Method for reducing content of metal ions in surfactant by using nanofiltration membrane

Abstract

The invention relates to the technical field of surfactant purification, and discloses a method for reducing the content of metal ions in a surfactant by using a nanofiltration membrane, which comprises the following steps: step 1, dissolving a water-soluble surfactant in deionized water to prepare a surfactant aqueous solution with the concentration lower than the critical micelle concentration; according to the method for reducing the content of the metal ions in the surfactant by using the nanofiltration membrane, the concentration of the aqueous solution of the surfactant is controlled to be lower than the critical micelle concentration (CMC), so that the aqueous solution of the surfactant exists in a single molecule form, the metal ions (in a hydrated ion form) penetrate through a membrane layer by using the aperture screening effect of the nanofiltration membrane, and the molecules of the surfactant are effectively intercepted, so that the content of the metal ions in the surfactant is reduced. Experiments show that after the surfactant is treated by the method, the content of various metal ions in the surfactant can be reduced to the ppb level, for example, the content of sodium ions can be reduced to about 2ppb, the content of calcium ions can be reduced to about 0.1 ppb, and the method is obviously superior to a traditional ion exchange resin method.

Description

Technical Field

[0001] This invention relates to the field of surfactant purification technology, and more particularly to a method for reducing the metal ion content in surfactants using nanofiltration membranes. Background Technology

[0002] In the fields of semiconductor manufacturing and micro / nano fabrication, photoresist development is a crucial step in forming precise patterns. Surfactants, as an important component of the developer, have a profound impact on photoresist performance due to variations in their metal ion content. Reducing the metal ion content in surfactants can significantly improve photoresist performance in several aspects, including pattern accuracy, development quality, and device stability. Reducing the metal ions in surfactants is of great significance. Reducing the metal ions can significantly improve the uniformity of photoresist development, making the developer more stable and uniform in properties. It can spread evenly on the photoresist surface and dissolve the photoresist, making the development process of the entire photoresist surface more consistent. Surfactants with lower metal ion content can make the dissolution process of photoresist in the developer more controllable, and can dissolve precisely according to the exposure area, thereby making the pattern edges smoother, the line width more uniform, and effectively improving the accuracy and resolution of photoresist patterns.

[0003] Furthermore, reducing the metal ion content in water-soluble surfactants greatly increases the application potential of surfactants. As the cornerstone of modern technology, the semiconductor industry has extremely stringent requirements for product precision and quality. Using photoresist development solutions with low metal ion content surfactants can effectively improve yield and reduce production costs. In the field of high-end materials, reducing the metal ion content of surfactants can effectively improve the stability, purity, and compatibility of materials with other materials. This will expand the application scope of this material in high-end fields, open up new market space, and lead technological changes in the materials field.

[0004] In the field of surfactant purification technology, especially for the removal of metal ions from water-soluble surfactants, existing technologies are limited and generally suffer from problems such as complex processes, unsatisfactory treatment effects, and narrow applicability.

[0005] Common purification methods include ion exchange resin method and electrodialysis method. For example, Chinese patent CN1096628C discloses a method for purifying surfactants using ion exchange resin. This method requires resin pretreatment, the process is complex, and it is significantly affected by the pH value of the solution. The removal effect of metal ions is limited, and the optimal treatment result can only reach about 20 ppb, which is difficult to meet the stringent requirements of high-end application scenarios such as semiconductors and photoresists for metal ion content. In addition, ion exchange resins have problems such as limited exchange capacity, easy saturation, and the need for frequent regeneration, resulting in poor long-term operational stability.

[0006] Another Chinese patent, CN101249385B, discloses the use of electrodialysis to remove inorganic salts from surfactants, but it does not clearly explain its selective removal effect on metal ions or the specific removal mechanism, which is uncertain in practical applications.

[0007] Therefore, there is an urgent need to develop a surfactant purification method that is simple in process, highly efficient in removal, suitable for continuous production, and can stably obtain extremely low metal ion content, in order to meet the growing demand for high-purity surfactants in fields such as electronic chemicals and high-end materials. Summary of the Invention

[0008] In view of the aforementioned existing problems, the present invention is proposed.

[0009] Therefore, the purpose of this invention is to provide a method for reducing the metal ion content in surfactants using nanofiltration membranes. The aim is to control the concentration of the surfactant aqueous solution below its critical micelle concentration (CMC), allowing it to exist in a single-molecule form. By utilizing the sieving effect of the nanofiltration membrane's pore size, metal ions (in the form of hydrated ions) permeate through the membrane layer, while surfactant molecules are effectively retained, thereby achieving efficient separation of metal ions. After treatment by the method of this invention, the content of various metal ions in the surfactant can be reduced to the ppb level, such as sodium ions to about 2 ppb and calcium ions to about 0.1 ppb, which is significantly better than the traditional ion exchange resin method.

