CN107308822B - Method for analyzing dissolution kinetics of ultrafiltration membrane pore-forming agent - Google Patents
Method for analyzing dissolution kinetics of ultrafiltration membrane pore-forming agent Download PDFInfo
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01D—SEPARATION
- B01D65/00—Accessories or auxiliary operations, in general, for separation processes or apparatus using semi-permeable membranes
- B01D65/10—Testing of membranes or membrane apparatus; Detecting or repairing leaks
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- Chemical & Material Sciences (AREA)
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Abstract
The invention relates to a method for analyzing dissolution kinetics of an ultrafiltration membrane pore-forming agent, which is simple and convenient to operate and stable in detection result, and uses an ultrafiltration membrane pore-forming agent dissolution kinetics experimental device, comprising a power driving device, an inner groove and an outer groove; a first stirring head is arranged in the inner tank, and a second stirring head is arranged in the outer tank; the power driving device is used for driving the first stirring head and the second stirring head to rotate; a bracket for fixing the inner groove is arranged in the outer groove; and a placing frame is arranged in the inner groove. The device and the method can effectively overcome the influence of sampling point positions on measurement results, so that the experimental results are more accurate, and the dissolution kinetics of the ultrafiltration membrane pore-forming agent can be more effectively researched.
Description
Technical Field
The invention relates to an experimental device, in particular to an experimental device for dissolution kinetics of a pore-forming agent of an ultrafiltration membrane and a method for analyzing the dissolution kinetics of the pore-forming agent of the ultrafiltration membrane.
Background
In 1950 s, the technology for preparing the asymmetric polymer ultrafiltration membrane by the immersion precipitation phase inversion method invented by Loeb and Sourirajan has become the most important and widely applied membrane preparation technology, and is widely applied to the preparation of organic ultrafiltration membranes. The film forming process by the immersion precipitation phase inversion method is a very complex multi-component mass transfer process accompanied with phase change, and a universal and strict mechanism explanation of the film forming process is not available so far. In the 1960 s, Kestin qualitatively analyzed the immersion precipitation phase inversion process from the perspective of molecular motion. The process has a complex multi-component mass transfer process and is accompanied with the change of a polymer phase state structure, so that the process is a comprehensive process of dynamics and thermodynamics, the two processes simultaneously influence the structure of the ultrafiltration membrane and further influence the performance of the ultrafiltration membrane, and the research on a membrane forming mechanism is relatively slow. Because the film forming mechanism of the ultrafiltration membrane is not very clear, the film forming dynamics is difficult to accurately and quantitatively describe by using a mathematical formula, and the film forming dynamics can not provide theoretical basis for the actual production of the ultrafiltration membrane. At present, in the production of the ultrafiltration membrane, the microstructure of a membrane product cannot be accurately predicted, and the accurate regulation and control of MWCO cannot be realized, so that the types of the currently marketed ultrafiltration membrane products are few, the MWCO range is wide, the ideal separation effect cannot be achieved, and the further widening of the application field of the ultrafiltration membrane is also hindered.
In the film formation process, the liquid-solid phase separation is a slow process, the liquid-liquid phase separation is a fast process, and the liquid-solid phase separation occurs before the liquid-liquid phase separation, so that the mass transfer speed determines which of two phase separation mechanisms occupies a dominant position in the film formation process, thereby influencing the structure and performance of the film. If the liquid-liquid phase separation is dominant, the system will undergo transient phase separation to form an asymmetric membrane with a porous structure, and if the liquid-solid phase separation is dominant, the system will undergo delayed phase separation to form a symmetric membrane with a granular crystalline structure. The above phase separation mechanism is determined based on the whole film formation process, i.e. depending on whether the film is the result of liquid-solid delayed phase separation or the result of liquid-liquid transient phase separation. However, it is known from the film forming process that the film formation progresses from the film/bath interface to the film/plate interface, and the formation of the skin layer hinders the exchange of the solvent with the non-solvent of the coagulation bath in the film sub-layer, thereby affecting the structure of the film, so that the structure and morphology of the film can be explained by using a two-step film forming mechanism, i.e., the skin layer and the sub-layer have different film forming mechanisms. The influence of additive types on the PVDF film forming process is researched by Erwinia and the like, and the result shows that the phase separation behavior is changed from liquid-solid phase to liquid-liquid phase along with the progress of precipitation.
