Ion exchange based ptmeg demethanation process
By employing an ion-exchange-based PTMEG sodium removal process, utilizing dual resin beds and online regeneration technology, the shortcomings of neutralization and water washing methods have been overcome, enabling continuous and high-efficiency PTMEG production, improving product quality, and reducing energy consumption.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- INNER MONGOLIA JUNZHENG CHEM IND CO LTD
- Filing Date
- 2026-04-01
- Publication Date
- 2026-05-29
AI Technical Summary
In the existing PTMEG sodium removal process, the neutralization method easily introduces impurities and is difficult to control in terms of precision, while the water washing method results in high product loss, long process and high energy consumption, making continuous production impossible and leading to low production efficiency.
The process employs a PTMEG-based sodium removal process using ion exchange, which includes controlling temperature and pressure in a reactive distillation column, using an ion exchanger with dual distributors and dual resin beds, and combining an automatic switching valve group to achieve online regeneration and alternating operation of the resin beds. Sodium removal is carried out through a styrene-based strong acid cation exchange resin in the ion exchanger, with online sodium ion concentration detection and resin regeneration parameter optimization.
It enables continuous and efficient PTMEG production, reduces production costs, extends resin lifespan, and improves product purity and the uniformity of molecular weight distribution.
Smart Images
Figure CN122103548A_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of PTMEG production and refining technology, and more particularly to a PTMEG demethylation sodium process based on ion exchange. Background Technology
[0002] PTMEG is a white, waxy solid or colorless liquid and a key raw material for the production of spandex and polyurethane elastomers. It imparts excellent properties such as high resilience and hydrolysis resistance to the materials. The production of PTMEG requires a refining process. Using tetrahydrofuran as a raw material, a crude product is generated through a catalytic polymerization reaction. Then, a series of physicochemical treatments, such as neutralization, filtration, dehydration, and distillation, are carried out to remove catalyst residues, moisture, and by-products, thereby obtaining a high-purity, high-quality PTMEG product.
[0003] Chinese patent CN111574703A discloses a high-efficiency method for preparing polytetramethylene ether glycol. The method involves: 1) mixing tetrahydrofuran with added diethyl ether and a catalyst using a strengthened disperser and performing a polymerization reaction at 50–52°C; 2) separating the catalyst from the reaction solution by centrifugation; 3) removing most of the tetrahydrofuran and all of the diethyl ether from the remaining reaction solution by distillation; centrifuging the concentrated solution after mixing it with an extractant; 4) adsorbing the remaining mixture onto an adsorption column to completely remove the catalyst, followed by distillation to remove the tetrahydrofuran; 5) settling the remaining mixture at 38°C and then purifying it to obtain polytetramethylene ether glycol. This invention improves the upper limit of polytetramethylene ether glycol production by adding an appropriate amount of diethyl ether to tetrahydrofuran and by using a strengthened disperser to increase catalyst dispersion and reaction rate, while appropriately lowering the reaction temperature through circulating heat exchange to increase the equilibrium conversion rate.
[0004] Regarding the above and existing related technologies, the inventors believe that the following defects often exist: the existing methods for removing sodium methanol from PTMEG commonly use neutralization and water washing. Neutralization by adding acid to neutralize sodium ions can easily introduce impurities, and the degree of neutralization is difficult to control precisely. Water washing can cause product loss due to the miscibility of PTMEG with water, and additional dehydration is required. The process is long and energy consumption is high. Both methods are difficult to use for continuous production, resulting in low production efficiency. Summary of the Invention
[0005] The technical problem to be solved by this invention is that existing technologies for removing sodium methanol from PTMEG mostly use neutralization and water washing methods. Neutralization is prone to introducing impurities and is difficult to control in terms of precision, while water washing results in high product loss, long process and high energy consumption. Neither of these methods can be used for continuous production, and the overall efficiency is low. Therefore, we propose a PTMEG sodium methanol removal process based on ion exchange.
