A dialysis membrane spinning ternary raw material integrated micro water precision measuring device and method

Abstract

The application discloses a dialysis membrane spinning ternary raw material integrated micro water precision determination device and method, the device includes coulomb method Karl Fischer electrolytic titration host computer, sealed liquid diaphragm sampling unit, double temperature zone program control Karl solid sample introduction unit, three-way switching electromagnetic valve, closed micro weighing module, spinning formula intelligent operation control system; the beneficial effect is, only a set of coul coul host computer is used, the ppm level precision moisture detection of DMAC, PES, PVP three different forms, different characteristics spinning raw materials is realized, unified detection reference, reduce equipment cost and system error; at the same time, the problems such as raw material detection side reaction, incomplete release of solid moisture, sample hygroscopicity interference are avoided, and the spinning formula intelligent accounting system is matched, the detection data directly guide production ratio correction are realized, and the ultra-high precision moisture control demand of high-end dialysis membrane spinning is met.

Description

Technical Field

[0001] This invention relates to the field of polymer membrane material detection technology, and in particular to an integrated micro-moisture precision determination device and method for dialysis membrane spinning ternary raw materials. Background Technology

[0002] The molding quality, pore size uniformity, water flux, sieving coefficient, and biocompatibility of hollow fiber hemodialysis membranes are highly dependent on the precise stability of the spinning solution formulation. Among these, the moisture content of the raw materials is a core key parameter affecting the phase separation rate, spinning solution viscosity, and membrane microstructure. The core spinning raw materials for dialysis membranes include three types of materials: polyethersulfone (PES) solid particles, polyvinylpyrrolidone (PVP) solid powder, and dimethylacetamide (DMAC) organic solvent. All three types of raw materials contain trace amounts of moisture, and even a very small fluctuation in moisture content can cause quality defects in mass production. Existing industrial testing technologies suffer from the following industry pain points, severely restricting the stability of mass production of high-end dialysis membranes: 1. The equipment is scattered and the testing standards are not uniform, resulting in high testing costs. Currently, the industry requires three different devices to test three types of raw materials: DMAC low moisture depends on the coulomb Karl Fischer apparatus, PES insoluble solids require a separate Karl Fischer furnace, and PVP conventional testing uses a volumetric Karl Fischer apparatus. The cost of purchasing, maintaining and occupying multiple devices is high, and different devices have inherent system deviations, which makes it impossible to unify and benchmark the moisture data of the three types of raw materials. The total moisture calculation error of spinning solution is large and cannot meet the requirements of high-precision formula control.

[0003] 2. Poor compatibility, large testing errors, and poor repeatability; conventional Karl Fischer equipment cannot simultaneously adapt to three sample forms: liquid DMAC, sparingly soluble PES solid, and easily decomposed PVP solid; ordinary KF electrolyte contains a high proportion of methanol, which undergoes esterification with the amide groups of DMAC, continuously generating false moisture, resulting in overestimated DMAC moisture detection results and severe drift; PES cannot dissolve in conventional KF solvent, and direct titration can only detect surface moisture, while the internal bound water cannot be released, resulting in significantly underestimated detection results; PVP is easily decomposed at high temperatures, and a single high-temperature furnace parameter can cause impurities to interfere with PVP detection, affecting detection accuracy; 3. Sample weighing and injection processes are prone to moisture absorption, leading to distortion in trace moisture detection. Existing detection methods are mostly separate operations, requiring samples to be weighed and transferred in an open environment. Porous solids such as PES and PVP easily absorb moisture from the air, and DMAC solvent is also prone to moisture absorption. For the detection of trace moisture below 1% ppm, the error caused by environmental moisture absorption is far greater than the error of the equipment itself, resulting in the detection data failing to accurately reflect the background moisture content of the raw materials. 4. Lack of industry-specific formula calculation function, resulting in a disconnect between testing and production; Existing commercial moisture meters can only output the moisture value of a single raw material and cannot automatically calculate the total moisture content of the ternary mixed spinning solution in combination with the standard spinning ratio of dialysis membrane. Manual conversion and correction are required, which is inefficient and prone to human error, and cannot achieve closed-loop precise control of moisture detection, raw material drying and feeding ratio. In summary, there is currently a lack of an integrated precision moisture detection device that can simultaneously adapt to three types of spinning raw materials—DMAC liquid, PES solid, and PVP solid—with a unified testing standard, eliminate environmental interference, and automatically calculate the total moisture content of the spinning formula. This makes it difficult to meet the high-precision and high-stability mass production quality control requirements of high-end hollow fiber dialysis membranes. Summary of the Invention

