Polyester solid-phase tackifying method and system

Abstract

The invention discloses a solid-phase tackifying method and system for polyester. According to the solid-phase tackifying method of the polyester, the polyester polymer passes through the crystallization preheater and then is introduced into the polycondensation tower for solid-phase tackifying, while negative pressure is pumped into the polycondensation tower, process gas is continuously introduced in the whole solid-phase tackifying process, and under the action of the negative pressure, the flow rate of the gas entering the polycondensation tower is increased, so that the solid-phase tackifying effect is improved. Not only is the use amount of process gas saved, but also micromolecular monomers and oligomers can be taken away by gas flow, so that the purpose of quickly removing micromolecules is achieved, and the polymers grow towards the chain growth direction; the process gas flowing out of the polycondensation tower enters the gas purification device, the process gas with small molecules is subjected to spray cooling and gas-liquid separation through the gas purification device, monomers and oligomers are removed from the process gas and recycled, the process gas is purified, and the purified process gas can return to the gas supply port for cyclic utilization.

Description

Technical Field

[0001] The invention relates to the technical field of new material preparation, and in particular to a method and system for solid phase viscosity enhancement of polyester. Background Art

[0002] Polyester has good mechanical properties and molding processing properties. It has been widely used in fibers, packaging, films, engineering plastics, etc., and has become one of the most important chemical synthetic materials in the world. Among them, aliphatic polyesters such as polyglycolic acid and polylactic acid can be decomposed by water, microorganisms or enzymes existing in nature. With the increasing problems of resource shortage and environmental pollution in recent years, such biodegradable polymer materials have received more and more attention.

[0003] At present, the synthesis methods of polyglycolic acid mainly include ring-opening polymerization and direct polycondensation. The ring-opening polymerization method first requires obtaining glycolide with high purity, and then preparing polyglycolic acid through ring-opening polymerization of glycolide; the direct polycondensation method is synthesized by dehydration polycondensation of glycolic acid and / or methyl glycolate. The polyglycolic acid prepared by this method has a low molecular weight and a high residual monomer content, which cannot meet the application requirements of most scenarios. Therefore, solid-state polycondensation is required in the later stage to increase the molecular weight while further reducing the residual monomer content to meet product requirements.

[0004] The current solid phase thickening or solid phase polycondensation system usually makes the polyester polymer undergo polycondensation reaction under negative pressure environment to take out small molecules and make the polymer proceed in the direction of chain growth. For example, patent CN106432698B discloses a method for preparing polyglycolic acid by polymerization of glycolic acid: the obtained polyglycolic acid polymer is crushed to obtain 100 mesh polyglycolic acid solid powder, and the obtained polyglycolic acid solid powder is further solid phase polymerized to obtain polyglycolic acid with higher intrinsic viscosity; solid phase polycondensation adopts a gradually increasing heating method, the pressure of solid phase polymerization is 20-30Pa, the temperature is 195-215℃, and the time is 4-8 hours. The size and stability of negative pressure in the reactor are easy to affect the final effect. Therefore, not only the sealing requirements for equipment and pipelines are high, but also the energy consumption is large. Summary of the invention

[0005] In view of the shortcomings of the above-mentioned prior art, the purpose of the present invention is to provide a method and system for solid-phase thickening of polyester. While negative pressure is drawn into the polycondensation tower, process gas is continuously introduced into the polycondensation tower during the entire solid-phase thickening process. Under the action of negative pressure, the flow rate of the gas entering the polycondensation tower is increased, which not only saves the amount of process gas, but also the airflow can carry away small molecules (monomers, oligomers), thereby achieving the purpose of rapid removal of small molecules and allowing the polymer to grow in the direction of chain; the removed small molecules are recycled by spray cooling, and the process gas can be recycled after purification.

[0006] To achieve the above object, the present invention adopts the following technical solutions:

[0007] The polyester solid phase viscosity increasing method disclosed by the present invention comprises: passing the polyester polymer through a crystallization preheater and then passing it into a polycondensation tower for solid phase viscosity increasing; during the whole solid phase viscosity increasing process, continuously passing process gas into the polycondensation tower, the inlet pressure of the process gas is 0.1 bar-100 bar, the absolute pressure in the polycondensation tower is maintained at 1 kpa-50 kpa, the reaction temperature in the polycondensation tower is 190-220° C., and the reaction time is 2-30 hours; during the reaction process, the process gas is made to flow into a gas purification device from the gas outlet at the top of the polycondensation tower, and the process gas is spray-cooled and gas-liquid separated by the gas purification device to remove and recover monomers and oligomers in the process gas, purify the process gas, and the spray solvent can be circulated in the gas purification device, and the process gas is circulated after purification.

[0008] Furthermore, the particle size of the polyester polymer entering the polycondensation tower is 0-5 mm, preferably, between 0.5-2 mm.

[0009] Furthermore, the polyester polymer is controlled to enter and exit the polycondensation tower from top to bottom, and the process gas is controlled to enter the polycondensation tower in at least two ways. Preferably, the flow rate, temperature, or pressure of each gas path is different.

