Acid treatment and precipitation separation purification method of fluorine-containing copolymer resin

Abstract

The invention relates to a fluorine-containing copolymer resin acid treatment and precipitation separation purification method which comprises the following steps: S1, pretreatment: soaking and cleaning powdery fluorine-containing copolymer resin with ultrapure water to remove suspended pollutants; s2, dissolving: dissolving the fluorine-containing copolymer resin pretreated and dried in the step S1 into an organic solvent; s3, acid treatment: adding an acid solution into the fluorine-containing copolymer solution obtained in the step S2, and fully mixing; s4, precipitation: adding the solution obtained in the step S3 into ultrapure water under a stirring condition, and precipitating to separate out a white solid; s5, solid-liquid separation: filtering or centrifuging the dispersion liquid containing the white solid obtained in the step S4 to obtain a fluorine-containing copolymer resin solid, and drying the fluorine-containing copolymer resin solid; and S6, repeated purification: repeating the steps S2-S5 on the fluorine-containing copolymer resin solid obtained in the step S5. According to the invention, trace metal and other impurity residues can be removed, the subsequent polarization requirement is met, and the electric breakdown probability is greatly reduced.

Description

Technical Field

[0001] The invention belongs to the technical field of fluorine-containing copolymer resin treatment, and in particular relates to an acid treatment and precipitation separation and purification method for fluorine-containing copolymer resin. Background Art

[0002] Fluorinated copolymer poly(vinylidene fluoride-trifluoroethylene) [P(VDF-TrFE)] has good piezoelectric properties and is widely used in the development of tactile sensors, acoustic transducers, etc. The piezoelectric performance of P(VDF-TrFE) comes from the piezoelectric activity of the β-crystalline phase formed by polymer crystallization. The fluorinated copolymer element obtained by molding contains a large proportion of β-crystalline phase. After high-field electric field polarization, it can further induce crystal orientation, so that the fluorinated copolymer element has an excellent piezoelectric coefficient to meet the needs of high-sensitivity sensing applications.

[0003] P(VDF-TrFE) is usually prepared by free radical addition polymerization of two monomers, vinylidene fluoride (VDF) and trifluoroethylene (TrFE), through solution polymerization or emulsion polymerization. In order to achieve batch preparation, it is necessary to use a large reactor and select an efficient catalyst to complete the polymerization reaction. In the large-scale chemical production process, the fluorinated copolymer resin inevitably contains catalysts and residual metals dropped in the polymerization environment. Before the resin raw materials leave the factory, they also undergo certain post-treatments, but some residues are still difficult to eliminate, and the residual metal content may reach hundreds of ppm. In the polarization step of the development of acoustic sensor elements, too much metal and other impurities will cause defects in the element and increase the probability of electrical breakdown during the polarization process. After electrical breakdown, the sensor element loses its performance and becomes scrap, increasing the scrap rate.

[0004] Therefore, before using fluorine-containing copolymer resins to develop acoustic sensor elements, it is necessary to propose a special piezoelectric copolymer resin purification method to remove trace metal and other impurity residues. Summary of the invention

[0005] The technical problem to be solved by the present invention is to provide an acid treatment and precipitation separation purification method for fluorine-containing copolymer resin, which can remove trace metal and other impurity residues, meet subsequent polarization requirements, and greatly reduce the probability of electrical breakdown.

[0006] The technical solution of the present invention is to provide a method for acid treatment and precipitation separation and purification of fluorinated copolymer resin, comprising the following steps: S1, pretreatment: soaking and cleaning the powdered fluorinated copolymer resin with ultrapure water to remove suspended pollutants, and drying the fluorinated copolymer resin; S2, dissolving: dissolving the fluorinated copolymer resin pre-treated and dried in step S1 in an organic solvent; S3, acid treatment: adding the prepared acid solution to the fluorinated copolymer solution obtained in step S2, and mixing thoroughly; S4, precipitation: slowly adding the solution obtained in step S3 into ultrapure water under stirring conditions to precipitate a white solid, and continue stirring for at least 1 hour; S5, solid-liquid separation: filtering or centrifuging the dispersion containing the white solid obtained in step S4 to obtain a fluorine-containing copolymer resin solid, and drying it; S6, repeated purification: Repeating steps S2-S5 on the fluorinated copolymer resin solid obtained in step S5, removing a small amount of water-soluble impurities and trace metal residues contained in the fluorinated copolymer resin through multiple dissolution, acid treatment, precipitation and solid-liquid separation treatments, to obtain a high-purity fluorinated copolymer resin, and the number of repetitions is 2-4 times.

