Method for preparing various kinds of organic acids by depolymerization of polyester and application thereof

Abstract

The application discloses a method for preparing various kinds of organic acids by depolymerization of polyester and application thereof, and relates to the technical field of solid waste resource utilization, and comprises the following steps: mixing polyester material, metal catalyst, iodine-containing catalytic additive and solvent, introducing carbon monoxide, and reacting under the condition of greater than or equal to 140 DEG C for greater than or equal to 2 hours to prepare various kinds of organic acids; the polyester material comprises polyethylene terephthalate, polyethylene succinate and the like; the metal catalyst is a soluble salt of Ru, Pd, Rh, Ir or Ni; and the product organic acids comprise at least two of terephthalic acid, succinic acid, propionic acid, glutaric acid and 4-hydroxybutyric acid. The method can depolymerize polyester with high selectivity at a lower temperature, and can directionally prepare various kinds of organic carboxylic acids with high yield; for example, the conversion of PET can obtain terephthalic acid TPA with a yield of 99%, and propionic acid with a yield of more than 95%, and the method has a good application prospect in the treatment of waste polyester.

Description

Technical Field

[0001] This invention relates to the field of solid waste resource utilization technology, specifically to a method for preparing various organic acids by polyester depolymerization and its application. Background Technology

[0002] Plastic products, with their excellent performance, are widely used in daily life and industry. However, their lifespan is relatively short, and the vast majority of plastic waste is directly incinerated or landfilled, leading to serious environmental problems. Waste plastics are mainly composed of hydrocarbons, some containing oxygen-containing functional groups. The types of chemical bonds and monomer units in their polymer chain structure are similar to those of biomass, making them a potential alternative to fossil resources for the production of fuels and high-value-added chemicals. Through resource utilization technologies such as directed catalytic conversion, not only can the selective synthesis of high-value chemicals be achieved, but plastic waste can also be effectively reduced, providing a sustainable solution for plastic pollution control.

[0003] Polyethylene terephthalate (PET) is the most widely used polyester plastic and a key contributor to plastic pollution. Waste PET is difficult to degrade naturally, and existing mechanical recycling methods degrade material properties, making closed-loop utilization difficult. Chemical recycling methods depolymerize PET through a series of chemical processes to obtain monomers such as terephthalic acid (TPA) and ethylene glycol (EG). However, these processes are highly dependent on the efficiency and selectivity of the catalyst. Although catalytic systems can regulate reaction kinetics (reaction rate and selectivity), they cannot overcome the incomplete depolymerization caused by thermodynamic limitations. Furthermore, in aqueous reaction systems, the generated EG is difficult to separate and recover efficiently due to its high boiling point, and its economic value is low. Therefore, researching the complete depolymerization of PET and its precise conversion into high-value-added chemicals has significant scientific and practical value.

[0004] Chinese patent document CN116219486A discloses the application of a non-precious metal catalyst in the electrocatalytic depolymerization of PET. This non-precious metal catalyst includes a support and a loading material; the support is nickel foam, and the loading material includes Ni(OH)2 grown in situ on the surface of the nickel foam. This non-precious metal catalyst can achieve the electrocatalytic depolymerization of waste PET products at room temperature and pressure with a conversion rate of 99%, and the resulting products are only hydrogen, terephthalate, and formate. Chinese patent document CN114436806A discloses a one-step low-temperature conversion method for preparing disodium terephthalate and hydrogen from waste PET polyester plastics. Waste PET polyester plastics are mixed with a catalyst in a certain proportion and added to a low-concentration NaOH solution. Under specific low-temperature hydrothermal conditions, the hydrothermal depolymerization reaction of PET and the in-situ reforming reaction of the PET depolymerization products are coupled, enabling the one-step conversion of PET into high-purity hydrogen and disodium terephthalate. The inventions mentioned above all involve the efficient conversion of PET, but there are currently few reports on the depolymerization of PET into a variety of high-value organic acids.

