyl carbonate. Due to the stable structure of the five-membered ring of ethylene carbonate, it can promote the equilibrium of PET depolymerization reaction to proceed in the forward direction. Therefore, ethylene carbonate can be used to capture the EG component from the waste PET in a targeted manner, thereby solving the problem of ethylene glycol separation and achieving high-value conversion of ethylene glycol. This high-value recovery strategy helps to fully utilize PET waste at the molecular level, and to a certain extent helps to alleviate the consumption of petroleum resources and improve the recycling value of PET waste. Summary of the invention

[0006] The present invention aims at the needs of depolymerization and product-oriented upgrading of PET waste plastics and the shortcomings of the prior art, and provides a method for upgrading polyester materials to dicarboxylic acid esters and ethylene carbonate. Taking PET as a typical representative, the method uses an ionic liquid catalyst to catalyze the methanolysis reaction of PET, and the dimethyl carbonate is captured and depolymerized in situ to generate the product ethylene glycol, which is then formed into ethylene carbonate through a nucleophilic cyclization reaction.

[0007] The specific technical solutions adopted by the present invention are as follows:

[0008] A method for upgrading polyester materials to dicarboxylic acid esters and ethylene carbonate, comprising:

[0009] S1. Put crushed polyester materials, methanol, ionic liquid catalyst and dimethyl carbonate into a reaction kettle to form a reaction system; wherein the polyester materials are polyethylene terephthalate (PET), polyethylene succinate, polyethylene adipate and polyethylene 2,5-furandicarboxylate; the ionic liquid catalyst is an imidazole type ionic liquid [Bmim][Cl], [Emim][Br], [Mmim][I], [Emim][Ac] or [Bmim][Ac], and the structural formula is as follows:

[0010]

[0011] S2, placing the reactor containing the reaction system at a depolymerization temperature of 100-140° C. for 2-4 hours of depolymerization reaction, and cooling to room temperature after the reaction is completed to obtain a depolymerization product containing dicarboxylic acid ester and ethylene carbonate.

[0012] Preferably, in the reaction system, the amount of dimethyl carbonate added is 2-4 mL / mmol of polyester material, and the amount of dimethyl carbonate added is more preferably 3.5 mL / mmol of polyester material.

[0013] Preferably, in the reaction system, the amount of the ionic liquid catalyst added is 3-10 mol %, more preferably 5 mol %, of the polyester material.

[0014] Preferably, in the reaction system, the amount of the methanol solvent added is 4 to 30 times the molar amount of the polyester material.

[0015] Preferably, the polyester material is waste of polyethylene terephthalate.

[0016] Furthermore, the waste is in the form of discarded bottles made of polyethylene terephthalate, discarded matrix films, colored ropes or non-woven fabrics.

[0017] Furthermore, the waste needs to be pre-crushed into centimeter-sized flakes, particles or powders before being added to the reactor, which can ensure the resource utilization effect of waste PET materials and obtain dimethyl terephthalate and ethylene carbonate in a targeted manner with high yield.

[0018] Preferably, the depolymerization temperature is 130°C.

[0019] Preferably, the depolymerization time is 2 hours.

[0020] Preferably, the ionic liquid catalyst is [Emim][Ac].

[0021] Compared with the prior art, the present invention has the following beneficial effects:

[0022] (1) The present invention uses dimethyl carbonate to capture ethylene glycol for coupling PET depolymerization, thereby overcoming the bottleneck problem that PET depolymerization is not completely reacted due to thermodynamic limitations. By using ionic liquid as a catalyst for the transesterification reaction, combined with hydrogen bond promotion and ethylene glycol coupling reaction, the complete depolymerization of PET at 130°C and the directional upgrading and recovery of ethylene glycol can be achieved.

[0023] (2) The methanol depolymerization strategy for waste plastic PET developed in the present invention has the advantages of short reaction time, mild conditions and high catalytic efficiency. The strategy has a wide range of applications and a variety of waste PET raw materials. Various types of waste PET materials, such as various types of PET waste bottles, PET matrix waste films, PET colored ropes and PET non-woven fabrics, can all be efficiently upgraded and converted in a short period of time.