[0010] Furthermore, the volume ratio of the process gas entering the polycondensation tower during the solid phase viscosity increasing process to the mass ratio of the polyester polymer in the polycondensation tower is defined as the gas-to-material ratio, and the gas-to-material ratio is controlled to be 1: (0.5-5) L / kg.

[0011] Furthermore, the process gas is nitrogen or an inert gas.

[0012] Furthermore, the polyester polymer is a polyglycolic acid copolymer, the residual monomer content of the polyglycolic acid copolymer before entering the polycondensation tower is 1%-5%, and the residual monomer content after solid phase viscosity enhancement is 0.5%-1.5%.

[0013] Furthermore, the temperature in the polycondensation tower is set to be the same as the temperature in the crystallization preheater; the heating method of the crystallization preheater is a fluidized bed, screw conveying or infrared drying.

[0014] Furthermore, the process gas is preheated before entering the polycondensation tower. The polycondensation system is combined with external electric heating (or jacket) and process gas preheating to ensure uniform heating of the polyester particles. This allows the material in the polycondensation tower to have a smaller temperature difference in both the horizontal and vertical directions, greatly improving the space utilization and processing efficiency of the polycondensation tower.

[0015] Furthermore, the gas purification device includes a condensation spray device and a gas-liquid separation tank; the process gas flows into the condensation spray device through the gas outlet of the condensation tower, and the temperature of the condensation spray device is controlled to be lower than 85°C to cool the monomers and oligomers in the process gas flow to below their melting point. When the temperature in the condenser is low, the small molecules in the process gas precipitate quickly, and when the temperature is high, the precipitation is slower.

[0016] Furthermore, in the condensation spray device, a spray solvent is used to spray the process gas through a circulating liquid sprayer. The spray solvent can be selected from methyl glycolate, ethyl glycolate, butyl glycolate, isobutyl glycolate and other solvents that are good at dissolving small molecules. The small molecule content in the circulating gas can be significantly reduced. At the same time, the spray solvent containing small molecules is circulated into the condensation spray device after passing through the gas-liquid separation tank for repeated utilization, so as to spray the process gas and improve the solvent utilization rate.

[0017] Furthermore, the process gas and the spray solvent enter the gas-liquid separation tank after passing through the condensation spray device, and the process gas returns to the gas supply port through the vacuum pump after passing through the gas-liquid separation tank for recycling. By controlling the liquid level of the solvent in the gas-liquid separation tank, the entrainment amount of the liquid solvent in the gas flow can be reduced. At the same time, a packing layer or a molecular sieve layer is set above the interior of the gas-liquid separation tank to further remove monomers and oligomers in the process gas, and further process small particles and solvents in the gas, which can significantly increase the service life of the vacuum pump.

[0018] Furthermore, the gas purification device is preferably provided with two gas-liquid separation tanks connected in parallel, one gas-liquid separation tank is connected to the condensation spray device, and the other gas-liquid separation tank is provided with a spray liquid replenishing port for replenishing the spray solvent.

[0019] Furthermore, when the process gas flow enters the condenser of the condensation spray device, it is inevitable that small molecular particles begin to precipitate when entering the condensation spray device, which can easily cause the condensation spray device to be blocked over time. The circulating liquid sprayer is arranged below the process gas inlet and is located in the lower middle part of the condensation spray device. It is impossible to spray all positions inside the condensation spray device, especially the position above the process gas inlet. Therefore, a hot solvent sprayer is installed on the top of the condensation spray device. By spraying a spray solvent of 100°C or above in the condensation spray device to regularly flush the top of the condensation spray device, the high-temperature spray solvent can increase the solubility of monomers and oligomers in the solvent, and can avoid the blockage problem caused by condensation of monomers or small molecules on the top of the condenser due to a sudden drop in temperature, which can greatly improve the operation cycle of the entire device and carry out continuous production.

[0020] The present invention also provides a system for carrying out the above-mentioned solid phase viscosity increasing method for polyester, the system comprising:

[0021] A polycondensation tower, wherein the polycondensation tower has a feed inlet, a discharge port, a gas supply pipeline and a gas outlet, the number of gas supply pipelines is at least two, and each gas supply pipeline is provided with a flow meter, a preheater, a pressure gauge and a pressure regulating valve;

[0022] A gas supply port, the gas supply port is connected to each gas supply pipeline, and the process gas is introduced into the polycondensation tower through the gas supply pipeline;

[0023] A gas purification device, the gas purification device comprising a condensation spray device and a gas-liquid separation tank, the condensation spray device having a circulation sprayer and a gas-liquid outlet; the gas-liquid separation tank having a gas-liquid inlet, a gas outlet, and a liquid outlet; the gas-liquid outlet of the condensation spray device is connected to the gas-liquid inlet of the gas-liquid separation tank through a pipeline, the liquid outlet of the gas-liquid separation tank is connected to the circulation sprayer through a pipeline, and a circulation spray pump is provided therebetween; the gas outlet of the gas-liquid separation tank is connected to the gas supply port through a pipeline, and a vacuum pump is provided therebetween;

[0024] A crystallizer is connected to a feed inlet of the polycondensation tower through a pipeline.