[0007] Preferably, the drying process in step S1 is drying in an oven at a temperature below 80°C.

[0008] Preferably, in step S2, the organic solvent is any one of N,N-dimethylformamide, N-methylpyrrolidone or 2-butanone, and the amount of the organic solvent is 8-12 L per kg of the fluorine-containing copolymer resin.

[0009] Preferably, in step S3, the acid solution is a mixed solution of 0.1-1 mol / L HCl, 0.25-1 mol / L hydrogen peroxide and 0.125-1 mol / L citric acid, and the volume ratio of the acid solution to the fluorinated copolymer solution obtained in step S2 is 1:2-1:5.

[0010] Preferably, in step S4, the volume ratio of the ultrapure water used to the solution obtained in step S3 is 20:1 or above.

[0011] Preferably, in step S5, the drying process is drying in an oven at a temperature below 80°C.

[0012] Compared with the prior art, the present invention has the following advantages: (1) Through the acid treatment method, various metals remaining in the fluorinated copolymer resin can be ionized into water-soluble components, which are convenient for separation from the resin in the precipitation step; (2) Ultrapure water, high-purity organic solvents and acid substances are used in the entire step, and no new metal ion impurities are introduced; (3) Repeated purification can ensure better impurity removal effect and improve resin cleanliness; (4) The metal content of the fluorinated copolymer resin treated by the above steps is low and can reach 5ppm or less, which can meet the subsequent polarization requirements and greatly reduce the probability of electrical breakdown. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Figure 1 It is a process flow chart of the present invention. DETAILED DESCRIPTION

[0014] The present invention will be further described below with regard to specific embodiments: A method for acid treatment and precipitation separation and purification of fluorinated copolymer resin, such as Figure 1 As shown, the specific steps include: (1) Pretreatment: The powdered fluorinated copolymer resin is cleaned by soaking in ultrapure water to remove suspended pollutants, and the fluorinated copolymer resin is dried in an oven at 76°C; (2) Dissolving: dissolving the fluorinated copolymer resin after pretreatment and drying in step (1) in an organic solvent. The organic solvent may be selected from one of N,N-dimethylformamide (DMF), N-methylpyrrolidone (NMP) or 2-butanone (MEK). The amount of organic solvent used is 10 L per kg of fluorinated copolymer resin. (3) Acid treatment: adding the prepared acid solution to the fluorinated copolymer solution obtained in step (2), wherein the acid solution is a mixed solution of 0.5 mol / L HCl, 0.65 mol / L hydrogen peroxide, and 0.35 mol / L citric acid, and the volume ratio of the acid solution to the solution obtained in step (2) is 1:3, and the mixture is mixed thoroughly; (4) Precipitation: The solution obtained in step (3) is slowly added to ultrapure water under stirring to precipitate a white solid, and stirring is continued for 3 hours, so that the volume ratio of ultrapure water from which the fluorinated copolymer solid is precipitated to the solution obtained in step (3) is 20:1; (5) Solid-liquid separation: filtering or centrifuging the dispersion containing white solid obtained in step (4) to obtain a fluorinated copolymer resin solid, and drying it. The drying conditions are the same as those described in step (1); (6) Repeated purification: The fluorinated copolymer resin solid obtained in step (5) is subjected to steps (2) to (5) again. After three times of dissolution, acid treatment, precipitation and solid-liquid separation, a small amount of water-soluble impurities and trace metal residues contained in the fluorinated copolymer resin are removed to obtain a high-purity fluorinated copolymer resin.