[0006] To achieve the above objectives, this application adopts the following technical solution: a PTMEG desodium methanol removal process based on ion exchange, comprising the following steps: S1: 99.8% PTMEA and 99.2% methanol, along with sodium methoxide catalyst that has been temporarily stored in the feed tank and filtered to remove impurities, are fed into a static mixer and mixed thoroughly before being transferred to a reactive distillation column. The temperature inside the column is controlled to be stable at 70℃~75℃ and the pressure is stabilized at 22kPa. Methanol gas at 85℃ is used as stripping gas to remove the methyl acetate byproduct from the top of the column, and a 72.6% PTMEG solution is continuously produced from the bottom of the column. S2: The 72.6% PTMEG solution is filtered through a precision filter to remove impurities, cooled to 58℃~62℃, diluted with 99.2% methanol to 25%w / w~35%w / w according to the PTMEG molecular weight grade, and allowed to stand for 10min~15min to ensure that the solution is uniform and free of impurities. After being preheated and stabilized in a flow bath, it is sent to the subsequent ion exchange desodium removal process. S3: The pretreated PTMEG solution is fed into the ion exchanger at a flow rate of 1.2 m³ / h to 1.8 m³ / h, with the temperature controlled at 58℃ to 62℃ and the pressure stabilized at 18 kPa to 22 kPa. The exchanger is equipped with a dual distributor and a dual resin bed, filled with styrene-based strong acid cation exchange resin that is methanol resistant, has an adsorption capacity ≥2.0 eq / L, a particle size of 0.3 mm to 1.2 mm, and a porosity of 40% to 50%. The dual bed switching is controlled by a valve group. S4: When the resin adsorption in the ion exchanger is about to reach the saturation threshold, the resin bed is switched to regeneration mode. The residual liquid is discharged after sodium removal. The exhausted resin is regenerated by sequentially being rinsed with methanol, washed with deionized water, rinsed with dilute sulfuric acid, washed with water until neutral, and protected with methanol. It is used as a standby bed and alternates with the working bed to achieve continuous production without stopping the machine.
[0007] Preferably, in S1, the sodium methoxide catalyst has a sodium methoxide concentration of 30%, the filter is a filtration device with a precision capable of removing impurities larger than 20 micrometers, and the sodium methoxide catalyst is sent to the static mixer after being filtered by the filter.
[0008] Preferably, in S1, the 85°C high-temperature methanol gas is supplied by the methanol evaporator, the inert gas in the reactive distillation column is vented after cryogenic treatment, and the pressure of the reactive distillation column is maintained stable by a range-controlled vent valve and a nitrogen replenishment valve.
[0009] Preferably, in S2, the PTMEG solution is cooled to 58°C to 62°C to avoid side reactions in the presence of strong acid resin in subsequent ion exchange processes, and the solution is diluted to 25% w / w to 35% w / w to prevent excessive pressure differential in the resin bed within the ion exchanger.
[0010] Preferably, the temperature of the preheating tank in S2 is matched with the temperature of the cooled PTMEG solution to ensure that the temperature of the PTMEG solution fed into the ion exchanger is stable at 58°C to 62°C.
[0011] Preferably, in S3, the dual distributor is a symmetrical liquid distributor, which can make the PTMEG solution uniformly distributed on the surface of the resin bed. The valve group is an automatic switching valve group, which can realize uninterrupted switching between online and regeneration modes of the dual resin bed.
[0012] Preferably, the adsorption capacity of the strong acid cation exchange resin in S3 is 2.0 eq / L to 2.5 eq / L, and the resin is a styrene-based strong acid cation exchange resin resistant to methanol corrosion.
[0013] Preferably, in S4, the sodium ion concentration detector is an online real-time detection device. When the sodium ion concentration in the PTMEG solution reaches the preset threshold, it is determined that the resin adsorption is about to reach the saturation threshold. Then, the resin bed is switched to regeneration mode through the valve group, and the feed of the ion exchanger is switched to the standby resin bed to ensure the continuous operation of the ion exchange sodium removal process.