The immersion precipitation phase inversion method is the most commonly used method for preparing polymer membranes, and is a non-equilibrium dynamic process in which the interdiffusion of solvent-non-solvent, i.e., the dynamic mass transfer process, has a great influence on the final membrane structure. Therefore, the process is an important part in the research of the film forming mechanism. The research of the dynamic mass transfer process generally comprises two methods of theoretical calculation and experimental determination. A mass transfer model of theoretical calculation is firstly proposed by Cohen, then Reuvers, McHugh, Radoanovis, Cheng and the like perfect and expand the mass transfer model, the model calculation well predicts the delay time of delay phase separation and the distribution condition of each component in a membrane before phase separation, but the model establishment involves many thermodynamic and kinetic parameters, a plurality of parameters such as binary friction coefficients of a non-solvent and a polymer and the like are difficult to determine through experiments, and the determination conditions of some parameters are difficult to keep consistent with the film forming conditions, so the application of the theoretical calculation method is greatly limited due to the lack of model parameters. The experimental research method of the dynamic mass transfer process comprises the following steps: microscopic observation of gel front, in-situ optical observation of dark background, immersion precipitation phase inversion method, etc. The immersion precipitation phase inversion experiments performed were all similar: scraping a film on a clean glass plate or placing the film casting solution into a small container, then quickly placing the small container into a gel bath with stirring or without stirring, extracting a certain amount of samples from the position close to the interface of the film and the gel bath at certain intervals, and analyzing the samples by gas chromatography. Firstly, if the scraped film is directly put into a gel bath, the size of the scraped film is difficult to ensure to be the same every time, and the dosage of the casting solution is not easy to determine; secondly, if the casting solution is placed in a small container, although the size of the membrane surface can be ensured to be the same, the dosage of the casting solution can be controlled, the thickness of the casting solution is greatly different from that of the actual membrane preparation, the dissolution rate and the dissolution amount of the additive can be influenced by the thickness of the membrane, and in addition, by adopting a method of sampling from the position close to the interface of the membrane and the gel bath, the sampling points are difficult to ensure to be consistent every time, so that the concentration and the total amount of the additive are difficult to determine.
Model calculations of solvent distribution during PVDF film formation and its mechanism of macropore formation, proceedings of the university of eastern science, 2007,33 (5): 610-. And secondly, taking out the membrane at certain time intervals, fully stirring the rest gel bath, then sampling, and researching the dissolution kinetics of the solvent by adopting a method for measuring the total organic carbon and the total nitrogen concentration of the gel bath, thereby effectively overcoming the defect of inconsistent sampling points. Zhengqingzhu (Zhengqingzhu, nanometer TiO)2Research on the film forming mechanism and the anti-pollution capability of polysulfone organic-inorganic hybrid ultrafiltration membrane, China university of oceans, 2015, 41-46) by utilizing the developed ultrafiltration membrane additive dissolution kinetic experimental device,PEG dissolution kinetics were studied using an autosampler to sample from the gel bath and determine the PEG concentration in the gel bath. The equipment can realize uniform mixing of the gel bath, can sample at different time points, can accurately detect the concentration of PEG in the gel bath, and can calculate the total amount of dissolved PEG in the casting solution. However, the device cannot accurately calculate the elution amount and elution rate of PEG in the casting solution.
Disclosure of Invention
Aiming at the problems in the prior art, the invention aims to provide an experimental device for ultrafiltration membrane pore-forming agent dissolution kinetics, which is simple and convenient to operate and stable in detection result, and a method for analyzing the dissolution kinetics of the ultrafiltration membrane pore-forming agent.
An experimental device for dissolution kinetics of a pore-forming agent of an ultrafiltration membrane comprises a power driving device, an inner groove and an outer groove; a first stirring head is arranged in the inner tank, and a second stirring head is arranged in the outer tank; the power driving device is used for driving the first stirring head and the second stirring head to rotate; a bracket for fixing the inner groove is arranged in the outer groove; the inner groove is internally provided with a placing rack, and the angle between the placing rack and the horizontal plane is 30-45 degrees.
In order to effectively control the temperature of the gel bath and ensure that the whole experiment is carried out at the designed experiment temperature, the experimental device also comprises a temperature controller; a temperature sensor is arranged on the inner wall of the inner groove; a heating pipe is arranged in the outer groove; the heating pipe and the temperature sensor are electrically connected with the temperature controller.
For more rapid and effective control of the temperature of the gelling bath, the heating tube is circular and fixed around the second stirring head.
In order to realize uniform temperature and concentration of the whole experiment, a plurality of fins are arranged on the inner walls of the inner groove and the outer groove.
Under the condition of ensuring the temperature control of the device to be stable, the ultrafiltration membrane is prevented from falling off due to the flowing of an inner groove gel bath in the using process, and the rotating speed of the first stirring head is 30-120 r/min; the rotating speed of the second stirring head is 50-150 revolutions per minute.
The advantages of the invention are as follows:
the experimental device for the dissolution kinetics of the ultrafiltration membrane additive comprises a heating pipe, a temperature sensor, a temperature controller and the like, wherein the inner tank and the outer tank are filled with water, and the inner tank and the outer tank are respectively provided with a stirring device, so that the liquid is in a completely mixed state, the gel bath temperature can be accurately controlled, and the related experimental research on the influence of the temperature on the dissolution kinetics of the additive and the like can be developed. The power driving device is matched with the first stirring head and the second stirring head, so that the gel bath in the inner groove is in a completely mixed state, the concentration of the additive at each point position in the gel bath is uniform all the time since the casting solution is put into the gel bath, the influence of the sampling point position on the measurement result is effectively overcome, the experimental result is more accurate, and the dissolution kinetics of the ultrafiltration membrane pore-forming agent is more effectively researched.