[0004] To solve the above-mentioned technical problems, the present invention provides an integrated micro-moisture precision determination device for ternary raw materials used in dialysis membrane spinning, comprising a coulometric Karl Fischer electrolytic titration main unit, a sealed liquid diaphragm sample injection unit, a dual-temperature zone programmable Karl Fischer thermal desorption solid sample injection unit, a three-way switching solenoid valve, a closed micro-weighing module, and an intelligent calculation and control system for spinning formulations. The three-way switching solenoid valve is connected to the sealed liquid diaphragm injection unit, the dual-temperature zone programmable Karl Fischer thermal desorption solid injection unit, and the sealed electrolytic cell of the coulometric Karl Fischer electrolytic titration host, respectively, and is used to switch between the liquid sample detection path and the solid sample detection path. The dual-temperature zone programmable Karl Fischer thermal desorption solid sample introduction unit is independently equipped with a PES high-temperature water release station and a PVP low-temperature anti-decomposition station. The coulometric Karl Fischer electrotitration unit is filled with a low-methanol imidazole buffered Karl Fischer electrolyte adapted for dimethylacetamide DMAC detection. The intelligent calculation and control system for spinning formulation has a built-in liquid DMAC, solid polyethersulfone (PES), and solid polyvinylpyrrolidone (PVP) ternary dialysis membrane spinning ratio model and moisture calculation program.

[0005] The device can accurately detect trace amounts of moisture in liquid DMAC, solid polyethersulfone (PES), and solid polyvinylpyrrolidone (PVP) using a single device, and automatically calculate the total moisture content of the mixed spinning solution.

[0006] As a further supplement to this technical solution, the sealed liquid diaphragm injection unit adopts a double-layer airtight silicone diaphragm structure, and is equipped with an airtight micro-injection needle and a nitrogen micro-positive pressure protection pipeline. The pipeline is equipped with a constant temperature heating structure to prevent DMAC condensation and external water vapor intrusion.

[0007] As a further supplement to this technical solution, the temperature control range of the PES high-temperature water release station is 160-180℃, and the temperature control range of the PVP low-temperature anti-decomposition station is 120-140℃; the dual-temperature zone programmable Karl Fischer thermal desorption solid sample introduction unit is equipped with a high-purity dry nitrogen carrier gas system with full-process heating and an automatic puncture and sealing headspace sample vial.

[0008] As a further supplement to this technical solution, the sealed micro-weighing module integrates a 1 / 100,000 analytical balance and is equipped with an external constant temperature drying protective cover. The entire process of sample weighing, filling, and injection is carried out in a sealed low humidity environment, eliminating sample moisture absorption error.

[0009] As a further supplement to this technical solution, the methanol content of the low-methanol imidazole buffered Karl Fischer electrolyte is ≤15%, and the pH value is stable at 5.5-7.0. It is used to suppress the esterification side reaction of DMAC and methanol and eliminate baseline drift in low moisture detection.

[0010] As a further supplement to this technical solution, the intelligent calculation and control system for spinning formula has the functions of automatic conversion, storage, and over-threshold alarm of moisture data. It can automatically output the drying time of raw materials and the correction scheme of feeding ratio based on the measured moisture value of raw materials and feeding parameters, and can be connected to the production line DCS system to realize closed-loop management.

[0011] A method for detecting trace moisture in an integrated ternary raw material for dialysis membrane spinning includes the following steps: S1. The equipment is preheated and stabilized, and the baseline blank calibration of the electrolytic cell and pipeline drift compensation are completed. S2. Switch the liquid injection path using a three-way solenoid valve, and use a sealed diaphragm injection method to complete the DMAC liquid raw material moisture detection and store the data. S3. Switch the solid thermal desorption pathway, start the PES high-temperature station, complete the moisture detection of PES solid particles, and store the data. S4. Keep the solid thermal desorption pathway open, switch to the PVP low-temperature station, complete the PVP solid powder moisture detection, and store the data. S5. The control system imports the detection data of three types of raw materials and the actual feeding parameters, automatically calculates the total moisture content of the spinning solution, and automatically outputs a process correction plan if the deviation exceeds the limit.

[0012] As a further supplement to this technical solution, in step S3, the PES detection high-temperature constant temperature purging temperature is 170℃ and the purging time is 180s.

[0013] As a further supplement to this technical solution, in step S4, the low-temperature constant temperature purging temperature for PVP detection is 130℃, and the purging time is 120s.

