Low-migrating pbs products and methods and systems for making same

Abstract

The application discloses a low-migration PBS product and a preparation method and system thereof. The preparation method comprises the following steps: mixing succinic acid and / or succinic anhydride with 1,4-butanediol and bacterial cellulose to perform an esterification reaction, collecting a tetrahydrofuran by-product, and obtaining an esterification oligomer with an esterification rate of greater than or equal to 90%; inputting the esterification oligomer and optionally added catalyst into a first evaporator, countercurrently adding the tetrahydrofuran by-product as an entraining agent, performing pre-polycondensation under heating and vacuumizing, and obtaining a prepolymer; inputting the prepolymer and optionally added catalyst into a second evaporator, countercurrently adding the tetrahydrofuran by-product as an entraining agent, performing final polycondensation under heating and vacuumizing, and obtaining a polycondensation product; cooling the polycondensation product to 130-150 DEG C, conveying the polycondensation product to a double-screw reaction extruder through a melt pump, adding a chain extender to perform extrusion reaction and chain extension, simultaneously performing devolatilization treatment in the extrusion process, and obtaining the low-migration PBS product through vacuum devolatilization drying of the extrusion product.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of polybutylene succinate (PBS) production, and particularly relates to a low-migration PBS product and a preparation method and system thereof. BACKGROUND

[0002] As one of new biodegradable materials, PBS has a low processing temperature and a decomposition temperature of up to 300 DEG C, and thus is likely to become a substitute for polyethylene, polypropylene and other polyolefins in future development.

[0003] PBS has good processing performance and is the best degradable material for processing at present, and so far, PBS has a strong application potential in the field of food contact materials such as disposable tableware and straws.

[0004] With the continuous expansion of the application of biological materials, PBS will gradually replace conventional polyolefins or ABS plastics (a ternary copolymer of acrylonitrile (A)-butadiene (B)-styrene (S)) in the field of thin-walled injection molding, but the cyclic oligomers or oligomers generated in the synthesis process of PBS will migrate from the material during use, which cannot meet the requirements of food contact materials, or the surface will be powdery after migration, affecting the appearance of the injection molding product, and to some extent, limiting the application and promotion of PBS products, and therefore it is necessary to develop a low-migration PBS product.

[0005] In the prior art, there is a study on reducing the generation of cyclic by-products by means of reaction catalysis control, for example, tin catalyst and titanate catalyst are used together for catalytic reaction to exert the catalytic ability of tin catalyst on the ring-opening of cyclic by-products, but through the experimental research of the inventor, the reduction effect of cyclic by-products or oligomers by reaction control or catalyst adjustment is limited, and the migration amount in the ethanol simulation liquid cannot meet the requirements and the product still has the problem of powdering after being placed.

[0006] It is actually difficult to inhibit the generation of cyclic oligomers or oligomers in the synthesis process of PBS, and under the conventional kettle esterification and polycondensation process conditions, it is difficult to avoid the generation of cyclic oligomers or oligomers due to molecular chain degradation in the polycondensation reaction process.

[0007] To further reduce the migration of PBS products in the prior art, the existing technology is improved by post-processing, such as dissolving polyester products in an organic solvent, preparing a polyester solution with a certain concentration, then adding another organic solvent for extraction, removing oligomers after separation to obtain a PBS concentrate, then adding a precipitating agent to realize solid-liquid separation, and drying to obtain a high-purity PBS product. This process route involves a large amount of organic solvent, is not environmentally friendly, and is difficult to mass-produce. Another technology is to soak and extract PBS particles in an organic solvent, which also involves a large amount of solvent and a long processing time. In the extraction process, the material may be degraded, affecting the quality stability of the product, and there are problems of unstable migration amount.

[0008] In summary, there is an urgent need for an efficient, easy-to-industrialize and environmentally friendly process for preparing low-migration PBS products. SUMMARY

[0009] To solve the above technical problems and the deficiencies in the field, the present application provides a preparation method of low-migration PBS products, which is made of succinic acid and / or succinic anhydride, 1,4-butanediol and bacterial cellulose and other raw materials. The preparation method has esterification, polycondensation, chain extension and other steps. Bacterial cellulose participates in esterification and polycondensation using a multi-stage evaporator device. The tetrahydrofuran (THF) byproduct of the esterification reaction is used for melt purification to remove cyclic oligomers generated during the reaction process. The oligomer content is further reduced by chain extension reaction, thereby obtaining low-migration PBS products. Compared with the traditional preparation process, the catalyst usage is less, the high-temperature reaction time is short, the tackifying efficiency is high, the production continuity is good, and no post-treatment purification is required to meet the food contact requirements.

[0010] A preparation method of low-migration PBS products, comprising the steps of:

[0011] S1, mixing succinic acid and / or succinic anhydride with 1,4-butanediol and bacterial cellulose for esterification reaction, separating and collecting tetrahydrofuran byproduct, and obtaining esterification oligomers with an esterification rate of ≥90%;

[0012] S2, inputting the esterification oligomers and optionally added catalyst into a first evaporator, while countercurrently adding the tetrahydrofuran byproduct as an entraining agent to remove cyclic oligomers generated during the reaction process, pre-polycondensation by heating and vacuumizing, and obtaining a pre-polymer;

[0013] S3, inputting the pre-polymer and optionally added catalyst into a second evaporator, while countercurrently adding the tetrahydrofuran byproduct as an entraining agent to remove cyclic oligomers generated during the reaction process, final polycondensation by heating and vacuumizing, and obtaining a polycondensation product;

[0014] S4, cooling the polycondensation product to 130-150 DEG C, conveying to a twin-screw reaction extruder through a melt pump, adding a chain extender to perform an extrusion reaction chain extension, and performing a devolatilization treatment during the extrusion process, and drying the extrusion product through vacuum devolatilization to obtain the low-migration PBS product.

