A method for preparing polyethylene succinate

Abstract

The present invention relates to a method for preparing polyethylene succinate, belonging to the technical field of polymer material synthesis. The technical problem solved by the present invention is to provide a method for preparing polyethylene succinate that can shorten the reaction time and improve the product performance. The method includes: adding succinic acid, ethylene glycol and a catalyst into a reaction kettle for negative-pressure esterification reaction, and after the esterification is completed, carrying out low-vacuum polycondensation reaction to obtain a polymer melt, and then obtaining polyethylene succinate slices through cooling and pelletizing. The method of the present invention has low cost and short reaction time. The esterification time is shortened through negative-pressure esterification, and a self-made catalyst is used to participate in the reaction, with high catalytic performance and being green. The synthesized product has excellent mechanical properties. The polyethylene succinate polyester prepared by this method has Mw > 150000 g / mol, tensile strength > 30 MPa, and elongation at break > 350%, which is beneficial to industrialization.

Description

Technical Field

[0001] The present invention belongs to the technical field of biodegradable polyesters and their preparation methods, and particularly relates to a preparation method of polyethylene succinate. Background Art

[0002] Plastics are one of the most important materials in the modern chemical industry and are widely used in various fields of life. However, the recycling rate of plastics is low, and they cause relatively large environmental pollution. Currently, more than 60 countries around the world have introduced policies to restrict or ban disposable non-degradable plastic products. Plastic restriction and prohibition are becoming a global consensus and common measure to protect the environment, and degradable plastics are an inevitable choice to solve the above problems.

[0003] Currently, the commercially available aliphatic polyesters mainly include poly(butylene adipate-co-terephthalate) (PBAT), polylactic acid (PLA), poly(butylene succinate) (PBS), and polycaprolactone (PCL). Among them, PBS has good comprehensive properties and is a hot spot in the research and attention of biodegradable polyesters. However, its production cost is relatively high, making it difficult to be widely promoted. As a homolog of PBS, polyethylene succinate (PES) uses ethylene glycol and succinic acid as raw materials, which has the advantages of rich raw material sources, good thermal stability and mechanical properties, faster degradation rate, lower cost, and a number-average relative molecular mass (Mn) of more than 40,000, and can replace general plastics. It is a type of environmentally friendly polyester with great development prospects.

[0004] The synthesis methods of polyethylene succinate (PES) mainly include solution polymerization, melt polymerization, and a process combining solution-melt polymerization. The solution polymerization reaction temperature is relatively low, and the polymerization reaction rate is also slow (usually more than 10 hours). The solvent needs to be recovered and treated, resulting in relatively high production costs and relatively low relative molecular mass of the product. The direct melt polycondensation process has a simple process flow, a short reaction time, and a relatively high relative molecular mass of the product. However, it needs to be carried out under high temperature and high vacuum conditions, has high requirements for equipment, and is prone to side reactions, leading to adverse effects such as the deepening of the product color. The process combining solution-melt polymerization carries out the esterification stage in a solvent. After the esterification is completed, the solvent is removed, and then melt polymerization is carried out under high temperature and high vacuum to obtain a polymer with a high relative molecular mass. However, the total reaction time still exceeds 10 hours, and the operation is relatively complicated.

[0005] Patent CN101628972A discloses a method for preparing polyethylene succinate, which includes putting succinic acid, ethylene glycol and a catalyst into a reaction kettle. Among them, the molar ratio of succinic acid to ethylene glycol is 1-3:1; the molar ratio of the catalyst to succinic acid is 1:1-1000. Then a high-boiling solvent is added to the system. First, it reacts at 100-180°C for 1-5 hours, and then reacts at 180-240°C for 8-24 hours. Finally, the solvent is removed, and then a chain extender such as diisocyanate, dicarboxylic acid chloride or dianhydride is used to react at 50-200°C for 0.5-5 hours. The polyester prepared by the present invention has a number-average molecular weight that can reach more than 200,000, is a thermoplastic plastic, and has good mechanical properties. However, the total reaction time of this preparation method is as high as nearly 30 hours. In addition, this preparation method needs to use high-boiling solvents such as dimethyl sulfoxide and N,N-dimethylformamide. After the esterification stage is completed, the solvent needs to be removed. Incomplete removal will directly affect the performance of the final product. In addition, the removal and recovery treatment of the solvent have high production costs and are difficult to be actually utilized.

