A method for synthesizing bio-based high molecular weight polybutylene succinate

Abstract

The present invention belongs to the technical field of organic synthesis, and in particular to a method for synthesizing bio-based high molecular weight polybutylene succinate. The present invention adjusts the ratio of monomers used for producing polybutylene succinate, utilizes succinic acid and 1,4-butanediol to first esterify and pre-polycondense, obtains a product of higher molecular weight, and then further carries out transesterification reaction with bio-based dialkanol succinate, and realizes the production of bio-based high molecular weight polybutylene succinate by two-step polycondensation. The synthetic method of the present invention can obtain higher molecular weight, and avoids the harsh conditions of high temperature and high vacuum. The present invention adds bio-based dialkanol succinate in the later stage of the reaction, so that polycondensation is changed from the original generation of water to the generation of dialkanol, reduces the difficulty of esterification, improves the molecular weight of the intermediate product, and simultaneously reduces the reaction temperature, so as to achieve the purpose of reducing energy consumption, saving time, and improving product quality.

Description

Technical Field

[0001] The invention belongs to the technical field of organic synthesis, and particularly relates to a method for synthesizing bio-based high molecular weight butylene succinate. Background Art

[0002] Bio-based polybutylene succinate, also known as PBS, has the following chemical structure:

[0003]

[0004] Due to the presence of a large number of ester bonds in its molecular chain, it is easily metabolized and decomposed by various microorganisms or enzymes in animals and plants in nature after use, and finally converted into water and carbon dioxide. It is a green material that can achieve a complete ecological cycle production from nature and return to nature.

[0005] At present, there are three main methods for the synthesis of polybutylene succinate (PBS), namely direct esterification, transesterification and chain extension. The main process routes of the three methods are compared as follows:

[0006] 1. Direct esterification: First, succinic acid and excess butanediol are subjected to esterification reaction under nitrogen and low temperature, and intermolecular dehydration is performed to generate oligomers with terminal hydroxyl groups. Then, under high temperature and high vacuum conditions, the oligomers are degassed with diols by the action of a catalyst to obtain high molecular weight PBS. In addition, the direct esterification method can be divided into three methods, namely solution polycondensation, melt polycondensation and solution melting, depending on whether a solution is used. The disadvantage of the direct esterification method is that it has many by-products and requires high temperature and high vacuum.

[0007] 2. Transesterification method: Under the action of a catalyst, an equimolar amount of dimethyl diacid and 1,4-butanediol undergo transesterification reaction, and the dialkyl alcohol is removed to obtain a PBS prepolymer, and a high molecular weight PBS is obtained under high vacuum and high temperature conditions. The disadvantage of this method is that the relative molecular weight of the final product is relatively low.

[0008] 3. Chain extension method: The active groups of the chain extender are used to react with the terminal hydroxyl or carboxyl groups of the PBS prepolymer to achieve the effect of chain extension, so as to increase the relative molecular weight of the product. The disadvantage of this method is that the chain extender has a certain toxicity and remains in the product, affecting the scope of use of the product.

[0009] The water generated in the later stage of the direct esterification method is difficult to remove from the reaction system. To achieve a higher molecular weight, the temperature and vacuum must be increased, and the reaction time must also be increased. To this end, the present application improves the direct esterification method using bio-based raw materials to address the technical problems existing in the prior art, and adjusts the reaction sequence and process parameters to avoid high temperatures during the reaction and shorten the reaction time. Summary of the invention

[0010] In view of the problems existing in the prior art, the purpose of the present invention is to provide a method for synthesizing bio-based high molecular weight polybutylene succinate (PBS), which can obtain a higher molecular weight and avoid the harsh conditions of high temperature and high vacuum by combining an ester exchange method and a direct esterification method, and ultimately reduce the synthesis cycle and energy consumption to obtain high-quality bio-based PBS products.

