CN116836191B

CN116836191B - Method for depolymerizing and upgrading polyester material to generate dicarboxylic acid ester and boric acid ester

Info

Publication number: CN116836191B
Application number: CN202310544293.9A
Authority: CN
Inventors: 梅清清; 张铭浩; 阎炳会; 余云开
Original assignee: Zhejiang University ZJU
Current assignee: Zhejiang University ZJU
Priority date: 2023-05-15
Filing date: 2023-05-15
Publication date: 2025-01-14
Anticipated expiration: 2043-05-15
Also published as: CN116836191A

Abstract

The invention discloses a method for depolymerizing and upgrading polyester materials to generate dicarboxylic acid esters and boric acid esters, and relates to the comprehensive utilization of waste resources and the cascade utilization of raw materials. The method uses a heterogeneous solid alkali magnesium aluminum hydrotalcite or a composite oxide derived therefrom to catalyze the methanolysis reaction of PET, and then phenylboronic acid captures the generated ethylene glycol in situ, and dehydrates and cyclizes to form different types of five-membered cyclic boric acid esters. The products of the method of the invention are dimethyl terephthalate and different five-membered cyclic boric acid esters. The invention can be used for the depolymerization and upgrading of waste PET materials, and can also be used for other similar polyesters and polycarbonates, such as polyethylene adipate, polyethylene succinate and polypropylene carbonate, which are also suitable for the recovery strategy of the invention, and the products are corresponding boric acid esters, dimethyl succinate and dimethyl adipate. In addition, the catalyst in the reaction has high catalytic efficiency, is easy to separate and recycle, can be reused, and effectively reduces the reaction cost.

Description

Method for depolymerizing and upgrading polyester material to generate dicarboxylic acid ester and boric acid ester

Technical Field

The invention relates to a method for producing dimethyl terephthalate and boric acid ester by depolymerizing and upgrading high-selectivity PET, which relates to comprehensive utilization of waste resources and cascade utilization of raw materials. More particularly, the present invention relates to a method for methanol depolymerizing of a variety of polyester raw materials and polycarbonates including PET, and obtaining high yields of dicarboxylic acid esters and a variety of five-membered cyclic boric acid esters.

Background

Polyethylene terephthalate (PET) is a polymer widely used in plastic packaging and fibers. The "disposable" nature and short service life (typically 6 months) of PET bottles make them the most common plastic waste, accounting for about 10% of the world's total. However, only 42% of the PET bottles are recycled, and the remaining 58% of the waste plastic is eventually thrown into landfills or burned. Currently, the main methods of processing PET are heat recovery, mechanical recovery, or chemical recovery, but only chemical recovery can convert the polymer into virgin monomer, fuel, or other value added product, extending the value chain and improving product quality. Chemical depolymerization of PET occurs by hydrolysis, alcoholysis, aminolysis or ammonolysis, which involves the selection of different nucleophiles to attack the c=o bonds in the polyester. However, the chemical depolymerization can be regarded as a monomer recovery strategy to some extent, and ethylene glycol produced simultaneously in the reaction is difficult to separate and recover due to the high boiling point characteristic and is usually abandoned. The ethylene glycol units of PET, however, also have a great potential for conversion to high value chemicals, and have been used for conversion of precursor materials to higher value-added small molecule carboxylic acids and light olefins. The innovative recycling of ethylene glycol units is therefore an important problem to be solved in the field of PET depolymerization at present.