[0025] Furthermore, a thermometer is provided inside the polycondensation tower, and a heater is provided outside the polycondensation tower, the heater is a jacket or an electric heating device, and a high material level meter is provided above the polycondensation tower.

[0026] Furthermore, a hot solvent sprayer is provided on the top of the spray condenser.

[0027] Furthermore, an airflow filtration layer is provided above the interior of the gas-liquid separation tank, and the airflow filtration layer is a packing layer or a molecular sieve layer.

[0028] Furthermore, the gas-liquid separation tank has a spray liquid replenishment port and a liquid level meter is arranged inside.

[0029] Furthermore, a sampling and recovery port is also provided on the pipeline between the liquid outlet of the gas-liquid separation tank and the circulating liquid sprayer.

[0030] The beneficial effects of the present invention are as follows:

[0031] 1. The present invention performs a solid-phase viscosity-increasing reaction under a negative pressure atmosphere and continuously introduces process gas into the polycondensation tower to ensure that the process gas in the polycondensation tower is in a flowing state, thereby ensuring that the material is heated evenly in the polycondensation tower, and the airflow flowing in the polycondensation tower can take away unreacted monomers and oligomers, thereby improving the quality / performance of the final product; the gas phase partial pressure of small molecules in the circulating gas can be reduced by circulating spraying, so that the reaction continues to proceed in the direction of chain growth.

[0032] 2. According to the ideal gas state equation PV=nRT, when the gas flows from a high-pressure state to a low-pressure state, its volume will increase. Therefore, when a small amount of gas flows from a high-pressure direction to a low-pressure direction, its flow rate can be equivalent to the gas flow rate of a large amount of gas in positive pressure solid phase thickening, which can significantly reduce the gas consumption and reduce the energy consumption of the process gas preheater.

[0033] 3. It is equipped with a process gas circulation system and a monomer / oligomer recovery system. The gas phase temperature is reduced to below the melting point of the monomers and oligomers by spraying. The spray solvent further dissolves the small molecules. The spray solvent can be transported to the polymerization reaction system for repolymerization, thereby achieving high monomer conversion rate and low gas consumption in the polymerization system. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 A schematic diagram of a polyester solid phase viscosity increasing system provided in one embodiment of the present invention. DETAILED DESCRIPTION

[0035] In order to better explain the present invention, the present invention is described in detail with reference to the embodiments of the present invention, and the main contents of the present invention are further illustrated in conjunction with specific examples, but the content of the present invention is not limited to the following examples. If no specific technology or conditions are indicated in the examples, the technology or conditions described in the literature in this area or the product instructions are used. If the manufacturer of the reagents or instruments is not indicated, they are all conventional products that can be obtained commercially.

[0036] The present invention provides a polyester solid phase viscosity increasing method and system: while negative pressure is pumped into a polycondensation tower, gas is continuously introduced during the whole solid phase viscosity increasing process; under the action of negative pressure, the flow rate of the gas entering the polycondensation tower is increased, which not only saves the amount of gas, but also allows the airflow to take away small molecules, so as to achieve the purpose of rapid removal of small molecules and allow the polymer to grow in the direction of chain growth; the removed small molecules can also be recycled by spray cooling; the gas can be recycled after purification.

[0037] If the negative pressure is not pumped into the polycondensation tower, and the gas is continuously introduced throughout the solid phase viscosity increase process, although the flowing gas can carry away small molecules, as the production capacity increases, the gas consumption and the energy consumption required for gas preheating are huge, and the economic efficiency is reduced. In addition, as the gas flow rate increases, it is difficult for traditional heat exchange methods to completely purify the small molecules in the system. A small amount of small molecules will be carried in the circulating gas. As the production continues, the concentration of small molecules in the system gradually increases, affecting the removal effect of small molecules in the material.

[0038] See also Figure 1, which intuitively illustrates the system of the solid-phase viscosity increasing method for polyester of the present invention, the system comprises a polycondensation tower 1, an air supply port 2, a condensation spray device 3, a gas-liquid separation tank 4, a crystallizer 6, and a silo 7; wherein the polycondensation tower has a feed port 11, a discharge port 12, a gas supply pipeline 13 and a gas outlet 14, the number of the gas supply pipelines 13 is set to at least two, and each gas supply pipeline 13 is provided with a flow meter 15, a preheater 16, a pressure regulating valve 17 and a pressure gauge 18.

[0039] The feed port 11 of the silo 7, the crystallizer 6 and the polycondensation tower 1 are connected in sequence through pipelines, and feed rotary valves 71 and 72 are arranged in sequence on the feed pipelines; when feeding, the feed rotary valve 71 is opened, and the material enters the crystallizer 6 from the silo 7 for preheating. After the material is preheated, the feed rotary valve 72 between the crystallizer 6 and the polycondensation tower is opened, and the material enters the polycondensation tower 1 for solid phase viscosity enhancement. A discharge rotary valve 73 is arranged at the discharge port 12 of the polycondensation tower 1. After the solid phase viscosity enhancement reaction is completed, the discharge rotary valve 73 is opened, and the material is discharged from the discharge port 12 of the polycondensation tower 1.

