A method for reducing monomers in polylactic acid polyols

Abstract

The application relates to a method for reducing monomers in polylactic acid polyols. The method provided by the application comprises subjecting polylactic acid polyols to distillation treatment in a molecular distillation device to obtain treated polylactic acid polyols. The method provided by the application can not only ensure the reduction of monomer content, but also reduce the occurrence of side reactions such as cracking and yellowing of polylactic acid polyols caused by the distillation process, ensure that the acid value and hydroxyl value of the product are qualified and stable, and to some extent, can narrow the molecular weight distribution of the product and improve the uniformity of the product.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of bio-based materials, and particularly relates to a method for reducing monomers in polylactic acid polyols. BACKGROUND

[0002] At present, in the synthesis method of polylactic acid polyols, the ring-opening polymerization method of lactide is the best method with simple process. The research focuses on the improvement of polymerization process and the removal of residual components in the later stage of reaction, i.e. removing low molecular weight volatile substances from the polymerization product with high viscosity as much as possible, so as to improve the purity of the polymer. In the method for producing polylactic acid polyols from lactide, the removal of small molecule residues is an important link to improve product quality. Since the viscosity of polylactic acid polyols is high, and the boiling point of lactide monomer is also relatively high, how to remove lactide while ensuring that the acid value and hydroxyl value of the product are qualified has been a difficult problem.

[0003] In the polylactic acid polyol devolatilization device in the prior art, there are generally problems such as large thickness of the stagnant layer at the inlet pipe wall, large heat transfer resistance, slow downward flow of the material, easy storage of the material, low working efficiency and the like. In the devolatilization process, the material is not uniformly heated, which can cause insufficient devolatilization; the devolatilization temperature is low, and the volatile components cannot escape smoothly from the viscous material after gasification in the devolatilization process, so the devolatilization effect is not ideal; the devolatilization temperature is high, which can easily cause side reactions such as cracking and yellowing of polylactic acid polyols, so that the monomer content of the material after devolatilization increases and the color is yellowish, in addition, high temperature can also cause the acid value of the material to increase and the hydroxyl value to decrease, thereby affecting the quality of the product. Therefore, there is an urgent need for an improved technology to solve the problem existing in the prior art. SUMMARY

[0004] In view of the above problems in the prior art, the present application provides a method for reducing monomers in polylactic acid polyols. The method provided by the present application can not only reduce the monomer content, but also reduce the occurrence of side reactions such as cracking and yellowing of polylactic acid polyols caused by the distillation process, ensure that the acid value and hydroxyl value of the product are qualified and stable, and at the same time, to a certain extent, the molecular weight distribution of the product can be narrowed, and the uniformity of the product can be improved.

[0005] The method for reducing monomers in polylactic acid polyols provided by the present application comprises distilling polylactic acid polyols in a molecular distillation device to obtain treated polylactic acid polyols.

[0006] In some embodiments, the method further comprises pre-heating the polylactic acid polyol before the distillation treatment, wherein the pre-heating temperature is 80-170°C. In some embodiments, the pre-heating temperature is 85°C, 90°C, 95°C, 100°C, 105°C, 110°C, 115°C, 120°C, 125°C, 130°C, 135°C, 140°C, 145°C, 150°C, 155°C, 160°C, 165°C, or any value therebetween. In some embodiments, the pre-heating temperature is 130-160°C.

[0007] In some embodiments, the distillation treatment is performed at a temperature of 120-200°C. In some embodiments, the distillation treatment is performed at a temperature of 125°C, 130°C, 135°C, 140°C, 145°C, 150°C, 155°C, 160°C, 165°C, 170°C, 175°C, 180°C, 185°C, 190°C, 195°C, or any value therebetween. In some embodiments, the distillation treatment is performed at a temperature of 160-190°C.

[0008] In some embodiments, the polylactic acid polyol is fed into the molecular distillation device at a rate of 5-50 kg / h•m 2 -50kg / h•m 2 In some embodiments, the polylactic acid polyol is fed into the molecular distillation device at a rate of 10-30 kg / h•m 2 , 15-25 kg / h•m 2 , 20-30 kg / h•m 2 , 25-35 kg / h•m 2 , 30-40 kg / h•m 2 , 35-45 kg / h•m 2 , 40-50 kg / h•m 2 , 45-50 kg / h•m 2 In some embodiments, the polylactic acid polyol is fed into the molecular distillation device at a rate of 15-30 kg / h•m 2 . 2 .