[0015] In the present application, the "selective addition" means optional addition or non-addition.

[0016] The bacterial cellulose used in the present application has a crystallinity of up to 95% or more, a three-dimensional network structure of interwoven, a tensile strength and an elastic modulus several times to 10 times of that of lignin, and high fiber purity. The bacterial cellulose added into the PBS polymerization system can take advantage of the three-dimensional network skeleton and large porosity, not only can optimize the binding effect of macromolecular segments on oligomers through the promotion of PBS crystallization, but also can increase the adsorption of residual oligomers in the system through the pores to reduce the migration and precipitation of oligomers. At the same time, the high tensile strength and elastic modulus of the bacterial cellulose do not affect the mechanical properties of the PBS product when added into the PBS system.

[0017] The present application uses tetrahydrofuran as the entraining agent, which not only reduces the introduction of new solvents and effectively utilizes by-products, but also experimental results show that the treatment effect of tetrahydrofuran as the entraining agent on cyclic oligomers and oligomers is higher than that of water, ethanol and other solvents.

[0018] In an embodiment, in step S1, the molar ratio of the 1,4-butanediol to the succinic acid and / or succinic anhydride is 1.05-1.4:1.

[0019] In an embodiment, in step S1, the amount of the bacterial cellulose is 3%-10% of the total mass of the esterified oligomer.

[0020] In an embodiment, in step S1, the esterification reaction is performed in a reaction kettle.

[0021] In an embodiment, in step S1, the esterification reaction is performed in a nitrogen protective atmosphere.

[0022] In an embodiment, in step S1, the temperature of the esterification reaction is 140-200 DEG C, and the time of the esterification reaction is 5-10 h.

[0023] In an embodiment, in step S2, the primary evaporator is a thin film evaporator.

[0024] In an embodiment, in step S2, the film thickness of the esterified oligomer in the primary evaporator is less than 5 mm, preferably less than 2 mm, which can significantly improve the removal effect of cyclic oligomers and oligomers in the melt.

[0025] In an embodiment, in step S2, the flow rate of the esterified oligomer in the primary evaporator is 100-500 kg / h.

[0026] In an embodiment, in step S2, the average residence time of the esterified oligomer in the primary evaporator is 0.3-2 h. To ensure the average residence time of the esterified oligomer in the primary evaporator, multiple sets of evaporator devices can be connected in series.

[0027] In an embodiment, in step S2, the catalyst is one or more of tetrabutyl titanate, tetraisopropyl titanate, tetraethyl titanate, and tetramethyl titanate.

[0028] In an embodiment, in step S2, the amount of the catalyst is 50-150 ppm of the total mass of the esterified oligomer.

[0029] In an embodiment, in step S2, the flow rate of the catalyst in the primary evaporator is 0.005-0.075 kg / h.

[0030] In an embodiment, in step S2, the amount of the tetrahydrofuran byproduct is 10%-30% of the total mass of the esterified oligomer.

[0031] In an embodiment, in step S2, the flow rate of the tetrahydrofuran byproduct in the primary evaporator is 10-150 kg / h.

[0032] In an embodiment, in step S2, the heating and vacuuming condition is heating at 200-220 °C and vacuuming to a pressure lower than 500 mbar.

[0033] In an embodiment, in step S3, the secondary evaporator is a short-path molecular distillation evaporator.

[0034] In an embodiment, in step S3, the film thickness of the prepolymer in the secondary evaporator is lower than 5 mm, preferably lower than 2 mm, which can significantly improve the removal effect of the cyclic oligomers and oligomers in the melt.

[0035] In an embodiment, in step S3, the flow rate of the prepolymer in the secondary evaporator is 50-200 kg / h.

[0036] In an embodiment, in step S3, the average residence time of the prepolymer in the secondary evaporator is 0.3-2 h. To ensure the average residence time of the prepolymer in the secondary evaporator, multiple sets of evaporator devices can be connected in series.

[0037] In an embodiment, in step S3, the catalyst is one or more of tetrabutyl titanate, tetraisopropyl titanate, tetraethyl titanate, and tetramethyl titanate.

[0038] In one embodiment, in step S3, the amount of the catalyst is 30-80 ppm of the total mass of the prepolymer.

[0039] In one embodiment, in step S3, the flow rate of the catalyst in the secondary evaporator is 0.0015-0.016 kg / h.

[0040] In one embodiment, in step S3, the amount of the tetrahydrofuran byproduct is 5%-15% of the total mass of the prepolymer.

[0041] In one embodiment, in step S3, the flow rate of the tetrahydrofuran byproduct in the secondary evaporator is 2.5-30 kg / h.

[0042] In one embodiment, in step S3, the heating and vacuuming condition is: heating at 220-240℃, vacuuming to a pressure lower than 50 mbar.

[0043] In one embodiment, in step S4, the chain extender is at least one of isocyanate, isocyanurate, peroxide, and epoxide, preferably diisocyanate, further preferably at least one of aliphatic diisocyanate and alicyclic diisocyanate, and more further preferably hexamethylene diisocyanate.

[0044] In one embodiment, in step S4, the amount of the chain extender added is 0.5%-5% of the total mass of the polycondensation product.

[0045] In one embodiment, in step S4, the temperature of the extrusion reaction chain extension is 120-230℃.

[0046] In one embodiment, in step S4, the devolatilization treatment is achieved by vacuuming to a pressure lower than 100 mbar.

[0047] In one embodiment, in step S4, the temperature of the vacuum devolatilization drying is 60-80℃.

[0048] In one embodiment, in step S4, the vacuum pressure of the vacuum devolatilization drying is lower than 500 mbar.

[0049] The present application also provides a low-migration PBS product prepared by the preparation method.