[0040] The polycondensation tower 1 is provided with a plurality of thermometers 19 inside and a heater 20 outside. The solid phase polycondensation system of the present invention adopts a combination of external heating (or jacket) and process gas preheating to ensure the uniformity of heating of the polyester particles. The heater 20 is a jacket or electric heating, and the heater 20 has a heat transfer oil inlet 21 and a heat transfer oil outlet 22. A high material level meter 23 for controlling the material height is also provided above the polycondensation tower 1.

[0041] The gas supply port 2 is connected to each gas supply pipeline 13, and the process gas is introduced into the condensation tower 1 through the gas supply pipeline 13; compared with the traditional bottom air intake method, the present invention can set multiple air intakes along the height of the condensation tower, and the gas supply pipeline can also be set in the upper and middle part of the condensation tower 1. The heating effect of the material in the condensation tower 1 will be better, the material temperature will be more uniform, and the flow rate, temperature and pressure of different gas supply pipelines 13 can be different.

[0042] The gas purification device includes a condensation spray device 3 and a gas-liquid separation tank 4. The condensation spray device 3 has a circulating liquid sprayer 31 and a gas-liquid outlet 32; the gas-liquid separation tank 4 has a gas-liquid inlet 41, a gas outlet 42, and a liquid outlet 43; the gas-liquid outlet 32 ​​of the condensation spray device 3 is connected to the gas-liquid inlet 41 of the gas-liquid separation tank 4 through a pipeline, the liquid outlet 43 of the gas-liquid separation tank 4 is connected to the circulating liquid sprayer 31 through a pipeline, and a circulating spray pump 33 is provided therebetween; the gas outlet 42 of the gas-liquid separation tank 4 is connected to the gas supply port 2 through a pipeline, and a vacuum pump 5 is provided therebetween.

[0043] The circulating liquid sprayer 31 sprays and cools the process gas entering the condensation spray device 3, and controls the temperature in the condensation spray device 3 to be lower than 85°C. The monomers and oligomers in the process gas flow can be cooled to below their melting point and removed, and the small molecule content in the circulating gas can be further reduced by dissolving the small molecules in the process gas by spraying solvent.

[0044] After passing through the condensation spray device 3, the process gas and the spray solvent enter the gas-liquid separation tank 4. After passing through the gas-liquid separation tank 4, the process gas returns to the gas supply port 2 through the vacuum pump 5 for recycling, and the spray solvent circulates into the condensation spray device 3 through the circulation spray pump 33 for spraying. It is also possible to recover part of the spray solvent through the sampling and recovery port 35 set on the circulation pipeline, and transport the small molecules therein to the polycondensation system to react and synthesize polyester, and recycle the monomers and oligomers; or, when it is detected that the impurities in the circulating spray liquid are higher than a certain value, the circulating spray solvent can be completely recovered and sprayed again with fresh spray solvent. The gas-liquid separation tank 4 is provided with a spray liquid replenishing port 46 for replenishing the spray solvent, and the spray liquid replenishing port 46 can also be set on the circulation pipeline. The temperature of the spray solvent is preferably between -20 and 70°C, and the temperature in the condensation spray device 3 can be adjusted by adjusting the temperature of the spray solvent, the amount of replenishment, and the flow rate of the circulation spray pump 33.

[0045] A liquid level meter 47 is provided in the gas-liquid separation tank 4. The liquid level of the spray solvent in the gas-liquid separation tank 4 is monitored and controlled by the liquid level meter 47, so that the amount of liquid solvent entrained in the airflow can be reduced. At the same time, an airflow filtration layer 45, such as a packing layer or a molecular sieve layer, is provided above the interior of the gas-liquid separation tank 4 to further remove monomers and oligomers in the process gas, and further process small particles and solvents in the gas, which can significantly improve the service life of the vacuum pump.

[0046] Two gas-liquid separation tanks 4 can be provided, and the two gas-liquid separation tanks 4 are connected in parallel. The condensation spray device 3 is connected to one of the gas-liquid separation tanks 4, and the spray liquid replenishing port 46 is provided on the other gas-liquid separation tank 4. By providing two parallel gas-liquid separation tanks 4, it is beneficial to maintain the liquid level stability of the gas-liquid separation tank 4 connected to the condensation spray device 3, while reducing the frequency of liquid replenishment.

[0047] When the process gas flow enters the condensation spray device 3, it is inevitable that small molecular particles will begin to precipitate when it encounters cold. Over time, it is easy to cause the condensation spray device 3 to be blocked, and the circulating liquid sprayer 31 is arranged below the process gas inlet 36 in the lower middle part of the condensation spray device, and cannot spray to all positions inside the condensation spray device 3, especially the position above the process gas inlet 36. Therefore, a hot solvent sprayer 34 is installed on the top of the condensation spray device 3, and a spray solvent of 100°C or above is regularly sprayed in the condensation spray device to regularly flush the top of the condensation spray device 3.