[0014] Preferably, when rinsing the failed resin with methanol in S4, the rinsing flow rate is the same as the feed flow rate of the PTMEG solution in S3, and the methanol rinsing time is 15 min to 20 min to ensure that the residual PTMEG solution in the resin bed is completely replaced.
[0015] Preferably, when regenerating the failed resin in S4, the dilute sulfuric acid used is a dilute sulfuric acid solution with a mass concentration of 5% to 8%. The criterion for determining neutrality by washing with water is that the pH value of the rinsing water is 6.5 to 7.5. Methanol protection involves filling the regenerated resin bed with methanol to prevent the resin from absorbing moisture and becoming ineffective.
[0016] The technical effects and advantages of this invention are as follows: This invention achieves complete PTMEA conversion by precisely controlling the temperature and pressure of the alcoholysis reaction tower and removing byproducts through high-temperature methanol stripping. Simultaneously, targeted pretreatment of the PTMEA solution, including filtration, temperature control, and dilution, avoids side reactions under strong acid resin conditions, prevents excessive pressure differential in the resin bed, and ensures the efficiency and stability of sodium removal through ion exchange. The invention employs a dual-distributor + dual-resin-bed ion exchanger structure, coupled with an automatic switching valve group, to achieve online regeneration and alternating operation of the resin bed without downtime, significantly improving the efficiency of continuous production. Furthermore, it optimizes resin selection and regeneration parameters, extends resin life, and reduces production costs. Attached Figure Description
[0017] The disclosure of this invention is illustrated with reference to the accompanying drawings. It should be understood that the drawings are for illustrative purposes only and are not intended to limit the scope of protection of this invention. In the drawings, the same reference numerals are used to refer to the same parts: Figure 1 This is an overall flow diagram of the PTMEG sodium removal process of the present invention; Figure 2 This is a schematic diagram of the online resin regeneration process of the present invention. Detailed Implementation
[0018] It is readily understood that, based on the technical solution of this invention, those skilled in the art can propose various interchangeable structural methods and implementations without altering the essential spirit of the invention. Therefore, the following detailed embodiments and accompanying drawings are merely illustrative examples of the technical solution of this invention and should not be considered as the entirety of the invention or as limitations or restrictions on the technical solution of this invention.
[0019] Comparative Example A PTMEG process for removing sodium methanol based on ion exchange includes the following steps: S1: PTMEA with a purity of 99.8%, methanol with a purity of 99.2%, and sodium methoxide catalyst with 30% purity are directly mixed and fed into a reactive distillation column. The temperature inside the column is controlled at 70-75℃ and the pressure at 22kPa. Methyl acetate byproduct is removed by stripping with methanol gas at 85℃. A 72.6% PTMEG solution is produced at the bottom of the column. S2: The 72.6% PTMEG solution is pumped to a conventional coarse filter for filtration. The filtered solution is then directly sent to the ion exchange desodium removal process through the delivery pipeline. S3: The above PTMEG solution is fed into a single resin bed ion exchanger at a flow rate of 2.0 m³ / h and operated at ambient pressure and natural temperature. The exchanger is filled with a strong acidic cation exchange resin with an adsorption capacity of 1.8 eq / L for adsorption. S4: After the resin adsorbs, stop the ion exchange desodium removal process and regenerate the resin. During regeneration, rinse with methanol and then rinse directly with dilute sulfuric acid. After completion, restart the ion exchange process to continue working.