[0006] Saint and Chen et al. used n-succinic acid / n-ethylene glycol = 1.0 as the raw material, 0.1% of titanium tetraisopropoxide as the catalyst, the reaction temperature was 190°C, the amount of water generated reached 70%-80% of the theoretical value, the pressure was reduced to 133 Pa, and after reacting for 3 h, the temperature was raised to 220°C and maintained under this condition for 20 h to obtain PES with an intrinsic viscosity of 1.08 dL / g, Mn of 105,000, and a relative molecular mass distribution of 1.6. The polyester obtained by this method has a high relative molecular mass and a relatively narrow relative molecular mass distribution, but the reaction time is relatively long. Hiroshi et al. used titanium tetraisopropoxide as the catalyst, the reaction temperature was 200°C, and reacted at 1330 Pa to atmospheric pressure for 17 h. The prepolymerization reaction of succinic acid and ethylene glycol with different molar ratios was studied. When n-succinic acid / n-ethylene glycol = 1 / 2, a prepolymer with a relative molecular mass of 5500 could be obtained; the prepolymer still used titanium tetraisopropoxide as the catalyst and was further polycondensed at 240°C and a vacuum degree of 145-160 Pa for 3.5 h to obtain PES with Mn of 74,000, but the total reaction time exceeded 20 h. Using a traditional single titanium-based catalyst as the esterification catalyst, PES polyester can be successfully prepared, but there are generally problems of low relative molecular mass and long reaction time, which is also one of the factors leading to the ultimate failure of PES to be industrialized.

[0007] To sum up, the following problems exist in the current synthesis of polyethylene succinate (PES) polyester: (1) The reaction time is long, resulting in high production costs and low production efficiency; (2) The synthesized PES polyester has a low relative molecular mass and poor mechanical properties. Therefore, there is an urgent need to develop a preparation method for polyethylene succinate that can shorten the reaction time and has excellent product performance. Summary of the Invention

[0008] In view of the above problems existing in the prior art, the present invention provides a method for preparing polyethylene succinate. This method can shorten the reaction time, increase the relative molecular mass and mechanical properties of PES polyester.

[0009] To achieve the above object of the invention, the technical solution adopted by the present invention is as follows:

[0010] A method for preparing polyethylene succinate, the preparation method comprising the following sequential steps:

[0011] a. Esterification: Succinic acid, ethylene glycol and a catalyst are added to a reaction kettle, heated to 180 - 200 °C, and subjected to esterification reaction under negative pressure for 1.5 - 3 h to obtain an esterified product;

[0012] b. Pre - polycondensation: The esterified product obtained in step a is controlled at a reaction temperature of 200 - 230 °C and a vacuum degree of 0.5 - 5 kPa, and reacted for 0.5 - 2 h to obtain a prepolymer;

[0013] c. Polycondensation: A reactive assistant is added to the prepolymer obtained in step b, the reaction temperature is controlled at 200 - 250 °C, the vacuum degree is 20 - 200 Pa, and the reaction is carried out for 3 - 8 h to obtain a polyethylene succinate melt;

[0014] d. Cooling and pelletizing: The polyethylene succinate melt obtained in step c is cooled and pelletized to obtain polyethylene succinate chips.

[0015] In the present invention, the catalyst is a liquid titanium - based catalyst.

[0016] In the present invention, the components of the liquid titanium - based catalyst are a ligand, an organic titanate, a complexing agent and ethylene glycol. The mass ratio of the organic titanate to the ligand, ethylene glycol and complexing agent is 1:0.01 - 0.6:0.5 - 2.1:0.01 - 0.7.

[0017] In the present invention, the organic titanate in the components of the liquid titanium - based catalyst includes one or more of tetraethyl titanate, tetramethyl titanate, tetra - n - butyl titanate; the ligand is one or more of diethanolamine, triethanolamine, ethylene glycol monobutyl ether, octylphenol polyoxyethylene ether; the complexing agent is one or more of trimethyl phosphate, triethyl phosphate, tributyl phosphate, trimethyl phosphite, triethyl phosphite.