[0050] As a general inventive concept, the present application also provides a preparation system of a low-migration PBS product, comprising:

[0051] an esterification reactor for mixing succinic acid and / or succinic anhydride with 1,4-butanediol and bacterial cellulose to perform an esterification reaction, with an esterification rate ≥ 90% to obtain an esterification oligomer;

[0052] a third condenser connected with the esterification reactor, for condensing and separating the tetrahydrofuran by-product discharged from the esterification reactor;

[0053] a tetrahydrofuran by-product collector connected with the third condenser, for collecting the tetrahydrofuran by-product condensed and separated from the third condenser;

[0054] a first evaporator with a first vacuum device, connected with the esterification reactor and the tetrahydrofuran by-product collector; the esterification oligomer from the esterification reactor and the catalyst added optionally are contacted with the tetrahydrofuran by-product from the tetrahydrofuran by-product collector as an entraining agent in the first evaporator in countercurrent, for melt purification to remove the cyclic oligomer generated in the reaction process and pre-polymerization under the condition of heating and vacuumizing, to obtain a pre-polymer;

[0055] a second evaporator with a second vacuum device, connected with the first evaporator and the tetrahydrofuran by-product collector; the pre-polymer from the first evaporator and the catalyst added optionally are contacted with the tetrahydrofuran by-product from the tetrahydrofuran by-product collector as an entraining agent in the second evaporator in countercurrent, for melt purification to remove the cyclic oligomer generated in the reaction process and final polycondensation under the condition of heating and vacuumizing, to obtain a polycondensation product;

[0056] a cooler connected with the second evaporator, for cooling the polycondensation product from the second evaporator to 130-150℃;

[0057] a melt pump connected with the cooler, for conveying the polycondensation product cooled by the cooler to the twin-screw reaction extruder;

[0058] a twin-screw reaction extruder connected with a chain extender adding device and a devolatilization equipment; the chain extender adding device is used for adding a chain extender into the twin-screw reaction extruder; the devolatilization equipment is used for devolatilization treatment in the extrusion process of the twin-screw reaction extruder; the polycondensation product and the chain extender are subjected to extrusion reaction and chain extension in the twin-screw reaction extruder, to obtain an extrusion product;

[0059] a dry bin with a third vacuum device, for vacuum devolatilization drying of the extrusion product, to obtain the low-migration PBS product.

[0060] In an embodiment, the preparation system of the low-migration PBS product, the first evaporator is a thin-film evaporator.

[0061] In an embodiment, the preparation system of the low-migration PBS product, the second evaporator is a short-path molecular distillation evaporator.

[0062] In an embodiment, the system for preparing the low-migration PBS product further comprises a first condenser, a first separator, and a first cyclic oligomer collector.

[0063] In an embodiment, the system for preparing the low-migration PBS product further comprises a first condenser, a first separator, and a first cyclic oligomer collector.

[0064] In an embodiment, the system for preparing the low-migration PBS product further comprises a second condenser, a second separator, and a second cyclic oligomer collector.

[0065] In an embodiment, the system for preparing the low-migration PBS product further comprises a second condenser, a second separator, and a second cyclic oligomer collector.

[0066] In an embodiment, the system for preparing the low-migration PBS product further comprises a wastewater collector.

[0067] In an embodiment, the system for preparing the low-migration PBS product further comprises a wastewater collector.

[0068] In an embodiment, the system for preparing the low-migration PBS product further comprises a wastewater collector.

[0069] In an embodiment, the system for preparing the low-migration PBS product further comprises a wastewater collector.

[0070] In an embodiment, the system for preparing the low-migration PBS product further comprises an intermediate tank.

[0071] In an embodiment, the system for preparing the low-migration PBS product further comprises an intermediate tank.

[0072] In an embodiment, the system for preparing the low-migration PBS product further comprises a pelletizing device.

[0073] In an embodiment, the system for preparing the low-migration PBS product, the twin-screw reactive extruder is connected with the drying bin through the pelletizing device; the pelletizing device is used for pelletizing the extruded product and conveying the pelletized product to the drying bin.

[0074] In an embodiment, the system for preparing the low-migration PBS product, the devolatilization device comprises a fourth vacuumizing device and a fifth vacuumizing device arranged in sequence along the extrusion direction of the twin-screw reactive extruder, so that multi-stage devolatilization can be realized during the extrusion of the twin-screw reactive extruder.

[0075] The system for preparing the low-migration PBS product of the present application can perform the method for preparing the low-migration PBS product.

[0076] Compared with the prior art, the present application has the following beneficial effects:

[0077] 1. The bacterial cellulose is introduced into the PBS synthesis formula, which can improve the crystallization of PBS, has a binding and adsorption effect on residual trace cyclic oligomers and oligomers, and does not affect the mechanical properties and heat resistance of the PBS product.

[0078] 2. The two-stage evaporator (especially the thin-film evaporator and the molecular distillation evaporator) is used in the present application, the polycondensation and viscosity increase are performed in the evaporator, the high-temperature reaction time is short, the degree of side reactions of end group cyclization degradation is effectively reduced, cyclic oligomers and oligomers are directly removed from the melt during the reaction process, and the by-product tetrahydrofuran is used as an entraining agent, without introducing other solvents, and the entraining effect of tetrahydrofuran on the by-products is better than that of other solvent extraction systems.

[0079] 3. In the technical route of the present application, further chain extension and devolatilization are performed after polymerization, the residual oligomers in the polymerization process are subjected to chain extension reaction to form macromolecules, and the cyclic oligomers and tetrahydrofuran odor are removed under the shearing action of the screw, so that the migration amount of the PBS product is further optimized, the migration amount tested by using ethanol simulation liquid can meet the requirement of ≤10 mg / dm 2 , and the injection-molded product does not powder after being placed for several months, which can meet the application requirements of food contact materials and low-migration injection-molded products.