[0020] Example 1 Reference Figures 1-2 A PTMEG demethylation process based on ion exchange includes the following steps: S1: PTMEA with a purity of 99.8% and methanol with a purity of 99.2% and sodium methoxide catalyst containing 30% methanol are fed into a static mixer and stirred. The mixture is then transferred to a reactive distillation column. Subsequently, the 30% sodium methoxide catalyst, filtered through a 20-micron precision filter, is fed into the static mixer and stirred thoroughly. The mixture is then transferred to the reactive distillation column, where the temperature is controlled at 72°C and the pressure at 22 kPa. High-temperature methanol gas at 85°C is provided by a methanol evaporator as stripping gas to continuously remove the methyl acetate byproduct generated at the top of the column. A stable 72.6% PTMEG solution is produced at the bottom of the column. The inert gas in the column is vented after being cryogenically treated at -40°C. The pressure in the column is maintained stable by using a split-range control vent valve and a nitrogen replenishment valve. S2: The 72.6% PTMEG solution is pumped to a precision filter to remove residual small solid impurities. The solution temperature is then precisely cooled to 60°C using a cooling device. It is then diluted to a concentration of 30% w / w with 99.2% methanol. After pretreatment, the solution is allowed to stand for 12 minutes to ensure that it is homogeneous, free of stratification and impurities. After stabilizing the temperature in a 60°C preheated flow bath, it is sent to the ion exchange sodium removal process. S3: The pretreated PTMEG solution is fed into the ion exchanger at a flow rate of 1.5 m³ / h. The temperature inside the controller is 60℃ and the pressure is 20 kPa. The symmetrical dual distributor inside the ion exchanger ensures that the solution is evenly distributed in the resin bed. The exchanger is filled with methanol-resistant styrene-based strong acid cation exchange resin with an adsorption capacity of 2.5 eq / L. The dual resin beds are alternately in working and standby states by an automatic switching valve group. S4. An online sodium ion concentration detector is used to monitor the sodium ion concentration of the PTMEG solution after sodium removal in real time. When the concentration reaches the preset threshold, it is determined that the resin adsorption is about to reach the saturation threshold. Then, the resin bed is switched to regeneration mode through an automatic switching valve group. At the same time, the feed is seamlessly switched to the standby resin bed. The remaining PTMEG solution in the original working bed chamber is discharged after further sodium removal through this resin bed, with no product waste. The failed resin is regenerated in a standardized online manner using methanol rinsing at a flow rate of 1.5 m³ / h for 18 minutes, followed by deionized water rinsing, 6% dilute sulfuric acid rinsing, and water washing until the effluent pH=7.0 → methanol full protection. After regeneration, it is used as a standby bed, realizing continuous operation of the process without downtime.
[0021] Example 2 Reference Figures 1-2 A PTMEG demethylation process based on ion exchange includes the following steps: S1: PTMEA with a purity of 99.8% and methanol with a purity of 99.2% and sodium methoxide catalyst containing 30% methanol are fed into a static mixer and stirred. The mixture is then transferred to a reactive distillation column. Subsequently, the 30% sodium methoxide catalyst, filtered through a 20-micron precision filter, is fed into the static mixer and stirred thoroughly. The mixture is then transferred to the reactive distillation column, where the temperature is controlled at 72°C and the pressure at 22 kPa. High-temperature methanol gas at 85°C is provided by a methanol evaporator as stripping gas to continuously remove the methyl acetate byproduct generated at the top of the column. A stable 72.6% PTMEG solution is produced at the bottom of the column. The inert gas in the column is vented after being cryogenically treated at -40°C. The pressure in the column is maintained stable by using a split-range control vent valve and a nitrogen replenishment valve. S2: The 72.6% PTMEG solution is pumped to a precision filter to remove residual small solid impurities. The solution temperature is then precisely cooled to 60°C using a cooling device. It is then diluted to a concentration of 30% w / w with 99.2% methanol. After pretreatment, the solution is allowed to stand for 12 minutes to ensure that it is homogeneous, free of stratification and impurities. After stabilizing the temperature in a 60°C preheated flow bath, it is sent to the