Synthetic method for improving PBAT hue and PBAT product

Abstract

The invention belongs to the technical field of polyester preparation, and particularly relates to a synthetic method for improving a PBAT hue and a PBAT product. The synthesis method comprises the following steps: preparing PBAT by adopting a one-step method; in the preparation process, the refluxed 1, 4-butanediol is rectified to obtain rectified BDO (1, 4-butanediol); the purity of the rectified BDO is not lower than 99.7%, and the content of the 2-hydroxymethyl cyclohexanone is not higher than 500ppm. The PBAT is prepared by adopting a one-step method, the esterification rate can be ensured and the esterification time can be shortened by adopting excessive BDO, and the reflux BDO in the esterification process is rectified, so that on one hand, the reflux BDO can realize material recycling, and on the other hand, the reflux BDO is rectified to improve the purity of the BDO and reduce the impurity content, the content of 2-hydroxymethyl cyclohexanone is not higher than 500ppm, the hue of the PBAT is ensured, and the yield of the PBAT is improved. The conditions of redness, yellowing, purple and the like of the product are avoided, and the requirements of downstream products are met.

Description

Technical Field

[0001] The present invention belongs to the technical field of polyester preparation, and in particular relates to a synthesis method for improving the hue of PBAT and a PBAT product. Background Art

[0002] PBAT is a thermoplastic biodegradable plastic, a copolymer of butylene adipate and butylene terephthalate, with the properties of polybutyl acrylate (PBA) and polybutylene terephthalate (PBT), with good ductility and elongation at break, as well as good heat resistance and impact resistance. In addition, it has excellent biodegradability, making it a very popular biodegradable material in biodegradable plastic research and one of the best biodegradable materials in the market.

[0003] As a new distillation technology based on process intensification theory, controlled cycle distillation changes the flow mode of gas and liquid phases in traditional distillation towers by adopting specific tower internal components and control schemes, realizing the operation mode of periodic independent movement of gas and liquid phases. Theoretically, controlled cycle distillation technology can achieve zero back mixing of liquid phase in the tower, maximize the separation driving force, and has the advantages of large processing capacity, low energy consumption and good separation performance. Compared with traditional distillation operation, cycle distillation technology can increase the efficiency of a single plate to 140% to 300% and reduce energy consumption by 20% to 30%.

[0004] PBAT synthesis is divided into one-step and two-step methods. The one-step method requires polycondensation to form a high molecular weight PBAT with a molecular weight of more than 100,000 and a melt index of 3 to 5. The reaction time is relatively long, usually 5 to 7 hours; the two-step method requires polycondensation to form a low molecular weight PBAT with a melt index of 60 to 80, and then a chain extender is used to increase the molecular weight. The reaction time of the chain extender is shorter than that of the polycondensation, usually only 3 to 4 hours. However, since the two-step method adds a chain extender, it is not conducive to degradation. Therefore, the one-step method is currently used to synthesize PBAT.

[0005] The existing technology uses a one-step method to synthesize PBAT, but due to the high reaction temperature, long time, and high viscosity of PBAT, the product generally has problems such as dark color, red, yellow or purple color, and the hue a value is generally greater than 3 and the b value is greater than 6; the one-step method is accompanied by inevitable side reactions during the preparation process, and the use of reflux BDO in the synthesis process further deteriorates the color value of the product, affecting the scope of downstream application of the product. Summary of the invention

[0006] Therefore, the technical problem to be solved by the present invention is to overcome the defects of the prior art one-step method for preparing PBAT products, such as darker color, higher hue a value and b value, which affect the downstream application of the product, and the use of reflux BDO in the one-step synthesis process, which further causes the color of the product to deteriorate, thereby providing a synthesis method and PBAT product with improved hue of PBAT.

[0007] To this end, the present invention provides the following technical solutions.

[0008] The present invention provides a synthesis method for improving the hue of PBAT, comprising preparing PBAT by a one-step method; in the preparation process, reflux 1,4-butanediol is distilled to obtain distilled BDO; the purity of the distilled BDO is not less than 99.7%, and the content of 2-hydroxymethylcyclohexanone is not higher than 500ppm.

[0009] The parameters of the distillation are as follows: the bottom temperature is 150-158° C., the top temperature is 140-147° C., and the absolute vacuum is 3-7 KPa.

[0010] The content of 2-methyl-1,4-butanediol in the distilled BDO is not higher than 1000 ppm.

[0011] The content of 2-(4-hydroxybutoxy)-tetrahydrofuran in the distilled BDO is not higher than 1000 ppm.

[0012] The one-step method comprises the following steps:

[0013] (1) esterifying terephthalic acid and an excess of 1,4-butanediol to obtain a first esterified liquid;

[0014] (2) esterifying adipic acid and an excess of 1,4-butanediol to obtain a second esterified liquid;

[0015] (3) The first esterification liquid and the second esterification liquid are mixed to carry out esterification reaction and polycondensation reaction.

[0016] In the step (1), the temperature of the esterification reaction is 200-260° C.; and / or,

[0017] The vacuum degree of the esterification reaction is -65 to -30 KPa; and / or,

[0018] The molar ratio of 1,4-butanediol to terephthalic acid is (2-6):1; and / or,

[0019] The esterification rate of the esterification reaction is not less than 95%.

[0020] In step (2), the temperature of the esterification reaction is 180-250° C.; and / or,

[0021] The vacuum degree of the esterification reaction is -65 to -30 KPa; and / or,

[0022] The molar ratio of 1,4-butanediol to adipic acid is (1.5-5):1; and / or,

[0023] The esterification rate of the esterification reaction is not less than 95%.

[0024] In the step (3), the temperature of the esterification reaction is 200-250° C.; and / or,

[0025] The vacuum degree of the esterification reaction is -60 to -30 KPa; and / or,

[0026] The esterification rate of the esterification reaction is not less than 98%; and / or,

[0027] The temperature of the polycondensation reaction is 210-270° C.; and / or,

[0028] The absolute vacuum of the polycondensation reaction is not higher than 100Pa.