Historically, most chemical recovery strategies have not been effectively implemented and eventually failed due to the low economic value of the derivative product. To advance the development of this field, it is important to simplify the monomer purification procedure and reduce the energy consumption. In various processing methods, PET methanolysis-derived dimethyl terephthalate (DMT) is more easily extracted and purified from the reaction system due to lower water solubility, making it a suitable alternative substrate for synthesizing recycled PET materials or other chemicals. Furthermore, the methanol decomposition system has a high contamination resistance, making it a cost-effective option for the treatment of complex PET-based waste materials. However, generally methanol decomposition requires relatively high temperatures (typically 200 ℃ C. Gtoreq.s.) to promote slow decomposition PET depolymerization reactions, and the product DMT yields are only between 80-85%. In order to pursue high yield of DMT, there are few research projects of supercritical methanol or microwave-assisted methanol decomposition systems, but the research projects are not advocated in consideration of equipment operation, economic benefit and the like. Furthermore, the use of homogeneous catalysts in most reactions results in difficulty in their separation from the system, causing additional economic costs, which also to some extent limit the industrial progress of the methanolysis of PET waste plastics. Therefore, developing a mild and efficient methanolysis strategy is important. Therefore, how to provide a means for reducing the cost of recycling catalyst in a PET methanol hydrolysis catalytic system, a directional upgrading recycle strategy of glycol in a depolymerization process and the catalyst in the catalytic system is a problem to be solved by those skilled in the art.

The cyclic borate is an important organic boron compound, and has been widely used in efficient construction of drugs and natural products due to the advantages of good functional group compatibility, simple preparation process of boric acid derivatives, low toxicity of boron byproducts, and the like. In addition, borates exhibit better chemoselectivity and regioselectivity than boric acid in some metal-catalyzed cross-coupling reactions (such as Heck and Suzuki reactions). In general, borates are obtained by reversible combination of glycol and boric acid, and thus, aryl boric acid can be used to capture EG components from waste PET, thereby achieving high value conversion of glycol while solving the glycol separation problem. The high-value recycling strategy is beneficial to complete comprehensive utilization of PET waste molecular layers, byproducts are only water, consumption of petroleum resources is relieved to a certain extent, and the recycling value of PET waste is improved.

Disclosure of Invention

Aiming at the requirements of PET waste plastic depolymerization and product directional upgrading and the defects existing in the prior art, the invention provides a method for depolymerizing and upgrading polyester materials to generate dicarboxylic acid esters and boric acid esters.

The specific technical scheme adopted by the invention is as follows:

a method for depolymerizing and upgrading polyester materials to generate dicarboxylic acid esters and boric acid esters comprises the following steps:

S1, placing a crushed polyester material, arylboronic acid, a heterogeneous catalyst and a methanol solvent into a reaction kettle, wherein the polyester material is polyethylene terephthalate (PET), polypropylene carbonate, polyethylene adipate or polyethylene succinate, the arylboronic acid is phenylboronic acid, p-methylphenylboronic acid, 3-methylphenylboronic acid or 4-fluorobenzeneboronic acid, and the heterogeneous catalyst is magnesium aluminum hydrotalcite or magnesium aluminum hydrotalcite derivative composite oxide which is baked at 350-600 ℃ and has a Mg/Al ratio of (4-1): 1;

And S2, carrying out depolymerization reaction on the reaction kettle at 160-200 ℃ for 1-4 hours, and cooling to room temperature after the reaction is finished to obtain a depolymerization product containing dicarboxylic acid ester and arylboric acid ester.

Taking PET as an example, the reaction formula of the depolymerization reaction can be expressed as:

preferably, the arylboronic acid is added in the same molar amount as the polyester-based material.

Preferably, the addition amount of the heterogeneous catalyst is 0.05-0.5 wt% of the polyester material.

Preferably, the addition amount of the methanol solvent is 3-6 mL/mmol of the polyester material.

Preferably, the polyester material is waste of polyethylene terephthalate (PET) material, and the waste is crushed into centimeter-level slices, particles or powder before being added into the reaction kettle, so that the recycling effect of the waste PET material can be ensured, and the dimethyl terephthalate and the Arylborate (ABE) can be obtained in a directional upgrading and high yield.

Preferably, the waste is in the form of PET waste bottles, PET matrix waste films, PET color strapping or PET non-woven fabrics.

Preferably, the roasting temperature of the heterogeneous catalyst is preferably 450-500 ℃.