ion exchange sodium removal process. S3: The pretreated PTMEG solution is fed into the ion exchanger at a flow rate of 1.2 m³ / h. The temperature inside the controller is 60℃ and the pressure is 20 kPa. The symmetrical dual distributor inside the ion exchanger ensures that the solution is evenly distributed in the resin bed. The exchanger is filled with methanol-resistant styrene-based strong acid cation exchange resin with an adsorption capacity of 2.5 eq / L. The dual resin beds are alternately in working and standby states by an automatic switching valve group. S4. An online sodium ion concentration detector is used to monitor the sodium ion concentration of the PTMEG solution after sodium removal in real time. When the concentration reaches the preset threshold, it is determined that the resin adsorption is about to reach the saturation threshold. Then, the resin bed is switched to regeneration mode through an automatic switching valve group. At the same time, the feed is seamlessly switched to the standby resin bed. The remaining PTMEG solution in the original working bed chamber is discharged after further sodium removal through this resin bed, with no product waste. The failed resin is regenerated in a standardized online manner using methanol rinsing at a flow rate of 1.5 m³ / h for 18 minutes, followed by deionized water rinsing, 6% dilute sulfuric acid rinsing, and water washing until the effluent pH=7.0 → methanol full protection. After regeneration, it is used as a standby bed, realizing continuous operation of the process without downtime.
[0022] Example 3 Reference Figures 1-2 A PTMEG demethylation process based on ion exchange includes the following steps: S1: PTMEA with a purity of 99.8% and methanol with a purity of 99.2% and sodium methoxide catalyst containing 30% methanol are fed into a static mixer and stirred. The mixture is then transferred to a reactive distillation column. Subsequently, the 30% sodium methoxide catalyst, filtered through a 20-micron precision filter, is fed into the static mixer and stirred thoroughly. The mixture is then transferred to the reactive distillation column, where the temperature is controlled at 72°C and the pressure at 22 kPa. High-temperature methanol gas at 85°C is provided by a methanol evaporator as stripping gas to continuously remove the methyl acetate byproduct generated at the top of the column. A stable 72.6% PTMEG solution is produced at the bottom of the column. The inert gas in the column is vented after being cryogenically treated at -40°C. The pressure in the column is maintained stable by using a split-range control vent valve and a nitrogen replenishment valve. S2: The 72.6% PTMEG solution is pumped to a precision filter to remove residual small solid impurities. The solution temperature is then precisely cooled to 60°C using a cooling device. It is then diluted to a concentration of 35% w / w with 99.2% methanol. After pretreatment, the solution is allowed to stand for 12 minutes to ensure that it is homogeneous, free of stratification and impurities. After stabilizing the temperature in a 60°C preheated flow bath, it is sent to the ion exchange sodium removal process. S3: The pretreated PTMEG solution is fed into the ion exchanger at a flow rate of 1.5 m³ / h. The temperature inside the controller is 60℃ and the pressure is 20 kPa. The symmetrical dual distributor inside the ion exchanger ensures that the solution is evenly distributed in the resin bed. The exchanger is filled with methanol-resistant styrene-based strong acid cation exchange resin with an adsorption capacity of 2.5 eq / L. The dual resin beds are alternately in working and standby states by an automatic switching valve group. S4. An online sodium ion concentration detector is used to monitor the sodium ion concentration of the PTMEG solution after sodium removal in real time. When the concentration reaches the preset threshold, it is determined that the resin adsorption is about to reach the saturation threshold. Then, the resin bed is switched to regeneration mode through an automatic switching valve group. At the same time, the feed is seamlessly switched to the standby resin bed. The remaining PTMEG solution in the original working bed chamber is discharged after further sodium removal through this resin bed, with no product waste. The failed resin is regenerated in a standardized online manner using methanol rinsing at a flow rate of 1.5 m³ / h for 18 minutes, followed by deionized water rinsing, 6% dilute sulfuric acid rinsing, and water washing until the effluent pH=7.0 → methanol full protection. After regeneration, it is used as a standby bed, realizing continuous operation of the process without downtime.