[0029] The present invention also provides a PBAT product obtained by the above synthesis method.

[0030] The present invention also provides the use of 1,4-butanediol having a purity of not less than 99.7% and a 2-hydroxymethylcyclohexanone content of not more than 500 ppm in the preparation of PBAT.

[0031] The technical solution of the present invention has the following advantages:

[0032] 1. The present invention provides a synthetic method for improving the hue of PBAT, which comprises preparing PBAT by a one-step method; during the preparation process, reflux 1,4-butanediol is distilled to obtain distilled BDO; the purity of the distilled BDO is not less than 99.7%, and the content of 2-hydroxymethylcyclohexanone is not higher than 500ppm. The present invention adopts a one-step method to prepare PBAT, and the use of excess BDO can ensure the esterification rate and shorten the esterification time. The reflux BDO in the esterification process is distilled. On the one hand, the reflux BDO can realize the recycling of materials, and on the other hand, the reflux BDO is distilled to improve the purity of BDO, reduce the impurity content, and make the content of 2-hydroxymethylcyclohexanone not higher than 500ppm, so as to ensure the hue of PBAT, avoid the product from being red, yellow, purple, etc., and meet the requirements of downstream products. In particular, the present invention controls the mass content of 2-hydroxymethylcyclohexanone to be not higher than 500ppm, so that the hue a value of the synthesized PBAT is less than 3 and the b value is less than 6.

[0033] 2. The present invention provides a synthetic method for improving the hue of PBAT. The present invention further regulates the content of 2-methyl-1,4-butanediol and 2-(4-hydroxybutoxy)-tetrahydrofuran in the distilled BDO, which can further improve the hue of the product and reduce the hue b value.

[0034] The esterification reaction of the present invention is generally carried out under negative pressure, and the esterification rate is not less than 98% after all esterification reactions are completed. The polycondensation reaction is carried out under high temperature and vacuum conditions. The adipic acid that has not been completely reacted during the esterification process undergoes decarboxylation, dehydration, cyclization and other reactions in the polycondensation stage to generate substances such as 1,6-dioxacyclododecane-7,12-dione and 2-hydroxymethylcyclohexanone. These substances have a great impact on the hue and quality of the product. When removing 1,4-butanediol, these substances will reflux with 1,4-butanediol. If these BDO are directly recycled to the reaction system, the PBAT product will be greatly affected. The present invention first distills the refluxed BDO and then uses it to prepare PBAT, which reduces the impact of impurities and ensures the hue and quality of the product.

[0035] 3. The use of 1,4-butanediol with a purity of not less than 99.7% and a 2-hydroxymethylcyclohexanone content of not more than 500 ppm provided by the present invention in the preparation of PBAT, especially controlling the mass content of 2-hydroxymethylcyclohexanone to not more than 500 ppm, the prepared PBAT has excellent color value and color stability, meets the downstream processing and molding performance requirements, and the hue a value of the synthesized PBAT is less than 3 and the b value is less than 6. DETAILED DESCRIPTION

[0036] The following examples are provided for a better understanding of the present invention, but are not intended to limit the best mode of implementation, nor to limit the content and protection scope of the present invention. Any product identical or similar to the present invention obtained by anyone under the inspiration of the present invention or by combining the features of the present invention with other prior arts shall fall within the protection scope of the present invention.

[0037] If no specific experimental steps or conditions are specified in the examples, the conventional experimental steps or conditions described in the literature in the field can be used. If no manufacturer is specified for the reagents or instruments used, they are all conventional reagent products that can be obtained commercially.

[0038] PBAT products prepared by the prior art generally have problems such as redness and yellowing. To this end, the present invention provides the following technical solutions.

[0039] The present invention provides a method for improving the synthesis of PBAT, comprising the following steps:

[0040] (1) esterifying terephthalic acid and an excess of 1,4-butanediol to obtain a first esterified liquid;

[0041] (2) esterifying adipic acid and an excess of 1,4-butanediol to obtain a second esterified liquid;

[0042] (3) the first esterification liquid and the second esterification liquid are mixed to carry out esterification reaction and polycondensation reaction, and the reaction is stopped when the viscosity reaches 1.4-1.6 dL / g, and the pressure is restored to normal to obtain a PBAT melt, and granulation is performed;

[0043] During the esterification process, excess BDO will volatilize together with water and tetrahydrofuran produced during the esterification process, and after separation, reflux BDO will be formed, and then the reflux BDO will be distilled to obtain distilled BDO; the purity of the distilled BDO is not less than 99.7%, and the content of 2-hydroxymethylcyclohexanone is not higher than 500ppm.

[0044] The PBAT product obtained by the synthesis method of the present invention has good hue and quality, does not have the problems of yellowing, redness, etc., the hue a value is less than 3, and the b value is less than 6.

[0045] In an optional embodiment, the distillation parameters are: the bottom temperature is 150-158°C, the top temperature is 140-147°C, and the absolute vacuum is 3-7KPa;

[0046] The content of 2-methyl-1,4-butanediol in the distilled BDO is not higher than 1000 ppm.

[0047] The content of 2-(4-hydroxybutoxy)-tetrahydrofuran in the distilled BDO is not higher than 1000 ppm.

[0048] In an optional embodiment, in step (1), the temperature of the esterification reaction is 200-260° C., preferably, the temperature of the esterification reaction is 220-240° C.; and / or,

[0049] The vacuum degree of the esterification reaction is -65 to -30 KPa; preferably, the vacuum degree of the esterification reaction is -55 to -45 KPa; and / or,

[0050] The molar ratio of 1,4-butanediol to terephthalic acid is (2-6):1; preferably, the molar ratio of 1,4-butanediol to terephthalic acid is (2.5-4):1; and / or,

[0051] The esterification rate of the esterification reaction is not less than 95%, preferably 95-97%.