[0080] 4. The technical route of the present application is one-step preparation of low-migration PBS product, without the need for solvent extraction and other post-processing steps, and the process route is continuous and efficient, which is suitable for large-scale production. BRIEF DESCRIPTION OF DRAWINGS

[0081] Figure 1 FIG. 1 is a structural schematic diagram of a system for preparing a low-migration PBS product according to an embodiment of the present application. Detailed Implementation

[0082] The present invention will be further described below with reference to the accompanying drawings and specific embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the invention.

[0083] See Figure 1 A system for preparing a low-migration PBS product includes an esterification reactor 1, a primary evaporator 2, a first condenser 3, a first separator 4, a third condenser 5, a first cyclic oligomer collector 6, a tetrahydrofuran byproduct collector 7, a wastewater collector 8, a waste alcohol collector 9, a secondary evaporator 10, a second condenser 11, a second separator 12, a second cyclic oligomer collector 13, a cooler 16, an intermediate tank 17, a melt pump 18, a twin-screw reactive extruder 19, a pelletizing device 21, and a drying silo 22.

[0084] Esterification reactor 1 is used to mix succinic acid and / or succinic anhydride with 1,4-butanediol and bacterial cellulose for esterification reaction, and the esterification rate is ≥90% to obtain esterified oligomers.

[0085] The third condenser 5 is connected to the esterification reactor 1 and is used to condense and separate the tetrahydrofuran byproduct, wastewater and waste alcohol discharged from the esterification reactor 1. The tetrahydrofuran byproduct collector 7, wastewater collector 8 and waste alcohol collector 9 are connected to the third condenser 5 and are used to collect the tetrahydrofuran byproduct, wastewater and waste alcohol separated by the third condenser 5, respectively.

[0086] The primary evaporator 2 is equipped with a first vacuum device 14. The primary evaporator 2 is a thin-film evaporator. The primary evaporator 2 is connected to the esterification reactor 1 and the tetrahydrofuran by-product collector 7. The esterified oligomers from the esterification reactor 1 and a selectively added catalyst, along with the tetrahydrofuran by-products from the tetrahydrofuran by-product collector 7 (acting as an entrainer), come into countercurrent contact within the primary evaporator 2. This process involves melt purification to remove the cyclic oligomers generated during the reaction, while simultaneously undergoing pre-condensation under heating and vacuum conditions to obtain a prepolymer. The primary evaporator 2, the first condenser 3, the first separator 4, and the tetrahydrofuran by-product collector 7 are sequentially connected to form a first tetrahydrofuran by-product circulation loop. The first condenser 3 and the first separator 4 are used to condense and separate the tetrahydrofuran by-products and cyclic oligomers discharged from the primary evaporator 2, respectively. The first cyclic oligomer collector 6 is connected to the first separator 4 and is used to collect the cyclic oligomers separated by the first separator 4.

[0087] The secondary evaporator 10 is provided with a second vacuum pump 15. The secondary evaporator 10 is a short path molecular distillation evaporator. The secondary evaporator 10 is connected with the primary evaporator 2 and the tetrahydrofuran by-product collector 7. The prepolymer and the optional catalyst from the primary evaporator 2 and the tetrahydrofuran by-product from the tetrahydrofuran by-product collector 7 as an entrainer are countercurrently contacted in the secondary evaporator 10 to remove the cyclic oligomers generated in the reaction process while performing the final polycondensation under the conditions of heating and vacuumizing to obtain the polycondensation product. The secondary evaporator 10, the second condenser 11, the second separator 12 and the tetrahydrofuran by-product collector 7 are sequentially connected to form a second tetrahydrofuran by-product circulation loop. The second condenser 11 and the second separator 12 are respectively used for condensing and separating the tetrahydrofuran by-product and the cyclic oligomers discharged from the secondary evaporator 10. The second cyclic oligomer collector 13 is connected with the second separator 12 for collecting the cyclic oligomers separated from the second separator 12.

[0088] The cooler 16 is connected with the secondary evaporator 10 for cooling the polycondensation product from the secondary evaporator 10 to 130-150°C.

[0089] The cooler 16 is connected with the melt pump 18 through the intermediate tank 17. The intermediate tank 17 is used for storing the polycondensation product cooled by the cooler 16 and providing the melt pump 18. The melt pump 18 is used for conveying the polycondensation product cooled by the cooler 16 to the twin-screw reaction extruder 19.

[0090] The twin-screw reaction extruder 19 is connected with the chain extender adding device 20 and the devolatilization equipment. The chain extender adding device 20 is used for adding the chain extender to the twin-screw reaction extruder 19. The devolatilization equipment is used for performing the devolatilization treatment during the extrusion process of the twin-screw reaction extruder 19. The devolatilization equipment includes the fourth vacuum pump 23 and the fifth vacuum pump 24 arranged in sequence along the extrusion direction of the twin-screw reaction extruder 19, so that the multi-stage devolatilization can be realized during the extrusion process of the twin-screw reaction extruder 19. The polycondensation product and the chain extender are subjected to the extrusion reaction and chain extension in the twin-screw reaction extruder 19 to obtain the extrusion product.

[0091] The twin-screw reaction extruder 19 is connected with the drying bin 22 through the pelletizing device 21. The pelletizing device 21 is used for pelletizing the extrusion product and conveying the extrusion product to the drying bin 22.

[0092] The drying bin 22 is provided with a third vacuum pump 25 for performing the vacuum devolatilization drying on the extrusion product to obtain the low-migration PBS product.

[0093] The following examples all adopt the preparation system of the low-migration PBS product.