[0011] Based on the above purpose, the present invention adopts the following technical solutions:

[0012] A method for synthesizing bio-based high molecular weight polybutylene succinate (PBS), the process route of the method being: (one)

[0014] (two)

[0016]

[0017] The synthesis method of the bio-based high molecular weight polybutylene succinate (PBS) comprises the following steps:

[0018] (1) Normal pressure reaction: Bio-based succinic acid and 1,4-butanediol (BDO) are mixed and placed in a reaction vessel (four-necked flask), and then a catalyst is added under the condition of forming an inert atmosphere in the reaction vessel, and the mixture is heated to 130-160°C while being stirred for a pre-polycondensation reaction. The reaction time is 1-4 hours to obtain a reactant. Water is continuously generated during the reaction. During the reaction, an oil-water separator is used to remove water until the amount of water separated in the oil-water separator no longer increases significantly.

[0019] (2) Negative pressure reaction I: The reaction vessel is evacuated to a negative pressure state with a vacuum pump, the negative pressure being 50 to 1000 Pa, and then the temperature is raised to 160 to 230° C. under negative pressure conditions for a reaction time of 1 to 4 hours, at which time the molecular weight of the pre-polycondensation reactant in step (1) is further increased;

[0020] (3) Negative pressure reaction II: using a constant pressure titration funnel, adding bio-based dialkylsuccinate to the product obtained in step (2) for ester exchange reaction, the reaction temperature is 160-230° C., the reaction time is 1-2 h, during the reaction, the molecular weight of the reactant is further increased, and at the same time, the bio-based dialkylsuccinate further reacts with the hydroxyl group in the material to remove the dialkyls; after the reaction, the material is post-treated to obtain the final product.

[0021] Furthermore, in step (1), a bio-based monomer (bio-based succinic acid) and 1,4-butanediol monomer are used for a pre-condensation reaction, wherein the molar ratio of bio-based succinic acid to 1,4-butanediol is (35-55):(75-45), preferably (38-47):(62-53), and more preferably (42-47):(58-53).

[0022] Furthermore, in step (1), an inert atmosphere is formed by introducing nitrogen into the reaction container to exclude air.

[0023] Furthermore, in step (1), the amount of catalyst added is 0.1-0.2% of the total mass of bio-based succinic acid, 1,4-butanediol and the catalyst, preferably 0.1%; the catalyst is a non-toxic metal catalyst and / or a non-metal catalyst, preferably tetrabutyl titanate.

[0024] Furthermore, in step (1), the total amount of material added during the reaction is 1 / 3-1 / 2 of the volume of the reaction container.

[0025] Furthermore, in step (1), the reaction temperature is preferably 150-160° C.; the reaction time is preferably 1-2.5 h, more preferably 1.5-2.5 h.

[0026] Furthermore, in step (2), the negative pressure of the reaction system is preferably 50 to 500 Pa, more preferably 50 to 300 Pa.

[0027] Furthermore, in step (2), the reaction temperature is preferably 190 to 230°C, more preferably 200 to 220°C.

[0028] Furthermore, in step (2), the reaction time is preferably 1 to 3 h, more preferably 1.5 to 2.5 h.

[0029] Furthermore, in step (3), the bio-based dialkyl succinates include but are not limited to dimethyl succinate, diethyl succinate, dibutyl succinate, etc.

[0030] Furthermore, in step (3), the amount of bio-based dialkyl succinate added is 1 to 10% of the total mass of bio-based succinic acid and 1,4-butanediol, preferably 4 to 9%, and more preferably 5 to 9%.

[0031] Furthermore, in step (3), the reaction time is preferably 1.5 to 2 hours.

[0032] Furthermore, in step (3), the post-treatment of the reaction material is as follows: placing the reaction material in an organic alcohol, precipitating the precipitate at room temperature, filtering, centrifuging, and drying to obtain the product.