[0052] In an optional embodiment, in step (2), the temperature of the esterification reaction is 180-250° C.; preferably, the temperature of the esterification reaction is 210-230° C.; and / or,

[0053] The vacuum degree of the esterification reaction is -65 to -30 KPa; preferably, the vacuum degree of the esterification reaction is -55 to -45 KPa; and / or,

[0054] The molar ratio of 1,4-butanediol to adipic acid is (1.5-5):1; preferably, the molar ratio of 1,4-butanediol to adipic acid is (2-3.5):1; and / or,

[0055] The esterification rate of the esterification reaction is not less than 95%, preferably 95-97%.

[0056] In an optional embodiment, in step (3), the temperature of the esterification reaction is 200-250° C.; preferably, the temperature of the esterification reaction is 220-240° C.; and / or,

[0057] The vacuum degree of the esterification reaction is -60 to -30 KPa; preferably, the vacuum degree of the esterification reaction is -55 to -45 KPa; and / or,

[0058] The esterification rate of the esterification reaction is not less than 98%; and / or,

[0059] The temperature of the polycondensation reaction is 210-270°C; preferably, the temperature of the polycondensation reaction is 220-260°C, more preferably 230-250°C; and / or,

[0060] The absolute vacuum of the polycondensation reaction is not higher than 100 Pa; preferably, the absolute vacuum is less than 80 Pa, and more preferably, the absolute vacuum is less than 60 Pa.

[0061] In an optional embodiment, the main impurities of the refluxing BDO include 2-methyl-1,4-butanediol, 2-(4-hydroxybutoxy)-tetrahydrofuran, 2-hydroxymethylcyclohexanone, 1,6-dioxacyclododecane-7,12-dione, polyester oligomers, and cyclopentanone; more specifically, in terms of mass percentage, the refluxing BDO includes: 95-97wt% BDO, 0.1-0.4wt% 2-methyl-1,4-butanediol, 0.1-0.5wt% 2-(4-hydroxybutoxy)-tetrahydrofuran, 0.1-0.3wt% 2-hydroxymethylcyclohexanone, 1-2wt% 1,6-dioxacyclododecane-7,12-dione, 0.2-0.6wt% cyclopentanone, and 0.2-0.5wt% linear polyester.

[0062] The refluxed BDO is distilled to obtain distilled BDO, wherein main impurities of the distilled BDO include 2-methyl-1,4-butanediol, 2-(4-hydroxybutoxy)-tetrahydrofuran and 2-hydroxymethylcyclohexanone.

[0063] It should be noted that the weight average molecular weight, melt index (MFR), hue, esterification rate, mass content of compounds such as 2-hydroxymethylcyclohexanone are obtained by testing using methods known in the art, and a specific testing method is listed here.

[0064] The weight average molecular weight was measured by Shimadzu gel permeation chromatography (GPC).

[0065] Melt Flow Index (MFR): The melt flow index (MFR) of PBAT was measured at 190°C and 2.16 kg.

[0066] The hue includes L value, a value and b value, which are automatically measured using an Agera automatic colorimeter from Hunter Lab; wherein the L value represents glossiness, the a value represents the degree of redness and greenness, and the b value represents the degree of yellowness and blueness.

[0067] Esterification rate: Determined by the ratio of the water content in the esterification fraction to the theoretical water content. The esterification rate calculation formula is as follows:

[0068]

[0069] The mass content of compounds such as 2-hydroxymethylcyclohexanone in BDO: measured by gas chromatography-quadrupole mass spectrometry-Agilent 7890A-5975C (GC-MS). Taking 2-hydroxymethylcyclohexanone as an example, the refluxing BDO is mixed with a solvent to prepare a test solution; the peak area of ​​2-hydroxymethylcyclohexanone in the test solution is tested by gas chromatography-mass spectrometry (GC-MS), and the content of 2-hydroxymethylcyclohexanone in the refluxing BDO is calculated based on the peak area of ​​2-hydroxymethylcyclohexanone in the test solution and the standard curve of 2-hydroxymethylcyclohexanone.

[0070] Example 1

[0071] This embodiment provides a synthesis method for improving the hue of PBAT, comprising the following steps:

[0072] (1) Weigh 1788.0 g of terephthalic acid, 2914.4 g of 1,4-butanediol, and 4.80 g of tetraisopropyl titanate and add them to a 10 L reactor. Stirring is started and nitrogen is replaced three times. The esterification reaction is carried out at a negative pressure of -48 KPa and 235° C. for 120 min, and the esterification rate is 96.0%. After the esterification reaction is completed, the esterified liquid is transferred to a 10 L esterification kettle.

[0073] (2) 1773.6 g of adipic acid and 3284.0 g of 1,4-butanediol were weighed and added to a 10 L reactor. Stirring was started and nitrogen was replaced three times. The esterification reaction was carried out at a negative pressure of -46 KPa and 220° C. for 120 min. The esterification rate was 96.1%. After the esterification reaction was completed, the esterified liquid was transferred to a 10 L esterification kettle.

[0074] (3) After the esterification liquids from (1) and (2) were transferred to a 10 L esterification kettle, the esterification reaction was carried out at a negative pressure of -53 KPa and 230°C for 60 min. The esterification rate was 98.3%. After the esterification reaction was completed, the esterification liquid was transferred to a 10 L polycondensation kettle.

[0075] (4) After the esterification liquid is transferred to the polycondensation reactor, the reactor is decompressed to an absolute pressure of 50 Pa in 40 minutes, and the polycondensation reaction is carried out at 240° C. for 3 hours. When the viscosity reaches 1.4 to 1.6 dL / g, stirring is stopped, and nitrogen is filled into the reactor to restore the reactor to normal pressure to obtain a PBAT melt, which is extruded under nitrogen protection, cooled to room temperature, and pelletized to obtain the PBAT particles.