[0010] To solve the above-mentioned technical problems, the present invention provides the following technical solution: a method for reducing the metal ion content in surfactants using nanofiltration membranes, comprising the following steps: Step 1: Dissolve the water-soluble surfactant in deionized water to prepare an aqueous surfactant solution with a concentration lower than its critical micelle concentration. Step 2: Pre-treat the surfactant aqueous solution to remove suspended particles; Step 3: Under pressure, the pretreated solution is passed through a nanofiltration membrane, allowing metal ions to pass through while surfactant molecules are retained, resulting in a preliminarily purified surfactant aqueous solution. Step four: The preliminarily purified surfactant aqueous solution is subjected to rotary distillation to remove water and low-boiling-point impurities, resulting in a surfactant with reduced metal ion content.

[0011] As a preferred embodiment of the method for reducing the metal ion content in a surfactant using a nanofiltration membrane according to the present invention, the concentration of the surfactant aqueous solution is 1wt% to 5wt%.

[0012] As a preferred embodiment of the method for reducing the metal ion content in a surfactant using a nanofiltration membrane according to the present invention, the surfactant has a molecular weight greater than 1000 Da.

[0013] As a preferred embodiment of the method for reducing the metal ion content in surfactants using nanofiltration membranes according to the present invention, the pretreatment includes filtration using a filter membrane with a pore size of 0.1 μm to 1 μm.

[0014] As a preferred embodiment of the method for reducing the metal ion content in surfactants using nanofiltration membranes according to the present invention, the nanofiltration membrane is of model FAE-310.

[0015] As a preferred embodiment of the method for reducing the metal ion content in surfactants using nanofiltration membranes according to the present invention, the pressure range of the pressure drive is 1.0 MPa to 2.0 MPa.

[0016] As a preferred embodiment of the method for reducing the metal ion content in surfactants using nanofiltration membranes according to the present invention, the rotary distillation conditions include: distillation temperature ≤ 70°C, rotation speed ≥ 60 rpm, and the process is carried out under reduced pressure.

[0017] As a preferred embodiment of the method for reducing the metal ion content in surfactants using nanofiltration membranes according to the present invention, wherein the metal ions include Na+. + K + Ca 2+ Mg 2+ Fe 3+ Cu 2+ Zn 2+ Ag + Al 3+ Ba 2+ Cr 3+ At least one of them.

[0018] In a preferred embodiment of the present invention, the surfactant is used in a semiconductor photoresist developer.

[0019] As a preferred embodiment of the present invention, a surfactant product is characterized in that it is prepared by reducing the metal ion content in the surfactant using a nanofiltration membrane, wherein the sodium ion content is ≤5 ppb and the calcium ion content is ≤0.2 ppb.

[0020] Compared with the prior art, the present invention has at least the following beneficial effects: 1. This invention controls the concentration of the surfactant aqueous solution below its critical micelle concentration (CMC), allowing it to exist in a single-molecule form. By utilizing the pore size sieving effect of the nanofiltration membrane, metal ions (in the form of hydrated ions) permeate through the membrane layer, while the surfactant molecules are effectively retained, thereby achieving highly efficient separation of metal ions. Experiments show that after treatment by the method of this invention, the content of various metal ions in the surfactant can be reduced to the ppb level, such as sodium ions to about 2 ppb and calcium ions to about 0.1 ppb, which is significantly better than the traditional ion exchange resin method.

[0021] 2. This invention eliminates the need for complex resin pretreatment or regeneration steps, as well as pH adjustment of the solution. The process is simple and easy to implement for continuous or batch production, reducing equipment investment and operation and maintenance costs. It has a wide range of applications, suitable for various water-soluble surfactants with molecular weights greater than 1000 Da. Especially in applications sensitive to metal ions, such as semiconductor photoresist developers and high-end cleaning agents, it can significantly improve product performance and process stability. Moreover, it can be flexibly integrated with subsequent processes. After nanofiltration, rotary distillation can be performed directly to further remove water and low-boiling-point impurities, achieving the concentration and purification of surfactants. The process is highly integrated. Attached Figure Description

[0022] Figure 1 This is a schematic diagram of the process flow for the method of reducing the metal ion content in surfactants using nanofiltration membranes according to the present invention. Detailed Implementation

[0023] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, the specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings.