Preferably, the roasting time of the heterogeneous catalyst is 4-8 hours.

Preferably, the Mg/Al ratio in the heterogeneous catalyst is preferably 4:1.

Preferably, the depolymerization temperature is 180 ℃.

Compared with the prior art, the invention has the following beneficial effects:

(1) The heterogeneous solid magnesium aluminum hydrotalcite derivative composite oxide catalyst adopted by the invention has the advantages of high efficiency, simple and convenient recovery and repeated cyclic utilization, and can promote the implementation of the methanolysis reaction of PET and the directional upgrading recovery of glycol in a short time.

(2) The waste plastic PET methanol depolymerization strategy developed by the invention has the advantages of short reaction time and high catalytic efficiency, and can finish the PET-DMT and glycol-borate directional conversion process with 99% yield under standard reaction conditions. The strategy has wide application range, various types of waste PET raw materials and various waste PET materials such as various PET waste bottles, PET matrix waste films, PET color binding ropes and PET non-woven fabrics can be used for efficiently finishing the directional upgrading conversion in a short time.

(3) The PET waste plastic matrix material can be replaced by various polyesters and polycarbonates with similar glycol units, such as polyethylene glycol succinate, polyethylene glycol adipate and polypropylene carbonate, so that the high applicability range of the strategy is displayed to a certain extent, the field range of waste plastic treatment materials is further widened, and corresponding conversion can be completed to obtain dicarboxylic acid ester and boric acid ester on the premise of ensuring high depolymerization efficiency and rapid reaction time.

Drawings

FIG. 1 is a graph showing the effect of recycling the catalyst of the present invention.

Detailed Description

The foregoing objects, features and advantages of the invention will be more readily apparent from the following detailed description of the invention. In the following description, numerous specific details are set forth in order to provide a thorough understanding of the present invention. The present invention may be embodied in many other forms than described herein and similarly modified by those skilled in the art without departing from the spirit of the invention, whereby the invention is not limited to the specific embodiments disclosed below. The technical features of the embodiments of the invention can be combined correspondingly on the premise of no mutual conflict.

Example 1

An autoclave reactor equipped with an electromagnetic stirrer, a thermocouple and a program temperature controller was charged with 0.192 g of PET powder (1 mmol), 0.13 g of p-methylphenylboric acid (1 mmol), 0.03 g of calcined commercial magnesium aluminum hydrotalcite (Mg/Al=3:1) and 5mL of methanol, and after the autoclave reactor was set, stirring and heating were started. The reaction system was warmed to 180 ℃ and reacted at that temperature for 2h. After the reaction is completed, the temperature is reduced to room temperature, and the obtained mixed solution is the product. The obtained mixed solution was diluted with methylene chloride, and the yield of the diluted solution was measured by GC, and mesitylene was found to be an internal standard, which showed that the PET decomposition rate of this example was 100%, the yield of dimethyl terephthalate was 87%, and the yield of p-methylphenyl borate was 90%.

It should be noted that the catalyst in the invention is a composite oxide derived from magnesium aluminum hydrotalcite, but the ratio of Mg/Al can be controlled to change the catalytic performance, and the ratio of Mg/Al can be controlled to be (4-1): 1. Experiments show that the composite oxide with the Mg/Al ratio to be controlled to be 4:1 can achieve the optimal depolymerization reaction catalysis performance. In addition, in the experiment, the commercial hydrotalcite material can be used as a catalyst precursor, and the derivative composite oxide of the catalyst precursor can be synthesized by roasting to be used as a reaction catalyst. Another preferred method of preparing the magnesium aluminum hydrotalcite derived composite oxide catalyst is shown below by example 2.

