Preparation method of low-color-value polyethylene furandicarboxylate

Abstract

The invention provides a preparation method of low-color-value polyethylene furandicarboxylate. The germanium-titanium composite catalyst is used as the catalyst for preparing the polyethylene furandicarboxylate, so that the problems of slow reaction and dark color of the polyethylene furandicarboxylate are solved. According to the preparation method of the polyethylene furandicarboxylate, all the raw materials are only added before the reaction, additives or other catalysts do not need to be added in the middle process, the process is very simple, the process is environment-friendly, and industrialization is facilitated.

Description

Technical Field

[0001] This invention relates to the field of polymer material synthesis technology, specifically to a method for preparing low-color-value polyethylene furanate. Background Technology

[0002] Polyethylene terephthalate (PET) is currently the most widely used polyester material, but its raw materials mainly come from non-renewable petroleum resources and are difficult to degrade in the natural environment, causing serious "white pollution" problems. Finding bio-based plastics to replace traditional petroleum-based polyesters has become the most effective solution. Since ethylene glycol already has bio-based sources, polyethylene furanate (PEF), synthesized using bio-based 2,5-furandicarboxylic acid (FDCA) instead of PTA (terephthalic acid) as a monomer, is considered one of the ideal alternatives to PET. PEF has a lower melting temperature, making it easier to process, and possesses higher tensile modulus and glass transition temperature. Most importantly, it has excellent gas barrier properties. However, the synthesis of PEF has some inherent drawbacks: 1. Due to the effects of side reactions such as decarboxylation, the PEF polyester prepared by melt is dark yellow or black, and the unattractive color makes PEF less suitable for the market.

[0003] 2. The polycondensation reaction rate is slow and the reaction time is long, usually 4-8 hours. The resulting polyester chips have a low intrinsic viscosity, only about 0.5 dL / g.

[0004] The most effective way to overcome these shortcomings is to improve the catalyst, such as traditional antimony-based, titanium-based, and germanium-based catalysts. While antimony-based catalysts have high catalytic efficiency, the heavy metals pose a potential toxicity and may cause the polymer to have a yellowish color, affecting the product's appearance. Titanium-based catalysts, although non-toxic, highly active, and with short reaction times, also have high catalytic activity for side reactions, resulting in a yellowish polymer color and affecting appearance. Germanium-based catalysts, while having low toxicity and producing products with good color, have relatively low catalytic activity, leading to large addition amounts, long reaction times, and high prices, resulting in high production costs.

[0005] Gruter et al. synthesized PEF using various catalysts and screened them, concluding that tin-based and antimony-based catalysts were good for PEF synthesis, and the synthesized PEF had a viscosity of only about 0.4 dL / g. WUJ et al. used an organic non-metallic catalyst to catalyze the synthesis of PEF, and the synthesized PEF had a medium molecular weight and a viscosity of 0.54 dL / g.

[0006] CN 111269405 A discloses a method for preparing bio-based polyester that inhibits discoloration. The method requires esterification and transesterification reactions in the esterification stage. The esterification products of the two reactions are mixed and then polymerized. The reaction process is relatively complex and the production cost is high. The prepared bio-based polyester has a b value of more than 15 and the color is still relatively dark.

[0007] CN 106243331 B discloses a method for preparing polyethylene furanate dicarboxylate using a nitrogen-containing catalyst. The polyester prepared has an intrinsic viscosity of 0.6 dL / g and an absorbance of 0.1. However, the esterification time is 4 hours and the polycondensation time is 5 hours, which is too long and the process is cumbersome.

[0008] The selection and use of catalysts are important reasons for the darkening of PEF color. Currently, there is no catalyst that can efficiently prepare PEF with a suitable molecular weight and good color. Summary of the Invention

[0009] To overcome the shortcomings of the prior art, the present invention provides a method for preparing polyethylene 2,5-furandicarboxylate, which improves the problems of slow reaction and dark color of polyethylene 2,5-furandicarboxylate.

[0010] To achieve the above objectives, the present invention adopts the following technical solution: The method for preparing the PEF polyester pellets includes the following steps: a. Esterification reaction stage: A one-step esterification method is adopted. A certain amount of ethylene glycol is added to the pulping vessel, and stirring is started. Then, furanyl dicarboxylic acid, germanium-titanium composite catalyst and stabilizer are added. The esterification reaction is carried out under the protection of inert gas. The molar ratio of furanyl dicarboxylic acid to ethylene glycol is 1:1.1-2.0. During the esterification reaction, the pressure is maintained at 0.3-0.5 MPa, the temperature is 180-200℃, and the time is 2.0-3.0 hours. The reaction endpoint is judged when the amount of esterified water distilled reaches 96% of the theoretical output. After the esterification reaction is completed, the pressure of the reaction system is released to atmospheric pressure, and the polycondensation stage begins.

[0011] b. Polycondensation Stage: The polycondensation reaction stage is divided into a pre-polycondensation stage and a high-vacuum stage. In the pre-polycondensation stage, the pressure is steadily reduced from atmospheric pressure to below 1 kPa absolute pressure, the temperature is controlled at 230-250℃, and the reaction time is 0.5 hours. After pre-polycondensation, the high-vacuum stage begins, and the vacuum is further reduced to below 50 Pa absolute pressure. The reaction temperature is controlled at 230-250℃, and the reaction time is 2.5-3.5 hours. Stirring is stopped once the stirring torque reaches the preset value, thus ending the reaction.