[0018] The liquid titanium - based catalyst in the present invention can provide active sites for PES polymerization, reduce the initiation temperature of the reaction. Among them, each component can effectively inhibit hydrolysis and oxidation during the polymerization process, promote the forward progress of the polymerization reaction, induce the highly ordered arrangement of molecular chain segments, thereby enhancing the PES polymerization activity. It reduces the catalyst usage content, simultaneously reduces the reaction temperature during the preparation process, improves the product quality, and has guiding significance for industrialization.

[0019] In the present invention, the catalyst content is 0.2% - 0.4% of the theoretical yield. Preferably, the catalyst dosage is 0.25%.

[0020] In the present invention, the negative pressure is achieved by a vacuum device connected to the reaction kettle. The vacuum degree range in step a is 100 - 40 kPa.

[0021] Under this vacuum degree, it is ensured that the ethylene glycol vapor after heating is condensed in the condenser and then refluxed into the reaction kettle to continue participating in the reaction, while the esterification water vapor and aldehyde by - product vapor are taken out of the system, accelerating the esterification reaction in the positive direction. On the premise of ensuring the esterification rate, the esterification time is shortened.

[0022] In the present invention, the molar ratio of succinic acid to ethylene glycol is 1:1.1 - 1:1.5. Preferably, the molar ratio of succinic acid to ethylene glycol is 1:1.3.

[0023] In the present invention, the reactive assistant is one or a combination of hexamethylene diisocyanate, phthalic anhydride, 2,4 - toluene diisocyanate, 4,4 - dimethylbenzylidene diisocyanate, polypropylene glycol diglycidyl ether. The above assistants can be used alone or in combination, and there are differences in the synthetic products. They are selected according to specific requirements during use.

[0024] In the present invention, the dosage of the reactive assistant is 0.01% - 0.8% of the theoretical yield. Preferably, the dosage of the reactive assistant is 0.01% - 0.5%. The usage amount of the reactive assistant is adjusted according to the specific requirements of the final product.

[0025] The present invention also provides polyethylene succinate (PES) prepared by the preparation method described in the above technical solution.

[0026] The polyethylene succinate prepared by the present invention has Mw > 150000 g / mol, tensile strength > 30 MPa, and elongation at break > 350%.

[0027] A method for preparing polyethylene succinate of the present invention has a short reaction time, a simple process, and the prepared polyethylene succinate (PES) has a high number - average molecular weight, high tensile strength, and high elongation at break. The present invention has the following beneficial effects:

[0028] 1. The present invention uses the melt polycondensation method to prepare PES polyester, without using high - boiling - point solvents, with a simple process and low production cost.

[0029] 2. The present invention uses negative - pressure esterification in the esterification process. On the premise of ensuring the esterification rate, the esterification reaction time is shortened.

[0030] 3. The catalyst used in the present invention is a self - made catalyst, which is efficient and green.

[0031] 4. The poly(ethylene succinate) prepared by the present invention has a high weight-average molecular weight and excellent mechanical properties. Detailed implementation mode

[0032] The present invention will be further described below in conjunction with embodiments. It should be noted that the embodiments do not constitute a limitation on the scope of protection required by the invention.

[0033] In the present invention, succinic acid and ethylene glycol are used for melt polycondensation. First, negative-pressure esterification is carried out. After the esterification is completed, pre-polycondensation is carried out under low vacuum. After the pre-polycondensation is completed, a reactive assistant is added to enter the polycondensation stage. By adopting the negative-pressure esterification process and the method of self-made catalyst, the reaction time is shortened, the molecular mass and mechanical properties of the product are improved, and a polyester with Mw>150000 g / mol, tensile strength>30 Mpa, and elongation at break greater than 350% is prepared.

[0034] The succinic acid and ethylene glycol used in the examples are all industrial-grade products self-produced by the enterprise.

[0035] All the catalyst raw materials and reactive assistants in the examples are of analytical purity and are commercially available.

[0036] The catalyst adopted by the present invention is a self-made liquid titanium-based catalyst.

[0037] Calculated based on 100 parts by weight of the theoretical output of the product, the catalyst dosage is 0.1-0.3 parts by weight, preferably 0.25 parts by weight.