[0033] Further preferably, in step (3), the material post-processing operation after the reaction is completed is specifically:

[0034] The material after the reaction is placed in an organic alcohol, stirred at room temperature, filtered, and a polymer (precipitate) with a size of 20 to 100 meshes is precipitated, and then centrifuged for 50 to 10 minutes under a pressure of 1.80 to 2.0 MPa. After centrifugation, it is dried at 40 to 50° C. for 1 to 2 hours to obtain the product; the organic alcohol is methanol, ethanol, etc.

[0035] The present invention adjusts the ratio of monomers (succinic acid and 1,4-butanediol) used to produce polybutylene succinate, utilizes succinic acid and 1,4-butanediol to esterify and pre-condense to obtain a product with a higher molecular weight, and then further carries out an ester exchange reaction with bio-based dialkanol succinate to further increase the molecular weight, thereby realizing the production of bio-based high molecular weight polybutylene succinate through a two-step condensation method.

[0036] Compared with the prior art, the present invention adopts the method of adding bio-based dialkylsuccinate to prepare the synthesis process of bio-based polydialkylsuccinate using succinic acid and 1,4-butanediol, which has the following advantages:

[0037] 1. Based on the existing bio-based high molecular weight butylene succinate (PBS) synthesis process, the present invention combines the ester exchange method with the direct esterification method, adds bio-based dialkylsuccinate during the reaction process, and uses bio-based dialkylsuccinate to replace a part of bio-based succinic acid, so that the esterification reaction is easier to carry out.

[0038] 2. The present invention increases the intrinsic viscosity of the obtained product by increasing the molecular weight, thereby improving the quality of the product; in the synthesis process of the present invention, no new catalyst needs to be added during the reaction, thus avoiding the entry of intermediate oxygen and preventing the product from turning yellow.

[0039] 3. Compared with the direct polymerization method in the prior art, the prepared PBS has lower acidity, and when used, it can improve its compatibility with other additives, the dispersibility of the additives, and improve the yield of the finished product.

[0040] 4. The present invention adds bio-based dialkyl succinate in the later stage of the reaction, so that the condensation reaction changes from the original generation of water to the generation of dialkyl alcohol, reduces the difficulty of esterification, increases the molecular weight of the intermediate product, and reduces the reaction temperature at the same time, thereby achieving the purpose of reducing energy consumption, saving time, and improving product quality.

[0041] 5. The synthesis process of the present invention can solve the problems of too high reaction temperature and long reaction time in the existing bio-based poly(dialkyl succinate) synthesis process.

[0042] 6. In the process of producing bio-based polydialkyl succinate, the present invention pre-condenses bio-based succinic acid and bio-based 1,4-butanediol to reach a certain molecular weight, and then adds a certain amount of bio-based dialkyl succinate to make the esterification reaction easier to proceed and the molecular weight is more easily doubled.

[0043] 7. The by-product dialkyl alcohol (mainly methanol, etc.) obtained during the reaction is easier to remove from the reaction system, reducing the reaction activation energy, shortening the reaction time, creating conditions conducive to the super-forward reaction, further improving product quality and product molecular weight, reducing energy consumption, and shortening the reverse cycle to achieve the purpose of increasing production capacity. BRIEF DESCRIPTION OF THE DRAWINGS

[0044] Figure 1 It is a process flow chart of the present invention. DETAILED DESCRIPTION

[0045] In order to make the technical purpose, technical scheme and beneficial effects of the present invention clearer, the technical scheme of the present invention is further described below in conjunction with specific embodiments. However, the embodiments are intended to explain the present invention and cannot be understood as limiting the present invention. If no specific technology or conditions are specified in the embodiments, the technology or conditions described in the literature in the field or the product manual shall be followed.

[0046] In the following examples, the instruments and equipment used in the reaction process include a four-necked flask, a mechanical stirrer, an oil-water separator, a spherical condenser, an oil bath, a vacuum pump, a nitrogen bottle, a constant pressure titration funnel, etc., and the instruments and equipment are all common equipment in the prior art, and the specific method of use adopts the conventional usage in the prior art.