[0015] In the above steps, the pretreatment mainly deals with the water-soluble impurities and dust that may exist in the fluorinated copolymer resin; the dissolution process provides preparation for the subsequent steps. If the dissolution at room temperature is too slow, the dissolution can be accelerated by appropriate heating and increased stirring; the acid treatment step promotes the ionization and dissolution of residual metals by providing an acidic environment and an oxidizing environment. The amount of acid solution added in this step should not be too large to avoid premature precipitation of the copolymer resin; precipitation is carried out by using the insoluble nature of the fluorinated copolymer, and the copolymer resin is precipitated by using organic solvents and water. In this process, water-soluble impurities and metal ions remain in the water medium. This step requires water to adjust the pH until it is basically neutral; solid-liquid separation can be carried out by filtration or centrifugation. The centrifugation speed is relatively fast and the separation effect is relatively good. Repeating this step two or three times can obtain a better purification effect.

[0016] The metal content of the fluorinated copolymer resin treated by the above steps is low, which can reach below 5 ppm, and can meet the subsequent polarization requirements and greatly reduce the probability of electrical breakdown.

[0017] The above is only an explanation of the preferred embodiments of the present invention, which should not be construed as a limitation on the claims. Any equivalent process changes made using the present invention specification are included in the patent protection scope of the present invention.

Claims

1. A method for acid treatment and precipitation separation and purification of a fluorinated copolymer resin, characterized in that: The following steps are included: S1, pretreatment: soaking and cleaning the powdered fluorinated copolymer resin with ultrapure water to remove suspended pollutants, and drying the fluorinated copolymer resin; S2, dissolving: dissolving the fluorinated copolymer resin pre-treated and dried in step S1 in an organic solvent; S3, acid treatment: adding the prepared acid solution to the fluorinated copolymer solution obtained in step S2, and mixing thoroughly; S4, precipitation: adding the solution obtained in step S3 into ultrapure water under stirring to precipitate a white solid, and continuing stirring for at least 1 hour; S5, solid-liquid separation: filtering or centrifuging the dispersion containing the white solid obtained in step S4 to obtain a fluorine-containing copolymer resin solid, and drying it; S6, repeated purification: Repeating steps S2-S5 on the fluorinated copolymer resin solid obtained in step S5, removing water-soluble impurities and metal residues contained in the fluorinated copolymer resin through multiple dissolution, acid treatment, precipitation and solid-liquid separation treatments to obtain a high-purity fluorinated copolymer resin, and the number of repetitions is 2-4 times.

2. The method for acid treatment and precipitation separation and purification of fluorinated copolymer resin according to claim 1, characterized in that: The drying process in step S1 is drying in an oven at a temperature below 80°C.

3. The method for acid treatment and precipitation separation and purification of fluorinated copolymer resin according to claim 1, characterized in that: In step S2, the organic solvent is any one of N,N-dimethylformamide, N-methylpyrrolidone or 2-butanone, and the amount of the organic solvent is 8-12 L per kg of the fluorine-containing copolymer resin.

4. The method for acid treatment and precipitation separation and purification of fluorinated copolymer resin according to claim 1, characterized in that: In step S3, the acid solution is a mixed solution of 0.1-1 mol / L HCl, 0.25-1 mol / L hydrogen peroxide, and 0.125-1 mol / L citric acid, and the volume ratio of the acid solution to the fluorinated copolymer solution obtained in step S2 is 1:2-1:

5.

5. The method for acid treatment and precipitation separation and purification of fluorinated copolymer resin according to claim 1, characterized in that: In step S4, the volume ratio of the ultrapure water used to the solution obtained in step S3 is 20:1 or more.

6. The method for acid treatment and precipitation separation and purification of fluorinated copolymer resin according to claim 1, characterized in that: In step S5, the drying process is drying in an oven at a temperature below 80°C.

Images