Process for reducing trace salt of quinacridone pigment red

Abstract

The invention belongs to the technical field of pigment red purification, and particularly provides a process for reducing trace salt of quinacridone pigment red, which comprises the following steps: 1) mixing a pigment red PR122 crude product with DMF (Dimethyl Formamide), performing pigmentation treatment, dropwise adding sodium hydroxide after the pigmentation treatment is finished to enable the pH value of the material to be 7, filtering, washing with alcohol, filtering, adding water, and pulping to obtain slurry; 2) pumping the slurry into a primary circulation tank, diluting the slurry with water until the solid content is 7-9%, performing primary nanofiltration treatment, supplementing water to maintain the solid content in the treatment process, and pumping the slurry into a secondary circulation tank when the conductivity is less than or equal to 1000 [mu] S / cm, and performing secondary nanofiltration treatment; a polyamide nanofiltration membrane is adopted in the first-stage nanofiltration treatment, and a composite aluminum oxide ceramic nanofiltration membrane is adopted in the second-stage nanofiltration treatment. The process for reducing the trace salt content of quinacridone pigment red has the advantages of good purification effect and high pigment yield.

Description

Technical Field

[0001] This application belongs to the field of pigment red purification technology, and in particular relates to a process for reducing trace salt content in quinacridone pigment red. Background Technology

[0002] Quinacridone Pigment Red PR122 possesses remarkable properties such as weather resistance, heat resistance, and solvent resistance. It is widely used in numerous industries including building materials, engineering plastics, cosmetics, metallic inks, and melt spinning. With the development of high-end organic pigments, the application and research of core technologies for the production of quinacridone Pigment Red has become a key focus for companies in the industry.

[0003] Industrially, the production of quinacridone pigment red PR122 generally employs the succinate diester process, which can be divided into two types: oxidation followed by ring-closure reaction, and ring-closure reaction followed by oxidation. In the oxidation-then-ring-closure process, dimethyl 2,5-diphenylamino-3,6-dihydroterephthalate is first oxidized to remove hydrogen, yielding the intermediate dimethyl 2,5-diphenylamino-terephthalate. Then, polyphosphate (PPA) is added to the reaction solution to induce a ring-closure reaction, resulting in quinacridone or its derivatives. In this process, sodium m-nitrobenzenesulfonate is traditionally used as the oxidant, which easily generates solid waste. Currently, hydrogen peroxide is more commonly used as the oxidant, producing water as a byproduct and avoiding hazardous waste.

[0004] To ensure the pigment's effectiveness, the crude quinacridone pigment red PR122 needs to be washed with water to remove residual sodium hydrogen phosphate, phosphoric acid, and other salts. Traditional washing processes rely on experience and offline monitoring, resulting in low efficiency, delayed feedback, and incomplete salt removal, which negatively impacts pigment purity and coloring performance. Therefore, further removal of trace salts from the quinacridone pigment red PR122 product is a key factor in improving its quality. Summary of the Invention

[0005] To address the aforementioned problems and further remove trace salts from quinacridone pigment red products, this application provides a process for reducing trace salts in quinacridone pigment red.

[0006] This application provides a process for reducing the trace salt content of quinacridone pigment red, comprising the following steps: 1) Take crude pigment red PR122 and DMF and mix them for pigmentation treatment. After the treatment, add sodium hydroxide to make the pH of the material 7. After filtration, wash with alcohol, then filter again and add water to make pulp to obtain slurry. 2) Pump the slurry into the primary circulation tank, dilute it with water to a solid content of 7-9%, and perform primary nanofiltration treatment. During the treatment, water is added to maintain the solid content. When the conductivity is ≤1000μS / cm, pump it to the secondary circulation tank for secondary nanofiltration treatment. The primary nanofiltration treatment uses a polyamide nanofiltration membrane, and the secondary nanofiltration treatment uses a composite alumina ceramic nanofiltration membrane.

[0007] Furthermore, the composite alumina ceramic nanofiltration membrane is prepared by immersing the alumina ceramic nanofiltration membrane in a betaine derivative solution for 3-5 hours, and then curing it at 80-100℃ for 1-2 hours.