[0094] Example 1

[0095] S1: Butanedioic acid 1000 kg and 1,4-butanediol 880 kg, bacterial cellulose 90 kg were reacted in a reaction kettle under nitrogen protection, esterification was carried out at 200°C for 8h, tetrahydrofuran by-product and waste water were separated and collected, and esterification oligomer was obtained after the esterification rate reached 95%;

[0096] S2: The esterification oligomer of S1 was input into a first evaporator device at a flow rate of 150 kg / h, and tetrabutyl titanate catalyst was input at a flow rate of 0.015 kg / h, by-product tetrahydrofuran was added as an entraining agent in countercurrent, the addition flow rate was 15 kg / h, and pre-polymerization was carried out at 220°C and 300 mbar to obtain a prepolymer, and the average residence time of the esterification oligomer in the evaporator was 60 min;

[0097] S3: The prepolymer of S2 was input into a molecular distillation evaporator device at a flow rate of 80 kg / h, and the catalyst tetrabutyl titanate was added at a flow rate of 0.0048 kg / h, by-product tetrahydrofuran was added as an entraining agent in countercurrent, the addition flow rate was 10 kg / h, and final polycondensation was carried out at 230°C and 20 mbar to obtain a polycondensation product, and the average residence time of the prepolymer in the molecular distillation evaporator was 100 min;

[0098] S4: The polycondensation product obtained in S3 was rapidly cooled to 140°C, and was transported to a twin-screw extruder casting device through a melt pump, 2% of the polycondensation product by mass fraction of chain extender hexamethylene diisocyanate was added for extrusion reaction chain extension, and multi-stage devolatilization treatment was carried out at the exhaust hole position of the extruder during the extrusion process, the pressure was 30 mbar, the reaction zone temperature of the extruder was set to 210°C, and the cooling zone was set to 150°C, and after granulation, it was transported to a bin, and after vacuum devolatilization drying at 70°C and a vacuum pressure lower than 500 mbar, a low-migration PBS product was obtained.

[0099] Example 2

[0100] S1: Butanedioic acid 2000 kg and 1,4-butanediol 1878 kg, bacterial cellulose 210 kg were reacted in a reaction kettle under nitrogen protection, esterification was carried out at 190°C for 9h, tetrahydrofuran by-product and waste water were separated and collected, and esterification oligomer was obtained after the esterification rate reached 96%;

[0101] S2: The esterification oligomer of S1 was input into a first evaporator device at a flow rate of 200 kg / h, and tetrabutyl titanate catalyst was input at a flow rate of 0.022 kg / h, by-product tetrahydrofuran was added as an entraining agent in countercurrent, the addition flow rate was 20 kg / h, and pre-polymerization was carried out at 215°C and 250 mbar to obtain a prepolymer, and the average residence time of the esterification oligomer in the evaporator was 45 min;

[0102] S3: The prepolymer of S2 was input into a molecular distillation evaporator device at a flow rate of 100 kg / h, and a catalyst tetrabutyl titanate was added at a flow rate of 0.005 kg / h, while a byproduct tetrahydrofuran was added as an entraining agent in countercurrent, at a flow rate of 7 kg / h, to obtain a polycondensation product under a pressure of 230°C and 20 mbar, and the average residence time of the prepolymer in the molecular distillation evaporator was 60 min;

[0103] S4: The polycondensation product obtained in S3 was rapidly cooled to 150°C, and was transported to a twin-screw extruder casting device through a melt pump, and a chain extender hexamethylene diisocyanate was added at a mass ratio of 2.5% to perform an extrusion reaction chain extension, while a multi-stage devolatilization treatment was performed at the exhaust hole position of the extruder during the extrusion process, the pressure was 40 mbar, the reaction zone temperature of the extruder was set to 205°C, and the cooling zone was set to 140°C, and after granulation, it was transported to a bin, and after vacuum devolatilization drying at 70°C and a vacuum pressure lower than 500 mbar, a low-migration PBS product was obtained.

[0104] Example 3

[0105] S1: 1000 kg of succinic anhydride, 1172 kg of 1,4-butanediol, and 91 kg of bacterial cellulose were reacted in a reaction kettle under the protection of nitrogen, and an esterification reaction was performed at 200°C for 7 h, the tetrahydrofuran byproduct and wastewater were separated and collected, and after the esterification rate reached 94%, an esterification oligomer was obtained;

[0106] S2: The esterification oligomer of S1 was input into a first evaporator device at a flow rate of 300 kg / h, and a catalyst tetraisopropyl titanate was added at a flow rate of 0.027 kg / h, while a byproduct tetrahydrofuran was added as an entraining agent in countercurrent, at a flow rate of 45 kg / h, to obtain a prepolymer under a pressure of 220°C and 450 mbar, and the average residence time of the esterification oligomer in the evaporator was 30 min;

[0107] S3: The prepolymer of S2 was input into a molecular distillation evaporator device at a flow rate of 60 kg / h, and a catalyst tetrabutyl titanate was added at a flow rate of 0.0024 kg / h, while a byproduct tetrahydrofuran was added as an entraining agent in countercurrent, at a flow rate of 8.4 kg / h, to obtain a polycondensation product under a pressure of 235°C and 35 mbar, and the average residence time of the prepolymer in the molecular distillation evaporator was 100 min;

[0108] S4: The polycondensation product obtained in S3 was rapidly cooled to 140°C, and was transported to a twin-screw extruder pouring device via a melt pump, and 1.5% of a chain extender hexamethylene diisocyanate by mass of the polycondensation product was added for chain extension by extrusion reaction, and at the same time, a multi-stage devolatilization treatment was performed by loading at the exhaust hole position of the extruder during the extrusion process, the pressure was 45 mbar, the reaction zone temperature of the extruder was set to 215°C, and the cooling zone was set to 130°C, and after granulation, it was transported to a bin, and after vacuum devolatilization drying at 70°C and a vacuum pressure lower than 500 mbar, a low-migration PBS product was obtained.