The method for researching the dissolution kinetics of the ultrafiltration membrane additive is combined with the experimental device, so that a high-precision test result can be obtained when the dissolution kinetics of the ultrafiltration membrane additive is researched, and the stable data and small fluctuation of the test result can be ensured, and the repeatability of the test result is very good.
Drawings
FIG. 1 is a schematic structural diagram of an experimental apparatus of the present invention (the power driving device is a motor and the first stirring head and the second stirring head are impeller stirrers);
FIG. 2 is a schematic structural diagram of an experimental apparatus of the present invention (the power driving device is a magnetic stirrer, and the first stirring head and the second stirring head are rotors);
FIG. 3 is a schematic diagram of the top view structure of the outer tank of the experimental apparatus of the present invention;
fig. 4 is a schematic structural view of a fin of the experimental apparatus of the present invention.
Fig. 5 is a schematic diagram (partially with a section) of an explosion structure at the matching part of the input shaft of the reducer and the rotating shaft of the second stirring head of the experimental device of the invention.
FIG. 6 is a standard curve of PEG-4000 solution in example 2 of the present invention;
FIG. 7 shows the PEG dissolution rate (20 ℃) within 5min at different PSF concentrations in example 2 of the present invention;
FIG. 8 shows the total PEG dissolution rate (20 ℃) at 5min for different PSF concentrations in example 2 of the present invention;
FIG. 9 shows the PEG dissolution rate (20 ℃) within 5min at different PSF concentrations in example 2 of the present invention;
FIG. 10 shows the PEG dissolution rate within 5min at different gel bath temperatures in example 3 of the present invention;
FIG. 11 shows the total PEG dissolution rate of example 3 of the present invention at different gel bath temperatures for 5 min;
FIG. 12 is a graph of the PEG dissolution rate within 5min at different gel bath temperatures in example 3 of the present invention;
FIG. 13 shows the PEG elution rate within 5min at different gel bath temperatures in comparative example 1 according to the present invention;
FIG. 14 shows the total PEG elution rate of comparative example 1 of the present invention at different gel bath temperatures for 5 min;
FIG. 15 is a graph showing the change in PEG concentration in the gel bath within 5min at different gel bath temperatures in comparative example 2 of the present invention;
FIG. 16 is a graph showing the PEG concentration in the gel bath at different gel bath temperatures for 5min in comparative example 2 of the present invention;
FIG. 17 shows the PEG elution rate within 5min at different gel bath temperatures in comparative example 3 according to the present invention;
FIG. 18 shows the total PEG elution rate of comparative example 3 of the present invention at different gel bath temperatures for 5 min.
Detailed Description
Example 1
As shown in fig. 1 and fig. 2, an experimental apparatus for dissolution kinetics of a pore-forming agent of an ultrafiltration membrane comprises a power driving device 1, an inner tank 2 and an outer tank 3; a first stirring head 4-1 is arranged in the inner tank 2, and a second stirring head 4-2 is arranged in the outer tank 3; the power driving device 1 is used for driving the first stirring head 4-1 and the second stirring head 4-2 to rotate; a bracket 6 for fixing the inner groove 2 is arranged in the outer groove 3; a placing frame 5 is arranged in the inner groove 2, and the placing frame 5 and the horizontal plane form an angle of 45 degrees.
Because most ultrafiltration membrane pore-forming agent dissolution kinetic experiments need to be carried out at a specific temperature, the experimental device needs to be additionally provided with a temperature controller 9; a temperature sensor 8 is arranged on the inner wall of the inner groove 2; a heating pipe 7 is arranged in the outer groove 3; the heating pipe 7 and the temperature sensor 8 are electrically connected with a temperature controller 9. The temperature sensor 8 will transmit the detected temperature condition to the temperature controller 9 from time to time, when the temperature in the inner tank 2 is lower than the set temperature, the temperature controller 9 will start the heating pipe 7 to heat, when the temperature reaches the set temperature, the heating pipe 7 will stop heating;
in order to achieve a better heating effect, the heating pipe 7 is designed into a circular ring shape and is fixed around the second stirring head 4-2, and in the design, when heating, heat can be rapidly transferred along with the second stirring head 4-2, so that the temperature control effect is more ideal. The structure is shown in fig. 3.