[0038] In the negative-pressure esterification reaction, when the amount of esterification wastewater is close to or exceeds the theoretical water output and no more esterification wastewater flows out, it is regarded as the end of esterification. The calculation formula for the theoretical amount of esterification wastewater is as follows:

[0039] Esterification water output: (Ms / 118)*18*2

[0040] Where Ms: the mass of the reactant succinic acid, 118 is the molecular weight of succinic acid

[0041] The reactive assistants adopted by the present invention are hexamethylene diisocyanate, phthalic anhydride, 2,4-toluene diisocyanate, 4,4-dimethylxylene methane diisocyanate, and polypropylene glycol diglycidyl ether.

[0042] Calculated based on 100 parts of the theoretical output of the product, the dosage of the reactive assistant is 0.1-0.8 parts by weight.

[0043] The molecular weight is measured by gel permeation method, using N,N-dimethylformamide as the mobile phase, polystyrene as the standard sample, and measuring at 25±0.5°C.

[0044] The tensile strength and elongation at break were tested according to the provisions of GB / T 1040.2-2006. 1A specimens were injection molded at 190 °C and 0.6 MPa using an injection molding machine, and tensile tests were carried out at a speed of 50 mm / min using a 5966 electronic universal material testing machine from Instron, USA.

[0045] According to the above factual manner, the present invention can be realized. Some embodiments are listed, but the present invention is not limited to these.

[0046] Example 1

[0047] 2450 g of ethylene glycol, 3350 g of succinic acid, and 15.5 g of catalyst were added to a reaction kettle. Under nitrogen protection, the temperature of the reaction kettle was raised to 200 °C, and the pressure was evacuated to 60 kPa. The reaction was carried out for 2 h 10 min, and the amount of esterification water discharged reached 1010 g. When no more esterification water flowed out after 20 min, the esterification was considered complete. After 30 min, the pressure was evacuated to 5 kPa, and the reaction was continued for 0.5 h under a vacuum of 5 kPa. Then, 28.5 g of the reactive auxiliary hexamethylene diisocyanate was added. After completion, the reaction temperature of the reaction kettle was increased and the vacuum degree inside the reaction kettle was started to be increased. The vacuum degree of the reaction kettle was maintained within 200 Pa, and the temperature of the reaction kettle was controlled at 235 °C for polycondensation reaction. After 6 h of high-vacuum polycondensation, the poly(ethylene succinate) (PES) chips were obtained by cold cutting.

[0048] Example 2

[0049] 2450 g of ethylene glycol, 3350 g of succinic acid, and 17.0 g of catalyst were added to a reaction kettle. Under nitrogen protection, the temperature of the reaction kettle was raised to 180 °C, and the reaction was carried out at 80 kPa for 2 h 45 min. The amount of esterification water discharged reached 1018 g. When no more esterification water flowed out after 20 min, the esterification was considered complete. After 35 min, the pressure was evacuated to 5 kPa, and the reaction was continued for 1.5 h under a vacuum of 5 kPa. Then, 28.5 g of the reactive auxiliary hexamethylene diisocyanate was added. After completion, the reaction temperature of the reaction kettle was increased and the vacuum degree inside the reaction kettle was started to be increased. The vacuum degree of the reaction kettle was maintained within 200 Pa, and the temperature of the reaction kettle was controlled at 238 °C for polycondensation reaction. After 5.5 h of high-vacuum polycondensation, the poly(ethylene succinate) (PES) chips were obtained by cold cutting.

[0050] Example 3

[0051] Add 2450 g of ethylene glycol, 3350 g of succinic acid, and 13.5 g of catalyst into the reaction kettle. Under the protection of nitrogen, heat the reaction kettle to 210 °C and react at 70 kPa for 2.5 h. The amount of water esterified reaches 1012 g. When no more esterification water flows out after 20 min, it is regarded as the end of esterification. After 40 min, pump it down to 5 kPa and continue to react at 5 kPa vacuum for 20 min. Then add 24.5 g of the reactive auxiliary phthalic anhydride. After completion, raise the reaction temperature of the reaction kettle and start to increase the vacuum degree inside the reaction kettle. Keep the vacuum degree of the reaction kettle within 200 Pa and control the reaction temperature of the reaction kettle at 238 °C for polycondensation reaction. After 5.5 h of high-vacuum polycondensation, obtain poly(ethylene succinate) (PES) chips by cold water pelletization.