[0048] The spraying cycle of the hot solvent can be determined by the pressure at the air outlet 14 of the condensation tower 1. When blockage occurs inside the condensation spray device 3, especially at the upper end, the pressure at the air outlet 14 at the top of the condensation tower 1 approaches the air inlet pressure. If the inside of the condensation spray device 3 is unobstructed, the pressure at the air outlet 14 at the top of the condensation tower 1 approaches the vacuum pump pressure. Specifically, the spraying cycle can be set to spray once every 2-6 hours.

[0049] An exhaust gas outlet 51 , a circulating gas detector 52 and a circulating gas recycling valve 53 are also provided on the circulating gas pipeline between the vacuum pump 5 and the gas supply port 2 .

[0050] The following is the overall process flow of the polyester solid phase viscosity enhancement of the present invention:

[0051] Material (polyester polymer): silo → crystallization preheater → polycondensation tower (for solid phase viscosity enhancement) → discharge.

[0052] Circulating gas flow (process gas) entering the polycondensation tower: the process gas flow delivered from the gas supply port is mixed with the circulating gas flow from the vacuum pump → enters the preheater in multiple ways → enters the polycondensation tower → rises to the top of the polycondensation tower and flows out → sprays and condenses in the condensation spray device (because the gas coming out of the polycondensation tower contains monomers and oligomers, the gas needs to be cooled to below the melting point of the monomers and oligomers, and the small molecules in the gas need to be dissolved and removed by spraying solvent) → gas-liquid separation tank → filler or molecular sieve → vacuum pump (or with fan) → returns to the gas supply port.

[0053] The present invention is described in detail below through examples and comparative examples.

[0054] The polyester polymers used in the following examples and comparative examples are all polyglycolic acid. The product properties of polyglycolic acid before entering the polycondensation tower are as follows: particle size of 0-3 mm, melt index of 20-50 g / 10 min, 230° C., 2.16 kg, weight average molecular weight of 10w-15w, and residual monomer of 1-5%.

[0055] The following methods were used to test the product performance in the embodiments and comparative examples:

[0056] Particle size testing

[0057] Place the particles in a 7-20 mesh sieve, and use mechanical vibration or manual method to make the particles pass through the sieve until the desired particles are obtained.

[0058] Melt index test

[0059] The melt index of the polymer is tested according to the following method: 1) Dry the polymer in a vacuum drying oven at 105°C for 3h; 2) Set the test temperature of the test instrument to 230°C and preheat the instrument; 3) After the temperature stabilizes, 4-7g of the dried polymer is loaded into the barrel through a funnel, and the piston is inserted into the barrel to compact the dried polymer and heat it for 4 minutes; 4) Keep it under a load of 2.16kg for 10s, and then cut a section every 10s, and get a total of ten sections; 5) Weigh the mass of each sample and calculate its MFR. MFR = 600W / t (g / 10min), where W is the average mass of each sample, and t is the cutting time interval of each section.

[0060] Weight average molecular weight determination

[0061] The sample was dissolved in a 5 mmol / L sodium trifluoroacetate hexafluoroisopropanol solution to obtain a 0.05-0.3 wt% (mass fraction) solution. The solution was then filtered through a polytetrafluoroethylene filter with a pore size of 0.4 μm. 20 μL of the filtered solution was added to a gel permeation chromatography (GPC) injector to determine the molecular weight of the sample. Five standard molecular weights of methyl methacrylate with different molecular weights were used for molecular weight calibration.

[0062] Residual monomer test

[0063] Take about 0.5g of the sample and place it in a sealed container. Accurately add 15ml of hexafluoroisopropanol to dissolve it. After the dissolution is complete, transfer the test solution to a 100ml round-bottom (flat-bottom) flask, add 15ml of hexafluoroisopropanol, brush it clean in a sealed container, transfer it to the flask, accurately add 10ml of acetone, shake to precipitate the polymer, shake to dissolve, filter, and take the filtrate; take 1μl of the above-mentioned reference solution and test solution respectively, inject them into the gas chromatograph, record the chromatogram, and calculate the content of residual small molecules.