[0005] Propionic acid (PA) is an important organic chemical raw material widely used in food, pharmaceuticals, and other fields. The traditional propionaldehyde oxidation method for PA production is complex, has low product selectivity, and is difficult to separate. Recovering PA from waste PET can avoid the environmental impact of traditional PA production, and this high-value recovery strategy facilitates the comprehensive utilization of PET waste at the molecular level, contributing to alleviating petroleum resource depletion and enhancing the recycling value of PET waste. Summary of the Invention

[0006] This invention addresses the need for targeted upgrading of waste polyester plastics and the bottleneck of existing chemical depolymerization processes being unable to overcome thermodynamic limitations. It provides a method for preparing various organic acids by depolymerizing polyester. This method can depolymerize polyester materials with high selectivity at lower temperatures and directionally prepare high-value chemical organic carboxylic acids, which has good application prospects in the treatment of waste polyester.

[0007] The specific technical solution adopted is as follows: A method for preparing various organic acids by depolymerization of polyester includes the following steps: Polyester material, metal catalyst, iodine-containing catalyst aid and solvent are mixed, carbon monoxide is introduced, and the reaction is carried out at ≥140°C for ≥2 h to prepare a variety of organic acids; The polyester material includes polyethylene terephthalate, polyethylene succinate, or polyethylene terephthalate; The metal catalyst is a soluble salt of Ru, Pd, Rh, Ir or Ni; The organic acids produced include at least two of the following: terephthalic acid, succinic acid, propionic acid, glutaric acid, and 4-hydroxybutyric acid.

[0008] Furthermore, when the polyester material is polyethylene terephthalate, the organic acids produced are terephthalic acid and propionic acid; when the polyester material is polyethylene succinate, the organic acids produced are succinic acid and propionic acid; when the polyester material is propylene terephthalate, the organic acids produced are terephthalic acid, glutaric acid and 4-hydroxybutyric acid.

[0009] This invention couples the depolymerization reaction of polyester materials and the carbonylation reaction of the depolymerization products with CO under heating conditions, enabling the reactants in the reaction system to be completely converted into various high-value organic acids in one step. This ensures high efficiency of the reaction and overcomes thermodynamic limitations. Specifically, the metal catalyst promotes the depolymerization of polyester materials and catalyzes the carbonylation reaction of CO insertion, while the iodine-containing catalyst stabilizes the metal catalyst and promotes the carbonylation reaction of CO insertion.

[0010] Furthermore, the metal catalyst is selected from ruthenium chloride, ruthenium nitrate, ruthenium iodide, palladium chloride, palladium acetate, palladium iodide, rhodium iodide, rhodium chloride, rhodium nitrate, iridium chloride, iridium iodide, iridium nitrate, nickel chloride, or nickel iodide, preferably rhodium chloride, iridium chloride, iridium iodide, or iridium nitrate. Experiments have shown that the above four preferred catalysts can synthesize organic acids in higher yields.

[0011] Furthermore, the iodine-containing catalytic aid is selected from hydroiodic acid, lithium iodide, sodium iodide, potassium iodide, ammonium iodide, zinc iodide, rubidium iodide, cesium iodide, calcium iodide, iodomethane, or iodoethane, preferably iodomethane or iodoethane.

[0012] Furthermore, the solvent is selected from water, acetic acid, cyclohexane, or hexafluoroisopropanol, preferably hexafluoroisopropanol.

[0013] Preferably, after carbon monoxide is introduced, the pressure in the reaction vessel is 0.3~3 MPa, the reaction temperature is 140~220°C, and the reaction time is 2~18 h.

[0014] Preferably, the amount of metal catalyst added is 0.005~0.10 mmol / mmol polyester material; the amount of iodine-containing catalyst aid added is 0.20~0.60 mmol / mmol polyester material.

[0015] The present invention also provides the application of the method for preparing various organic acids by depolymerization of polyester in the treatment of waste polyester.

[0016] The method of this invention can be used not only for the depolymerization and upgrading of waste PET materials, but also for other similar polyester materials, such as polyethylene succinate and polypropylene terephthalate. The recycling strategy of this invention is also applicable to these materials, and the products are the corresponding carboxylic acid monomers.

[0017] Furthermore, the waste polyester is waste containing polyethylene terephthalate, waste containing polyethylene succinate, and waste containing propylene terephthalate. The waste polyester is pre-crushed into centimeter-sized flakes, granules, or powder before processing.

[0018] Waste polyester includes, but is not limited to, waste polyethylene terephthalate (PET) bottles, PET ropes, waste PET films, PET braided ropes, PET nonwoven fabrics, PET trays, and fabrics with different PET contents. The method of this invention is applicable to the recycling of various waste polyester materials, has good applicability, and can prepare organic acids with high yield.