[0052] Example 4

[0053] Add 2300 g of ethylene glycol, 3350 g of succinic acid, and 17.0 g of catalyst into the reaction kettle. Under the protection of nitrogen, heat the reaction kettle to 180 °C and react at 60 kPa for 2 h. The amount of water esterified reaches 1022 g. When no more esterification water flows out after 20 min, it is regarded as the end of esterification. After 30 min, pump it down to 5 kPa and continue to react at 5 kPa vacuum for 1 h. Then add 27.5 g of the reactive auxiliary 2,4-toluene diisocyanate. After completion, raise the reaction temperature of the reaction kettle and start to increase the vacuum degree inside the reaction kettle. Keep the vacuum degree of the reaction kettle within 200 Pa and control the reaction temperature of the reaction kettle at 228 °C for polycondensation reaction. After 6 h of high-vacuum polycondensation, obtain poly(ethylene succinate) (PES) chips by cold water pelletization.

[0054] Example 5

[0055] Add 2300 g of ethylene glycol, 3350 g of succinic acid, and 13.5 g of catalyst into the reaction kettle. Under the protection of nitrogen, heat the reaction kettle to 200 °C and react at 45 kPa for 1.5 h. The amount of water esterified reaches 1015 g. When no more esterification water flows out after 20 min, it is regarded as the end of esterification. After 40 min, pump it down to 5 kPa and continue to react at 5 kPa vacuum for 1 h. Then add 29.5 g of the reactive auxiliary 4,4'-diphenylmethane diisocyanate. After completion, raise the reaction temperature of the reaction kettle and start to increase the vacuum degree inside the reaction kettle. Keep the vacuum degree of the reaction kettle within 200 Pa and control the reaction temperature of the reaction kettle at 230 °C for polycondensation reaction. After 5 h of high-vacuum polycondensation, obtain poly(ethylene succinate) (PES) chips by cold water pelletization.

[0056] Example 6

[0057] Add 2450 g of ethylene glycol, 3350 g of succinic acid, and 15.5 g of catalyst into the reaction kettle. Under nitrogen protection, heat the reaction kettle to 200 °C and react at 55 kPa for 1 h 55 min. The amount of esterification water discharged reaches 1018 g. When no more esterification water flows out after 20 min, it is regarded as the end of esterification. Pump it down to 5 kPa in 30 minutes and continue to react at 5 kPa vacuum for 0.5 h. Then add 30.8 g of the reactive auxiliary polypropylene glycol diglycidyl ether. After completion, increase the reaction temperature of the reaction kettle and start to increase the vacuum degree inside the reaction kettle. Keep the vacuum degree of the reaction kettle within 200 Pa and control the reaction temperature of the reaction kettle at 235 °C for polycondensation reaction. After 6.5 h of high-vacuum polycondensation, cut into pellets with cold water to obtain polyethylene succinate (PES) slices.

[0058] Example 7

[0059] Add 2450 g of ethylene glycol, 3350 g of succinic acid, and 17.0 g of catalyst into the reaction kettle. Under nitrogen protection, heat the reaction kettle to 210 °C and react at 50 kPa for 1 h 45 min. The amount of esterification water discharged reaches 1012 g. When no more esterification water flows out after 20 min, it is regarded as the end of esterification. Pump it down to 5 kPa in 30 minutes and continue to react at 5 kPa vacuum for 1 h. Then add 32.5 g of the reactive auxiliary polypropylene glycol diglycidyl ether. After completion, increase the reaction temperature of the reaction kettle and start to increase the vacuum degree inside the reaction kettle. Keep the vacuum degree of the reaction kettle within 200 Pa and control the reaction temperature of the reaction kettle at 237 °C for polycondensation reaction. After 6.5 h of high-vacuum polycondensation, cut into pellets with cold water to obtain polyethylene succinate (PES) slices.

[0060] Comparative Example 1

[0061] Prepare polyethylene succinate in the same method as in Example 1, except that a commercially available polyester catalyst is used to prepare polyethylene succinate (PES) slices.

[0062] Comparative Example 2

[0063] Prepare polyethylene succinate according to the same step method as in Example 1, except that the esterification reaction is carried out at atmospheric pressure, that is, no vacuum is drawn during the esterification reaction stage, to prepare polyethylene succinate (PES) slices.