[0076] Reflux BDO is generated during the esterification process. The reflux BDO is rectified through a distillation tower to obtain rectified BDO, thereby realizing the recycling of the reflux BDO. The distillation parameters are as follows: the tower top temperature is 144.1°C, the tower bottom temperature is 152°C, the absolute vacuum is 5.3KPa, the purity of the rectified BDO is 99.79%, the content of 2-methyl-1,4-butanediol is 0.033%, the content of 2-(4-hydroxybutoxy)-tetrahydrofuran is 0.043%, and the content of 2-hydroxymethylcyclohexanone is 0.048%.

[0077] Example 2

[0078] This embodiment provides a synthesis method for improving the hue of PBAT, comprising the following steps:

[0079] (1) Weigh 1788.0 g of terephthalic acid, 2618.4 g of 1,4-butanediol, and 4.71 g of tetraisopropyl titanate and add them to a 10 L reactor. Stirring is started and nitrogen is replaced three times. The esterification reaction is carried out at a negative pressure of -48 KPa and 235° C. for 120 min. The esterification rate is 95.4%. After the esterification reaction is completed, the esterified liquid is transferred to a 10 L esterification kettle.

[0080] (2) 1773.6 g of adipic acid and 2953.9 g of 1,4-butanediol were weighed and added to a 10 L reactor. Stirring was started and nitrogen was replaced three times. The esterification reaction was carried out at a negative pressure of -46 KPa and 220° C. for 120 min. The esterification rate was 95.5%. After the esterification reaction was completed, the esterified liquid was transferred to a 10 L esterification kettle.

[0081] (3) After the esterification liquids from (1) and (2) were transferred to a 10 L esterification kettle, the esterification reaction was carried out at a negative pressure of -53 KPa and 230°C for 60 min. The esterification rate was 98.2%. After the esterification reaction was completed, the esterification liquid was transferred to a 10 L polycondensation kettle.

[0082] (4) After the esterification liquid is transferred to the polycondensation reactor, the reactor is decompressed to an absolute pressure of 50 Pa in 40 minutes, and the polycondensation reaction is carried out at 250° C. for 3 hours. When the viscosity reaches 1.4 to 1.6 dL / g, stirring is stopped, and nitrogen is filled into the reactor to restore the reactor to normal pressure to obtain a PBAT melt, which is extruded under nitrogen protection, cooled to room temperature, and pelletized to obtain the PBAT particles.

[0083] Reflux BDO is generated during the esterification process. The reflux BDO is rectified through a distillation tower to obtain rectified BDO, thereby realizing the recycling of the reflux BDO. The distillation parameters are as follows: the tower top temperature is 144.1°C, the tower bottom temperature is 152°C, the absolute vacuum is 5.3KPa, the purity of the rectified BDO is 99.79%, the content of 2-methyl-1,4-butanediol is 0.033%, the content of 2-(4-hydroxybutoxy)-tetrahydrofuran is 0.043%, and the content of 2-hydroxymethylcyclohexanone is 0.048%.

[0084] Example 3

[0085] This embodiment provides a synthesis method for improving the hue of PBAT, comprising the following steps:

[0086] (1) Weigh 1788.0 g of terephthalic acid, 3200.0 g of 1,4-butanediol, and 4.93 g of tetraisopropyl titanate and add them to a 10 L reactor. Stirring is started and nitrogen is replaced three times. The esterification reaction is carried out at -48 KPa and 235° C. for 120 min. The esterification rate is 96.6%. After the esterification reaction is completed, the esterified liquid is transferred to a 10 L esterification kettle.

[0087] (2) 1773.6 g of adipic acid and 3610.4 g of 1,4-butanediol were weighed and added to a 10 L reactor. Stirring was started and nitrogen was replaced three times. The esterification reaction was carried out at a negative pressure of -46 KPa and 220° C. for 120 min. The esterification rate was 96.7%. After the esterification reaction was completed, the esterified liquid was transferred to a 10 L esterification kettle.

[0088] (3) After the esterification liquids from (1) and (2) were transferred to a 10 L esterification kettle, the esterification reaction was carried out at a negative pressure of -53 KPa and 230°C for 60 min. The esterification rate was 98.5%. After the esterification reaction was completed, the esterification liquid was transferred to a 10 L polycondensation kettle.

[0089] (4) After the esterification liquid is transferred to the polycondensation reactor, the reactor is decompressed to an absolute pressure of 50 Pa in 40 minutes, and the reaction is carried out at 240° C. for 3 hours. When the viscosity reaches 1.4 to 1.6 dL / g, stirring is stopped, and nitrogen is filled into the reactor to restore the reactor to normal pressure to obtain a PBAT melt, which is extruded under nitrogen protection, cooled to room temperature, and pelletized to obtain the PBAT particles.

[0090] Reflux BDO is generated during the esterification process. The reflux BDO is rectified through a distillation tower to obtain rectified BDO, thereby realizing the recycling of the reflux BDO. The distillation parameters are as follows: the tower top temperature is 144.1°C, the tower bottom temperature is 152°C, the absolute vacuum is 5.3KPa, the purity of the rectified BDO is 99.79%, the content of 2-methyl-1,4-butanediol is 0.033%, the content of 2-(4-hydroxybutoxy)-tetrahydrofuran is 0.043%, and the content of 2-hydroxymethylcyclohexanone is 0.048%.

[0091] Example 4

[0092] This embodiment provides a synthesis method for improving the hue of PBAT, comprising the following steps:

[0093] (1) Weigh 1788.0 g of terephthalic acid, 2914.4 g of 1,4-butanediol, and 4.80 g of tetraisopropyl titanate and add them to a 10 L reactor. Start stirring and replace with nitrogen three times. Perform post-esterification reaction at -48 KPa negative pressure and 235° C. for 120 min. The esterification rate is 96.2%. After the esterification reaction is completed, transfer the esterified liquid to a 10 L esterification reactor.

[0094] (2) 1773.6 g of adipic acid and 3284.0 g of 1,4-butanediol were weighed and added to a 10 L reactor. Stirring was started and nitrogen was replaced three times. The esterification reaction was carried out at a negative pressure of -46 KPa and 220° C. for 120 min. The esterification rate was 95.8%. After the esterification reaction was completed, the esterified liquid was transferred to a 10 L esterification kettle.