[0019] Compared with the prior art, the beneficial effects of the present invention are as follows: (1) The process of the present invention is simple and economically efficient. It realizes the green and high-value utilization of polyester materials, reduces the potential negative impact of organic acid production process on the environment, realizes one-step carbonylation treatment of PET and other polyester waste plastics and carbon monoxide, and can prepare a variety of organic acids with high yield. Taking PET as an example, the yield of terephthalic acid (TPA) obtained by its conversion can reach 99%, the yield of propionic acid can reach more than 95%, and the selectivity of propionic acid can reach 99%.

[0020] (2) The metal catalyst used in this invention has the advantages of high efficiency and recyclability. It can promote the depolymerization of polyester materials and the carbonylation reaction of depolymerization products with CO in a short time. The iodine-containing catalyst can stabilize the metal catalyst and promote the carbonylation reaction of CO insertion. The two work together and neither can be omitted.

[0021] (3) The method of the present invention has a wide range of applications and is applicable to the directional depolymerization and upgrading of various polyester wastes, such as various PET waste bottles, PET ropes, PET waste films, PET woven ropes or PET non-woven fabrics, PET trays, and fabrics with different PET contents. All of these can be efficiently upgraded and converted in a short time and organic acids can be prepared with high yield.

[0022] (4) The method of the present invention can process a variety of polyester materials, including but not limited to polyethylene terephthalate, polyethylene succinate or polyethylene terephthalate, etc. Other polyesters with similar diol units can be upgraded by the method of the present invention, which 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 high-value organic acids. Detailed Implementation

[0023] To make the objectives, features, and advantages of this invention more apparent and understandable, a detailed description is provided below through specific embodiments. Many specific details are set forth in the following description to provide a full understanding of the invention. However, the invention can be practiced in many ways different from those described herein, and those skilled in the art can make similar modifications without departing from the spirit of the invention. Therefore, the invention is not limited to the specific embodiments disclosed below. Technical features in various embodiments of the invention can be combined appropriately without conflict.

[0024] Unless otherwise specified, the operating methods in the following examples are generally performed under conventional conditions or as recommended by the manufacturer. Contents not described in detail in this specification are prior art known to those skilled in the art. Unless otherwise specified, the experimental materials used in the examples below can be purchased from conventional biochemical reagent companies.

[0025] Example 1 In a high-pressure reactor equipped with an electromagnetic stirrer, thermocouple, and programmable temperature controller, 0.192 g of PET powder (1 mmol), 500 μL of rhodium trichloride aqueous solution (containing 0.05 mmol RhCl3), 0.071 g of iodomethane (0.5 mmol), and 2 mL of hexafluoroisopropanol were added. The high-pressure reactor was then closed and carbon monoxide was introduced to reach a pressure of 2 MPa. After placing the reactor in place, stirring and heating were started. The reaction system was heated to 170 °C and reacted at this temperature for 12 h. After the reaction was completed, the mixture was cooled to room temperature to obtain a mixed solution. The supernatant of the obtained mixture was collected and the propionic acid yield was determined by GC, with 1,3,5-trimethylbenzene as an internal standard. An appropriate amount of 1 mmol / L NaOH was added to the precipitate, with deuterium water as the deuteration reagent and sodium fumarate as the internal standard, and the solution was analyzed by liquid chromatography. 1 ¹H NMR determination of terephthalic acid yield. Results showed that in this example, the PET decomposition rate was 100%, and the TPA yield was 99%. The NMR data for terephthalic acid were as follows: 1 ¹H NMR (500 MHz, D₂O) δ 7.89 (s, 4H), the yield of propionic acid (PA) was 94%, and the NMR data for propionic acid were as follows: 1 H NMR (500 MHz, DMSO-d6) δ 2.10 (m, 2H, COOH-C H 2-), 0.98 (t, 3H, C H 3-CH2-).

[0026] The reaction equation in this embodiment is as follows: .