[0012] c. Discharge stage: After the reaction is completed, nitrogen gas is introduced to positive pressure, and then the discharge valve is opened to extrude the melt from the casting strip head for underwater pelletizing and drying to obtain PEF polyester pellets.

[0013] The stabilizer is trimethyl phosphate; The amount of stabilizer added is 0.012-0.035 wt% of furanyl dicarboxylic acid; The germanium-titanium composite catalyst is added at an amount of 0.03-0.06 wt% of furanyl dicarboxylic acid. The germanium-titanium composite catalyst is prepared by the following method: Under a nitrogen atmosphere, a triblock copolymer of polyethylene oxide-propylene oxide-ethylene oxide (P123) was dissolved in anhydrous ethanol as a template agent and stirred until transparent. Then, tetraethyl orthosilicate (TEOS) was added dropwise, followed by deionized water. The mixture was placed in an Erlenmeyer flask, stirred on a magnetic stirrer, and heated to reflux at a speed of approximately 900 rpm. The heating temperature was maintained at 60°C for 2 hours for pre-hydrolysis to form a silica sol. Simultaneously, a germanium-titanium mixed liquid was prepared by dissolving tetrabutyl titanate (TBOT) and germanium tetrachloride in anhydrous ethanol, adding 1-2 drops of anhydrous acetic acid, and then adding citric acid (CA). After stirring for 30 minutes, the germanium-titanium mixed liquid was slowly added to the silica sol, and stirring continued until a wet gel was formed. The freshly formed wet gel was placed in a sealed container and immersed in anhydrous ethanol for aging for 24 hours. Subsequently, it was replaced three times with anhydrous ethanol and then placed in an autoclave for supercritical drying at 80°C and 15 MPa for 12 hours. The obtained solid is then ground and placed in a calcining furnace for calcination. The calcination process is as follows: the temperature is increased to 300℃ at 1℃ / min and held for 2 hours, then increased to 500℃ at 2℃ / min and calcined for 4 hours. After the time is up, the power switch is turned off and the calcining furnace is allowed to cool naturally for about 30 minutes. The product is then taken out to obtain the germanium-titanium composite catalyst.

[0014] In the preparation of the composite catalyst, the amount of P123 added is 2.5%-3.5% of the total mass of the silica sol; In the preparation process of the composite catalyst, the molar ratio n(TEOS):n(C2H5OH):n(H2O) = 1:8:4; In the preparation process of the composite catalyst, the molar ratio n(TBOT): n(CA) = 1:0.6-1.0; The molar ratio of the composite catalyst prepared in the process is n(Ti+Ge):n(Si)=4:1; The molar ratio n(Ge):n(Ti) during the preparation of the composite catalyst is 1-2.5:1.

[0015] FT-IR and SEM tests revealed that the prepared germanium-titanium composite catalyst used mesoporous silica as a support, with disordered mesoporous channels on the support surface, in which nano-germanium dioxide and nano-titanium dioxide particles were randomly dispersed. This composite catalyst exhibited a large specific surface area and a particle size of less than 30 nm.

[0016] Compared with the prior art, the beneficial effects of the present invention are: 1. Excellent Catalytic Effect: Titanium exhibits high catalytic activity, while germanium demonstrates good stability during the high-temperature polycondensation stage, effectively promoting the polycondensation reaction. The germanium-titanium composite catalyst leverages the synergistic catalytic effect of both. The germanium-titanium composite catalyst prepared by the sol-gel method has nanoscale particle size, good dispersibility, and is not prone to agglomeration, resulting in high catalytic activity. This composite catalyst exhibits high catalytic activity, avoiding the shortcomings of single catalysts, resulting in a fast reaction rate, and producing a pure white polyester with excellent color, thus solving the problem of yellowing products caused by high byproduct content in traditional catalysts.

[0017] 2. Due to their low catalytic activity, germanium-based catalysts require large addition amounts and are expensive, resulting in high production costs. By combining them with titanium-based catalysts, the amount of germanium-based catalysts required can be reduced.

[0018] 3. Germanium-based catalysts have low solubility in ethylene glycol. By using silica as a support, their solubility in ethylene glycol is increased, thereby improving catalytic efficiency.

[0019] 4. The preparation method of polyethylene furanate dicarboxylate described in this invention involves adding all raw materials only before the reaction, without adding any additives or other catalysts in the intermediate process. The process is very simple, environmentally friendly, and conducive to industrialization. Attached Figure Description

[0020] Figure 1 The image shows the FT-IR spectrum of the composite catalyst prepared in Example 1 of this invention.

[0021] Figure 2 This is a SEM image of the composite catalyst prepared in Example 1 of the present invention.

[0022] Figure 3 This is a granulated sample of polyethylene furanate prepared in Example 1 of the present invention. Detailed Implementation

[0023] The present invention will be further described below through specific embodiments, but the present invention is not limited thereto.

[0024] The test and analysis methods used in the following embodiments and comparative examples are as follows: Intrinsic viscosity: The intrinsic viscosity is tested using the same method as conventional polyester chips, according to national standard GB / T 14190-2017. The test temperature is 25℃, and the solvent is phenol / tetrachloroethane.