[0095] (3) After the esterification liquids from (1) and (2) were transferred to a 10 L esterification kettle, the esterification reaction was carried out at a negative pressure of -53 KPa and 230°C for 60 min. The esterification rate was 98.4%. After the esterification reaction was completed, the esterification liquid was transferred to a 10 L polycondensation kettle.

[0096] (4) After the esterification liquid is transferred to the polycondensation reactor, the reactor is decompressed to an absolute pressure of 50 Pa in 40 minutes, and the reaction is carried out at 240° C. for 3 hours. When the viscosity reaches 1.4 to 1.6 dL / g, stirring is stopped, and nitrogen is filled into the reactor to restore the reactor to normal pressure to obtain a PBAT melt, which is extruded under nitrogen protection, cooled to room temperature, and pelletized to obtain the PBAT particles.

[0097] Reflux BDO is generated during the esterification process. The reflux BDO is rectified through a distillation tower to obtain rectified BDO, thereby realizing the recycling of the reflux BDO. The distillation parameters are as follows: the tower top temperature is 144.5°C, the tower bottom temperature is 152.3°C, the absolute vacuum is 5.0KPa, the purity of the rectified BDO is 99.81%, the content of 2-methyl-1,4-butanediol is 0.030%, the content of 2-(4-hydroxybutoxy)-tetrahydrofuran is 0.042%, and the content of 2-hydroxymethylcyclohexanone is 0.025%.

[0098] Example 5

[0099] This embodiment provides a synthesis method for improving the hue of PBAT, comprising the following steps:

[0100] (1) Weigh 1788.0 g of terephthalic acid, 2618.4 g of 1,4-butanediol, and 4.80 g of tetraisopropyl titanate and add them to a 10 L reactor. Stirring is started and nitrogen is replaced three times. The esterification reaction is carried out at a negative pressure of -48 KPa and 235° C. for 120 min. The esterification rate is 96.0%. After the esterification reaction is completed, the esterified liquid is transferred to a 10 L esterification kettle.

[0101] (2) 1773.6 g of adipic acid and 2953.9 g of 1,4-butanediol were weighed and added to a 10 L reactor. Stirring was started and nitrogen was replaced three times. The esterification reaction was carried out at a negative pressure of -46 KPa and 220° C. for 120 min. The esterification rate was 96.3%. After the esterification reaction was completed, the esterified liquid was transferred to a 10 L esterification kettle.

[0102] (3) After the esterification liquids from (1) and (2) were transferred to a 10 L esterification kettle, the esterification reaction was carried out at a negative pressure of -53 KPa and 230°C for 60 min. The esterification rate was 98.3%. After the esterification reaction was completed, the esterification liquid was transferred to a 10 L polycondensation kettle.

[0103] (4) After the esterification liquid is transferred to the polycondensation reactor, the reactor is decompressed to an absolute pressure of 50 Pa in 40 minutes, and the reaction is carried out at 240° C. for 3 hours. When the viscosity reaches 1.4 to 1.6 dL / g, stirring is stopped, and nitrogen is filled into the reactor to restore the reactor to normal pressure to obtain a PBAT melt, which is extruded under nitrogen protection, cooled to room temperature, and pelletized to obtain the PBAT particles.

[0104] Reflux BDO is generated during the esterification process. The reflux BDO is rectified through a distillation tower to obtain rectified BDO, thereby realizing the recycling of the reflux BDO. The distillation parameters are as follows: the tower top temperature is 144.5°C, the tower bottom temperature is 152.3°C, the absolute vacuum is 5.0KPa, the purity of the rectified BDO is 99.81%, the content of 2-methyl-1,4-butanediol is 0.030%, the content of 2-(4-hydroxybutoxy)-tetrahydrofuran is 0.042%, and the content of 2-hydroxymethylcyclohexanone is 0.025%.

[0105] Example 6

[0106] This embodiment provides a synthesis method for improving the hue of PBAT, comprising the following steps:

[0107] (1) Weigh 1788.0 g of terephthalic acid, 3200.0 g of 1,4-butanediol, and 4.80 g of tetraisopropyl titanate and add them to a 10 L reactor. Stirring is started and nitrogen is replaced three times. The esterification reaction is carried out at a negative pressure of -48 KPa and 235° C. for 120 min. The esterification rate is 96.1%. After the esterification reaction is completed, the esterified liquid is transferred to a 10 L esterification kettle.

[0108] (2) 1773.6 g of adipic acid and 3610.4 g of 1,4-butanediol were weighed and added to a 10 L reactor. Stirring was started and nitrogen was replaced three times. The esterification reaction was carried out at a negative pressure of -46 KPa and 220° C. for 120 min. The esterification rate was 96.2%. After the esterification reaction was completed, the esterified liquid was transferred to a 10 L esterification kettle.

[0109] (3) After the esterification liquids from (1) and (2) were transferred to a 10 L esterification kettle, the esterification reaction was carried out at a negative pressure of -53 KPa and 230°C for 60 min. The esterification rate was 98.5%. After the esterification reaction was completed, the esterification liquid was transferred to a 10 L polycondensation kettle.

[0110] (4) After the esterification liquid is transferred to the polycondensation reactor, the reactor is decompressed to an absolute pressure of 50 Pa in 40 minutes, and the reaction is carried out at 240° C. for 3 hours. When the viscosity reaches 1.4 to 1.6 dL / g, stirring is stopped, and nitrogen is filled into the reactor to restore the reactor to normal pressure to obtain a PBAT melt, which is extruded under nitrogen protection, cooled to room temperature, and pelletized to obtain the PBAT particles.

[0111] During the esterification process, reflux BDO is generated, and the reflux BDO is rectified through a distillation tower to obtain rectified BDO, thereby realizing the recycling of the reflux BDO. The distillation parameters are as follows: the tower top temperature is 144.5° C., the tower bottom temperature is 152.3° C., the absolute vacuum is 5.0 KPa, the purity of the rectified BDO is 99.81%, the content of 2-methyl-1,4-butanediol is 0.030%, the content of 2-(4-hydroxybutoxy)-tetrahydrofuran is 0.042%, and the content of 2-hydroxymethylcyclohexanone is 0.025%.