[0024] Example 1

[0025] Experimental setup such as Figure 1 As shown; the experiment was conducted in a cleanroom, and the specific operating procedure was as follows: Step 1: Solution Pretreatment The water-soluble surfactant is fully dissolved in deionized water to prepare a surfactant aqueous solution with a concentration of 1wt%-5wt% in 5Kg. The surfactant aqueous solution is then filtered using a filter membrane with a pore size of 0.1μm-1μm to remove any suspended particles, mechanical impurities, etc. that may be present in the solution, and to prevent these substances from clogging the nanofiltration membrane pores and affecting the subsequent treatment effect.

[0026] Step 2: Pressure permeation through nanofiltration membrane This experiment used the FAE-310 nanofiltration membrane, which was installed in a high-pressure resistant membrane filtration device (such as...). Figure 1 As shown, the device has a PFA liner to ensure a good seal. The pretreated surfactant aqueous solution is injected into the membrane filtration device through port A. The sealing cap is tightened, and high-purity nitrogen gas is introduced through port B to apply a pressure of 1.0~2.0 MPa, causing the solution to permeate through the nanofiltration membrane under pressure. Valve D is opened, and the aqueous solution containing metal ions that has permeated through the nanofiltration membrane is collected through port C. After filtration is complete, the nitrogen gas is turned off, valve D is closed, and the filtered surfactant aqueous solution is collected through port A for further processing. Step 3: Rotary distillation treatment The collected high-purity surfactant aqueous solution, treated with a nanofiltration membrane, was transferred to the distillation flask of a rotary evaporator, and appropriate rotary distillation parameters were set. Generally, the rotation speed was controlled at 60 rpm. The pressure within the distillation system was reduced by adjusting the vacuum pump, ensuring the solution was distilled at 70°C to prevent surfactant decomposition or deterioration due to high temperatures. Distillation continued until the desired concentration was achieved. Distillation was then stopped, and the concentrated surfactant solution was collected for analysis of metal ion and water content. The results are shown in Tables 1 and 2 below.

[0027] Example 2

[0028] The experiment was conducted in a cleanroom, and the specific operating procedure was as follows: Step 1: Solution Pretreatment The water-soluble surfactant was fully dissolved in deionized water to prepare a surfactant aqueous solution with a concentration of 1wt%-5wt% in 5Kg. The surfactant aqueous solution was filtered using a filter membrane with a pore size of 0.1μm-1μm to remove any suspended particles, mechanical impurities, etc. that may be present in the solution.

[0029] Step 2: Resin Pretreatment Immerse the YS-2600 ion exchange resin in deionized water for 24 hours, stirring continuously to enhance the cleaning effect. After immersion, rinse the resin three times with deionized water to thoroughly remove surface impurities. Evenly fill the resin column with the pretreated ion exchange resin, filling it to one-third of the column volume. During filling, ensure the resin layer is evenly distributed and simultaneously remove air bubbles to avoid affecting subsequent ion exchange efficiency.

[0030] A 5% HCl solution was flowed into the resin column at a constant flow rate of 2 Bv / h (bed volume / hour) to pretreat the ion exchange resin. After the bed height remained constant, deionized water was circulated into the resin at a constant flow rate of 2 Bv / h (bed volume / hour) until the outlet solution was neutral.

[0031] Step 3: Ion exchange treatment The pretreated surfactant aqueous solution is introduced into the resin column at a constant flow rate of 2 Bv / h (bed volume / hour) through a slightly positive pressure nitrogen gas. It then fully contacts the ion exchange resin to complete the ion exchange process. The solution is then collected from the outlet for further processing.

[0032] Step 4: Rotary distillation treatment The collected high-purity surfactant aqueous solution, treated with ion exchange resin, was transferred to the distillation flask of a rotary evaporator, and appropriate rotary distillation parameters were set. Generally, the rotation speed was controlled at 60 rpm. The pressure within the distillation system was reduced by adjusting the vacuum pump, ensuring the solution was distilled at 70°C to prevent surfactant decomposition or deterioration due to high temperatures. Distillation continued until the desired concentration was achieved. Distillation was then stopped, and the concentrated surfactant solution was collected for analysis of metal ion and water content. The results are shown in Tables 1 and 2 below.