[0064] Example 1

[0065] use Figure 1The polyester solid phase thickening system shown is carried out as follows: the polyester polymer polyglycolic acid is preheated by the crystallization preheater 6 and then passed into the polycondensation tower 1 for solid phase thickening, the process gas nitrogen delivered by the gas supply port 2 is mixed with the circulating nitrogen gas flow from the vacuum pump 5, and then preheated by three gas supply pipelines 13, and the nitrogen enters the polycondensation tower 1 after preheating, and the nitrogen gas flows into the condensation spray device 3 from the gas outlet 14 at the top of the polycondensation tower 1, and the nitrogen gas flow is sprayed with the spray solvent methyl glycolate (MG) in the condensation spray device 3, and the nitrogen gas flow and the spray solvent MG enter the gas-liquid separation tank 4 after passing through the condensation spray device 3, and the spray solvent MG containing small molecules is circulated into the condensation spray device 3 after passing through the gas-liquid separation tank 3 for repeated use, and the nitrogen returns to the gas supply port 2 through the vacuum pump 5 after passing through the gas-liquid separation tank 3 for repeated use. The condensation spray device 3 is regularly sprayed and flushed with the hot spray solvent methyl glycolate (hot MG) through the hot solvent sprayer 34. After the solid phase thickening reaction is completed, the material polyglycolic acid is discharged from the discharge port 12 at the bottom of the polycondensation tower 1 to obtain the solid phase thickened polyglycolic acid.

[0066] Among them, the crystallization preheater temperature is 190°C, the crystallization reaction time is 20min, the condensation tower temperature is 190°C, the solid phase viscosity increasing reaction time is 2h, the condensation tower is a gas negative pressure atmosphere with an absolute pressure of 20kpa, and the gas-to-material ratio of the process gas entering the condensation tower to the polyester polymer in the condensation tower is 1:2L / kg; the inlet pressure of each nitrogen gas is 0.75bar, the condensation temperature of the condensation spray device is set to 30°C, and the hot MG temperature is 100°C.

[0067] The following are the performance parameters of the polyglycolic acid in Example 1 before and after entering the polycondensation tower.

[0068] Melt index Weight average molecular weight Residual monomer Before polycondensation 45g / 10min 107830 4.8％ After polycondensation 20g / 10min 148200 1.5％

[0069] Example 2

[0070] use Figure 1 The polyester solid phase viscosity increasing system shown in the embodiment is carried out. Compared with Example 1, the crystallization preheater temperature is 195°C, the crystallization reaction time is 20min, the polycondensation tower temperature is 195°C, the solid phase viscosity increasing reaction time is 2h, the polycondensation tower is a gas negative pressure atmosphere with an absolute pressure of 10kPa, and the gas-to-material ratio of the process gas entering the polycondensation tower to the polyester polymer in the polycondensation tower is 1:5L / kg;

[0071] The inlet pressure of nitrogen was 0.75 bar, the condensation temperature of the condensation spray device was set to 30 °C, and the hot MG temperature was 100 °C.

[0072] The following are the performance parameters of polyglycolic acid before and after entering the polycondensation tower in Example 2:

[0073] Melt index Weight average molecular weight Residual monomer Before polycondensation 42g / 10min 111500 3.5％ After polycondensation 24g / 10min 144100 1.50％

[0074] Example 3

[0075] use Figure 1 The polyester solid phase viscosity increasing system shown in the embodiment is carried out. Compared with Example 1, the crystallization preheater temperature is 200°C, the crystallization reaction time is 20min, the polycondensation tower temperature is 200°C, the solid phase viscosity increasing reaction time is 3h, the polycondensation tower is a gas negative pressure atmosphere with an absolute pressure of 30kpa, and the gas-to-material ratio of the process gas entering the polycondensation tower to the polyester polymer in the polycondensation tower is 1:3L / kg;

[0076] The inlet pressure of nitrogen was 0.75 bar, the condensation temperature of the condensation spray device was set to 30 °C, and the hot MG temperature was 100 °C.

[0077] The following are the performance parameters of the polyglycolic acid in Example 3 before and after entering the polycondensation tower.

[0078] Melt index Weight average molecular weight Residual monomer Before polycondensation 31g / 10min 137931 2.5％ After polycondensation 16g / 10min 178560 1.1％

[0079] Example 4

[0080] use Figure 1 The polyester solid phase viscosity increasing system shown in the embodiment is carried out. Compared with Example 1, the crystallization preheater temperature is 210°C, the crystallization reaction time is 30min, the polycondensation tower temperature is 210°C, the solid phase viscosity increasing reaction time is 6h, the polycondensation tower is a gas negative pressure atmosphere with an absolute pressure of 30kpa, and the gas-to-material ratio of the process gas entering the polycondensation tower to the polyester polymer in the polycondensation tower is 1:3L / kg;

[0081] The inlet pressure of nitrogen was 0.75 bar, the condensation temperature of the condensation spray device was set to 25 °C, and the hot MG temperature was 100 °C.

[0082] The following are the performance parameters of the polyglycolic acid in Example 4 before and after entering the polycondensation tower.

[0083] Melt index Weight average molecular weight Residual monomer Before polycondensation 28g / 10min 142385 2.1％ After polycondensation 13g / 10min 178400 0.81％

[0084] Example 5

[0085] use Figure 1 The polyester solid phase viscosity increasing system shown in the embodiment is carried out. Compared with Example 1, the crystallization preheater temperature is 205°C, the crystallization reaction time is 30min, the polycondensation tower temperature is 205°C, the solid phase viscosity increasing reaction time is 30h, the polycondensation tower is a gas negative pressure atmosphere with an absolute pressure of 50kpa, and the gas-to-material ratio of the process gas entering the polycondensation tower to the polyester polymer in the polycondensation tower is 1:2L / kg;

[0086] The inlet pressure of nitrogen was 0.75 bar, the condensation temperature of the condensation spray device was set to 25 °C, and the hot MG temperature was 100 °C.