[0112] Example 7

[0113] This embodiment provides a synthesis method for improving the hue of PBAT, comprising the following steps:

[0114] (1) Weigh 1788.0 g of terephthalic acid, 2914.4 g of 1,4-butanediol, and 4.80 g of tetraisopropyl titanate and add them to a 10 L reactor. Stirring is started and nitrogen is replaced three times. The esterification reaction is carried out at a negative pressure of -48 KPa and 235° C. for 120 min. The esterification rate is 96.2%. After the esterification reaction is completed, the esterified liquid is transferred to a 10 L esterification kettle.

[0115] (2) 1773.6 g of adipic acid and 3284.0 g of 1,4-butanediol were weighed and added to a 10 L reactor. Stirring was started and nitrogen was replaced three times. The esterification reaction was carried out at a negative pressure of -46 KPa and 220° C. for 120 min. The esterification rate was 96.0%. After the esterification reaction was completed, the esterified liquid was transferred to a 10 L esterification kettle.

[0116] (3) After the esterification liquids from (1) and (2) were transferred to a 10 L esterification kettle, the esterification reaction was carried out at a negative pressure of -53 KPa and 230°C for 60 min. The esterification rate was 98.2%. After the esterification reaction was completed, the esterification liquid was transferred to a 10 L polycondensation kettle.

[0117] (4) After the esterification liquid is transferred to the polycondensation reactor, the reactor is decompressed to an absolute pressure of 50 Pa in 40 minutes, and the reaction is carried out at 240° C. for 3 hours. When the viscosity reaches 1.4 to 1.6 dL / g, stirring is stopped, and nitrogen is filled into the reactor to restore the reactor to normal pressure to obtain a PBAT melt, which is extruded under nitrogen protection, cooled to room temperature, and pelletized to obtain the PBAT particles.

[0118] During the esterification process, reflux BDO is generated, and the reflux BDO is rectified through a distillation tower to obtain rectified BDO, thereby realizing the recycling of the reflux BDO. The distillation parameters are as follows: the tower top temperature is 144.8°C, the tower bottom temperature is 152.6°C, the absolute vacuum is 4.8KPa, the purity of the rectified BDO is 99.83%, the content of 2-methyl-1,4-butanediol is 0.031%, the content of 2-(4-hydroxybutoxy)-tetrahydrofuran is 0.041%, and the content of 2-hydroxymethylcyclohexanone is 0.0085%.

[0119] Example 8

[0120] This embodiment provides a synthesis method for improving the hue of PBAT, comprising the following steps:

[0121] (1) 1788.0 g of terephthalic acid, 2618.4 g of 1,4-butanediol, and 4.80 g of tetraisopropyl titanate were weighed and added to a 10 L reactor. Stirring was started and nitrogen was replaced three times. The post-esterification reaction was carried out at a negative pressure of -48 KPa and 235° C. for 120 min. The esterification rate was 96.1%. After the esterification reaction was completed, the esterified liquid was transferred to a 10 L esterification kettle.

[0122] (2) 1773.6 g of adipic acid and 2953.9 g of 1,4-butanediol were weighed and added to a 10 L reactor. Stirring was started and nitrogen was replaced three times. The esterification reaction was carried out at a negative pressure of -46 KPa and 220° C. for 120 min. The esterification rate was 96.3%. After the esterification reaction was completed, the esterified liquid was transferred to a 10 L esterification kettle.

[0123] (3) After the esterification liquids from (1) and (2) were transferred to a 10 L esterification kettle, the esterification reaction was carried out at a negative pressure of -53 KPa and 230°C for 60 min. The esterification rate was 98.2%. After the esterification reaction was completed, the esterification liquid was transferred to a 10 L polycondensation kettle.

[0124] (4) After the esterification liquid is transferred to the polycondensation reactor, the reactor is decompressed to an absolute pressure of 50 Pa in 40 minutes, and the reaction is carried out at 240° C. for 3 hours. When the viscosity reaches 1.4 to 1.6 dL / g, stirring is stopped, and nitrogen is filled into the reactor to restore the reactor to normal pressure to obtain a PBAT melt, which is extruded under nitrogen protection, cooled to room temperature, and pelletized to obtain the PBAT particles.

[0125] During the esterification process, reflux BDO is generated, and the reflux BDO is rectified through a distillation tower to obtain rectified BDO, thereby realizing the recycling of the reflux BDO. The distillation parameters are as follows: the tower top temperature is 144.8°C, the tower bottom temperature is 152.6°C, the absolute vacuum is 4.8KPa, the purity of the rectified BDO is 99.83%, the content of 2-methyl-1,4-butanediol is 0.031%, the content of 2-(4-hydroxybutoxy)-tetrahydrofuran is 0.041%, and the content of 2-hydroxymethylcyclohexanone is 0.0085%.

[0126] Example 9

[0127] This embodiment provides a synthesis method for improving the hue of PBAT, comprising the following steps:

[0128] (1) Weigh 1788.0 g of terephthalic acid, 3200.0 g of 1,4-butanediol, and 4.80 g of tetraisopropyl titanate and add them to a 10 L reactor. Stirring is started and nitrogen is replaced three times. The esterification reaction is carried out at a negative pressure of -48 KPa and 235° C. for 120 min. The esterification rate is 96.1%. After the esterification reaction is completed, the esterified liquid is transferred to a 10 L esterification kettle.

[0129] (2) 1773.6 g of adipic acid and 3610.4 g of 1,4-butanediol were weighed and added to a 10 L reactor. Stirring was started and nitrogen was replaced three times. The esterification reaction was carried out at a negative pressure of -46 KPa and 220° C. for 120 min. The esterification rate was 96.3%. After the esterification reaction was completed, the esterified liquid was transferred to a 10 L esterification kettle.