[0009] In some embodiments, the molecular distillation device is a wiped film molecular distillation device, and the speed of the wiper is 100-500 rpm. In some embodiments, the speed of the wiper is 150 rpm, 200 rpm, 250 rpm, 300 rpm, 350 rpm, 400 rpm, 450 rpm, or any value therebetween. In some embodiments, the speed of the wiper is 300-400 rpm. By controlling the speed of the wiper, the present application can effectively increase the surface area of the material, making it easier for the light components to escape.

[0010] In some embodiments, the molecular distillation apparatus is provided with a condensing system, and the condensing temperature is 80-100°C, for example 85°C, 90°C or 95°C.

[0011] In some embodiments, the distillation treatment is performed under vacuum. In some embodiments, the vacuum degree is less than or equal to 10.0 mbar, for example 1.0 mbar, 2.0 mbar, 3.0 mbar, 4.0 mbar, 5.0 mbar, 6.0 mbar, 7.0 mbar, 8.0 mbar or 9.0 mbar. In some embodiments, the vacuum degree is less than or equal to 5.0 mbar. In some embodiments, the vacuum degree is 1.0-5.0 mbar.

[0012] In some embodiments, the polylactic acid polyol is selected from one or more of modified or unmodified polylactic acid polyols.

[0013] In some embodiments, the raw material for preparing the polylactic acid polyol comprises lactide, an initiator and optionally a modifier.

[0014] In some embodiments, the modifier comprises one or more of cyclic ester compounds. In some embodiments, the modifier comprises one or more of trimethylene carbonate, valerolactone and caprolactone.

[0015] In some embodiments, the initiator is selected from one or more of polyols, for example dihydric alcohols such as ethylene glycol, propylene glycol, dipropylene glycol, 1,3-butanediol, 1,4-butanediol or 1,6-hexanediol; for example trihydric alcohols such as glycerol, trimethylolpropane, trimethylolethane or hexanetriol; for example tetrahydric alcohols such as pentaerythritol, methyl glucoside or diglycerol; or triglycerol, tetraglycerol, dipentaerythritol, tripentaerythritol or tetra(hydroxymethyl)cyclohexanol.

[0016] In some embodiments, the residual mass of monomers in the polylactic acid polyol is greater than or equal to 2.0% (m / m) based on the mass of the polylactic acid polyol.

[0017] In some embodiments, the residual mass of monomers in the treated polylactic acid polyol is less than or equal to 0.5% (m / m), for example less than or equal to 0.49%, for example less than or equal to 0.45%, for example less than or equal to 0.4%, for example less than or equal to 0.35%, for example less than or equal to 0.3%, for example less than or equal to 0.25%, for example less than or equal to 0.2%.

[0018] In some embodiments, the processed polylactic acid polyol has a molecular weight distribution coefficient of 1.35-1.45, for example 1.36, 1.37, 1.38, 1.39, 1.40, 1.41, 1.42, 1.43 or 1.44. In some embodiments, the processed polylactic acid polyol has a molecular weight distribution coefficient of 1.35-1.40.

[0019] In some embodiments, the processed polylactic acid polyol has a reduced acid value and a substantially unchanged hydroxyl value compared to the polylactic acid polyol before processing.

[0020] Compared with the prior art, the present application has the following advantages:

[0021] When distillation treatment is performed using a molecular distillation device, the polylactic acid polyol is devolatilized at low temperature, and the volatile components cannot be smoothly released from the viscous material after gasification, resulting in unsatisfactory devolatilization effect. At high temperature, side reactions such as cracking and yellowing are prone to occur, thereby causing the monomer content in the polylactic acid polyol product to be difficult to reduce, even to increase, the product color to deepen, and the acid value to increase, and the like. The method provided by the present application overcomes the difficulty of removing monomers from the polylactic acid polyol product. By adjusting the appropriate preheating temperature, distillation temperature and feed rate of the raw material, the polylactic acid polyol can be prevented from being heated at high temperature for a long time, thereby well solving the above problems, reducing the occurrence of side reactions such as cracking and yellowing of the polylactic acid polyol during distillation, ensuring that the acid value and hydroxyl value of the product are qualified and stable, and at the same time, to a certain extent, the molecular weight distribution of the product can be narrowed, and the uniformity of the product can be improved. DETAILED DESCRIPTION