[0023] Comparison table of process effects between the examples and comparative examples
[0024] Comparison table of process parameters between the examples and comparative examples
[0025] Working principle: High-purity PTMEA, methanol, and sodium methoxide catalyst (filtered and temporarily stored through a 20-micron filter) are first mixed in a static mixer and fed into a reactive distillation column. The temperature is precisely controlled at 70℃~75℃ and the pressure is stabilized at 22kPa. Methyl acetate byproducts from the top of the column are removed by methanol stripping at 85℃. Under the catalysis of sodium methoxide, the following alcoholysis reaction drives the equilibrium forward, achieving complete conversion of PTMEA. The formula for the alcoholysis reaction is:
[0026] After the alcoholysis reaction, a 72.6% PTMEG solution is produced at the bottom of the column. A small amount of inert gas is vented through cryogenic cooling and the material is recovered. The resulting solution is first subjected to precision filtration to remove impurities, cooled to 58℃~62℃, and then diluted with methanol to 25%w / w~35%w / w. After static homogenization and constant temperature pretreatment, side reactions caused by strong acid resins are avoided, and the bed pressure difference is stabilized. The pretreated material is stably fed into an ion exchanger equipped with a dual distributor. Under constant temperature and pressure, the exchange is completed with the help of methanol-resistant strong acid sulfonic acid resin. The resin dissociates hydrogen ions, and the negatively charged sulfonate groups adsorb sodium ions in the feed solution. The cation exchange reaction deeply removes sodium impurities. An online sodium ion detector monitors the resin saturation status in real time. The system automatically switches to the standby bed for continuous feeding via valve assembly. The residual liquid is fully treated with no product loss. The exhausted resin is regenerated online by sequentially undergoing methanol replacement, pure water washing, dilute sulfuric acid regeneration, water washing and neutralization, and methanol protection. Backwashing is used to reduce the bed pressure difference. The dual beds operate alternately without interruption. No external impurities are introduced throughout the process, and sodium ions are thoroughly removed. The resulting PTMEG has high purity and uniform molecular weight distribution. The resin life is extended, and energy consumption and product loss are reduced simultaneously, thus improving the efficiency of PTMEG production.
[0027] The technical scope of this invention is not limited to the content described above. Those skilled in the art can make various modifications and variations to the above embodiments without departing from the technical concept of this invention, and all such modifications and variations should fall within the protection scope of this invention.
Claims
1. A PTMEG sodium removal process based on ion exchange, characterized in that, Includes the following steps: S1: 99.8% PTMEA and 99.2% methanol, along with sodium methoxide catalyst that has been temporarily stored in the feed tank and filtered to remove impurities, are fed into a static mixer and mixed thoroughly before being transferred to a reactive distillation column. The temperature inside the column is controlled to be stable at 70℃~75℃ and the pressure is stabilized at 22kPa. Methanol gas at 85℃ is used as stripping gas to remove the methyl acetate byproduct from the top of the column, and a 72.6% PTMEG solution is continuously produced from the bottom of the column. S2: The 72.6% PTMEG solution is filtered through a precision filter to remove impurities, cooled to 58℃~62℃, diluted with 99.2% methanol to 25%w / w~35%w / w according to the PTMEG molecular weight grade, and allowed to stand for 10min~15min to ensure that the solution is uniform and free of impurities. After being preheated and stabilized in a flow bath, it is sent to the subsequent ion exchange desodium removal process. S3: The pretreated PTMEG solution is fed into the ion exchanger at a flow rate of 1.2 m³ / h to 1.8 m³ / h, with the temperature controlled at 58℃ to 62℃ and the pressure stabilized at 18 kPa to 22 kPa. The exchanger is equipped with a dual distributor and a dual resin bed, filled with styrene-based strong acid cation exchange resin that is methanol resistant, has an adsorption capacity ≥2.0 eq / L, a particle size of 0.3 mm to 1.2 mm, and a porosity of 40% to 50%. The dual bed switching is controlled by a valve group. S4: When the resin adsorption in the ion exchanger is about to reach the saturation threshold, the resin bed is switched to regeneration mode. The residual liquid is discharged after sodium removal. The exhausted resin is regenerated by sequentially being rinsed with methanol, washed with deionized water, rinsed with dilute sulfuric acid, washed with water until neutral, and protected with methanol. It is used as a standby bed and alternates with the working bed to achieve continuous production without stopping the machine.