[0130] (3) After the esterification liquids from (1) and (2) were transferred to a 10 L esterification kettle, the esterification reaction was carried out at a negative pressure of -53 KPa and 230°C for 60 min. The esterification rate was 98.6%. After the esterification reaction was completed, the esterification liquid was transferred to a 10 L polycondensation kettle.

[0131] (4) After the esterification liquid is transferred to the polycondensation reactor, the reactor is decompressed to an absolute pressure of 50 Pa in 40 minutes, and the reaction is carried out at 240° C. for 3 hours. When the viscosity reaches 1.4 to 1.6 dL / g, stirring is stopped, and nitrogen is filled into the reactor to restore the reactor to normal pressure to obtain a PBAT melt, which is extruded under nitrogen protection, cooled to room temperature, and pelletized to obtain the PBAT particles.

[0132] During the esterification process, reflux BDO is generated, and the reflux BDO is rectified through a distillation tower to obtain rectified BDO, thereby realizing the recycling of the reflux BDO. The distillation parameters are as follows: the tower top temperature is 144.8°C, the tower bottom temperature is 152.6°C, the absolute vacuum is 4.8KPa, the purity of the rectified BDO is 99.83%, the content of 2-methyl-1,4-butanediol is 0.031%, the content of 2-(4-hydroxybutoxy)-tetrahydrofuran is 0.041%, and the content of 2-hydroxymethylcyclohexanone is 0.0085%.

[0133] Comparative Example 1

[0134] This comparative example provides a method for synthesizing PBAT, comprising the following steps:

[0135] (1) 1788.0 g of terephthalic acid, 2914.4 g of 1,4-butanediol, and 4.80 g of tetraisopropyl titanate were weighed and added into a 10 L reactor. Stirring was started and nitrogen was replaced three times. The esterification reaction was carried out at a negative pressure of -48 KPa and 235° C. for 120 min. The esterification rate was 95.9%. After the esterification reaction was completed, the esterified liquid was transferred to a 10 L esterification kettle.

[0136] (2) 1773.6 g of adipic acid and 3284.0 g of 1,4-butanediol were weighed and added to a 10 L reactor. Stirring was started and nitrogen was replaced three times. The esterification reaction was carried out at a negative pressure of -46 KPa and 220° C. for 120 min. The esterification rate was 96.0%. After the esterification reaction was completed, the esterified liquid was transferred to a 10 L esterification kettle.

[0137] (3) After the esterification liquids from (1) and (2) were transferred to a 10 L esterification kettle, the esterification reaction was carried out at a negative pressure of -53 KPa and 230°C for 60 min. The esterification rate was 98.3%. After the esterification reaction was completed, the esterification liquid was transferred to a 10 L polycondensation kettle.

[0138] (4) After the esterification liquid is transferred to the polycondensation reactor, the reactor is decompressed to an absolute pressure of 50 Pa in 40 minutes, and the reaction is carried out at 240° C. for 3 hours. When the viscosity reaches 1.4 to 1.6 dL / g, stirring is stopped, and nitrogen is filled into the reactor to restore the reactor to normal pressure to obtain a PBAT melt, which is extruded under nitrogen protection, cooled to room temperature, and pelletized to obtain the PBAT particles.

[0139] The reflux BDO obtained in the esterification process was not distilled, and the purity of the reflux BDO was 96.76%, the content of 2-methyl-1,4-butanediol was 0.22%, the content of 2-(4-hydroxybutoxy)-tetrahydrofuran was 0.30%, the content of 2-hydroxymethylcyclohexanone was 0.12%, and the content of 1,6-dioxacyclododecane-7,12-dione was 1.2%.

[0140] Comparative Example 2

[0141] This comparative example provides a method for synthesizing PBAT, comprising the following steps:

[0142] (1) 1788.0 g of terephthalic acid, 2618.4 g of 1,4-butanediol, and 4.71 g of tetraisopropyl titanate were weighed and added into a 10 L reactor. Stirring was started and nitrogen was replaced three times. The esterification reaction was carried out at a negative pressure of -48 KPa and 235° C. for 120 min. The esterification rate was 95.8%. After the esterification reaction was completed, the esterified liquid was transferred to a 10 L esterification kettle.

[0143] (2) 1773.6 g of adipic acid and 2953.9 g of 1,4-butanediol were weighed and added to a 10 L reactor. Stirring was started and nitrogen was replaced three times. The esterification reaction was carried out at a negative pressure of -46 KPa and 220° C. for 120 min. The esterification rate was 95.8%. After the esterification reaction was completed, the esterified liquid was transferred to a 10 L esterification kettle.

[0144] (3) After the esterification liquids from (1) and (2) were transferred to a 10 L esterification kettle, the esterification reaction was carried out at a negative pressure of -53 KPa and 230°C for 60 min. The esterification rate was 98.1%. After the esterification reaction was completed, the esterification liquid was transferred to a 10 L polycondensation kettle.

[0145] (4) After the esterification liquid is transferred to the polycondensation reactor, the reactor is decompressed to an absolute pressure of 50 Pa in 40 minutes, and the reaction is carried out at 240° C. for 3 hours. When the viscosity reaches 1.4 to 1.6 dL / g, stirring is stopped, and nitrogen is filled into the reactor to restore the reactor to normal pressure to obtain a PBAT melt, which is extruded under nitrogen protection, cooled to room temperature, and pelletized to obtain the PBAT particles.

[0146] The reflux BDO obtained in the esterification process was not distilled, and the purity of the reflux BDO was 96.76%, the content of 2-methyl-1,4-butanediol was 0.22%, the content of 2-(4-hydroxybutoxy)-tetrahydrofuran was 0.30%, the content of 2-hydroxymethylcyclohexanone was 0.12%, and the content of 1,6-dioxacyclododecane-7,12-dione was 1.2%.