[0109] Example 4

[0110] S1: 1500 kg of succinic anhydride and 1596 kg of 1,4-butanediol and 248 kg of bacterial cellulose were reacted in a reaction kettle under nitrogen protection, and esterification was carried out at 200°C for 9 h, and the by-product tetrahydrofuran and wastewater were separated and collected, and after the esterification rate reached 96%, esterification oligomers were obtained;

[0111] S2: The esterification oligomers in S1 were input into a first evaporator device at a flow rate of 250 kg / h, and tetrabutyl titanate catalyst was input at a flow rate of 0.032 kg / h, and at the same time, the by-product tetrahydrofuran was added as an entraining agent in a countercurrent manner, and the addition flow rate was 37 kg / h, and pre-polycondensation was carried out at 220°C and a pressure of 400 mbar to obtain a prepolymer, and the average residence time of the esterification oligomers in the evaporator was 38 min;

[0112] S3: The prepolymer in S2 was input into a molecular distillation evaporator device at a flow rate of 50 kg / h, and tetrakis isopropyl titanate catalyst was added at a flow rate of 0.004 kg / h, and at the same time, the by-product tetrahydrofuran was added as an entraining agent in a countercurrent manner, and the addition flow rate was 4.5 kg / h, and final polycondensation was carried out at 230°C and a pressure of 20 mbar to obtain a polycondensation product, and the average residence time of the prepolymer in the molecular distillation evaporator was 110 min;

[0113] S4: The polycondensation product obtained in S3 was rapidly cooled to 140°C, and was transported to a twin-screw extruder pouring device via a melt pump, and 1.5% of a chain extender hexamethylene diisocyanate by mass of the polycondensation product was added for chain extension by extrusion reaction, and at the same time, a multi-stage devolatilization treatment was performed by loading at the exhaust hole position of the extruder during the extrusion process, the pressure was 45 mbar, the reaction zone temperature of the extruder was set to 215°C, and the cooling zone was set to 130°C, and after granulation, it was transported to a bin, and after vacuum devolatilization drying at 70°C and a vacuum pressure lower than 500 mbar, a low-migration PBS product was obtained.

[0114] Example 5

[0115] S1: Succinic acid 1500 kg and 1,4-butanediol 1260 kg, bacterial cellulose 125 kg were reacted in a reaction kettle under nitrogen protection, esterification was carried out at 200℃ for 8h, the by-product tetrahydrofuran and waste water were separated and collected, and the esterification oligomer was obtained after the esterification rate reached 95%;

[0116] S2: The esterification oligomer of S1 was input into a first evaporator device at a flow rate of 150 kg / h, and tetrabutyl titanate catalyst was input at a flow rate of 0.022 kg / h, and the by-product tetrahydrofuran was added as an entraining agent in countercurrent, and the flow rate was 15 kg / h, and the pre-polymerization was carried out at 220℃ and 200mbar, and the average residence time of the esterification oligomer in the evaporator was 65min;

[0117] S3: The pre-polymer of S2 was input into a molecular distillation evaporator device at a flow rate of 120 kg / h, and the catalyst tetrabutyl titanate was added at a flow rate of 0.007 kg / h, and the by-product tetrahydrofuran was added as an entraining agent in countercurrent, and the flow rate was 13.1 kg / h, and the final polycondensation was carried out at 235℃ and 30mbar, and the average residence time of the pre-polymer in the molecular distillation evaporator was 55min;

[0118] S4: The polycondensation product obtained in S3 was rapidly cooled to 140℃, and was transported to a twin-screw extruder casting device through a melt pump, and a chain extender hexamethylene diisocyanate was added at a mass ratio of 2.9% of the polycondensation product for extrusion reaction chain extension, and a multi-stage devolatilization treatment was carried out at the exhaust hole position of the extruder during the extrusion process, and the pressure was 55mbar, and the reaction zone temperature of the extruder was set to 215℃, and the cooling zone was set to 130℃, and after granulation, it was transported to a bin, and after vacuum devolatilization drying at 70℃ and a vacuum pressure lower than 500mbar, a low-migration PBS product was obtained.

[0119] Comparative Example 1

[0120] The difference from Example 1 is only that no bacterial cellulose is added, and the rest is the same, and a PBS product is obtained.

[0121] Comparative Example 2

[0122] The difference from Example 1 is only that no by-product tetrahydrofuran is added as an entraining agent in S2 and S3, and the rest is the same, and a PBS product is obtained.

[0123] Comparative Example 3

[0124] The difference from Example 1 is only that an equal amount of ethanol aqueous solution with an ethanol concentration of 95vol% is used as an entraining agent instead of the by-product tetrahydrofuran in S2 and S3, and the rest is the same, and a PBS product is obtained.

[0125] Comparative Example 4

[0126] S1: Butanedioic acid 1000 kg is reacted with 1,4-butanediol 880 kg, bacterial cellulose 90 kg in a reaction kettle under nitrogen protection, esterification is carried out at 200°C for 8h, tetrahydrofuran by-product and waste water are separated and collected, and esterification oligomer is obtained after the esterification rate reaches 95%;

[0127] S2: The esterification oligomer of S1 is transported to a pre-polycondensation kettle, catalyst tetrabutyl titanate 0.38 kg is added, pre-polycondensation is carried out at 220°C and a pressure of 1000 mbar for 6h, and a prepolymer is obtained;

[0128] S3: The prepolymer of S2 is transported to a tackifying kettle, catalyst tetrabutyl titanate 0.35 kg is added, terminal polycondensation is carried out at 235°C and a pressure of 90 mbar, and tackifying reaction is carried out for 5h; after the viscosity of the kettle material reaches the predetermined range, the kettle bottom is discharged, transported to a pelletizing system through a melt pump, and PBS product is obtained after pelletizing, drying in a bin at 70°C, and the like.