[0027] Example 2 0.192 g PET powder (1 mmol), rhodium-containing catalyst recovery solution (separated from the system in Example 1), 0.071 g iodomethane (0.5 mmol), and 2 mL hexafluoroisopropanol were added to a high-pressure reactor equipped with an electromagnetic stirrer, thermocouple, and programmable temperature controller. The high-pressure reactor was then closed and carbon monoxide was introduced to reach a pressure of 2 MPa. After placing the reactor in place, stirring and heating were started. The reaction system was heated to 170 °C and reacted at this temperature for 12 h. After the reaction was completed, the mixture was cooled to room temperature to obtain a mixture. The supernatant of the obtained mixture was collected and the yield was determined by GC, with 1,3,5-trimethylbenzene as an internal standard. An appropriate amount of 1 mmol / L NaOH was added to the precipitate, with deuterium water as the deuteration reagent and sodium fumarate as the internal standard, and the mixture was analyzed by liquid chromatography. 1 ¹H NMR analysis determined the yield. The results showed that the PET decomposition rate in this example was 100%, the TPA yield was 99%, and the propionic acid yield was 93.9%.

[0028] Example 3-13 The only difference between Examples 3-13 and Example 1 is that the PET powder is replaced with an equal mass of PET waste (the corresponding PET waste was crushed to the centimeter level beforehand). All other reaction conditions and steps are the same as in Example 1. The results are shown in Table 1.

[0029] Table 1. Depolymerization effect of different PET wastes

[0030] Examples 14-15 The only difference between Examples 14-15 and Example 1 is that the PET powder was replaced with equimolar amounts of polyethylene succinate powder and polyethylene terephthalate powder, respectively. All other reaction conditions and steps were the same as in Example 1. The results are shown in Table 2.

[0031] Table 2 Depolymerization effect of different polyester materials

[0032] The NMR data for succinic acid are as follows: 1 H NMR (500 MHz, D2O) δ 2.60 (s, 4H, HOOC-C H 2-C H 2-COOH).

[0033] The NMR data for glutaric acid are as follows: 1 H NMR (500 MHz, D2O) δ 2.4 (t, 2H, HOOC-C H2-CH2-), 1.8 (m, 2H, -CH2-C H 2-CH2-).

[0034] The NMR data for 4-hydroxybutyric acid are as follows: 1 H NMR (500 MHz, D2O) δ 3.60 (t, 2H, HO-C H 2-CH2-), 2.40 (t, 2H, -CH2-C H2 -COOH), 1.80 (m, 2H, -CH2-C H 2-CH2-).

[0035] Examples 16-18 The only difference between Examples 16-18 and Example 1 is that the solvent hexafluoroisopropanol was replaced with equal volumes of water, acetic acid, and cyclohexane, respectively. All other reaction conditions and steps were the same as in Example 1. The results are shown in Table 3.

[0036] Table 3 Depolymerization effect of PET under different solvent conditions

[0037] Examples 19-31 The difference between Examples 19-31 and Example 1 lies only in that the 500 μL rhodium trichloride aqueous solution (containing 0.05 mmol RhCl3) is replaced with equal volumes of 500 μL ruthenium trichloride aqueous solution (containing 0.05 mmol RuCl3), 500 μL ruthenium nitrate aqueous solution (containing 0.05 mmol Ru(NO3)3), 500 μL ruthenium iodide aqueous solution (containing 0.05 mmol RuI3), 500 μL palladium dichloride aqueous solution (containing 0.05 mmol PdCl2), 500 μL palladium acetate aqueous solution (containing 0.05 mmol Pd(OAc)2), 500 μL palladium iodide aqueous solution (containing 0.05 mmol PdI2), 500 μL rhodium triiodide aqueous solution (containing 0.05 mmol RhI3), 500 μL rhodium nitrate aqueous solution (containing 0.05 mmol Rh(NO3)3), and 500 μL iridium trichloride aqueous solution (containing 0.05 mmol RhCl3), respectively. The reaction conditions and steps were the same as in Example 1. The results are shown in Table 4.

[0038] Table 4. Depolymerization effect of PET under different metal catalysts

[0039] Examples 32-41 The only difference between Examples 32-41 and Example 1 is that the iodine-containing catalyst was replaced with 0.093 g hydroiodic acid (0.4 mmol), 0.067 g lithium iodide (0.5 mmol), 0.075 g sodium iodide (0.5 mmol), 0.075 g potassium iodide (0.5 mmol), 0.075 g ammonium iodide (0.5 mmol), 0.160 g zinc iodide (0.5 mmol), 0.106 g rubidium iodide (0.5 mmol), 0.130 g cesium iodide (0.5 mmol), 0.147 g calcium iodide (0.5 mmol), and 0.078 g iodoethane (0.5 mmol), respectively. All other reaction conditions and steps were the same as in Example 1. The results are shown in Table 5.