[0047] Example 1

[0048] A method for synthesizing bio-based high molecular weight polybutylene succinate (PBS), the specific steps are as follows:

[0049] (1) Normal pressure reaction: Bio-based succinic acid and 1,4-butanediol (BDO) were mixed in a molar ratio of 45:55 and placed in a reaction vessel (four-necked flask), and then nitrogen was repeatedly introduced into the reaction vessel three times to replace the air, and then a catalyst (tetrabutyl titanate) was added, and the mixture was heated to 148° C. while stirring to react, so as to achieve pre-polycondensation of bio-based succinic acid and 1,4-butanediol. The reaction time was 1.8 h to obtain a reactant. The total amount of materials added during the reaction was 1 / 2 of the volume of the reaction vessel. Water was continuously generated during the reaction. During the reaction, an oil-water separator was used to remove water until the amount of water separated in the oil-water separator no longer increased significantly. The amount of catalyst added was 0.1% of the total mass of bio-based succinic acid, 1,4-butanediol and the catalyst.

[0050] (2) Negative pressure reaction I: The reaction vessel was evacuated to a negative pressure state using a vacuum pump, and the negative pressure (absolute pressure) was 300 Pa. Then, the temperature was slowly raised to 210° C. under negative pressure to carry out the reaction. The reaction time was 2 h. At this time, the molecular weight of the pre-polycondensation reactant in step (1) was further increased.

[0051] (3) Negative pressure reaction II: using a constant pressure titration funnel, dimethyl succinate (DMS) is added to the reactant obtained in step (2) to carry out an ester exchange reaction, the reaction temperature is 210° C., the reaction time is 1.5 h, the molecular weight of the reactant is further increased during the reaction, and at the same time, dimethyl succinate further reacts with the hydroxyl group in the material to remove the dialkyl alcohol (mainly methanol, etc.); the amount of dimethyl succinate added is 9% of the total mass of bio-based succinic acid and 1,4-butanediol;

[0052] The material after the reaction was completed was placed in methanol, stirred at room temperature, filtered, and a polymer (precipitate) with a size of 20-100 mesh was precipitated, and then centrifuged at a pressure of 1.8 MPa for 10 minutes. After centrifugation, it was dried at 50°C for 1.5 hours to obtain a product with an intrinsic viscosity of 1.79 dL / g.

[0053] Example 2

[0054] The difference between Example 2 and Example 1 is that only the molar ratio of bio-based succinic acid to 1,4-butanediol in step (1) is changed to 42:58.

[0055] Example 3

[0056] The difference between Example 3 and Example 1 is that the amount of dimethyl succinate used in step (3) is reduced to 7% of the total mass of bio-based succinic acid and 1,4-butanediol.

[0057] Example 4

[0058] The difference between Example 4 and Example 1 is that only the reaction temperature of step (3) is changed to 220°C.

[0059] Example 5

[0060] The difference between Example 5 and Example 1 is that only the reaction time of step (3) is changed to 2 h.

[0061] Example 6

[0062] The difference between Example 6 and Example 1 is that only the reaction time of step (1) is changed to 2 h.

[0063] Example 7

[0064] The difference between Example 6 and Example 1 is that only the reaction temperature of step (2) is changed to 200°C.

[0065] The reaction conditions of Examples 1-7 and the comparison of the product properties are shown in Table 1 (the test was carried out according to the national standard GB / T30294-2013).