[0064] Comparative Example 3

[0065] Prepare polyethylene succinate in the same method as in Comparative Example 2, except that a commercially available polyester catalyst is used to prepare polyethylene succinate (PES) slices.

[0066] Test the weight-average molecular weight, tensile properties, and elongation at break of the polyethylene succinate (PES) slices prepared in the examples and comparative examples.

[0067] Table 1 Process parameters and properties of polyethylene succinate (PES)

[0068]

[0069] As can be seen from the data in Table 1, the use of the self-made liquid titanium-based catalyst can effectively improve the molecular weight and mechanical properties of polyethylene succinate (PES). The use of negative pressure esterification can effectively shorten the reaction time. The polyethylene succinate (PES) prepared by the method of the present invention has a high molecular weight, excellent mechanical properties and a short total reaction time, which will provide strong support for the industrial production of polyethylene succinate (PES).

Claims

1. A method for preparing polyethylene succinate, characterized in that: The preparation method includes the following sequential steps: a. Esterification: Add succinic acid, ethylene glycol, and a liquid titanium-based catalyst into a reaction kettle, heat up to 180 - 200 °C, and conduct an esterification reaction for 1.5 - 3 h under negative pressure conditions to obtain an esterified product; b. Pre-polycondensation: Control the reaction temperature of the esterified product obtained in step a at 200 - 230 °C and the vacuum degree at 0.5 - 5 kPa, and react for 0.5 - 2 h to obtain a prepolymer; c. Polycondensation: Add a reactive assistant to the prepolymer obtained in step b, control the reaction temperature at 200 - 250 °C and the vacuum degree at 20 - 200 Pa, and react for 3 - 8 h to obtain a polyethylene succinate melt; d. Cooling and pelletizing: Cool and pelletize the polyethylene succinate melt obtained in step c to obtain polyethylene succinate slices; The components of the liquid titanium-based catalyst in step a include: a ligand, an organic titanate, a complexing agent, and ethylene glycol. The mass ratio of the organic titanate to the ligand, ethylene glycol, and complexing agent is 1:0.01 - 0.6:0.5 - 2.1:0.01 - 0.7; The organic titanate is one or a combination of tetraethyl titanate, tetramethyl titanate, and tetra-n-butyl titanate. The ligand is one or a combination of diethanolamine, triethanolamine, ethylene glycol monobutyl ether, and octylphenol polyoxyethylene ether. The complexing agent is one or a combination of trimethyl phosphate, triethyl phosphate, tributyl phosphate, trimethyl phosphite, and triethyl phosphite; The negative pressure condition in step a is achieved by a vacuum device connected to the reaction kettle, and the vacuum degree ranges from 100 to 40 kPa.

2. The preparation method of polyethylene glycol succinate according to claim 1, characterized in that, In step a, the molar ratio of succinic acid to ethylene glycol is 1:1.1 - 1:1.

5.

3. A method for preparing polyethylene succinate according to claim 1, characterized in that, In step a, the molar ratio of succinic acid to ethylene glycol is 1:1.

3.

4. A method for preparing polyethylene succinate according to claim 1, characterized in that, The dosage of the liquid titanium-based catalyst is 0.2% - 0.4% of the theoretical yield.

5. A method for preparing polyethylene succinate according to claim 1, characterized in that, The dosage of the liquid titanium-based catalyst is 0.25% of the theoretical yield.

6. The preparation method of polyethylene glycol succinate according to claim 1, characterized in that, The reactive assistant is one or a combination of hexamethylene diisocyanate, phthalic anhydride, 2,4-toluene diisocyanate, 4,4-dimethylbenzene methane diisocyanate, and polypropylene glycol diglycidyl ether.

7. A method for preparing polyethylene succinate according to claim 1, characterized in that, The dosage of the reactive assistant is 0.01% - 0.8% of the theoretical yield.

8. A method for preparing polyethylene succinate according to claim 1, characterized in that The dosage of the reactive assistant is 0.01% - 0.5% of the theoretical yield.

9. The preparation method of polyethylene glycol succinate according to claim 1, characterized in that, The prepared polyethylene succinate has Mw > 150000 g / mol, a tensile strength > 30 MPa, and an elongation at break > 350%.

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