[0024] (3) The PET waste plastic matrix material of the present invention can be replaced by various polyesters having similar diol units such as polyethylene succinate, polyethylene adipate and polyethylene 2,5-furandicarboxylate, which to a certain extent shows the high applicability of the strategy and further broadens the scope of waste plastic treatment materials. Under the premise of ensuring high depolymerization efficiency and rapid reaction time, the corresponding conversion can be completed to obtain dicarboxylic acid esters and ethylene carbonate. DETAILED DESCRIPTION

[0025] In order to make the above-mentioned purpose, features and advantages of the present invention more obvious and easy to understand, 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 different from those described herein, and those skilled in the art can make similar improvements without violating the connotation of the present invention, so 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 conflicting with each other.

[0026] The present invention provides a method for upgrading polyester materials to dicarboxylic acid esters and ethylene carbonate, wherein the method uses multiple types of green ionic liquid catalysts to catalyze the methanolysis of PET, and then dimethyl carbonate captures the generated ethylene glycol in situ, and forms a five-membered cyclic ethylene carbonate through nucleophilic cyclization, thereby driving the reaction equilibrium to move forward and completely depolymerizing PET waste. The specific steps of the method are as follows:

[0027] S1. placing crushed polyester material, methanol, ionic liquid catalyst and dimethyl carbonate in a reaction kettle to form a reaction system;

[0028] S2, placing the reactor containing the reaction system at a depolymerization temperature of 100-140° C. for 2-4 hours of depolymerization reaction, and cooling to room temperature after the reaction is completed to obtain a depolymerization product containing dicarboxylic acid ester and ethylene carbonate.

[0029] In the subsequent examples, the raw materials in the above reaction system are as follows: the polyester materials are polyethylene terephthalate (PET), polyethylene succinate, polyethylene adipate and polyethylene 2,5-furandicarboxylate; the ionic liquid catalysts are [Bmim][Cl], [Emim][Br], [Mmim][I], [Emim][SO 3 ], [EMIm] [BF 4 ], [Emim][Ac] or [Bmim][Ac], the structural formula is as follows:

[0030]

[0031] If the polyester material is PET, pure PET or PET waste can be used. The waste is in the form of PET waste bottles, PET matrix waste film, PET colored rope or PET non-woven fabric. However, the waste must be pre-crushed into centimeter-level flakes, particles or powder before adding it to the reactor.

[0032] The following examples are used to demonstrate the reaction results under different raw materials and parameters.

[0033] Example 1

[0034] In an autoclave reactor equipped with an electromagnetic stirrer, a thermocouple, and a programmable temperature controller, 0.192 grams of CR-pure PET powder (1mmol), [Bmim][Cl] (10mol%), 1mL methanol, and 3mL dimethyl carbonate were added. After the autoclave reactor was placed, stirring and heating were turned on. The reaction system was heated to 130°C and reacted at this temperature for 2h. After the reaction was completed, the temperature was lowered to room temperature, and the resulting mixed solution was the product. The resulting mixed solution was diluted with dichloromethane, and the diluent was measured for yield by GC, with mesitylene as the internal standard. The results showed that the yield of dimethyl terephthalate in this embodiment was 95%, and the yield of ethylene carbonate was 69%.

[0035] Example 2

[0036] In an autoclave reactor equipped with an electromagnetic stirrer, a thermocouple, and a programmable temperature controller, 0.192 grams of CR-pure PET powder (1mmol), [Emim][Br] (10mol%), 1mL of methanol, and 3mL of dimethyl carbonate were added. After the autoclave reactor was placed, stirring and heating were turned on. The reaction system was heated to 130°C and reacted at this temperature for 2h. After the reaction was completed, the temperature was lowered to room temperature, and the resulting mixed solution was the product. The resulting mixed solution was diluted with dichloromethane, and the diluent was measured for yield by GC, with mesitylene as the internal standard. The results showed that the yield of dimethyl terephthalate in this embodiment was 92%, and the yield of ethylene carbonate was 60%.