[0008] Furthermore, the betaine derivative is prepared by reacting sulfobetaine methacrylate with an alkoxysilane monomer.

[0009] Furthermore, the molar ratio of the sulfobetaine methacrylate to the alkoxysilane monomer is (2.5-4):1.

[0010] Furthermore, the concentration of the betaine derivative in the betaine derivative solution is 2-3 wt%.

[0011] Furthermore, in step 1), the pigmentation process involves stirring at 70-75°C, then heating to reflux temperature and holding for 1.5-2 hours.

[0012] Furthermore, in step 1), the alcohol washing is performed using methanol.

[0013] Furthermore, in step 2), the crossflow velocity is set to 3 m / s and the operating pressure is 0.2-0.35 MPa during the first-stage nanofiltration process.

[0014] Furthermore, in step 2), a pulsed electric field is applied during the first-stage nanofiltration process, with the following parameters: field strength 300V / cm and pulse frequency 10Hz.

[0015] Furthermore, in step 2), a pulsed electric field is applied during the secondary nanofiltration process, with the following parameters: field strength 100V / cm and pulse frequency 3Hz.

[0016] Compared with the prior art, this application has the following beneficial effects: 1. This application employs a precision microfiltration membrane separation process and online real-time conductivity monitoring to achieve efficient and precise control of trace residual salts in quinacridone pigment red products. This solves the problems of low efficiency, delayed feedback, and incomplete salt removal associated with traditional water washing processes that rely on experience and offline detection. As a result, it ensures the excellent electrical insulation and long-term stability of the pigment in demanding applications such as advanced automotive paints and engineering plastics.

[0017] 2. This application employs a two-stage nanofiltration process. The first-stage nanofiltration removes easily migrating ions, providing a favorable environment for the subsequent second-stage nanofiltration. The second-stage nanofiltration uses a composite alumina ceramic nanofiltration membrane. This membrane has a hydration layer formed by betaine derivatives on its surface, which repels pigment molecules, reduces the impact of pigment particles on the permeation and mass transfer of the nanofiltration membrane, lowers concentration polarization on the membrane surface, promotes the removal of trace salt particles, and further reduces the salt content in the pigment red product. Attached Figure Description

[0018] Figure 1 This is a schematic diagram showing the decrease in pure water flux after different operating times of the alumina ceramic nanofiltration membranes in Examples 1-2 and Control Group 2 of this application. Detailed Implementation

[0019] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of this application.

[0020] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the application. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items.

[0021] When using “including,” “having,” and “contains” as described herein, the intention is to cover non-exclusive inclusion, unless an explicit qualifying term such as “only,” “consisting of,” etc., is used, in which case another component may be added.

[0022] The terms "preferred," "more preferably," "better," and "even better" used in this application refer to embodiments of this application that provide certain beneficial effects under certain circumstances. However, other embodiments may also be preferred under the same or other circumstances. Furthermore, the description of one or more preferred embodiments does not imply that other embodiments are unavailable, nor is it intended to exclude other embodiments from the scope of this application. That is, in this application, "preferred," "more preferably," "better," and "even better" are merely descriptions of implementations or embodiments with better effects, but do not constitute a limitation on the scope of protection of this application.

[0023] In this application, terms such as "further," "even more," and "particularly" are used for descriptive purposes and indicate differences in content, but should not be construed as limiting the scope of protection of this application.

[0024] In this application, "at least one" means one or more, such as one, two, or more. "Multiple" or "several" means at least two, such as two, three, etc., and "multi-layered" means at least two layers, such as two layers, three layers, etc., unless otherwise explicitly specified. In the description of this application, "several" means at least one, such as one, two, etc., unless otherwise explicitly specified.

[0025] When a numerical range is disclosed herein, the range is considered continuous and includes the minimum and maximum values ​​of the range, as well as every value between the minimum and maximum values. Furthermore, when the range refers to integers, it includes every integer between the minimum and maximum values ​​of the range. Additionally, when multiple ranges are provided to describe a feature or characteristic, the ranges may be combined. In other words, unless otherwise specified, all ranges disclosed herein should be understood to include any and all subranges to which they are incorporated.