[0014] Its beneficial effects are: 1. Hardware costs are reduced by more than 50%, a single device can replace three dedicated testing instruments, the structure is compact and integrated, and it is suitable for laboratory R&D and mass production workshop quality inspection scenarios; 2. Unified testing standards completely eliminate system errors from multiple devices, and can stably control the total moisture fluctuation of the spinning formula to ≤0.03%, significantly improving the pore size uniformity and flux stability of the dialysis membrane, and reducing the rate of broken fibers and defective products; 3. It specifically addresses four major pain points in detection errors: DMAC side reaction, incomplete PES water release, PVP high-temperature decomposition, and sample moisture absorption. Its detection accuracy and repeatability are far superior to traditional equipment. 4. It achieves integrated automated operation of detection, calculation, calibration and early warning, eliminating the need for manual conversion, greatly improving quality control efficiency, and adapting to the standardized and precise mass production needs of high-end medical device dialysis membranes. Detailed Implementation

[0015] To facilitate a clearer understanding of this technical solution by those skilled in the art, the technical solution of the present invention will be described in detail below: Example 1: Overall Structure and Parameter Configuration of the Device A precision micro-moisture determination device for ternary raw materials used in dialysis membrane spinning, with the following core parameters and structural configuration: 1. Coulomb Karl Fischer electrolytic titration unit: Equipped with dual platinum microelectrodes, moisture detection limit of 0.01μg, detection range of 1ppm~1wt%, suitable for full-range trace moisture detection of three types of raw materials; the electrolytic cell is a fully sealed structure, equipped with molecular sieve drying pipeline, and real-time automatic compensation for environmental drift; the internal electrolyte is filled with a low methanol imidazole buffer electrolyte, with methanol content ≤15%, pH value stable at 5.5~7.0, inhibiting DMAC esterification side reaction.

[0016] 2. Sealed liquid diaphragm injection unit: The injection port is sealed with a double-layer silicone sterile diaphragm and equipped with a 10-1000μL airtight micro-injection needle. The entire pipeline is heated and kept warm (constant temperature 25℃). It is equipped with high-purity nitrogen micro-positive pressure protection to prevent external moisture intrusion. It is specially designed for interference-free injection and detection of DMAC liquid samples.

[0017] 3. Dual-temperature zone Karl Fischer thermal desorption solid sample introduction unit: It is equipped with two independent temperature control stations. Station 1 is the PES detection station with a temperature control range of 160-180℃, preferably 170℃ constant temperature; Station 2 is the PVP detection station with a temperature control range of 120-140℃, preferably 130℃ constant temperature; It is equipped with a high-purity dry nitrogen carrier gas system with an adjustable gas flow rate of 0-150mL / min. The carrier gas pipeline is heated throughout to prevent water vapor condensation; It is equipped with an automatic puncture-sealed headspace sample vial to avoid moisture absorption during sample transfer.

[0018] 4. Three-way switching solenoid valve: Adopting corrosion-resistant and high-temperature resistant solenoid valves, which are respectively connected to the liquid injection unit, the dual-temperature zone solid injection unit, and the electrolytic cell, to realize one-button switching of detection modes. The two pipelines are physically isolated to prevent cross-contamination between liquid and solid samples.

[0019] 5. Sealed micro-weighing module: It integrates a 1 / 100,000 analytical balance, with an external constant temperature drying protective cover and an internal low humidity inert environment. The entire process of sample weighing and filling is sealed, with no air contact and moisture absorption.

[0020] 6. Intelligent computing and control system: Built-in standard spinning formula database for dialysis membranes, preset conventional feeding ratios of PES, PVP, and DMAC, and supports custom feeding parameters; It has real-time storage of moisture data, automatic conversion between ppm and wt%, intelligent calculation of total moisture content, over-threshold alarm, and correction functions for drying time and feeding ratio. It can export data to external terminals and connect to the production line DCS system.

[0021] Example 2: DMAC Liquid Raw Material Moisture Detection Process Step 1: Once the equipment is preheated and stable, activate the main unit drift compensation and allow the electrolytic cell blank balance to reach baseline stability. Step 2: Switch to the liquid injection channel using the three-way solenoid valve and close the solid thermal desorption pipeline; Step 3: Weigh an appropriate amount of low-moisture DMAC sample in a sealed weighing chamber and inject the sample by piercing the diaphragm with an airtight needle. Step 4: The host computer starts coulometric titration, and the detection is completed using a special low-interference electrolyte. Blank drift is automatically subtracted, and the DMAC (Digital Moisture Content) is output. The data is automatically stored in the system database.