[0025] The color value is obtained by measuring each sample five times in parallel using a benchtop spectrophotometer and calculating the average value. * (Brightness), a * (Red-green saturation), b * (Yellow-blue) Three color value parameters.

[0026] Comparative Example 1: A method for preparing polyethylene furanate includes the following steps: a. Esterification stage: A one-step esterification method is adopted. 250g of ethylene glycol is added to the pulping vessel and stirring is started. Then, 450g of furanyl dicarboxylic acid, 0.225g of tetrabutyl titanate and 0.11g of trimethyl phosphate are added. The esterification reaction is carried out under the protection of inert gas. The molar ratio of furanyl dicarboxylic acid to ethylene glycol is 1:1.4. The pressure is maintained at 0.4MPa and the temperature at 190℃ during the esterification reaction, and the time is 2.5 hours. The reaction endpoint is judged when the amount of esterified water distilled reaches 96% of the theoretical output. After the esterification reaction is completed, the pressure of the reaction system is released to atmospheric pressure, and the polycondensation stage begins.

[0027] b. Polycondensation Stage: The polycondensation reaction stage is divided into a pre-polycondensation stage and a high-vacuum stage. In the pre-polycondensation stage, the pressure is steadily reduced from atmospheric pressure to below 1 kPa absolute pressure, the temperature is controlled at 240℃, and the time is 0.5 h. After the pre-polycondensation is completed, the high-vacuum stage begins, and the vacuum is continued until the absolute pressure is below 50 Pa. The reaction temperature is controlled at 240℃, the polycondensation reaction is carried out for 2.0 hours, and the reaction ends when the stirring torque reaches the preset value.

[0028] c. Discharge stage: After the reaction is completed, nitrogen gas is introduced to positive pressure, and then the discharge valve is opened to extrude the melt from the casting strip head for underwater pelletizing and drying to obtain PEF polyester pellets.

[0029] Comparative Example 2: A method for preparing polyethylene furanate includes the following steps: a. Esterification stage: A one-step esterification method is adopted. 250g of ethylene glycol is added to the pulping vessel and stirring is started. Then, 450g of furanyl dicarboxylic acid, 0.225g of germanium oxide and 0.11g of trimethyl phosphate are added. The esterification reaction is carried out under the protection of inert gas. The molar ratio of furanyl dicarboxylic acid to ethylene glycol is 1:1.4. The pressure is maintained at 0.4MPa and the temperature is maintained at 190℃ for 2.5 hours during the esterification reaction. The reaction endpoint is judged when the amount of esterified water distilled reaches 96% of the theoretical output. After the esterification reaction is completed, the pressure of the reaction system is released to atmospheric pressure, and the polycondensation stage begins.

[0030] b. Polycondensation Stage: The polycondensation reaction stage is divided into a pre-polycondensation stage and a high-vacuum stage. In the pre-polycondensation stage, the pressure is steadily reduced from atmospheric pressure to below 1 kPa absolute pressure, the temperature is controlled at 240℃, and the time is 0.5 h. After the pre-polycondensation is completed, the high-vacuum stage begins, and the vacuum is continued until the absolute pressure is below 50 Pa. The reaction temperature is controlled at 240℃, the polycondensation reaction is carried out for 4.5 hours, and the reaction ends when the stirring torque reaches the preset value.

[0031] c. Discharge stage: After the reaction is completed, nitrogen gas is introduced to positive pressure, and then the discharge valve is opened to extrude the melt from the casting strip head for underwater pelletizing and drying to obtain PEF polyester pellets.

[0032] Comparative Example 3: A method for preparing polyethylene furanate includes the following steps: a. Esterification reaction stage: A one-step esterification method is adopted. 250g of ethylene glycol is added to the pulping vessel and stirring is started. Then, 450g of furanyl dicarboxylic acid, 0.071g of germanium oxide, 0.154g of tetrabutyl titanate and 0.11g of trimethyl phosphate are added. The esterification reaction is carried out under the protection of inert gas. The molar ratio of furanyl dicarboxylic acid to ethylene glycol is 1:1.4. The pressure is maintained at 0.4MPa, the temperature is 190℃, and the time is 2.5 hours during the esterification reaction. The reaction endpoint is judged when the amount of esterified water distilled reaches 96% of the theoretical output. After the esterification reaction is completed, the pressure of the reaction system is released to atmospheric pressure, and the polycondensation stage begins.

[0033] b. Polycondensation Stage: The polycondensation reaction stage is divided into a pre-polycondensation stage and a high-vacuum stage. In the pre-polycondensation stage, the pressure is steadily reduced from atmospheric pressure to below 1 kPa absolute pressure, the temperature is controlled at 240℃, and the time is 0.5 h. After the pre-polycondensation is completed, the high-vacuum stage begins, and the vacuum is continued until the absolute pressure is below 50 Pa. The reaction temperature is controlled at 240℃, the polycondensation reaction is carried out for 4.0 hours, and the reaction ends when the stirring torque reaches the preset value.