[0026] Unless otherwise specified, all steps in this application may be performed sequentially or randomly. For example, the method comprising steps (a) and (b) indicates that the method may include steps (a) and (b) performed sequentially, or it may include steps (b) and (a) performed sequentially. For example, the mention that the method may also include step (c) indicates that step (c) may be added to the method in any order; for example, the method may include steps (a), (b), and (c), or it may include steps (a), (c), and (b), or it may include steps (c), (a), and (b), etc. Unless otherwise stated, singular terms may include plural forms and should not be construed as having a quantity of one.

[0027] In this application, "above" or "below" includes the number itself. For example, "below 1" includes 1.

[0028] In this application, room temperature refers to 0~40℃, including but not limited to 10~40℃, or further to 20~30℃.

[0029] Based on extensive experimental research, this application provides a process for reducing the trace salt content of quinacridone pigment red, comprising the following steps: 1) Take crude pigment red PR122 and DMF and mix them for pigmentation treatment. After the treatment, add sodium hydroxide to make the pH of the material 7. After filtration, wash with alcohol, then filter again and add water to make pulp to obtain slurry. 2) Pump the slurry into the primary circulation tank, dilute it with water to a solid content of 7-9%, and perform primary nanofiltration treatment. During the treatment, water is added to maintain the solid content. When the conductivity is ≤1000μS / cm, pump it to the secondary circulation tank for secondary nanofiltration treatment. The primary nanofiltration treatment uses a polyamide nanofiltration membrane, and the secondary nanofiltration treatment uses a composite alumina ceramic nanofiltration membrane.

[0030] Furthermore, the composite alumina ceramic nanofiltration membrane is prepared by immersing the alumina ceramic nanofiltration membrane in a betaine derivative solution for 3-5 hours, and then curing it at 80-100℃ for 1-2 hours.

[0031] Furthermore, the betaine derivative is prepared by reacting sulfobetaine methacrylate with an alkoxysilane monomer.

[0032] In some specific embodiments, under normal circumstances, the experimental results are better when 3-methacryloyloxypropyltrimethoxysilane is selected as the alkoxysilane monomer.

[0033] Furthermore, the molar ratio of the sulfobetaine methacrylate to the alkoxysilane monomer is (2.5-4):1.

[0034] In some specific embodiments, the molar ratio of sulfobetaine methacrylate to alkoxysilane monomer can be 2.5:1, 2.6:1, 2.7:1, 2.8:1, 2.9:1, 3.0:1, 3.1:1, 3.2:1, 3.3:1, 3.4:1, 3.5:1, 3.6:1, 3.7:1, 3.8:1, 3.9:1, or 4.0:1. Generally, a molar ratio of sulfobetaine methacrylate to alkoxysilane monomer of 3.5:1 yields better experimental results.

[0035] Furthermore, the concentration of the betaine derivative in the betaine derivative solution is 2-3 wt%.

[0036] In some specific embodiments, the concentration of betaine derivative in the betaine derivative solution can be 2wt%, 2.1wt%, 2.2wt%, 2.3wt%, 2.4wt%, 2.5wt%, 2.6wt%, 2.7wt%, 2.8wt%, 2.9wt%, or 3wt%. Generally, a concentration of 2.5wt% of betaine derivative in the solution yields good experimental results.

[0037] Furthermore, in step 1), the pigmentation process involves stirring at 70-75°C, then heating to reflux temperature and holding for 1.5-2 hours.

[0038] Furthermore, in step 1), the alcohol washing is performed using methanol.

[0039] Furthermore, in step 2), the crossflow velocity is set to 3 m / s and the operating pressure is 0.2-0.35 MPa during the first-stage nanofiltration process.

[0040] Furthermore, in step 2), a pulsed electric field is applied during the first-stage nanofiltration process, with the following parameters: field strength 300V / cm and pulse frequency 10Hz.

[0041] Furthermore, in step 2), a pulsed electric field is applied during the secondary nanofiltration process, with the following parameters: field strength 100V / cm and pulse frequency 3Hz.

[0042] The present application will be further illustrated by the following examples, but these examples do not limit the scope of the present application.