As shown in fig. 2, as a specific implementation form of the power driving device 1, the first stirring head 4-1 and the second stirring head 4-2, the power driving device 1 is a magnetic stirrer, and the first stirring head 4-1 and the second stirring head 4-2 are rotors, in which case the magnetic stirrer drives the two rotors to rotate together, so as to realize a stirring function. However, the rotation speed of the rotor in the inner groove 2 is obviously low and is not well controlled, and in order to solve the problem, the invention provides another implementation form, which is as follows:
as shown in fig. 1, 3 and 5, the power driving device 1 is a motor and the first stirring head 4-1 and the second stirring head 4-2 are impeller stirrers; the power driving device 1 drives the first stirring head 4-1 and the second stirring head 4-2 to rotate through a shaft. This implementation mode can ensure that the rotation speed of the first stirring head 4-1 and the second stirring head 4-2 is controllable, and in fact, when the rotation speed of the first stirring head 4-1 is too high, the ultrafiltration membrane forming effect may be affected, in this case, under the condition of ensuring the rotation speed of the second stirring head 4-2, a reducer 20 is additionally arranged to realize the rotation speed difference between the first stirring head 4-1 and the second stirring head 4-2. The speed reducer 20 can be fixedly mounted on the bracket 6, an input shaft 21 of the speed reducer 20 is connected with a rotating shaft of the second stirring head 4-2, an output shaft 22 of the speed reducer 20 is a rotating shaft of the first stirring head 4-1, further, in order to facilitate the detachment of the inner groove 2, the input shaft 21 of the speed reducer 20 is in key connection with the rotating shaft of the second stirring head 4-2, the bottom of the input shaft 21 of the speed reducer 20 is recessed upwards to form an accommodating cavity, a key groove 31 is formed in the accommodating cavity, a key strip 30 matched with the key groove 31 is formed on the rotating shaft of the second stirring head 4-2, and the key strip 30 is in sliding connection with the key groove 31, so that the top end of the rotating shaft of the second stirring head 4-2 can be inserted into the accommodating cavity of the input shaft 21 of the speed reducer 20 or axially separated from the accommodating cavity of the.
As shown in fig. 4, in order to achieve more uniform mixing of the liquids in the inner and outer tanks 2 and 3 under stirring, a plurality of fins 11 are provided on the inner walls of the inner and outer tanks 2 and 3. Under the condition of ensuring the temperature control of the device to be stable, the ultrafiltration membrane is prevented from falling off due to the flowing of an inner groove gel bath in the using process, and the rotating speed of the first stirring head is 30-120 r/min; the rotating speed of the second stirring head is 50-150 revolutions per minute.
Example 2
The experimental device for the dissolution kinetics of the ultrafiltration membrane pore-forming agent is used for researching the influence of PSF concentration on PEG dissolution kinetics.
PEG and bismuth potassium iodide reagent (Dragendoff reagent) can generate orange red complex, so that the concentration of PEG dissolved out of the flat ultrafiltration membrane can be accurately determined by utilizing the complexing reaction principle. Since the complex is susceptible to decomposition by light, the reaction should be carried out in a brown vessel and then detected by uv-vis spectrophotometry. The preparation of the potassium bismuth iodide reagent is difficult because the potassium bismuth iodide reagent has more problems in the preparation, such as lower solubility and lower dissolution speed of bismuth subnitrate in glacial acetic acid at normal temperature, and particularly because the potassium bismuth iodide and PEG are insufficient in acid condition and easy to generate precipitate and the like, and the preparation method of the Dragendoff reagent is improved by the method, and the specific operation is as follows:
1. latest preparation method of bismuth potassium iodide reagent
Solution A: 0.8g of bismuth subnitrate was weighed into a small beaker under appropriate conditions, and then 5mL of concentrated nitric acid was added and stirred continuously to facilitate dissolution. And (3) preparing a NaOH solution (2 g of NaOH is weighed and dissolved in water) in another beaker for adjusting the pH value, uniformly mixing the NaOH solution and the NaOH solution in the beaker, then placing the mixed solution in a 50mL brown volumetric flask, adding 10mL of glacial acetic acid, adding distilled water, and diluting to the scale.
And B, liquid B: because potassium iodide is easily decomposed by light, 20.0g of potassium iodide is accurately weighed under the shading condition, dissolved in a beaker, placed in a 50mL brown volumetric flask, added with distilled water and diluted to the scale.
Dragendoff reagent: measuring 5mL of the solution A and the solution B, placing the solution A and the solution B into a 100mL brown volumetric flask, and adding distilled water to dilute the solution A to a scale, wherein the effective period is half a year.
2. Preparation of Standard solutions
Putting PEG-4000 into a drying oven, drying for 4h at 60 ℃, accurately weighing 0.5g of PEG0, dissolving in a 500mL volumetric flask, respectively sucking 0, 1, 1.5, 2, 2.5, 3 and 3.5(mL) of PEG solution, diluting in a 100mL volumetric flask, and preparing PEG standard solutions with the concentrations of 0, 10, 15, 20, 25, 30 and 35 mg/L.