[0147] Comparative Example 3

[0148] This comparative example provides a method for synthesizing PBAT, comprising the following steps:

[0149] (1) 1788.0 g of terephthalic acid, 3200.0 g of 1,4-butanediol, and 4.80 g of tetraisopropyl titanate were weighed and added to a 10 L reactor. Stirring was started and nitrogen was replaced three times. The esterification reaction was carried out at a negative pressure of -48 KPa and 235° C. for 120 min. The esterification rate was 96.4%. After the esterification reaction was completed, the esterified liquid was transferred to a 10 L esterification kettle.

[0150] (2) 1773.6 g of adipic acid and 3610.4 g of 1,4-butanediol were weighed and added to a 10 L reactor. Stirring was started and nitrogen was replaced three times. The esterification reaction was carried out at a negative pressure of -46 KPa and 220° C. for 120 min. The esterification rate was 96.2%. After the esterification reaction was completed, the esterified liquid was transferred to a 10 L esterification kettle.

[0151] (3) After the esterification liquids from (1) and (2) were transferred to a 10 L esterification kettle, the esterification reaction was carried out at a negative pressure of -53 KPa and 230°C for 60 min. The esterification rate was 98.4%. After the esterification reaction was completed, the esterification liquid was transferred to a 10 L polycondensation kettle.

[0152] (4) After the esterification liquid is transferred to the polycondensation reactor, the reactor is decompressed to an absolute pressure of 50 Pa in 40 minutes, and the reaction is carried out at 240° C. for 3 hours. When the viscosity reaches 1.4 to 1.6 dL / g, stirring is stopped, and nitrogen is filled into the reactor to restore the reactor to normal pressure to obtain a PBAT melt, which is extruded under nitrogen protection, cooled to room temperature, and pelletized to obtain the PBAT particles.

[0153] The reflux BDO obtained in the esterification process was not distilled, and the purity of the reflux BDO was 96.76%, the content of 2-methyl-1,4-butanediol was 0.22%, the content of 2-(4-hydroxybutoxy)-tetrahydrofuran was 0.30%, the content of 2-hydroxymethylcyclohexanone was 0.12%, and the content of 1,6-dioxacyclododecane-7,12-dione was 1.2%.

[0154] Test Case

[0155] The weight average molecular weight, melt index MFR, L value, a value, and b value of the PBAT prepared in each embodiment and comparative example are shown in Table 1; the contents of 1,4-butanediol, 2-methyl-1,4-butanediol, and 2-(4-hydroxybutoxy)-tetrahydrofuran in the distilled BDO or refluxed BDO are shown in Table 1.

[0156] Table 1 Impurity content and PBAT parameters in distilled BDO or refluxed BDO in various examples and comparative examples

[0157]

[0158] Conclusion: The a value of PBAT synthesized directly from refluxing BDO is generally greater than 4. The impurities in BDO are greatly reduced after distillation. The a value of PBAT synthesized from BDO after distillation is less than 3, and the color value is greatly improved. The content of 2-hydroxymethylcyclohexanone, an impurity in BDO, has a significant effect on the color value of PBAT.

[0159] Obviously, the above embodiments are merely examples for the purpose of clear explanation, and are not intended to limit the implementation methods. For those skilled in the art, other different forms of changes or modifications can be made based on the above description. It is not necessary and impossible to list all the implementation methods here. The obvious changes or modifications derived from these are still within the scope of protection of the invention.

Claims

1. A synthesis method for improving the hue of PBAT, characterized in that: The invention comprises preparing PBAT by a one-step method; during the preparation process, reflux 1,4-butanediol is distilled to obtain distilled BDO; the purity of the distilled BDO is not less than 99.7%, and the content of 2-hydroxymethylcyclohexanone is not higher than 500ppm.

2. The synthesis method according to claim 1, characterized in that The parameters of the distillation are as follows: the bottom temperature is 150-158° C., the top temperature is 140-147° C., and the absolute vacuum is 3-7 KPa.

3. The synthesis method according to claim 1 or 2, characterized in that The content of 2-methyl-1,4-butanediol in the distilled BDO is not higher than 1000 ppm.

4. The synthesis method according to claim 1 or 2, characterized in that The content of 2-(4-hydroxybutoxy)-tetrahydrofuran in the distilled BDO is not higher than 1000 ppm.

5. The synthesis method according to any one of claims 1 to 4, characterized in that: The one-step method comprises the following steps: (1) esterifying terephthalic acid and an excess of 1,4-butanediol to obtain a first esterified liquid; (2) esterifying adipic acid and an excess of 1,4-butanediol to obtain a second esterified liquid; (3) The first esterification liquid and the second esterification liquid are mixed to carry out esterification reaction and polycondensation reaction.

6. The synthesis method according to claim 5, characterized in that In the step (1), the temperature of the esterification reaction is 200-260° C.; and / or, The vacuum degree of the esterification reaction is -65 to -30 KPa; and / or, The molar ratio of 1,4-butanediol to terephthalic acid is (2-6):1; and / or, The esterification rate of the esterification reaction is not less than 95%.

7. The synthesis method according to claim 5, characterized in that In step (2), the temperature of the esterification reaction is 180-250° C.; and / or, The vacuum degree of the esterification reaction is -65 to -30 KPa; and / or, The molar ratio of 1,4-butanediol to adipic acid is (1.5-5):1; and / or, The esterification rate of the esterification reaction is not less than 95%.

8. The synthesis method according to claim 5, characterized in that In the step (3), the temperature of the esterification reaction is 200-250° C.; and / or, The vacuum degree of the esterification reaction is -60 to -30 KPa; and / or, The esterification rate of the esterification reaction is not less than 98%; and / or, The temperature of the polycondensation reaction is 210-270° C.; and / or, The absolute vacuum of the polycondensation reaction is not higher than 100Pa.

9. The PBAT product obtained by the synthesis method according to any one of claims 1 to 8.

10. Use of 1,4-butanediol with a purity of not less than 99.7% and a 2-hydroxymethylcyclohexanone content of not more than 500 ppm in the preparation of PBAT.

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