[0037] Example 3

[0038] In an autoclave reactor equipped with an electromagnetic stirrer, a thermocouple, and a programmable temperature controller, 0.192 grams of CR-pure PET powder (1mmol), [Mmim][I] (10mol%), 1mL of methanol, and 3mL of dimethyl carbonate were added. After the autoclave reactor was placed, stirring and heating were turned on. The reaction system was heated to 130°C and reacted at this temperature for 2h. After the reaction was completed, the temperature was lowered to room temperature, and the resulting mixed solution was the product. The resulting mixed solution was diluted with dichloromethane, and the diluent was measured for yield by GC, with mesitylene as the internal standard. The results showed that the yield of dimethyl terephthalate in this embodiment was 93%, and the yield of ethylene carbonate was 65%.

[0039] Example 4

[0040] In an autoclave reactor equipped with an electromagnetic stirrer, a thermocouple, and a programmable temperature controller, 0.192 grams of CR-pure PET powder (1mmol), [Emim][Ac] (10mol%), 1mL of methanol, and 3mL of dimethyl carbonate were added. After the autoclave reactor was placed, stirring and heating were turned on. The reaction system was heated to 130°C and reacted at this temperature for 2h. After the reaction was completed, the temperature was lowered to room temperature, and the resulting mixed solution was the product. The resulting mixed solution was diluted with dichloromethane, and the diluent was measured for yield by GC, with mesitylene as the internal standard. The results showed that the yield of dimethyl terephthalate in this embodiment was 94%, and the yield of ethylene carbonate was 82%.

[0041] Example 5

[0042] In an autoclave reactor equipped with an electromagnetic stirrer, a thermocouple, and a programmable temperature controller, 0.192 grams of CR-pure PET powder (1mmol), [Bmim][Ac] (10mol%), 1mL of methanol, and 3mL of dimethyl carbonate were added. After the autoclave reactor was placed, stirring and heating were turned on. The reaction system was heated to 130°C and reacted at this temperature for 2h. After the reaction was completed, the temperature was lowered to room temperature, and the resulting mixed solution was the product. The resulting mixed solution was diluted with dichloromethane, and the diluent was measured for yield by GC, with mesitylene as the internal standard. The results showed that the yield of dimethyl terephthalate in this embodiment was 95%, and the yield of ethylene carbonate was 69%.

[0043] Example 6

[0044] In an autoclave reactor equipped with an electromagnetic stirrer, a thermocouple, and a programmable temperature controller, 0.192 grams of CR-pure PET powder (1mmol), [Emim][Ac] (10mol%), 1mL of methanol, and 3.5mL of dimethyl carbonate were added. After the autoclave reactor was placed, stirring and heating were turned on. The reaction system was heated to 130°C and reacted at this temperature for 2h. After the reaction was completed, the temperature was lowered to room temperature, and the resulting mixed solution was the product. The resulting mixed solution was diluted with dichloromethane, and the diluent was measured for yield by GC, with mesitylene as the internal standard. The results showed that the yield of dimethyl terephthalate in this embodiment was 98%, and the yield of ethylene carbonate was 84%.

[0045] Example 7

[0046] In an autoclave reactor equipped with an electromagnetic stirrer, a thermocouple, and a programmable temperature controller, 0.192 grams of CR-pure PET powder (1mmol), [Emim][Ac] (10mol%), 8mmol methanol, and 3.5mL dimethyl carbonate were added. After the autoclave reactor was placed, stirring and heating were turned on. The reaction system was heated to 130°C and reacted at this temperature for 2h. After the reaction was completed, the temperature was lowered to room temperature, and the resulting mixed solution was the product. The resulting mixed solution was diluted with dichloromethane, and the diluent was measured for yield by GC, with mesitylene as the internal standard. The results showed that the yield of dimethyl terephthalate in this embodiment was 99%, and the yield of ethylene carbonate was 87%.