[0040] Table 5. Depolymerization effect of PET under different iodine-containing catalysts

[0041] Examples 42-46 The only difference between Examples 42-46 and Example 1 is that after carbon monoxide was introduced, the pressure was increased to 0.3 MPa, 0.5 MPa, 1.0 MPa, 1.5 MPa, and 2.5 MPa, respectively. All other reaction conditions and steps were the same as in Example 1. The results are shown in Table 6.

[0042] Table 6. Depolymerization effect of PET under different pressures

[0043] Examples 47-50 The only difference between Examples 47-50 and Example 1 is that the reaction temperatures were set to 150℃, 160℃, 180℃, and 190℃, respectively. All other reaction conditions and steps were the same as in Example 1. The results are shown in Table 7.

[0044] Table 7. Depolymerization effect of PET at different reaction temperatures

[0045] Examples 51-56 The only difference between Examples 51-56 and Example 1 is that the reaction time was set to 0.25 h, 1 h, 4 h, 8 h, 10 h, and 15 h, respectively. All other reaction conditions and steps were the same as in Example 1. The results are shown in Table 8.

[0046] Table 8. Depolymerization effect of PET at different reaction times

[0047] The embodiments described above provide a detailed explanation of the technical solutions of the present invention. It should be understood that the above descriptions are merely specific embodiments of the present invention and are not intended to limit the present invention. Any modifications, additions, or similar substitutions made within the scope of the principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing various organic acids by depolymerization of polyester, characterized in that, Includes the following steps: Polyester material, metal catalyst, iodine-containing catalyst aid and solvent are mixed, carbon monoxide is introduced, and the reaction is carried out at ≥140°C for ≥2 h to prepare a variety of organic acids; The polyester material includes polyethylene terephthalate, polyethylene succinate, or polyethylene terephthalate; The metal catalyst is a soluble salt of Ru, Pd, Rh, Ir or Ni; The organic acids produced include at least two of the following: terephthalic acid, succinic acid, propionic acid, glutaric acid, and 4-hydroxybutyric acid.

2. The method for preparing various organic acids by depolymerization of polyester according to claim 1, characterized in that, When the polyester material is polyethylene terephthalate, the organic acids produced are terephthalic acid and propionic acid; when the polyester material is polyethylene succinate, the organic acids produced are succinic acid and propionic acid; when the polyester material is propylene terephthalate, the organic acids produced are terephthalic acid, glutaric acid and 4-hydroxybutyric acid.

3. The method for preparing various organic acids by depolymerization of polyester according to claim 1, characterized in that, The metal catalyst is selected from ruthenium chloride, ruthenium nitrate, ruthenium iodide, palladium chloride, palladium acetate, palladium iodide, rhodium iodide, rhodium chloride, rhodium nitrate, iridium chloride, iridium iodide, iridium nitrate, nickel chloride, or nickel iodide.

4. The method for preparing various organic acids by depolymerization of polyester according to claim 1, characterized in that, The iodine-containing catalytic aid is selected from hydroiodic acid, lithium iodide, sodium iodide, potassium iodide, ammonium iodide, zinc iodide, rubidium iodide, cesium iodide, calcium iodide, iodomethane, or iodoethane.

5. The method for preparing various organic acids by depolymerization of polyester according to claim 1, characterized in that, The solvent is selected from water, acetic acid, cyclohexane, or hexafluoroisopropanol.

6. The method for preparing various organic acids by depolymerization of polyester according to claim 1, characterized in that, After carbon monoxide is introduced, the pressure in the reaction vessel is 0.3~3 MPa, the reaction temperature is 140~220°C, and the reaction time is 2~18 h.

7. The method for preparing various organic acids by depolymerization of polyester according to claim 1, characterized in that, The amount of metal catalyst added is 0.005~0.10 mmol / mmol polyester material; the amount of iodine-containing catalyst aid added is 0.20~0.60 mmol / mmol polyester material.

8. The application of the method for preparing various organic acids by depolymerization of polyester according to any one of claims 1-7 in the treatment of waste polyester.

9. The application according to claim 8, characterized in that, Waste polyester includes waste containing polyethylene terephthalate, waste containing polyethylene succinate, and waste containing propylene terephthalate. Before processing, the waste polyester is pre-crushed into centimeter-sized flakes, granules, or powder.

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