Example 2

Preparation of heterogeneous catalyst magnesium aluminum hydrotalcite derived composite oxide (LDOs):

at a constant pH of 10, various hydrotalcites are prepared by a coprecipitation method, and then a magnesium-aluminum hydrotalcite derivative composite oxide (LDOs) is prepared by roasting. Firstly, two solutions are prepared, namely, a flask A is prepared, naNO ₃.80 g (0.08 mol) is dissolved in 50mL of deionized water, a beaker B is prepared, 15.38g of Mg (NO ₃)₂6H₂ O (0.060 mol) and 5.63g of Al (NO ₃)₃9H₂ O (0.015 mol)) are dissolved in 50mL of deionized water, the content of the beaker B is added into the flask A in a dropwise manner, the pH value is kept to be 10 by using 1mol/L of NaOH solution in the dropwise process, the obtained mixed solution is reacted for two hours at the ambient temperature, then the mixed solution is heated to 80 ℃ for stirring and refluxing for 12 hours, the obtained precipitate is filtered, the mixture is washed by hot deionized water, then dried in a vacuum drying oven at 80 ℃ for 24 hours, and layered double hydroxide (Mg ₄-Al₁ -LDH) is obtained, specifically, the mixture is baked after the dried Mg ₄-Al₁ -LDH is ground into powder, the mixture is heated to 450 ℃ in an argon stream of a tubular furnace and kept for 4 hours and 500 ℃ for 4 hours, and the obtained composite magnesium oxide is kept in a tubular furnace for 4 ℃ for 4 hours, and the LDO-3 is a composite catalyst, namely, the composite magnesium oxide is obtained, and the composite catalyst is subjected to a heterogeneous phase is stored under the condition of LDO-3, and the LDO is a heterogeneous catalyst is used as a catalyst for the final catalyst.

Example 3

An autoclave reactor equipped with an electromagnetic stirrer, a thermocouple and a program temperature controller was charged with 0.192 g of CR-purity PET powder (1 mmol), 0.13 g of p-methylphenylboronic acid (1 mmol), 0.03 g of catalyst LDO-I and 5mL of methanol, and after the autoclave reactor was set, stirring and heating were started. The reaction system was warmed to 180 ℃ and reacted at that temperature for 2h. After the reaction is completed, the temperature is reduced to room temperature, and the obtained mixed solution is the product. The obtained mixed solution was diluted with methylene chloride, and the yield of the diluted solution was measured by GC, and mesitylene was used as an internal standard, which revealed that the PET decomposition rate of this example was 100%, the yield of dimethyl terephthalate was 99%, and the yield of p-methylphenyl borate was 99%.

In addition, in order to prove the recycling property of the catalyst, the reacted catalyst LDO-I is separated and recovered, and is dried at 150 ℃ after being rinsed and decontaminated, so that the obtained heterogeneous solid magnesium aluminum hydrotalcite derivative composite oxide catalyst is directly recycled to the next reaction. The test results are shown in FIG. 1, and the yields of p-methylphenylborate and dimethyl terephthalate after repeated use for 6 times still reach 85% and 99%, respectively. After repeating for 6 times, the catalyst is heated to 450-500 ℃ again and baked, the catalytic effect of the catalyst can be basically recovered, and the yields of the p-methylphenyl borate and the dimethyl terephthalate are respectively 98% and 99% when depolymerization is carried out after recovery.

Example 4

Waste PET plastic bottles (brands such as cola, coca-cola and farmer mountain spring) are crushed in centimeter level in advance, then an autoclave reactor equipped with an electromagnetic stirrer, a thermocouple and a program temperature controller is filled with centimeter level crushed materials (1 mmol) of 0.192 g PET plastic bottle, 0.13 g p-toluylboronic acid (1 mmol), 0.03 g catalyst LDO-I and 5mL methanol, and after the autoclave reactor is placed, stirring and heating are started. The reaction system was warmed to 180 ℃ and reacted at that temperature for 3h. After the reaction is completed, the temperature is reduced to room temperature, and the obtained mixed solution is the product. The obtained mixed solution was diluted with methylene chloride, and the yield of the diluted solution was measured by GC, and mesitylene was used as an internal standard, which revealed that the PET decomposition rate of this example was 100%, the yield of dimethyl terephthalate was 99%, and the yield of p-methylphenyl borate was 99%.