[0022] The preferred embodiments of the present application will be described in detail below with reference to the examples. It should be understood that the following examples are given only for the purpose of illustration and are not intended to limit the scope of the present application. Various modifications and replacements of the present application made by those skilled in the art without departing from the spirit and principles of the present application are considered to be within the technical scope of the present application.

[0023] The lactide monomer content involved in the following examples and comparative examples is determined by gas chromatography.

[0024] The acid value and hydroxyl value involved in the following examples and comparative examples are determined by potentiometric titration.

[0025] The molecular weight distribution involved in the following examples and comparative examples is determined by gel chromatography.

[0026] Example 1

[0027] Polylactic acid polyol material: Polylactide is prepared by polymerizing lactide under the action of stannous octoate and 1,4-butanediol initiator to produce polylactic acid polyol with a theoretical molecular weight of 1000, wherein the content of unreacted lactide monomer is 3.2% (m / m).

[0028] Deviation treatment: Turn on the heating system of the feeder and heat it to 140°C. This feeder is a scraped-film molecular distillation device. Add the prepared polylactic acid polyol liquid with a molecular weight of 1000 to the feeder of the molecular distillation device while it is still hot. Turn on the heating system of the distillation device and heat it to 170°C. Turn on the condensation system of the molecular distillation device, setting the condensation temperature to 80°C. Turn on the vacuum pump, achieving a vacuum pressure of approximately 4.0 mbar. After the polylactic acid polyol liquid has preheated to 140°C, start the scraper, open the feed valve, and control the feed rate to 15 kg / h·m. 2 Distillation was carried out at 170℃ with a scraper rotation speed of 300 rpm. The collected light components were water, lactide, and oligomers, which were recombined into polylactic acid polyol products. The resulting polylactic acid product was a colorless or slightly pale yellow viscous substance. The parameters of the polylactic acid polyol before and after treatment are detailed in Table 1.

[0029] Example 1-1

[0030] The only difference between Example 1-1 and Example 1 is that the preheating temperature is 180℃, resulting in a pale yellow viscous polylactic acid product. The polylactic acid polyol parameters before and after treatment are detailed in Table 1.

[0031] Examples 1-2

[0032] The only difference between Examples 1-2 and Example 1 is that the preheating temperature is 70°C, resulting in a colorless or slightly pale yellow viscous polylactic acid product. The polylactic acid polyol parameters before and after treatment are detailed in Table 1.

[0033] Examples 1-3

[0034] The only difference between Examples 1-3 and Example 1 is that the preheating temperature is 80°C, resulting in a colorless or slightly pale yellow viscous polylactic acid product. The polylactic acid polyol parameters before and after treatment are detailed in Table 1.

[0035] Examples 1-4

[0036] The only difference between Examples 1-4 and Example 1 is that the preheating temperature is 170°C, resulting in a colorless or slightly pale yellow viscous polylactic acid product. The polylactic acid polyol parameters before and after treatment are detailed in Table 1.

[0037] Examples 1-5

[0038] The only difference between Examples 1-5 and Example 1 is that the distillation temperature is 120°C, resulting in a colorless or slightly pale yellow viscous polylactic acid product. The polylactic acid polyol parameters before and after treatment are detailed in Table 1.

[0039] Examples 1-6

[0040] The only difference between Examples 1-6 and Example 1 is that the distillation temperature is 210℃, resulting in a pale yellow viscous polylactic acid product. The polylactic acid polyol parameters before and after treatment are detailed in Table 1.

[0041] Examples 1-7

[0042] The only difference between Examples 1-7 and Example 1 is that the feeding rate is 2 kg / h•m. 2 The resulting polylactic acid product was a yellow, viscous substance. The polylactic acid polyol parameters before and after treatment are detailed in Table 1.