3. Preparation of Standard Curve
30mL of PEG standard solutions with different concentrations are sequentially added into a 50mL brown volumetric flask respectively. 6mL of glacial acetic acid was added, followed by 6mL of the reagent LDragondoff, and finally diluted to the mark with distilled water. Standing for 15min, measuring absorbance with ultraviolet spectrophotometer at 510nm wavelength, and using glass cuvette with distilled water as blank. The standard curve for PEG-4000 is shown in FIG. 6.
The influence of PSF concentration on PEG dissolution kinetics is studied under the condition that the room temperature is 20 ℃, distilled water with fixed volume is added into the inner tank 2 and the outer tank 3, so that the liquid levels in the inner tank 2 and the outer tank 3 are flush or the liquid level in the outer tank 3 is higher than the liquid level in the inner tank 2; the temperature of the gel bath was set to 20 ℃.
Casting solution with PEG concentration of 10 wt% and PSF concentration of 15 wt%, 16 wt%, 17 wt% and 18 wt% respectively was prepared. Using the experimental apparatus of example 1, the mass of the aluminum alloy flat plate with the shallow grooves was accurately weighed, the uniform and stable casting film was dropped into the shallow grooves on the aluminum alloy flat plate, and then the film was scraped with the flat aluminum alloy blade, so as to ensure that the shallow grooves were filled with the casting film solution, and then the excess casting film solution outside the shallow grooves on the surface of the flat plate was wiped off with a paper towel, and the sum of the masses of the aluminum alloy flat plate and the casting film solution was accurately weighed, thereby obtaining the mass of the casting film solution filled in the shallow grooves. And then taking the aluminum alloy flat plate with the shallow grooves of the same specification, scraping the film, wiping off the redundant film casting liquid on the flat plate, pre-evaporating for 10s, and then placing the aluminum alloy flat plate with the film casting liquid film on a placing rack 5 in a gel bath. The included angle between the placing rack 5 and the horizontal plane is 45 degrees;
and starting the power driving device 1 to drive the first stirring head 4-1 and the second stirring head 4-2 to stir, and keeping the gel bath temperature constant at 20 ℃ under the coordination of the temperature controller 9, the temperature sensor 8 and the heating pipe 7. 30mL of each gel bath was taken out of the gel bath by a syringe with a fixed scale at 1, 2, 3, 4, and 5min, and the gel bath was taken out and put into a 50mL volumetric flask. The volumetric flask was filled with 6mL of glacial acetic acid, 6mL of Dragendorff reagent and diluted to the mark with distilled water. After standing for 15 minutes, the absorbance was measured at a wavelength of 510nm on a UV2102C model UV/Vis spectrophotometer using a glass cuvette with distilled water as a reference. The PEG concentration in the gel bath was determined using a standard curve.
The total amount Q of pore-forming agent (PEG) dissolved out is calculated by a formulanAnd Tn-1～TnZone dissolution rate Vn
Qn＝(M-(n-1)m)*An+m*(A1+A2+A3+.....+An-1)
Vn＝(Qn-Qn-1)/(Tn-Tn-1)
The elution amount of PEG with time was measured, and the elution rate of PEG was calculated to obtain the change pattern of the elution amount of PEG with time at different PSF concentrations, and the results are shown in Table 1-Table 3 and FIGS. 7-9. As can be seen from the figure, PEG is gradually dissolved out in the film forming process of the film casting solution film in the gel bath, the dissolving rate is maximum in the 1 st min, then the dissolving rate is gradually reduced, and after 3min, the PEG concentration tends to be smooth and the PEG dissolving rate is relatively low. The PSF concentration in the casting solution gradually increases, the PEG dissolution rate is reduced and then increased, but the change range is small. The total dissolution rate of PEG was minimal when the PSF concentration was 17 wt%, and increased gradually with increasing PSF concentration when the PSF concentration was greater than 17 wt%. The total PEG dissolution rate is firstly reduced and then increased along with the increase of the PSF concentration, and the total PEG dissolution rate reaches the lowest value when the PSF concentration is 17 wt%. The mean square error of the PEG dissolution rate is in the range of 0.04-1.17%, and the mean is 0.43%. The PEG dissolution rate mean square error is in the range of 0.01-0.23%, the average is 0.08%, the experimental precision is very high, the device is scientific and accurate, and the experimental method is reasonable and feasible.
TABLE 1 PEG dissolution Rate within 5min at different PSF concentrations (20 ℃ C.)