[0034] c. Discharge stage: After the reaction is completed, nitrogen gas is introduced to positive pressure, and then the discharge valve is opened to extrude the melt from the casting strip head for underwater pelletizing and drying to obtain PEF polyester pellets. Example 1

[0035] a. Esterification stage: A one-step esterification method is adopted. 250g of ethylene glycol is added to the pulping vessel and stirring is started. Then, 450g of furanyl dicarboxylic acid, 0.135g of germanium-titanium composite catalyst and 0.11g of trimethyl phosphate are added. The esterification reaction is carried out under the protection of inert gas. The molar ratio of furanyl dicarboxylic acid to ethylene glycol is 1:1.4. The pressure is maintained at 0.4MPa, the temperature is 190℃, and the time is 2.5 hours. The reaction endpoint is judged when the amount of esterified water distilled reaches 96% of the theoretical output. After the esterification reaction is completed, the pressure of the reaction system is released to atmospheric pressure, and the polycondensation stage begins.

[0036] b. Polycondensation Stage: The polycondensation reaction stage is divided into a pre-polycondensation stage and a high-vacuum stage. In the pre-polycondensation stage, the pressure is steadily reduced from atmospheric pressure to below 1 kPa absolute pressure, the temperature is controlled at 240℃, and the time is 0.5 h. After the pre-polycondensation is completed, the high-vacuum stage begins, and the vacuum is continued until the absolute pressure is below 50 Pa. The reaction temperature is controlled at 240℃, the polycondensation reaction is carried out for 3.5 hours, and the reaction ends when the stirring torque reaches the preset value.

[0037] c. Discharge stage: After the reaction is completed, nitrogen gas is introduced to positive pressure, and then the discharge valve is opened to extrude the melt from the casting strip head for underwater pelletizing and drying to obtain PEF polyester pellets.

[0038] The germanium-titanium composite catalyst is prepared by the following method: Under a nitrogen atmosphere, 0.19 g of polyethylene oxide-polypropylene oxide-polyethylene oxide triblock copolymer (P123) was dissolved in 4.3 g of anhydrous ethanol as a template agent and stirred until transparent. Then, 2.43 g of tetraethyl orthosilicate (TEOS) was added dropwise to the anhydrous ethanol, followed by 0.84 g of deionized water. The mixture was placed in an Erlenmeyer flask, stirred and heated to reflux on a magnetic stirrer at a speed of about 900 r / min and a temperature of 60 °C. After 2 hours of pre-hydrolysis, a silica sol was prepared. Simultaneously, a germanium-titanium mixed liquid was prepared. 7.94 g of tetrabutyl titanate (TBOT) and 5 g of germanium tetrachloride were dissolved in 10 ml of anhydrous ethanol. 1-2 drops of anhydrous acetic acid were added dropwise, followed by 4.48 g of citric acid (CA). After stirring for 30 min, the germanium-titanium mixed liquid was slowly added to the silica sol, and stirring continued until a wet gel was formed. The newly formed wet gel was placed in a sealed container and aged in anhydrous ethanol for 24 h. Subsequently, it was replaced three times with anhydrous ethanol and then placed in an autoclave for supercritical drying at 80 °C and 15 MPa for 12 h. The resulting solid was then ground and calcined in a calcining furnace. The calcination process was as follows: increasing the temperature to 300 °C at 1 °C / min, holding for 2 h, then increasing the temperature to 500 °C at 2 °C / min and calcining for 4 h. After the calcination time, the power switch was turned off, and the calcining furnace was allowed to cool naturally for approximately 30 min. The product was then removed to obtain the composite catalyst. Example 2

[0039] A method for preparing polyethylene furanate includes the following steps: a. Esterification stage: A one-step esterification method is adopted. 250g of ethylene glycol is added to the pulping vessel and stirring is started. Then, 450g of furanyl dicarboxylic acid, 0.18g of composite catalyst and 0.11g of trimethyl phosphate are added. The esterification reaction is carried out under the protection of inert gas. The molar ratio of furanyl dicarboxylic acid to ethylene glycol is 1:1.4. The pressure is maintained at 0.4MPa and the temperature is maintained at 190℃ during the esterification reaction, and the time is about 3 hours. The reaction endpoint is judged when the amount of esterified water distilled reaches 96% of the theoretical output. After the esterification reaction is completed, the pressure of the reaction system is released to atmospheric pressure, and the polycondensation stage begins.

[0040] b. Polycondensation Stage: The polycondensation reaction stage is divided into a pre-polycondensation stage and a high-vacuum stage. In the pre-polycondensation stage, the pressure is steadily reduced from atmospheric pressure to below 1 kPa absolute pressure, the temperature is controlled at 240℃, and the time is 0.5 h. After the pre-polycondensation is completed, the high-vacuum stage begins, and the vacuum is continued until the absolute pressure is below 50 Pa. The reaction temperature is controlled at 240℃, the polycondensation reaction is carried out for 3 hours, and the reaction ends and the material is discharged after the stirring torque reaches the preset value.

[0041] c. Discharge stage: After the reaction is completed, nitrogen gas is introduced to positive pressure, and then the discharge valve is opened to extrude the melt from the casting strip head for underwater pelletizing and drying to obtain PEF polyester pellets.