[0043] When numerical ranges are given in the embodiments, it should be understood that, unless otherwise stated in this application, both endpoints of each numerical range and any value between the two endpoints may be selected. Unless otherwise defined, all technical and scientific terms used in this application have the same meaning as commonly understood by one of ordinary skill in the art. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall apply. All reagents or instruments whose manufacturers are not specified are conventional products that can be purchased commercially. In addition to the specific methods, equipment, and materials used in the embodiments, based on the knowledge of the prior art possessed by one of ordinary skill in the art and the description in this application, any prior art methods, equipment, and materials similar to or equivalent to those described, used, or made by the methods, equipment, and materials in the embodiments of this application may be used to implement this application.

[0044] Example 1 The process for reducing trace salt content in quinacridone pigment red according to this embodiment includes the following steps: 1) Take crude pigment red PR122 and DMF and mix them in a mixing tank for 20 minutes. During the mixing process, keep the temperature at 70°C, then raise the temperature to the reflux temperature and keep it at that temperature for 1.5 hours. After the mixing is completed, lower the temperature to 60°C and add sodium hydroxide solution dropwise to make the pH of the material 7. If the pH does not change after stirring for 30 minutes, filter the obtained material, wash the filter cake with methanol, filter it again, add water and slurry to obtain the slurry. 2) Pump the slurry into the primary circulation tank, dilute it with water to a solid content of 7%, and perform primary nanofiltration treatment. During the treatment, replenish water to maintain the solid content. Set the crossflow velocity to 3 m / s, the operating pressure to 0.2 MPa, and apply a pulsed electric field with the following parameters: field strength 300 V / cm, pulse frequency 10 Hz. When the conductivity is ≤1000μS / cm, it is pumped to the secondary circulation tank for secondary nanofiltration until the conductivity is stable at ≤50μS / cm; a pulsed electric field is applied with the following parameters: field strength 100V / cm, pulse frequency 3Hz. In this embodiment, the primary nanofiltration process uses a polyamide nanofiltration membrane, model HNF40-4040.

[0045] The secondary nanofiltration process in this embodiment uses a composite alumina ceramic nanofiltration membrane, which is prepared by the following method: a tubular alumina ceramic nanofiltration membrane with an outer diameter of 12 mm, an inner diameter of 8 mm, a tube length of 110 mm, and a pore size of 0.1 μm is soaked in a 1 mol / L sodium hydroxide solution and a 1 mol / L hydrochloric acid solution, then washed with deionized water, dried at 120°C, and then immersed in a betaine derivative solution for 5 h. After that, it is taken out and drained, transferred to a vacuum drying oven and cured at 90°C for 1.5 h, and finally washed and dried with deionized water.

[0046] The preparation method of the betaine derivative solution in this embodiment is as follows: 0.35 mol of sulfobetaine methacrylate and 0.1 mol of 3-methacryloyloxypropyltrimethoxysilane are added to a three-necked flask, anhydrous ethanol is added as a solvent, and an appropriate amount of azobisisobutyronitrile is added. Under nitrogen protection, the reaction is carried out at 70°C for 10 h. Then, the solution is diluted with anhydrous ethanol to a concentration of 2 wt% of the betaine derivative. Finally, 0.1 wt% acetic acid is added and mixed evenly to obtain the solution.

[0047] The total anion content of Pigment Red PR122 in this embodiment is 46.3 ppm, and the Na ion content is 35.9 ppm. The pigment yield is 99.28%. Example 2 The process for reducing trace salt content in quinacridone pigment red according to this embodiment includes the following steps: 1) Take crude pigment red PR122 and DMF and mix them in a mixing tank for 20 minutes. During the mixing process, keep the temperature at 70°C, then raise the temperature to the reflux temperature and keep it at that temperature for 1.5 hours. After the mixing is completed, lower the temperature to 60°C and add sodium hydroxide solution dropwise to make the pH of the material 7. If the pH does not change after stirring for 30 minutes, filter the obtained material, wash the filter cake with methanol, filter it again, add water and slurry to obtain the slurry. 2) Pump the slurry into the primary circulation tank, dilute it with water to a solid content of 9%, and perform primary nanofiltration treatment. During the treatment, replenish water to maintain the solid content. Set the crossflow velocity to 3 m / s, the operating pressure to 0.3 MPa, and apply a pulsed electric field with the following parameters: field strength 300 V / cm, pulse frequency 10 Hz. When the conductivity is ≤1000μS / cm, it is pumped to the secondary circulation tank for secondary nanofiltration until the conductivity is stable at ≤50μS / cm; a pulsed electric field is applied with the following parameters: field strength 100V / cm and pulse frequency 3Hz.