[0087] The following are the performance parameters of the polyglycolic acid in Example 5 before and after entering the polycondensation tower.

[0088] Melt index Weight average molecular weight Residual monomer Before polycondensation 25g / 10min 148609 1.5％ After polycondensation 8g / 10min 194569 0.54％

[0089] Example 6

[0090] use Figure 1 The polyester solid phase viscosity increasing system shown in the embodiment is carried out. Compared with Example 1, the crystallization preheater temperature is 220°C, the crystallization reaction time is 30min, the polycondensation tower temperature is 220°C, the solid phase viscosity increasing reaction time is 2h, the gas negative pressure atmosphere absolute pressure is 40kPa, and the gas-to-material ratio of the process gas entering the polycondensation tower to the polyester polymer in the polycondensation tower is 1:3L / kg;

[0091] The inlet pressure of nitrogen was 0.75 bar, the condensation temperature of the condensation spray device was set to 25 °C, and the hot MG temperature was 100 °C.

[0092] The following are the performance parameters of the polyglycolic acid in Example 6 before and after entering the polycondensation tower.

[0093] Melt index Weight average molecular weight Residual monomer Before polycondensation 20g / 10min 150423 1.3％ After polycondensation 13g / 10min 173510 0.65％

[0094] Comparative Example 1

[0095] Compared with Example 1, the solid phase thickening is carried out under negative pressure, but nitrogen is not continuously introduced during the whole process of the solid phase thickening.

[0096] The same raw materials as in Example 1 were used, with a crystallization preheater temperature of 190°C, a crystallization reaction time of 20 min, a condensation tower temperature of 190°C, a solid phase viscosity increasing reaction time of 2 h, a gas negative pressure atmosphere in the condensation tower, and an absolute pressure of 20 kPa. Similarly, the condensation spray device was set to a condensation temperature of 30°C and a hot MG temperature of 100°C.

[0097] The following are the performance parameters of the polyglycolic acid in Comparative Example 1 before and after entering the polycondensation tower.

[0098] Melt index Weight average molecular weight Residual monomer Before polycondensation 45g / 10min 107830 4.8％ After polycondensation 38g / 10min 114671 3.7％

[0099] Comparative Example 2

[0100] Compared with Example 1, nitrogen was continuously introduced during the entire solid phase thickening process, but the solid phase thickening was carried out under positive pressure.

[0101] The same raw materials as in Example 1 were used, with a crystallization preheater temperature of 190°C, a crystallization reaction time of 20 min, a condensation tower temperature of 190°C, a solid-phase viscosity increasing reaction time of 2 h, a positive pressure atmosphere in the condensation tower, a gas-to-material ratio of the process gas entering the condensation tower to the polyester polymer in the condensation tower of 1:2 L / kg; the nitrogen inlet pressure was 3 bar, the condensation temperature of the condensation spray device was set to 30°C, and the hot MG temperature was 100°C.

[0102] The following are the performance parameters of the polyglycolic acid in Comparative Example 2 before and after entering the polycondensation tower.

[0103] Melt index Weight average molecular weight Residual monomer Before polycondensation 45g / 10min 107830 4.8％ After polycondensation 40g / 10min 110584 4.2％

[0104] Comparative Example 3

[0105] Compared with Example 1, during the gas purification process, only the tube-in-tube condenser is used to cool and purify the nitrogen flowing out of the condensation tower, and no spray solvent is used to spray the process gas flow. The nitrogen is condensed by the condenser and then recycled. The temperature of the condenser is set to 30°C.

[0106] The same raw materials as in Example 1 were used.

[0107] The following are the performance parameters of the polyglycolic acid in Comparative Example 3 before and after entering the polycondensation tower.

[0108] Melt index Weight average molecular weight Residual monomer Before polycondensation 45g / 10min 107830 4.8％ After polycondensation 37g / 10min 119104 3.5％

Claims

1. A solid phase viscosity increasing method for polyester, characterized in that: The method comprises: passing the polyester polymer through a crystallization preheater and then passing it into a polycondensation tower for solid phase viscosity enhancement; during the whole process of solid phase viscosity enhancement, continuously passing process gas into the polycondensation tower, the inlet pressure of the process gas is 0.1 bar-100 bar, the absolute pressure in the polycondensation tower is maintained at 1 kpa-50 kpa, the reaction temperature in the polycondensation tower is 190-220° C., and the reaction time is 2-30 hours; during the reaction process, the process gas is made to flow into a gas purification device from the gas outlet at the top of the polycondensation tower, the process gas is spray-cooled and gas-liquid separated by the gas purification device, and the purified process gas is returned to the polycondensation tower for recycling.