[0033] Table 1. Detection results of surfactant metal ions Sample ions Na(ppb) Mg(ppb) K(ppb) Fe(ppb) Cu(ppb) Zn(ppb) Ag(ppb) Ca(ppb) Al(ppb) Ba(ppb) Cr(ppb) Original sample 204.565 171.026 253.153 324.760 97.688 215.659 152.056 484.906 142.261 180.462 71.806 Nanofiltration membrane method 2.056 0.216 1.033 0.226 0.118 0.097 0.059 0.105 0.006 0.223 0.104 Resin method 85.366 49.161 77.534 124.011 64.037 86.230 61.256 167.232 25.806 42.313 57.509 Table 2. Results of surfactant moisture content detection sample Moisture content / % Original sample 0.26 Nanofiltration membrane method 0.24 Resin method 0.24 in conclusion Table 1 shows the detection results of metal ions in surfactants, revealing significant differences between the resin method and the nanofiltration membrane method in reducing the metal ion content in water-soluble surfactants. While the resin method reduced the metal ion content in the surfactant, the reduction was limited; for example, the residual sodium ion content remained as high as 85.336 ppb, and the residual calcium ion content was 167.232 ppb, failing to meet the stringent requirements of high-end applications for extremely low metal ion content. This is mainly because the resin method relies on the principle of ion exchange, and the selectivity and exchange capacity of resins for different metal ions are limited. Furthermore, with increasing usage time, resins are prone to adsorption saturation and performance degradation, making it difficult to further improve the treatment effect. In stark contrast, nanofiltration membrane technology, with its unique pore size sieving characteristics, can efficiently intercept metal ions. Test data shows that after treatment with nanofiltration membranes, the sodium ion content in surfactants drops sharply to 2.056 ppb, and the calcium ion content is only 0.105 ppb. In addition, the nanofiltration membrane process is simple and straightforward, requiring no complex regeneration steps and avoiding the secondary pollution problems that may occur with resin methods. While achieving highly efficient purification, it significantly reduces the operational difficulty and maintenance costs in the production process, making it more suitable for the production needs of high-end surfactant products and meeting the stringent requirements of high-end fields for extremely low metal ion content.

[0034] It should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention, and all such modifications or substitutions should be covered within the scope of the claims of the present invention.

Claims

1. A method for reducing the metal ion content in a surfactant using a nanofiltration membrane, characterized in that, Includes the following steps: Step 1: Dissolve the water-soluble surfactant in deionized water to prepare an aqueous surfactant solution with a concentration lower than its critical micelle concentration. Step 2: Pre-treat the surfactant aqueous solution to remove suspended particles; Step 3: Under pressure, the pretreated solution is passed through a nanofiltration membrane, allowing metal ions to pass through while surfactant molecules are retained, resulting in a preliminarily purified surfactant aqueous solution. Step four: The preliminarily purified surfactant aqueous solution is subjected to rotary distillation to remove water and low-boiling-point impurities, resulting in a surfactant with reduced metal ion content.

2. The method for reducing the metal ion content in a surfactant using a nanofiltration membrane according to claim 1, characterized in that: The concentration of the surfactant aqueous solution is 1wt% to 5wt%.

3. The method for reducing the metal ion content in a surfactant using a nanofiltration membrane according to claim 1, characterized in that: The surfactant has a molecular weight greater than 1000 Da.

4. The method for reducing the metal ion content in a surfactant using a nanofiltration membrane according to claim 3, characterized in that: The pretreatment includes filtration using a filter membrane with a pore size of 0.1 μm to 1 μm.

5. The method for reducing the metal ion content in a surfactant using a nanofiltration membrane according to claim 1, characterized in that: The nanofiltration membrane is model FAE-310.

6. The method for reducing the metal ion content in a surfactant using a nanofiltration membrane according to claim 1, characterized in that: The pressure range of the pressure drive is 1.0MPa to 2.0MPa.

7. The method for reducing the metal ion content in a surfactant using a nanofiltration membrane according to claim 1, characterized in that: The conditions for rotary distillation include: distillation temperature ≤ 70℃, rotation speed ≥ 60 rpm, and operation under reduced pressure.

8. The method for reducing the metal ion content in a surfactant using a nanofiltration membrane according to claim 1, characterized in that: The metal ions include Na. + K + Ca 2+ Mg 2+ Fe 3+ Cu 2+ Zn 2+ Ag + Al 3+ Ba 2+ Cr 3+ At least one of them.

9. The method for reducing the metal ion content in a surfactant using a nanofiltration membrane according to claim 1, characterized in that: The surfactant is used in semiconductor photoresist developer.

10. A surfactant product, characterized in that, It is prepared by the method described in any one of claims 1 to 9, wherein the sodium ion content is ≤5 ppb and the calcium ion content is ≤0.2 ppb.

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