[0048] In this embodiment, the primary nanofiltration process uses a polyamide nanofiltration membrane, model HNF40-4040.

[0049] The secondary nanofiltration process in this embodiment uses a composite alumina ceramic nanofiltration membrane, which is prepared by the following method: a tubular alumina ceramic nanofiltration membrane with an outer diameter of 12 mm, an inner diameter of 8 mm, a tube length of 110 mm, and a pore size of 0.1 μm is soaked in a 1 mol / L sodium hydroxide solution and a 1 mol / L hydrochloric acid solution, then washed with deionized water, dried at 120°C, and then immersed in a betaine derivative solution for 5 h. After that, it is taken out and drained, transferred to a vacuum drying oven and cured at 90°C for 1.5 h, and finally washed and dried with deionized water.

[0050] The preparation method of the betaine derivative solution in this embodiment is as follows: 0.35 mol of sulfobetaine methacrylate and 0.1 mol of 3-methacryloyloxypropyltrimethoxysilane are added to a three-necked flask, anhydrous ethanol is added as a solvent, and an appropriate amount of azobisisobutyronitrile is added. Under nitrogen protection, the reaction is carried out at 70°C for 10 h. Then, the solution is diluted with anhydrous ethanol to a concentration of 2.5 wt% of betaine derivative. Finally, 0.1 wt% of acetic acid is added, and the solution is mixed evenly to obtain the final product.

[0051] The total anion content of Pigment Red PR122 in this embodiment is 41.6 ppm, and the Na ion content is 30.3 ppm. The pigment yield is 99.62%.

[0052] Control group 1 The process for reducing trace salt content in quinacridone pigment red in this control group includes the following steps: 1) Take crude pigment red PR122 and DMF and mix them in a mixing tank for 20 minutes. During the mixing process, keep the temperature at 70°C, then raise the temperature to the reflux temperature and keep it at that temperature for 1.5 hours. After the mixing is completed, lower the temperature to 60°C and add sodium hydroxide solution dropwise to make the pH of the material 7. If the pH does not change after stirring for 30 minutes, filter the obtained material, wash the filter cake with methanol, filter it again, add water and slurry to obtain the slurry. 2) Pump the slurry into the primary circulation tank, dilute it with water to a solid content of 7%, and perform nanofiltration treatment. During the treatment, replenish water to maintain the solid content. Set the crossflow velocity to 3 m / s, the operating pressure to 0.2 MPa, and apply a pulsed electric field with the following parameters: field strength 300 V / cm, pulse frequency 10 Hz. In this control group, the nanofiltration treatment used a polyamide nanofiltration membrane, model HNF40-4040.

[0053] The total anion content of Pigment Red PR122 in this control group was 823.1 ppm, and the Na ion content was 528.5 ppm. The pigment yield was 83.69%.

[0054] Control group 2 The process for reducing trace salt content in quinacridone pigment red in this control group includes the following steps: 1) Take crude pigment red PR122 and DMF and mix them in a mixing tank for 20 minutes. During the mixing process, keep the temperature at 70°C, then raise the temperature to the reflux temperature and keep it at that temperature for 1.5 hours. After the mixing is completed, lower the temperature to 60°C and add sodium hydroxide solution dropwise to make the pH of the material 7. If the pH does not change after stirring for 30 minutes, filter the obtained material, wash the filter cake with methanol, filter it again, add water and slurry to obtain the slurry. 2) Pump the slurry into the primary circulation tank, dilute it with water to a solid content of 7%, and perform primary nanofiltration treatment. During the treatment, replenish water to maintain the solid content. Set the crossflow velocity to 3 m / s, the operating pressure to 0.2 MPa, and apply a pulsed electric field with the following parameters: field strength 300 V / cm, pulse frequency 10 Hz. When the conductivity is ≤1000μS / cm, it is pumped to the secondary circulation tank for secondary nanofiltration until the conductivity is stable at ≤50μS / cm; a pulsed electric field is applied with the following parameters: field strength 100V / cm, pulse frequency 3Hz; In this control group, the primary nanofiltration treatment used a polyamide nanofiltration membrane, model HNF40-4040.