2. The solid phase viscosity increasing method of polyester according to claim 1, characterized in that: The polyester polymer is controlled to enter and exit the polycondensation tower; along the height of the polycondensation tower, the process gas is controlled to enter the polycondensation tower in at least two ways, preferably, the flow rate, temperature, or pressure of each gas path is different.

3. The solid phase viscosity increasing method of polyester according to claim 1, characterized in that: The volume ratio of the process gas entering the polycondensation tower during the solid phase viscosity increasing process to the mass ratio of the polyester polymer in the polycondensation tower is defined as the gas-to-material ratio, and the gas-to-material ratio is controlled to be 1: (0.5-5) L / kg.

4. The solid phase viscosity increasing method of polyester according to claim 1, characterized in that: The polyester polymer is a polyglycolic acid copolymer. The residual monomer content of the polyglycolic acid copolymer before entering the polycondensation tower is 1%-5%, and the residual monomer content after solid phase viscosity enhancement is 0.5%-1.5%.

5. The solid phase viscosity increasing method of polyester according to claim 1, characterized in that: The temperature in the polycondensation tower is set to be the same as the temperature in the crystallization preheater; the heating method of the crystallization preheater is a fluidized bed, screw conveying or infrared drying.

6. The solid phase viscosity increasing method for polyester according to any one of claims 1 to 5, characterized in that: The gas purification device includes a condensation spray device and a gas-liquid separation tank; The process gas flows into the condensation spray device through the gas outlet of the polycondensation tower, and is sprayed and cooled by the spray solvent, and the temperature of the condensation spray device is controlled to be lower than 85° C. The spray solvent is selected from at least one of methyl glycolate, ethyl glycolate, butyl glycolate, and isobutyl glycolate; The process gas and the spray solvent enter the gas-liquid separation tank after passing through the condensation spray device, and the liquid level of the spray solvent in the gas-liquid separation tank is controlled by a liquid level meter; The process gas is returned to the polycondensation tower for recycling after passing through the gas-liquid separation tank, and the spray solvent is circulated into the condensation spray device after passing through the gas-liquid separation tank to spray the process gas.

7. The solid phase viscosity increasing method of polyester according to claim 6, characterized in that: A packing layer or a molecular sieve layer is provided above the gas-liquid separation tank, and the process gas flows out of the gas-liquid separation tank after passing through the packing layer or the molecular sieve layer provided above the gas-liquid separation tank, and returns to the polycondensation tower for recycling; Preferably, the gas purification device comprises two gas-liquid separation tanks connected in parallel, one gas-liquid separation tank is connected to the condensation spray device, and the other gas-liquid separation tank is provided with a spray liquid replenishing port for replenishing the spray solvent.

8. The solid phase viscosity increasing method of polyester according to claim 6, characterized in that: A hot solvent sprayer is provided on the top of the condensation spray device, and a spray solvent of 100°C or above is regularly sprayed in the condensation spray device through the hot solvent sprayer to regularly flush the top of the condensation spray device.

9. A system for carrying out the solid phase viscosity increasing method of polyester according to any one of claims 1 to 8, characterized in that: The system includes; A polycondensation tower (1), the polycondensation tower having a feed inlet (11), a discharge outlet (12), a gas supply pipeline (13) and a gas outlet (14), the number of the gas supply pipelines (13) being at least two, each gas supply pipeline being provided with a flow meter (15), a preheater (16) and a pressure regulating valve (17); A gas supply port (2), the gas supply port (2) being in communication with each gas supply pipeline (13), and the process gas is introduced into the polycondensation tower (1) through the gas supply pipeline (13); A gas purification device, the gas purification device comprising a condensation spray device (3) and a gas-liquid separation tank (4), the condensation spray device (3) having a circulating liquid sprayer (31) and a gas-liquid outlet (32); the gas-liquid separation tank (4) having a gas-liquid inlet (41), a gas outlet (42), and a liquid outlet (43); the gas-liquid outlet (32) of the condensation spray device (3) is connected to the gas-liquid inlet (41) of the gas-liquid separation tank (4) through a pipeline, the liquid outlet (43) of the gas-liquid separation tank (4) is connected to the circulating liquid sprayer (31) through a pipeline, and a circulating spray pump (33) is provided therebetween; the gas outlet (42) of the gas-liquid separation tank (4) is connected to the gas supply port (2) through a pipeline, and a vacuum pump (5) is provided therebetween; A crystallizer (6), wherein the crystallizer (6) is connected to a feed inlet (11) of a polycondensation tower (1) via a pipeline.

10. The system for solid phase viscosity enhancement of polyester according to claim 9, characterized in that: A hot solvent sprayer (34) is provided on the top of the spray condenser (3); An airflow filter layer (45) is provided above the interior of the gas-liquid separation tank (4), and the airflow filter layer (45) is a filler layer or a molecular sieve layer; A liquid level meter (47) is provided inside the gas-liquid separation tank (4); A sampling and recovery port (35) is also provided on the pipeline between the liquid outlet (43) of the gas-liquid separation tank (4) and the circulating liquid sprayer (31).

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