[0022] Example 3: Moisture Detection Process for PES Solid Particle Raw Materials Step 1: Switch the solenoid valve to the solid thermal desorption channel, close the liquid injection channel, start the PES high-temperature station to preheat to 170°C, pre-purge the pipeline with nitrogen carrier gas, and deduct the blank moisture in the furnace body and carrier gas. Step 2: Weigh 100-500 mg of PES granules in a sealed environment, put them into a sealed headspace vial and automatically puncture; Step 3: High-temperature constant temperature purging for 180s to completely release the adsorbed water inside the PES, and dry nitrogen gas carrying water vapor into the sealed electrolytic cell. Step 4: After coulometric titration to complete the moisture detection, the system automatically deducts blank error and outputs the PES moisture content.

[0023] Example 4: Moisture Detection Process for PVP Solid Powder Raw Materials Step 1: Keep the solid purging pipeline open, switch to the PVP low temperature station, preheat to 130°C, and ensure the pipeline is stable during blank purging. Step 2: Weigh the PVP powder sample in a sealed container and place it into a clean, sealed headspace vial. Step 3: Low-temperature constant temperature purging for 120s to completely release adsorbed water while avoiding thermal decomposition of PVP. The water vapor is then introduced into the electrolytic cell to complete the titration. Step 4: The system records and outputs the PVP moisture detection data.

[0024] Example 5: Intelligent correction process for total moisture content in spinning solution: After the three raw materials are tested, the actual feed quality for the day is input into the control system. The system then calls the built-in algorithm to automatically calculate the total water content of the ternary mixed spinning solution. If the test result exceeds the process threshold, the system will automatically pop up an alarm and simultaneously output a correction plan, including DMAC vacuum drying time, PES / PVP drying parameters, and correction values ​​for the feed ratio of each raw material, to guide precise production and ensure the stability of the spinning solution's moisture content.

[0025] Innovation of this invention: (1) Single device with multiple forms compatible, unified detection standard, cost reduction and accuracy improvement. This invention uses a single coulometric titration host with a dual-channel switching structure to simultaneously adapt to the detection of three spinning raw materials: liquid DMAC, solid PES, and solid PVP, replacing the traditional three independent detection devices, which greatly reduces the cost of equipment procurement, operation and maintenance, and floor space; the three types of raw materials share the same electrolytic titration system, which completely eliminates the deviation of multiple equipment systems and ensures the uniformity and accuracy of the moisture data of spinning formula.

[0026] (2) Customized detection system to completely solve the problem of interference in raw material detection. In view of the solvent characteristics of DMAC amide, a special electrolyte with low methanol + imidazole buffer is used to suppress esterification side reaction and eliminate low moisture detection drift; in view of the characteristics of the two solid raw materials, dual independent temperature control stations are set up. The high temperature station is adapted to allow PES to completely release the internal water, and the low temperature station avoids interference impurities caused by high temperature decomposition of PVP, thus taking into account the detection accuracy of the two polymer solids.

[0027] (3) The entire process is sealed and moisture-proof, eliminating environmental errors. The integrated sealed constant temperature micro-weighing module completes the entire process of sample weighing, transfer, injection and thermal desorption in a dry and sealed environment, which completely solves the problem of adsorption of water vapor in the air during the detection of PES, PVP solid powder and low moisture DMAC solvent, and achieves accurate detection of trace moisture at the ppm level.

[0028] (4) Industry-specific intelligent accounting system to achieve closed-loop linkage between inspection and production. Built-in dialysis membrane-specific spinning formula database can automatically calculate the total moisture content of spinning solution based on the measured moisture value of three types of raw materials and the actual feeding ratio. If the deviation exceeds the limit, an alarm will be automatically triggered and the raw material drying time and feeding ratio correction scheme will be given. This realizes precise linkage between moisture detection and production quality control, filling the technical gap of industry-specific testing equipment.

[0029] The above technical solutions only embody the preferred technical solutions of the present invention. Any modifications that may be made by those skilled in the art to certain parts thereof embody the principles of the present invention and fall within the protection scope of the present invention.