Example 5

An autoclave reactor equipped with an electromagnetic stirrer, a thermocouple and a program temperature controller was charged with 0.192 g of PET powder (1 mmol), 0.136 g of 3-methylphenylboronic acid (1 mmol), 0.03 g of catalyst LDO-I and 5mL of methanol, and after the autoclave reactor was set, stirring and heating were started. The reaction system was warmed to 180 ℃ and reacted at that temperature for 2h. After the reaction is completed, the temperature is reduced to room temperature, and the obtained mixed solution is the product. The resulting mixture was diluted with methylene chloride, and the yield of the diluted solution was measured by GC, and mesitylene was found to be an internal standard, which indicated that the PET decomposition rate of this example was 100%, the yield of dimethyl terephthalate was 99%, and the yield of 3-methylphenylborate was 99%.

Example 6

An autoclave reactor equipped with an electromagnetic stirrer, a thermocouple and a program temperature controller was charged with 0.192 g of PET powder (1 mmol), 0.139 g of 4-fluorobenzeneboronic acid (1 mmol), 0.03 g of catalyst LDO-I and 5mL of methanol, and after the autoclave reactor was set, stirring and heating were started. The reaction system was warmed to 180 ℃ and reacted at that temperature for 2h. After the reaction is completed, the temperature is reduced to room temperature, and the obtained mixed solution is the product. The obtained mixed solution was diluted with methylene chloride, and the yield of the diluted solution was measured by GC, and mesitylene was used as an internal standard, which revealed that the PET decomposition rate of this example was 100%, the yield of dimethyl terephthalate was 99%, and the yield of p-fluorobenzeneborate was 99%.

Example 7

An autoclave reactor equipped with an electromagnetic stirrer, a thermocouple and a program temperature controller was charged with 0.102 g of polypropylene carbonate particles (1 mmol), 0.136 g of p-methylphenylboronic acid (1 mmol), 0.03 g of catalyst LDO-I and 5mL of methanol, and after the autoclave reactor was set, stirring and heating were started. The reaction system was warmed to 180 ℃ and reacted at that temperature for 2h. After the reaction is completed, the temperature is reduced to room temperature, and the obtained mixed solution is the product. The resulting mixture was diluted with methylene chloride, and the yield of the diluted solution was measured by GC with mesitylene as an internal standard, and the result showed that the polypropylene carbonate particles of this example had a decomposition rate of 100% and produced dimethyl carbonate and p-methylphenyl borate, and the yield of p-methylphenyl borate was 95%.

Example 8

An autoclave reactor equipped with an electromagnetic stirrer, a thermocouple and a program temperature controller was charged with 0.172 g of polyethylene glycol adipate (1 mmol), 0.136 g of p-methylphenylboronic acid (1 mmol), 0.03 g of catalyst LDO-I and 5mL of methanol, and after the autoclave reactor was set, stirring and heating were started. The reaction system was warmed to 180 ℃ and reacted at that temperature for 2h. After the reaction is completed, the temperature is reduced to room temperature, and the obtained mixed solution is the product. The obtained mixed solution was diluted with methylene chloride, and the yield of the diluted solution was measured by GC, and mesitylene was used as an internal standard, which revealed that the decomposition rate of polyethylene glycol adipate of this example was 100%, the yield of dimethyl adipate was 98%, and the yield of p-methylphenyl borate was 99%.

Example 9

An autoclave reactor equipped with an electromagnetic stirrer, a thermocouple and a program temperature controller was charged with 0.144 g of polyethylene succinate (1 mmol), 0.136 g of p-methylphenylboronic acid (1 mmol), 0.03 g of catalyst LDO-I and 5mL of methanol, and after the autoclave reactor was set, stirring and heating were started. The reaction system was warmed to 180 ℃ and reacted at that temperature for 1 hour. After the reaction is completed, the temperature is reduced to room temperature, and the obtained mixed solution is the product. The obtained mixed solution was diluted with methylene chloride, and the yield of the diluted solution was measured by GC, and mesitylene was used as an internal standard, and the result showed that the decomposition rate of polyethylene glycol succinate in this example was 100%, the yield of dimethyl succinate was 88%, and the yield of p-methylphenyl borate was 99%.