[0066] Table 1 Comparison of product indicators and product performance under different conditions

[0067]

[0068] As can be seen from Table 1, when the normal pressure reaction temperature is controlled at 148°C, the reaction time is 2 hours, and the negative pressure (absolute pressure) is 300Pa, at the same time, the reaction temperature is controlled at about 200-220°C during the negative pressure reaction, the reaction time is 2 hours, and the DMS addition amount is 7-9%, the obtained product characteristic viscosity can be greater than 1.75dL / g, and the color value and other indicators also meet the requirements of Class I products in the national standard GB / T30294-2013. The existing commercially available products have characteristic viscosities mostly less than 1.75dL / g, and the color values ​​are mostly unbalanced. Compared with common commercially available products, the products prepared by the present invention have the advantages of high characteristic viscosity and good chromaticity. In addition, the synthesis method of the present invention also has a higher yield (mass yield).

[0069] It should be noted that the embodiments described above are only used to explain the present invention and do not constitute any limitation to the present invention. The present invention has been described with reference to typical embodiments, but it should be understood that the words used therein are descriptive and explanatory words, rather than restrictive words. The present invention may be modified as specified within the scope of the claims of the present invention, and the present invention may be revised without departing from the scope and spirit of the present invention. Although the present invention described therein relates to specific methods, materials and embodiments, it does not mean that the present invention is limited to the specific examples disclosed therein, on the contrary, the present invention can be extended to all other methods and applications with the same functions.

Claims

1. A method for synthesizing bio-based high molecular weight polybutylene succinate, characterized in that: The steps include: (1) Normal pressure reaction: bio-based succinic acid and 1,4-butanediol are mixed and placed in a reaction vessel. Then, under the condition of forming an inert atmosphere in the reaction vessel, a catalyst is added and heated to 130-160°C while stirring to perform a pre-polycondensation reaction. The reaction time is 1-4 hours to obtain a reactant. (2) Negative pressure reaction I: The reaction vessel is evacuated to a negative pressure state of 50-1000 Pa, and then the temperature is raised to 160-230 °C under negative pressure conditions for reaction, and the reaction time is 1-4 h; (3) Negative pressure reaction II: adding bio-based dialkyl succinate to the product obtained in step (2) to carry out ester exchange reaction, the reaction temperature is 160-230° C., and the reaction time is 1-2 h; after the reaction is completed, the material is post-treated to obtain the final product.

2. The synthesis method according to claim 1, characterized in that In step (1), the molar ratio of bio-based succinic acid to 1,4-butanediol is (35-55): (75-45).

3. The synthesis method according to claim 1, characterized in that In step (1), the amount of catalyst added is 0.1-0.2% of the total mass of bio-based succinic acid, 1,4-butanediol and the catalyst.

4. The synthesis method according to claim 1, characterized in that In step (1), the reaction temperature is 150-160° C. and the reaction time is 1-2.5 h.

5. The synthesis method according to claim 1, characterized in that In step (2), the negative pressure is 50-500 Pa; the reaction temperature is 190-230° C.; and the reaction time is 1-3 h.

6. The synthesis method according to claim 1, characterized in that In step (3), the bio-based dialkanol succinate is dimethyl succinate, diethyl succinate or dibutyl succinate.

7. The synthesis method according to claim 1, characterized in that In step (3), the amount of bio-based succinic acid dialkanol ester added is 1-10% of the total mass of bio-based succinic acid and 1,4-butanediol.

8. The synthesis method according to claim 1, characterized in that In step (3), the reaction time is 1.5 to 2 hours.

9. The synthesis method according to claim 1, characterized in that In step (3), the post-treatment of the reaction material is as follows: placing the reaction material in an organic alcohol, precipitating the precipitate at room temperature, filtering, centrifuging, and drying to obtain the product.

10. The synthesis method according to claim 9, characterized in that In step (3), the material post-processing operation after the reaction is completed is specifically as follows: The material after the reaction is completed is placed in an organic alcohol, stirred at room temperature, filtered, and a precipitate with a size of 20-100 mesh is precipitated, and then centrifuged at a pressure of 1.80-2.0 MPa for 50-10 minutes. After centrifugation, it is dried at 40-50°C for 1-2 hours to obtain the product.

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