[0043] Examples 1-8

[0044] The only difference between Examples 1-8 and Example 1 is that the feeding rate is 5 kg / h•m. 2 The resulting polylactic acid product was a slightly yellow, viscous substance. The polylactic acid polyol parameters before and after treatment are detailed in Table 1.

[0045] Examples 1-9

[0046] The only difference between Examples 1-9 and Example 1 is that the feeding rate is 30 kg / h•m. 2 The resulting polylactic acid product was a colorless or slightly yellow viscous substance. The polylactic acid polyol parameters before and after treatment are detailed in Table 1.

[0047] Examples 1-10

[0048] The only difference between Examples 1-10 and Example 1 is that the feeding rate is 60 kg / h•m. 2 The resulting polylactic acid product was a colorless or slightly yellow viscous substance. The polylactic acid polyol parameters before and after treatment are detailed in Table 1.

[0049] Examples 1-11

[0050] The only difference between Examples 1-11 and Example 1 is that the scraper speed is 50 rpm, resulting in a colorless or slightly pale yellow viscous polylactic acid product. The polylactic acid polyol parameters before and after treatment are detailed in Table 1.

[0051] Examples 1-12

[0052] The only difference between Examples 1-12 and Example 1 is that the scraper speed is 100 rpm, resulting in a colorless or slightly pale yellow viscous polylactic acid product. The polylactic acid polyol parameters before and after treatment are detailed in Table 1.

[0053] Examples 1-13

[0054] The only difference between Examples 1-13 and Example 1 is that the scraper speed is 600 rpm, resulting in a colorless or slightly pale yellow viscous polylactic acid product. The polylactic acid polyol parameters before and after treatment are detailed in Table 1.

[0055] Comparative Example 1

[0056] Polylactic acid polyol material: Polylactide is prepared by polymerizing lactide under the action of stannous octoate and 1,4-butanediol initiator to produce polylactic acid polyol with a theoretical molecular weight of 1000, wherein the content of unreacted lactide monomer is 3.2% (m / m).

[0057] Deviation treatment: A conventional devolatilization process was adopted. Specifically, the prepared polylactic acid polyol liquid with a molecular weight of 1000 was added hot into a conventional distillation apparatus. The heating system of the reaction vessel was turned on, stirring was started, and the temperature was heated to 170°C. The condensation system in the distillation apparatus was turned on, and the condensation temperature was set to 80°C. The vacuum pump was turned on, and the vacuum pressure reached approximately 4.0 mbar, at which point devolatilization began. The collected light components were water, lactide, and oligomers. The recombined components were converted into polylactic acid polyol product, which was a deep yellow viscous liquid. The parameters of the polylactic acid polyol before and after treatment are detailed in Table 1.

[0058] Table 1

[0059]

[0060] Example 2

[0061] Polylactic acid polyol material: Modified polylactic acid polyol with a theoretical molecular weight of 5000 is prepared by polymerizing lactide and trimethylene carbonate under the action of stannous octoate and 1,4-butanediol initiator, wherein the content of unreacted lactide monomer is 5.2% (m / m).

[0062] Deviation treatment: Turn on the heating system of the feeder and heat it to 150°C. This feeder is a scraped-film molecular distillation device. Add the prepared modified polylactic acid polyol liquid with a molecular weight of 5000 to the feeder of the molecular distillation device while it is still hot. Turn on the heating system of the distillation device and heat it to 180°C. Turn on the condensation system of the molecular distillation device, setting the condensation temperature to 100°C. Turn on the vacuum pump, achieving a vacuum pressure of approximately 3.0 mbar. Once the polylactic acid polyol liquid has preheated to 150°C, start the scraper, open the feed valve, and control the feed rate at 20 kg / h·m. 2Distillation was carried out at 180°C with a scraper speed of 400 rpm. The collected light components were water, lactide, and oligomers, which were recombined into polylactic acid polyol products. The polylactic acid product was a colorless or slightly pale yellow solid. The parameters of the polylactic acid polyol before and after treatment are detailed in Table 2.