[0042] The germanium-titanium composite catalyst is prepared by the following method: Under a nitrogen atmosphere, 0.19 g of polyethylene oxide-polypropylene oxide-polyethylene oxide triblock copolymer (P123) was dissolved in 3.58 g of anhydrous ethanol as a template agent and stirred until transparent. Then, 2.02 g of tetraethyl orthosilicate (TEOS) was added dropwise to the anhydrous ethanol, followed by 0.7 g of deionized water. The mixture was placed in an Erlenmeyer flask, stirred on a magnetic stirrer, and heated to reflux. The stirring speed was controlled at about 900 r / min, and the heating temperature was maintained at 60℃. After 2 hours of pre-hydrolysis, a silica sol was prepared. Simultaneously, a germanium-titanium mixed liquid was prepared. 5.29 g of tetrabutyl titanate (TBOT) and 5 g of germanium tetrachloride were dissolved in 10 ml of anhydrous ethanol. 1-2 drops of anhydrous acetic acid were added dropwise, followed by 2.39 g of citric acid (CA). After stirring for 30 min, the germanium-titanium mixed liquid was slowly added to the silica sol, and stirring continued until a wet gel was formed. The newly formed wet gel was placed in a sealed container and aged in anhydrous ethanol for 24 h. Subsequently, it was replaced three times with anhydrous ethanol and then placed in an autoclave for supercritical drying at 80 °C and 15 MPa for 12 h. The resulting solid was then ground and calcined in a calcining furnace. The calcination process was as follows: increasing the temperature to 300 °C at 1 °C / min, holding for 2 h, then increasing the temperature to 500 °C at 2 °C / min and calcining for 4 h. After the calcination time, the power switch was turned off, and the calcining furnace was allowed to cool naturally for approximately 30 min. The product was then removed to obtain the composite catalyst. Example 3

[0043] a. Esterification stage: A one-step esterification method was adopted. 197g of ethylene glycol was added to the pulping vessel and stirred. Then, 450g of furanyl dicarboxylic acid, 0.1575g of composite catalyst (germanium:titanium = 1.5), and 0.11g of trimethyl phosphate were added. The esterification reaction was carried out under the protection of an inert gas. The molar ratio of furanyl dicarboxylic acid to ethylene glycol was 1:1.1. The pressure was maintained at 0.3MPa and the temperature at 180℃ during the esterification reaction, and the time was 3 hours. The reaction endpoint was determined when the amount of esterified water distilled reached 96% of the theoretical output. After the esterification reaction was completed, the pressure of the reaction system was released to atmospheric pressure, and the polycondensation stage began.

[0044] b. Polycondensation Stage: The polycondensation reaction stage is divided into a pre-polycondensation stage and a high-vacuum stage. In the pre-polycondensation stage, the pressure is steadily reduced from atmospheric pressure to below 1 kPa absolute pressure, the temperature is controlled at 230℃, and the time is 0.5 h. After the pre-polycondensation is completed, the high-vacuum stage begins, and the vacuum is continued until the absolute pressure is below 50 Pa. The reaction temperature is controlled at 230℃, the polycondensation reaction is carried out for 3.4 hours, and the reaction ends and the material is discharged after the stirring torque reaches the preset value.

[0045] c. Discharge stage: After the reaction is completed, nitrogen gas is introduced to positive pressure, and then the discharge valve is opened to extrude the melt from the casting strip head for underwater pelletizing and drying to obtain PEF polyester pellets.

[0046] The germanium-titanium composite catalyst is prepared by the following method: Under a nitrogen atmosphere, 0.19 g of polyethylene oxide-polypropylene oxide-polyethylene oxide triblock copolymer (P123) was dissolved in 3.58 g of anhydrous ethanol as a template agent and stirred until transparent. Then, 2.02 g of tetraethyl orthosilicate (TEOS) was added dropwise to the anhydrous ethanol, followed by 0.7 g of deionized water. The mixture was placed in an Erlenmeyer flask, stirred on a magnetic stirrer, and heated to reflux. The stirring speed was controlled at about 900 r / min, and the heating temperature was maintained at 60℃. After 2 hours of pre-hydrolysis, a silica sol was prepared. Simultaneously, a germanium-titanium mixed liquid was prepared. 5.29 g of tetrabutyl titanate (TBOT) and 5 g of germanium tetrachloride were dissolved in 10 ml of anhydrous ethanol. 1-2 drops of anhydrous acetic acid were added dropwise, followed by 2.39 g of citric acid (CA). After stirring for 30 min, the germanium-titanium mixed liquid was slowly added to the silica sol, and stirring continued until a wet gel was formed. The newly formed wet gel was placed in a sealed container and aged in anhydrous ethanol for 24 h. Subsequently, it was replaced three times with anhydrous ethanol and then placed in an autoclave for supercritical drying at 80 °C and 15 MPa for 12 h. The resulting solid was then ground and calcined in a calcining furnace. The calcination process was as follows: increasing the temperature to 300 °C at 1 °C / min, holding for 2 h, then increasing the temperature to 500 °C at 2 °C / min and calcining for 4 h. After the calcination time, the power switch was turned off, and the calcining furnace was allowed to cool naturally for approximately 30 min. The product was then removed to obtain the composite catalyst. Example 4

[0047] a. Esterification stage: A one-step esterification method was adopted. 358g of ethylene glycol was added to the pulping vessel and stirred. Then, 450g of furanyl dicarboxylic acid, 0.18g of composite catalyst, and 0.11g of trimethyl phosphate were added. The esterification reaction was carried out under the protection of an inert gas. The molar ratio of furanyl dicarboxylic acid to ethylene glycol was 1:2.0. The pressure was maintained at 0.5MPa and the temperature at 200℃ during the esterification reaction, and the time was 2 hours. The reaction endpoint was determined when the amount of esterified water distilled reached 96% of the theoretical output. After the esterification reaction was completed, the pressure of the reaction system was released to atmospheric pressure, and the polycondensation stage began.