[0047] Example 8

[0048] In an autoclave reactor equipped with an electromagnetic stirrer, a thermocouple, and a programmable temperature controller, 0.192 grams of CR-pure PET powder (1 mmol), [Emim][Ac] (5 mol%), 8 mmol methanol, and 3.5 mL dimethyl carbonate were added. After the autoclave reactor was placed, stirring and heating were turned on. The reaction system was heated to 130°C and reacted at this temperature for 2 hours. After the reaction was completed, the temperature was lowered to room temperature, and the resulting mixed solution was the product. The resulting mixed solution was diluted with dichloromethane, and the diluent was measured for yield by GC, with mesitylene as the internal standard. The results showed that the yield of dimethyl terephthalate in this embodiment was 99%, and the yield of ethylene carbonate was 91%.

[0049] Example 9

[0050] Discarded PET plastic bottles (Coca-Cola, Pepsi-Cola and Nongfu Spring brands) were crushed in centimeters in advance, and then 0.192 grams of PET plastic bottles were crushed in centimeters (1mmol), [Emim][Ac] (5mol%), 8mmol methanol and 3.5mL dimethyl carbonate were added to an autoclave reactor equipped with an electromagnetic stirrer, a thermocouple and a program temperature controller. After placing the autoclave reactor, stirring and heating were turned on. The reaction system was heated to 130°C and reacted at this temperature for 3h. After the reaction was completed, it was cooled to room temperature, and the resulting mixed solution was the product. The resulting mixed solution was diluted with dichloromethane, and the diluent was measured for yield by GC, with mesitylene as the internal standard. The results showed that the yield of dimethyl terephthalate in this embodiment was 99%, and the yield of ethylene carbonate was 91%.

[0051] Example 10

[0052] In an autoclave reactor equipped with an electromagnetic stirrer, a thermocouple, and a programmable temperature controller, 0.144 g of polyethylene succinate (1 mmol), [Emim][Ac] (5 mol%), 8 mmol of methanol, and 3.5 mL of dimethyl carbonate were added. After the autoclave reactor was placed, stirring and heating were turned on. The reaction system was heated to 130° C. and reacted at this temperature for 2 h. After the reaction was completed, the temperature was lowered to room temperature, and the resulting mixed solution was the product. The yield was determined by HNMR, with mesitylene as the internal standard. The results showed that the yield of dimethyl succinate in this embodiment was 99%, and the yield of ethylene carbonate was 95%.

[0053] Embodiment 11

[0054] In an autoclave reactor equipped with an electromagnetic stirrer, a thermocouple, and a programmable temperature controller, 0.172 g of polyethylene adipate (1 mmol), [Emim][Ac] (5 mol%), 8 mmol of methanol, and 3.5 mL of dimethyl carbonate were added. After the autoclave reactor was placed, stirring and heating were turned on. The reaction system was heated to 130°C and reacted at this temperature for 2 hours. After the reaction was completed, the temperature was lowered to room temperature, and the resulting mixed solution was the product. The yield was determined by H NMR, with mesitylene as the internal standard. The results showed that the yield of dimethyl adipate in this embodiment was 99%, and the yield of ethylene carbonate was 75%.

[0055] Example 12

[0056] In an autoclave reactor equipped with an electromagnetic stirrer, a thermocouple, and a programmable temperature controller, 0.192 polyethylene 2,5-furandicarboxylate (1mmol), [Emim][Ac] (5mol%), 8mmol methanol, and 3.5mL dimethyl carbonate were added. After the autoclave reactor was placed, stirring and heating were turned on. The reaction system was heated to 130°C and reacted at this temperature for 2.5h. After the reaction was completed, the temperature was lowered to room temperature, and the resulting mixed solution was the product. The yield was determined by H NMR, with mesitylene as the internal standard. The results showed that the yield of dimethyl 2,5-furandicarboxylate in this embodiment was 99%, and the yield of ethylene carbonate was 80%.