[0055] The secondary nanofiltration treatment in this control group used an alumina ceramic nanofiltration membrane, which was prepared by the following method: a tubular alumina ceramic nanofiltration membrane with an outer diameter of 12 mm, an inner diameter of 8 mm, a tube length of 110 mm, and a pore size of 0.1 μm was soaked in a 1 mol / L sodium hydroxide solution and a 1 mol / L hydrochloric acid solution, then washed with deionized water, and dried at 120 °C.

[0056] The total anion content of Pigment Red PR122 in this control group was 518.7 ppm, and the Na ion content was 364.6 ppm. The pigment yield was 88.12%.

[0057] Performance testing The test investigated the decrease in pure water flux of the alumina ceramic nanofiltration membranes in Examples 1-2 and Control Group 2 after different operating times, with an operating pressure of 0.5 MPa. The test results are as follows: Figure 1 As can be seen from the above, the ceramic membrane of control group 2 is prone to fouling and clogging, while the alumina ceramic membrane of this application has a smaller flux attenuation, a better retention effect on pigments and an anti-fouling and clogging effect, and can improve the yield and purity of pigments.

[0058] Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the protection scope of this application.

Claims

1. A process for reducing the amount of salt in a quinacridone pigment red, characterized in that: Includes the following steps: 1) Take crude pigment red PR122 and DMF and mix them for pigmentation treatment. After the treatment, add sodium hydroxide to make the pH of the material 7. After filtration, wash with alcohol, then filter again and add water to make pulp to obtain slurry. 2) Pump the slurry into the primary circulation tank, dilute it with water to a solid content of 7-9%, and perform primary nanofiltration treatment. During the treatment, water is added to maintain the solid content. When the conductivity is ≤1000μS / cm, pump it to the secondary circulation tank for secondary nanofiltration treatment. The primary nanofiltration treatment uses a polyamide nanofiltration membrane, and the secondary nanofiltration treatment uses a composite alumina ceramic nanofiltration membrane.

2. The process for reducing trace salt content in quinacridone pigment red according to claim 1, characterized in that: The composite alumina ceramic nanofiltration membrane is prepared by immersing the alumina ceramic nanofiltration membrane in a betaine derivative solution for 3-5 hours, and then curing it at 80-100℃ for 1-2 hours.

3. The process for reducing trace salt content in quinacridone pigment red according to claim 2, characterized in that: The betaine derivative was obtained by reacting sulfobetaine methacrylate with an alkoxysilane monomer.

4. The process for reducing trace salt content in quinacridone pigment red according to claim 3, characterized in that: The molar ratio of the sulfobetaine methacrylate to the alkoxysilane monomer is (2.5-4):

1.

5. The process for reducing trace salt content in quinacridone pigment red according to claim 2, characterized in that: The concentration of betaine derivative in the betaine derivative solution is 2-3 wt%.

6. The process for reducing trace salt content in quinacridone pigment red according to claim 1, characterized in that: In step 1), the pigmentation process involves stirring at 70-75°C and then heating to reflux temperature and holding for 1.5-2 hours.

7. The process for reducing trace salt content in quinacridone pigment red according to claim 1, characterized in that: In step 1), the alcohol washing is performed using methanol.

8. The process for reducing trace salt content in quinacridone pigment red according to claim 1, characterized in that: In step 2), the crossflow velocity is set to 3 m / s and the operating pressure is 0.2-0.35 MPa during the first-stage nanofiltration process.

9. The process for reducing trace salt content in quinacridone pigment red according to claim 1, characterized in that: In step 2), a pulsed electric field is applied during the first-stage nanofiltration process, with the following parameters: field strength 300V / cm and pulse frequency 10Hz.

10. The process for reducing trace salt content in quinacridone pigment red according to claim 1, characterized in that: In step 2), a pulsed electric field is applied during the secondary nanofiltration process, with the following parameters: field strength 100V / cm and pulse frequency 3Hz.

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