[0048] b. Polycondensation Stage: The polycondensation reaction stage is divided into a pre-polycondensation stage and a high-vacuum stage. In the pre-polycondensation stage, the pressure is steadily reduced from atmospheric pressure to below 1 kPa absolute pressure, the temperature is controlled at 250℃, and the time is 0.5 h. After the pre-polycondensation is completed, the high-vacuum stage begins, and the vacuum is continued until the absolute pressure is below 50 Pa. The reaction temperature is controlled at 250℃, the polycondensation reaction is carried out for 2.5 hours, and the reaction ends and the material is discharged after the stirring torque reaches the preset value.

[0049] c. Discharge stage: After the reaction is completed, nitrogen gas is introduced to positive pressure, and then the discharge valve is opened to extrude the melt from the casting strip head for underwater pelletizing and drying to obtain PEF polyester pellets.

[0050] The germanium-titanium composite catalyst is prepared by the following method: Under a nitrogen atmosphere, 0.19 g of polyethylene oxide-polypropylene oxide-polyethylene oxide triblock copolymer (P123) was dissolved in 3.58 g of anhydrous ethanol as a template agent and stirred until transparent. Then, 2.02 g of tetraethyl orthosilicate (TEOS) was added dropwise to the anhydrous ethanol, followed by 0.7 g of deionized water. The mixture was placed in an Erlenmeyer flask, stirred on a magnetic stirrer, and heated to reflux. The stirring speed was controlled at about 900 r / min, and the heating temperature was maintained at 60℃. After 2 hours of pre-hydrolysis, a silica sol was prepared. Simultaneously, a germanium-titanium mixed liquid was prepared. 5.29 g of tetrabutyl titanate (TBOT) and 5 g of germanium tetrachloride were dissolved in 10 ml of anhydrous ethanol. 1-2 drops of anhydrous acetic acid were added dropwise, followed by 2.39 g of citric acid (CA). After stirring for 30 min, the germanium-titanium mixed liquid was slowly added to the silica sol, and stirring continued until a wet gel was formed. The newly formed wet gel was placed in a sealed container and aged in anhydrous ethanol for 24 h. Subsequently, it was replaced three times with anhydrous ethanol and then placed in an autoclave for supercritical drying at 80 °C and 15 MPa for 12 h. The resulting solid was then ground and calcined in a calcining furnace. The calcination process was as follows: increasing the temperature to 300 °C at 1 °C / min, holding for 2 h, then increasing the temperature to 500 °C at 2 °C / min and calcining for 4 h. After the calcination time, the power switch was turned off, and the calcining furnace was allowed to cool naturally for approximately 30 min. The product was then removed to obtain the composite catalyst. Example 5

[0051] a. Esterification stage: A one-step esterification method is adopted. 250g of ethylene glycol is added to the pulping vessel and stirred. Then, 450g of furanyl dicarboxylic acid, 0.225g of composite catalyst and 0.11g of trimethyl phosphate are added. The esterification reaction is carried out under the protection of inert gas. The molar ratio of furanyl dicarboxylic acid to ethylene glycol is 1:1.4. The pressure is maintained at 0.4MPa and the temperature at 190℃ during the esterification reaction, and the time is 2.5 hours. The reaction endpoint is judged when the amount of esterified water distilled reaches 96% of the theoretical output. After the esterification reaction is completed, the pressure of the reaction system is released to atmospheric pressure, and the polycondensation stage begins.

[0052] b. Polycondensation Stage: The polycondensation reaction stage is divided into a pre-polycondensation stage and a high-vacuum stage. In the pre-polycondensation stage, the pressure is steadily reduced from atmospheric pressure to below 1 kPa absolute pressure, the temperature is controlled at 240℃, and the time is 0.5 h. After the pre-polycondensation is completed, the high-vacuum stage begins, and the vacuum is continued until the absolute pressure is below 50 Pa. The reaction temperature is controlled at 240℃, the polycondensation reaction is carried out for 2.7 hours, and the reaction ends and the material is discharged after the stirring torque reaches the preset value.

[0053] c. Discharge stage: After the reaction is completed, nitrogen gas is introduced to positive pressure, and then the discharge valve is opened to extrude the melt from the casting strip head for underwater pelletizing and drying to obtain PEF polyester pellets.