TABLE 2 Total PEG dissolution rate at 5min (20 ℃ C.) at different PSF concentrations
TABLE 3 PEG dissolution Rate within 5min (20 ℃ C.) at different PSF concentrations
Example 3
By using the method of example 2, the PEG dissolution rate within 5min at different gel bath temperatures (15, 20, 25, 30 ℃) and the change rule of the PEG dissolution rate with time were measured, and the PEG dissolution rate was calculated, and the results of three parallel experiments are shown in table 4-table 6 and fig. 10-fig. 12. As can be seen from the figure, PEG is gradually dissolved out from the film casting solution film in the film forming process in the gel bath, the dissolving rate is gradually reduced, the PEG concentration tends to be gentle after 1-3min, the dissolving rate of PEG is smaller, and the time for the PEG concentration to tend to be gentle along with the gradual increase of the temperature of the gel bath is gradually shortened. The experimental device and the detection and calculation method for dissolution kinetics of the ultrafiltration membrane additive can accurately obtain the dissolution rates of PEG in the casting solution at different time points (0 min, 1min, 2 min, 3min, 4 min and 5min), the detection result data is stable, the fluctuation is very small, the parallelism of the detection results of the PEG dissolution rate in three times is very good, the mean square error is within the range of 0-1%, and the average value is 0.31%. The mean square deviations of the PEG dissolution rate calculation results are all within the range of 0.01-0.23%, the average value is 0.07%, the repeatability of the experimental results is very good, and the accuracy is high.
TABLE 4 PEG dissolution rate within 5min at different gel bath temperatures (PSF15 wt%, PEG10 wt%)
TABLE 5 Total PEG dissolution rate at 5min at different gel bath temperatures (PSF15 wt%, PEG10 wt%)
TABLE 6 PEG dissolution Rate within 5min at different gel bath temperatures (PSF15 wt%, PEG10 wt%)
Comparative example 1
A comparative experiment was carried out using an experimental apparatus and a detection method proposed by the university of eastern Engineers, Yangtze-Daizian et al (Yangtze-Daizian et al, model calculation of solvent distribution during PVDF film formation and mechanism of macropore formation, proceedings of the university of eastern Engineers (Nature science edition), 2007,33 (5): 610-. And covering the glass plate with one hole plate to expose film casting liquid film in certain area. Keeping the thickness of the film of the casting solution consistent, scraping the casting solution on the whole area of the whole glass plate, determining the total mass of the casting solution on the whole glass plate by adopting a weight method, determining the mass of the casting solution on a unit area, and designing holes with proper sizes to ensure that the mass of the casting solution exposed to the blank is about 0.2g, wherein the holes are similar to the mass of the casting solution used in the invention, and the errors caused by different volumes of the casting solutions are reduced as much as possible. Determining the PSF concentration of 15 wt%, the PEG concentration of 10 wt%, the pre-evaporation time of 10s, and the PEG dissolution rate within 5min at different gel bath temperatures (15, 20, 25, 30 ℃). The glass plate covered with the well plate is put into a temperature-controlled gel bath with a certain volume, the mass of the gel bath is 600g, the glass plate is taken out after a certain time (for reducing the system error, the time is 1, 2, 3, 4 and 5min, which is the same as the experimental condition of the invention, in order to reduce the system error), the concentration of PEG in the gel bath is detected by the same method, the dissolution rate of PEG in different times is calculated, the result is shown in Table 7 and figure 13, and the total dissolution rate of PEG in the casting solution at 5min is calculated at the same time, and the result is shown in Table 8 and figure 14. As can be seen from the table, the PEG dissolution rate in the casting solution at different time points can be obtained by the method, but the result fluctuation is large, the mean square error is generally between 3.33% and 12.46%, and the mean square error is 6.04%.
TABLE 7 PEG dissolution rate in 5min at different gel bath temperatures
TABLE 8 Total PEG dissolution rate at 5min at different gel bath temperatures
Comparative example 2
The samples were analyzed by gas chromatography using a method described in the literature (dawn, et al, model calculation of solvent distribution during PVDF film formation and mechanism of macropore formation, university of eastern Engineers, Nature science, ed., second Page left column) by scraping the film onto a clean glass plate or placing the film casting solution in a small container, which was then quickly placed in a stirred or unstirred gel bath, and withdrawing a quantity of sample from the vicinity of the interface between the film and the gel bath at intervals. The method can not accurately quantify the mass of the casting solution put into the gel bath, so that the dissolution rate of PEG can not be calculated, and only can the sampling at regular time be carried out to detect the concentration of PEG in the gel bath. The PSF concentration in the casting solution is 15 wt%, the PEG concentration is 10 wt%, the pre-evaporation time is 10s, the scraped casting solution thin film and a glass plate are put into a gel bath at different gel bath temperatures (15, 20, 25 and 30 ℃), the PEG concentration in the gel bath is detected by sampling from the position close to the interface of the film and the gel bath at regular time (for reducing system errors, the sampling time is the same as the experimental conditions of the invention, and the sampling time is 1, 2, 3, 4 and 5min), and the results of three parallel experiments are shown in Table 9, FIG. 15, Table 10 and FIG. 16. As the method can not accurately obtain the quality of the casting solution, only the concentration of PEG dissolved in the gel bath in the casting solution at different time points can be obtained, the results show that the fluctuation of three parallel experiments is large, the mean square error is between 8.25 and 14.34 percent, the average is 10.61 percent, and the mean square error of most PEG is more than 10 percent, which indicates that the method has poor precision.