[0063] Table 2

[0064]

[0065] Example 3

[0066] Polylactic acid polyol material: Polylactide is prepared by polymerizing lactide under the action of stannous octoate and 1,4-butanediol initiator to produce polylactic acid polyol with a theoretical molecular weight of 500, wherein the content of unreacted lactide monomer is 2.2% (m / m).

[0067] Deviation treatment: Turn on the heating system of the feeder and heat it to 100°C. This feeder is a scraped-film molecular distillation device. While still hot, add the prepared polylactic acid polyol liquid with a molecular weight of 500 into the feeder of the molecular distillation device. Turn on the heating system of the molecular distillation device and heat it to 160°C. Turn on the condenser system of the molecular distillation device, setting the condensation temperature to 80°C. Turn on the vacuum pump, achieving a vacuum pressure of approximately 5.0 mbar. Once the polylactic acid polyol liquid has preheated to 100°C, start the scraper, open the feed valve, and control the feed rate at 30 kg / h·m. 2 Distillation was carried out at 160℃ with a scraper rotation speed of 500 rpm. The collected light components were water, lactide, and oligomers, which were recombined into polylactic acid polyol products. The polylactic acid product was a colorless or slightly pale yellow liquid. The parameters of the polylactic acid polyol before and after treatment are detailed in Table 3.

[0068] Table 3

[0069]

[0070] Although the present invention has been described in detail above with general descriptions, specific embodiments, and examples, certain supplements or improvements can be made to the discrimination model of this method based on the present invention, which will be obvious to those skilled in the art. Therefore, all such modifications or improvements made without departing from the spirit of the present invention fall within the scope of protection claimed by the present invention.

Claims

1. A method for reducing monomers in polylactic acid polyol, comprising distilling the polylactic acid polyol in a molecular distillation apparatus to obtain the treated polylactic acid polyol; Before distillation, the polylactic acid polyol is preheated at a temperature of 80℃-170℃; the distillation temperature is 130℃-200℃; and the feed rate of the polylactic acid polyol in the molecular distillation apparatus is 5 kg / h•m. 2 -50kg / h•m 2 The molecular distillation apparatus is selected from a scraped molecular distillation apparatus, and the rotation speed of the scraper is 100 rpm-500 rpm.

2. The method according to claim 1, characterized in that, The preheating temperature is 130℃-160℃.

3. The method according to claim 1 or 2, characterized in that, The distillation process is carried out at a temperature of 160℃-190℃.

4. The method according to any one of claims 1-2, characterized in that, In the molecular distillation apparatus, the feed rate of the polylactic acid polyol is 15 kg / h•m. 2 -30kg / h•m 2 .

5. The method according to any one of claims 1-2, characterized in that, The scraper rotates at a speed of 300 rpm to 400 rpm.

6. The method according to any one of claims 1-2, characterized in that, The molecular distillation apparatus is equipped with a condensation system, and the condensation temperature of the condensation system is 80℃-100℃.

7. The method according to any one of claims 1-2, characterized in that, The distillation process is carried out under vacuum conditions, wherein the vacuum degree is less than or equal to 10.0 mbar.

8. The method according to claim 7, characterized in that, The vacuum level under the specified vacuum conditions is less than or equal to 5.0 mbar.

9. The method according to any one of claims 1-2, characterized in that, The polylactic acid polyol is selected from one or more of modified or unmodified polylactic acid polyols; When the polylactic acid polyol is selected from modified polylactic acid polyols, the raw materials for preparing the polylactic acid polyol include lactide, initiator and modifier, wherein the modifier is selected from one or more of trimethylene carbonate, valproic acid lactone and caprolactone.

10. The method according to any one of claims 1-2, characterized in that, Based on the mass of the polylactic acid polyol, before distillation, the residual mass of monomers in the polylactic acid polyol is greater than or equal to 2.0%, in m / m units.

11. The method according to any one of claims 1-2, characterized in that, In the polylactic acid polyol after distillation, the residual mass of monomer is less than or equal to 0.5%, in m / m units, the acid value decreases, and the hydroxyl value remains basically unchanged. and / or The molecular weight distribution coefficient of the polylactic acid polyol after distillation is 1.35-1.

45.

12. The method according to claim 11, characterized in that, The molecular weight distribution coefficient of the polylactic acid polyol after distillation is 1.35-1.40.

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