2. The PTMEG demethylation process based on ion exchange as described in claim 1, characterized in that: The sodium methoxide catalyst in S1 has a sodium methoxide concentration of 30%, and the filter is a filtration device with a precision capable of removing impurities larger than 20 micrometers. The sodium methoxide catalyst is filtered by the filter and then sent to the static mixer.
3. The PTMEG sodium removal process based on ion exchange as described in claim 1, characterized in that: In S1, the 85°C high-temperature methanol gas is supplied by the methanol evaporator, the inert gas in the reactive distillation column is vented after cryogenic treatment, and the pressure of the reactive distillation column is maintained stable by a range-controlled vent valve and a nitrogen replenishment valve.
4. The PTMEG demethylation process based on ion exchange as described in claim 1, characterized in that: In step S2, the PTMEG solution is cooled to 58°C to 62°C to prevent side reactions from occurring in the presence of strong acid resin in subsequent ion exchange processes. The solution is also diluted to 25% w / w to 35% w / w to prevent excessive pressure differential in the resin bed within the ion exchanger.
5. The PTMEG demethylation process based on ion exchange as described in claim 1, characterized in that: The temperature of the preheating tank in S2 is matched with the temperature of the cooled PTMEG solution to ensure that the temperature of the PTMEG solution fed into the ion exchanger is stable at 58℃~62℃.
6. The PTMEG sodium removal process based on ion exchange as described in claim 1, characterized in that: The dual distributor in S3 is a symmetrical liquid distributor, which can make the PTMEG solution evenly distributed on the surface of the resin bed. The valve group is an automatic switching valve group, which can realize uninterrupted switching between online and regeneration modes of the dual resin bed.
7. The PTMEG demethylation process based on ion exchange as described in claim 1, characterized in that: The adsorption capacity of the strong acid cation exchange resin in S3 is 2.0 eq / L to 2.5 eq / L, and the resin is a styrene-based strong acid cation exchange resin resistant to methanol corrosion.
8. The PTMEG sodium removal process based on ion exchange as described in claim 1, characterized in that: The sodium ion concentration detector in S4 is an online real-time detection device. When the sodium ion concentration in the PTMEG solution reaches the preset threshold, it is determined that the resin adsorption is about to reach the saturation threshold. Then, the resin bed is switched to regeneration mode through the valve group, and the feed of the ion exchanger is switched to the standby resin bed to ensure the continuous operation of the ion exchange sodium removal process.
9. The PTMEG demethylation process based on ion exchange as described in claim 1, characterized in that: When the failed resin is flushed with methanol in S4, the flushing flow rate is the same as the feed flow rate of the PTMEG solution in S3, and the methanol flushing time is 15 min to 20 min to ensure that the residual PTMEG solution in the resin bed is completely replaced.
10. A process for the removal of sodium methoxide from PTMEG based on ion exchange as claimed in claim 1, wherein: When regenerating the failed resin in S4, the dilute sulfuric acid used is a dilute sulfuric acid solution with a mass concentration of 5% to 8%. The criterion for determining neutrality by washing with water is that the pH value of the rinsing water is 6.5 to 7.
5. Methanol protection involves filling the regenerated resin bed with methanol to prevent the resin from absorbing moisture and failing.