TABLE 9 PEG concentration in the gel bath at different gel bath temperatures within 5min
TABLE 10 PEG concentration in the gel bath at 5min at different gel bath temperatures
Comparative example 3
According to the literature (Nano TiO)2The method for evaluating and researching the film forming mechanism and the anti-pollution capability of the polysulfone organic-inorganic hybrid ultrafiltration membrane, the university of China at sea 2015, 41-46) comprises the steps of adding 600ml of distilled water into a beaker 5, and weighing a certain amount of casting solution to scrape a film on a glass plate. After a certain pre-evaporation time, the gel is placed on the rack 3 in a gel bath in a beaker 5. The magnetic stirrer 1 was turned on, the rotor speed was 120rpm, 10mL of the sample was taken from the beaker 5 at 1, 2, 3, 4, and 5min using the autosampler 6, and the sample was added to a 50mL volumetric flask. Glacial acetic acid and Dragendoff reagent are respectively added into a volumetric flask by 6mL, and the volume is determined by distilled water. Standing for 15min, measuring absorbance A at 510nm wavelength of ultraviolet-visible spectrophotometer, and obtaining PEG concentration in gel bath with distilled water as reference. The comparative experiment simulates the experimental conditions in the literature, and in order to improve the comparative effect, the concentration of PSF in the casting solution is 15 wt%, the concentration of PEG is 10 wt%, the pre-evaporation time is 10s, the scraped casting solution film and the glass plate are put into the gel bath together, and the PEG concentration in the gel bath is detected by sampling from the gel bath (the sampling time is 1, 2, 3, 4, 5min, which is the same as the experimental conditions of the present invention in order to reduce the system error), and the results of three parallel experiments are shown in table 11, fig. 17, table 12, and fig. 18. From the results, it can be seen that the fluctuation of the three parallel experiments is large, the mean square error is between 5.12% and 13.20%, the average is 8.27%, and the partial mean square error is more than 10%, which indicates that the method is also poor in accuracy, mainly due to automatic samplingWhen the device samples, a certain amount of liquid is stored in the pipeline, and the concentration of PEG in the gel bath stored in the pipeline is the concentration of the PEG in the last sampling, so that the accuracy of the concentration of the PEG in the sampling is influenced, and a certain experimental error is brought.
TABLE 11 PEG dissolution rate in 5min at different gel bath temperatures
TABLE 12 Total PEG dissolution rate at 5min in different gel bath temperatures
The foregoing is directed to preferred embodiments of the present invention, other and further embodiments of the invention may be devised without departing from the basic scope thereof, and the scope thereof is determined by the claims that follow. However, any simple modification, equivalent change and modification of the above embodiments according to the technical essence of the present invention are within the protection scope of the technical solution of the present invention.
Claims (8)
1. A method for analyzing dissolution kinetics of an ultrafiltration membrane pore-forming agent is characterized by comprising the following specific steps:
(1) preparing a plurality of aluminum alloy flat plates with the same specification and shallow grooves, wherein the shallow grooves have the same size and the depth of the shallow grooves is 0.05-0.30 mm;
(2) accurately weighing the quality of the aluminum alloy flat plate, dripping uniform and stable casting film liquid into the shallow grooves for film scraping, wiping off the redundant casting film liquid outside the shallow grooves after ensuring that the shallow grooves are filled with the casting film liquid, accurately weighing the quality of the aluminum alloy flat plate after film scraping, and obtaining the quality of the casting film liquid in the shallow grooves by a quality difference method;
(3) starting an ultrafiltration membrane pore-forming agent dissolution kinetic experiment device, and scraping a membrane on a new aluminum alloy flat plate by using the method in the step (2) after the temperature of a gel bath with the volume of M is constant;
(4) after pre-evaporation for a certain time, putting the aluminum alloy flat plate scraped in the step (3) into a gel bath; taking gel baths with fixed volumes m at different time points T respectively, and measuring the concentration A of the pore-forming agent of the ultrafiltration membrane contained in the gel baths;
(5) calculating the total dissolution quantity Q of the pore-forming agent of the ultrafiltration membranenAnd Tn-1～TnZone dissolution rate Vn，
Wherein: qn＝(M-(n-1)m)*An+m*(A1+A2+A3+……+An-1)
Vn＝(Qn-Qn-1)/(Tn-Tn-1)
In the formula: n is the sampling frequency;
the experimental device for the dissolution kinetics of the ultrafiltration membrane pore-forming agent comprises a power driving device (1), an inner groove (2) and an outer groove (3); a first stirring head (4-1) is arranged in the inner tank (2), and a second stirring head (4-2) is arranged in the outer tank (3); the power driving device (1) is used for driving the first stirring head (4-1) and the second stirring head (4-2) to rotate; a bracket (6) for fixing the inner groove (2) is arranged in the outer groove (3); a placing rack (5) is arranged in the inner groove (2), and an included angle between the placing rack (5) and the horizontal plane is 30-45 degrees;
the experimental device for dissolution kinetics of the ultrafiltration membrane pore-forming agent also comprises a temperature controller (9); a temperature sensor (8) is arranged on the inner wall of the inner groove (2); a heating pipe (7) is arranged in the outer groove (3); the heating pipe (7) and the temperature sensor (8) are electrically connected with the temperature controller (9).