[0129] Comparative Example 5

[0130] The PBS product obtained in Comparative Example 4 is weighed at 1 kg and placed in a 10L reactor, then 4L of tetrahydrofuran solvent is added, heated to 60°C, kept under condensation reflux and constant temperature stirring, immersed for 6h, then cooled to filter out the PBS particles, washed with water to remove the THF solvent attached to the particles, then placed in a 100°C oven for drying for 24h, and the post-treated PBS product is obtained.

[0131] Comparative Example 6

[0132] The PBS product obtained in Comparative Example 4 is weighed at 1 kg and placed in a 10L reactor, then 4L of ethanol aqueous solution with an ethanol concentration of 95vol% is added, heated to 60°C, kept under condensation reflux and constant temperature stirring, immersed for 6h, then cooled to filter out the PBS particles, washed with water to remove the ethanol solvent attached to the particles, then placed in a 100°C oven for drying for 24h, and the post-treated PBS product is obtained.

[0133] Tables 1 and 2 show the specific performance detection data of the PBS products of each example and comparative example, wherein the mass content of cyclic oligomer can be obtained by gas chromatography-mass spectrometry (GC-MS) detection, and the mass content of tetrahydrofuran (THF) can be obtained by gas chromatography detection.

[0134] Table 1

[0135]

[0136] Table 2

[0137]

[0138] It can be seen from the data in Table 1 and Table 2 that the technical scheme of the present application can prepare the PBS product with a larger market demand at present, and the oligomer content and the migration amount of the ethanol simulation liquid immersion cooking are significantly reduced, the migration amount can meet the requirement of food contact ≤10 mg / dm 2 Compared with the solvent immersion post-processing method, the migration amount is also superior, and the THF content does not increase to cause abnormal odor, and the risk of increasing the melt index does not occur.

[0139] In addition, it should be understood that, after reading the above description of the present application, those skilled in the art can make various modifications or modifications to the present application, and these equivalent forms also fall within the scope defined by the claims attached to the present application.

Claims

1. A method of preparing a low-migrating PBS product, characterized in that, The method comprises the steps of: S1, esterification reaction of succinic acid and / or succinic anhydride and 1,4-butanediol, bacterial cellulose is mixed, the byproduct of tetrahydrofuran is separated and collected, the esterification rate is greater than or equal to 90%, and the esterification oligomer is obtained; The amount of said bacterial cellulose is 3% to 10% of the total mass of said esterification oligomer; S2, the esterification oligomer and the optional catalyst are input into the first evaporator, and the byproduct of tetrahydrofuran is added as an entraining agent to remove the cyclic oligomer generated in the reaction process by melt purification, and the pre-polymer is obtained by heating and vacuumizing; The first evaporator is a thin film evaporator; S3, the pre-polymer and the optional catalyst are input into the second evaporator, and the byproduct of tetrahydrofuran is added as an entraining agent to remove the cyclic oligomer generated in the reaction process by melt purification, and the polycondensation product is obtained by heating and vacuumizing; The second evaporator is a short path molecular distillation evaporator; S4, the polycondensation product is cooled to 130-150℃, and is transported to the twin-screw reaction extruder through the melt pump, the chain extender is added for extrusion reaction chain extension, and the devolatilization treatment is carried out during the extrusion process, and the extrusion product is dried by vacuum devolatilization to obtain the low-migration PBS product; The chain extender is at least one of isocyanate, isocyanurate, peroxide and epoxide; The addition amount of the chain extender is 0.5% to 5% of the total mass of the polycondensation product.

2. The production method according to claim 1, characterized by, In step S1: The molar ratio of 1,4-butanediol to succinic acid and / or succinic anhydride is 1.05-1.4:1; The esterification reaction is carried out in a reaction kettle, the esterification reaction is carried out in a nitrogen protective atmosphere, the temperature of the esterification reaction is 140-200℃, and the time of the esterification reaction is 5-10h.

3. The preparation method according to claim 1, characterized in that, In step S2: The film thickness of the esterification oligomer in the first evaporator is less than 5mm; The flow rate of the esterification oligomer in the first evaporator is 100-500kg / h; The average residence time of the esterification oligomer in the first evaporator is 0.3-2h; The catalyst is one or more of tetrabutyl titanate, tetraisopropyl titanate, tetraethyl titanate and tetramethyl titanate; The amount of the catalyst is 50-150ppm of the total mass of the esterification oligomer; The flow rate of the catalyst in the first evaporator is 0.005-0.075kg / h; The amount of the byproduct of tetrahydrofuran is 10%-30% of the total mass of the esterification oligomer; The flow rate of the byproduct of tetrahydrofuran in the first evaporator is 10-150kg / h; The heating and vacuumizing conditions are: heating at 200-220℃, and vacuumizing to a pressure lower than 500mbar.

4. The production method according to claim 3, characterized by, In step S2, the film thickness of the esterification oligomer in the first evaporator is less than 2mm.

5. The preparation method according to claim 1, characterized in that, In step S3: The film thickness of the pre-polymer in the second evaporator is less than 5mm; The flow rate of the pre-polymer in the second evaporator is 50-200kg / h; The average residence time of the pre-polymer in the second evaporator is 0.3-2h; The catalyst is one or more of tetrabutyl titanate, tetraisopropyl titanate, tetraethyl titanate, tetramethyl titanate; The amount of the catalyst is 30-80 ppm of the total mass of the prepolymer; The flow rate of the catalyst in the secondary evaporator is 0.0015-0.016 kg / h; The amount of the tetrahydrofuran byproduct is 5%-15% of the total mass of the prepolymer; The flow rate of the tetrahydrofuran byproduct in the secondary evaporator is 2.5-30 kg / h; The heating and vacuumizing condition is: heating at 220-240℃ and vacuumizing to a pressure lower than 50 mbar.