Claims

1. A precision micro-moisture determination device for ternary raw materials used in dialysis membrane spinning, characterized in that, Includes a coulometric Karl Fischer electrolytic titration unit, a sealed liquid diaphragm injection unit, a dual-temperature zone programmable Karl Fischer thermal desorption solid injection unit, a three-way switching solenoid valve, a closed micro-weighing module, and an intelligent calculation and control system for spinning formulations; The three-way switching solenoid valve is connected to the sealed liquid diaphragm injection unit, the dual-temperature zone programmable Karl Fischer thermal desorption solid injection unit, and the sealed electrolytic cell of the coulometric Karl Fischer electrolytic titration host, respectively, and is used to switch between the liquid sample detection path and the solid sample detection path. The dual-temperature zone programmable Karl Fischer thermal desorption solid sample introduction unit is independently equipped with a PES high-temperature water release station and a PVP low-temperature anti-decomposition station. The coulometric Karl Fischer electrotitration unit is filled with a low-methanol imidazole buffered Karl Fischer electrolyte adapted for dimethylacetamide DMAC detection. The intelligent calculation and control system for spinning formulation has a built-in liquid DMAC, solid polyethersulfone (PES), and solid polyvinylpyrrolidone (PVP) ternary dialysis membrane spinning ratio model and moisture calculation program.

2. The integrated micro-moisture precision determination device for ternary raw materials used in dialysis membrane spinning according to claim 1, characterized in that, The sealed liquid diaphragm injection unit adopts a double-layer airtight silicone diaphragm structure, and is equipped with an airtight micro-injection needle and a nitrogen micro-positive pressure protection pipeline. The pipeline is equipped with a constant temperature heating structure to prevent DMAC condensation and external moisture intrusion.

3. The integrated micro-moisture precision determination device for ternary raw materials used in dialysis membrane spinning according to claim 2, characterized in that, The temperature control range of the PES high-temperature water release station is 160-180℃, and the temperature control range of the PVP low-temperature anti-decomposition station is 120-140℃; the dual-temperature zone programmable Karl Fischer thermal desorption solid sample introduction unit is equipped with a high-purity dry nitrogen carrier gas system with full-process heating and an automatic puncture and seal headspace sample vial.

4. The integrated micro-moisture precision determination device for ternary raw materials used in dialysis membrane spinning according to claim 3, characterized in that, The sealed micro-weighing module integrates a 1 / 100,000 analytical balance and is equipped with an external constant temperature drying protective cover. The entire process of sample weighing, filling, and injection is carried out in a sealed low humidity environment, eliminating sample moisture absorption error.

5. The integrated micro-moisture precision determination device for ternary raw materials used in dialysis membrane spinning according to claim 1, characterized in that, The low-methanol imidazole buffered Karl Fischer electrolyte has a methanol content of ≤15% and a pH value that is stable between 5.5 and 7.

0. It is used to suppress the esterification side reaction of DMAC and methanol and eliminate baseline drift in low-moisture detection.

6. The integrated micro-moisture precision determination device for ternary raw materials used in dialysis membrane spinning according to claim 5, characterized in that, The intelligent calculation and control system for spinning formulation has functions such as automatic conversion and storage of moisture data and alarm for exceeding threshold. It can automatically output the drying time of raw materials and the correction scheme of feeding ratio based on the measured moisture value of raw materials and feeding parameters. It can also be connected to the production line DCS system to achieve closed-loop management.

7. The detection method of the integrated trace moisture precision determination device for dialysis membrane spinning ternary raw materials according to any one of claims 1-6, characterized in that, Includes the following steps: S1. The equipment is preheated and stabilized, and the baseline blank calibration of the electrolytic cell and pipeline drift compensation are completed. S2. Switch the liquid injection path using a three-way solenoid valve, and use a sealed diaphragm injection method to complete the DMAC liquid raw material moisture detection and store the data. S3. Switch the solid thermal desorption pathway, start the PES high-temperature station, complete the moisture detection of PES solid particles, and store the data. S4. Keep the solid thermal desorption pathway open, switch to the PVP low-temperature station, complete the PVP solid powder moisture detection, and store the data. S5. The control system imports the detection data of three types of raw materials and the actual feeding parameters, automatically calculates the total moisture content of the spinning solution, and automatically outputs a process correction plan if the deviation exceeds the limit.

8. The method for precise detection of trace moisture in ternary raw materials integrated for dialysis membrane spinning according to claim 7, characterized in that, In step S3, the PES detection temperature for high-temperature constant-temperature purging is 170℃, and the purging time is 180s.

9. The method for precise detection of trace moisture in ternary raw materials integrated for dialysis membrane spinning according to claim 8, characterized in that, In step S4, the PVP detection low-temperature constant temperature purging temperature is 130℃, and the purging time is 120s.