[0057] Comparative Example 1

[0058] In an autoclave reactor equipped with an electromagnetic stirrer, a thermocouple, and a programmable temperature controller, 0.192 g of CR-pure PET powder (1 mmol), [Emim] [SO 3](10mol%), 1mL methanol and 3mL dimethyl carbonate, after placing the autoclave reactor, start stirring and heating. The reaction system is heated to 130°C and reacted at this temperature for 2h. After the reaction is completed, it is cooled to room temperature, and the resulting mixed solution is the product. The resulting mixed solution is diluted with dichloromethane, and the diluent is measured by GC for yield, with mesitylene as the internal standard. The results show that the yield of dimethyl terephthalate in this embodiment is 0%, and the yield of ethylene carbonate is 0%.

[0059] Comparative Example 2

[0060] In an autoclave reactor equipped with an electromagnetic stirrer, a thermocouple, and a programmable temperature controller, 0.192 g of CR-pure PET powder (1 mmol), [EMIm][BF 4 ](10mol%), 1mL methanol and 3mL dimethyl carbonate, after placing the autoclave reactor, start stirring and heating. The reaction system is heated to 130°C and reacted at this temperature for 2h. After the reaction is completed, it is cooled to room temperature, and the resulting mixed solution is the product. The resulting mixed solution is diluted with dichloromethane, and the diluent is measured by GC for yield, with mesitylene as the internal standard. The results show that the yield of dimethyl terephthalate in this embodiment is 0%, and the yield of ethylene carbonate is 0%.

[0061] The above Examples 1 to 12 and Comparative Examples 1 to 2 show that not all ionic liquids can be used as catalysts for the above depolymerization reaction. Compared with other ionic liquid catalysts, the five ionic liquid catalysts [Bmim][Cl], [Emim][Br], [Mmim][I], [Emim][Ac] or [Bmim][Ac] have extremely high catalytic performance in catalyzing the depolymerization and upgrading of polyester to carboxylic acid ester and boric acid ester.

[0062] The above-described embodiment is only a preferred solution of the present invention, but it is not intended to limit the present invention. A person skilled in the relevant technical field may make various changes and modifications without departing from the spirit and scope of the present invention. Therefore, any technical solution obtained by equivalent replacement or equivalent transformation falls within the protection scope of the present invention.

Claims

1. A method for upgrading polyester materials to dicarboxylic acid esters and ethylene carbonate, characterized in that: include: S1. Put crushed polyester material, methanol, ionic liquid catalyst and dimethyl carbonate into a reaction kettle to form a reaction system; wherein the polyester material is polyethylene terephthalate (PET) or polyethylene succinate; and the ionic liquid catalyst is imidazole ionic liquid [Emim][Ac], and the structural formula is as follows: In the reaction system, the amount of dimethyl carbonate added is 3.5 mL / mmol of the polyester material, the amount of the ionic liquid catalyst added is 5 mol% of the polyester material, and the amount of the methanol solvent added is 8 times the molar amount of the polyester material; S2, placing the reactor containing the reaction system at a depolymerization temperature of 100-140° C. for 2-4 hours of depolymerization reaction, and cooling to room temperature after the reaction is completed to obtain a depolymerization product containing dicarboxylic acid ester and ethylene carbonate.

2. The method for upgrading polyester materials to dicarboxylic acid esters and ethylene carbonate according to claim 1, characterized in that: The polyester material is waste of polyethylene terephthalate.

3. The method for upgrading polyester materials to dicarboxylic acid esters and ethylene carbonate according to claim 2, characterized in that: The waste is in the form of discarded bottles made of polyethylene terephthalate, discarded matrix films, colored ropes or non-woven fabrics.

4. The method for upgrading polyester materials to dicarboxylic acid esters and ethylene carbonate according to claim 3, characterized in that: The waste must be crushed into centimeter-sized flakes, particles or powders before being added to the reactor.

5. The method for upgrading polyester materials to dicarboxylic acid esters and ethylene carbonate according to claim 1, characterized in that: The depolymerization temperature was 130°C.

6. The method for upgrading polyester materials to dicarboxylic acid esters and ethylene carbonate according to claim 1, characterized in that: The depolymerization time was 2 hours.

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