6. The preparation method according to claim 5, characterized in that, In step S3, the film thickness of the prepolymer in the secondary evaporator is lower than 2 mm.

7. The preparation method according to claim 1, characterized in that, In step S4: The chain extender is diisocyanate; The temperature of the extrusion reaction chain extension is 120-230℃; The devolatilization treatment is achieved by vacuumizing to a pressure lower than 100 mbar; The temperature of the vacuum devolatilization drying is 60-80℃; The vacuum pressure of the vacuum devolatilization drying is lower than 500 mbar.

8. The preparation method according to claim 7, characterized in that, In step S4, the chain extender is at least one of aliphatic diisocyanate and alicyclic diisocyanate.

9. The preparation method according to claim 8, characterized in that, In step S4, the chain extender is hexamethylene diisocyanate.

10. A low-migration PBS product prepared by the preparation method according to any one of claims 1-9.

11. A system for the preparation of a low-migration PBS product, characterized in that, It comprises: An esterification reactor (1) for mixing succinic acid and / or succinic anhydride with 1,4-butanediol and bacterial cellulose to perform esterification reaction, the esterification rate being ≥90% to obtain esterified oligomer; A third condenser (5) connected with the esterification reactor (1) for condensing and separating the tetrahydrofuran byproduct discharged from the esterification reactor (1); A tetrahydrofuran byproduct collector (7) connected with the third condenser (5) for collecting the tetrahydrofuran byproduct condensed and separated from the third condenser (5); A primary evaporator (2) with a first vacuumizing device (14) connected with the esterification reactor (1) and the tetrahydrofuran byproduct collector (7); the esterified oligomer from the esterification reactor (1) and the optional catalyst and the tetrahydrofuran byproduct from the tetrahydrofuran byproduct collector (7) as an entraining agent are countercurrently contacted in the primary evaporator (2) to perform melt purification to remove cyclic oligomers generated in the reaction process and pre-polycondensation under the condition of heating and vacuumizing to obtain a prepolymer; A secondary evaporator (10) with a second vacuumizing device (15) connected with the primary evaporator (2) and the tetrahydrofuran byproduct collector (7); the prepolymer from the primary evaporator (2) and the optional catalyst and the tetrahydrofuran byproduct from the tetrahydrofuran byproduct collector (7) as an entraining agent are countercurrently contacted in the secondary evaporator (10) to perform melt purification to remove cyclic oligomers generated in the reaction process and final polycondensation under the condition of heating and vacuumizing to obtain a polycondensation product; A cooler (16) connected with the secondary evaporator (10) for cooling the polycondensation product from the secondary evaporator (10) to 130-150℃; a melt pump (18) connected with the cooler (16) and used for conveying the polycondensation product cooled by the cooler (16) to the twin-screw reaction extruder (19); the twin-screw reaction extruder (19) is connected with the chain extender adding device (20) and a devolatilization device; the chain extender adding device (20) is used for adding the chain extender into the twin-screw reaction extruder (19); the devolatilization device is used for devolatilization treatment during the extrusion process of the twin-screw reaction extruder (19); the polycondensation product and the chain extender are subjected to extrusion reaction and chain extension in the twin-screw reaction extruder (19) to obtain an extrusion product; a drying bin (22) with a third vacuumizing device (25) is used for vacuum devolatilization drying of the extrusion product to obtain the low-migration PBS product.

12. The production system of claim 11, wherein, The primary evaporator (2) is a thin-film evaporator. The secondary evaporator (10) is a short-path molecular distillation evaporator.

13. The manufacturing system of claim 11, wherein, The preparation system further comprises a first condenser (3), a first separator (4), a first cyclic oligomer collector (6), a second condenser (11), a second separator (12), a second cyclic oligomer collector (13), a waste water collector (8) and a waste alcohol collector (9); The primary evaporator (2), the first condenser (3), the first separator (4) and the tetrahydrofuran by-product collector (7) are sequentially connected to form a first tetrahydrofuran by-product circulation loop; the first condenser (3) and the first separator (4) are respectively used for condensing and separating the tetrahydrofuran by-product and the cyclic oligomer discharged from the primary evaporator (2); the first cyclic oligomer collector (6) is connected with the first separator (4) and is used for collecting the cyclic oligomer separated from the first separator (4); The secondary evaporator (10), the second condenser (11), the second separator (12) and the tetrahydrofuran by-product collector (7) are sequentially connected to form a second tetrahydrofuran by-product circulation loop; the second condenser (11) and the second separator (12) are respectively used for condensing and separating the tetrahydrofuran by-product and the cyclic oligomer discharged from the secondary evaporator (10); the second cyclic oligomer collector (13) is connected with the second separator (12) and is used for collecting the cyclic oligomer separated from the second separator (12); The third condenser (5) is further used for condensing and separating the waste water and the waste alcohol discharged from the esterification reactor (1); the waste water collector (8) and the waste alcohol collector (9) are connected with the third condenser (5) and are respectively used for collecting the waste water and the waste alcohol condensed and separated from the third condenser (5).

14. The system for producing according to claim 11, characterized in that, The preparation system further comprises an intermediate tank (17) and a pelletizing device (21); The cooler (16) is connected with the melt pump (18) through the intermediate tank (17); the intermediate tank (17) is used for storing the polycondensation product cooled by the cooler (16) and providing the polycondensation product to the melt pump (18); The twin-screw reaction extruder (19) is connected with the drying bin (22) through the pelletizing device (21); the pelletizing device (21) is used for pelletizing the extrusion product and conveying the extrusion product to the drying bin (22); The devolatilization device comprises a fourth vacuum pumping device (23) and a fifth vacuum pumping device (24) arranged in sequence along the extrusion direction of the twin-screw reaction extruder (19).

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