2. The method for analyzing dissolution kinetics of an ultrafiltration membrane pore former according to claim 1, wherein the heating tube (7) is circular and fixed around the second stirring head (4-2).
3. The method of analyzing elution kinetics of a pore former of an ultrafiltration membrane according to claim 2, characterized in that said power driving means (1) is a magnetic stirrer and the first stirring head (4-1) and the second stirring head (4-2) are rotors.
4. The method of analyzing elution kinetics of a pore former of an ultrafiltration membrane according to claim 3, characterized in that said power driving means (1) is a motor and the first stirring head (4-1) and the second stirring head (4-2) are impeller stirrers; the power driving device (1) drives the first stirring head (4-1) and the second stirring head (4-2) to rotate through a shaft.
5. The method for analyzing dissolution kinetics of ultrafiltration membrane pore former according to claim 4, characterized in that the inner walls of the inner tank (2) and the outer tank (3) are provided with a plurality of fins (11).
6. The method for analyzing dissolution kinetics of an ultrafiltration membrane pore former according to claim 5, wherein the rotation speed of the first stirring head (4-1) is 30-120 r/min; the rotating speed of the second stirring head (4-2) is 50-150 revolutions per minute.
7. The method of analyzing elution kinetics of a pore former of an ultrafiltration membrane according to claim 6, wherein the method of measuring the concentration of the pore former of the ultrafiltration membrane is:
when the pore-forming agent is PEG, the principle that the PEG and the potassium bismuth iodide can generate an orange complex is adopted, and the detection is carried out by using an ultraviolet-visible spectrophotometry;
when the pore-forming agent is PVP, measuring by adopting a chromatography method;
when the pore-forming agent is an inorganic salt pore-forming agent, the determination is carried out by adopting atomic absorption or ion chromatography.
8. A method for analyzing the dissolution kinetics of a pore former of an ultrafiltration membrane when the pore former is PEG by using the method of claim 7, which is characterized by comprising the following specific steps:
(1) preparing a plurality of aluminum alloy flat plates with the same specification and shallow grooves, wherein the shallow grooves have the same size and the depth of 0.05-0.30 mm;
(2) accurately weighing the quality of the aluminum alloy flat plate, dripping uniform and stable casting film liquid into the shallow grooves for film scraping, wiping off the redundant casting film liquid outside the shallow grooves after ensuring that the shallow grooves are filled with the casting film liquid, accurately weighing the quality of the aluminum alloy flat plate after film scraping, and obtaining the quality of the casting film liquid in the shallow grooves by a quality difference method;
(3) putting PEG-4000 into a drying oven, drying for 4h at 60 ℃, accurately weighing 0.5g of PEG, dissolving the PEG in a 500mL volumetric flask, respectively sucking 0.1, 1.5, 2, 2.5, 3 and 3.5(mL) of PEG solution, diluting the PEG solution in a 100mL volumetric flask, and preparing PEG standard solutions with the concentrations of 0, 10, 15, 20, 25, 30 and 35 mg/L; sequentially adding 30mL of PEG standard solutions with different concentrations into 50mL of brown volumetric flasks respectively; firstly adding 6mL of glacial acetic acid, then adding 6mL of Dragendorff reagent, and finally diluting with distilled water to a scale; standing for 15min, measuring absorbance with a glass cuvette at 510nm wavelength with an ultraviolet spectrophotometer, and drawing a standard curve with distilled water as a blank;
(4) starting an ultrafiltration membrane pore-forming agent dissolution kinetic experiment device, and scraping a membrane on a new aluminum alloy flat plate by using the method in the step (2) after the temperature of a gel bath with the volume of M is constant;
(5) after pre-evaporation for a certain time, putting the aluminum alloy flat plate scraped in the step (3) into a gel bath; taking gel bath with fixed volume m (30mL) at different time points T respectively, taking out the gel bath, and adding the gel bath into 50mL volumetric flasks respectively; adding 6mL of glacial acetic acid into a volumetric flask, adding 6mL of Dragendorff reagent, and diluting with distilled water to a scale; after standing for 15 minutes, measuring the absorbance at the wavelength of 510nm on a UV2102C ultraviolet-visible spectrophotometer by using a glass cuvette with distilled water as a reference; determining the concentration A of PEG in the taken gel bath by using a standard curve;
(6) calculating the total dissolution quantity Q of the pore-forming agent of the ultrafiltration membranenAnd Tn-1～TnZone dissolution rate Vn，
Wherein: qn＝(M-(n-1)m)*An+m*(A1+A2+A3+……+An-1)
Vn＝(Qn-Qn-1)/(Tn-Tn-1)
In the formula: n is the number of samples.
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