The above embodiment is only a preferred embodiment of the present invention, but it is not intended to limit the present invention. Various changes and modifications may be made by one of ordinary skill in the pertinent art without departing from the spirit and scope of the present invention. Therefore, all the technical schemes obtained by adopting the equivalent substitution or equivalent transformation are within the protection scope of the invention.

Claims

1. A method for depolymerizing and upgrading polyester materials to generate dicarboxylic acid esters and boric acid esters is characterized by comprising the following steps:

S1, placing crushed polyester materials, arylboronic acid, heterogeneous catalyst and methanol solvent into a reaction kettle; wherein the polyester material is polyethylene terephthalate (PET), polypropylene carbonate, polyethylene adipate or polyethylene succinate; the preparation method comprises the steps of dissolving 6.80g of NaNO ₃ in 50mL of deionized water to obtain a first solution, dissolving 15.38g of Mg (NO ₃)₂6H₂ O and 5.63g of Al (NO ₃)₃9H₂ O) in 50mL of deionized water to obtain a second solution, dropwise adding the second solution into the first solution, reacting the obtained mixed solution for two hours at the ambient temperature by using a NaOH solution with the pH value of 1mol/L in the dropwise adding process, heating the mixed solution to 80 ℃ for stirring and refluxing for 12 hours, filtering the obtained precipitate, washing the precipitate with hot deionized water, drying the washed precipitate in a vacuum drying box with the temperature of 80 ℃ for 24 hours to obtain layered double hydroxide, grinding the dried layered double hydroxide into powder, heating the layered double hydroxide in an argon flow of a tubular furnace to 450 ℃ and maintaining the temperature for 4 hours, and heating the layered double hydroxide to the temperature for 500 ℃ for maintaining the magnesium oxide for another 500 ℃ to obtain the calcined composite oxide;

S2, carrying out depolymerization reaction for 1-4 hours at a depolymerization temperature of 160-200 ℃ on the reaction kettle, and cooling to room temperature after the reaction is finished to obtain a depolymerization product containing dicarboxylic acid ester and arylboric acid ester;

The dicarboxylic acid ester is dimethyl terephthalate, dimethyl carbonate, dimethyl adipate or dimethyl succinate;

the aryl borate is 3-methyl phenyl borate, p-fluoro phenyl borate or p-methyl phenyl borate.

2. The method for upgrading a polyester-based material to dimethyl terephthalate and boric acid esters according to claim 1, wherein the arylboronic acid is added in the same molar amount as the polyester-based material.

3. The method for upgrading a polyester-based material to produce dimethyl terephthalate and boric acid ester according to claim 1, wherein the heterogeneous catalyst is added in an amount of 0.05 wt% -0.5 wt% of the polyester-based material.

4. The method for producing dimethyl terephthalate and boric acid ester by upgrading a polyester material according to claim 1, wherein the addition amount of the methanol solvent is 3-6 mL/mmol of the polyester material.

5. The method for upgrading a polyester material to produce dimethyl terephthalate and boric acid ester according to claim 1, wherein the polyester material is waste of polyethylene terephthalate (PET) material, and the waste is crushed into a centimeter-level flake, granule or powder before being added into a reaction kettle.

6. The method for upgrading a polyester-based material to dimethyl terephthalate and boric acid ester according to claim 5, wherein the waste is in the form of PET waste bottles, PET matrix waste films, PET color strapping or PET nonwoven fabrics.

7. The method for upgrading a polyester-based material to dimethyl terephthalate and boric acid esters according to claim 1, wherein the depolymerization temperature is 180 ℃.