[0054] The germanium-titanium composite catalyst is prepared by the following method: Under a nitrogen atmosphere, 0.17 g of polyethylene oxide-polypropylene oxide-polyethylene oxide triblock copolymer (P123) was dissolved in 3.22 g of anhydrous ethanol as a template agent and stirred until transparent. Then, 1.82 g of tetraethyl orthosilicate (TEOS) was added dropwise to the anhydrous ethanol, followed by 0.63 g of deionized water. The mixture was placed in an Erlenmeyer flask, stirred on a magnetic stirrer, and heated to reflux. The stirring speed was controlled at about 900 r / min, and the heating temperature was maintained at 60℃. After 2 hours of pre-hydrolysis, a silica sol was prepared. Simultaneously, a germanium-titanium mixed liquid was prepared. 3.97 g of tetrabutyl titanate (TBOT) and 5 g of germanium tetrachloride were dissolved in 10 ml of anhydrous ethanol. 1-2 drops of anhydrous acetic acid were added dropwise, followed by 1.57 g of citric acid (CA). After stirring for 30 min, the germanium-titanium mixed liquid was slowly added to the silica sol, and stirring continued until a wet gel was formed. The newly formed wet gel was placed in a sealed container and aged in anhydrous ethanol for 24 h. Subsequently, it was replaced three times with anhydrous ethanol and then placed in an autoclave for supercritical drying at 80 °C and 15 MPa for 12 h. The resulting solid was then ground and calcined in a calcining furnace. The calcination process was as follows: increasing the temperature to 300 °C at 1 °C / min, holding for 2 h, then increasing the temperature to 500 °C at 2 °C / min and calcining for 4 h. After the calcination time, the power switch was turned off, and the calcining furnace was allowed to cool naturally for approximately 30 min. The product was then removed to obtain the composite catalyst. Example 6

[0055] a. Esterification stage: A one-step esterification method is adopted. 250g of ethylene glycol is added to the pulping vessel and stirring is started. Then, 450g of furanyl dicarboxylic acid, 0.27g of composite catalyst and 0.11g of trimethyl phosphate are added. The esterification reaction is carried out under the protection of inert gas. The molar ratio of furanyl dicarboxylic acid to ethylene glycol is 1:1.4. The pressure is maintained at 0.4MPa and the temperature at 190℃ during the esterification reaction, and the time is 2.5 hours. The reaction endpoint is judged when the amount of esterified water distilled reaches 96% of the theoretical output. After the esterification reaction is completed, the pressure of the reaction system is released to atmospheric pressure, and the polycondensation stage begins.

[0056] b. Polycondensation Stage: The polycondensation reaction stage is divided into a pre-polycondensation stage and a high-vacuum stage. In the pre-polycondensation stage, the pressure is steadily reduced from atmospheric pressure to below 1 kPa absolute pressure, the temperature is controlled at 240℃, and the time is 0.5 h. After the pre-polycondensation is completed, the high-vacuum stage begins, and the vacuum is continued until the absolute pressure is below 50 Pa. The reaction temperature is controlled at 240℃, and the polycondensation reaction is carried out for 2.5 hours to obtain polyethylene furanate dicarboxylate (PEF9).

[0057] c. Discharge stage: After the reaction is completed, nitrogen gas is introduced to positive pressure, and then the discharge valve is opened to extrude the melt from the casting strip head for underwater pelletizing and drying to obtain PEF polyester pellets.

[0058] The germanium-titanium composite catalyst is prepared by the following method: Under a nitrogen atmosphere, 0.19 g of polyethylene oxide-polypropylene oxide-polyethylene oxide triblock copolymer (P123) was dissolved in 3.01 g of anhydrous ethanol as a template agent and stirred until transparent. Then, 1.7 g of tetraethyl orthosilicate (TEOS) was added dropwise to the anhydrous ethanol, followed by 0.59 g of deionized water. The mixture was placed in an Erlenmeyer flask, stirred and heated to reflux on a magnetic stirrer at a speed of about 900 r / min and a temperature of 60 °C. After 2 hours of pre-hydrolysis, a silica sol was prepared. Simultaneously, a germanium-titanium mixed liquid was prepared. 3.17 g of tetrabutyl titanate (TBOT) and 5 g of germanium tetrachloride were dissolved in 10 ml of anhydrous ethanol. 1-2 drops of anhydrous acetic acid were added dropwise, followed by 1.08 g of citric acid (CA). After stirring for 30 min, the germanium-titanium mixed liquid was slowly added to the silica sol, and stirring continued until a wet gel was formed. The newly formed wet gel was placed in a sealed container and aged in anhydrous ethanol for 24 h. Subsequently, it was replaced three times with anhydrous ethanol and then placed in an autoclave for supercritical drying at 80 °C and 15 MPa for 12 h. The resulting solid was then ground and calcined in a calcining furnace. The calcination process was as follows: increasing the temperature to 300 °C at 1 °C / min, holding for 2 h, then increasing the temperature to 500 °C at 2 °C / min and calcining for 4 h. After the calcination time, the power switch was turned off, and the calcining furnace was allowed to cool naturally for approximately 30 min. The product was then removed to obtain the composite catalyst.

[0059] The index results of PEF polyester prepared by the above methods are shown in Table 1.

[0060] Table 1: PEF Polyester Specifications

[0061] As shown in Table 1, Comparative Example 1, using only tetrabutyl titanate as a single catalyst, had a short polycondensation time but a darker, less appealing product color. Comparative Example 2, using only germanium oxide as a catalyst, produced a slightly lighter color compared to Comparative Example 1, but it was still relatively dark and less appealing, and the reaction time was longer. Comparative Example 3, using a direct mixture of germanium oxide and tetrabutyl titanate as a catalyst, achieved a reaction time and product color that fell between Comparative Examples 1 and 2. Examples 1-6, using this method to prepare polyethylene furanate dicarboxylate, produced products with excellent color and a fast reaction rate, effectively improving the quality of polyethylene furanate dicarboxylate and expanding its market applications.

[0062] The FT-IR test results of the composite catalyst prepared in Example 1 of this invention are as follows: Figure 1 As shown, the spectrum displays 1099 cm⁻¹ -1 The absorption peak at 977 cm⁻¹ is attributed to the Si-O-Si antisymmetric stretching vibration. -1The absorption peak at 870 cm⁻¹ corresponds to the Si-O-Ti stretching vibration. -1 The absorption peak at 788 cm⁻¹ corresponds to the Si-O-Ge stretching vibration. -1 The absorption peak at 510 cm⁻¹ corresponds to the Si-O-Si symmetric stretching vibration. -1 The absorption peak at 480 cm⁻¹ corresponds to the Ge-O-Ge bending vibration. -1 The absorption peak at that point corresponds to the Si-O-Si bending vibration. Figure 2 The image shows a SEM image of the germanium-titanium composite catalyst, with particle sizes below 30 nm. Figure 3 This is a granulated sample of the polyethylene furanate prepared in Example 1, with a low color value.

[0063] The above description is merely a preferred embodiment of the present invention, and therefore should not be construed as limiting the scope of the present invention. All equivalent changes and modifications made in accordance with the scope of the patent and the contents of the specification should still fall within the scope of the present invention.

Claims

1. A method for preparing low-color-value polyethylene furanate, characterized in that, Includes the following steps: (1) Esterification reaction stage: A one-step esterification method is adopted. A certain amount of ethylene glycol is added to the pulping kettle, and stirring is started. Then, furanyl dicarboxylic acid, germanium-titanium composite catalyst and stabilizer are added. The esterification reaction is carried out under the protection of inert gas. The molar ratio of furanyl dicarboxylic acid to ethylene glycol is 1:1.1-2.

0. The pressure is maintained at 0.3-0.5 MPa, the temperature is 180-200℃, and the time is 2.0-3.0 hours. After the esterification reaction is completed, the pressure of the reaction system is released to atmospheric pressure and the polycondensation stage begins. (2) Polycondensation stage: The polycondensation reaction stage is divided into a pre-polycondensation stage and a high vacuum stage; in the pre-polycondensation stage, the pressure is steadily reduced from atmospheric pressure to below 1 kPa absolute pressure, the temperature is controlled at 230-250℃, and the time is 0.5 hours; after the pre-polycondensation is completed, the high vacuum stage is entered, and the vacuum is continued to be reduced to below 50 Pa absolute pressure, the reaction temperature is controlled at 230-250℃, and the reaction time is 2.5-3.5 hours; (3) Discharge stage: After the reaction is completed, nitrogen gas is purged to positive pressure, and then the discharge valve is opened to extrude the melt from the casting strip head for underwater pelletizing and drying to obtain the low color value polyurethane dicarboxylate.

2. The method according to claim 1, characterized in that, The stabilizer is trimethyl phosphate.

3. The method according to claim 1, characterized in that, The amount of stabilizer added is 0.012-0.035 wt% of furanyl dicarboxylic acid.

4. The method according to claim 1, characterized in that, The amount of germanium-titanium composite catalyst added is 0.03-0.06 wt% of furanyl dicarboxylic acid.

5. The method according to claim 1, characterized in that, The preparation method of the germanium-titanium composite catalyst includes the following steps: 1) Under N2 atmosphere protection, P123 as template agent was dissolved in anhydrous ethanol and stirred until transparent. Then, tetraethyl orthosilicate (TEOS) and deionized water were added. The mixture was magnetically stirred and heated to reflux. The heating temperature was maintained at 60℃. After 2 hours of pre-hydrolysis, silica sol was prepared. 2) Simultaneously prepare germanium-titanium mixed liquid. Dissolve tetrabutyl titanate (TBOT) and germanium tetrachloride in anhydrous ethanol, add 1-2 drops of anhydrous acetic acid, then add citric acid (CA), stir for 30 min, and then slowly add the germanium-titanium mixed liquid to the silica sol. Continue stirring until a wet gel is formed. 3) The freshly formed wet gel was placed in a sealed container and aged in anhydrous ethanol for 24 hours. Then, it was replaced with anhydrous ethanol three times and then placed in an autoclave for supercritical drying at 80°C and 15MPa for 12 hours. The resulting solid was then ground and placed in a calcining furnace for calcination. The calcination process was as follows: the temperature was increased to 300°C at 1°C / min and held for 2 hours. Then, the temperature was increased to 500°C at 2°C / min and calcined for 4 hours. The mixture was then naturally cooled to room temperature to obtain the germanium-titanium composite catalyst.

6. The method according to claim 5, characterized in that, In the preparation process of the germanium-titanium composite catalyst, the amount of P123 added is 2.5%-3.5% of the total mass of the silica sol.

7. The method according to claim 5, characterized in that, In the preparation process of the germanium-titanium composite catalyst, the molar ratio n(TEOS):n(C2H5OH):n(H2O) = 1:8:

4.

8. The method according to claim 5, characterized in that, In the preparation process of the germanium-titanium composite catalyst, the molar ratio n(TBOT): n(CA) = 1:0.6-1.

0.

9. The method according to claim 5, characterized in that, The molar ratio of the germanium-titanium composite catalyst prepared in this process is n(Ti+Ge):n(Si)=4:

1.

10. The method according to claim 5, characterized in that, The molar ratio n(Ge):n(Ti) during the preparation of the germanium-titanium composite catalyst is 1-2.5:1.

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